U.S. patent application number 16/399165 was filed with the patent office on 2020-03-26 for rooftop liquid desiccant systems and methods.
The applicant listed for this patent is 7AC Technologies, Inc. Invention is credited to Peter F. Vandermeulen.
Application Number | 20200096241 16/399165 |
Document ID | / |
Family ID | 54145483 |
Filed Date | 2020-03-26 |
View All Diagrams
United States Patent
Application |
20200096241 |
Kind Code |
A1 |
Vandermeulen; Peter F. |
March 26, 2020 |
ROOFTOP LIQUID DESICCANT SYSTEMS AND METHODS
Abstract
Liquid desiccant air-conditioning systems cool and dehumidify a
space in a building when operating in a cooling operation mode, and
heat and humidify the space when operating in a heating operation
mode.
Inventors: |
Vandermeulen; Peter F.;
(Newburyport, MA) |
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Applicant: |
Name |
City |
State |
Country |
Type |
7AC Technologies, Inc |
Beverly |
CA |
US |
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|
Family ID: |
54145483 |
Appl. No.: |
16/399165 |
Filed: |
April 30, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14664219 |
Mar 20, 2015 |
10323867 |
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16399165 |
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61978539 |
Apr 11, 2014 |
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61968333 |
Mar 20, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 3/147 20130101;
F25B 29/006 20130101; F24F 11/65 20180101; F25B 30/04 20130101;
F25B 25/005 20130101; F24F 2221/54 20130101; F24F 3/1417 20130101;
F24F 2003/1435 20130101; F24F 2003/1452 20130101; F24F 2003/1458
20130101 |
International
Class: |
F25B 30/04 20060101
F25B030/04; F24F 3/14 20060101 F24F003/14; F24F 3/147 20060101
F24F003/147 |
Claims
1-95. (canceled)
96. An air-conditioning system operable in a cooling operation mode
or in a heating operation mode, or selectably operable in either of
said modes, said air conditioning system cooling and dehumidifying
a space in a building when operating in the cooling operation mode,
and heating and humidifying the space when operating in the heating
operation mode, the system comprising: a first coil acting as a
refrigerant evaporator for evaporating a refrigerant flowing
therethrough and cooling a first air stream to be provided to the
space in the building in the cooling operation mode, or for acting
as a refrigerant condenser for condensing a refrigerant flowing
therethrough and heating the first air stream to be provided to the
space in the building in the heating operation mode, said first air
stream comprising a return air stream from the space combined with
a treated outside air stream; a refrigerant compressor in fluid
communication with the first coil for receiving refrigerant from
the first coil and compressing the refrigerant in the cooling
operation mode, or for compressing a refrigerant to be provided to
the first coil in the heating operation mode; a second coil in
fluid communication with the refrigerant compressor and acting as a
refrigerant condenser for condensing refrigerant received from the
refrigerant compressor and heating an outside air stream to be
exhausted in the cooling operation mode, or for acting as a
refrigerant evaporator for evaporating a refrigerant to be provided
to the refrigerant compressor and cooling an outside air stream to
be exhausted in the heating operation mode; an expansion valve in
fluid communication with the first coil and with the second coil
for expanding and cooling refrigerant received from the second coil
to be provided to the first coil in the cooling operation mode, or
for expanding and cooling refrigerant received from the first coil
to be provided to the second coil in the heating operation mode; a
liquid desiccant conditioner including a plurality of structures,
each of the structures having at least one surface across which a
liquid desiccant can flow and an internal passage in fluid
communication with the first coil and the refrigerant compressor
such that refrigerant flowing between the first coil and the
refrigerant compressor flows through said internal passage, wherein
the liquid desiccant conditioner cools and dehumidifies an outside
air stream flowing between the structures in the cooling operation
mode, or heats and humidifies an outside air stream flowing between
the structures in the heating operation mode, said outside air
stream so treated by the liquid desiccant conditioner to be
combined with the return air stream from the space in the building
to form the first air stream to be cooled or heated by the first
coil; and a liquid desiccant regenerator in fluid communication
with the liquid desiccant conditioner for receiving the liquid
desiccant used in the liquid desiccant conditioner, concentrating
the liquid desiccant in the cooling operation mode or diluting the
liquid desiccant in the heating operation mode, and then returning
the liquid desiccant to the conditioner, said liquid desiccant
regenerator including a plurality of structures, each of the
structures having at least one surface across which the liquid
desiccant can flow and an internal passage in fluid communication
with the second coil and the refrigerant compressor such that
refrigerant flowing between the second coil and the refrigerant
compressor flows through said internal passage, wherein the liquid
desiccant humidifies and heats the air stream to be exhausted in
the cooling operation mode or dehumidifies and cools the outside
air stream to be exhausted in the heating operation mode.
97. The air conditioning system of claim 96, wherein the plurality
of structures in the liquid desiccant conditioner and the plurality
of structures in the liquid desiccant regenerator are arranged in a
substantially vertical orientation.
98. The air conditioning system of claim 96, wherein the plurality
of structures in the liquid desiccant conditioner and the plurality
of structures in the liquid desiccant regenerator are generally
flat and parallel to each other.
99. The air conditioning system of claim 96, wherein the plurality
of structures in the liquid desiccant conditioner and the plurality
of structures in the liquid desiccant regenerator are tubular and
arranged concentrically.
100. The air conditioning system of claim 96, wherein each of the
structures in the liquid desiccant conditioner and each of the
structures in the liquid desiccant regenerator further includes a
separate desiccant collector at a lower end of the at least one
surface for collecting liquid desiccant that has flowed across the
at least one surface of the structures, said desiccant collectors
being spaced apart from each other to permit airflow
therebetween.
101. The air-conditioning system of claim 96, wherein the air
stream flowing between the structures in the liquid desiccant
regenerator comprises an outside air stream, a portion of the
return air stream from the space in the building, or a mixture of
both.
102. The air conditioning system of claim 96, wherein each of said
structures in the liquid desiccant conditioner and the liquid
desiccant regenerator includes a sheet of material positioned
proximate to the at least one surface of each structure between the
liquid desiccant and the air stream, said sheet of material guiding
the liquid desiccant into a desiccant collector and permitting
transfer of water vapor between the liquid desiccant to the air
stream.
103. The air conditioning system of claim 102, wherein the sheet of
material comprises a membrane.
104. The air conditioning system of claim 102, wherein the sheet of
material comprises a hydrophilic material.
105. The air conditioning system of claim 102, wherein the sheet of
material comprises a flocking material.
106. The air conditioning system of claim 102, wherein each
structure includes two opposite surfaces across which the liquid
desiccant can flow, and wherein a sheet of material covers or
retains the liquid desiccant on each opposite surface.
107. The air conditioning system of claim 96, further comprising a
water injection system for adding water to the liquid desiccant
used in the liquid desiccant conditioner.
108. The air conditioning system of claim 107, wherein the water
injection system comprises: an enclosure having one or more
selectively permeable microporous hydrophobic structures defining
alternate channels on opposite sides of each structure for flow of
the water or the liquid containing primarily water in one channel
and for flow of the liquid desiccant separately in an adjacent
channel, wherein each structure enables selective diffusion through
the structure of water molecules from the water or the liquid
containing primarily water to the liquid desiccant; a water inlet
port and a water outlet port in the enclosure in fluid
communication with each channel through which the water or liquid
containing primarily water flows; and a liquid desiccant inlet port
and a liquid desiccant output port in the enclosure in fluid
communication with each channel through which the liquid desiccant
flows, wherein the liquid desiccant inlet port receives liquid
desiccant from the liquid desiccant regenerator, and the liquid
desiccant outlet port provides liquid desiccant to the liquid
desiccant conditioner, or wherein the liquid desiccant inlet port
receives liquid desiccant from the liquid desiccant conditioner,
and the liquid desiccant outlet port provides liquid desiccant to
the liquid desiccant regenerator.
109. The air conditioning system of claim 107, wherein the flow or
refrigerant through the first coil, the refrigerant compressor, the
second coil, and the expansion valve is reversed in order to change
between the cooling operation mode and the heating operation
mode.
110. A method of cooling and dehumidifying a space in a building
using a liquid desiccant air conditioning system operating in a
cooling operation mode, the method comprising: (a) circulating
refrigerant in a refrigerant circuit including a first coil acting
as a refrigerant evaporator for evaporating the refrigerant flowing
therethrough, a refrigerant compressor in fluid communication with
the first coil for receiving refrigerant from the first coil and
compressing the refrigerant, a second coil in fluid communication
with the refrigerant compressor and acting as a refrigerant
condenser for condensing refrigerant received from the refrigerant
compressor and heating an outside air stream to be exhausted, and
an expansion valve in fluid communication with the first coil and
with the second coil for expanding and cooling refrigerant received
from the second coil to be provided to the first coil; (b) cooling
and dehumidifying an outside air stream in a liquid desiccant
conditioner, wherein the outside air stream is dehumidified using a
liquid desiccant, and wherein the refrigerant flowing between the
first coil and the refrigerant compressor flows through the liquid
desiccant conditioner to cool the outside air stream; (c) combining
the air stream treated by the conditioner in (b) with a return air
stream from the space; (d) cooling the combined air stream in (c)
using the first coil, and providing the air stream cooled by the
first coil to the space in the building; and (e) concentrating the
liquid desiccant used in the liquid desiccant conditioner in a
liquid desiccant regenerator, and returning the concentrated liquid
desiccant to the liquid desiccant conditioner, wherein refrigerant
flowing between the refrigerant compressor and the second coil
flows through said liquid desiccant regenerator.
111. The method of claim 110, further comprising switching
operation of the liquid desiccant air conditioning system to a
heating operation mode to heat and humidify the space by reversing
flow of the refrigerant in the refrigerant circuit.
112. The method of claim 110, wherein in the heating operation
mode: a first coil acts as a refrigerant condenser for condensing a
refrigerant flowing therethrough and heating the first air stream
to be provided to the space in the building; a refrigerant
compressor compresses the refrigerant to be provided to the first
coil; a second coil acts as a refrigerant evaporator for
evaporating a refrigerant to be provided to the refrigerant
compressor and cooling an outside air stream to be exhausted; the
expansion valve expands and cools refrigerant received from the
first coil to be provided to the second coil; a liquid desiccant
conditioner heats and humidifies the outside air stream to be
combined with the return air stream to be heated by the first coil;
and a liquid desiccant regenerator dilutes the liquid desiccant
used in the liquid desiccant conditioner and then returns the
liquid desiccant to the conditioner.
113. The method of claim 110, further comprising adding water to
the liquid desiccant used in the liquid desiccant conditioner.
114. A method of heating and humidifying a space in a building
using a liquid desiccant air conditioning system operating in a
heating operation mode, the method comprising: (a) circulating
refrigerant in a refrigerant circuit including a first coil acting
as a refrigerant condenser for condensing the refrigerant flowing
therethrough, a refrigerant compressor compressing the refrigerant
provided to the first coil, a second coil acting as a refrigerant
evaporator for evaporating refrigerant to be provided to the
refrigerant compressor and cooling an outside air stream to be
exhausted, and an expansion valve in fluid communication with the
first coil and with the second coil for expanding and cooling
refrigerant received from the first coil to be provided to the
second coil; (b) heating and humidifying an outside air stream in a
liquid desiccant conditioner, wherein the outside air stream is
humidified using a liquid desiccant, and wherein the refrigerant
flowing between the refrigerant compressor and the first coil flows
through the liquid desiccant conditioner to heat the outside air
stream; (c) combining the air stream treated by the conditioner in
(b) with a return air stream from the space; (d) heating the
combined air stream in (c) using the first coil, and providing the
air stream heated by the first coil to the space in the building;
and (e) diluting the liquid desiccant used in the liquid desiccant
conditioner in a liquid desiccant regenerator, and returning the
diluted liquid desiccant to the liquid desiccant conditioner,
wherein refrigerant flowing between the refrigerant compressor and
the second coil flows through said liquid desiccant
regenerator.
115. The method of claim 114, further comprising switching
operation of the liquid desiccant air conditioning system to a
cooling operation mode to cool and dehumidify the space by
reversing flow of the refrigerant in the refrigerant circuit.
116. The method of claim 114, further comprising adding water to
the liquid desiccant used in the liquid desiccant conditioner.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/664219, filed on Mar. 20, 2015 entitled ROOFTOP LIQUID
DESICCANT SYSTEMS AND METHODS, which claims priority from U.S.
Provisional Patent Application No. 61/968,333 filed on Mar. 20,
2014 entitled METHODS AND SYSTEMS FOR LIQUID DESICCANT ROOFTOP
UNIT, and from U.S. Provisional Patent Application No. 61/978,539
filed on Apr. 11, 2014 entitled METHODS AND SYSTEMS FOR LIQUID
DESICCANT ROOFTOP UNIT, all of which are hereby incorporated by
reference.
BACKGROUND
[0002] The present application relates generally to the use of
liquid desiccant membrane modules to dehumidify and cool an outside
air stream entering a space. More specifically, the application
relates to the use of micro-porous membranes to keep separate a
liquid desiccant that is treating an outside air stream from direct
contact with that air stream while in parallel using a conventional
vapor compression system to treat a return air stream. The membrane
allows for the use of turbulent air streams wherein the fluid
streams (air, optional cooling fluids, and liquid desiccants) are
made to flow so that high heat and moisture transfer rates between
the fluids can occur. The application further relates to combining
cost reduced conventional vapor compression technology with a more
costly membrane liquid desiccant and thereby creating a new system
at approximately equal cost but with much lower energy
consumption.
[0003] Liquid desiccants have been used in parallel with
conventional vapor compression HVAC (heating, ventilation, and air
conditioning) equipment to help reduce humidity in spaces,
particularly in spaces that either require large amounts of outdoor
air or that have large humidity loads inside the building space
itself. Humid climates, such as for example Miami, Fla. require a
large amount of energy to properly treat (dehumidify and cool) the
fresh air that is required for a space's occupant comfort.
Conventional vapor compression systems have only a limited ability
to dehumidify and tend to overcool the air, oftentimes requiring
energy intensive reheat systems, which significantly increase the
overall energy costs because reheat adds an additional heat-load to
the cooling coil. Liquid desiccant systems have been used for many
years and are generally quite efficient at removing moisture from
the air stream. However, liquid desiccant systems generally use
concentrated salt solutions such as solutions of LiCl, LiBr or
CaCl2 and water. Such brines are strongly corrosive, even in small
quantities so numerous attempt have been made over the years to
prevent desiccant carry-over to the air stream that is to be
treated. One approach--generally categorized as closed desiccant
systems--is commonly used in equipment dubbed absorption chillers,
places the brine in a vacuum vessel which then contains the
desiccant and since the air is not directly exposed to the
desiccant; such systems do not have any risk of carry-over of
desiccant particles to the supply air stream. Absorption chillers
however tend to be expensive both in terms of first cost and
maintenance costs. Open desiccant systems allow a direct contact
between the air stream and the desiccant, generally by flowing the
desiccant over a packed bed similar to those used in cooling towers
and evaporators. Such packed bed systems suffer from other
disadvantages besides still having a carry-over risk: the high
resistance of the packed bed to the air stream results in larger
fan power and pressure drops across the packed bed, thus requiring
more energy. Furthermore, the dehumidification process is
adiabatic, since the heat of condensation that is released during
the absorption of water vapor into the desiccant has no place to
go. As a result both the desiccant and the air stream are heated by
the release of the heat of condensation. This results in a warm,
dry air stream where a cool dry air stream was desired,
necessitating the need for a post-dehumidification cooling coil.
Warmer desiccant is also exponentially less effective at absorbing
water vapor, which forces the system to supply much larger
quantities of desiccant to the packed bed which in turn requires
larger desiccant pump power, since the desiccant is doing double
duty as a desiccant as well as a heat transfer fluid. But the
larger desiccant flooding rate also results in an increased risk of
desiccant carryover. Generally air flow rates need to be kept well
below the turbulent region (at Reynolds numbers of less than
.about.2,400) to prevent carryover. Applying a micro-porous
membrane to the surface of these open liquid desiccant systems has
several advantages. First it prevents any desiccant from escaping
(carrying-over) to the air stream and becoming a source of
corrosion in the building. And second, the membrane allows for the
use of turbulent air flows enhancing heat and moisture transfer,
which in turn results in a smaller system since it can be build
more compactly. The micro-porous membrane retains the desiccant
typically by being hydrophobic to the desiccant solution and
breakthrough of desiccant can occur but only at pressures
significantly higher than the operating pressure. The water vapor
in an air stream that is flowing over the membrane diffuses through
the membrane into the underlying desiccant resulting in a drier air
stream. If the desiccant is at the same time cooler than the air
stream, a cooling function will occur as well, resulting in a
simultaneous cooling and dehumidification effect.
[0004] U.S. Patent Application Publication No. 2012/0132513, and
PCT Application No. PCT/US11/037936 by Vandermeulen et al. disclose
several embodiments for plate structures for membrane
dehumidification of air streams. U.S. Patent Application
Publication Nos. 2014-0150662, 2014-0150657, 2014-0150656, and
2014-0150657, PCT Application No. PCT/US13/045161, and U.S. Patent
Application Nos. 61/658,205, 61/729,139, 61/731,227, 61/736,213,
61/758,035, 61/789,357, 61/906,219, and 61/951,887 by Vandermeulen
et. al. disclose several manufacturing methods and details for
manufacturing membrane desiccant plates. Each of these patent
applications is hereby incorporated by reference herein in its
entirety.
[0005] Conventional Roof Top Units (RTUs), which are a common means
of providing cooling, heating, and ventilation to a space are
inexpensive systems that are manufactured in high volumes. However,
these RTUs are only able to handle small quantities of outside air,
since they are generally not very good at dehumidifying the air
stream and their efficiency drops significantly at higher outside
air percentages. Generally RTUs provide between 5 and 20% outside
air, and specialty units such as Make Up Air (MAUs) or Dedicated
Outside Air Systems (DOAS) exist that specialize in providing 100%
outside air and they can do so much more efficiently. However, the
cost of a MAU or DOAS is often well over $2,000 per ton of cooling
capacity compared to less than $1,000 per ton of a RTU. In many
applications RTUs are the only equipment utilized simply because of
their lower initial cost since the owner of the building and the
entity paying for the electricity are often different. But the use
of RTUs often results in poor energy performance, high humidity and
buildings that feel much too cold. Upgrading a building with LED
lighting for example can possibly lead to humidity problems and the
cold feeling is increased because the internal heat load from
incandescent lighting which helps heat a building, largely
disappears when LEDs are installed.
[0006] Furthermore, RTUs generally do not humidify in winter
operation mode. In winter the large amount of heating that is
applied to the air stream results in very dry building conditions
which can also be uncomfortable. In some buildings humidifiers are
installed in ductwork or integrated to the RTU to provide humidity
to the space. However, the evaporation of water in the air
significantly cools that air requiring additional heat to be
applied and thus increases energy costs.
[0007] There thus remains a need for a system that provides cost
efficient, manufacturable and thermally efficient methods and
systems to capture moisture from an air stream, while
simultaneously cooling such an air stream in a summer operating
mode, while also heating and humidifying an air stream in a winter
operating mode and while also reducing the risk of contaminating
such an air stream with desiccant particles.
SUMMARY
[0008] Provided herein are methods and systems used for the
efficient dehumidification of an air stream using liquid
desiccants. In accordance with one or more embodiments the liquid
desiccant runs down the face of a support plate as a falling film
in a conditioner for treating an air stream. In accordance with one
or more embodiments, the liquid desiccant is covered by a
microporous membrane so that liquid desiccant is unable to enter
the air stream, but water vapor in the air stream is able to be
absorbed into the liquid desiccant. In accordance with one or more
embodiments the liquid desiccant is directed over a plate structure
containing a heat transfer fluid. In accordance with one or more
embodiments the heat transfer fluid is thermally coupled to a
liquid to refrigerant heat exchanger and is pumped by a liquid
pump. In accordance with one or more embodiments the refrigerant in
the heat exchanger is cold and picks up heat through the heat
exchanger. In accordance with one or more embodiments the warmer
refrigerant leaving the heat exchanger is directed to a refrigerant
compressor. In accordance with one or more embodiments the
compressor compresses the refrigerant and the exiting hot
refrigerant is directed to another heat transfer fluid in a
refrigerant heat exchanger. In accordance with one or more
embodiments the heat exchanger heats the hot heat transfer fluid.
In accordance with one or more embodiments the hot heat transfer
fluid is directed to a liquid desiccant regenerator through a
liquid pump. In accordance with one or more embodiments a liquid
desiccant in a regenerator is directed over a plate structure
containing the hot heat transfer fluid. In accordance with one or
more embodiments the liquid desiccant in the regenerator runs down
the face of a support plate as a falling film. In accordance with
one or more embodiments, the liquid desiccant in the regenerator is
also covered by a microporous membrane so that liquid desiccant is
unable to enter the air stream, but water vapor in the air stream
is able to be desorbed from the liquid desiccant. In accordance
with one or more embodiments the liquid desiccant is transported
from the conditioner to the regenerator and from the regenerator
back to the conditioner. In one or more embodiments, the liquid
desiccant is pumped by a pump. In one or more embodiments, the
liquid desiccant is pumped through a heat exchanger between the
conditioner and the regenerator. In accordance with one or more
embodiments the air exiting the conditioner is directed to a second
air stream. In accordance with one or more embodiments the second
air stream is a return air stream from a space. In accordance with
one or more embodiments a portion of said return air stream is
exhausted from the system and the remaining air stream is mixed
with the air stream from the conditioner. In one or more
embodiments, the exhausted portion is between 5 and 25% of the
return air stream. In one or more embodiments, the exhausted
portion is directed to the regenerator. In one or more embodiments,
the exhausted portion is mixed with an outside air stream before
being directed to the regenerator. In accordance with one or more
embodiments the mixed air stream between the return air and the
conditioner air is directed through a cooling or evaporator coil.
In one or more embodiments, the cooling coil receives cold
refrigerant from a refrigeration circuit. In one or more
embodiments, the cooled air is directed back to the space to be
cooled. In accordance with one or more embodiments the cooling coil
receives cold refrigerant from an expansion valve or similar
device. In one or more embodiments, the expansion valve receives
liquid refrigerant from a condenser coil. In one or more
embodiments, the condenser coil receives hot refrigerant gas from a
compressor system. In one or more embodiments, the condenser coil
is cooled by an outside air stream. In one or more embodiments, the
hot refrigerant gas from the compressor is first directed to the
refrigerant to liquid heat exchanger from the regenerator. In one
or more embodiments, multiple compressors are used. In one or more
embodiments, separate compressors serve the liquid to refrigerant
heat exchangers from the compressors serving the evaporator and
condenser coils. In one or more embodiments, the compressors are
variable speed compressors. In one or more embodiments, the air
streams are moved by a fan or blower. In one or more embodiments,
such fans are variable speed fans.
[0009] Provided herein are methods and systems used for the
efficient humidification of an air stream using liquid desiccants.
In accordance with one or more embodiments a liquid desiccant runs
down the face of a support plate as a falling film in a conditioner
for treating an air stream. In accordance with one or more
embodiments, the liquid desiccant is covered by a microporous
membrane so that liquid desiccant is unable to enter the air
stream, but water vapor in the air stream is able to be absorbed
into the liquid desiccant. In accordance with one or more
embodiments the liquid desiccant is directed over a plate structure
containing a heat transfer fluid. In accordance with one or more
embodiments the heat transfer fluid is thermally coupled to a
liquid to refrigerant heat exchanger and is pumped by a liquid
pump. In accordance with one or more embodiments the refrigerant in
the heat exchanger is hot and rejects heat to the conditioner and
hence to the air stream passing through said conditioner. In
accordance with one or more embodiments the air exiting the
conditioner is directed to a second air stream. In accordance with
one or more embodiments the second air stream is a return air
stream from a space. In accordance with one or more embodiments a
portion of said return air stream is exhausted from the system and
the remaining air stream is mixed with the air stream from the
conditioner. In one or more embodiments, the exhausted portion is
between 5 and 25% of the return air stream. In one or more
embodiments, the exhausted portion is directed to the regenerator.
In one or more embodiments, the exhausted portion is mixed with an
outside air stream before being directed to the regenerator. In
accordance with one or more embodiments the mixed air stream
between the return air and the conditioner air is directed through
a condenser coil. In one or more embodiments, the condenser coil
receives hot refrigerant from a refrigeration circuit. In one or
more embodiments, the condenser coil warms the mixed air stream
coming from the conditioner and the remaining return air from the
space. In one or more embodiments, the warmer air is directed back
to the space to be cooled. In accordance with one or more
embodiments the condenser coil receives hot refrigerant from the
liquid to refrigerant heat exchanger. In one or more embodiments,
the condenser coil receives hot refrigerant gas from a compressor
system directly. In one or more embodiments, the colder, liquid
refrigerant leaving the condenser coil is directed to an expansion
valve or similar device. In one or more embodiments, the
refrigerant expands in the expansion valve and is directed to an
evaporator coil. In one or more embodiments, the evaporator coil
also receives an outside air stream from which it pulls heat to
heat the cold refrigerant from the expansion valve. In one or more
embodiments, the warmer refrigerant from the evaporator coil is
directed to a liquid to refrigerant heat exchanger. In one or more
embodiments, the liquid to refrigerant heat exchanger receives the
refrigerant from the evaporator and absorbs additional heat from a
heat transfer fluid loop. In one or more embodiments, the heat
transfer fluid loop is thermally coupled to a regenerator. In one
or more embodiments, the regenerator collects heat and moisture
from an air stream. In accordance with one or more embodiments the
liquid desiccant in the regenerator is directed over a plate
structure containing the cold heat transfer fluid. In accordance
with one or more embodiments the liquid desiccant in the
regenerator runs down the face of a support plate as a falling
film. In accordance with one or more embodiments, the liquid
desiccant in the regenerator is also covered by a microporous
membrane so that liquid desiccant is unable to enter the air
stream, but water vapor in the air stream is able to be desorbed
from the liquid desiccant. In one or more embodiments, the air
stream is an air stream rejected from the return air stream. In one
or more embodiments, the air stream is an outside air stream. In
one or more embodiments, the air stream is a mixture of the
rejected air stream and an outside air stream. In one or more
embodiments, the refrigerant leaving the liquid to refrigerant heat
exchanger is directed to a refrigerant compressor. In one or more
embodiments, the compressor compresses the refrigerant which is
then directed to a conditioner heat exchanger. In accordance with
one or more embodiments the heat exchanger heats the hot heat
transfer fluid. In accordance with one or more embodiments the hot
heat transfer fluid is directed to the liquid desiccant conditioner
through a liquid pump. In accordance with one or more embodiments
the liquid desiccant is transported from the conditioner to the
regenerator and from the regenerator back to the conditioner. In
one or more embodiments, the liquid desiccant is pumped by a pump.
In one or more embodiments, the liquid desiccant is pumped through
a heat exchanger between the conditioner and the regenerator. In
one or more embodiments, separate compressors serve the liquid to
refrigerant heat exchangers from the compressors serving the
evaporator and condenser coils. In one or more embodiments, the
compressors are variable speed compressors. In one or more
embodiments, the air streams are moved by a fan or blower. In one
or more embodiments, such fans are variable speed fans. In one or
more embodiments, multiple compressors are used. In accordance with
one or more embodiments the cooler refrigerant leaving the heat
exchanger is directed to a condenser coil. In accordance with one
or more embodiments the condenser coil is receiving an air stream
and the still hot refrigerant is used to heat such an air stream.
In one or more embodiments, water is added to the desiccant during
operation. In one or more embodiments, water is added during winter
heating mode. In one or more embodiments, water is added to control
the concentration of the desiccant. In one or more embodiments,
water is added during dry hot weather.
[0010] Provided herein are methods and systems used for the
efficient dehumidification of an air stream using liquid
desiccants. In accordance with one or more embodiments the liquid
desiccant runs down the face of a support plate as a falling film
in a conditioner for treating an air stream. In accordance with one
or more embodiments, the liquid desiccant is covered by a
microporous membrane so that liquid desiccant is unable to enter
the air stream, but water vapor in the air stream is able to be
absorbed into the liquid desiccant. In accordance with one or more
embodiments the liquid desiccant is thermally coupled to a
desiccant to refrigerant heat exchanger and is pumped by a liquid
pump. In accordance with one or more embodiments the refrigerant in
the heat exchanger is cold and picks up heat through the heat
exchanger. In accordance with one or more embodiments the warmer
refrigerant leaving the heat exchanger is directed to a refrigerant
compressor. In accordance with one or more embodiments the
compressor compresses the refrigerant and the exiting hot
refrigerant is directed to another refrigerant to desiccant heat
exchanger. In accordance with one or more embodiments the heat
exchanger heats a hot desiccant. In accordance with one or more
embodiments the hot desiccant is directed to a liquid desiccant
regenerator through a liquid pump. In accordance with one or more
embodiments a liquid desiccant in a regenerator is directed over a
plate structure. In accordance with one or more embodiments the
liquid desiccant in the regenerator runs down the face of a support
plate as a falling film. In accordance with one or more
embodiments, the liquid desiccant in the regenerator is also
covered by a microporous membrane so that liquid desiccant is
unable to enter the air stream, but water vapor in the air stream
is able to be desorbed from the liquid desiccant. In accordance
with one or more embodiments the liquid desiccant is transported
from the conditioner to the regenerator and from the regenerator
back to the conditioner. In one or more embodiments, the liquid
desiccant is pumped by a pump. In one or more embodiments, the
liquid desiccant is pumped through a heat exchanger between the
conditioner and the regenerator. In accordance with one or more
embodiments the air exiting the conditioner is directed to a second
air stream. In accordance with one or more embodiments the second
air stream is a return air stream from a space. In accordance with
one or more embodiments a portion of said return air stream is
exhausted from the system and the remaining air stream is mixed
with the air stream from the conditioner. In one or more
embodiments, the exhausted portion is between 5 and 25% of the
return air stream. In one or more embodiments, the exhausted
portion is directed to the regenerator. In one or more embodiments,
the exhausted portion is mixed with an outside air stream before
being directed to the regenerator. In accordance with one or more
embodiments the mixed air stream between the return air and the
conditioner air is directed through a cooling or evaporator coil.
In one or more embodiments, the cooling coil receives cold
refrigerant from a refrigeration circuit. In one or more
embodiments, the cooled air is directed back to the space to be
cooled. In accordance with one or more embodiments the cooling coil
receives cold refrigerant from an expansion valve or similar
device. In one or more embodiments, the expansion valve receives
liquid refrigerant from a condenser coil. In one or more
embodiments, the condenser coil receives hot refrigerant gas from a
compressor system. In one or more embodiments, the condenser coil
is cooled by an outside air stream. In one or more embodiments, the
hot refrigerant gas from the compressor is first directed to the
refrigerant to desiccant heat exchanger from the regenerator. In
one or more embodiments, multiple compressors are used. In one or
more embodiments, separate compressors serve the desiccant to
refrigerant heat exchangers from the compressors serving the
evaporator and condenser coils. In one or more embodiments, the
compressors are variable speed compressors. In one or more
embodiments, the air streams are moved by a fan or blower. In one
or more embodiments, such fans are variable speed fans. In one or
more embodiments, the flow direction of the refrigerant is reversed
for a winter heating mode. In one or more embodiments, water is
added to the desiccant during operation. In one or more
embodiments, water is added during winter heating mode. In one or
more embodiments, water is added to control the concentration of
the desiccant. In one or more embodiments, water is added during
dry hot weather.
[0011] Provided herein are methods and systems used for the
efficient dehumidification of an air stream using liquid
desiccants. In accordance with one or more embodiments the liquid
desiccant runs down the face of a support plate as a falling film
in a conditioner for treating an air stream. In accordance with one
or more embodiments, the liquid desiccant is covered by a
microporous membrane so that liquid desiccant is unable to enter
the air stream, but water vapor in the air stream is able to be
absorbed into the liquid desiccant. In accordance with one or more
embodiments the liquid desiccant is thermally coupled to a
refrigerant heat exchanger embedded in the conditioner. In
accordance with one or more embodiments the refrigerant in the
conditioner is cold and picks up heat from the desiccant and hence
from the air stream flowing through the conditioner. In accordance
with one or more embodiments the warmer refrigerant leaving the
conditioner is directed to a refrigerant compressor. In accordance
with one or more embodiments the compressor compresses the
refrigerant and the exiting hot refrigerant is directed to a
regenerator. In accordance with one or more embodiments the hot
refrigerant is embedded into a structure in the regenerator. In
accordance with one or more embodiments a liquid desiccant in the
regenerator is directed over a plate structure. In accordance with
one or more embodiments the liquid desiccant in the regenerator
runs down the face of a support plate as a falling film. In
accordance with one or more embodiments, the liquid desiccant in
the regenerator is also covered by a microporous membrane so that
liquid desiccant is unable to enter the air stream, but water vapor
in the air stream is able to be desorbed from the liquid desiccant.
In accordance with one or more embodiments the liquid desiccant is
transported from the conditioner to the regenerator and from the
regenerator back to the conditioner. In one or more embodiments,
the liquid desiccant is pumped by a pump. In one or more
embodiments, the liquid desiccant is pumped through a heat
exchanger between the conditioner and the regenerator. In
accordance with one or more embodiments the air exiting the
conditioner is directed to a second air stream. In accordance with
one or more embodiments the second air stream is a return air
stream from a space. In accordance with one or more embodiments a
portion of said return air stream is exhausted from the system and
the remaining air stream is mixed with the air stream from the
conditioner. In one or more embodiments, the exhausted portion is
between 5 and 25% of the return air stream. In one or more
embodiments, the exhausted portion is directed to the regenerator.
In one or more embodiments, the exhausted portion is mixed with an
outside air stream before being directed to the regenerator. In
accordance with one or more embodiments the mixed air stream
between the return air and the conditioner air is directed through
a cooling or evaporator coil. In one or more embodiments, the
cooling coil receives cold refrigerant from a refrigeration
circuit. In one or more embodiments, the cooled air is directed
back to the space to be cooled. In accordance with one or more
embodiments the cooling coil receives cold refrigerant from an
expansion valve or similar device. In one or more embodiments, the
expansion valve receives liquid refrigerant from a condenser coil.
In one or more embodiments, the condenser coil receives hot
refrigerant gas from a compressor system. In one or more
embodiments, the condenser coil is cooled by an outside air stream.
In one or more embodiments, the hot refrigerant gas from the
compressor is first directed to the refrigerant to desiccant heat
exchanger from the regenerator. In one or more embodiments,
multiple compressors are used. In one or more embodiments, separate
compressors serve the desiccant to refrigerant heat exchangers from
the compressors serving the evaporator and condenser coils. In one
or more embodiments, the compressors are variable speed
compressors. In one or more embodiments, the air streams are moved
by a fan or blower. In one or more embodiments, such fans are
variable speed fans. In one or more embodiments, the flow direction
of the refrigerant is reversed for a winter heating mode. In one or
more embodiments, water is added to the desiccant during operation.
In one or more embodiments, water is added during winter heating
mode. In one or more embodiments, water is added to control the
concentration of the desiccant. In one or more embodiments, water
is added during dry hot weather.
[0012] Provided herein are methods and systems used for the
efficient humidification of a desiccant stream using water and
selective membranes. In accordance with one or more embodiments a
set of pairs of channels for liquid transport are provided wherein
the one side of the channel pair receives a water stream and the
other side of the channel pair receives a liquid desiccant. In one
or more embodiments, the water is tap water, sea water, waste water
and the like. In one or more embodiments, the liquid desiccant is
any liquid desiccant that is able to absorb water. In one or more
embodiments, the elements of the channel pair are separated by a
membrane selectively permeable to water but not to any other
constituents. In one or more embodiments, the membrane is a reverse
osmosis membrane, or some other convenient selective membrane. In
one or more embodiments, multiple pairs can be individually
controlled to vary the amount of water that is added to the
desiccant stream from the water stream. In one or more embodiments,
other driving forces besides concentration potential differences
are used to assist the permeation of water through the membrane. In
one or more embodiments, such driving forces are heat or
pressure.
[0013] Provided herein are methods and systems used for the
efficient humidification of a desiccant stream using water and
selective membranes. In accordance with one or more embodiments, a
water injector comprising a series of channel pairs is connected to
a liquid desiccant circuit and a water circuit wherein one half of
the channel pairs receives a liquid desiccant and the other half
receives the water. In one or more embodiments, the channel pairs
are separated by a selective membrane. In accordance with one or
more embodiments the liquid desiccant circuit is connected between
a regenerator and a conditioner. In one or more embodiments, the
water circuit receives water from a water tank through a pumping
system. In one or more embodiments, excess water that is not
absorbed through the selective membrane is drained back to the
water tank. In one or more embodiments, the water tank is kept full
by a level sensor or float switch. In one or more embodiments,
precipitates or concentrated water is drained from the water tank
by a drain valve also known as a blow-down procedure.
[0014] Provided herein are methods and systems used for the
efficient humidification of a desiccant stream using water and
selective membranes while at the same time providing a heat
transfer function between two desiccant streams. In accordance with
one or more embodiments, a water injector comprising a series of
channel triplets is connected to two liquid desiccant circuits and
a water circuit wherein a third of the channel triplets receives a
hot liquid desiccant, a second third of the triplets receives a
cold liquid desiccant and the remaining third of the triplets
receives the water. In one or more embodiments, the channel
triplets are separated by a selective membrane. In accordance with
one or more embodiments the liquid desiccant channels are connected
between a regenerator and a conditioner. In one or more
embodiments, the water circuit receives water from a water tank
through a pumping system. In one or more embodiments, excess water
that is not absorbed through the selective membrane is drained back
to the water tank. In one or more embodiments, the water tank is
kept full by a level sensor or float switch. In one or more
embodiments, precipitates or concentrated water is drained from the
water tank by a drain valve also known as a blow-down
procedure.
[0015] Provided herein are methods and systems used for the
efficient dehumidification or humidification of an air stream using
liquid desiccants. In accordance with one or more embodiments a
liquid desiccant stream is split into a larger and a smaller
stream. In accordance with one or more embodiments, the larger
stream is directed into a heat transfer channel that is constructed
to provide fluid flow in a counter-flow direction to an air stream.
In one or more embodiments, the larger stream is a horizontal fluid
stream and the air stream is a horizontal stream in a direction
counter to the fluid stream. In one or more embodiments, the larger
stream is flowing vertically upward or vertically downward, and the
air stream is flowing vertically downward or vertically upward in a
counter-flow orientation. In one or more embodiments, the mass flow
rates of the larger stream and the air flow stream are
approximately equal within a factor of two. In one or more
embodiments, the larger desiccant stream is directed to a heat
exchanger coupled to a heating or cooling device. In one or more
embodiments, the heat or cooling device is a heat pump, a
geothermal source, a hot water source, and the like. In one or more
embodiments, the heat pump is reversible. In one or more
embodiments, the heat exchanger is made from a non-corrosive
material. In one or more embodiments, the material is titanium or
any suitable material non-corrosive to the desiccant. In one or
more embodiments, the desiccant itself is non-corrosive. In one or
more embodiments, the smaller desiccant stream is simultaneously
directed to a channel that is flowing downward by gravity. In one
or more embodiments, the smaller stream is bound by a membrane that
has an air flow on the opposite side. In one or more embodiments,
the membrane is a micro-porous membrane. In one or more
embodiments, the mass flow rate of the smaller desiccant stream is
between 1 and 10% of the mass flow rate of the larger desiccant
stream. In one or more embodiments, the smaller desiccant stream is
directed to a regenerator for removing excess water vapor after
exiting the (membrane) channel.
[0016] Provided herein are methods and systems used for the
efficient dehumidification or humidification of an air stream using
liquid desiccants. In accordance with one or more embodiments a
liquid desiccant stream is split into a larger and a smaller
stream. In one or more embodiments, the larger stream is directed
into a heat transfer channel that is constructed to provide fluid
flow in a counter-flow direction to an air stream. In one or more
embodiments, the smaller stream is directed to a membrane bound
channel. In one or more embodiments, the membrane channel has an
air stream on the opposite side of the desiccant. In one or more
embodiments, the larger stream is directed to a heat pump heat
exchanger after leaving the heat transfer channel and is directed
back to the heat transfer channel after being cooled or heated by
the heat pump heat exchanger. In one or more embodiments, the air
stream is an outside air stream. In one or more embodiments, the
air stream after being treated by the desiccant behind the membrane
is directed into a larger air stream that is returning from a
space. In one or more embodiments, the larger air stream is
subsequently cooled by a coil that is coupled to the same heat pump
refrigeration circuit as the heat exchanger heat pump. In one or
more embodiments, the desiccant stream is a single desiccant stream
and the heat transfer channel is configured as a two-way heat and
mass exchanger module. In one or more embodiments, the two-way heat
and mass exchanger module is bound by a membrane. In one or more
embodiments, the membrane is a micro-porous membrane. In one or
more embodiments, the two-way heat and mass exchanger module is
treating an outside air stream. In one or more embodiments, the air
stream after being treated by the desiccant behind the membrane is
directed into a larger air stream that is returning from a space.
In one or more embodiments, the larger air stream is subsequently
cooled by a coil that is coupled to the same heat pump
refrigeration circuit as the heat exchanger heat pump.
[0017] In no way is the description of the applications intended to
limit the disclosure to these applications. Many construction
variations can be envisioned to combine the various elements
mentioned above each with its own advantages and disadvantages. The
present disclosure in no way is limited to a particular set or
combination of such elements.
BRIEF DESCRIPTION OF THE FIGURES
[0018] FIG. 1 illustrates an exemplary 3-way liquid desiccant air
conditioning system using a chiller or external heating or cooling
sources.
[0019] FIG. 2 shows an exemplary flexibly configurable membrane
module that incorporates 3-way liquid desiccant plates.
[0020] FIG. 3 illustrates an exemplary single membrane plate in the
liquid desiccant membrane module of FIG. 2.
[0021] FIG. 4A schematically illustrates a conventional mini-split
air conditioning system operating in a cooling mode.
[0022] FIG. 4B schematically illustrates a conventional mini-split
air conditioning system operating in a heating mode.
[0023] FIG. 5A schematically illustrates an exemplary chiller
assisted liquid desiccant air conditioning system for 100% outside
air in a summer cooling mode.
[0024] FIG. 5B schematically illustrates an exemplary chiller
assisted liquid desiccant air conditioning system for 100% outside
air in a winter heating mode.
[0025] FIG. 6 schematically illustrates an exemplary chiller
assisted partial outside air liquid desiccant air conditioning
system using a 3-way heat and mass exchanger in a summer cooling
mode in accordance with one or more embodiments.
[0026] FIG. 7 schematically illustrates an exemplary chiller
assisted partial outside air liquid desiccant air conditioning
system using a 3-way heat and mass exchanger in a heating mode in
accordance with one or more embodiments.
[0027] FIG. 8 illustrates the psychrometric processes involved in
the cooling of air for a conventional RTU and the equivalent
processes in a liquid-RTU.
[0028] FIG. 9 illustrates the psychrometric processes involved in
the heating of air for a conventional RTU and the equivalent
processes in a liquid-RTU.
[0029] FIG. 10 schematically illustrates an exemplary chiller
assisted partial outside air liquid desiccant air conditioning
system using a 2-way heat and mass exchanger in a summer cooling
mode in accordance with one or more embodiments wherein the liquid
desiccant is pre-cooled and pre-heated before entering the heat and
mass exchangers.
[0030] FIG. 11 schematically illustrates an exemplary chiller
assisted partial outside air liquid desiccant air conditioning
system using a 2-way heat and mass exchanger in a summer cooling
mode in accordance with one or more embodiments wherein the liquid
desiccant is cooled and heated inside the heat and mass
exchangers.
[0031] FIG. 12 illustrates a water extraction module that pulls
pure water into the liquid desiccant for use in winter
humidification mode.
[0032] FIG. 13 shows how the water extraction module of FIG. 12 can
be integrated into the system of FIG. 7.
[0033] FIG. 14 illustrates two sets of channel triplets that
simultaneously provide a heat exchange and desiccant humidification
function.
[0034] FIG. 15 shows two of the 3-way membrane modules of FIG. 3
integrated into a DOAS, wherein the heat transfer fluid and the
liquid desiccant fluid have been combined into a single desiccant
fluid system, while retaining the advantage of separate paths for
the fluid that is performing the dehumidification function and the
fluid that is doing the heat transfer function.
[0035] FIG. 16 shows the system of FIG. 15 integrated to the system
of FIG. 6.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] FIG. 1 depicts a new type of liquid desiccant system as
described in more detail in U.S. Patent Application Publication No.
20120125020, which is incorporated by reference herein. A
conditioner 101 comprises a set of plate structures that are
internally hollow. A cold heat transfer fluid is generated in cold
source 107 and entered into the plates. Liquid desiccant solution
at 114 is brought onto the outer surface of the plates and runs
down the outer surface of each of the plates. The liquid desiccant
runs behind a thin sheet of material such as a membrane that is
located between the air flow and the surface of the plates. The
sheet of material can also comprise a hydrophilic material or a
flocking material in which case the liquid desiccant runs more or
less inside the material rather than over its surface. Outside air
103 is now blown through the set of plates. The liquid desiccant on
the surface of the plates attracts the water vapor in the air flow
and the cooling water inside the plates helps to inhibit the air
temperature from rising. The treated air 104 is put into a building
space. The liquid desiccant conditioner 101 and regenerator 102 are
generally known as 3-way liquid desiccant heat and mass exchangers,
because they exchange heat and mass between the air stream, the
desiccant, and a heat transfer fluid, so that there are three fluid
streams involved. Two-way heat and mass exchangers generally have
only a liquid desiccant and an air stream involved as will be seen
later.
[0037] The liquid desiccant is collected at the lower end of each
plate at 111 without the need for either a collection pan or bath
so that the air flow can be horizontal or vertical. Each of the
plates may have a separate desiccant collector at a lower end of
the outer surfaces of the plate for collecting liquid desiccant
that has flowed across the surfaces. The desiccant collectors of
adjacent plates are spaced apart from each other to permit airflow
therebetween. The liquid desiccant is then transported through a
heat exchanger 113 to the top of the regenerator 102 to point 115
where the liquid desiccant is distributed across the plates of the
regenerator. Return air or optionally outside air 105 is blown
across the regenerator plate 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.
The hot heat transfer fluid 110 from the heat source can be put
inside the plates of the regenerator similar to the cold heat
transfer fluid on the conditioner. Again, the liquid desiccant is
collected at the bottom of the plates 102 without the need for
either a collection pan or bath so that also on the regenerator the
air flow can be horizontal or vertical. An optional heat pump 116
can be used to provide cooling and heating of the liquid desiccant,
however it is generally more favorable 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 from the
desiccant.
[0038] FIG. 2 describes a 3-way heat and mass exchanger as
described in further detail in U.S. Patent Application Publication
Nos. 2014-0150662 filed on Jun. 11, 2013, 2014-0150656 filed on
Jun. 11, 2013, and US 2014-0150657 filed on Jun. 11, 2013, which
are all incorporated by reference herein. 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 more 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.
[0039] FIG. 3 describes a 3-way heat exchanger as described in more
detail in U.S. Provisional Patent Applications Ser. No. 61/771,340
filed on Mar. 1, 2013 and U.S. Patent Application Publication No.
US 2014-0245769, which are incorporated by reference herein. 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 contain a heat transfer fluid 254. Water vapor
256 entrained in the air stream is able to transition 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.
[0040] FIG. 4A illustrates a schematic diagram of a conventional
packaged Roof-Top Unit (RTU) air conditioning system as is
frequently installed on buildings, operating in a cooling mode. The
unit comprises a set of components that generate cool, dehumidified
air and a set of components that release heat to the environment.
In a packaged unit, the cooling and heating components are
generally inside a single enclosure. It is however possible to
separate the cooling and heating components into separate
enclosures or locate them in separate locations. The cooling
components comprise a cooling (evaporator) coil 405 through which a
fan 407 pulls return air (labeled RA) 401 that has been returned
(usually through a duct work--which is not shown) from a space.
Prior to reaching the cooling coil 405, some of the return air RA
is exhausted from the system as exhaust air EA2 402, which is
replaced by outside air OA 403 which is mixed with the remaining
return air to a mixed air stream MA 404. In summer, this outside
air OA is often warm and humid and adds a significant contribution
to the cooling load on the system. The cooling coil 405 cools the
air and condenses water vapor on the coil which is collected in
drain pan 424 and ducted to the outside 425. The resulting cooler,
drier air CC 408 however, is now cold and very close to 100%
relative humidity (saturated). Oftentimes and particularly in
outdoor conditions that are not very warm but humid such as on a
rainy spring day, the air CC 408 coming directly from the cooling
coil 10 can be uncomfortably cold. In order to increase occupant
comfort and control space humidity, the air 408 is re-heated to a
warmer temperature. There are several ways to accomplish this, such
as using a hot water coil with hot water fed from a boiler or a
steam coil receiving heat from a steam generator or by using
electric resistance heaters. This heating of air results in an
additional heat load on the cooling system. More modern systems use
an optional re-heat coil 409 which contains hot refrigerant from a
compressor 416. The re-heat coil 409 heats the air stream 408 to a
warmer air stream HC 410, which is then recirculated back to the
space, provides occupant comfort and allows one to better control
humidity in the space.
[0041] The compressor 416 receives a refrigerant through line 423
and receives power through conductor 417. The refrigerant can be
any suitable refrigerant such as R410A, R407A, R134A, R1234YF,
Propane, Ammonia, CO.sub.2, etc. The refrigerant is compressed by
the compressor 416 and compressed refrigerant is conducted to a
condenser coil 414 through line 418. The condenser coil 414
receives outside air OA 411, which is blown through the coil 414 by
fan 413, which receives power through conductor 412. The resulting
exhaust air stream EA 415 carries with it the heat of compression
generated by the compressor. The refrigerant condenses in the
condenser coil 414 and the resulting cooler, (partially) liquid
refrigerant 419 is conducted to the re-heat coil 409 where
additional heat is removed from the refrigerant, which turns into a
liquid in this stage. The liquid refrigerant in line 420 is then
conducted to expansion valve 421 before reaching the cooling coil
405. The cooling coil 405 receives liquid refrigerant at pressure
of typically 50-200 psi through line 422. The cooling coil 405
absorbs heat from the air stream MA 404 which re-evaporates the
refrigerant which is then conducted through line 423 back to the
compressor 416. The pressure of the refrigerant in line 418 is
typically 300-600 psi. In some instances the system can have
multiple cooling coils 405, fans 407 and expansion valves 421 as
well as compressors 416 and condenser coils 414 and condenser fans
413. Oftentimes the system also has additional components in the
refrigerant circuit or the sequence of components is ordered
differently which are all well known in the art. As will be shown
later, one of these components can be a diverter valve 426 which
bypasses the re-heat coil 409 in winter mode. There are many
variations of the basic design described above, but all
recirculating rooftop units generally have a cooling coil that
condenses moisture and introduce a small amount of outside air that
is added to a main air stream that returns from the space, is
cooled and dehumidified and the ducted back to the space. In many
instances the larges load is the dehumidification of outside air
and dealing with the reheat energy, as well as the average fan
power required to move the air.
[0042] The primary electrical energy consuming components are the
compressor 416 through electrical line 417, the condenser fan
electrical motor through supply line 412 and the evaporator fan
motor through line 406. In general the compressor uses close to 80%
of the electricity required to operate the system, with the
condenser and evaporator fans taking about 10% of the electricity
each at peak load. However when one averages power consumption over
the year, the average fan power is closer to 40% of the total load
since fans generally run all the time and the compressor switches
off on an as needed basis. In a typical RTU of 10 ton (35 kW)
cooling capacity, the air flow RA is around 4,000 CFM. The amount
of outside air OA mixed in is between 5% and 25% so between 200 and
1,000 CFM. Clearly the larger the amount of outside air results in
larger cooling loads on the system. The return air that is
exhausted EA2 is roughly equal to the amount of outside air taken
in so between 200 and 1,000 CFM. The condenser coil 414 is
generally operated with a larger air flow than the evaporator coil
405 of about 2,000 CFM for a 10 ton RTU. This allows the condenser
to be more efficient and reject the heat of compression more
efficiently to the outside air OA.
[0043] FIG. 4B is a schematic diagram of the system of FIG. 4A
operating in a winter heating mode as a heat pump. Not all RTUs are
heat pumps, and generally a cooling only system as shown in FIG. 4A
can be used, possibly supplemented with a simple gas or electric
furnace air heater. However, heat pumps are gaining popularity
particularly in moderate climates since they can provide heating as
well as cooling with better efficiency than electric heat and
without the need to run gas lines to the RTU. For ease of
illustration, the flow of refrigerant from the compressor 417 has
simply been reversed. In actuality the refrigerant is usually
diverted by a 4-way valve circuit which accomplishes the same
effect. As the compressor produces hot refrigerant in line 423
which is now conducted to the coil 405, which is now functioning as
a condenser rather than an evaporator. The heat of compression is
carried to the mixed air stream MA 404 resulting in a warm air
stream CC 408. Again, the mixed air stream MA 404 is the result of
removing some air EA2 402 from the return air RA 401 and replacing
it with outside air OA 403. The warm air stream CC 408 however is
now relatively dry because heating by the condenser coil 405
results in air with low relative humidity and thus oftentimes a
humidification system 427 is added to provide the required humidity
for occupant comfort. The humidification system 427 requires a
water supply 428. However this humidification also results in a
cooling effect, meaning that the air stream 408 has to be
overheated to compensate for the cooling effect of the humidifier
427. The refrigerant 422 leaving the coil 405 then enters the
expansion valve 421 which results in a cold refrigerant stream in
line 420, which is why diverter valve 426 can be used to bypass the
re-heat coil 409. This diverts the cold refrigerant to coil 414
which is now functioning as an evaporator coil. The cold outside
air OA 411 is blown by fan 413 through the evaporator coil 414. The
cold refrigerant in line 419 now results in the exhaust air EA 415
to be even colder. This effect can result in water vapor in the
outside air OA 411 to condense on the coil 414 which now runs the
risk of ice formation on the coil. For that reason, in heat pumps,
the refrigerant flow is regularly switched back from heating mode
to cooling mode resulting in a warming of the coil 414 which allows
ice to fall off the coil, but also resulting in much worse energy
performance in winter. Furthermore, particularly in cold climates,
it is common that the heating capacity of a system for winter
heating needs to be about twice the cooling capacity of the system
for summer cooling. It is therefore common to find supplemental
heating systems 429 that heat the air stream EV 410 further before
it returns to the space. Such supplemental systems can be gas
furnaces, electric resistance heaters and the like. These
additional components add a significant amount to the air stream
pressure drop resulting in more power required for fan 407. The
reheat coil--even if not active--can still be in the air stream as
are the humidification system and heating components.
[0044] FIG. 5A illustrates a schematic representation of a liquid
desiccant air conditioner system. A 3-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 3-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 3-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. It is worth noting that the system of FIG. 5A does not
require a condensate drain line like line 425 in FIG. 4A. Rather,
any moisture that is condensed into the desiccant is removed as
part of the desiccant itself. This also eliminates problems with
mold growth in standing water that can occur in the conventional
RTU condensate pan 424 systems of FIG. 4A.
[0045] The liquid desiccant 528 leaves the conditioner 503 and is
moved through the optional heat exchanger 526 to the regenerator
522 by pump 525.
[0046] 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 3-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.
[0047] The compressor 511 receives electrical power 512 and
typically accounts for 80% of electrical power consumption of the
system. The fans 502 and 524 also receive electrical power 505 and
529 respectively and account for most of the remaining power
consumption. Pumps 508, 520 and 525 have relatively low power
consumption. The compressor 511 will operate more efficiently than
the compressor 416 in FIG. 4A for several reasons: the evaporator
507 in FIG. 5A will typically operate at higher temperature than
the evaporator 405 in FIG. 4A because the liquid desiccant will
condense water at much higher temperature without needing to reach
saturation levels in the air stream. Furthermore the condenser 515
in FIG. 5A will operate at lower temperatures than the condenser
414 in FIG. 4A because of the evaporation occurring on the
regenerator 522 which effectively keeps the condenser 515 cooler.
As a result the system of FIG. 5A will use about 40% less
electricity than the system of FIG. 4A for similar compressor
isentropic efficiencies.
[0048] FIG. 5B shows essentially the same system as FIG. 5A except
that the compressor 511's refrigerant direction has been reversed
as indicated by the arrows on refrigerant lines 514 and 510.
Reversing the direction of refrigerant flow can be achieved by a
4-way reversing valve (not shown) or other convenient means in the
chiller 530. It is also possible to instead of reversing the
refrigerant flow to direct the hot heat transfer fluid 518 to the
conditioner 503 and the cold heat transfer fluid 506 to the
regenerator 522. This will provide heat to the conditioner which
will now create hot, humid air 504 for the space for operation in
winter mode. In effect the system is now working as a heat pump,
pumping heat from the outside air 521 to the space supply air 504.
However unlike the system of FIG. 4A, which is oftentimes also
reversible, there is much less of a risk of the coil freezing
because the desiccant usually has much lower crystallization limit
than water vapor. In the system of FIG. 4B, the air stream 411
contains water vapor and if the evaporator coil 414 gets too cold,
this moisture will condense on the surfaces and create ice
formation on the coil. The same moisture in the regenerator 522 of
FIG. 5B will condense in the liquid desiccant which--when managed
properly--will not crystalize until -60.degree. C. for some
desiccants such as LiCl and water. This will allow the system to
continue to operate at much lower outside air temperatures without
freezing risk.
[0049] As before in FIG. 5A, outside air 501 is directed through
the conditioner 503 by fan 502 which is operated by electrical
power 505. The compressor 511 discharges hot refrigerant through
line 510 into condenser heat exchanger 507 and out through line
510. The heat exchanger rejects heat to heat transfer fluid
circulated by pump 508 through line 509 into the conditioner 503
which results in the air stream 501 picking up heat and moisture
from the desiccant. Dilute desiccant is supplied by line 527 to the
conditioner. The dilute desiccant is directed from regenerator 522
by pump 525 through heat exchanger 526. However in winter
conditions it is possible that not enough water is recovered in the
regenerator 522 to compensate for the water lost in the conditioner
503 which is why additional water 531 can be added to the liquid
desiccant in line 527. Concentrated liquid desiccant is collected
from the conditioner 503 and drained through line 528 and heat
exchanger 526 to the regenerator 522. The regenerator 522 takes in
either outside air OA or preferably return air RA 521 which is
directed through the regenerator by fan 524 which is powered by
electrical connection 529. Return air is preferred because is
usually much warmer and contains much more moisture than outside
air, which allows the regenerator to capture more heat and moisture
from the air stream 521. The regenerator 522 thus produces colder,
drier exhaust air EA 523. A heat transfer fluid in line 518 absorbs
heat from the regenerator 522 which is pumped by pump 520 to heat
exchanger 515. The heat exchanger 515 received cold refrigerant
from expansion valve 516 through line 514 and the heated
refrigerant is conducted through line 513 back to the compressor
511 which receives power from conductor 512.
[0050] FIG. 6 illustrates an air-conditioning system in accordance
with one or more embodiments wherein a modified liquid desiccant
section 600A is connected to a modified RTU section 600B but
wherein the two systems share a single chiller system 600C. The
outside air OA 601 which as shown in FIG. 4A is typically 5-25% of
the return air stream RA 604, is now directed through the
conditioner 602 which is similar in construction to the 3-way heat
and mass exchange conditioner described in FIG. 2. The conditioner
602 can be significantly smaller than the conditioner 503 of FIG.
5A because the air stream 601 is much smaller than in the 100%
outside air stream 501 of FIG. 5A. The conditioner 602 produces a
colder, dehumidified air stream SA 603 which is mixed with the
return air RA 604 to make mixed air MA2 606. Excess return air 605
is directed out of the system or towards the regenerator 612. The
mixed air MA2 is pulled by fan 608 through evaporator coil 607
which primarily provides sensible only cooling so that the coil 607
can be much shallower and less expensive than the coil 405 in FIG.
4A which needs to be deeper to allow moisture to condense. The
resulting air stream CC2 609 is ducted to the space to be cooled.
The regenerator 612 receives either outside air OA 610 or the
excess return air 605 or a mixture 611 thereof.
[0051] The regenerator air stream 611 can be pulled through the
regenerator 612 which again is similar in construction to the 3-way
heat and mass exchanger described in FIG. 2 by a fan 637 and the
resulting exhaust air stream EA2 613 is generally much warmer and
contains more water vapor than the mixed air stream 611 that is
entering. Heat is provided by circulating a heat transfer fluid
through line 621 using pump 622.
[0052] The compressor 618 compresses a refrigerant similar to the
compressors in FIG. 4A and FIG. 5A. The hot refrigerant gas is
conducted through line 619 to a condenser heat exchanger 620. A
smaller amount of heat is conducted through this
liquid-to-refrigerant heat exchanger 620 into the heat transfer
fluid in circuit 621. The still hot refrigerant is now conducted
through line 623 to a condenser coil 616, which receives outside
air OA 614 from fan 615. The resulting hot exhaust air EA3 617 is
ejected into the environment. The refrigerant which is now a cooler
liquid after exiting the condenser coil 616 is conducted through
line 624 to an expansion valve 625, where it is expanded and
becomes cold. The cold liquid refrigerant is conducted through line
626 to the evaporator coil 607 where it absorbs heat from the mixed
air stream MA2 606. The still relatively cold refrigerant which has
partially evaporated in the coil 607 is now conducted through line
627 to evaporator heat exchanger 628 where additional heat is
removed from the heat transfer fluid circulating in line 629 by
pump 630. Finally the gaseous refrigerant exiting the heat
exchanger 628 is conducted through line 631 back to the compressor
618.
[0053] In addition, a liquid desiccant is circulated between the
conditioner 602 and the regenerator 612 through lines 635, the heat
exchanger 633 and is circulated back to the conditioner by pump 632
and through line 634. Optionally a water-injection module 636 can
be added to one or both of the desiccant lines 634 and 635. Such a
module injects water into the desiccant in order to reduce the
concentration of the desiccant and is described in FIG. 12 in more
detail. Water injection is useful in conditions in which the
desiccant concentration gets higher than desired, e.g., in hot, dry
conditions such as can occur in the summer or in cold, dry
conditions such as can occur in winter which will be described in
more detail in FIG. 7.
[0054] FIG. 7 illustrates an embodiment of the present invention of
FIG. 6, wherein a modified liquid desiccant section 700A is
connected to a modified RTU section 700B but wherein the two
systems share a single chiller system 700C operating in a heating
mode. The outside air OA 701 which as shown in FIG. 4B is typically
5-25% of the return air stream RA 704, is now directed through the
conditioner 702 which is similar in construction to the 3-way heat
and mass exchange conditioner described in FIG. 2. The conditioner
702 can be significantly smaller than the conditioner 503 of FIG.
5B because the air stream 701 is much smaller than in the 100%
outside air stream 501 of FIG. 5B. The conditioner 702 produces a
warmer, humidified air stream RA3 703 which is mixed with the
return air RA 704 to make mixed air MA3 706. Excess return air RA
705 is directed out of the system or towards the regenerator 712.
The mixed air MA3 706 is pulled by fan 708 through condenser coil
707 which provides sensible only heating. The resulting air stream
SA2 709 is ducted to the space to be heated and humidified. The
regenerator 712 receives either outside air OA 710 or the excess
return air RA 705 or a mixture 711 thereof.
[0055] The regenerator air stream 711 can be pulled through the
regenerator 712 which again is similar in construction to the 3-way
heat and mass exchanger described in FIG. 2 by a fan 737 and the
resulting exhaust air stream EA2 713 is generally much colder and
contains less water vapor than the mixed air stream 711 that is
entering. Heat is removed by circulating a heat transfer fluid
through line 721 using pump 722.
[0056] The compressor 718 compresses a refrigerant similar to the
compressors in FIG. 4B and FIG. 5B. The hot refrigerant gas is
conducted through line 731 to a condenser heat exchanger 728, which
is the same heat exchanger 628 in FIG. 6, but used as a condenser
instead of an evaporator. A smaller amount of heat is conducted
through this liquid-to-refrigerant heat exchanger 728 into the heat
transfer fluid in circuit 729 by using pump 730. The still hot
refrigerant is now conducted through line 727 to a condenser coil
707, which receives the mixed return air MA3 706. The resulting hot
supply air SA2 709 is directed through a duct to the space to be
heated and humidified. The refrigerant which is now a cooler liquid
after exiting the condenser coil 707 is conducted through line 726
to an expansion valve 725, where it is expanded and becomes cold.
The cold liquid refrigerant is conducted through line 724 to the
evaporator coil 716 where it absorbs heat from the outside air
stream OA 714 resulting in a cold exhaust air stream EA 717 which
is emitted to the environment by using fan 715. The still
relatively cold refrigerant which has partially evaporated in the
coil 716 is now conducted through line 723 to evaporator heat
exchanger 720 where additional heat is removed from the air stream
711 going through the regenerator 712 by transfer fluid circulating
in line 721 by using pump 722. Finally the gaseous refrigerant
exiting the heat exchanger 720 is conducted through line 719 back
to the compressor 718.
[0057] In addition, a liquid refrigerant is circulated between the
conditioner 702 and the regenerator 712 through lines 735, the heat
exchanger 733 and is circulated back to the conditioner by pump 732
and through line 734. In some conditions, for example when both the
return air RA 705 and the outside air OA 710 are relatively dry, it
is possible that the conditioner 702 provides more moisture to the
space than is collected in the regenerator 712. In that case a
provision for adding water 736 is required to maintain the
desiccant at the proper concentration. A provision for adding water
736 can be provided in any location that gives convenient access to
the desiccant, however the water added, should be relatively pure
since a lot of water will evaporate, which is why reverse osmosis
or de-ionized or distilled water would be preferable to straight
tap water. This provision for adding water 736 will be discussed in
more detail in FIG. 12.
[0058] The advantages of integrating a system in the configuration
of FIG. 6 and FIG. 7 are several. The combination of 3-way liquid
desiccant heat exchanger modules and a shared compressor system
allows one to combine the advantages of dehumidification without
condensation that are possible in the 3-way heat and mass exchanger
with the inexpensive construction of a conventional RTU, whereby
the integrated solution becomes very cost competitive. As mentioned
before, the coil 607 can be thinner, since no moisture condensation
is needed, and the condensate pan and drain from FIG. 4A can be
eliminated. Furthermore as will be seen in FIG. 8, the overall
cooling capacity of the compressor can be reduced and the condenser
coil can be smaller as well. In addition, the heating mode of the
system adds humidity to the air stream unlike any other heat pump
in the market today. The refrigerant, desiccant and heat transfer
fluid circuits are actually simpler than those in the systems of
FIGS. 4A, 4B, 5A and 5B, and the supply air stream 609 and 709
encounter fewer components than the conventional systems of FIGS.
4A and 4B, which means less pressure drop in the air stream leading
to additional energy savings.
[0059] FIG. 8 illustrates a psychrometric chart of the processes of
FIG. 4A and FIG. 6. The horizontal axis denotes temperature in
degrees Fahrenheit and the vertical axis denotes humidity in grains
of water per pound of dry air. As can be seen in the figure, and by
way of example, outside air OA is provided at 95 F and 60% relative
humidity (or 125 gr/lb). Also by example we selected a 1,000 CFM
supply air requirement with a 25% outside air contribution (250
CFM) to the space at 65 F and 70% RH (65 gr/lb). The conventional
system of FIG. 4A takes in 1,000 CFM of return air RA at 80 F and
50% RH (78 gr/lb). 250 CFM of this return air RA is discarded as
EA2 (the stream EA2 402 in FIG. 4A). 750 CFM of the return air RA
is mixed with 250 CFM of outside air (the stream OA 403 in FIG. 4A)
resulting in a mixed air condition MA (the stream MA 404 in FIG.
4A). The mixed air MA is directed through the evaporator coil
resulting in a cooling and dehumidification process resulting in
air CC leaving the coil at 55 F and 100% RH (65 gr/lb). In many
cases that air is reheated (possibly by a small condenser coil as
was shown in FIG. 4A) resulting in the actual supply air HC at 65F
and 70% RH (65 gr/lb).
[0060] The system of FIG. 6 under the same outside air conditions
will create a supply air stream SA leaving the conditioner (602 in
FIG. 6) at 65 F and 43% RH (40 gr/lb). This relatively dry air is
now mixed with the 750 CFM of return air RA (604 in FIG. 6)
resulting in mixed air condition MA2 (MA2 606 in FIG. 6). The mixed
air MA2 is now directed through the evaporator coil (607 in FIG. 6)
which sensible cools the air to supply air condition CC2 (CC2, 609
in FIG. 6). As can be seen in the figure and calculated from the
psychrometrics, the cooling power of the conventional system is
48.7 kBTU/hr, whereas the cooling power of the system of FIG. 6 is
35.6 kBTU/hr (23.2 kBTU/hr for the outside air OA and 12.4 kBTU/hr
for the mixed air MA2) thus requiring about a 27% smaller
compressor.
[0061] Also shown in FIG. 8 is the change in the outside air OA
used to reject heat. The conventional system of FIG. 4A use about
2,000 CFM through the condenser 414 to reject heat to the outside
air OA (OA 411 in FIG. 4A) resulting in exhaust air EA at 119 F and
25% RH (125 gr/lb) (EA 415 in FIG. 4A). However, the system of FIG.
6 rejects two air streams, the regenerator 612 rejects air EA2 at
107 F and 49% RH (178 gr/lb) (EA2 613 in FIG. 6) which is hot and
moist, as well as air stream EA3 at 107 F and 35% RH (125 gr/lb)
(EA3 617 in FIG. 6). Because of the lower compressor capacity, less
heat has to be rejected to the outside air resulting in a lower
condenser temperature. The effects of lower compressor power and
higher evaporator temperatures and lower condenser temperature as
well as lower pressure drop in the main air stream in FIG. 6
combine make a system with much better energy performance than a
conventional RTU as was shown in FIG. 4A.
[0062] Likewise, FIG. 9 illustrates a psychrometric chart of the
processes of FIG. 4B and FIG. 7. The horizontal axis denotes
temperature in degrees Fahrenheit and the vertical axis denotes
humidity in grains of water per pound of dry air. As can be seen in
the figure, and by way of example, outside air OA is provided at 30
F and 60% relative humidity (or 14 gr/lb). Also by example we again
selected a 1,000 CFM supply air requirement with a 25% outside air
contribution (250 CFM) to the space at 120 F and 12% RH (58 gr/lb).
The conventional system of FIG. 4B takes in 1,000 CFM of return air
RA at 80 F and 50% RH (78 gr/lb). 250 CFM of this return air RA is
discarded as EA2 (the stream EA2 402 in FIG. 4B). 750 CFM of the
return air RA is mixed with 250 CFM of outside air (the stream OA
403 in FIG. 4B) resulting in a mixed air condition MA (the stream
MA 404 in FIG. 4B). The mixed air MA is directed through the
condenser coil (405 in FIG. 4B) resulting in a heating process
resulting in air SA leaving the coil at 128 F and 8% RH (46 gr/lb).
In many cases that air is too dry for occupant comfort and the air
is receiving moisture from a humidification system (427 in FIG. 4B)
resulting in the actual supply air EV at 120 F and 12% RH (58
gr/lb). Humidification can be done to a higher level, but as will
be clear that would possibly result in an additional heating
requirement. The water consumption of the evaporation in this
example is around 1.0 gallon per hour.
[0063] The system of FIG. 7 under the same outside air conditions
will create a supply air stream RA3 703 leaving the conditioner
(702 in FIG. 7) at 70 F and 48% RH (63 gr/lb). This relatively
moist air is now mixed with the 750 CFM of return air RA (704 in
FIG. 7) resulting in mixed air condition MA3 (MA3 706 in FIG. 7).
The mixed air MA3 is now directed through the condenser coil (707
in FIG. 7) which sensible heats the air to supply air condition SA2
(SA2, 709 in FIG. 7). As can be seen in the figure and calculated
from the psychrometrics, the heating power of the conventional
system is 78.3 kBTU/hr, whereas the heating power of the system of
FIG. 7 is 79.3 kBTU/hr (20.4 kBTU/hr for the outside air OA and
58.9 kBTU/hr for the mixed air MA2) essentially the same as the
system of FIG. 4B.
[0064] Also shown in FIG. 9 is the change in the outside air OA
used to absorb heat. The conventional system of FIG. 4B use about
2,000 CFM through the evaporator 414 to absorb heat from the
outside air OA (OA 411 in FIG. 4B) resulting in exhaust air EA at
20 F and 100% RH (9 gr/lb) (EA 415 in FIG. 4B). However, the system
of FIG. 6 absorbs heat from two air streams, the regenerator 612
absorbs heat from air stream between MA2 (which comprises 250 CFM
of RA air at 65 F and 60% RH or 55 gr/lb and 150 CFM of OA air at
30 F and 60% RH or 14 gr/lb for a mixed air condition MA2 (711 in
FIG. 7) of 400 CFM of 52 F air at 70% RH or 40 gr/lb) and air
stream EA2 at 20 F and 50% RH (10 gr/lb) (EA2 713 in FIG. 7) which
is cool and dry, as well as air stream EA at 20 F and 95% RH (14
gr/lb) (EA 717 in FIG. 7). As can be seen in the figure this setup
has three effects: the temperature of EA and EA2 is higher than the
temperature CC, and thus the evaporator coil 707 of FIG. 6B runs at
a higher temperature as the evaporator coil 405 which improves
efficiency. Furthermore, the conditioner 702 is absorbing moisture
from the mixed air stream MA2 which is subsequently released in the
air stream MA3, eliminating the need for makeup water. And lastly,
the evaporator coil 405 is condensing moisture as can be seen from
the process between OA and CC in the figure. In practice this
results in ice formation on the coil and the coil will thus have to
be heated the remove ice buildup, which is usually done by
switching the refrigerant flow in the direction of FIG. 6. The coil
707 does not reach saturation and will thus not have to be heated.
As a result the actual cooling in coil 405 in the system of FIG. 4B
is around 21.7 kBRU/hr, whereas the combination of coil 707 and
conditioner 702 results in 45.2 kBTU/hr in the system of FIG. 7.
This means a significantly better Coefficient of Performance (CoP)
even though the heating output is the same and no water is consumed
in the system of FIG. 7.
[0065] FIG. 10 illustrates an alternate embodiment of the system in
FIG. 6, wherein the 3-way heat and mass exchangers 602 and 612 of
FIG. 6 have been replaced by 2-way heat and mass exchangers. In two
way heat and mass exchangers which are well known in the art, a
desiccant is exposed directly to an air stream, sometimes with a
membrane therebetween and sometimes without. Typically two-way heat
and mass exchangers exhibit an adiabatic heat and mass transfer
process since there often is no place for the latent heat of
condensation to be absorbed, safe for the desiccant itself. This
usually increases the required desiccant flow rate because the
desiccant now has to function as a heat transfer fluid as well.
Outside air 1001 is directed through the conditioner 1002 which
produces a colder, dehumidified air stream SA 1003 which is mixed
with the return air RA 1004 to make mixed air MA2 1006. Excess
return air 1005 is directed out of the system or towards the
regenerator 1012. The mixed air MA2 is pulled by fan 1008 through
evaporator coil 1007 which primarily provides sensible only
cooling. The resulting air stream CC2 1009 is ducted to the space
to be cooled. The regenerator 1012 receives either outside air OA
1010 or the excess return air 1005 or a mixture 1011 thereof.
[0066] The regenerator air stream 1011 can be pulled through the
regenerator 1012 which again is similar in construction to the
2-way heat and mass exchanger as used as a conditioner 1002 by a
fan (not shown) and the resulting exhaust air stream EA2 1013 is
generally much warmer and contains more water vapor than the mixed
air stream 1011 that is entering.
[0067] The compressor 1018 compresses a refrigerant similar to the
compressors in FIG. 4A, FIG. 5A and FIG. 6. The hot refrigerant gas
is conducted through line 1019 to a condenser heat exchanger 1020.
A smaller amount of heat is conducted through this
liquid-to-refrigerant heat exchanger 1020 into the desiccant in
line 1031. Since desiccant is often highly corrosive, the heat
exchanger 1020 is made from Titanium or other suitable material.
The still hot refrigerant is now conducted through line 1021 to a
condenser coil 1016, which receives outside air OA 1014 from fan
1015. The resulting hot exhaust air EA3 1017 is ejected into the
environment. The refrigerant which is now a cooler liquid after
exiting the condenser coil 1016 is conducted through line 1022 to
an expansion valve 1023, where it is expanded and becomes cold. The
cold liquid refrigerant is conducted through line 1024 to the
evaporator coil 1007 where it absorbs heat from the mixed air
stream MA2 1006. The still relatively cold refrigerant which has
partially evaporated in the coil 1007 is now conducted through line
1025 to evaporator heat exchanger 1026 where additional heat is
removed from the liquid desiccant that is circulated to the
conditioner 1002. As before the heat exchanger 1026 will have to be
constructed from a corrosion resistant material such as Titanium.
Finally the gaseous refrigerant exiting the heat exchanger 1026 is
conducted through line 1027 back to the compressor 1018.
[0068] In addition, a liquid desiccant is circulated between the
conditioner 1002 and the regenerator 1012 through lines 1030, the
heat exchanger 1029 and is circulated back to the conditioner by
pump 1028 and through line 1031.
[0069] FIG. 11 illustrates an alternate embodiment of the system in
FIG. 10, wherein the 2-way heat and mass exchanger 1002 and the
liquid to liquid heat exchangers 1026 of FIG. 10 have been
integrated into single 3-way heat and mass exchangers where the
air, the desiccant and the refrigerant exchange heat and mass
simultaneously. In concept this is similar to using a refrigerant
instead of a heat transfer fluid in FIG. 6. The same integration
can be done on the regenerator 1012 and the heat exchanger 1020.
These integrations essentially eliminate a heat exchanger on each
side making the system more efficient.
[0070] Outside air 1101 is directed through the conditioner 1102
which produces a colder, dehumidified air stream SA 1103 which is
mixed with the return air RA 1104 to make mixed air MA2 1106.
Excess return air 1105 is directed out of the system or towards the
regenerator 10112. The mixed air MA2 is pulled by fan 10108 through
evaporator coil 1107 which primarily provides sensible only
cooling. The resulting air stream CC2 1109 is ducted to the space
to be cooled. The regenerator 11012 receives either outside air OA
1110 or the excess return air 1105 or a mixture 1111 thereof.
[0071] The regenerator air stream 1111 can be pulled through the
regenerator 1112 which again is similar in construction to the
2-way heat and mass exchanger as used as a conditioner 1102 by a
fan (not shown) and the resulting exhaust air stream EA2 1113 is
generally much warmer and contains more water vapor than the mixed
air stream 1111 that is entering.
[0072] The compressor 1118 compresses a refrigerant similar to the
compressors in FIG. 4A, FIG. 5A, FIG. 6 and FIG. 10. The hot
refrigerant gas is conducted through line 1119 to a 3-way condenser
heat and mass exchanger 1112. A smaller amount of heat is conducted
through this regenerator 1120 into the refrigerant in line 1119.
Since desiccant is often highly corrosive, the regenerator 1112
needs to be constructed as for example is shown in FIG. 80 of
application Ser. No. 13/915,262. The still hot refrigerant is now
conducted through line 1120 to a condenser coil 1116, which
receives outside air OA 1114 from fan 1115. The resulting hot
exhaust air EA3 1117 is ejected into the environment. The
refrigerant which is now a cooler liquid after exiting the
condenser coil 1116 is conducted through line 1121 to an expansion
valve 1122, where it is expanded and becomes cold. The cold liquid
refrigerant is conducted through line 1123 to the evaporator coil
1107 where it absorbs heat from the mixed air stream MA2 1106. The
still relatively cold refrigerant which has partially evaporated in
the coil 1107 is now conducted through line 1124 to the evaporator
heat exchanger/conditioner 1102 where additional heat is removed
from the liquid desiccant. Finally the gaseous refrigerant exiting
the conditioner 1102 is conducted through line 1125 back to the
compressor 1118.
[0073] In addition, the liquid desiccant is circulated between the
conditioner 1102 and the regenerator 1112 through lines 1129, the
heat exchanger 1128 and is circulated back to the conditioner by
pump 1127 and through line 1126.
[0074] The systems from FIG. 10 and FIG. 11 are also reversible for
winter heating mode similar to the system in FIG. 7. Under some
conditions in the winter heating mode, additional water should be
added to maintain proper desiccant concentration because if too
much water is evaporated in dry conditions, the desiccant is at
risk of crystalizing. As mentioned, one option is to simply add
reverse osmosis or de-ionized water to keep the desiccant dilute,
but the processes to generate this water are also very energy
intensive.
[0075] FIG. 12 illustrates an embodiment of a much simpler water
injection system that generates pure water directly into the liquid
desiccant by taking advantage of the desiccants' ability to attract
water. The structure in FIG. 12 (which was labeled 736 in FIG. 7)
comprises a series of parallel channels, which can be flat plates
or rolled up channels. Water enters the structure at 1201 and is
distributed to several channels through distribution header 1202.
This water can be tap water, sea water or even filtered waste water
or any water containing fluid that has primarily water as a
constituent and if any other materials are present, those materials
are not transportable through the selective membrane 1210 as will
be explained shortly. The water is distributed to each of the even
channels labeled "A" in the figure. The water exits the channels
labeled "A" through a manifold 1203 and is collected in drain line
1204. At the same time concentrated desiccant is introduced at
1205, which is distributed through header 1206 to each of the
channels labeled "B" in the figure. The concentrated desiccant 1209
flows along the B channels. The wall between the "A" and the "B:
channels comprises a selective membrane 1210 which is selective to
water so that water molecules can come through the membrane but
ions or other materials cannot. This thus prevents for example
Lithium and Chloride ions from crossing the membrane into the water
"A" channel and vice versa prevents Sodium and Chloride ions from
seawater crossing into the desiccant in the "B" channel. Since the
concentration of Lithium Chloride in the desiccant is typically
25-35%, this provides a strong driving force for the diffusion of
water from the "A" to the "B" channel since the concentration of
for example Sodium Chloride in sea water is typically less than 3%.
Selective membranes of this type are commonly found in membrane
distillation or reverse osmosis processes and are well known in the
art. The structure of FIG. 12 can be executed in many form factors
such as a flat plate structure or a concentric stack of channels or
any other convenient form factor. It is also possible to construct
the plate structure of FIG. 3 by replacing the wall 255 with a
selective membrane as is shown in FIG. 12. However, such a
structure would only make sense if one wants to continuously add
water to the desiccant. It would make little sense in summer mode
when one is trying to remove water from the desiccant. It is
therefore easier to implement the structure of FIG. 12 in a
separate module as is shown in FIG. 7 and FIG. 13 which can be
bypassed in a summer cooling mode. Although in some instances
adding water to the desiccant in summer cooling mode may also make
sense for example if the outdoor temperature is very hot but also
very dry as in a desert. The membrane may be a microporous
hydrophobic structure comprising a polypropylene, a polyethylene,
or an ECTFE (Ethylene ChloroTriFluoroEthylene) membrane.
[0076] FIG. 13 illustrates how the water injection system from FIG.
12 can be integrated to the desiccant pumping subsystem of FIG. 7.
The desiccant pump 732 pumps desiccant through the water injection
module 1301 and through the heat exchanger 733 as was shown in FIG.
7. The desiccant returns from the conditioner (702 in FIG. 7)
through line 735 and through the heat exchanger 733 back to the
regenerator (712 in FIG. 7). A water reservoir 1304 is filled with
water 1305 or a water containing liquid. A pump 1302 pumps the
water to the water injection system 1301, where it enters through
port 1201 (as shown in FIG. 12). The water flows through the "A"
channels in FIG. 12 and exits through port 1204 after which is
drains back to the tank 1303. The water injection system 1301 is
sized in such a way that the diffusion of water through the
selective membranes 1210 is matched to the amount of water that
would have to be added to the desiccant. The water injection system
can comprise several independent sections that are individually
switchable so that water could be added to the desiccant in several
stages.
[0077] The water 1304 flowing through the injection module 1301 is
partially transmitted through the selective membranes 1210. Any
excess water exits through the drain line 1204 and falls back in
the tank 1303. As the water is pumped from the tank 1304 again by
pump 1302, less and less water will return to the tank. A float
switch 1307 such as is commonly used on cooling towers can be used
to maintain a proper water level in the tank. When the float switch
detects a low water level, it opens valve 1308 which lets
additional water in from supply water line 1306. However, since the
selective membrane only pass pure water through, any residuals such
as Calcium Carbonates, or other non-passible materials will collect
in the tank 1303. A blow-down valve 1305 can be opened to get rid
of these unwanted deposits as is commonly done on cooling
towers.
[0078] It should be clear to those skilled in the art that the
water injection system of FIG. 12 can be used in other liquid
desiccant system architectures for example in those described in
Ser. No. 13/115,686, US 2012/0125031 A1, Ser. No. 13/115,776, and
US 2012/0125021 A1.
[0079] FIG. 14 illustrates how the water injection system from FIG.
12 and FIG. 13 can be integrated to the desiccant to desiccant heat
exchanger 733 from FIG. 13. The water flows through the "A"
channels 1402 in FIG. 14 and exits through a port after which is
drains back to the tank as described in FIG. 13. A cold desiccant
is introduced in the "B" channels 1401 in FIG. 14 and a warm
desiccant is introduced in the "C" channels in FIG. 14. The walls
1404 between the "A" and "B" and "A" and "C" channels respectively
are again constructed with a selectively permeable membrane. The
wall 1405 between the "B" and the "C" channel is a non-permeable
membrane such as a plastic sheet which can conduct heat but not
water molecules. The structure of FIG. 14 thus accomplishes two
tasks simultaneously: it provides a heat exchange function between
the hot and the cold desiccant and it transmit water from the water
channel to the two desiccant channels in each channel triplet.
[0080] FIG. 15 illustrates an embodiment wherein two of the
membrane modules of FIG. 3 have been integrated into a DOAS but
wherein the heat transfer fluid and the desiccant that were two
separate fluids in FIGS. 1, 2 and 3 (the desiccant--labeled 114 and
115 in FIG. 1--is typically a lithium chloride/water solution and
the heat transfer fluid--labeled 110 in FIG. 1 is typically water
or a water/glycol mixture) are combined in a single fluid (which
would typically be lithium chloride and water, but any suitable
liquid desiccant will do). By using a single fluid the pumping
system can be simplified because the desiccant pump (for example
632 in FIG. 6), can be eliminated. However, it is desirable to
still maintain a counter-flow arrangement between the air stream
1501 and/or 1502 and the heat transfer path 1505 and/or 1506. In
two-way membrane modules the desiccant is oftentimes not able to
maintain a counter-flow path to the air stream, since the desiccant
generally moves vertical with gravity and the air stream often is
desired to be horizontal resulting in a cross-flow arrangement. As
described in application 61/951,887 (for example in FIG. 400 and
FIG. 900), in a 3-way membrane module, it is possible to create a
counter-flow between the air stream and a heat transfer fluid
stream, while a small desiccant stream (typically 5-10% of the mass
flow of the heat transfer fluid stream) is mostly absorbing or
desorbing the latent energy from or to the air stream. By using the
same fluid for the latent absorption and the heat transfer but
having separate paths for each, one can obtain a much better
efficiency of the membrane module since the primary air and heat
transfer fluid flows are arranged in a counter-flow arrangement,
and the small desiccant stream that is absorbing or desorbing the
latent energy may still be in a cross-flow arrangement, but because
the mass flow rate of the small desiccant stream is small, the
effect on efficiency is negligible.
[0081] Specifically, in FIG. 15, an air stream 1501 which can be
outside air, or return air from a space or a mixture between the
two, is directed over a membrane structure 1503. The membrane
structure 1503 is the same structure from FIG. 3. However, the
membrane structure (only a single plate structure is shown although
generally multiple plate structures would be used in parallel) is
now supplied by pump 1509 with a large desiccant stream 1511
through tank 1513. This large desiccant stream runs in the heat
transfer channel 1505 counter to the air stream 1501. A smaller
desiccant stream 1515 is also simultaneously pumped by the pump
1509 to the top of the membrane plate structures 1503 where it
flows by gravity behind the membranes 1532 in flow channel 1507.
The flow channel 1507 is generally vertical; however the heat
transfer channel 1505 can be either vertical or horizontal,
depending on whether the air stream 1501 is vertical or horizontal.
The desiccant exiting the heat transfer channel 1505 is now
directed to a condenser heat exchanger 1517, which, because of the
corrosive nature of most liquid desiccants such as lithium
chloride, is usually made from Titanium or some other non-corrosive
material. To prevent excessive pressure behind the membranes 1532,
an overflow device 1528 can be employed that results in excess
desiccant being drained through tube 1529 back to the tank 1513.
Desiccant that has desorbed latent energy into the air stream 1501
is now directed through drain line 1519 through heat exchanger 1521
to pump 1508.
[0082] The heat exchanger 1517 is part of a heat pump comprising
compressor 1523, hot gas line 1524, liquid line 1525, expansion
valve 1522, cold liquid line 1526, evaporator heat exchanger 1518
and gas line 1527 which directs a refrigerant back to the
compressor 1523. The heat pump assembly can be reversible as
described earlier for allowing switching between a summer operation
mode and a winter operation mode.
[0083] Further, in FIG. 15, a second air stream 1502 which can also
be outside air, or return air from a space or a mixture between the
two, is directed over a second membrane structure 1504. The
membrane structure 1504 is the same structure from FIG. 3. However,
the membrane structure (only a single plate structure is shown
although generally multiple plate structures would be used in
parallel) is now supplied by pump 1510 with a large desiccant
stream 1512 through tank 1514. This large desiccant stream runs in
heat transfer channel 1506 counter to the air stream 1502. A
smaller desiccant stream 1516 is also pumped by the pump 1510 to
the top of the membrane plate structures 1504 where it flows by
gravity behind the membranes 1533 in flow channel 1508. The flow
channel 1508 is generally vertical; however the heat transfer
channel 1506 can be either vertical or horizontal, depending on
whether the air stream 1502 is vertical or horizontal. The
desiccant exiting the heat transfer channel 1506 is now directed to
a evaporator heat exchanger 1518, which, because of the corrosive
nature of most liquid desiccants such as lithium chloride, is
usually made from Titanium or some other non-corrosive material. To
prevent excessive pressure behind the membranes 1533, an overflow
device 1531 can be employed that results in excess desiccant being
drained through tube 1530 back to the tank 1514. Desiccant that has
absorbed latent energy from the air stream 1502 is now directed
through drain line 1520 through heat exchanger 1521 to pump
1509.
[0084] The structure described above has several advantages in that
the pressure on the membranes 1532 and 1533 is very low and can
even be negative essentially syphoning the desiccant through the
channels 1507 and 1508. This makes the membrane structure
significantly more reliable since the pressure on the membranes
will be minimized or even be negative resulting in performance
similar to that described in application 13/915,199. Furthermore,
since the main desiccant streams 1505 and 1506 are counter to the
air flow 1501 and 1502 respectively, the effectiveness of the
membrane plate structures 1503 and 1504 is much higher than a
cross-flow arrangement would be able to achieve.
[0085] FIG. 16 illustrates how the system from FIG. 15 can be
integrated to the system in FIG. 6 (or FIG. 7 for winter mode). The
major components from FIG. 15 are labeled in the figure as are the
components from FIG. 6. As can be seen in the figure, the system
1600A is added as an outside air treatment system where the outside
air OA (1502) is directed over the conditioner membrane plates
1504. As before, the main desiccant stream 1506 is pumped by pump
1510 in counter-flow to the air stream 1502 and the small desiccant
stream 1508 is carrying off the latent energy from the air stream
1502. The small desiccant stream is directed through heat exchanger
1521 to pump 1509 where it is pumped through regenerator membrane
plate structure 1503. The main desiccant stream 1505 is again
counter to the air stream 1501, which comprises an outside air
stream 1601 mixed with a return air stream 605. A small desiccant
stream 1507 is now used to desorb moisture from the desiccant. As
before in FIG. 6, the system of FIG. 16 is reversible by reversing
the direction of the heat pump system comprising compressor 1523,
heat exchangers 1517 and 1518, and coils 616 and 607 as well as
expansion valve 625.
[0086] It should also be clear from FIG. 16 that a conventional
two-way liquid desiccant module could be employed in lieu of
modules 1503 and 1504. Such a two-way liquid desiccant module could
have a membrane or could have no membrane and are well known in the
art.
[0087] 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.
* * * * *