U.S. patent application number 16/702126 was filed with the patent office on 2020-06-04 for liquid desiccant air-conditioning systems using antifreeze-free heat transfer fluids.
The applicant listed for this patent is 7AC Technologies, Inc.. Invention is credited to Mark A. Allen, Peter Luttik, Scott N. Rowe.
Application Number | 20200173671 16/702126 |
Document ID | / |
Family ID | 70848831 |
Filed Date | 2020-06-04 |
![](/patent/app/20200173671/US20200173671A1-20200604-D00000.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00001.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00002.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00003.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00004.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00005.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00006.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00007.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00008.png)
![](/patent/app/20200173671/US20200173671A1-20200604-D00009.png)
United States Patent
Application |
20200173671 |
Kind Code |
A1 |
Rowe; Scott N. ; et
al. |
June 4, 2020 |
LIQUID DESICCANT AIR-CONDITIONING SYSTEMS USING ANTIFREEZE-FREE
HEAT TRANSFER FLUIDS
Abstract
This application relates generally to liquid desiccant air
conditioning (LDAC) systems and, more specifically, to liquid
desiccant air-conditioning systems configured to use
antifreeze-free heat transfer fluids.
Inventors: |
Rowe; Scott N.; (Dover,
NH) ; Allen; Mark A.; (Essex, MA) ; Luttik;
Peter; (Beverly, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
7AC Technologies, Inc. |
Beverly |
MA |
US |
|
|
Family ID: |
70848831 |
Appl. No.: |
16/702126 |
Filed: |
December 3, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62774448 |
Dec 3, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 3/06 20130101; F24F
3/1417 20130101; F24F 2221/52 20130101 |
International
Class: |
F24F 3/14 20060101
F24F003/14; F24F 3/06 20060101 F24F003/06 |
Claims
1. A liquid desiccant air-conditioning system for treating an air
stream entering a building space, comprising: a compressor-based
cooling system through which a refrigerant flows; a liquid
desiccant conditioner utilizing a liquid desiccant and a heat
transfer fluid to cool, heat, humidify, or dehumidify a first air
stream flowing therethrough depending on a mode of operation of the
liquid desiccant air conditioning system, wherein the heat transfer
fluid used in the conditioner contains substantially no antifreeze
additive; a liquid desiccant regenerator receiving the liquid
desiccant used in the liquid desiccant conditioner, and utilizing a
heat transfer fluid and a second air stream flowing therethrough to
concentrate or dilute the liquid desiccant depending on the mode of
operation of the liquid desiccant air conditioning system, and then
returning the liquid desiccant to the conditioner, wherein the heat
transfer fluid and the liquid desiccant cool, heat, humidify, or
dehumidify the second air stream depending on the mode of operation
of the liquid desiccant air conditioning system, wherein the heat
transfer fluid used in the regenerator contains substantially no
antifreeze additive; a first heat exchanger thermally coupled to
the heat transfer fluid used in the liquid desiccant conditioner
and to the refrigerant flowing through the compressor-based cooling
system for exchanging heat between the refrigerant and the heat
transfer fluid; a second heat exchanger thermally coupled to the
heat transfer fluid used in the liquid desiccant regenerator and to
the refrigerant flowing through another portion of the
compressor-based cooling system for exchanging heat between the
refrigerant and the heat transfer fluid; a first enclosure
containing the liquid desiccant conditioner, the first enclosure
including an inlet for receiving the first air stream and an outlet
for outputting a supply air stream to the building space comprising
the first air stream after treatment by the conditioner; a second
enclosure containing the liquid desiccant regenerator, said second
enclosure including an inlet for receiving the second air stream
and an outlet for exhausting the second air stream after treatment
by the regenerator; a third enclosure containing the
compressor-based cooling system, the first heat exchanger, and the
second heat exchanger; one or more dampers between the first
enclosure, the second enclosure, and the third enclosure
selectively permitting flow of the supply air stream from the first
enclosure to the second enclosure and the third enclosure during
operation of the liquid desiccant air-conditioning system in a
heating operation mode to prevent freezing of the heat transfer
fluid; and a heating system positioned in the first enclosure to
heat the first air stream prior to the air stream entering the
conditioner.
2. The system of claim 1, wherein space in the first enclosure is
in fluid communication with the building space.
3. The system of claim 1, wherein the liquid desiccant conditioner
includes a plurality of structures arranged in a substantially
parallel orientation, each of the structures has at least one
surface across which the liquid desiccant can flow and an internal
passage through which the heat transfer fluid can flow, wherein the
first air stream flows between the plurality of structures.
4. The system of claim 1, wherein the liquid desiccant regenerator
includes a plurality of structures arranged in a substantially
parallel orientation, each of the structures has at least one
surface across which the liquid desiccant can flow and an internal
passage through which a heat transfer fluid can flow, wherein a
second air stream flows between the plurality of structures.
5. The system of claim 1, further comprising a heating system in
the second enclosure to heat the air or heat transfer fluid therein
and obviate need for an advanced dehumidification coil.
6. The system of claim 5, wherein the heating system comprises a
water heater to heat the heat transfer fluid or a space heater.
7. The system of claim 1, wherein one or more of the enclosures
include a low point from which the heat transfer fluid can be
drained.
8. The system of claim 1, wherein the compressor-based cooling
system comprises a chiller.
9. A method of operating a liquid desiccant air-conditioning system
for treating an air stream entering a building space, wherein the
liquid desiccant air conditioning system includes: a
compressor-based cooling system through which a refrigerant flows;
a liquid desiccant conditioner utilizing a liquid desiccant and a
heat transfer fluid to cool, heat, humidify, or dehumidify a first
air stream flowing therethrough depending on the mode of operation
of the liquid desiccant air conditioning system, wherein the heat
transfer fluid used in the conditioner contains substantially no
antifreeze additive; a liquid desiccant regenerator receiving the
liquid desiccant used in the liquid desiccant conditioner, and
utilizing a heat transfer fluid and a second air stream flowing
therethrough to concentrate or dilute the liquid desiccant
depending on the mode of operation of the liquid desiccant air
conditioning system, and then returning the liquid desiccant to the
conditioner, wherein the heat transfer fluid and the liquid
desiccant cool, heat, humidify, or dehumidify the second air stream
depending on the mode of operation of the liquid desiccant air
conditioning system, wherein the heat transfer fluid used in the
regenerator contains substantially no antifreeze additive; a first
heat exchanger thermally coupled to the heat transfer fluid used in
the liquid desiccant conditioner and to the refrigerant flowing
through the compressor-based cooling system for exchanging heat
between the refrigerant and the heat transfer fluid; a second heat
exchanger thermally coupled to the heat transfer fluid used in the
liquid desiccant regenerator and to the refrigerant flowing through
another portion of the compressor-based cooling system for
exchanging heat between the refrigerant and the heat transfer
fluid; a first enclosure containing the liquid desiccant
conditioner, the first enclosure including an inlet for receiving
the first air stream and an outlet for outputting a supply air
stream to the building space comprising the first air stream after
treatment by the conditioner; a second enclosure containing the
liquid desiccant regenerator, said second enclosure including an
inlet for receiving the second air stream and an outlet for
exhausting the second air stream after treatment by the
regenerator; and a third enclosure containing the compressor-based
cooling system, the first heat exchanger, and the second heat
exchanger; wherein the method comprises heating the first air
stream prior to the air stream entering the conditioner and
selectively permitting flow of the supply air stream from the first
enclosure to the second enclosure and the third enclosure during
operation of the liquid desiccant air-conditioning system in a
heating operation mode to prevent freezing of the heat transfer
fluid.
10. The method of claim 9, wherein space in the first enclosure is
in fluid communication with the building space.
11. The method of claim 9, further comprising heating the heat
transfer fluid using a water heater.
12. The method of claim 9, further comprising heating space in the
second enclosure or the third enclosure using one or more space
heaters.
13. The method of claim 9, further comprising draining the heat
transfer fluid from a low point in the liquid desiccant air
conditioning system in the event of power failure.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Provisional
Patent Application No. 62/774,448 filed on Dec. 3, 2018 entitled
LIQUID DESICCANT AIR-CONDITIONING SYSTEMS USING ANTIFREEZE-FREE
HEAT TRANSFER FLUIDS, which is hereby incorporated by
reference.
BACKGROUND
[0002] The present application relates generally to liquid
desiccant air conditioning (LDAC) systems and, more specifically,
to liquid desiccant air-conditioning systems using antifreeze-free
heat transfer fluids.
BRIEF SUMMARY
[0003] A liquid desiccant air-conditioning system is disclosed for
treating an air stream entering a building space. The system
includes a compressor-based cooling system through which a
refrigerant flows. A liquid desiccant conditioner utilizes a liquid
desiccant and a heat transfer fluid to cool, heat, humidify, or
dehumidify a first air stream flowing therethrough depending on a
mode of operation of the liquid desiccant air conditioning system.
The heat transfer fluid used in the conditioner contains
substantially no antifreeze additive. A liquid desiccant
regenerator receives the liquid desiccant used in the liquid
desiccant conditioner, and utilizes a heat transfer fluid and a
second air stream flowing therethrough to concentrate or dilute the
liquid desiccant depending on the mode of operation of the liquid
desiccant air conditioning system, and then return the liquid
desiccant to the conditioner. The heat transfer fluid and the
liquid desiccant cool, heat, humidify, or dehumidify the second air
stream depending on the mode of operation of the liquid desiccant
air conditioning system. The heat transfer fluid used in the
regenerator contains substantially no antifreeze additive. The
system also includes a first heat exchanger thermally coupled to
the heat transfer fluid used in the liquid desiccant conditioner
and to the refrigerant flowing through the compressor-based cooling
system for exchanging heat between the refrigerant and the heat
transfer fluid. A second heat exchanger is thermally coupled to the
heat transfer fluid used in the liquid desiccant regenerator and to
the refrigerant flowing through another portion of the
compressor-based cooling system for exchanging heat between the
refrigerant and the heat transfer fluid. A first enclosure contains
the liquid desiccant conditioner. The first enclosure includes an
inlet for receiving the first air stream and an outlet for
outputting a supply air stream to the building space comprising the
first air stream after treatment by the conditioner. A second
enclosure contains the liquid desiccant regenerator. The second
enclosure includes an inlet for receiving the second air stream and
an outlet for exhausting the second air stream after treatment by
the regenerator. A third enclosure contains the compressor-based
cooling system, the first heat exchanger, and the second heat
exchanger. The system includes one or more dampers between the
first enclosure, the second enclosure, and the third enclosure
selectively permitting flow of the supply air stream from the first
enclosure to the second enclosure and the third enclosure during
operation of the liquid desiccant air-conditioning system in a
heating operation mode to prevent freezing of the heat transfer
fluid. The system also includes a heating system positioned in the
first enclosure to heat the first air stream prior to the air
stream entering the conditioner.
[0004] A method is disclosed for operating a liquid desiccant
air-conditioning system for treating an air stream entering a
building space. The liquid desiccant air conditioning system
includes a compressor-based cooling system through which a
refrigerant flows. A liquid desiccant conditioner utilizes a liquid
desiccant and a heat transfer fluid to cool, heat, humidify, or
dehumidify a first air stream flowing therethrough depending on the
mode of operation of the liquid desiccant air conditioning system.
The heat transfer fluid used in the conditioner contains
substantially no antifreeze additive. The system also includes a
liquid desiccant regenerator receiving the liquid desiccant used in
the liquid desiccant conditioner, and utilizing a heat transfer
fluid and a second air stream flowing therethrough to concentrate
or dilute the liquid desiccant depending on the mode of operation
of the liquid desiccant air conditioning system, and then returning
the liquid desiccant to the conditioner. The heat transfer fluid
and the liquid desiccant cool, heat, humidify, or dehumidify the
second air stream depending on the mode of operation of the liquid
desiccant air conditioning system, wherein the heat transfer fluid
used in the regenerator contains substantially no antifreeze
additive. The system includes a first heat exchanger thermally
coupled to the heat transfer fluid used in the liquid desiccant
conditioner and to the refrigerant flowing through the
compressor-based cooling system for exchanging heat between the
refrigerant and the heat transfer fluid. A second heat exchanger is
thermally coupled to the heat transfer fluid used in the liquid
desiccant regenerator and to the refrigerant flowing through
another portion of the compressor-based cooling system for
exchanging heat between the refrigerant and the heat transfer
fluid. The system includes a first enclosure containing the liquid
desiccant conditioner, the first enclosure including an inlet for
receiving the first air stream and an outlet for outputting a
supply air stream to the building space comprising the first air
stream after treatment by the conditioner. The system includes a
second enclosure containing the liquid desiccant regenerator. The
second enclosure includes an inlet for receiving the second air
stream and an outlet for exhausting the second air stream after
treatment by the regenerator. A third enclosure contains the
compressor-based cooling system, the first heat exchanger, and the
second heat exchanger. The method comprises heating the first air
stream prior to the air stream entering the conditioner and
selectively permitting flow of the supply air stream from the first
enclosure to the second enclosure and the third enclosure during
operation of the liquid desiccant air-conditioning system in a
heating operation mode to prevent freezing of the heat transfer
fluid.
BRIEF DESCRIPTION OF THE FIGURES
[0005] FIG. 1 is a simplified diagram illustrating a prior art
liquid desiccant air-conditioning system.
[0006] FIG. 2 illustrates a prior art three-way heat exchanger
block of a liquid desiccant air conditioning system.
[0007] FIG. 3 is a simplified diagram illustrating a prior art
three-way heat exchanger panel assembly in the heat exchanger
block.
[0008] FIG. 4 is a simplified diagram illustrating another prior
art liquid desiccant air conditioning system.
[0009] FIG. 5 is a simplified diagram showing the layout of a
liquid desiccant air conditioning system with the conditioner,
regenerator, and chiller sections.
[0010] FIG. 6 is a simplified block diagram illustrating an
antifreeze-free liquid desiccant air-conditioning system in
accordance with one or more embodiments.
[0011] FIGS. 7-10 are simplified block diagrams illustrating
alternate layouts of liquid desiccant air-conditioning systems in
accordance with one or more embodiments.
DETAILED DESCRIPTION
[0012] FIG. 1 illustrates an exemplary prior art liquid desiccant
air conditioning system as disclosed in U.S. Patent Application
Publication No. 20120125020 and U.S. Pat. Nos. 9,243,810 and
9,631,848 used in a cooling and dehumidifying mode of operation. A
conditioner 101 comprises a set of three-way heat exchange plate
structures that are internally hollow. A cold heat transfer fluid
is generated in a cold source 107 and introduced into the plates. A
liquid desiccant solution at 114 is flowed onto the outer surface
of the plates. The liquid desiccant runs over the outer surface of
each of the plates behind a thin membrane, which is located between
the air flow and the surface of the plates. Return air, outside air
103, or mixture thereof is blown between the set of conditioner
plates. The liquid desiccant on the surface of the plates attracts
the water vapor in the air flow and the cooling water (heat
transfer fluid) inside the plates helps to inhibit the air
temperature from rising. The treated air 104 is introduced into a
building space.
[0013] The liquid desiccant is collected at the other end of the
conditioner plates at 111 and is transported through a heat
exchanger 113 to the liquid desiccant entry point 115 of the
regenerator 102 where the liquid desiccant is distributed across
similar plates in the regenerator. Return air, outside air 105, or
a mixture thereof is blown across the regenerator plates and water
vapor is transported from the liquid desiccant into the leaving air
stream 106. An optional heat source 108 provides the driving force
for the regeneration. A hot heat transfer fluid 110 from a heat
source can be flowed inside the plates of the regenerator similar
to the cold heat transfer fluid in the conditioner. Again, the
re-concentrated liquid desiccant is collected at one end of the
plates and returned via the heat exchanger to the conditioner.
Since there is no need for either a collection pan or bath, the
desiccant flow through the regenerator can be horizontal or
vertical. Air and water is preferably in counterflow to each other.
They can also be a horizontal or vertical flow. A variety of
configurations are possible from all flows being vertical, to a
combination of horizontal and vertical flows in crossflow, to all
flows being horizontal in flat plate structures.
[0014] An optional heat pump 116 can be used to provide cooling and
heating of the liquid desiccant. It is also possible to connect a
heat pump between the cold source 107 and the hot source 108, which
is thus pumping heat from the cooling fluids rather than the liquid
desiccant. Cold sources could comprise an indirect evaporative
cooler, a cooling tower, geothermal storage, cold water networks,
black roof panel that cools down water during the night, and cold
storage options like an ice box. Heat sources could include waste
heat from power generation, solar heat, geothermal heat, heat
storage, and hot water networks. Those skilled in the art will
understand that a wide variety of other sources for heating and
cooling are possible including, e.g., heat from refrigeration in
stores to heat from compressors in industrial applications.
[0015] FIG. 2 illustrates an exemplary prior art three-way heat
exchanger comprising a set of plate structures stacked in a block
as disclosed in U.S. Pat. No. 9,308,490. A liquid desiccant enters
the structure through ports 304 and is directed behind a series of
membranes as described in FIG. 1. The liquid desiccant is collected
and removed through ports 305. A cooling or heating fluid is
provided through ports 306 and runs counter to the air stream 301
inside the hollow plate structures, again as described in FIG. 1
and in greater detail in FIG. 3. The cooling or heating fluids exit
through ports 307. The treated air 302 is directed to a space in a
building or is exhausted as the case may be. The figure illustrates
a three-way heat exchanger in which the air and heat transfer fluid
are in a primarily vertical orientation, though other orientations
(e.g., a substantially horizontal orientation) are also
possible.
[0016] FIG. 3 schematically illustrates operation of an exemplary
prior art membrane plate assembly or structure as disclosed in U.S.
Pat. No. 9,631,848. The air stream 251 flows counter to a cooling
fluid stream 254. Membranes 252 contain a liquid desiccant 253 that
is falling along the wall 255 that contains the heat transfer fluid
254. Water vapor 256 entrained in the air stream is able to
transfer through the membrane 252 and is absorbed into the liquid
desiccant 253. The heat of condensation of water 258 that is
released during the absorption is conducted through the wall 255
into the heat transfer fluid 254. Sensible heat 257 from the air
stream is also conducted through the membrane 252, liquid desiccant
253 and wall 255 into the heat transfer fluid 254.
[0017] FIG. 4 illustrates a schematic representation of another
prior art liquid desiccant air conditioner system operating in a
cooling mode, as disclosed in U.S. patent Ser. No. 10/323,867.
Similar liquid air conditioning systems are disclosed in U.S.
Patent Application Publication No. 20120125020 and U.S. Pat. Nos.
9,243,810 and 9,631,848. A three-way heat and mass exchanger
conditioner 503 (which is similar to the conditioner 101 of FIG. 1)
receives an air stream 501 from the outside ("OA"). Fan 502 pulls
the air 501 through the conditioner 503 wherein the air is cooled
and dehumidified. The resulting cool, dry air 504 ("SA") is
supplied to a space for occupant comfort. The three-way conditioner
503 receives a concentrated desiccant 527 in the manner explained
under FIGS. 1-3. It is preferable to use a membrane on the
three-way conditioner 503 to contain the desiccant and inhibit it
from being distributed into the air stream 504. The diluted
desiccant 528, which contains the captured water vapor is
transported to a heat and mass exchanger regenerator 522.
Furthermore, chilled water 509 is provided by pump 508, which
enters the conditioner module 503 where it picks up heat from the
air as well as latent heat released by the capture of water vapor
in the desiccant 527. The warmer water 506 is brought to the heat
exchanger 507 on the chiller system 530. The liquid desiccant 528
leaves the conditioner 503 and is moved through the optional heat
exchanger 526 to the regenerator 522 by pump 525. The chiller
system 530 comprises a water to refrigerant evaporator heat
exchanger 507, which cools the circulating cooling fluid 506. The
liquid, cold refrigerant 517 evaporates in the heat exchanger 507
thereby absorbing the thermal energy from the cooling fluid 506.
The gaseous refrigerant 510 is now re-compressed by compressor 511.
The compressor 511 ejects hot refrigerant gas 513, which is
liquefied in the condenser heat exchanger 515. The liquid
refrigerant exiting the condenser 514 then enters expansion valve
516, where it rapidly cools and exits at a lower pressure. The
condenser heat exchanger 515 now releases heat to another cooling
fluid loop 519 which brings hot heat transfer fluid 518 to the
regenerator 522. Circulating pump 520 brings the heat transfer
fluid back to the condenser 515. The three-way regenerator 522 thus
receives a dilute liquid desiccant 528 and hot heat transfer fluid
518. A fan 524 brings outside air 521 ("OA") through the
regenerator 522. The outside air picks up heat and moisture from
the heat transfer fluid 518 and desiccant 528 which results in hot
humid exhaust air ("EA") 523. The compressor 511 receives
electrical power 512. The fans 502 and 524 receive electrical power
505 and 529, respectively. Pumps 508, 520, and 525 have relatively
low power consumption.
[0018] The liquid desiccant air conditioning systems disclosed
herein can operate in various modes including cooling, heating,
cooling and dehumidification, cooling and humidification, heating
and dehumidification, and heating and humidification modes.
[0019] Many chillers and other compressor-based cooling systems
have a separate heating subsystem using gas, steam, or other heat
sources. These heating systems are used when outside air
temperatures require the air to be heated, and also when latent and
sensible loads require additional heating, e.g., in a greenhouse
with many plants, a freezer section of a department store, and
similar spaces with low Sensible Heat Ratio (SHR) cooling loads.
Such heating systems are only used for reheat in ASHRAE Zone 1
(Tropical conditions). In ASHRAE Zone 2, they are used for both
reheat and limited heating in winter time. Heat loads are small and
may be provided by electric power. Design conditions only require a
low concentration of Glycol to fully protect the unit, typically
about 10%. For colder zones (ASHRAE Zones 3, 4, 5 USA), heating is
often done with oil or gas and can be the main energy load of the
unit. Lower minimum design temperatures require higher
concentrations of Glycol (30-50%), but these cannot be accommodated
without major changes in the sizing of heat exchangers and pumps.
The disclosed design configurations for protecting the unit without
the use of Glycol are especially important for the colder zones
(ASHRAE Zones 2+ USA).
[0020] Both the electric and the oil/gas heating systems can be
used for reheating the air directly or alternatively the heat
transfer fluid to the regenerator during low SHR cooling and
dehumidification in the summer. They can be either the main source
of heating in winter time or they can augment the chiller when it
is operating in a heatpump mode.
[0021] The heat transfer fluid in liquid desiccant air-conditioning
systems described above can be a refrigerant in some
configurations, and also water or antifreeze solutions such as a
water-based solution containing a Propylene or Polyethylene Glycol.
Use of Glycol is particularly important in heating applications
where the probability of below freezing temperatures affecting the
heat transfer fluid is high. Mini-split systems like those
described in U.S. Patent Application Publication No. 20140260399
and U.S. Pat. No. 9,470,426 are a special case. In these systems,
the conditioner is inside the building, but the regeneration unit
and chiller/compressor components are kept outside the building, so
that only these components require protection of the heat transfer
fluid from freezing.
[0022] Traditional chillers use Glycol for antifreeze even when the
compressor is not used in a heatpump mode. When the chiller
components are exposed to outside air, they risk freezing without
the Glycol. However, the use of Glycol and other antifreeze
additives reduces system performance or requires an increase in the
size of key components because of the lower heat capacity compared
to pure water.
[0023] Various embodiments disclosed herein relate to liquid
desiccant air-conditioning systems using antifreeze-free heat
transfer fluids, which comprise heat transfer fluids like water
with no antifreeze additive or only minimal amounts of antifreeze
additives, e.g., the heat transfer fluid is no more than 10%
antifreeze additive. These systems provide freeze protection
through system design rather than reliance on Glycol or other
antifreeze additives.
[0024] A large part of the United States, e.g., areas south of
Virginia, has a very limited number of freezing hours, but still a
significant number of heating hours at temperatures >32.degree.
F. Systems in accordance with various embodiments are configured to
include all water (i.e., heat transfer fluid) systems in fluid
communication with the conditioned space during a heating operation
mode. Since building owners do not allow conditioned space is to
freeze, this prevents freezing without using Glycol, while
maintaining high cooling and heating performance.
[0025] Increasing the size of the refrigerant-to-water heat
exchangers (liquid cooled evaporator (LCE) coils and liquid cooled
condenser (LCC) coils) and the air cooled water coils to handle
increased heat transfer flows can maintain heat transfer capacity
of the heat transfer fluid, but it involves significant additional
cost and weight increases. Changing the unit layout, on the other
hand, does not involve additional costs and can even reduce system
size by avoiding the need for an air cooled coil for advanced
dehumidification.
[0026] To maintain performance, Glycol based systems may require a
>50% higher water flow and similarly larger refrigerant-to-heat
transfer fluid heat exchangers (LCE/LCC coils) to maintain heat
transfer capacity. Without such configuration, Polyethylene Glycol
can reduce performance by 25-30% in terms of Integrated Energy
Efficiency Ratio (JEER) and Integrated Seasonal Moisture Removal
Efficiency (ISMRE). With such a configuration, performance will be
affected by higher pump power requirements especially at high
concentrations and low temperatures. For liquid desiccant air
conditioning systems designed for heating in a heat pump mode, this
would at least enable improved heating performance compared to gas
or steam. In the current system, the Glycol is only used as freeze
protection and reduces performance. Finding alternatives to protect
the system during freezing periods therefore becomes more
important.
[0027] Various embodiments disclosed herein relate to design
alternative approaches to freeze protection that seek to eliminate
or reduce the need for Glycol. The systems include a change in
design with optional additional components.
[0028] In many instances the LDAC system conditioner is already
positioned inside the conditioned space. This improves energy
efficiency. Freezing protection can be achieved by positioning all
water heat transfer fluid components inside or in fluid
communication with the conditioned space. In addition, the water
and air in the unit can be heated directly when the unit is closed
down and outside temperatures fall below zero degrees C.
[0029] As long as all water components are in spaces that can be
closed to the outside air and connected to the inside of the
building via a ducting system, above freezing conditions can be
maintained. The LDAC water system will need to be treated as part
of the building water system, meaning that in extreme emergencies,
where freezing temperatures inside the building cannot be avoided,
the water system may need to be drained. This can be accomplished
using a drainage point at the lowest point of the water system.
[0030] In accordance with one or more embodiments, winter heating
coils used for heating an air stream are positioned before rather
than after the conditioner (in the direction of the airflow).
Currently, the heater is generally positioned behind the cooling
coil. This allows the heater to be used for reheat as well as
winter heating. In accordance with one or more embodiments, during
the use of the unit as a heater, heated air could still mostly
bypass the liquid desiccant heat exchanger as long as the liquid
desiccant heat exchanger components are in the conditioned space.
With the heater on, both the regenerator and compressor sections
are closed to the outside but opened to the conditioned space
through a set of dampers. Keeping the regenerator in a conditioned
space during times the cooling system is not operating can be done
by allowing some of the supply air to be provided to the building
by the conditioner to heat up the regenerator and the heat
exchanger through a damper, while at the same time closing off
dampers and louvers used to provide air to the regenerator and any
heat dump coil used in cooling mode.
[0031] An alternative solution is to heat regenerator air with an
air or water heater that can, be gas, oil or waste heat based. In
summer cooling conditions, such a regenerator heater can be a
replacement for an AdvDH (advanced dehumidification) coil. By
circulating regenerator air in a closed circuit, air entering the
regenerator can be kept above freezing and the compressor can be
used in a heat pump mode. In this arrangement, the delta T across
the heat pump between conditioner and regenerator can be less than
20 C/40 F, which makes the heat pump significantly more effective
than when outside air is used. Managing humidity levels in the
building can involve water addition, which can take the form of
direct evaporative cooling, vaporization or a membrane water
addition as disclosed, e.g., in U.S. Patent Application Publication
No. 20150338140.
[0032] In a heat pump mode, the air or water heater can maintain
conditions above freezing to avoid the use of Glycol. Typically the
airflow*delta T*spec. heat air of the conditioner in BTU should be
less than the water flow*(T high-32 F)*spec. heat water for the
regenerator and the conditioner. The high water temperature
T(Whigh) can be between 40-50 C (100-120 F).
[0033] Alternatively, a water heater can be added to the
regenerator water circuit or by using a gas heater to preheat
regenerator air. During cool and humid periods, the water heater
can then be used as an alternative for the advanced
dehumidification coil by adding regeneration capacity using gas for
heating the water when the supply air is already sufficiently
cooled.
[0034] For systems in areas with significant deep freezing
conditions, passive protection is to be used for times that the
power system or the heating system is down. During power outages,
the whole unit can be treated as part of the building water system
by ensuring air from the building is used to warm up the unit and
by connecting the water system to protective systems for the
building water system. When these protective systems also fail,
e.g., during prolonged outages, the building water system may need
to be drained to avoid freezing of pipes. This will also involve
the unit being fully closed while it is not operational. This is
different from traditional DX systems where the condenser part of
the unit can be exposed to freezing conditions when the unit is not
used.
[0035] To avoid the use of Glycol, other alternatives are also
possible. For instance, a water heater can be added at the lowest
point in the regenerator water circuit to prevent freezing. This
heating unit can also be used for the advanced dehumidification
process. Another option is to add a space heater to the LDAC
housing to maintain temperatures above freezing in the unit.
[0036] In split systems, the conditioner and its water system can
be positioned inside the building through a refrigerant link. In
that case, the freeze protection alternatives disclosed herein
apply to the regenerator/condenser unit.
[0037] Since heating days always outnumber freezing days, efficient
heating capacity will be available in all buildings that have
freezing risks at least during some hours of the year.
[0038] FIG. 5 illustrates shows a liquid desiccant air conditioning
unit comprising a liquid desiccant conditioner 600 and a liquid
desiccant regenerator 602, which are connected through heat
transfer fluid lines 604 and 606 with heat transfer
fluid-to-refrigerant heat exchangers (LCE coil 608 and LCC coil
610, respectively) with a chiller 612.
[0039] The conditioner 600 is in an enclosure in space 622, the
regenerator 602 is in an enclosure in space 623, and the chiller
612 is in an enclosure in space 625, all in an insulated housing
621.
[0040] The air stream 614 supplied to the conditioner 600 can be
outside air or return air from the building or a mixture of the
two. Similarly, the air supply 616 to the regenerator 602 can be
outside air, air from the building or a mixture thereof. The
conditioner 600 supplies air 618 to the building space through a
duct or directly into the space, and is therefore in open fluid
communication with the building. In a cooling and dehumidification
mode of operation, the air stream 616 is heated and humidified by
the regenerator 602 and is exhausted at 620.
[0041] The liquid desiccant air conditioning unit can be run in
different modes, including: a cooling mode, a heating and
dehumidification mode, a cooling and humidification mode, a cooling
and dehumidification mode, a heating mode, and a heating and
dehumidification mode. The unit depicted in FIG. 5 can be a single
rooftop unit. It can also be a split unit, in which the conditioner
600 is inside the building and the regenerator 602 and chiller 612
can be on the roof or otherwise outside of the building or in a
technical space.
[0042] The chiller 612 can comprise a heatpump or a simple
compressor system.
[0043] The conditioner 600 is positioned in the cooled space 622 in
the unit when the unit is performing cooling. A heating coil 624 is
positioned after the conditioner 100.
[0044] The positioning of the heating coil 624 after the
conditioner 600 allows it to be used for reheat as well as for
winter heating. Traditionally with a heating coil after the
conditioner during the winter period, all parts of the unit before
the heating coil remain at outside air conditions. By switching the
position, the parts containing heat transfer fluid can be
protected.
[0045] FIG. 6 shows a Glycol-free liquid desiccant air conditioning
unit in accordance with one or more embodiments. The unit of FIG. 6
is similar to FIG. 5 in that in contains many of the same or
similar components indicated by the same reference numbers.
[0046] The FIG. 6 unit comprises a liquid desiccant conditioner 600
and regenerator 602, which are connected through cooling fluid
lines 604 and 606 with cooling fluid-to-refrigerant heat exchangers
(LCE coil 608 and LCC coil 610, respectively) with a chiller
612.
[0047] The heating coil 624 is moved from the position shown in
FIG. 5 to the air intake side of the unit such that the supply air
to the conditioner 600 is heated. The heated supply air can bypass
the conditioner 600 to reduce pressure drop as long as the
conditioner 600 remains in the heated space.
[0048] Unlike the FIG. 5 unit, in the FIG. 6 unit, the regenerator
space 623 is connected to the conditioner space 622 at duct 670.
The chiller space 625 is connected to the regenerator space 623 by
duct 674. The ducting prevents freezing of the heat transfer fluid
when the outside air temperature is low. In emergencies where the
heater breaks down, freezing of the heat transfer fluid is
prevented through the connection of the conditioned space through
the ducting to the inside of the building.
[0049] FIG. 7 shows how moving the heating coil and connecting the
conditioner and regenerator spaces can be used to prevent freezing
of system components. The hot water supply or a space heater can
directly heat the regenerator block and the piping space.
Alternatively, the regenerator can be connected to the conditioner
space, which is already connected to the building via ducts.
[0050] FIG. 8 shows how a single heating coil can be used for
heating/freeze protection in winter, while replacing the advanced
dehumidification coil in the cooling season. Bypasses can be used
to minimize pressure drop.
[0051] FIG. 9 shows a system in which the heating coil is
positioned in the outside air intake without the need for a damper
between the regenerator and the conditioner spaces. The capacity to
add heat directly to the regenerator can replace the advanced
dehumidification coil. Various configurations are possible that
allow a single coil or gas supply to serve both the regenerator and
the conditioner. Air can bypass the blocks so long as the blocks
are in the conditioned space.
[0052] If during an emergency, the building itself cools below
freezing then additional measures are needed. These can vary from
using a backup power supply 662 in combination with a space heater
640 or a water heater 660, which can be used to maintain
temperatures above freezing.
[0053] FIG. 10 shows how instead of heating the air, water flowing
through the regenerator and conditioner can be heated directly to
prevent freezing of the water and allow outside air to be heated in
winter time and in the advanced dehumidification mode. Sources of
heat can include, e.g., condensers, and solar, gas, and waste heat
sources.
[0054] A further protection measure during extreme emergencies
where all power and backup fails is to drain the system from the
low point in the water/heat transfer fluid circuit. Since the unit
is connected to the building this can be done at the same time that
water pipes in the building are drained to prevent pipes from
bursting.
[0055] Use of Glycol might not be avoided in the regenerator when
the unit is used in heatpump mode, where the regenerator is cooled
and the conditioner is heated. In that case, the additional sizing
of the system can be justified by the improved heating
performance.
[0056] The capacity to add heat directly to the regenerator can
avoid the need for an advanced dehumidification (AdvDH) coil.
Various configurations are possible that allow a single coil or gas
supply to serve both the regenerator and the conditioner. Air can
bypass the units as long as the units are in the conditioned
space.
[0057] In one or more alternate embodiments, gas is used to heat
water through the regenerator/conditioner rather than heating the
air itself. This is similar to indirect heating of the air with
gas. With direct gas heating there is an additional humidification
benefit during the dry winter conditions.
[0058] Having thus described several illustrative embodiments, it
is to be appreciated that various alterations, modifications, and
improvements will readily occur to those skilled in the art. Such
alterations, modifications, and improvements are intended to form a
part of this disclosure, and are intended to be within the spirit
and scope of this disclosure. While some examples presented herein
involve specific combinations of functions or structural elements,
it should be understood that those functions and elements may be
combined in other ways according to the present disclosure to
accomplish the same or different objectives. In particular, acts,
elements, and features discussed in connection with one embodiment
are not intended to be excluded from similar or other roles in
other embodiments. Additionally, elements and components described
herein may be further divided into additional components or joined
together to form fewer components for performing the same
functions. Accordingly, the foregoing description and attached
drawings are by way of example only and are not intended to be
limiting.
* * * * *