U.S. patent application number 16/351046 was filed with the patent office on 2019-07-11 for liquid-to-air membrane energy exchanger.
The applicant listed for this patent is Nortek Air Solutions Canada, Inc., University of Saskatchewan. Invention is credited to Robert Besant, Blake Norman Erb, Howard Brian Hermingson, Carey Simonson.
Application Number | 20190212020 16/351046 |
Document ID | / |
Family ID | 45371881 |
Filed Date | 2019-07-11 |
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United States Patent
Application |
20190212020 |
Kind Code |
A1 |
Besant; Robert ; et
al. |
July 11, 2019 |
LIQUID-TO-AIR MEMBRANE ENERGY EXCHANGER
Abstract
An energy exchanger is provided. The exchanger includes a
housing having a front and a back. A plurality of panels forming
desiccant channels extend from the front to the back of the
housing. Air channels are formed between adjacent panels. The air
channels are configured to direct an air stream in a direction from
the front of the housing to the back of the housing. A desiccant
inlet is provided in flow communication with the desiccant
channels. A desiccant outlet is provided in flow communication with
the desiccant channels. The desiccant channels are configured to
channel desiccant from the desiccant inlet to the desiccant outlet
in at least one of a counter-flow or cross-flow direction with
respect to the direction of the air stream.
Inventors: |
Besant; Robert; (Saskatoon,
CA) ; Simonson; Carey; (Corman Park, CA) ;
Erb; Blake Norman; (Warman, CA) ; Hermingson; Howard
Brian; (Saskatoon, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Saskatchewan
Nortek Air Solutions Canada, Inc. |
SASKATOON
SASKATOON |
|
CA
CA |
|
|
Family ID: |
45371881 |
Appl. No.: |
16/351046 |
Filed: |
March 12, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14957795 |
Dec 3, 2015 |
10302317 |
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16351046 |
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13702596 |
Apr 15, 2013 |
9234665 |
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PCT/IB2011/002145 |
Jun 22, 2011 |
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14957795 |
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61358321 |
Jun 24, 2010 |
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61359193 |
Jun 28, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 12/002 20130101;
Y02B 30/54 20130101; F24F 1/0007 20130101; F24F 2003/1435 20130101;
Y02B 30/56 20130101; F24F 3/1417 20130101; F28D 21/0015 20130101;
Y02B 30/545 20130101; F24F 12/006 20130101; Y02B 30/563 20130101;
F24F 3/147 20130101; F24F 12/001 20130101; F28D 15/00 20130101 |
International
Class: |
F24F 3/147 20060101
F24F003/147; F28D 21/00 20060101 F28D021/00; F24F 1/0007 20060101
F24F001/0007; F24F 12/00 20060101 F24F012/00; F24F 3/14 20060101
F24F003/14 |
Claims
1. (canceled)
2. An energy exchanger comprising: a housing; a plurality of panels
forming liquid channels and air channels separated by at least one
semi-permeable membrane, the air channels configured to direct an
air stream through the housing; a liquid inlet in flow
communication with the liquid channels; and a liquid outlet in flow
communication with the liquid channels, the liquid channels
configured to channel liquid from the liquid inlet to the liquid
outlet in at least one of a counter-flow or cross-flow direction
with respect to the direction of the air stream to facilitate heat
and water vapor transfer between the liquid in the liquid channels
and the air stream in the air channels; wherein the liquid inlet
has an inlet length and the liquid channels each have a channel
length, and wherein the inlet length and the channel length are
selected to provide a predetermined ratio.
3. The energy exchanger of claim 1, wherein the liquid channels are
configured to channel the liquid from the liquid inlet to the
liquid outlet in the counter-flow direction with respect to the
direction of the air stream.
4. The energy exchanger of claim 3, wherein the predetermined ratio
is between 0.02 and 0.2.
5. The energy exchanger of claim 2, wherein the liquid channels are
configured to channel the liquid from the liquid inlet to the
liquid outlet in the cross-flow direction with respect to the
direction of the air stream.
6. The energy exchanger of claim 5, wherein the predetermined ratio
is between 0.5 and 1.0.
7. The energy exchanger of claim 2, wherein the liquid inlet is
offset from the liquid outlet along a direction of the air
stream.
8. The energy exchanger of claim 2, wherein the liquid flow
channels are configured to direct the liquid along a flow path
having a cross segment and a counter segment, the cross segment
extending in a direction substantially perpendicular to a direction
of the air stream, the counter segment extending in a direction
substantially parallel to a direction of the air stream.
9. The energy exchanger of claim 2, wherein the liquid flow
channels are configured to direct the liquid along a flow path in a
direction upstream with respect to a direction of the air
stream.
10. The energy exchanger of claim 2, wherein the liquid outlet has
an outlet length equal to the inlet length.
11. The energy exchanger of claim 2, wherein the liquid inlet
extends through a bottom support of each of the plurality of
panels, and wherein the liquid outlet extends through a top support
of each of the plurality of panels, and wherein the liquid channels
extend from a first side support to a second support, and wherein
the top support, the bottom support, and the first and the second
side supports are configured to retain the at least semi-permeable
membrane.
12. An energy exchanger comprising: a housing; a plurality of
panels that extend from a base support to a top support and from a
first side support to a second side support, and wherein the
plurality of panels each form liquid channels and air channels
separated by at least one semi-permeable membrane, the air channels
configured to direct an air stream through the housing, a liquid
inlet that extends through the bottom support and is in flow
communication with the liquid channels; and a liquid outlet that
extends through the top support and is in flow communication with
the liquid channels, the liquid channels configured to channel
liquid from the liquid inlet to the liquid outlet in at least one
of a counter-flow or cross-flow direction with respect to the
direction of the air stream to facilitate heat and water vapor
transfer between the liquid in the liquid channels and the air
stream in the air channels; wherein the liquid inlet has an inlet
length and each of the plurality of panels have a panel length, and
wherein the inlet length and the panel length are selected to
provide a predetermined ratio.
13. The energy exchanger of claim 12, wherein the liquid channels
are configured to channel the liquid from the liquid inlet to the
liquid outlet in the counter-flow direction with respect to the
direction of the air stream.
14. The energy exchanger of claim 13, wherein the predetermined
ratio is between 0.02 and 0.2.
15. The energy exchanger of claim 12, wherein the liquid channels
are configured to channel the liquid from the liquid inlet to the
liquid outlet in the cross-flow direction with respect to the
direction of the air stream.
16. The energy exchanger of claim 15, wherein the predetermined
ratio is between 0.5 and 1.0.
17. The energy exchanger of claim 12, wherein the liquid inlet is
offset from the liquid outlet along a direction of the air
stream.
18. The energy exchanger of claim 12, wherein the liquid flows
through the liquid channels along a non-linear flow path between
the inlet and outlet.
19. The energy exchanger of claim 12, wherein the liquid channels
have an approximately constant liquid channel width through the
housing and the air channels have an approximately constant air
channel width through the housing.
20. The energy exchanger of claim 12, wherein the liquid outlet has
an outlet length equal to the inlet length.
21. The energy exchanger of claim 12, wherein the top support, the
bottom support, and the first and the second side supports are
configured to retain the at least one semi-permeable membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 13/702,596 titled "Liquid-To-Air Membrane
Energy Exchanger" filed Apr. 15, 2013, which is a U.S. national
stage entry of co-pending International Application Number
PCT/IB2011/002145 titled "Liquid-To-Air Membrane Energy Exchanger"
filed Jun. 22, 2011 (published as WO 2011/161547), which relates to
and claims priority from U.S. Provisional Patent Application
61/358,321 titled "Liquid-to-air Membrane Energy Exchanger" filed
Jun. 24, 2010, and U.S. Provisional Patent Application 61/359,193
titled "System and Method for Energy Exchange" filed Jun. 28, 2010.
All of the applications noted above are hereby incorporated by
reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] The subject matter described herein relates generally to an
energy exchange system for conditioning air in an enclosed
structure, and more particularly, to a liquid-to-air membrane
energy exchanger (LAMEE).
[0003] Enclosed structures, such as occupied buildings, factories
and animal barns, generally include an HVAC system for conditioning
ventilated and/or recirculated air in the structure. The HVAC
system includes a supply air flow path and an exhaust air flow
path. The supply air flow path receives pre-conditioned air, for
example outside air or outside air mixed with re-circulated air,
and channels and distributes the air into the enclosed structure.
The pre-conditioned air is conditioned by the HVAC system to
provide a desired temperature and humidity of supply air discharged
into the enclosed structure. The exhaust air flow path discharges
air back to the environment outside the structure. Without energy
recovery, conditioning the supply air typically requires a
significant amount of auxiliary energy. This is especially true in
environments having extreme outside air conditions that are much
different than the required supply air temperature and humidity.
Accordingly, energy exchange or recovery systems are typically used
to recover energy from the exhaust air flow path. Energy recovered
from air in the exhaust flow path is utilized to reduce the energy
required to condition the supply air.
[0004] Conventional energy exchange systems may utilize energy
recovery devices (e.g. energy wheels and permeable plate
exchangers) or heat exchange devices (e.g. heat wheels, plate
exchangers, heat-pipe exchangers and run-around heat exchangers)
positioned in both the supply air flow path and the return air flow
path. LAMEEs are fluidly coupled so that a desiccant liquid flows
between the LAMEEs in a nm-around loop, similar to run-around heat
exchangers that typically use aqueous glycol as a coupling fluid.
When the only auxiliary energy used for such a loop is for
desiccant liquid circulation pumps and external air-flow fans, the
run-around system is referred to as a passive run-around membrane
energy exchange (RAMEE) system, otherwise it is an active RAMEE
system with controlled auxiliary heat and/or water inputs or
extractions.
[0005] For the passive RAMEE system with one or more LAMEEs in each
of the exhaust and supply air ducts, energy in the form of heat and
water vapor is transferred between the LAMEEs in the supply and
exhaust ducts, which is interpreted as the transfer of sensible and
latent energy between the exhaust air and the supply air. For
example, the exhaust air LAMEE may recover heat and moisture from
the exhaust air to transfer the heat and moisture to the supply air
during winter conditions to heat and humidify the supply air.
Conversely, during summer conditions, the supply air LAMEE may
transfer heat and moisture from the supply air to the exhaust air
to cool and dehumidify the supply air.
[0006] Laboratory prototype LAMEEs have been constructed and tested
in passive RAMEE loops to utilize both cross-flow and counter-flow
arrangements for each LAMEE. In a counter-flow configuration, the
desiccant liquid flows in a direction 180.degree. away from the air
flow direction in the adjacent air flow channel (i.e. counter-flow
with respect to the air flow direction for each pair of flow
channels) and heat and water vapor are transferred through the
semi-permeable, energy exchange, membrane of each LAMEE. In the
cross-flow arrangement, the liquid desiccant in the LAMEE flows at
90.degree. or perpendicular to the air flow direction through each
pair of channels in the LAMEE energy exchange membrane area.
[0007] Both counter-flow and cross-flow LAMEE devices can be used
to recover energy from exhaust air-flows. This energy can be used
to condition the supply air using another LAMEE device. Cross-flow
LAMEEs are not without disadvantages. In certain circumstances,
cross-flow exchangers generally have lower energy transfer
effectiveness in comparison to counter-flow exchangers of the same
energy exchange membrane area and inlet operating conditions.
Accordingly, it may be desirable to have an energy exchange system
that utilizes counter-flow LAMEEs. However, counter-flow LAMEEs are
generally more difficult and expensive to construct. In particular,
counter-flow LAMEEs require headers positioned on each end of the
LAMEE and require tighter design specifications. Accordingly,
conventional counter-flow LAMEEs may be impractical for some
applications but, where higher performance factors are needed, they
may be cost effective for other applications.
[0008] Cross-flow and counter-flow LAMEE devices have been
constructed and tested in laboratory RAMEE system loops. The
laboratory test prototypes for LAMEE devices have not performed as
expected. In particular, the test systems have not reached
steady-state operating conditions during a reasonable test period.
Moreover, the internal geometry of the air and liquid flow channels
are known to be far from the simple geometric configurations with
uniform, equally distributed mass flow conditions assumed in the
reported theoretical models.
[0009] Several key problems exist with the past research and
development efforts for LAMEE devices. First, simple theoretical
models of RAMEE or HVAC systems containing LAMEE devices, with
overly simplified internal geometries and physics, fail to model
what is physically occurring within the system. For example, each
fluid flow will self adjust in a few seconds to distribute its
local mass flux to minimize the pressure drop across the exchanger
as a whole unit for each type of fluid, flow channel geometry,
Reynolds number, Rayleigh number, and total mass flow rate. Within
a fluid, both viscous flow forces and buoyancy forces can alter the
flow streamlines. For example, buoyancy forces, caused by fluid
density gradients, may result in unstable mal-distributed flow when
the fluid density increases with height (i.e. counter to gravity)
and the viscous forces are not sufficient to cause a uniform flow
and so avoid a mal-distribution of flow within an exchanger. With
some flow configurations in an exchanger, such flow conditions are
likely to occur for laminar liquid flows but not the air flows. The
enhanced performance of stable flows with enhancing buoyancy
effects that self correct mal-distributions of flow are not
exploited in existing systems.
[0010] When the self-adjusted flow is steady, the rate of entropy
generation due to viscous (laminar or turbulent) flow will be a
minimum for each flow channel and collectively for all the channels
for each fluid (air or liquid desiccant) in the LAMEE. Due to small
geometric variations and destabilizing buoyancy effects in each
channel and among all the flow channels for each fluid, the
self-adjusted flow distribution will not, in general, be such that
the fluid mass flux is equally distributed among all channels or is
uniformly distributed in each channel for heat and mass transfer
through the semi-permeable membrane surfaces in a LAMEE. In order
to minimize the declination of performance of each LAMEE due to the
non-uniformities of flow distribution, the design specifications
must be very complete for each and all independent performance
influencing factors. When the uneven flow distribution leads to
unequal flows among channels and/or poor non-uniform area
integrated or locally averaged heat and water vapor transfer rates,
the flow is mal-distributed in the exchanger for energy exchange.
Mal-distribution of flows in any LAMEE in a RAMEE system will cause
the performance of the system to be sub-optimal. Mal-distribution
of flow will be especially prevalent for laminar flows with
destabilizing buoyancy effects within each liquid channel and among
the many liquid flow channels of a LAMEE. However, mal-distribution
can also occur with transition and turbulent flows. Local flow
instabilities, due to channel flow surface geometry when the flow
is above threshold Reynolds numbers, will induce local turbulent
mixing that can reduce mal-distributed flow in each channel and
will increase both the pressure drop and convection coefficients.
Exploiting fluid flow turbulence instabilities for enhanced
convection coefficients and reduction of flow mal-distribution in
exchangers has not been fully recognized or exploited in HVAC
exchanger designs.
[0011] Further, LAMEE devices constructed with very flexible
membranes need more detailed design and construction specifications
for each local flow region in flow channels than more rigid
flat-plate heat exchangers if they are to exceed the performance
factors required for buildings {i.e. ASHRAE Std. 90.1 and 189.1}
when tested using an accepted international standard {i.e. ASHRAE
Std. 84} and/or approach the theoretical performance factors put
forward by modelers. There is no indication that previous
researchers and inventors have fully understood the complexities of
the physical problems or were aware of the large number of
independent design factors that influence the performance of the
exchangers.
[0012] The key problems with existing RAMEE type energy recovery
systems and HVAC systems having one or more LAMEE type devices for
air conditioning supply air for buildings are closely related to
the research and development problems set forth above. Typically,
the factors that impact on the performance are not considered as a
complete set if they are considered at all.
[0013] The steady-state performance of a passive RAMEE system is
not characterized by a single factor as are some simple systems
(e.g. pumps and motors). Rather, the performance may be
characterized by a set of six dimensionless performance factors
(i.e. four system effectiveness values for the measured fraction of
the maximum possible steady-state sensible and latent energy
transfer under summer and winter standard test conditions and two
RER values for the measured fraction of auxiliary energy used with
respect to the total energy transferred between the supply and
exhaust air streams for the summer and winter test conditions). The
set of performance factors, Pf, can be referred to as the dependent
objective dimensionless ratios determined by analyzing the data
from two standard steady-state tests for a passive RAMEE
system.
[0014] The set of dimensionless ratios or factors that cause
changes to the values in Pf are independent factors, If, because
each one, or collectively several or all, will, if changed
significantly, change one or more of the factors in the set, Pf.
Mathematically, the relationship is expressed such that the
dependent dimensionless set Pf is only a function of a
predetermined dimensionless set, If, the operating conditions for
the inlet air temperature and humidity (i.e. one standard test
condition for winter and another for summer), and the uncertainty
in the measured test data for both Pf and If or in short Pf(If) and
where the standard test conditions are constrained by steady-state
or quasi-steady-state operating conditions for each test.
[0015] Existing LAMEE devices and passive RAMEE systems have not
been designed to meet specified performance factors other than
designing the LAMEE device with an internal geometry similar to
flat plate heat exchangers constructed using stiff elastic solids.
That is, the systems have not met the desired set Pf because not
all the factors in the set If were understood, considered, measured
or specified.
[0016] A need remains to specify or predetermine a complete set of
design parameters to construct a LAMEE and, for any inlet air
conditions, select a narrow range of system operating conditions
(i.e. the complete set If) if the RAMEE systems using two identical
LAMEEs are to exceed all the required performance factors in the
set Pf. When the design specifications are complete, the set Pf for
a passive RAMEE and its two LAMEEs will be predictable in design,
reproducible in manufacturing, and with reproducible and
certifiable steady-state standard test results. Another need
remains for LAMEEs used in a passive RAMEE system having an
increased effectiveness. The LAMEEs need to be designed and
operated to satisfy conditions that are typical for conventional
energy exchange systems and that are required through international
standards or local or state building codes.
SUMMARY OF THE INVENTION
[0017] In one embodiment, an energy exchanger is provided having a
housing constructed to meet a predetermined exchanger aspect ratio.
A plurality of panels extend through the housing. The panels have a
semi-permeable membrane forming an energy exchange area of the
panel. The panels form desiccant channels and air channels that are
separated by the semi-permeable membranes to facilitate contact
between an air stream flowing through the air channels and
desiccant flowing through the desiccant channels within the energy
exchange areas of the panels. The energy exchange area of each
panel has a top and a bottom. A height of the energy exchange area
is defined between the top and the bottom. The energy exchange area
of each panel has a front and a back. A length of the energy
exchange area is defined between the front and the back. The
exchanger aspect ratio is defined by the height of the energy
exchange area of each panel divided by the length of the energy
exchange area of each panel A desiccant inlet is provided in flow
communication with the desiccant channels. A desiccant outlet is
provided in flow communication with the desiccant channels. The
desiccant channels are configured to channel the desiccant from the
desiccant inlet to the desiccant outlet in at least one of a
counter-flow or cross-flow direction with respect to the direction
of the air stream to facilitate heat and water vapor transfer
through the semi-permeable membranes. The exchanger aspect ratio is
selected to provide at least one of a predetermined membrane area,
a predetermined length, or a predetermine duration of exposure of
the air stream to the desiccant.
[0018] In another embodiment, an energy exchanger is provided
having a housing. A plurality of panels form desiccant channels and
air channels that extend through the housing. The air channels are
configured to direct an air stream through the housing. The
plurality of panels are spaced apart based on a predetermined air
to desiccant channel rates that defines an air channel width and a
desiccant channel width. A desiccant inlet is provided in flow
communication with the desiccant channels. A desiccant outlet is
provided in flow communication with the desiccant channels. The
desiccant channels are configured to channel desiccant from the
desiccant inlet to the desiccant outlet in at least one of a
counter-flow or cross-flow direction with respect to the direction
of the air stream to facilitate heat and water vapor transfer
between the desiccant in the desiccant channels and the air stream
in the air channels. The air to desiccant channel rates are
selected to provide a predetermined mass or volume rate of air
stream flowing through the air channels and a predetermined mass or
volume rate of desiccant flowing through the desiccant
channels.
[0019] In another embodiment, an energy exchanger is provided
having a housing. A plurality of panels form desiccant channels and
air channels that extend through the housing. The air channels are
configured to direct an air stream through the housing. A desiccant
inlet is provided in flow communication with the liquid desiccant
channels. A desiccant outlet is provided in flow communication with
the liquid desiccant channels. The desiccant channels are
configured to channel liquid desiccant from the desiccant inlet to
the desiccant outlet in at least one of a counter-flow or
cross-flow direction with respect to the direction of the air
stream. A semi-permeable membrane extends through each panel to
facilitate heat and water vapor transfer between the desiccant in
the desiccant channels and the air stream in the air channels. The
air stream and the liquid desiccant pressure cause the
semi-permeable membrane to deflect during operation. The desiccant
membrane is selected based on predetermined channel deflection
ranges that are defined to limit the amount of membrane
deflection.
[0020] In another embodiment, an energy exchanger is provided
having a housing. A plurality of panels form liquid desiccant
channels and air channels that extend through the housing. The air
channels are configured to direct an air stream through the
housing. A desiccant inlet is in flow communication with the liquid
desiccant channels. A desiccant outlet is in flow communication
with the desiccant channels. The desiccant channels are configured
to channel desiccant from the desiccant inlet to the desiccant
outlet in at least one of a counter-flow or cross-flow direction
with respect to the direction of the air stream to facilitate heat
and water vapor transfer between the desiccant in the desiccant
channels and the air stream in the air channels. The desiccant is
selected based on predetermined salt solution concentration ranges
for a selected life span and cost of the desiccant.
[0021] In another embodiment, an energy exchanger includes a
housing. A plurality of panels form desiccant channels that extend
through the housing. Each of the plurality of panels has a
semi-permeable membrane that is selected to meet predetermined
membrane resistance ranges defining physical properties of the
membrane. Air channels are formed between the desiccant channels.
The air channels are configured to direct an air stream through the
housing. A desiccant inlet is in flow communication with the
desiccant channels. A desiccant outlet is in flow communication
with the desiccant channels. The desiccant channels are configured
to channel desiccant from the desiccant inlet to the desiccant
outlet so that the desiccant membranes facilitate heat exchange
between the desiccant and the air stream. The membrane resistance
ranges are selected to limit a flow of the desiccant through the
desiccant membrane.
[0022] In another embodiment, an energy exchanger is provided
having a housing. A plurality of panels form desiccant channels
that extend through the housing. The plurality of panels each have
a desiccant membrane. Air channels are formed between the desiccant
channels. The air channels are configured to direct an air stream
through the housing. The air stream flows through the air channels
at a predetermined air flow ratio. A desiccant inlet is in flow
communication with the desiccant channels. A desiccant outlet is in
flow communication with the desiccant channels. The desiccant
channels are configured to channel liquid desiccant from the
desiccant inlet to the desiccant outlet so that the semi-permeable
membranes facilitate heat and water vapor exchange between the
liquid desiccant and air streams. The air mass flow rate ratio of
the air stream selected to meet a predetermined exposure of the air
stream to the semi-permeable membranes.
[0023] In another embodiment, an energy exchanger is provided
having a housing. A plurality of panels form desiccant channels
extending through the housing. Air channels are formed between
adjacent desiccant channels. The air channels are configured to
direct an air stream through the housing. A desiccant inlet is in
flow communication with the desiccant channels. A desiccant outlet
is in flow communication with the desiccant channels. The desiccant
channels are configured to channel desiccant from the desiccant
inlet to the desiccant outlet so that the desiccant membranes
facilitate heat exchange between the desiccant and the air stream.
The energy exchanger operates within predetermined exchanger
performance ratios that define a sensible and latent energy
exchange between the desiccant and the air stream.
[0024] In another embodiment, a method of exchanging energy between
a desiccant and an air stream is provided. The method includes
extending a plurality of panels through a housing of the energy
exchanger to form desiccant channels and air channels. A desiccant
membrane is selected for each of the panels. An air stream is
directed at a predetermined air flow ratio through the air
channels. Desiccant is directed through the desiccant channels. The
desiccant membrane is selected based on membrane resistance ranges
defined to limit a flow of the desiccant through the desiccant
membrane. The air flow ratio of the air stream is selected to meet
a predetermined exposure of the air stream to the desiccant
membrane. A flow rate of the desiccant with respect to a flow rate
of the air stream is controlled to achieve predetermined exchanger
performance ratios that define a thermal energy exchange between
the desiccant and the air stream.
[0025] In another embodiment, a method of exchanging energy between
a desiccant and an air stream is provided. The method includes
extending a plurality of panels through a housing of the energy
exchanger. The plurality of panels are spaced based on
predetermined air to desiccant channel rates to form desiccant
channels and air channels between adjacent panels. The
predetermined air to desiccant channel mass or volume flow rates
help to design an air channel width and a desiccant channel width.
A membrane is selected to extend through the panels based on
predetermined channel deflection ranges that are defined to limit
an amount of membrane deflection with respect to the channel width.
An air stream is directed through the air channels. A desiccant is
directed through the liquid desiccant channels in at least one of a
counter-flow or cross-flow direction with respect to the direction
of the air stream so that the membrane facilitates heat and water
vapor exchange between the liquid desiccant in the desiccant
channels and the air stream in the air channels. The predetermined
air to desiccant channel rates provide a predetermined volume rate
of air stream flowing through the air channels and a predetermined
volume rate of liquid desiccant flowing through the desiccant
channels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic view of an energy exchange system
formed in accordance with an embodiment.
[0027] FIG. 2 is a side perspective view of a liquid-to-air
membrane energy exchanger formed in accordance with an
embodiment.
[0028] FIG. 3a is a side perspective view of the liquid-to-air
membrane energy exchanger shown in FIG. 2 having a cutout along the
line 3-3 shown in FIG. 2
[0029] FIG. 3b is a front view of the panels shown in FIG. 3a.
[0030] FIG. 4 is a side perspective view of a liquid-to-air
membrane energy exchanger panel formed in accordance with an
embodiment.
[0031] FIG. 5a is an exploded view of the panel shown in FIG.
4.
[0032] FIG. 5b is a plan view of a screen and mounted or bonded
flexible space flow guides for desiccant liquid flow channels
formed in accordance with an embodiment.
[0033] FIG. 6a is a view of an air channel formed in accordance
with an embodiment.
[0034] FIG. 6b is a front view of the air channels shown in FIG. 6
and being deformed.
[0035] FIG. 6c is a front view of the air channels shown in FIG. 6
and being deformed.
[0036] FIG. 7 is a graph of mass flow rates as a ratio of the mass
flow rate of a desiccant with respect to a mass flow rate of
air.
[0037] FIG. 8 is a graph of salt solution concentrations formed in
accordance with an embodiment.
[0038] FIG. 9 is a side perspective view of a liquid-to-air
membrane energy exchanger formed in accordance with an alternative
embodiment.
[0039] FIG. 10 is a side perspective view of a liquid-to-air
membrane energy exchanger formed in accordance with an alternative
embodiment.
[0040] FIG. 11 is a side perspective view of a liquid-to-air
membrane energy exchanger formed in accordance with an alternative
embodiment.
[0041] FIG. 12 is a side perspective view of a liquid-to-air
membrane energy exchanger formed in accordance with an alternative
embodiment.
[0042] FIG. 13 is a side perspective view of a liquid-to-air
membrane energy exchanger formed in accordance with an alternative
embodiment.
[0043] FIG. 14 is a schematic view of an alternative energy
exchange system formed in accordance with an embodiment.
[0044] FIG. 15 is a schematic view of another energy exchange
system formed in accordance with an alternative embodiment
DETAILED DESCRIPTION OF THE DRAWINGS
[0045] The foregoing summary, as well as the following detailed
description of certain embodiments will be better understood when
read in conjunction with the appended drawings. As used herein, an
element or step recited in the singular and proceeded with the word
"a" or "an" should be understood as not excluding plural of said
elements or steps, unless such exclusion is explicitly stated.
Furthermore, references to "one embodiment" are not intended to be
interpreted as excluding the existence of additional embodiments
that also incorporate the recited features. Moreover, unless
explicitly stated to the contrary, embodiments "comprising" or
"having" an element or a plurality of elements having a particular
property may include additional such elements not having that
property.
[0046] In one embodiment, a LAMEE energy exchanger is provided.
Each embodiment will represent at least one factor in the set If
(presented below in Table 1 as independent factors G1-G10 and
P1-P12). Many factors of the set If pertain to the LAMEE design and
operation. Other factors pertain to the passive RAMEE system,
comprising two identical LAMEEs, under a standard steady-state
summer or winter test condition. The energy exchanger includes a
housing having a front and a back and two sides. The housing has a
top and a bottom extending between the front and the back. The
housing is constructed to contain a set of air and liquid desiccant
flow channels which are each separated by a semi-permeable membrane
that permits heat and water vapor to be transferred between the air
and liquid desiccant flows. Each of the flow channel energy
exchange membrane areas is rectangular in shape, with liquid
desiccant flow either nearly counter-flow or cross-flow relative to
the direction of the air flow in each adjacent fluid channel pair.
Other predetermined geometric length ratios that may be specified
for each LAMEE are the exchanger panel aspect ratio and liquid flow
entrance/exit length ratio. The exchanger panel aspect ratio is
defined by the height of each panel energy exchange membrane area
divided by the length of the energy exchange membrane area in the
panel. A plurality of panels forming desiccant liquid channels and
air channels extend through the housing. The air channels are
configured to direct an air stream uniformly, with equal mass flow
rate among the total number of air channels in the housing.
Likewise, the fluid flow through each liquid flow channel is
uniformly distributed in each liquid flow channel and the mass flow
rate for each channel is the same for all liquid flow channels. In
alternative embodiments, the air stream and the fluid flow through
the heat exchanger may be non-uniform. A desiccant inlet is
provided in flow communication with the liquid desiccant channels
in the housing. A desiccant outlet is provided in flow
communication with the liquid desiccant channels.
[0047] The design and operational parameters of the LAMEEs and
passive RAMEE system will include all of the geometric (G) and
physical (P) ratios set forth in Table 1.
TABLE-US-00001 TABLE 1 Defined Set of Dimensionless Independent
Factors IF and their Ranges Parameter Description Suggested Range
Parameter Meaning G1 Counter or Cross 180.degree. or 90.degree.
Dominant relative flow for the liquid flow directions for desiccant
and air air and liquid streams in each desiccant in each exchanger
exchanger G2 Aspect ratio (AR = 0.1 < AR < 3.0 Energy
Exchange H/L) of each panel Aspect Ratio for in the LAMEE, each
panel in a wherein AR is the LAMEE (Since this aspect ratio, H is
the ratio is also a factor height of the energy in reducing
exchange area in the buoyancy induced flow panel, and L is
mal-distributions the air flow length effects the factor's of the
energy magnitude may be exchange area of restricted.) the LAMEE G3
Inlet/outlet ratio 0.02 < Le/L < 0.2 ratio of the flow for
primarily Channel liquid counter-flow inlet/outlet length, LAMEE
Le, divided by the 0.5 < Le/L < or = flow channel length, L
1.0 for primarily cross-flow LAMEE G4 Ratio of the 0.0 <
sig(d.sub.w,air)/d.sub.w,air < Air and liquid operating flow 0.2
desiccant channel channel average 0.0 <
sig(d.sub.w,liq)/d.sub.w,liq < manufactured and hydraulic
diameter 0.2 operating width standard deviation characteristic for
all channels variations causing [sig(d.sub.w,air) and flow mal-
sig(d.sub.w,liq) for air and distributions due to liquid channels]
channel geometry with respect to the variations for each average
hydraulic LAMEE diameter for all air d.sub.w,air and liquid
d.sub.w,liq channels (including membrane deflections) in a LAMEE G5
Ratio of the 0.0 < sig(d.sub.st)/d.sub.st < Flow channel
standard deviation 0.2 variations in each of the flow channel
typical flow channel hydraulic diameter to reduce flow mal- to mean
hydraulic distributions due to diameter for a geometric variations
typical flow in a channel and so channel in a make each LAMEE LAMEE
for air or more compact in liquid desiccant size G6 Ratio of the
solid 0.05 < (Ass/Ast).sub.air < The screen area surface area
of (a) 0.2 ratios are (a) the air flow channel 0.1 <
(Ass/Ast).sub.liq < directly proportional structural membrane .3
to the area blockage support screen to its factor for the total
area and (b) the membrane for water liquid flow channel vapor
transfer and screen solid area to (a&b) directly its total area
related to the turbulence enhancement ratio for each flow G7
Support Spacer Dssa/Dsa = m/n and distance between Ratios 0.3 <
m/n < 5.0, the air channel where m and n are spacer support
whole numbers structures in the average bulk flow streamline
direction, Dssa, divided by the distance between spacer support
structures normal to the average bulk flow spacer support
structures, Dsa, is a fraction or whole number G8 Liquid flow
liquid flow direction minimize mal- direction through the liquid
distribution effects flow channels is and maintain high controlled
with performance factors respect to the for the RAMEE direction of
gravity system G9 Flow channel angle 45 < Z.sub.g <
135.degree. angle Z.sub.g between a vector normal to the plane of
each flow channel and the vector for the acceleration of gravity
G10 Flow channel edge 60 < O* < 120.degree. angle O* between
angle the vector parallel to the edge of each flow channel along
its length and the acceleration of gravity P1 Dimensionless flow
.sub.(a) Re.sub.dh > Re.sub.c Where the characterization (b)
Ra.sub.dh < Ra.sub.c characteristic length numbers (a) is the
hydraulic Reynolds number diameter (dh) and (Re) for each typical
the subscript `c` flow channel is such refers to (a) the that the
flow is critical transition turbulent for the air from laminar to
flow and, where turbulent flow and practical, for the (b) the
critical liquid flow channels transition from (b) Rayleigh stable
uniform flow number (Ra) is to unstable mal- favorable for stable
distributed liquid uniform especially flow due to density when the
liquid flow variations is laminar P2 Exchanger number 1.0 < NTU
< 15 Exchanger operating of transfer units condition (NTU) for
heat characteristic ratio transfer during a to obtain a good RAMEE
test exchanger and system effectiveness P3 Exchanger thermal 1.0
< Cr* < 10.0 Exchanger operating capacity ratio (Cr*)
condition during a RAMEE characteristic ratio test to obtain a good
exchanger and system effectiveness P4 Ratio of the 0.1 <
R.sub.m,wv/R.sub.air,wv < Membrane water membrane water 3.0
vapor to air flow vapor resistance convection (R.sub.m,wv) to
resistance ratio to convective water obtain a good vapor mass
transfer exchanger and resistance (R.sub.air,wv) system latent
energy effectiveness P5 Air flow pressure 10.sup.3 <
p.sub.hA.sub.c/V.sub.c < 10.sup.4 Air flow pressure drop ratio
drop ratio for each LAMEE to obtain a good performance RER for the
RAMEE system P6 flow channel ratio laminar flow channel average of
convective heat convective heat friction flow transfer coefficient,
h transfer coefficient, coefficients for h.sub.lam, at the same
turbulent and channel Reynolds laminar flow, f and number is [1.1
< f.sub.lam, satisfy [f/f.sub.lam < h/h.sub.lam <
2.0].sub.Re h/h.sub.lam].sub.Re P7 Air flow pressure
p.sub.m,bt/(rho * g * H) > 20 Membrane liquid drop ratio
(p.sub.hA.sub.c/V.sub.c), penetration wherein p.sub.h is the
resistance pressure pressure drop across with respect to the the
LAMEE in units maximum static of length, A.sub.c is the pressure
difference area of the air in each LAMEE channel, and V.sub.c is
liquid flow channel the channel volume to prevent leaks in for air
flow in the the LAMEE during LAMEE normal operation P8 Membrane
liquid p.sub.cs,bt/(rho * g * H) > 20 Membrane edge seal
break-through liquid penetration pressure ratio pressure with
[p.sub.m,bt/(rho * g * H)], respect to the static wherein
p.sub.m,bt is the liquid flow channel membrane liquid in each LAMEE
to break-through prevent leaks in the pressure, g is LAMEE under
gravity, and H is the normal operation height of the membrane panel
energy exchange area P9 Elastic tensile yield 0.02 < Membrane
tensile limit ratio for the T.sub.m,yl/(p.sub.l,op * S.sub.ws) <
1.5 elastic yield limit membrane pressure per unit
[T.sub.m,yl/(p.sub.l,op * S.sub.ws)], length with respect wherein
T.sub.m,yl is the to the support screen tensile yield limit
pressure per unit for the membrane, length to reduce p.sub.l,op is
a typical membrane operating pressure defections on the for the
liquid in support screen for each LAMEE, and the membrane S.sub.ws
is a wire spacing distance for a screen used to resist the liquid
pressure for each liquid flow channel P10 Time duration for a
t.sub.salt,risk/t.sub.op < 0.15 Risk time duration risk of of
salt solution crystallization in the crystallization salt solution
over compared to the the year divided by total time duration the
total yearly time for RAMEE system duration of system operation to
reduce operation (t.sub.salt,risk/t.sub.op) the relative time
duration required for active control to avoid crystallization in
the RAMEE system P11 cost of salt or C.sub.salt,mix/C.sub.LiCl <
1.0 Salt solution cost mixture of salts used compared to the cost
in the system of a lithium chloride divided by the salt solution
for the corresponding cost same RAMEE of LiCl for the system system
P12 LAMEE heat 0.0 < Q.sub.sur/Q.sub.exch < LAMEE heat
exchange rate 0.05 exchange rate with the surroundings (Q.sub.sur)
divided by the heat rate transferred to or from the air flowing
through the exchanger (Q.sub.exch) during a standard test of a
RAMEE system using two identical LAMEEs
[0048] With respect to factor G1, the desiccant channels are
configured to channel equally the liquid desiccant mass flow rate
through each of the liquid flow channels from the desiccant inlet
to the desiccant outlet in at least one of a counter-flow or
cross-flow direction with respect to the direction of the adjacent
air streams to facilitate heat and water vapor transfer through the
semi-permeable membrane between the liquid desiccant flow in the
desiccant channels and the air stream in the air channels.
[0049] With respect to factor G2, the exchanger panel aspect ratio
is selected to provide a predetermined exposure through the
semi-permeable membrane between the air and liquid flow for
adjacent channels in each LAMEE.
[0050] The liquid flow entrance/exit length ratio with respect to
the length of the membrane energy transfer area (factor G3) may be
utilized for flow channels that are primarily counter-flow within a
LAMEE. The effectiveness of the LAMEE may be partly determined
using each of the factors G1-G3. Accordingly, fluid flow direction
(factor G1), aspect ratio (factor G2) and entrance/exit flow length
ratio (factor G3) in the set If may be used to partly determine the
LAMEE performance.
[0051] With respect to the factor G3, for primarily counter-flow
LAMEE exchangers, the ratio of the flow channel liquid inlet/outlet
length, Le, divided by the flow channel length, L is approximately
0.02<Le/L<0.2. For primarily cross-flow LAMEE exchangers, the
ratio of the liquid flow inlet/outlet the ratio of the liquid flow
channel inlet, Le, divided by the flow channel length, L is
approximately 0.5<Le/L<or =1.0.
[0052] The determination of the statistical channel averaged
hydraulic diameter variation for the liquid flow channels will be
more difficult to determine for the liquid flow channels than the
air flow channels because the volume flow rates and channel
dimensions are small (e.g. 2 to 10 times smaller than the air
channels). The decrease in the effectiveness due to
mal-distribution of mass flows among the fluid flow channels of
each LAMEE in the passive RAMEE system, comprising two identical
LAMEEs, will be partly determined using the ratio of standard
deviation of average channel hydraulic diameters to mean average
channel hydraulic diameter (factor G4). For example, assuming a
uniform flow through each channel but different flow rates among
the set of channels in a LAMEE for air flow through a large set of
channels, with a standard deviation of hydraulic diameter for the
channels divided by the mean hydraulic diameter equal to 0.1
compared with one that has no variations in the liquid flow
channels, the decrease in air pressure drop across the flow
channels in a LAMEE relative to the same channels with no width
variations will be about 3% for laminar flow and 6% for turbulent
flow and the corresponding drop in RAMEE system effectiveness will
be about 6% for laminar flow and 8% for turbulent flow (it will be
made clear that laminar flows in the liquid channels may have
strong destabilizing effects unless the buoyancy forces
re-stabilize the flows). If the variations in flow channel widths
are relatively identical for the liquid flow channels then the
total decrease in the effectiveness for the RAMEE system would be
approximately 8.5% and 11% for laminar and turbulent flows,
respectively. Variations in the channel widths for the typical flow
channels, characterized by factor G5, will further decrease the
system performance. Furthermore, since there may be a strong
correlation between the liquid flow and air flow channel hydraulic
diameters (widths) (i.e. the variation in channel widths are not
statistically independent for each fluid), the drops in system
effectiveness can be significantly larger. Furthermore, and as
discussed below, mal-distribution of flow due to buoyancy effects
in each liquid flow channel can result in an additional drop in
effectiveness. Since the flow channel ratio of flow channel
hydraulic diameters only deals with the variations in the average
flow channel hydraulic diameters, other independent parameters will
be needed to complete the set If in Table 1.
[0053] Another embodiment is provided wherein the distance between
the membranes of air and liquid flow channels (also called channel
widths or hydraulic diameters) are designed to be nearly uniform
over each channel in a LAMEE during typical operating conditions.
Due to manufacturing and operational tolerances, when averaged over
each flow channel, the locally averaged hydraulic diameter may be
different for each fluid (i.e. air or liquid desiccant), for local
flow regions within each channel and among all the channels in a
LAMEE. Manufactured LAMEEs under typical operating conditions will
have a distribution of average channel hydraulic diameters that is
statistically normal (i.e. Gaussian) or nearly normal in
distribution considering the uncertainty bounds. The variation in
channel average flow channel hydraulic diameters in a LAMEE will
cause air and liquid flow mal-distributions for each fluid among
the many flow channels in each LAMEE. Consequently the energy
transfer effectiveness and the fluid pressure drop of the LAMEE
will be lower than that for an ideal theoretical design with equal
mass flow rates for each fluid channel. The variations among all
the flow channel average hydraulic diameters that cause variations
in each fluid mass flow rate should be designed to be small (i.e.
the standard deviation of the flow channel hydraulic diameters for
both the air and liquid flow channels should be small with respect
to the mean average flow channel hydraulic diameter for each fluid
within the LAMEE, G4). The flow channel average hydraulic diameter
variation in a LAMEE is also a factor for counter-flow liquid
channels because the pressure drop for the liquid flow entrance and
exit regions in the channel may be a larger fraction of the total
channel pressure drop and the flow path lengths may be longer (e.g.
longer than the air flow path length through each channel). Channel
width variations will be present for the typical air and liquid
flow channels. Due to their normal distribution, these width
variations within each panel are best characterized by their
statistical properties as defined by geometric factor G5. In an
exemplary embodiment a width of the air channels is selected based
on a width of the desiccant channels.
[0054] As a summary of the geometric factors G6 to 010, the liquid
channel screen insures a minimum spacing for the channel width and
enhances the transition to turbulent flow for large liquid flow
rates. The air and liquid flow channel screen area ratios (factor
G6) is yet another predetermined embodiment because the ratios are
directly related to turbulence enhancement and blockage fraction of
the membrane for water vapor transfer on the air side of the
membrane. The air channel spacer support structure ratio (factor
G7) is another geometric embodiment that assists the transition to
turbulent flow and partly determines the geometry of the flow
channel through its structural supports. Factor G8 defines the best
liquid flow direction with respect to gravity through each LAMEE
exchanger which may be controlled to avoid liquid flow
mal-distribution and factors G9 and G10 define LAMEE angles with
respect to gravitational acceleration to get high performance
factors for the RAMEE system and all its LAMEEs.
[0055] The new ratio of standard deviation for each liquid flow
stream-tube hydraulic diameter in each liquid flow channel divided
by the mean value can be used to analyze the decrease in expected
effectiveness of each LAMEE and the passive RAMEE system in which
it is used or tested. For example, if the flow tube standard
deviation ratio is 0.05 (i.e. 5%) for the typical liquid flow
channel in each identical LAMEE in the RAMEE system, then the
decrease in total system effectiveness will be about 4% for
turbulent flows but the loss of effectiveness may be much higher
for laminar liquid flows where the flow field is unstable due to
buoyancy effects.
[0056] Average or bulk mean flow streamlines in each of the air
flow channels will, depending on the air channel support structure,
be on average nearly parallel straight lines through the energy
exchange area. The air flow channels are mostly a void region with
parallel flow spacer guide structures that cause the streamlines to
be nearly straight while the inertial to viscous forces in the
flow, characterized by the Reynolds numbers (i.e.
Re.sub.dh=Vd.sub.h/k.sub.v where V is the bulk mean channel fluid
speed, d.sub.h is the hydraulic diameter of the flow channel, and
k.sub.v is the kinematic viscosity of the fluid) are moderately
high (i.e. 300<Re.sub.dh,air<1500 which, as will be discussed
in more detail later, may be laminar or turbulent). This is not the
case for the liquid desiccant channels in counter/cross flow LAMEEs
where the Reynolds numbers will be much lower and the flow is
likely to be laminar at low values of Cr*. The average liquid flow
streamlines can be much more complex than for the channel flow of
air because the liquid flow passages cannot lead to parallel
straight lines and when unstable buoyancy forces are much greater
than the viscous forces, characterized by the Rayleigh number, Ra,
they induce flow instabilities that cause very complex streamlines
(i.e. Ra>Ra.sub.c) for counter-flow exchangers with parallel
membranes (where Ra=-a*B*gd.sub.h.sup.2H.sup.2/(k.sub.vt.sub.d)
where a* is the temperature gradient in the vertical direction
(i.e. with respect to gravitational acceleration when the tilt
angle is small), B* is the coefficient of thermal expansion, g is
the acceleration due to gravity, H is the vertical height of the
flow channel and t.sub.d is the thermal diffusivity of the fluid).
Since the viscous forces for turbulent flows are much higher than
they are for laminar flows, the critical Rayleigh number, Ra.sub.c,
at which buoyancy induced instabilities cause significant flow
mal-distributions changes significantly with the type of flow. That
is, the screens used in each fluid flow channel and the spacers
used in the air flow channels can be used to enhance turbulence in
each flow but, at the same time it is not desirable to
unnecessarily increase the pressure drop due to each fluid flow.
The preferred screen solid area to total screen area is given by
factor G6. Even cross flow exchangers will have complex streamline
patterns when Ra>Ra.sub.c and so their performance factors will
be lower than expected from theoretical values derived from typical
simplifying assumptions. Operating LAMEE exchangers so that the
Rayleigh number is always in the stable flow region (i.e.
Ra.sub.dn<Ra.sub.c) allows the performance factors to be high
compared to exchangers that are not designed and operated to
account for the instability. The value for the critical Rayleigh
number for a particular exchanger is an empirical quantity that
depends on the exchanger design and its fluid properties and
Reynolds number.
[0057] With respect to the factor G7, the distance between the air
channel spacer support structures in the average bulk flow
streamline direction, Dssa, divided by the distance between spacer
support structures normal to the average bulk flow spacer support
structures, Dsa, is a fraction or whole number, such that
Dssa/Dsa=m/n and 0.01<m/n<5.0, where m and n are whole or
integer numbers.
[0058] With respect to factor G8, the liquid flow direction through
the liquid flow channels is controlled with respect to the
direction of gravity (i.e. from the bottom inlet to the top outlet
for liquid flows that are heated within the channel and vice versa
for liquid flows that are cooled in the channel) to minimize
mal-distribution effects and maintain high performance factors for
the RAMEE system.
[0059] With respect to factor G9, an angle Z.sub.g between a vector
normal to the plane of each flow channel and the vector for the
acceleration of gravity is such that 45<Z.sub.g<135.degree..
The angle Z=90.degree. for most applications so that buoyancy
effects will enhance the LAMEE performance when the correct flow
direction is chosen for each exchanger.
[0060] With respect to factor G10, an angle O* between the vector
parallel to the edge of each flow channel along its length and the
acceleration of gravity is such that 60<O*<120.degree.. This
angle, or the LAMEE tilt angle (90.degree.-O*), is normally
selected to result in a positive enhancement of performance due to
buoyancy effects.
[0061] Further embodiments are provided for with the flow channel
flow conditions and their orientation, or combinations of several
geometric and operational factors, for each LAMEE which involves
flow field characterization through the Reynolds number and the
flow stability factor, Rayleigh number. The Rayleigh number can be
selected to be most favorable by arranging the temperature
gradients in each LAMEE to be such that the fluid density always
increases in the downward direction of gravitational acceleration.
This implies that the flow channels in a LAMEE should be aligned so
that their normal area vector is horizontal and the length vector
of the flow channel is tilted with a large enough angle to cause a
favorable and significant density gradient for uniform flows in
each channel and among all the channels. Channel flows in long thin
channels with small or negligible entrance lengths for the flows
are well known to be one of: (a) fully developed laminar flow at
low Reynolds number, (b) fully developed turbulent flow at high
Reynolds number, or (c) transition turbulent flows at intermediate
Reynolds numbers between the two low and high transition Reynolds
numbers. The flow transition Reynolds number that causes the flow
to transfer from laminar to transition turbulence tends to be fixed
for any given channel (see factor P1) where the Rayleigh number
indicates no buoyancy induced mal-distributions (see factors G8,
G9, & G10), but very small changes to the surfaces inside each
channel can cause large changes to the transition Reynolds number.
That is, the flow in a channel can become turbulent when small
increased surface roughness or flow separations within the channel
flow changes are introduced at some low Reynolds numbers compared
to laminar flow in the same channels with no roughness additions.
In one embodiment, a characteristic Reynolds number for the air
stream through the air channels is greater than a critical Reynolds
number for turbulent flow in the air channels. In another
embodiment, a characteristic Rayleigh number for desiccant flow in
the desiccant channels is less than a critical Rayleigh number for
thermally induced liquid density instability causing non-uniform
mal-distributed flow at a Reynolds number for desiccant flow.
[0062] The fluid inertial, viscous and buoyancy forces all play
important roles for a well designed and operated LAMEE and their
ratios are characterized by the Reynolds number and Rayleigh number
in factor P1 where it is stated that we prefer to have turbulent
flow when practical and we should always avoid adverse buoyancy
effects in the liquid flows. The Reynolds number for the liquid
flow through the liquid flow channels will typically be very low
(i.e. 0.1<Re.sub.dh,Hq<100). Under these circumstances, the
liquid flow may be laminar for the lowest Reynolds numbers in the
range but, for some specially designed internal geometries the flow
will become complex-laminar-turbulent or turbulent as the Reynolds
number is increased from the low to the high end of this Reynolds
number range. Therefore the liquid channel flow, which may exhibit
laminar flow mass flux channeling or fingering of the liquid for
unfavorable Rayleigh numbers at the low Reynolds numbers in the
above range, will, due to turbulent mixing, locally self adjust at
higher Reynolds number so that mal-distribution effects are much
smaller. On the other hand, the air flow channels will most likely
have turbulent flow, especially if some surface roughness is
introduced to cause the flow to be turbulent. In an exemplary
embodiment, the air channels include turbulence enhancing surface
roughness features to facilitate increasing energy transfer that
exceeds an additional air pressure drop energy loss when convective
heat and latent energy transfer increase. In another embodiment,
the desiccant include turbulence enhancing surface roughness
features when a Rayleigh number is less than a critical Rayleigh
number at a Reynolds number for the flow.
[0063] Since the liquid is under a pressure greater than the
adjacent channel air pressure, it causes the flexible
semi-permeable membrane and its support structure in the air
channel on either side of each liquid flow channel to deflect or
deform elastically. As previously noted, the liquid flow should be
directed through each channel so that it minimizes flow
mal-distributions (i.e. Ra<Ra.sub.c for laminar flow and, when
flow rates are higher, Re>Re.sub.c for turbulent flow). The
design and operational conditions imply that the liquid flow
direction will be such that the liquid flow will be from a bottom
inlet to the top outlet for the supply LAMEE exchanger and from the
top inlet to the bottom outlet for the exhaust LAMEE exchanger for
the standard summer test conditions. The flow directions through
each LAMEE will be reversed for the winter standard test
conditions. That is, a liquid flow direction controller will be
used so that the inlet direction will be bottom or top of each
LAMEE exchanger depending on the value of the Rayleigh number for
each exchanger and the angles of the flow channels with respect to
the acceleration direction of gravity as defined in Table 1 for
factors G9 and G10. With these controlled liquid flow directions
and a small performance enhancing tilt angle for the LAMEE, the
problems of flow mal-distribution will have been reduced to a
minimum for the geometric configurations of the flow channels and
the channel Reynolds number. In fact, the restoring forces of
favorable buoyancy forces that induce flow uniformity into the
liquid flow channels that, due to flow channel width variations,
can reduce the declination of performance factors for a LAMEE using
factors G9 and G10 compared to the case of no restorative buoyancy
forces.
[0064] On the liquid flow side of the membrane, turbulent mixing
within the flow channel may be a factor if there is a tendency
toward laminar flow buoyancy induced mass flux fingering at high
Rayleigh numbers and very low Reynolds numbers result in
non-uniform exposure of the bulk flow to the molecular diffusion
transfer process in the liquid. In one embodiment, for the factor
P1, turbulence enhancement of the air and liquid flows through the
LAMEE energy exchange channels is used to enhance turbulent
transition and liquid flow directions are chosen for each LAMEE
operating condition to decrease buoyancy induced instabilities in
the liquid flow channels. For a given flow channel geometry, which
is characterized by the hydraulic diameter and surface roughness,
the Reynolds number is the only operating factor that determines
whether the flow is laminar or turbulent. The performance
effectiveness and RER of the passive RAMEE and its LAMEEs will be
enhanced with some turbulent mixing.
[0065] In other embodiments, an energy exchanger is provided. The
exchanger includes a housing for the air and liquid desiccant
channels each separated by a semi-permeable membrane. A plurality
of panels forming desiccant channels and air channels extend
through the housing. The air channels are configured to direct an
air stream through the housing. The plurality of panels are spaced
apart partly based on predetermined air to desiccant mass rates
(P3) and the air channel width or spacing and a desiccant channel
width or spacing. The air to desiccant mass flow rate may be
selected to achieve predetermined exchanger performance ratios that
define a sensible and latent energy exchange rate between the
desiccant and the air stream. The panel spacing may also be
dependent on factors G4, G5, and P5. The air to desiccant mass flow
rates may define an air channel width and/or a desiccant channel
width. The air-to-desiccant channel mass flow rates may be selected
to provide a predetermined mass or volume of air stream flowing
through the air channels and/or a predetermined mass or volume of
desiccant flowing through the desiccant channels. The desiccant
channels may have an approximately constant desiccant channel
width. Additionally, the air channels may have an approximately
constant air channel width. In one embodiment, a ratio of the
average air channel width divided by the average desiccant channel
width is within a range of 1 to 5.
[0066] A desiccant inlet header is provided in flow communication
with all the desiccant channels. A desiccant outlet is provided in
flow communication with the desiccant channels. The desiccant
channels are configured to channel desiccant from the desiccant
inlet to the desiccant outlet in at least one of a counter-flow or
cross-flow direction with respect to the direction of the air
stream to facilitate heat and water vapor transfer between the
desiccant in the desiccant channels and the air stream in the air
channels.
[0067] For a predetermined test condition of the passive RAMEE
system, a predetermined equal mass flow rate of supply and exhaust
air pass through each identical LAMEE. By so doing, the number of
transfer units for heat transfer (NTU) in each LAMEE is
predetermined (factor P2). When the pumping rate of liquid
desiccant is chosen, the heat capacity rate ratio (i.e. the mass
flow rate times the specific heat of desiccant liquid flow divided
by the mass flow rate of air) through each LAMEE, Cr*, is
predetermined (factor P3). There may be a trade-off for the
selection of Cr* because increasing the liquid flow rate may
enhance turbulence in the liquid flow channels and will increase
Cr*, which can have positive and negative effects on the
effectiveness. Accordingly, the value of Cr* should be selected so
that the effectiveness of the LAMEE is a maximum when the highest
performance is required.
[0068] Other embodiments for energy exchangers are provided. The
exchanger includes a housing containing the air and liquid flow
channels each separated by a semi-permeable membrane. A plurality
of panels forming desiccant channels and air channels extend
through the housing. The air channels are configured to direct an
air stream through the housing. A desiccant inlet header is
provided in flow communication with all the desiccant channels. A
desiccant outlet is provided in flow communication with the
desiccant channels. The desiccant channels are configured to
channel liquid desiccant from the desiccant inlet to the desiccant
outlet in at least one of a counter-flow or cross-flow direction
with respect to the direction of the air stream. A semi-permeable
membrane extends through each panel to facilitate heat and water
vapor transfer between the desiccant liquid in the desiccant
channels and the air stream in the air channels. The membrane may
be selected based on membrane resistance ranges defined to reduce a
flow of desiccant through the membrane. The semi-permeable membrane
possesses a resistance to water vapor diffusion which, relative to
the typical convection water vapor transport resistance in the air
channels, lies within a specified range given by factor P4. A water
vapor transfer resistance ratio is defined by a ratio of the
membrane water vapor resistance (R.sub.m,wv) to convective water
vapor mass transfer resistance (R.sub.air,wv). The ratio of the
membrane water vapor resistance (R.sub.m,wv) to convective water
vapor mass transfer resistance (R.sub.air,wv) may be within a range
of 0.2 to 3.
[0069] The static air pressure drop as it passes from air inlet to
outlet in each LAMEE in a RAMEE system is the same for each air
channel. The range of acceptable air pressure drops for a LAMEE so
that the passive RAMEE system will have a high RER value in the set
Pf is presented using factor P5. In one embodiment, the air flow
pressure drop ratio is defined as (p.sub.hA.sub.c/V.sub.c), wherein
p.sub.h is a pressure drop of the air stream across the energy
exchanger, A.sub.c is an area of an air channel, and V.sub.c is a
volume of the air channel. In one embodiment, the air flow pressure
drop ratio is between 1.times.10.sup.3 and 1.times.10.sup.4,
[0070] With respect to factor P6, a flow channel ratio of
convective heat transfer coefficient, h, (i.e. for turbulent flow)
with respect to the theoretical laminar flow convective beat
transfer coefficient, h.sub.lam, at the same channel Reynolds
number is [1.1<h/h.sub.lam<2.0].sub.Re. The channel average
friction flow coefficients for turbulent and laminar flow, f and
f.sub.lam, satisfy [f/f.sub.lam<h/h.sub.lam].sub.Re.
[0071] Turbulent flows in channels with flow at a particular
Reynolds number will have enhanced heat and mass transfer rates
compared with those with laminar flows. Taking advantage of this
fact is the purpose of factor P6. Accordingly, the internal surface
roughness may be enhanced for channel flows that would have been
laminar for smooth internal surfaces but turbulent for the same
channel with rough surfaces or flow separation causing surfaces at
the same Reynolds number (i.e. operating close to the flow
transition Reynolds number between laminar and transition
turbulence so as to cause the laminar flow to become turbulent).
The heat or mass transfer enhancement is a factor for the air flow
channels where the relatively high laminar flow characteristic
convection resistance dominates the total resistance and the design
need for the LAMEE energy exchange total area and LAMEE total
volume and geometry. Air channel support structures must be chosen
and positioned to provide the desired membrane channel width and
concurrently induce a turbulent flow transition from laminar to
turbulent flow, but not cause an excessive increase air pressure
drop for the flow channel. The ratios for the same channel flow
Reynolds number are empirically selected for enhanced heat and mass
transfer coefficients compared to laminar flow heat and mass
transfer coefficients, which may be large, while the ratios for
increased friction coefficients compared to laminar flow friction
coefficients may be smaller (i.e. there is a net heat and mass
transfer benefit for the turbulence enhancement relative to the air
flow pressure drop increase).
[0072] The semi-permeable membrane is designed (or selected) and
operated to avoid the transfer of any liquid from the liquid
channels to the air channels. Factors P7 and P8 define the
acceptable liquid pressure ratios that should be used for selecting
the semi-permeable membrane and its edge seals in each LAMEE.
[0073] The difference between the static desiccant liquid pressure
and the adjacent static air pressure cause the semi-permeable
membrane to deflect during normal operation and the deflections
will, as discussed above, result in a distribution of typical
inter-channel hydraulic diameters that decrease the LAMEE and RAMEE
system effectiveness. The deflections of the semi-permeable
membrane through its air side support screen will be determined
using its elastic properties, the geometry of the screen pores, and
the liquid pressure. The operating properties are combined into a
ratio (factor P9) that should be selected within a specified range
for the design and operation of each LAMEE. In one embodiment, the
membrane is selected based on a predetermined channel deflection
range that is defined to limit the amount of membrane deflection. A
standard deviation of the hydraulic diameter of all of the air
channels and desiccant channels divided by a mean value of a
hydraulic diameter for one of the air channels or desiccant
channels may be within a range of 0.0 to 0.2. A standard deviation
of a hydraulic diameter for one air channel or desiccant channel
divided by a mean hydraulic diameter for the air channel or
desiccant channel may be within a range of 0.0 to 0.2.
[0074] In another embodiment, an energy exchanger is provided. The
exchanger includes a housing containing the air and liquid flow
channels separated by a semi-permeable membrane. A plurality of
panels forming desiccant channels and air channels extend through
the housing. The air channels are configured to direct an air
stream through the housing air channels. A desiccant inlet is
provided in flow communication with the desiccant liquid channels.
A desiccant outlet is provided in flow communication with the
desiccant liquid channels. The desiccant channels are configured to
channel desiccant from the desiccant inlet to the desiccant outlet
in at least one of a counter-flow or cross-flow direction with
respect to the direction of the air stream to facilitate heat and
water vapor transfer between the desiccant in the desiccant liquid
channels and the air stream in the air channels. The liquid
desiccant salt concentration mixture is selected based on
predetermined salt solution saturation concentration limit and
membrane surface air side relative humidity for each climatic
region in which the RAMEE system is to operate in applications. In
one embodiment, the desiccant is selected based on at least one of
an operating temperature or humidity ratio of the air stream,
wherein the humidity ratio is defined by a moisture to air content
of the air stream. The annual time fraction duration of RAMEE
system operation without the risk of salt crystallization problems
for a particular climatic region (factor P10) and the expected
life-cycle costs relative to that for a system using pure LiCl or
LiBr for the system (factor P11) are partly based on the desiccant
selection. Each of the above embodiments (factors P10 and P11) are
uniquely defined for the LAMEEs operating within a passive RAMEE
system under steady-state test conditions.
[0075] With respect to factor P12, the LAMEE heat exchange rate
with the surroundings (Q.sub.sur) divided by the heat rate
transferred to or from the air flowing through the exchanger
(Q.sub.exch) during a standard test of a RAMEE system using two
identical LAMEEs is 0.0<Q.sub.sur/Q.sub.exch<0.05.
[0076] Since the liquid is under a pressure greater than the
adjacent channel air pressure, it causes the flexible
semi-permeable membrane and its support structure in the air
channel on either side of each liquid flow channel to deflect or
deform elastically. As previously noted, the liquid flow should be
directed through each channel so that it minimizes flow
mal-distributions (i.e. Ra<Ra.sub.c for laminar flow and, when
flow rates are higher, Re>Re.sub.c for turbulent flow). The
design and operational conditions imply that the liquid flow
direction will be such that the liquid flow will be from a bottom
inlet to the top outlet for the supply LAMEE exchanger and from the
top inlet to the bottom outlet for the exhaust LAMEE exchanger for
the standard summer test conditions. The flow directions through
each LAMEE will be reversed for the winter standard test
conditions. That is, a liquid flow direction controller will be
used so that the inlet direction will be bottom or top of each
LAMEE exchanger depending on the value of the Rayleigh number for
each exchanger and the angles of the flow channels with respect to
the acceleration direction of gravity as defined in Table 1 for
factors G9 and G10. With these controlled liquid flow directions
and a small performance enhancing tilt angle for the LAMEE, the
problems of flow mal-distribution will have been reduced to a
minimum for the geometric configurations of the flow channels and
the channel Reynolds number.
[0077] The Reynolds number for the liquid flow through the liquid
flow channels will typically be very low (i.e.
0.1<Re.sub.dh,liq<100). Under these circumstances, the liquid
flow may be laminar for the lowest Reynolds numbers in the range
but, for some specially designed internal geometries the flow will
become complex-laminar-turbulent or turbulent as the Reynolds
number is increased from the low to the high end of this Reynolds
number range. Therefore the liquid channel flow, which may exhibit
laminar flow mass flux channeling or fingering of the liquid for
unfavorable Rayleigh numbers at the low Reynolds numbers in the
above range, will, due to turbulent mixing, locally self adjust at
higher Reynolds number so that mal-distribution effects are much
smaller.
[0078] This is also a problem for laminar flows and heat and mass
transfer coefficients. The liquid channel screen insures a minimum
spacing for the channel width and enhances the transition to
turbulent flow for large liquid flow rates. The air and liquid flow
channel screen area ratios (factor G6) is yet another predetermined
embodiment because the ratios are directly related to turbulence
enhancement and blockage fraction of the membrane for water vapor
transfer on the air side of the membrane. The air channel spacer
support structure ratio (factor G7) is another geometric embodiment
that assists the transition to turbulent flow and partly determines
the geometry of the flow channel through its structural supports.
Factor G8 defines the best liquid flow direction with respect to
gravity through each LAMEE exchanger which may be controlled to
avoid liquid flow mal-distribution and factors G9 and G10 define
LAMME angles with respect to gravitational acceleration to get high
performance factors for the RAMEE system and all its LAMEEs.
[0079] The new ratio of standard deviation for each liquid flow
stream-tube hydraulic diameter in each liquid flow channel divided
by the mean value can be used to analyze the decrease in expected
effectiveness of each LAMEE and the passive RAMEE system in which
it is used or tested. For example, if the flow tube standard
deviation ratio is 0.05 (i.e. 5%) for the typical liquid flow
channel in each identical LAMEE in the RAMEE system, then the
decrease in total system effectiveness will be about 4% for
turbulent flows but the loss of effectiveness may be much higher
for laminar liquid flows where the flow field is unstable due to
buoyancy effects.
[0080] Another embodiment is provided for the flow channels in each
LAMEE which involves flow field characterization through the
Reynolds number and the flow stability factor, Rayleigh number. The
Rayleigh number can be selected to be most favorable by arranging
the temperature gradients in each LAMEE to be such that the fluid
density always increases in the downward direction of gravitational
acceleration. This implies that the flow channels in a LAMEE should
be aligned so that their normal area vector is horizontal and the
length vector of the flow channel is tilted with a large enough
angle to cause a favorable and significant density gradient for
uniform flows in each channel and among all the channels. Channel
flows in long thin channels with small or negligible entrance
lengths for the flows are well known to be one of: (a) fully
developed laminar flow at low Reynolds number, (b) fully developed
turbulent flow at high Reynolds number, or (c) transition turbulent
flows at intermediate Reynolds numbers between the two low and high
transition Reynolds numbers. The flow transition Reynolds number
that causes the flow to transfer from laminar to transition
turbulence tends to be fixed for any given channel where the
Rayleigh number indicates no buoyancy induced mal-distributions,
but very small changes to the surfaces inside each channel can
cause large changes to the transition Reynolds number. That is, the
flow in a channel can become turbulent when small increased surface
roughness or flow separations within the channel flow changes are
introduced at some low Reynolds numbers compared to laminar flow in
the same channels with no roughness additions.
[0081] Turbulent flows in channels with flow at a particular
Reynolds number will have enhanced heat and mass transfer rates
compared with those with laminar flows. Accordingly, the internal
surface roughness may be enhanced for channel flows that would have
been laminar for smooth internal surfaces but turbulent for the
same channel with rough surfaces or flow separation causing
surfaces at the same Reynolds number (i.e. operating close to the
flow transition Reynolds number between laminar and transition
turbulence so as to cause the laminar flow to become turbulent).
The heat or mass transfer enhancement is a factor for the air flow
channels where the relatively high laminar flow characteristic
convection resistance dominates the total resistance and the design
need for the LAMEE energy exchange total area and LAMEE total
volume and geometry. Air channel support structures must be chosen
and positioned to provide the desired membrane channel width and
concurrently induce a turbulent flow transition from laminar to
turbulent flow, but not cause an excessive increase air pressure
drop for the flow channel. The ratios for the same channel flow
Reynolds number are empirically selected for enhanced heat and mass
transfer coefficients compared to laminar flow heat and mass
transfer coefficients, which may be large, while the ratios for
increased friction coefficients compared to laminar flow friction
coefficients may be smaller (i.e. there is a net heat and mass
transfer benefit for the turbulence enhancement relative to the air
flow pressure drop increase).
[0082] On the liquid flow side of the membrane, turbulent mixing
within the flow channel may be a factor if there is a tendency
toward laminar flow buoyancy induced mass flux fingering at high
Rayleigh numbers and very low Reynolds numbers result in
non-uniform exposure of the bulk flow to the molecular diffusion
transfer process in the liquid. In one embodiment, for the factor
P1, turbulence enhancement of the air and liquid flows through the
LAMEE energy exchange channels is used to enhance turbulent
transition and liquid flow directions are chosen for each LAMEE
operating condition to decrease buoyancy induced instabilities in
the liquid flow channels. For a given flow channel geometry, which
is characterized by the hydraulic diameter and surface roughness,
the Reynolds number is the only operating factor that determines
whether the flow is laminar or turbulent. The performance
effectiveness and RER of the passive RAMEE and its LAMEEs will be
enhanced with some turbulent mixing.
[0083] In other embodiments, an energy exchanger is provided. The
exchanger includes a housing for the air and liquid desiccant
channels each separated by a semi-permeable membrane. A plurality
of panels forming desiccant channels and air channels extend
through the housing. The air channels are configured to direct an
air stream through the housing. The plurality of panels are spaced
apart based on predetermined air to desiccant channel rates that
define an air channel width or spacing and a desiccant channel
width or spacing. A desiccant inlet header is provided in flow
communication with all the desiccant channels. A desiccant outlet
is provided in flow communication with the desiccant channels. The
desiccant channels are configured to channel desiccant from the
desiccant inlet to the desiccant outlet in at least one of a
counter-flow or cross-flow direction with respect to the direction
of the air stream to facilitate heat and water vapor transfer
between the desiccant in the desiccant channels and the air stream
in the air channels. For a predetermined test condition of the
passive RAMEE system, a predetermined equal mass flow rate of
supply and exhaust air pass through each identical LAMEE. By so
doing, the number of transfer units for heat transfer (NTU) in each
LAMEE is predetermined (factor P2). When the pumping rate of liquid
desiccant is chosen, the heat capacity rate ratio (i.e. the mass
flow rate times the specific heat of desiccant liquid flow divided
by the mass flow rate of air) through each LAMEE, Cr*, is
predetermined (factor P3). There may be a trade-off for the
selection of Cr* because increasing the liquid flow rate may
enhance turbulence in the liquid flow channels and will increase
Cr*, which can have positive and negative effects on the
effectiveness. Accordingly, the value of Cr* should be selected so
that the effectiveness of the LAMEE is a maximum when the highest
performance is required.
[0084] Other embodiments for energy exchangers are provided. The
exchanger includes a housing containing the air and liquid flow
channels each separated by a semi-permeable membrane. A plurality
of panels forming desiccant channels and air channels extend
through the housing. The air channels are configured to direct an
air stream through the housing. A desiccant inlet header is
provided in flow communication with all the desiccant channels. A
desiccant outlet is provided in flow communication with the
desiccant channels. The desiccant channels are configured to
channel desiccant from the desiccant inlet to the desiccant outlet
in at least one of a counter-flow or cross-flow w direction with
respect to the direction of the air stream. A desiccant membrane
extends through each panel to facilitate heat and water vapor
transfer between the desiccant liquid in the desiccant channels and
the air stream in the air channels. The semi-permeable membrane
possesses a resistance to water vapor diffusion which, relative to
the typical convection water vapor transport resistance in the air
channels, lies within a specified range given by factor P4.
[0085] The static air pressure drop as it passes from air inlet to
outlet in each LAMEE in a RAMEE system is the same for each air
channel. The range of acceptable air pressure drops for a LAMEE so
that the passive RAMEE system will have a high RER value in the set
Pf is presented using factor P5.
[0086] As discussed previously, inducing turbulence for otherwise
laminar flows, for both the air-flow and liquid-flow channels, can
enhance the heat and mass transfer coefficients more than the flow
friction coefficients. Factor P6 defines the circumstance when
there will be a net benefit for inducing turbulence in either the
air or liquid channels.
[0087] In another embodiment for a passive RAMEE system, the
exchanger includes a housing. A plurality of panels forming
desiccant channels extend through the housing. Each of the
plurality of panels has a semi-permeable membrane separating the
air flow channels from the liquid flow channels. Air channels are
formed between the desiccant liquid channels. The air channels are
configured to direct an air stream through the housing. A desiccant
inlet is provided in flow communication with the desiccant
channels. A desiccant outlet is provided in flow communication with
the desiccant channels. The desiccant channels are configured to
channel desiccant from the desiccant inlet to the desiccant outlet
so that the semi-permeable membranes facilitate heat and water
vapor exchange between the liquid desiccant and the adjacent air
streams in a LAMEE. During a standard test with two identical
LAMEEs in a passive RAMEE test loop, heat will be transferred
between the LAMEEs and their surroundings. The relative magnitude
of the heat transfer between the surroundings and each LAMEE is
designed to be a small fraction of the heat rate between the air
flows passing through the LAMEEs (factor P12).
[0088] FIG. 1 illustrates a passive run-around membrane energy
exchange (RAMEE) system 100 formed in accordance with an
embodiment. The RAMEE system 100 is configured to partly or fully
condition air supplied to a structure 101. The RAMEE system 100
includes an inlet 102 for a pre-conditioned air flow path 104. The
pro-conditioned air flow path 104 may include outside air, air from
a building adjacent to the enclosed structure 101, or air from a
room within the enclosed structure 101. Airflow in the
pre-conditioned air flow path 104 is moved through the
pro-conditioned air flow path 104 by a fan 106. The illustrated
embodiment includes one fan 106 located upstream of the LAMEE 108.
Optionally, the pre-conditioned air flow path 104 may be moved by a
down-stream fan and by multiple fans or a fan array or before and
after each LAMEE in the system. The fan 106 directs the
pre-conditioned air flow through path 104 to a supply liquid-to-air
membrane energy exchanger (LAMEE) 108. The supply LAMEE 108
conditions the pre-conditioned air flow in path 104 to generate a
change in air temperature and humidity (i.e. to pre-conditioned the
air partly or fully) toward that which is required for a supply air
flow condition to be discharged into the enclosed space 101. During
a winter mode operation, the supply LAMEE 108 may condition the
pre-conditioned air flow path 104 by adding heat and moisture to
the pro-conditioned air in flow path 104. In a summer mode
operation, the supply LAMEE 108 may condition the pre-conditioned
air flow path 104 by removing heat and moisture from the
pre-conditioned air in flow path 104. The pre-conditioned air 110
is channeled to a HVAC system 112 of the enclosed structure 101.
The HVAC system 112 may further condition the pro-conditioned air
110 to generate the desired temperature and humidity for the supply
air at 114 that is supplied to the enclosed structure 101.
[0089] Return air 116 is channeled out of the enclosed structure
101. A mass flow rate portion 118 of the return air 116 is returned
to the HVAC system 112. Another mass flow rate portion 119 of the
return air 116 is channeled to a return LAMEE 120. The portions 118
and 119 may be separated with a damper 121 or the like. For
example, 80% of the return air 116 may be channeled to the HVAC
system 112 and 20% of the return air 116 may be channeled to the
return air regeneration LAMEE 120 in the RAMEE loop. The return air
LAMEE 120 exchanges energy between the portion 118 of the return
air 116 and the preconditioned air 110 in the supply air LAMEE 108.
During a winter mode, the return air LAMEE 120 collects heat and
moisture from the portion 118 of the return air 116. During a
summer mode, the return air LAMEE 120 discharges heat and moisture
into the regeneration air flow 119. The return air LAMEE 120
generates exhaust air 122. The exhaust air 122 is discharged from
the structure through an outlet 124. A fan 126 is provided to move
the exhaust air 122 from the return air LAMEE 120. The RAMEE system
100 may includes multiple fans 126 or one or more fan arrays
located either up-stream or down-stream (as in FIG. 1) of the
exhaust air LAMEE 120.
[0090] A desiccant fluid 127 flows between the supply air LAMEE 108
and the return air LAMEE 120. The desiccant fluid 127 transfers the
heat and moisture between the supply air LAMEE 108 and the return
air LAMEE 120. The RAMEE system 100 includes desiccant storage
tanks 128 in fluid communication between the supply air LAMEE 108
and the return air LAMEE 120. The storage tanks 128 store the
desiccant fluid 127 as it is channeled between the supply air LAMEE
108 and the return air LAMEE 120. Optionally, the RAMEE system 100
may not include both storage tanks 128 or may have more than two
storage tanks. Pumps 130 are provided to move the desiccant fluid
127 from the storage tanks 128 to one of the supply LAMEE 108 or
the return LAMEE 120. The illustrated embodiment includes two pumps
130. Optionally, the RAMEE system 100 may be configured with as few
as one pump 130 or more than two pumps 130. The desiccant fluid 127
flows between the supply air LAMEE 108 and the return air LAMEE 120
to transfer heat and moisture between the conditioned air 110 and
the portion 118 of the return air 116.
[0091] The embodiments described herein utilize a set of
predetermined geometric design factors (G1-G10) and physical
property and operating parameters (P1-P12) for the supply and
exhaust air LAMEEs 108 and 120 and the RAMEE system 100 and
maintain predetermined ranges for each parameter for LAMEEs 108 and
120 and for the RAMEE system 100, as illustrated in Table 1. As a
set, the design and operating parameters enable the systems to meet
selected performance factors. The set of predetermined geometric
design and physical property and operating parameters is comprised
of a subset of geometric design length ratios and a subset of
physical property and operating parameters each comprised of
physical property or operating condition ratios that may include
some geometric lengths as well as other physical properties in some
cases. The defined geometric design and physical ratios represent
dimensionless ratios or factors that do not require specific length
scales or property units except with respect to another defined
length or parameter with the same units in the same ratio (i.e.
each of them is dimensionless). The geometric design and physical
parameters are discussed herein in connection with various
embodiments.
[0092] The performance factors for a RAMEE system 100 employing
supply and exhaust air counter-flow or cross-flow LAMEEs 108 and
120, in accordance with the embodiments, may be determined using
ASHRAE Std. 84-2008 using a defined set of steady-state test
conditions defined in AHRI Std. 1060-2005. In one embodiment, a
thermal insulation surrounding the panels is such that a heat
exchange rate between the panels is less than 5% of a heat rate
between supply and exhaust air flow streams during standard summer
or winter testing with AHRI 1060 air inlet operating conditions.
The operating conditions for the RAMEE system 100 during a test
with balanced air flows and with the system at or very near
steady-state will be determined by specifying: Cr*, NTU, NTU.sub.m
and the relative flow direction and geometry of each LAMEE (where
each of the dimensionless terms have been defined previously or
will be defined herein). The deduction of the effectiveness of
performance of a single LAMEE 108 from the steady-state or
quasi-steady-state RAMEE system 100 test data, which includes two
similar LAMEEs, 108 and 120, may be deduced from steady-state
energy and mass balance equations. That is, both the overall
run-around system effectiveness, E.sub.0, and the individual
exchanger effectiveness, E, in the run-around loop depends on Cr*,
NTU and NTU.sub.m at or near steady state so the relationship for E
can be readily determined once E.sub.0 is measured. For the simple
example of a run-around heat exchanger system with equal supply and
exhaust air flow rates using two identical counter flow heat
exchangers, it can be shown that Cr=1.0 at the maximum heat rate
and system overall effectiveness, E.sub.0, and the individual
supply or exhaust exchanger effectiveness is given by. [0093]
E=2Ed/(1+E.sub.0) which will have a relative uncertainty of U(E)/E
2U(E.sub.0)/[E.sub.0(1+E.sub.0).sup.2] where both E and E.sub.0 are
less than 1.0 for heat exchangers [0094] {e.g. when E.sub.0=2/3 (or
67%) (calculated from the measured data) and
U(E.sub.0)/E.sub.0=0.05 (also determined from data) then
E=0.80+/-0.04 (or 80+/-4%)}
[0095] In one embodiment, the flow panel aspect ratio is defined by
the height of the energy exchange area of each flow panel divided
by the length of the same exchange area in the LAMEE. In another
embodiment, the entrance length to total panel length ratio is
defined for LAMEEs that are either primarily counter-flow or
cross-flow exchangers. In another embodiment, the ratio of the flow
channel standard deviation of average panel channel hydraulic
diameters (widths) for each fluid with respect to average flow
hydraulic diameter (width) for each fluid for the LAMEE is limited
to reduce mal-distribution of fluid flows among the channels. In
another embodiment, the ratio of the stream-tube standard deviation
in hydraulic diameter to mean stream-tube hydraulic diameter is
limited to reduce flow mal-distributions within a typical flow
channel. The liquid desiccant to air capacity rate ratio also
implies a particular mass flow rate ratio. Therefore, for a
predetermined volume or mass flow rate of air flowing through the
air channels of a LAMEE and a particular volume or mass flow rate
of liquid desiccant may be required to flow through the adjacent
liquid desiccant channels.
[0096] In another embodiment, turbulent flow conditions are induced
in the air and liquid flow channels of the LAMEE by selecting a
distribution and geometric shape for the air and liquid flow
channel spacers in the LAMEE. The turbulence can be used to enhance
the heat and mass transfer convection coefficients in the air flow
channels which can be used to increase the effectiveness and/or
decrease the LAMEE size. In other embodiments for the liquid flow
channels, turbulence in the liquid flow channels is facilitated to
enhance the bulk mean flow distribution (and eliminate laminar flow
fingering and mal-distributions) and increase the convective heat
and moisture transfer coefficients (i.e. decrease mal-distributions
in the liquid flows) because the physical effect increases the
effectiveness of a given LAMEE and its RAMEE system and can be used
to decrease the physical size of each LAMEE.
[0097] In another embodiment, the elastic tensile limit for the
semi-permeable membrane is selected to partly limit the deflection
of the semi-permeable membrane with respect to its structural
support screen in the LAMEE.
[0098] In another embodiment, the membrane and membrane frame
liquid flow penetration resistance ranges are selected to eliminate
any flow of the liquid desiccant through the semi-parmeable
membrane and its edge seal frame for each panel pair of channels in
the LAMEE.
[0099] In another embodiment, the air mass flow ratio of the two
air streams inlet to the two identical LAMEEs in the RAMEE system
is selected to meet a predetermined exposure of the air stream to
the semi-permeable membranes.
[0100] In another embodiment, the air pressure drop ratio for a
selected mass flow rate of air is selected to ensure a high RER
performance factor for a RAMEE system.
[0101] In another embodiment, the salt solution concentration
ranges are used to limit the time fraction when there may be a risk
of crystallization for a climatic region for particular application
and reduce the life-cycle costs for an application.
[0102] In another embodiment, the heat exchange with the
surroundings is by using appropriate energy exchange cavity
insulation reduced to a small fraction of the heat rate for the
RAMEE system under a standard test.
[0103] FIG. 2 illustrates a LAMEE 300 formed in accordance with an
embodiment. The LAMEE 300 may be used as the supply air LAMEE 108
and/or the return or exhaust air LAMEE 120 (shown in FIG. 1). The
LAMEE 300 includes a housing 302 having a body 304. The body 304
includes an air inlet end 306 and an air outlet end 308. A top 310
extends between the air inlet end 306 and the air outlet end 308. A
stepped-down top 312 is positioned at the air inlet end 306. The
stepped-down top 312 is stepped a distance 314 from the top 310. A
bottom 316 extends between the air inlet end 306 and the air outlet
end 308. A stepped-up bottom 318 is positioned at the air outlet
end 308. The stepped-up bottom 318 is stepped a distance 320 from
the bottom 316. In alternative designs the stepped-up 318 or
stepped-down 312 sections may have different sizes of steps or no
step at all.
[0104] An air inlet 322 is positioned at the air inlet end 306. An
air outlet 324 is positioned at the air outlet end 308. Sides 326
extend between the air inlet 322 and the air outlet 324. Each panel
in the LAMEE 300 has a semi-permeable membrane length 364, as shown
in FIG. 3a. Also shown in FIG. 3a, each panel in the LAMEE 300 has
a semi-permeable membrane height 362 defining an energy exchange
area extends a height (H) between a top and a bottom defined by the
top and bottom of the semi-permeable membrane. The energy exchange
area extends a length (L) between a front and a back that is
defined by the front and the back of the semi-permeable membrane.
An exchanger aspect ratio (AR) is defined by a height (H) 362 of
each semi-permeable membrane energy exchange area divided by a
length (L) 364 of the energy exchange area. The exchanger aspect
ratio (AR) represents the physical design factor G2 (shown in Table
1) and is at least one factor for partly achieving a predetermined
performance of the LAMEE 300. The aspect ratio (AR) is a
dimensionless ratio. The aspect ratio (AR) is determined using the
equation AR=H/L. In an exemplary embodiment for a counter/cross
flow LAMEE, factor G2, the aspect ratio (AR), is within a range of
0.1<AR<3.0. In one embodiment, the exchanger aspect ration is
within a range of 0.5 to 2. The exchanger aspect ratio is selected
to provide at least one of a predetermined membrane area, a
predetermined length, or a predetermined duration of exposure of
the air stream to the desiccant.
[0105] An energy exchange cavity 330 extends through the housing of
the LAMEE. The energy exchange cavity 330 extends from the air
inlet end 306 to the air outlet end 308. An air stream 332 is
received in the air inlet 322 and flows through the energy exchange
cavity 330. The air stream 332 is discharged from the energy
exchange cavity 330 at the air outlet 324. The energy exchange
cavity 330 includes a plurality of panels 334. Each liquid flow
panel forms a liquid desiccant channel 376 that is confined by the
semi-permeable membranes 378 on either side and is configured to
carry desiccant 341 therethrough. The semi-permeable membranes 378
are arranged in parallel to form air channels 336 with an average
flow channel width (d.sub.w,air) of 337 and liquid desiccant
channels 376 with an average flow channel width (d.sub.w,liq) of
377. In one embodiment, the semi-permeable membranes 378 are spaced
to form uniform air channels 336 and liquid desiccant channels 376
with d.sub.w,air and d.sub.w,liq implied by what is practical to
reduce statistical variations for each as illustrated in factor G4
of Table 1. The air stream 332 travels through the air channels 336
between the semi-permeable membranes 378. The desiccant 341 in each
desiccant channel 376 exchanges heat and moisture with the air
stream 332 in the air channels 336 through the semi-permeable
membranes 378.
[0106] A desiccant inlet reservoir 338 is positioned on the
stepped-up bottom 318. The desiccant inlet reservoir 338 may have a
height 340 equal to the distance 320 between the bottom 316 and the
stepped-up bottom 318. Alternatively, the liquid desiccant inlet
reservoir 338 may have any height 340 that meets a predetermined
performance of the LAMEE 300. The desiccant inlet reservoir 338
extends a length 339 of the LAMEE body 304. The desiccant inlet
reservoir 338 extends a length 339 that is configured to meet a
predetermined performance of the LAMEE 300. In one embodiment the
desiccant inlet reservoir 338 extends no more than one fourth of
the length 327 of the LAMEE body 304. Alternatively, the desiccant
inlet reservoir 338 may extend along one fifth of the length 327 of
the LAMEE body 304.
[0107] The liquid desiccant inlet reservoir 338 is configured to
receive desiccant 341 from a storage tank 128 (shown in FIG. 1).
The desiccant inlet reservoir 338 includes an inlet 342 in flow
communication with the storage tank 128. The desiccant 341 is
received through the inlet 342. The desiccant inlet reservoir 338
includes an outlet 344 that is in fluid communication with the
desiccant channels 376 in the energy exchange cavity 330. The
liquid desiccant 341 flows through the outlet 344 into the
desiccant channels 376. The desiccant 341 flows along the panels
334 through desiccant channel 376 to a desiccant outlet reservoir
346.
[0108] The desiccant outlet reservoir 346 is positioned on the
stepped-down top 312 of the LAMEE housing 302. Alternatively, the
desiccant outlet reservoir 346 may be positioned at any location
along the top 312 of the LAMEE housing 302 or alternatively on the
side of the reservoir with a flow path connected to all the panels.
The desiccant outlet reservoir 346 has a height 348 that may be
equal to the distance 314 between the top 310 and the stepped-down
top 312. The desiccant outlet reservoir 346 extends along the top
312 of the LAMEE housing 302 for a length 350. In one embodiment of
a counter/cross flow exchanger, the desiccant outlet reservoir 346
extends a length 350 that is no more than one fourth the length 327
of the flow panel exchange area length 302. In another embodiment
of a counter/cross flow LAMEE the desiccant outlet reservoir 346
extends a length 350 that is one fifth the length 327 of the panel
exchange area length 302 (i.e. factor G3).
[0109] The desiccant outlet reservoir 346 is configured to receive
desiccant 341 from the desiccant channels 376 in the energy
exchange cavity 330. The desiccant outlet reservoir 346 includes an
inlet 352 in flow communication with the desiccant channels 376.
The desiccant 341 is received from the desiccant channels 376
through the inlet 352. The desiccant outlet reservoir 346 includes
an outlet 354 that is in fluid communication with a storage tank
128. The desiccant 341 flows through the outlet 354 to the storage
tank 128 where the desiccant 341 is stored for use in another LAMEE
300. In an alternative embodiment, the desiccant outlet reservoir
346 may be positioned along the bottom 318 of the LAMEE housing 302
and the desiccant inlet reservoir 338 may be positioned along the
top 310 of the LAMEE housing 302.
[0110] In the illustrated embodiment, the LAMEE 300 includes one
liquid desiccant outlet reservoir 346 and one liquid desiccant
inlet reservoir 338. Alternatively, the LAMEE 300 may include
liquid desiccant outlet reservoirs 346 and liquid desiccant inlet
reservoirs 338 on the top and bottom of each of each end of a LAMEE
300. A liquid flow controller may direct the liquid flow to either
the top or bottom depending on the value of Ra for factor P1 in the
independent factor set If in Table 1.
[0111] During testing of the RAMEE system 100 using ASHRAE Std.
84-2008 and the steady-state test conditions defined in AHRI Std.
1060-2005, wherein the RAMEE system 100 has balanced air flows and
is at or very near steady-state, an exchanger thermal capacity
ratio Cr* (operational independent factor P3 as illustrated in
Table 1) is defined. Cr* is a dimensionless ratio representing the
mass flow rate of the liquid desiccant times the heat capacity of
the liquid desiccant divided by the mass flow rate of the air times
the heat capacity of the air. Cr* is measured by measuring the flow
rates of the air and liquid desiccant and using known heat
capacities of the liquid desiccant and the air. In one embodiment,
Cr* falls within a range during RAMEE testing that is between
1.0<Cr*<10.0. In one example for a run-around heat exchanger
system having equal supply and exhaust air flow rates and using two
identical counter flow heat exchangers, Cr* may equal 1.0 at a
maximum heat rate and overall effectiveness, E.
[0112] During RAMEE testing, the exchanger number of transfer units
(NTU) for heat transfer (operational independent factor P2 as
illustrated in Table 1) may also be defined. In general, the
effectiveness of a heat exchanger increases directly with the value
of NTU. A heat capacity rate for the air stream 332 and the
desiccant 341 is used to determine the maximum feasible heat
transfer between the air stream 332 and the desiccant 341. The
effectiveness of the RAMEE system for heat transfer between the
supply air flow and the exhaust air flow is determined by measuring
the two mass flow rates of air and the temperature increase of the
air flowing through the supply air exchanger and the temperature
difference between the inlet air to the supply and exhaust air
exchangers. In one embodiment, NTU is within a range
1<NTU<15. Having an NTU within this range may provide a
predetermined performance of the RAMEE system. In one embodiment,
the range of NTU may function concurrently with other performance
factors defined herein to achieve the predetermined performance of
the LAMEE 300 and the RAMEE system 100.
[0113] During RAMEE 100 testing, an air flow pressure drop ratio
(operational design factor P4 as illustrated in Table 1) may also
be defined for the LAMEEs 300. The air flow pressure drop ratio is
calculated using the ratio p.sub.hA.sub.c/V.sub.c, wherein p.sub.h
is the air flow pressure head drop across the LAMEE 300, A.sub.c is
the energy exchange area of one air flow channel in LAMEE 300, and
V.sub.c is the volume of each air channel. The air flow pressure
drop ratio is used to define a pressure drop in the air stream 332
between the air inlet 322 and the air outlet 324 of the LAMEE 300.
In one embodiment, the air flow pressure drop ratio is with a range
of 10.sup.3 to 10.sup.4 to achieve a predetermined RER performance
factor for the RAMEE system 100.
[0114] FIG. 3a illustrates the LAMEE 300 having a cutout along the
line 3-3 shown in FIG. 2. The top 310 and the bottom 318 of the
LAMEE housing 302 include insulation 360 joined thereto. The sides
326 of the LAMEE housing 302 also include insulation 360. Except
for the air inlet and outlet areas, the insulation 360 extends
around the energy exchange cavity 330. The insulation 360 limits an
amount of heat that may be exchanged between the air and liquid
desiccant flowing through the energy exchange cavity and the
surroundings as the air and liquid desiccant flow through the
channels in the energy exchange cavity compared to the heat rate
for the air for the supply and exhaust air flows (i.e. factor P12).
The insulation 360 may include foam insulation, fiber insulation,
gel insulation, or the like. The insulation 360 is selected to at
least partially meet a predetermined performance of the LAMEE
300.
[0115] The energy exchange cavity 330 has a height 362, a length
364, and a width 366. The height 362 is defined between the top and
bottom of the energy exchange cavity 330. The width 366 is defined
between the insulation side walls of the energy exchange cavity
330. The length 364 is defined between the air inlet 322 and the
air outlet 324 of the energy exchange cavity 330. Each energy
exchange panel 334 extends the height 362 and length 364 of the
energy exchange cavity 330. The panels 334 are spaced along the
width 366 of the energy exchange cavity 330.
[0116] For the counter/cross flow LAMEE, the liquid desiccant flow
inlet 334 of the desiccant inlet reservoir 338 is in flow
communication with the energy exchange cavity 330 at the air outlet
end 308 of the LAMEE 300. The liquid desiccant outlet 352 of the
desiccant outlet reservoir 346 is in flow communication with the
energy exchange cavity 330 at the air inlet end 306 of the LAMEE
300. The desiccant inlet reservoir 338 and the desiccant outlet
reservoir 346 are in fluid communication with the liquid channel
376. The panels 334 define a non-linear liquid desiccant flow path
368 between the desiccant inlet reservoir 338 and the desiccant
outlet reservoir 346. The flow path 368 illustrates one embodiment
of a counter/cross flow path with respect to the direction of the
air stream 332. In one embodiment, a desiccant flow direction
through the desiccant channels 376 is controlled so that lower
density desiccant flows separately from higher density
desiccant
[0117] FIG. 3b illustrates a front view of the panels 334. The
panels 334 are spaced to form air channels 336 and the liquid
desiccant channels 376 there-between separated by semi-permeable
membranes 378. The air channels 336 alternate with the liquid
desiccant channels 376. Except for the two side panels of the
energy exchange cavity, each air channel 336 is positioned between
adjacent liquid desiccant channels 376. The liquid desiccant
channels 376 are positioned between adjacent air channels 336. The
air channels 336 have an average channel width 337 defined between
adjacent panels 334. The liquid desiccant channels 376 have an
average channel width 377 defined between adjacent panels 334. The
width 337 of the air channels 336 and the width 377 of the liquid
desiccant channels 376 are nearly constant over the area of each
panel and for the set of panels in the LAMEE energy exchange cavity
with the exception of independent geometric design factors G4 and
G5 as illustrated in Table 1. In one embodiment, the standard
deviation of the average channel hydraulic diameter (directly
related to the width 337 of the air channels 336 or average channel
width 377 of the liquid desiccant channels 376) divided by the
corresponding mean average channel hydraulic diameter for each
fluid is an independent geometric design factor (physical design
factor G4 as illustrated in Table 1) restricted for each type of
fluid channel to at least partly achieve the predetermined set of
performance factors Pf of the RAMEE system with its LAMEEs 300. In
another embodiment, the statistical variations in the stream-tube
hydraulic diameters will be such that the standard deviation of the
flow tubes hydraulic diameters for a typical type of fluid channel
in a LAMEE divided by the mean stream-tube hydraulic diameter for
the typical flow channel of a fluid will be restricted as specified
by factor G5 in Table 1.
[0118] FIG. 4 illustrates a panel 334 to contain the desiccant
liquid flow for one channel formed in accordance with an
embodiment. The panel 334 includes support structures including a
top support 370, a bottom support 372 that is opposite the top
support 370, and a pair of opposite side supports 374 extending
between the top support 370 and the bottom support 372. The
supports 370, 372, and 374 retain the membranes 392 and a liquid
desiccant inlet diffuser 396 and outlet diffuser 400. The panel 334
includes a top 381 and a bottom 383. The panel 334 has an overall
height 382 defined between the top 381 and the bottom 383. The
energy exchange membrane 392 includes a top 385 and a bottom 387.
The membrane 392 has an overall height 384 defined between the top
385 and the bottom 387. The height 384 of the membrane 392 is less
than the height 382 of the panel 334. The panel 334 has a front end
389 and a back end 391. The panel 334 has an overall length 386
defined between the front end 389 and the back end 391. The
membrane 392 includes a front end 393 and a back end 395
corresponding to the air inlet and outlet for the adjacent air flow
channels respectively. The membrane 392 has an overall length 388
defined between the front end 393 and the back end 395. The length
388 of the membrane 392 is less than the length 386 of the panel
334. Ratios of the heights 382 and 384 to the lengths 386 and 388,
respectively, may be configured based at least partly on a
predetermined performance of the LAMEE 300. In one embodiment for a
counter/cross-flow panel, the height 384 of the membrane 392 is
within a range of 0.1 to 3.0 times the length 388 of the membrane
392 (i.e. factor G2).
[0119] The panel 334 has a desiccant inlet end 378 and a desiccant
outlet end 380. A desiccant flow path 368 shows a typical bulk mean
streamline for flow from the liquid desiccant inlet 396 to the
desiccant outlet 400 in a non-linear flow path that is primarily
opposite to the direction of the air stream 332. The desiccant
inlet end 378 includes an inlet 390 that extends through the bottom
support 372 and between adjacent panels 334. The inlet 390 has a
length 396. A ratio of the length 396 of the inlet 390 to the
length 388 of the panel 334 is selected based on a predetermined
performance of the LAMEE. The desiccant outlet end 380 includes an
outlet 398 that extends through the top support 370 and between
adjacent panels 334. The outlet 398 has a length 400 which is equal
to the inlet length 396. A ratio of the length 400 of the outlet
398 to the length 388 of the panel 334 is selected based at least
partly on a predetermined performance of the LAMEE 300. The
desiccant flow path 368 flows from the inlet 390 to the outlet
398.
[0120] The liquid desiccant flow path-line 368 is the same as one
possible bulk-mean streamline which is necessarily curved,
especially near the liquid ingest and egress regions of the
channel, through a counter/cross-flow panel of a LAMEE. The curved
streamline is contrasted with the essentially straight bulk-mean
air streamline 332 in the air channels 336. The bulk-mean liquid
desiccant flow path direction or velocity is mostly upstream of
that for the adjacent channel bulk-mean air stream 332. An inlet
flow ingest region cross segment 402 of the liquid desiccant
bulk-mean streamline 368 is formed as the desiccant enters the
desiccant channel 376 from the inlet 390. Liquid desiccant 341
flowing from the inlet 390 into the desiccant channel 376 flows
upward through the inlet cross segment 402. Liquid desiccant 341 in
the inlet cross segment 402 flows partly in a cross flow direction
to that for the adjacent air flow channel streamline 332.
[0121] Since the liquid desiccant 341 is channeled from the inlet
390, the desiccant 341 fills the channel 376 and flows through a
primarily an air/liquid counter flow segment 404 of the liquid
desiccant bulk-mean streamline 368. The liquid/air counter flow
segment 404 extends approximately a length 406 through the liquid
desiccant flow channel 376. The length 406 is based partly on a
predetermined performance of the LAMEE 300. The liquid/air counter
flow segment 404 is essentially parallel to direction of the air
stream 332 in the air channels 336. The liquid/air counter flow
segment 404 has the liquid flow opposite to the direction of the
adjacent air flow 332. The counter flow arrangement at least partly
provides a predetermined heat and moisture exchange effectiveness
between the liquid desiccant 341 in the desiccant channel 376 and
the air stream 332 in the air channels 336.
[0122] The liquid desiccant 341 in the counter segment 404 flows
into a counter/cross-flow liquid flow egress region 408 of the
liquid desiccant flow path 368. The liquid desiccant 341 in the
outlet counter/cross flow region segment 408 flows with curved bulk
mean streamlines from the counter segment 404 to the outlet 398.
The liquid desiccant 341 in the outlet counter/cross flow region
408 flows at least partly in a cross flow direction that is
perpendicular to the direction of the air stream 332 in the air
channels 336.
[0123] The counter/cross-flow arrangement of the liquid desiccant
bulk-mean streamline flow path 368 provides a liquid desiccant
nearly counter flow with respect to the air stream 332. The counter
flow arrangement improves the effectiveness of the LAMEE 300
compared to a unit with equal mass flow rates, inlet properties and
exchanger energy exchange area. The counter/cross flow arrangement
does not require large headers that increase the space required for
the LAMEE 300. The illustrated embodiment shows the desiccant flow
path 368 flowing upward from the inlet 390 to the outlet 398.
Optionally, the inlet 390 may be positioned at the top support 370,
but at the same end of the panel 334 and the outlet 398 may be
positioned at the bottom support 372 but at the same end of the
panel 334. In such an embodiment, the desiccant flow path 368 may
flow downward from the inlet 390 to the outlet 398. The flow
direction option facilitates avoiding liquid channel flow
mal-distributions caused by buoyancy induced instability in one of
the two LAMEEs under typical summer and winter operating for a
RAMEE system.
[0124] FIG. 5a is an exploded view of the liquid desiccant flow
panel 334. The panel 334 includes a liquid-desiccant flow guide and
turbulence-enhancement screen diffuser 410 and a pair of
semi-permeable membranes 412. The liquid-desiccant screen diffuser
410 is retained between the semi-permeable membranes 412. The
semi-permeable membranes 412 are bonded (by heat scaling or glue)
to the membrane support structural elements 418 and 424. The
membrane support screens 414 in the adjacent air flow channels 336
may also include air flow channel spacers. An air channel support
screen may include a solid area that is a fraction of a total area
of the air channel support screen. Additionally, a desiccant
channel support screen may have a solid area that is a fraction of
a total area of the desiccant channel support screen. In one
embodiment, a distance between air channel support screens in the
flow direction of the air stream divided by a distance between air
channel support screens normal to the flow direction of the air
steam is within a range of 0.01 to 5.0. The air flow channels 336
are formed between adjacent liquid-desiccant flow panels 334. The
desiccant 341 is configured to have a bulk-mean flow parallel to
the semi-permeable membranes 412. The semi-permeable membranes 412
allow heat and moisture exchange between the flowing
liquid-desiccant 341 in the desiccant channels 376 and the flowing
air stream 332 in the air channels 336. The membrane 412 is
semi-permeable and formed with a high density of micron-sized pores
that allow water vapor to diffuse through the membrane 412 between
the liquid desiccant 341 and the air stream 332. The pores have a
size that, due to air-liquid suffice tension forces, prevents the
liquid desiccant 341 from flowing through the pores of the membrane
412. The semi-permeable membrane material may be selected in part
based on a required performance of the LAMEE 300.
[0125] FIG. 5b is a more detailed view of the air flow channels
comprising two membranes, two structural support screens and many
air flow channel structural spacers. In an alternative design the
spacers may be porous rigid tubes. The parameters for structurally
supporting the flexible membranes for the air channel are specified
by factor G7.
[0126] The membrane material may be selected, in part, based on a
water vapor resistance diffusion (R.sub.m,wv) divided by a
convective water vapor transfer resistance into the adjacent air
flow channels (R.sub.air,wv) (independent operational design factor
P4 as illustrated in Table 1). The water vapor resistance
(R.sub.m,wv) is defined as the membrane's resistance to water vapor
diffusing through the membrane 412 between the air channel 336 and
the liquid channel 376. The convective water vapor transfer
resistance (R.sub.air,wv) is defined as the membrane's ability to
resist water vapor transfer between the bulk-mean flow of air in
channels 336 and the liquid channels 376 through the semi-permeable
membrane 412. The ratio of the water vapor diffusion resistance
(R.sub.m,wv) of the semi-permeable membrane 412 to the convective
water vapor transfer resistance (R.sub.air,wv) of the membrane 412
may have a range of 0.1<(R.sub.m,wv)/(R.sub.air,wv)<3.0 in
factor P4. In one embodiment, the ratio is selected to be as small
as practical.
[0127] The semi-permeable membrane 412 may also be partly selected
based on a liquid break through pressure of the membrane 412
(operational design factor P7 as illustrated in Table 1). The
liquid break through pressure is defined by a standard test as a
liquid pressure within the LAMEE 300 that is required for liquid
desiccant 341 to flow through the semi-permeable membrane 412. In
one embodiment, factor P8, the membrane liquid break through
pressure (p.sub.m,bt), is selected to satisfy the inequality
(p.sub.m,bt)/(rho*g*H)>20, where rho is the density of the
liquid desiccant solution, g is the acceleration of gravity and H
is the height of the semi-permeable membrane in the energy exchange
area of the surface for each channel. A liquid break through
pressure ratio is defined by p.sub.m,bt/(rho*g*H), wherein
p.sub.m,bt is the membrane liquid break-through pressure, g is
gravity, and H is the height of the membrane panel energy exchange
area. In one embodiment, the membrane liquid break through pressure
may be greater than 20.
[0128] A channel edge seal liquid break-through pressure
(p.sub.es,bt) (operational design factor P8 as illustrated in Table
1) defines a pressure within the LAMEE 300 that is required for the
desiccant 341 to flow through the edge seal of the membrane 412.
The channel edge seal liquid break-through pressure (p.sub.es,bt)
is selected to satisfy the inequality p.sub.es,bt/(rho*g*H)>20.
When the operating pressure of the liquid flow channels is less
than p.sub.m,bt or p.sub.es,bt no liquid leeks will occur through
the membrane 412 or the edge seals. In one embodiment, the edge
seal liquid break through pressure may be greater than 20.
[0129] The membrane material may also be at least partly selected
based on an elastic tensile yield limit (T.sub.m,yl) (operational
design factor P9 as illustrated in Table 1). The elastic tensile
yield limit (T.sub.m,yl) defines the membrane's elastic deformation
limits when subjected to liquid pressure from the desiccant 341
flowing through the desiccant channel 376. In one embodiment,
factor P9, the elastic tensile yield limit (T.sub.m,yl) for the
membrane 412, will lie in the range of
0.02<(T.sub.m,yl)/(p.sub.l,op*s.sub.ws)<1.5, where p.sub.l,op
is a typical operating pressure for the liquid in each LAMEE and
s.sub.ws is a wire spacing distance for the air-side screen 416
used to resist the liquid pressure for each desiccant channel 376.
The operating pressure of the LAMEE is confined to a value that
will not exceed the elastic deformation limits for the membrane 412
for each desiccant channel 376. An elastic tensile yield limit
ratio for the membrane is defined by
T.sub.m,yl/(p.sub.l,op*s.sub.ws), wherein T.sub.m,yl is the tensile
yield limit for the membrane, p.sub.l,op is a typical operating
pressure for the liquid in each LAMEE, and s.sub.ws is a wire
spacing distance for a screen used to resist the liquid pressure
for each liquid flow channel
[0130] Membrane air-side screen support structures 414 are
positioned adjacent to the membranes 412. Each membrane 412 is
positioned between an air-side membrane support structure 414 and
the desiccant flow channel liquid-flow-guide screen diffuser 410.
The membrane support structures 414 retain the membranes 412 to
limit the elastic deflections of the membranes 412. Deflection of
the membranes 412 will occur due to liquid static pressure that is
higher than that for the adjacent air channels 332. The liquid
desiccant will create pressure on the membranes 412 that causes the
membranes 412 to bow and/or elastically deform. The mass flow
mal-distribution on the adjacent liquid and air sides is tightly
controlled for the design and quality control of the manufacturing
process and operation of the RAMEE system and its LAMEEs.
[0131] In an example embodiment, the membrane air-side support
structures 414 are formed from a screen material. Optionally, the
membrane support structures 414 may be formed from a permeable
backing, plastic support structures, rods, metal screens, spacers
and/or the like. The membrane support structures 414 include
openings 416 therethrough that allow the transfer of heat and
moisture between the liquid desiccant and the air stream 332.
[0132] The liquid-side structural spacers 418 and 424 are
positioned around the liquid-desiccant flow guide screen 410. The
spacers separate the two membranes 412 that are bonded onto each
side of the spacers 418 and 424. The membranes 412 are coupled to
the diffuser spacers 418 to form a gap or liquid-flow channel
between each membrane 412. Ends 424 and 420 form the air-flow
entrance and exit supports of the liquid flow panel 334. A top 422
of one liquid-flow channel spacer 418 forms a portion of the top
support 370 of the liquid-flow panel 334. A bottom 424 of the other
liquid-flow channel spacer 418 forms a portion of the bottom
support 372 of the liquid-flow panel 334. The top support 370 and
the bottom support 372 are also formed by air channel spacers 426.
The air channel spacers 426 are configured to abut the air channel
spacers 426 of an adjacent panel 334. The air channel spacers 426
form an air-flow gap between adjacent liquid-flow panels 334. The
air-flow gaps between adjacent liquid-flow panels 334 form the air
channels 336 within the energy exchange cavity.
[0133] FIG. 6a illustrates an air channel 336 formed between
adjacent membranes for liquid-flow panels 334. The air channel 336
is configured to carry the air stream 332 therethrough. The air
channel 336 is designed to have a uniform width 430 along a length
432 of the air channel 336. However, due to elastic deformations of
the membrane support structures 414 of the panel 334, there may be
significant variations in the air channel width. The air-side
membrane support structures 414 limits the amount of membrane
deflection restricting the air flow channel width that is caused by
the difference in static pressure in the liquid channel 334 and air
channel 332. For example, the membrane support structures 414 limit
the amount of deflection over small fraction, but a finite region,
of each membrane. With respect to factor G4, the air and liquid
flow channel statistical variations for typical individual flow
tube hydraulic diameter variations may limited. With respect to
factor G3, the average channel widths statistical variations for
each fluid, among all the channels in the LAMEE, may be
limited.
[0134] FIG. 6b illustrates an air-flow channel 336 that has been
deformed by liquid air static pressure difference between adjacent
liquid-flow and air-flow channels for a small finite region of the
air-flow panel 334. Statistical variations in the deflections in
the membrane air-flow and liquid flow channels can be deduced using
mass or volume of liquid in the LAMEE under typical liquid
pressures measurements, carefully developed pressure drop
measurements across flow channels for each fluid and optical laser
beam measurements for the minimum air-flow channel widths. The
measurements can then be used along with other data for the
determinations of the air and liquid channel average and standard
deviations of flow hydraulic diameters for each fluid, which may be
specified separately for the typical channel (factor G4) and the
set of channels in each LAMEE (factor G3). The design and
manufacturing quality control and operation of a LAMEE may depend
in part on knowing the data.
[0135] FIG. 7 is a graph 450 showing simulation results for optimum
thermal capacity rate ratio as a parameter on a chart of air
humidity ratio versus air temperature for a passive RAMEE system,
at steady-state operating conditions with the assumed indoor air at
a wide range of outdoor air conditions. The graph 450 presents the
optimum value of the thermal capacity rate ratio lines 452 that
should be selected for maximum energy transfer effectiveness of the
passive RAMEE system with two identical LAMEE units subject to the
assumed constraints with each and every air channel with a uniform
width of 4.4 mm (with no internal support structure) and
liquid-desiccant channel with a uniform width of 2.7 mm (also with
no internal structure), a membrane water vapor permeability of
1.66E-6 kg/(m*s), and with fully developed laminar air and liquid
flow in each channel. For different operating conditions and
geometric ratios graph 450 would have different values for the
optimum value of Cr*, as described below.
[0136] The results for the optimum thermal capacity rate ratio with
the assumed constant widths of the air and liquid-desiccant
channels and fully developed laminar flow for each fluid is
exemplary of one theoretical case only that differs significantly
from what is physically possible. Although variable channel widths
and turbulent channel flows are likely to occur, presenting similar
results for these cases would be much more complex; but, it can be
done using the same computational procedures. In such cases, the
optimum thermal capacity rate ratios will be very different than
those presented in graph 450 for the same outdoor air
conditions.
[0137] Using graph 450 as an exemplary illustration of the design
and operational procedure to obtain the optimum steady-state
effectiveness (and energy transfer rate) of a passive RAMEE system
with two identical LAMEEs each subject to the same mass flow rate
of air, the system operator or automatic controller selects or
controls the pumping rate of the liquid desiccant based on the
outdoor air conditions of temperature and humidity. That is, the
optimum thermal capacity rate ratio 452 for the particular outdoor
air condition is selected to compute the mass flow rate of liquid
desiccant knowing the mass flow rate of air. The result is used to
set the optimum pumping rate. When the outdoor air conditions
change significantly or the air flow rate is changed significantly,
a new optimum pumping rate is determined. In one embodiment, the
flow rate of the desiccant with respect to the flow rate of the air
stream is controlled to achieve predetermined exchanger performance
ratios that at least partially define a sensible and latent energy
exchange between the desiccant and the air stream.
[0138] FIG. 8 is a graph 500 showing equilibrium, saturation,
salt-solution concentration lines 502 superimposed on a
psychrometric chart of humidity ratio versus temperature for
several salts that may be used as liquid desiccants with the system
100. The graph 500 illustrates a temperature 504 of the air flowing
through the LAMEE and a humidity ratio 506 of the air at standard
atmospheric pressure flowing through the LAMEE. The equilibrium,
saturation, salt-solution concentration lines 502 depend only on
the type of salt, air temperatures 504 and the humidity ratios 506
at which the desiccant will start to crystallize within the panels
of the LAMEE. At the saturation concentration, a particular salt
solution will crystallize salt on the nearby membrane surfaces
within the liquid-desiccant flow channel for any decrease in the
adjacent air flow channel temperature or humidity ratio (i.e. below
the line 502 for the particular salt). Based on the expected
conditions for a particular climatic region of the air flow through
the LAMEE, the graph 500 may be used along with other data to
select an appropriate desiccant for the air flow conditions for an
HVAC application.
[0139] Line 508 represents the adjacent air temperatures 504 and
humidity ratios 506 at which a saturation magnesium chloride
solution crystallizes if the air temperature and humidity were to
drop below this line. Line 510 represents the similar saturation
calcium chloride solution crystallization line. Line 512 represents
the similar saturation lithium iodide solution crystallization
line. Line 514 represents the similar saturation lithium chloride
crystallization line. Line 516 represents the similar saturation
lithium bromide crystallization line.
[0140] Lithium bromide is capable of functioning as a liquid
desiccant in the harshest conditions because only very low adjacent
air humidity ratios would cause crystallization. However, lithium
bromide is relatively expensive in comparison to other salts with
no lithium content. In an exemplary embodiment, the system 100
utilizes a desiccant mixture of magnesium chloride with other
salts. The mixture may include magnesium chloride and at least one
of lithium chloride or lithium bromide. Alternatively, the mixture
includes calcium chloride in place of magnesium chloride and at
least one of lithium chloride or lithium bromide. In another
embodiment, the mixture includes at least three of magnesium
chloride, calcium chloride, lithium chloride and/or lithium
bromide. The concentration of magnesium chloride can range from 0%
to 35.5% (i.e. saturation salt concentration). Above the saturation
salt solution line for a particular salt in graph 500, the
equilibrium salt concentration is based on a temperature and
humidity of the air flowing through the LAMEE. A salt solution is
comprised of water and ions of salts. The concentration of lithium
chloride can range from 0% to 45.9% (i.e. saturation salt
concentration). In one embodiment, the mixture is 50% magnesium
chloride and 50% lithium chloride. The mixture can operate without
crystallization at temperatures 504 and humidity ratios 506 below
the line 508 for magnesium chloride. The mixture provides a liquid
desiccant that can operate at dryer air conditions for the outdoor
air conditions for the RAMEE system than pure magnesium chloride or
calcium chloride solutions.
[0141] In one embodiment, the desiccant is selected based on
operational design parameters P10 and P11 as illustrated in Table
1. The desiccant may be selected based on a time duration
(t.sub.salt,risk) for a risk of crystallization in the desiccant
over a typical year of weather data for a building located in a
particular climate. In particular, the time duration
(t.sub.salt,risk) for a risk of crystallization in the desiccant is
divided by the total yearly time duration of system operation
(t.sub.op). In one embodiment, the parameter P10 is within a range
of t.sub.salt,risk/t.sub.op<0.15. In another embodiment, the
desiccant is selected based on a cost of salt or mixture of salts
used in the RAMEE system 100 divided by the corresponding cost of
LiCl for the system (C.sub.salt,risk/CLiCl). In one embodiment, the
parameter P11 is within a range of C.sub.salt,risk/CLiCl<1. The
parameters P10 and P11 may be individually selected in part to
achieve a predetermined performance of the LAMEE 300 and the RAMEE
system 100. In another embodiment, both of the design parameters
P10 and P11 may be utilized to achieve the predetermined
performance.
[0142] The geometric design and operating factors G1 to 08 and the
physical operational and design factors P1 to P12 shown in Table 1
are selected to achieve a predetermined performance of the LAMEE
300 and/or the RAMEE system 100. The geometric factors G1-G10 and
the physical factors P1-P12 may each be selected to achieve the
predetermined performance of the LAMEE 300 and/or the RAMEE system
100. In another embodiment, at least some of the factors G1-G10 and
P1-P12 may be selected to achieve the predetermined performance of
the LAMEE 300 and the RAMEE system 100.
[0143] When LAMEE devices are used in passive RAMEE systems for
energy recovery, the aforementioned performance factors are
sufficient for applications where the system operates at or near
steady-state. When the LAMEE devices are installed in actively
controlled RAMEE and HVAC systems for air conditioning supply air,
most of the above described LAMEE performance factors still apply;
however, the HVAC system performance may be characterized using
different dimensionless ratios. For the purpose a coefficient of
performance (COP) or energy efficiency ratio (EER) can be used for
any typical steady-state or quasi-steady-state operating condition
of the controlled RAMEE system and the ratios can be modified for
the annual integrated time average values called seasonal energy
efficiency ratio (SEER) for both the heating and cooling of a
building located in a particular city. The COP or EER for the HVAC
system is defined as the useful energy rate change of the supply
air from inlet to discharge conditions divided by all the auxiliary
energy rate inputs to the HVAC system. Data for the calculation of
COP or EER could be measured occasionally or continuously.
[0144] Because the cost of auxiliary energy is usually very
different for cooling and heating, the ratios should be treated
separately. The SEER value for cooling the supply air in summer may
be listed separate from the SEER value for heating supply air in
winter. Since both heating and cooling are used with mechanical
cooling and desiccant dehumidification systems, both forms of input
energy may be used for the summer operations. To obtain a high SEER
for the HVAC system in a building, waste energy from exhaust air or
other process sources can be used directly to condition or partly
condition the supply air using RAMEE systems or indirectly using
heat pumps (and/or refrigerators) with ambient air or ground water
as the energy sources. The use of an economizer by-pass may also
raise the SEER.
[0145] When modified RAMEE systems are used over the year in both
active and passive modes, the calculation of the SEER values for
the HVAC system should account for the changes of mode as well as
any extra energy use for all the energy recovery or pumped
energy.
[0146] From the above discussion of active HVAC system options, it
is evident that claims for high SEER values are likely to change
significantly for the same or different buildings in different
climates. Comparisons of the dimensionless performance ratios for
actively controlled modified RAMEE systems within an HVAC system
may be done with software to show the life-cycle cost savings and
the payback period for a particular design in a particular climate.
Passive performance of a RAMEE system is still very useful because
it will vary directly with cost savings for energy recovery and it
can provide the best quantifiable proof of performance for both the
RAMEE system and its two LAMEEs. As well, the passive performance
should be used directly for the estimation of the HVAC system
performance, with a heat pump assisted RAMEE system and its cost
savings.
[0147] FIG. 9 illustrates a LAMEE 200 formed in accordance with an
alternative embodiment. The LAMEE 200 may be used as the supply air
LAMEE 108 and/or the return air LAMEE 120 (shown in FIG. 1). The
LAMEE 200 includes a housing 202 having a body 204. The body 204
includes a front 206 and a back 208 opposite the front 206. The
body 204 is elongated to extend along a length 210 between the
front 206 and the back 208. The body 204 includes a top 212 and a
bottom 214 that are parallel to one another. The body 204 includes
a height 216 that extends between the top 212 and the bottom 214.
The body 204 includes a first side 218 and a second side 220. The
first side 218 and the second side 220 span the length 210 between
the front 206 and the back 208. The first side 218 and the second
side 220 span the height 216 between the top 212 and the bottom
214. The first side 218 and the second side 220 are arranged
parallel to one another and are separate by a width 222.
[0148] The LAMEE body 204 includes an air inlet 205 at the front
206 of the body 204 and an air outlet 207 at the back 208 of the
body 204. The LAMEE body 204 forms an energy exchange cavity 224.
The energy exchange cavity 224 extends the length 210, height 216,
and width 222 between the front 206, the back 208, the top 212, the
bottom 214, the first side 218, and the second side 220. The length
210, height 216, and/or width 222 represent physical design factors
that are selected to satisfy predetermined ratios with one another
and/or with predetermined ratios with other design parameters, as
explained hereafter. The ratios of the height 216 to the length
210, the width 222 to the length 210, and/or the width 222 to the
height 216 represent dimensionless physical ratios, and more
generally, dimensionless design factors.
[0149] The energy exchange cavity 224 includes a plurality of
energy exchange panels 226 extending therethrough. The panels 226
extend the length 210 and height 216 of the energy exchange cavity
224. Each panel 226 forms a desiccant channel that carries
desiccant 241 through the energy exchange cavity 224. The panels
226 are arranged parallel to one another and spaced apart to form
air channels 230 and desiccant channels 231 therebetween. The air
channels 230 extend between the air inlet 205 and the air outlet
207. Each air channel 230 is formed between adjacent desiccant
channels 231. The air channels 230 direct an air stream 234 from
the front 206 of the LAMEE 200 to the back 208 of the LAMEE
200.
[0150] A desiccant inlet housing 236 is joined to the LAMEE housing
202. In the illustrated embodiment, the desiccant inlet housing 236
is joined to the bottom 214 of the LAMEE housing 202. The desiccant
inlet housing 236 is positioned adjacent the back 208 of the LAMEE
housing 202. The desiccant inlet housing 236 extends from the back
208 of the LAMEE housing 202 along the bottom 214 of the LAMEE
housing 202. The desiccant inlet housing 236 extends partially
between the back 208 and front 206 of the LAMEE housing 202.
Alternatively, the desiccant inlet housing 236 may positioned at
any location along the LAMME body 204. In one embodiment, the LAMEE
200 may include more than one desiccant inlet body 204. The
desiccant inlet housing 236 extends a length 238 along the bottom
214 of the LAMEE housing 202. The length 238 that the desiccant
inlet housing 236 extends is based on a predetermined performance
of the LAMEE 200. In one embodiment, the desiccant inlet housing
202 extends no more than one fourth of the length 210 of the LAMEE
body 204. In another embodiment, the desiccant inlet housing 236
extends one fifth of the length 210 of the LAMEE body 204.
[0151] The desiccant inlet housing 236 includes an inlet 240 and an
outlet 242. The inlet 240 is configured to receive desiccant 241
from a storage tank 128 (shown in FIG. 1). The inlet 240 and the
outlet 242 are in fluid communication with the desiccant channels
231 extending through the energy exchange cavity 224. The desiccant
241 flows from the desiccant inlet housing 236 into the desiccant
channels 231. The desiccant 241 flows through the desiccant
channels 231 from the back 208 of the LAMEE housing 202 toward the
front 206 of the LAMEE housing 202. The desiccant 241 flows in a
direction opposite the direction of the air stream 234. The
desiccant 241 flows through the desiccant channels 231 toward a
desiccant outlet housing 244.
[0152] The desiccant outlet housing 244 is joined to the top 212 of
the LAMEE housing 202. The desiccant outlet housing 244 is
positioned proximate to the front 206 of the LAMEE housing 202.
Alternatively, the desiccant outlet housing 244 may be positioned
at any location along the top 212 of the LAMEE housing 202. The
desiccant outlet housing 244 is offset from the desiccant inlet
housing 236 along the direction of the air stream 234. The
desiccant outlet housing 244 extends from the front 206 of the
LAMEE housing 202 along the top 212 of the LAMEE housing 202. The
desiccant outlet housing 244 extends partially between the front
206 and the back 208 of the LAMEE housing 202. The desiccant outlet
housing 244 extends a length 246 along the top 212 of the LAMEE
housing 202. The length 246 that the desiccant outlet housing 244
extends is based on a predetermined performance of the LAMEE 200.
In one embodiment, the desiccant outlet housing 244 extends a
length 246 that is no more than one fifth the channel energy
exchange length 210 of the LAMEE body 204. In one embodiment, the
desiccant outlet housing 244 extends a length 246 that is one fifth
of the length 210 of the LAMEE body 204.
[0153] The desiccant outlet housing 244 includes an inlet 248 and
an outlet 250. The inlet 248 is in fluid communication with the
desiccant channels 231. The desiccant outlet housing 244 receives
desiccant 241 from the desiccant channels 231. The desiccant outlet
housing 244 channels the desiccant 241 through the outlet 250. The
outlet 250 is in fluid communication with a storage tank 128 (shown
in FIG. 1).
[0154] The desiccant inlet housing 236 and the desiccant outlet
housing 244 form a non-linear desiccant flow path 252 through the
panels 226. The desiccant flow path 252 flows in a direction
opposite to the air stream 234. The desiccant flow path 252 travels
upstream with respect to the direction of the air stream 234. The
desiccant flow path 252 is a cross/counter flow path with respect
to the air stream 234 flowing through the air channels 230. An
inlet cross segment 254 of the desiccant flow path 252 is formed as
the desiccant 241 enters the panels 226 from the desiccant inlet
housing 236. Desiccant 241 flowing from the desiccant inlet housing
236 into the panels 226 flows upward through the inlet cross
segment 254. Desiccant in the inlet cross segment 254 flows in a
cross flow arrangement that is substantially perpendicular to the
direction of the air stream 234.
[0155] As the desiccant 241 is channeled from the desiccant inlet
housing 236 fills the panels 226, the desiccant 241 begins flowing
through a counter segment 256 of the desiccant flow path 252. The
counter segment 256 extends a length 258 through the panels 226.
The length 258 is based on a predetermined performance of the LAMEE
200. The counter segment 256 flows in a counter flow arrangement
with respect to the direction of the air stream 234 flowing through
the air channels 230. The counter segment 256 flows substantially
parallel to the direction of the air stream 234. The counter
segment 256 flows upstream with respect to the direction of the air
stream 234. The counter flow arrangement provides a predetermined
heat and moisture exchange between the desiccant in the panels 226
and the air stream 234 in the air channels 230.
[0156] The desiccant 241 in the counter segment 256 flows into an
outlet cross segment 260 of the desiccant flow path 252. The outer
cross segment 260 flows substantially perpendicular to the
direction of the air stream 234. The desiccant in the outlet cross
segment 260 flows in a cross flow arrangement with respect to the
air 234 in the air channels 230. The desiccant in the outlet cross
segment 260 flows upward from the counter segment 256 to the
desiccant outlet housing 244.
[0157] The cross/counter flow arrangement of the desiccant flow
path 252 provides desiccant counter flow with respect to the
direction of the air stream 234. The counter flow arrangement
improves an efficiency of the LAMEE 200. The cross/counter flow
arrangement does not require large headers that would otherwise
increase the space required for the LAMEE 200. The illustrated
embodiment shows the desiccant flow path 252 flowing upward from
the bottom 214 of the LAMEE 200 to the top 212 of the LAMEE 200.
Optionally, the desiccant inlet housing 236 may be positioned on
the top 212 of the LAMEE 200 and the desiccant outlet housing 244
may be positioned on the bottom 214 of the LAMEE 200. In such an
embodiment, the desiccant flow path 252 may flow downward from the
top 212 of the LAMEE 200 to the bottom 214 of the LAMEE 200.
[0158] The geometric design factors G1-G8 and the physical
operational and design factors P1-P12 shown in Table 1 should be
used to achieve a predetermined performance of the LAMEE 200.
Although each of the dimensionless independent factors in the set,
G1-G10 and P1-P12, should be selected within the specified ranges
in Table 1 to achieve the predetermined performance of the passive
RAMEE system with its two LAMEE 200 units operating at
steady-state, it may be possible to relax the design and
operational range of a few independent factors in Table 1 for some
narrow range of system operating conditions and still achieve an
acceptable system performance. Therefore, in another embodiment,
only some of the factors, G1-G10 and P1-P12, need to be selected in
the ranges specified in Table 1 to achieve an acceptable
predetermined performance of the LAMEE 200 when tested as part of a
passive RAMEE system.
[0159] FIG. 10 illustrates a LAMEE 600 formed in accordance with an
alternative embodiment. The LAMEE 600 includes a housing 602 having
a body 604 with a top 606 and a bottom 608. The LAMEE 600 includes
an air inlet 610 and an air outlet 612. An energy exchange cavity
614 extends through the body 604 between the air inlet 610 and the
air outlet 612. An air stream 616 flows through the energy exchange
cavity 614 from the air inlet 610 to the air outlet 612. The energy
exchange cavity 614 includes panels 618 that form desiccant
channels 615 to carry desiccant therethrough.
[0160] A desiccant inlet 620 is provided at the bottom 608 of the
LAMEE body 604. The desiccant inlet 620 may be positioned at any
location along the bottom 608 of the LAMEE body 604. Alternatively,
the LAMEE 600 may include any number of desiccant inlets 620. The
desiccant inlet 620 is in flow communication with the desiccant
channels 615. A first desiccant outlet 622 and a second desiccant
outlet 624 are positioned at the top 606 of the LAMEE body 604. The
first and second desiccant outlets 622 and 624 may be positioned at
any location along the top 606 of the LAMEE body 604. The first and
second desiccant outlets 622 and 624 are offset from the desiccant
inlet 620 along the direction of the air stream 616. The desiccant
inlet 620 and the desiccant outlets 622 and 624 from desiccant flow
paths from the bottom 608 of the LAMME body 604 to the top 606 of
the LAMEE body 604. Alternatively, the desiccant inlet 620 may be
positioned along the top 606 of the LAMEE body 604 and the
desiccant outlets 622 and 624 may be positioned along the bottom
608 of the LAMEE body 604. In such an embodiment, the desiccant
flows from the top 606 of the LAMEE body 604 to the bottom 608 of
the LAMEE body 604.
[0161] The desiccant inlet 620 and the first desiccant outlet 622
form a first desiccant flow path 626 that flows non-linearly
through the panels 618. The first desiccant flow path 626 includes
an inlet segment 628 that flow from the desiccant inlet 620. The
inlet segment 628 flows in a cross flow direction substantially
perpendicular to the direction of the air stream 616. The inlet
segment 628 flow into an intermediate segment 630 that flows
substantially parallel to the direction of the air stream 616. The
intermediate segment 630 flows in the same direction as the
direction of the air stream 616. The intermediate segment 630 flows
into an outlet segment 632 that flows to the desiccant outlet 622.
The outlet segment 632 flows in a direction that is substantially
perpendicular to the direction of the air stream 616.
[0162] The desiccant inlet 620 and the second desiccant outlet 624
form a second desiccant flow path 634 that flows non-linearly
through the panels 618. The second desiccant flow path 634 includes
an inlet segment 636 that flows from the desiccant inlet 620. The
inlet segment 636 flows in a cross flow direction substantially
perpendicular to the direction of the air stream 616. The inlet
segment 636 flows into an intermediate segment 638 that flows
substantially parallel to the direction of the air stream 616. The
intermediate segment 638 flows in an opposite direction to the
direction of the air stream 616. The intermediate segment 638 flows
into an outlet segment 640 that flows to the second desiccant
outlet 624. The outlet segment 640 flows in a direction that is
substantially perpendicular to the direction of the air stream
616.
[0163] The physical design geometric factors G1-G10 and the
operational design factors P1-P12 shown in Table 1 may be used to
achieve a predetermined performance of the LAMEE 600. The physical
design geometric factors G1-G10 and the operational design factors
P1-P12 may each be selected to achieve the predetermined
performance of the LAMEE 600. In another embodiment, only some of
the physical design geometric factors G1-G10 and the operational
design factors P1-P12 may be selected to achieve the predetermined
performance of the LAMEE 600.
[0164] FIG. 11 illustrates a LAMEE 650 formed in accordance with an
alternative embodiment. The LAMEE 650 includes a housing 652 having
a body 654 with a top 656 and a bottom 658. The LAMEE 650 includes
an air inlet 660 and an air outlet 662. An energy exchange cavity
664 extends through the body 654 between the air inlet 660 and the
air outlet 662. An air stream 666 flows through the energy exchange
cavity 664 from the air inlet 660 to the air outlet 662. The energy
exchange cavity 664 includes panels 668 that form desiccant
channels 669 to carry a desiccant therethrough.
[0165] A desiccant outlet 670 is provided at the top 656 of the
LAMEE body 654. The desiccant outlet 670 may be positioned at any
location along the top 656 of the LAMEE body 654. Alternatively,
the LAMEE 650 may include any number of desiccant outlets 670. The
desiccant outlet 670 is in flow communication with the desiccant
channels 669. A first desiccant inlet 672 and a second desiccant
inlet 674 are positioned at the bottom 658 of the LAMEE body 654.
The first and second desiccant inlets 672 and 674 may be positioned
at any location along the bottom 658 of the LAMEE body 654. The
first and second desiccant inlets 672 and 674 are offset from the
desiccant outlet 670 along the direction of the air stream 666. The
desiccant outlet 670 and the desiccant inlets 672 and 674 form
desiccant flow paths from the bottom 658 of the LAMME body 654 to
the top 656 of the LAMEE body 654. Alternatively, the desiccant
outlet 670 may be positioned along the bottom 658 of the LAMEE body
654 and the desiccant inlets 672 and 674 may be positioned along
the top 656 of the LAMEE body 654. In such an embodiment, the
desiccant flows from the top 656 of the LAMEE body 654 to the
bottom 658 of the LAMEE body 654.
[0166] The desiccant outlet 670 and the first desiccant inlet 672
form a first desiccant flow path 676 that flows non-linearly
through the panels 668. The first desiccant flow path 676 includes
an inlet segment 678 that flow from the first desiccant inlet 672.
The inlet segment 678 flows in a cross flow direction substantially
perpendicular to the direction of the air stream 666. The inlet
segment 678 flows into an intermediate segment 680 that flows
substantially parallel to the direction of the air stream 666. The
intermediate segment 680 flows in a direction opposite to the
direction of the air stream 666. The intermediate segment 680 flows
into an outlet segment 682 that flows to the desiccant outlet 670.
The outlet segment 682 flows in a direction that is substantially
perpendicular to the direction of the air stream 666.
[0167] The desiccant outlet 670 and the second desiccant inlet 674
form a second desiccant flow path 684 that flows non-linearly
through the panels 668. The second desiccant flow path 684 includes
an inlet segment 686 that flows from the first desiccant inlet 674.
The inlet segment 686 flows in a cross flow direction substantially
perpendicular to the direction of the air stream 666. The inlet
segment 686 flows into an intermediate segment 688 that flows
substantially parallel to the direction of the air stream 666. The
intermediate segment 688 flows in the same direction as the
direction of the air stream 666. The intermediate segment 688 flows
into an outlet segment 690 that flows to the desiccant outlet 670.
The outlet segment 690 flows in a direction that is substantially
perpendicular to the direction of the air stream 666.
[0168] The physical design geometric factors G1-G10 and the
operational design factors P1-P12 shown in Table 1 may be used to
achieve a predetermined performance of the LAMEE 650. The physical
design geometric factors G1-G10 and the operational design factors
P1-P12 may each be selected to achieve the predetermined
performance of the LAMEE 650. In another embodiment, only some of
the physical design geometric factors G1-G10 and the operational
design factors P1-P12 may be selected to achieve the predetermined
performance of the LAMEE 650.
[0169] FIG. 12 illustrates a LAMEE 700 formed in accordance with an
alternative embodiment. The LAMEE 700 includes a housing 702 having
a body 704 with a top 706 and a bottom 708. The LAMEE 700 includes
a first end 710 and a second end 712. An energy exchange cavity 714
extends through the body 704 between the first end 710 and the
second end 712. An air stream 716 flows through the energy exchange
cavity 714 from the first end 710 to the second end 712. The energy
exchange cavity 714 includes panels 718 that form desiccant
channels 719 to carry a desiccant therethrough.
[0170] A desiccant flow path 726 flows through the desiccant
channels 719 from the second end 712 to the first end 710. The
desiccant flow path 726 is arranged in a counter-flow arrangement
with respect to the air stream 716. Heat is transferred through the
panels 719 between the desiccant flow path 726 and the air stream
716.
[0171] The physical design geometric factors G1-G10 and the
operational design factors P1-P12 shown in Table 1 may be used to
achieve a predetermined performance of the LAMEE 700. The physical
design geometric factors G1-G10 and the operational design factors
P1-P12 may each be selected to achieve the predetermined
performance of the LAMEE 700. In another embodiment, only some of
the physical design geometric factors G1-G10 and the operational
design factors P1-P12 may be selected to achieve the predetermined
performance of the LAMEE 700.
[0172] FIG. 13 illustrates a LAMEE 750 formed in accordance with an
alternative embodiment. The LAMEE 750 includes a housing 752 having
a body 754 with a top 756 and a bottom 758. The LAMEE 750 includes
a first end 760 and a second end 762. An energy exchange cavity 764
extends through the body 754 between the first end 760 and the
second end 762. An air stream 766 flows through the energy exchange
cavity 764 from the first end 760 to the second end 762. The energy
exchange cavity 764 includes panels 768 that form desiccant
channels to carry a desiccant therethrough.
[0173] A desiccant flow path 776 flows through the desiccant
channels from the top 756 to the bottom 758. The desiccant flow
path 776 is arranged in a cross-flow arrangement with respect to
the air stream 766. Heat is transferred through the panels 768
between the desiccant flow path 776 and the air stream 766.
[0174] The physical design geometric factors G1-G10 and the
operational design factors P1-P12 shown in Table 1 may be used to
achieve a predetermined performance of the LAMEE 750. The physical
design geometric factors G1-G10 and the operational design factors
P1-P12 may each be selected to achieve the predetermined
performance of the LAMEE 750. In another embodiment, only some of
the physical design geometric factors C1-G10 and the operational
design factors P1-P12 may be selected to achieve the predetermined
performance of the LAMEE 750.
[0175] FIG. 14 illustrates an exemplary energy exchange system 850
formed in accordance with the set of embodiments specified in Table
1. The energy exchange system 850 is configured to condition air
supplied to an enclosed structure 852 having a plurality of rooms
854. The energy exchange system 850 receives pre-conditioned air
856 that is direct through the system 850 with a fan 858. The
pre-conditioned air 856 is directed to a supply LAMEE 860 that
conditions the pre-conditioned air 856 to generate supply air 862.
The supply LAMEE 860 conditions the pre-conditioned air 856 by
adding or removing heat and moisture to or from the pre-conditioned
air 856. The supply air 862 is discharged into the rooms 854.
[0176] Each room 854 includes a return air LAMEE 864 configured to
receive return air 866 from the room 854. The return air LAMEE 864
conditions the return air 866 by adding or removing heat and
moisture to or from the return air 866. The return air LAMEEs 864
exchange the heat and moisture with the supply air LAMEE 860 to
transfer the heat and moisture between the return air 866 and the
pre-conditioned air 856. The return LAMEEs 864 generate exhaust air
868 that is discharged from the energy exchange system 850 by a fan
870.
[0177] Liquid desiccant 872 flows between the supply LAMEE 860 and
the return air LAMEEs 864. The desiccant 872 transfers the heat and
moisture between the supply LAMEE 860 and the return air LAMEEs
864. Storage tanks 874 are provided to retain the desiccant 872 as
it flows between the supply LAMEE 860 and the return air LAMEEs
864. Pumps 876 may be provided to move the liquid desiccant 872
between the supply LAMEE 860 and the return air LAMEEs 864.
[0178] FIG. 15 illustrates an alternative exemplary energy exchange
system 900 formed in accordance with the set of embodiments. The
energy exchange system 900 is configured to condition air supplied
to a structure 901. The structure 901 includes a plurality of rooms
903. The energy exchange system 900 includes an inlet 902 that
receives pre-conditioned air 904 that may be moved by a fan 905.
The pre-conditioned air 904 is divided into each of the rooms 903
of the structure 901. The pre-conditioned air 904 is moved through
the energy exchange system 900 with a fan 905. The pre-conditioned
air 904 may be divided equally between each of the rooms 903.
Optionally, the pre-conditioned air 904 may be divided between the
rooms 903 based on a capacity of each room 903 and/or a supply air
need in each room 903. Each room 903 includes a supply LAMEE 906
that is configured to condition the pre-conditioned air 904. The
supply LAMEE 906 conditions the per-conditioned air by adding or
removing heat and moisture to the preconditioned air 904. The
supply LAMEE 906 generates supply air 908 that is discharged into
the room 903.
[0179] Return air 910 from each room 903 is channeled to a return
LAMEE 912. The return LAMEE 912 conditions the return air 910 to
generate exhaust air 915. The exhaust air 915 is moved through the
energy exchange system 900 with a fan 907 that directs the exhaust
air 915 to an outlet 909. The return LAMEE 912 conditions the
return air 910 by adding or removing heat and moisture from the
return air 910. Heat and moisture is transferred between the supply
LAMEE 906 and the return LAMEE 912 to exchange the heat and
moisture between the return air 910 and the pre-conditioned air
904.
[0180] Desiccant 914 flows between the supply LAMEE 906 and the
return LAMEE 912. The desiccant 914 transfers the heat and moisture
between the supply LAMEE 906 and the return LAMEE 912. Storage
tanks 916 are provided between the supply LAMEE 906 and the return
LAMEE 912. The storage tanks 916 retain desiccant traveling between
the supply LAMEE 906 and the return LAMEE 912. Pumps 918 are
provided to move the desiccant 914 between the supply LAMEE 906 and
the return LAMEE 912.
[0181] In another embodiment, an energy exchange system may be
provided that includes individual supply LAMEEs and return LAMEEs
for each room of a structure. Alternatively, an energy exchange
system may be provided that utilizes heat and moisture from a first
room of a structure to condition air in a second room of the
structure. Such an embodiment would include a first LAMEE
positioned within the first room and a second LAMEE positioned
within the second room. The heat and moisture from the first room
would be transferred from the first LAMEE to the second LAMEE to
add the heat and moisture to the air in the second room.
[0182] The embodiments described herein provide a LAMEE that
utilizes either a counter/cross-flow or cross-flow to improve the
effectiveness of the LAMEE. The dimensions of the LAMEE are
selected to provide a predetermined performance of the LAMEE. The
predetermined performance of the LAMEE is based on the surrounding
environment. The LAMEE is configured to reach the predetermined
performance based on the conditions of the air flow through the
LAMEE. The embodiments herein also provide a desiccant solution
that is configured to operate at dry ambient air conditions.
[0183] It should be noted that the LAMEEs illustrated in FIGS. 2
and 9-13 are exemplary only and the physical design geometric
factors G1-G10 and the operational design factors P1-P12 may be
utilized with any LAMEE having any suitable geometry. Further, the
energy exchange systems illustrated in FIGS. 14 and 15 are
exemplary only and the physical design geometric factors G1-G10 and
the operational design factors P1-P12 may be utilized with any
suitable energy exchange system.
[0184] It is to be understood that the above description is
intended to be illustrative, and not restrictive. For example, the
above-described embodiments (and/or aspects thereof) may be used in
combination with each other. In addition, many modifications may be
made to adapt a particular situation or material to the teachings
of the various embodiments of the invention without departing from
their scope. While the dimensions and types of materials described
herein are intended to define the parameters of the various
embodiments of the invention, the embodiments are by no means
limiting and are exemplary embodiments. Many other embodiments will
be apparent to those of skill in the art upon reviewing the above
description. The scope of the various embodiments of the invention
should, therefore, be determined with reference to the appended
claims, along with the full scope of equivalents to which such
claims are entitled. In the appended claims, the terms "including"
and "in which" are used as the plain-English equivalents of the
respective terms "comprising" and "wherein." Moreover, in the
following claims, the terms "first," "second," and "third," etc.
are used merely as labels, and are not intended to impose numerical
requirements on their objects. Further, the limitations of the
following claims are not written in means-plus-function format and
are not intended to be interpreted based on 35 U.S.C. .sctn. 112,
sixth paragraph, unless and until such claim limitations expressly
use the phrase "means for" followed by a statement of function void
of further structure.
[0185] This written description uses examples to disclose the
various embodiments of the invention, including the best mode, and
also to enable any person skilled in the art to practice the
various embodiments of the invention, including making and using
any devices or systems and performing any incorporated methods. The
patentable scope of the various embodiments of the invention is
defined by the claims, and may include other examples that occur to
those skilled in the art. Such other examples are intended to be
within the scope of the claims if the examples have structural
elements that do not differ from the literal language of the
claims, or if the examples include equivalent structural elements
with insubstantial differences from the literal languages of the
claims.
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