U.S. patent application number 16/706340 was filed with the patent office on 2020-06-11 for liquid desiccant air-conditioning systems and methods for greenhouses and growth cells.
The applicant listed for this patent is 7AC Technologies, Inc.. Invention is credited to Peter Luttik.
Application Number | 20200182493 16/706340 |
Document ID | / |
Family ID | 70972456 |
Filed Date | 2020-06-11 |
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United States Patent
Application |
20200182493 |
Kind Code |
A1 |
Luttik; Peter |
June 11, 2020 |
LIQUID DESICCANT AIR-CONDITIONING SYSTEMS AND METHODS FOR
GREENHOUSES AND GROWTH CELLS
Abstract
This application relates generally to liquid desiccant air
conditioning (LDAC) systems and, more specifically, to liquid
desiccant air-conditioning systems for use in greenhouses and
growth cells.
Inventors: |
Luttik; Peter; (Beverly,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
7AC Technologies, Inc. |
Beverly |
MA |
US |
|
|
Family ID: |
70972456 |
Appl. No.: |
16/706340 |
Filed: |
December 6, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62776210 |
Dec 6, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 3/1417 20130101;
F24F 12/006 20130101; F24F 3/06 20130101 |
International
Class: |
F24F 3/14 20060101
F24F003/14; F24F 3/06 20060101 F24F003/06 |
Claims
1. A liquid desiccant air-conditioning system for managing
temperature and humidity conditions in a greenhouse or a growth
cell, comprising: a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough,
said first air stream entering the liquid desiccant conditioner
from a space within the greenhouse or growth cell and exiting the
liquid desiccant conditioner as supply air to the greenhouse or
growth cell; a liquid desiccant regenerator receiving the liquid
desiccant used in the liquid desiccant conditioner, and humidifying
a second air stream flowing therethrough to concentrate the liquid
desiccant and then returning the liquid desiccant to the
conditioner; and an air-to-air heat exchanger thermally coupled to
the air stream exiting the liquid desiccant conditioner or an air
stream drawn from the space within the greenhouse or growth cell
and the second air stream exiting the liquid desiccant regenerator
for cooling the second air stream and producing water therefrom;
wherein the second air stream circulates between the liquid
desiccant regenerator and the air-to-air heat exchanger within a
closed enclosure.
2. The system of claim 1, further comprising a heat source for
heating the liquid desiccant regenerator and a cold source for
cooling the liquid desiccant conditioner.
3. The system of claim 2, wherein the heat source comprises a power
generator.
4. The system of claim 3, wherein the power generator supplies
carbon dioxide to the greenhouse or growth cell.
5. The system of claim 1, further comprising a chiller system for
heating the liquid desiccant regenerator and cooling the liquid
desiccant conditioner.
6. The system of claim 1, wherein the water is used to water soil
in the greenhouse or growth cell.
7. The system of claim 1, wherein the water drives a cooling tower
that provides cooling water to the liquid desiccant
conditioner.
8. The system of claim 7, further comprising a chiller for
controlling temperature of the cooling water provided to the liquid
desiccant conditioner.
9. A method of managing temperature and humidity conditions in a
greenhouse or a growth cell using a liquid desiccant air
conditioning system, comprising: dehumidifying a first air stream
flowing through a liquid desiccant conditioner utilizing a liquid
desiccant, said first air stream being drawn into the liquid
desiccant conditioner from a space within the greenhouse or growth
cell and exiting the liquid desiccant conditioner as supply air to
the greenhouse or growth cell; receiving, in a liquid desiccant
regenerator, the liquid desiccant used in the liquid desiccant
conditioner, and humidifying a second air stream flowing through
the liquid desiccant regenerator to concentrate the liquid
desiccant and then returning the liquid desiccant to the
conditioner; and cooling the second air stream humidified by the
liquid desiccant regenerator and producing water therefrom using an
air-to-air heat exchanger thermally coupled to the air stream
exiting the liquid desiccant conditioner or an air stream drawn
from the space within the greenhouse or growth cell; and
circulating the second air stream between the liquid desiccant
regenerator and the air-to-air heat exchanger within a closed
enclosure.
10. The method of claim 9, further comprising heating the liquid
desiccant regenerator and cooling the liquid desiccant
conditioner.
11. The method of claim 10, wherein heating is performed utilizing
heat from a power generator.
12. The method of claim 11, wherein the power generator supplies
carbon dioxide to the greenhouse or growth cell.
13. The method of claim 9, further comprising using the water to
water soil in the greenhouse or growth cell.
14. The method of claim 9, further comprising providing the water
to a cooling tower that provides cooling water to the liquid
desiccant conditioner.
15. The method of claim 14, further comprising controlling
temperature of the cooling water provided to the liquid desiccant
conditioner using a chiller.
16. A method of managing temperature and humidity conditions in a
greenhouse or a growth cell using a liquid desiccant air
conditioning system, comprising: (a) dehumidifying, using a liquid
desiccant, a first air stream drawn from a space within the
greenhouse or growth cell to be provided as supply air to the
greenhouse or growth cell; (b) concentrating the liquid desiccant
used in (a) by humidifying a second air stream; (c) cooling the
second air stream to produce water therefrom using the first air
stream or an air stream received from the space within the
greenhouse or growth cell; and (d) circulating the second air
stream in a closed enclosure for repeating (b) and (c).
17. A liquid desiccant air-conditioning system for managing
temperature and humidity conditions in a greenhouse or a growth
cell, comprising: a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough to
be provided as supply air to the greenhouse or growth cell, said
first air stream entering the liquid desiccant conditioner from a
space within the greenhouse or growth cell; a liquid desiccant
regenerator receiving the liquid desiccant used in the liquid
desiccant conditioner, and utilizing a second air stream flowing
therethrough to concentrate the liquid desiccant, and then
returning the liquid desiccant to the conditioner, wherein the
liquid desiccant regenerator heats and humidifies the second air
stream, said second air stream entering the liquid desiccant
regenerator from outside the greenhouse or growth cell and exiting
the liquid desiccant regenerator to be exhausted outside the
greenhouse or growth cell; an air-to-air heat exchanger thermally
coupled to the first air stream exiting the liquid desiccant
conditioner and the second air stream exiting the liquid desiccant
regenerator for heating the first air stream before the first air
stream is provided as the supply air to the greenhouse or growth
cell and the second air stream is exhausted from the greenhouse or
growth cell.
18. The system of claim 17, further comprising a heat source for
heating the liquid desiccant regenerator and a cold source for
cooling the liquid desiccant conditioner.
19. The system of claim 18, wherein the heat source comprises a
power generator.
20. The system of claim 19, wherein the power generator supplies
carbon dioxide to the greenhouse or growth cell.
21. The system of claim 17, further comprising a chiller system for
heating the liquid desiccant regenerator and cooling the liquid
desiccant conditioner.
22. A liquid desiccant air-conditioning system for managing
temperature and humidity conditions in a greenhouse or a growth
cell, comprising: a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough to
be provided as supply air to the greenhouse or growth cell, said
first air stream entering the liquid desiccant conditioner from a
space within the greenhouse or growth cell; a liquid desiccant
regenerator receiving the liquid desiccant used in the liquid
desiccant conditioner, and utilizing a second air stream flowing
therethrough to concentrate the liquid desiccant, and then
returning the liquid desiccant to the conditioner, wherein the
liquid desiccant regenerator heats and humidifies the second air
stream, said second air stream provided to the liquid desiccant
regenerator from outside the greenhouse or growth cell and exiting
the liquid desiccant regenerator to be exhausted outside the
greenhouse or growth cell; an air-to-air heat exchanger thermally
coupled to the second air stream prior to entering the liquid
desiccant regenerator and the second air stream exiting the liquid
desiccant regenerator for preheating the second air stream entering
the liquid desiccant regenerator and post cooling the second air
stream exiting the liquid desiccant regenerator.
23. The system of claim 22, further comprising a heat source for
heating the liquid desiccant regenerator and a cold source for
cooling the liquid desiccant conditioner.
24. The system of claim 23, wherein the heat source comprises a
power generator.
25. The system of claim 24, wherein the power generator supplies
carbon dioxide to the greenhouse or growth cell.
26. The system of claim 22, further comprising a chiller system for
heating the liquid desiccant regenerator and cooling the liquid
desiccant conditioner.
27. A liquid desiccant air-conditioning system for managing
temperature and humidity conditions in a greenhouse or a growth
cell, comprising: a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough to
be provided as supply air to the greenhouse or growth cell, said
first air stream entering the liquid desiccant conditioner from a
space within the greenhouse or growth cell; a liquid desiccant
regenerator receiving the liquid desiccant used in the liquid
desiccant conditioner, and utilizing a second air stream flowing
therethrough to concentrate the liquid desiccant, and then
returning the liquid desiccant to the conditioner, wherein the
liquid desiccant regenerator heats and humidifies the second air
stream, said second air stream provided to the liquid desiccant
regenerator from outside the greenhouse or growth cell and exiting
the liquid desiccant regenerator to be exhausted outside the
greenhouse or growth cell; an air-to-air heat exchanger thermally
coupled to the first air stream prior to entering the liquid
desiccant conditioner and the first air stream exiting the liquid
desiccant conditioner for precooling the first air stream entering
the liquid desiccant conditioner and post heating the first air
stream exiting the liquid desiccant conditioner.
28. The system of claim 27, further comprising a heat source for
heating the liquid desiccant regenerator and a cold source for
cooling the liquid desiccant conditioner.
29. The system of claim 28, wherein the heat source comprises a
power generator.
30. The system of claim 29, wherein the power generator supplies
carbon dioxide to the greenhouse or growth cell.
31. The system of claim 27, further comprising a chiller system for
heating the liquid desiccant regenerator and cooling the liquid
desiccant conditioner.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Provisional
Patent Application No. 62/776210 filed on Dec. 6, 2018 entitled
LIQUID DESICCANT AIR-CONDITIONING SYSTEMS AND METHODS FOR
GREENHOUSES, which is hereby incorporated by reference.
BACKGROUND
[0002] The present application relates generally to liquid
desiccant air conditioning (LDAC) systems and, more specifically,
to liquid desiccant air-conditioning systems for greenhouses and
closed building growth cells (also known as grow rooms).
[0003] High value added agricultural production is increasingly
done in completely controlled production environment in closed
greenhouses and growth cells.
[0004] Greenhouses have direct access to sunlight, and have large
sensible and latent loads during the summer, while heating and
dehumidification is required in the winter. In winter, lights are
an additional heat source to maintain 12-16 hour growth
periods.
[0005] Growth cells are within closed buildings with limited or no
ventilation. Lighting is artificial. Large volumes of water are
added to the plants, which use it for growth and evaporation. This
will also significantly cool the space. Heating sources are lights
and production of carbon dioxide (CO2) supplied to the space. The
lights can be low efficiency sodium and natrium lights or high
efficiency LEDs. CO2 can be provided from burning gas or from
bottled gas.
[0006] While most greenhouses and growth cells require significant
cooling, growth cells with LEDs and bottled CO2 have much lower or
even negative cooling or heating requirements year round.
[0007] Greenhouse and growth-cell production conditions differ not
only by crop but also by crop maturity. For example, many products
maximize production at high relatively humidity (60-80%), but
humidity levels above 80% can lead to significant damage to crops
due to growth of pathogens. Some crops require much lower
humidities, e.g., 50% RH for some marijuana products.
[0008] Various embodiments disclosed herein relate to combining
superior dehumidification of liquid desiccants with appropriate
energy management to maintain the required conditions at minimum
temperature requirements.
BRIEF SUMMARY
[0009] A liquid desiccant air-conditioning system in accordance
with one or more embodiments is provided for managing temperature
and humidity conditions in a greenhouse or a growth cell. The
system includes a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough.
The first air stream enters the liquid desiccant conditioner from a
space within the greenhouse or growth cell and exits the liquid
desiccant conditioner as supply air to the greenhouse or growth
cell. The system also includes a liquid desiccant regenerator
receiving the liquid desiccant used in the liquid desiccant
conditioner, and humidifying a second air stream flowing
therethrough to concentrate the liquid desiccant and then returning
the liquid desiccant to the conditioner. An air-to-air heat
exchanger is thermally coupled to the air stream exiting the liquid
desiccant conditioner or an air stream drawn from the space within
the greenhouse or growth cell and the second air stream exiting the
liquid desiccant regenerator for cooling the second air stream and
producing water therefrom. The second air stream circulates between
the liquid desiccant regenerator and the air-to-air heat exchanger
within a closed enclosure.
[0010] In accordance with one or more embodiments, a method is
provided for managing temperature and humidity conditions in a
greenhouse or a growth cell using a liquid desiccant air
conditioning system. The method incudes the steps of: dehumidifying
a first air stream flowing through a liquid desiccant conditioner
utilizing a liquid desiccant, the first air stream being drawn into
the liquid desiccant conditioner from a space within the greenhouse
or growth cell and exiting the liquid desiccant conditioner as
supply air to the greenhouse or growth cell; receiving, in a liquid
desiccant regenerator, the liquid desiccant used in the liquid
desiccant conditioner, and humidifying a second air stream flowing
through the liquid desiccant regenerator to concentrate the liquid
desiccant and then returning the liquid desiccant to the
conditioner; and cooling the second air stream humidified by the
liquid desiccant regenerator and producing water therefrom using an
air-to-air heat exchanger thermally coupled to the air stream
exiting the liquid desiccant conditioner or an air stream drawn
from the space within the greenhouse or growth cell; and
circulating the second air stream between the liquid desiccant
regenerator and the air-to-air heat exchanger within a closed
enclosure.
[0011] A liquid desiccant air-conditioning system in accordance
with one or more embodiments is disclosed for managing temperature
and humidity conditions in a greenhouse or a growth cell. The
system includes a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough to
be provided as supply air to the greenhouse or growth cell, the
first air stream entering the liquid desiccant conditioner from a
space within the greenhouse or growth cell. The system also
includes a liquid desiccant regenerator receiving the liquid
desiccant used in the liquid desiccant conditioner, and utilizing a
second air stream flowing therethrough to concentrate the liquid
desiccant, and then returning the liquid desiccant to the
conditioner. The liquid desiccant regenerator heats and humidifies
the second air stream. The second air stream enters the liquid
desiccant regenerator from outside the greenhouse or growth cell
and exits the liquid desiccant regenerator to be exhausted outside
the greenhouse or growth cell. The system further includes an
air-to-air heat exchanger thermally coupled to the first air stream
exiting the liquid desiccant conditioner and the second air stream
exiting the liquid desiccant regenerator for heating the first air
stream before the first air stream is provided as the supply air to
the greenhouse or growth cell and the second air stream is
exhausted from the greenhouse or growth cell.
[0012] A liquid desiccant air-conditioning system in accordance
with one or more embodiments is provided for managing temperature
and humidity conditions in a greenhouse or a growth cell. The
system includes a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough to
be provided as supply air to the greenhouse or growth cell. The
first air stream enters the liquid desiccant conditioner from a
space within the greenhouse or growth cell. A liquid desiccant
regenerator receives the liquid desiccant used in the liquid
desiccant conditioner, and utilizes a second air stream flowing
therethrough to concentrate the liquid desiccant, and then returns
the liquid desiccant to the conditioner, wherein the liquid
desiccant regenerator heats and humidifies the second air stream,
the second air stream provided to the liquid desiccant regenerator
from outside the greenhouse or growth cell and exiting the liquid
desiccant regenerator to be exhausted outside the greenhouse or
growth cell. An air-to-air heat exchanger is thermally coupled to
the second air stream prior to entering the liquid desiccant
regenerator and the second air stream exiting the liquid desiccant
regenerator for preheating the second air stream entering the
liquid desiccant regenerator and post cooling the second air stream
exiting the liquid desiccant regenerator.
[0013] A liquid desiccant air-conditioning system in accordance
with one or more embodiments is provided for managing temperature
and humidity conditions in a greenhouse or a growth cell. The
system includes a liquid desiccant conditioner utilizing a liquid
desiccant to dehumidify a first air stream flowing therethrough to
be provided as supply air to the greenhouse or growth cell. The
first air stream enters the liquid desiccant conditioner from a
space within the greenhouse or growth cell. A liquid desiccant
regenerator receives the liquid desiccant used in the liquid
desiccant conditioner, and utilizes a second air stream flowing
therethrough to concentrate the liquid desiccant, and then returns
the liquid desiccant to the conditioner, wherein the liquid
desiccant regenerator heats and humidifies the second air stream,
the second air stream provided to the liquid desiccant regenerator
from outside the greenhouse or growth cell and exits the liquid
desiccant regenerator to be exhausted outside the greenhouse or
growth cell. An air-to-air heat exchanger is thermally coupled to
the first air stream prior to entering the liquid desiccant
conditioner and the first air stream exiting the liquid desiccant
conditioner for precooling the first air stream entering the liquid
desiccant conditioner and post heating the first air stream exiting
the liquid desiccant conditioner.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 is a simplified diagram illustrating a prior art
liquid desiccant air-conditioning system.
[0015] FIG. 2 illustrates a prior art three-way heat exchanger
block of a liquid desiccant air conditioning system.
[0016] FIG. 3 is a simplified diagram illustrating a prior art
three-way heat exchanger panel assembly in the heat exchanger
block.
[0017] FIG. 4 is a simplified diagram illustrating another prior
art liquid desiccant air conditioning system.
[0018] FIG. 5 is a Psychrometric charts showing air properties in
summer operation.
[0019] FIG. 6 is a simplified block diagram illustrating a liquid
desiccant air-conditioning system in accordance with one or more
embodiments.
[0020] FIG. 7 is a Psychrometric chart showing air properties in a
winter operation.
[0021] FIGS. 8A and 8B are simplified block diagrams illustrating
liquid desiccant air-conditioning systems with energy recovery for
improved efficiency.
[0022] FIG. 9 is a simplified block diagram illustrating another
liquid desiccant air-conditioning system in accordance with one or
more embodiments.
DETAILED DESCRIPTION
[0023] FIG. 1 illustrates an exemplary prior art liquid desiccant
air conditioning system as disclosed in U.S. Patent Application
Publication No. 20120125020 and U.S. Pat. Nos. 9,243,810 and
9,631,848 used in a cooling and dehumidifying mode of operation.
(Liquid desiccant air conditioning systems can also operate in
various other modes including cooling, heating, cooling and
humidification, heating and dehumidification, and heating and
humidification modes.) A conditioner 101 comprises a set of 3-way
heat exchange plate structures that are internally hollow. A cold
heat transfer fluid is generated in a cold source 107 and
introduced into the plates. A liquid desiccant solution at 114 is
flowed onto the outer surface of the plates. The liquid desiccant
runs over the outer surface of each of the plates behind a thin
membrane, which is located between the air flow and the surface of
the plates. Return air, outside air 103, or mixture thereof is
blown between the set of conditioner plates. The liquid desiccant
on the surface of the plates attracts the water vapor in the air
flow and the cooling water (heat transfer fluid) inside the plates
helps to inhibit the air temperature from rising. The treated air
104 is introduced into a building space.
[0024] The liquid desiccant is collected at the other end of the
conditioner plates at 111 and is transported through a heat
exchanger 113 to the liquid desiccant entry point 115 of the
regenerator 102 where the liquid desiccant is distributed across
similar plates in the regenerator. Return air, outside air 105, or
a mixture thereof is blown across the regenerator plates and water
vapor is transported from the liquid desiccant into the leaving air
stream 106. An optional heat source 108 provides the driving force
for the regeneration. A hot heat transfer fluid 110 from a heat
source can be flowed inside the plates of the regenerator similar
to the cold heat transfer fluid in the conditioner. Again, the
re-concentrated liquid desiccant is collected at one end of the
plates and returned via the heat exchanger to the conditioner.
Since there is no need for either a collection pan or bath, the
desiccant flow through the regenerator can be horizontal or
vertical. Air and water is preferably in counterflow to each other.
They can also be a horizontal or vertical flow. A variety of
configurations are possible from all flows being vertical, to a
combination of horizontal and vertical flows in crossflow, to all
flows being horizontal in flat plate structures.
[0025] An optional heat pump 116 can be used to provide cooling and
heating of the liquid desiccant. It is also possible to connect a
heat pump between the cold source 107 and the hot source 108, which
is thus pumping heat from the cooling fluids rather than the liquid
desiccant. Cold sources could comprise an indirect evaporative
cooler, a cooling tower, geothermal storage, cold water networks,
black roof panel that cools down water during the night, and cold
storage options like an ice box. Heat sources could include waste
heat from power generation, solar heat, geothermal heat, heat
storage, and hot water networks. Those skilled in the art will
understand that a wide variety of other sources for heating and
cooling are possible including, e.g., heat from refrigeration in
stores to heat from compressors in industrial applications.
[0026] FIG. 2 illustrates an exemplary prior art 3-way heat
exchanger comprising a set of plate structures stacked in a block
as disclosed in U.S. Pat. No. 9,308,490. A liquid desiccant enters
the structure through ports 304 and is directed behind a series of
membranes as described in FIG. 1. The liquid desiccant is collected
and removed through ports 305. A cooling or heating fluid is
provided through ports 306 and runs counter to the air stream 301
inside the hollow plate structures, again as described in FIG. 1
and in greater detail in FIG. 3. The cooling or heating fluids exit
through ports 307. The treated air 302 is directed to a space in a
building or is exhausted as the case may be. The figure illustrates
a 3-way heat exchanger in which the air and heat transfer fluid are
in a primarily vertical orientation.
[0027] FIG. 3 schematically illustrates operation of an exemplary
prior art membrane plate assembly or structure as disclosed in U.S.
Pat. No. 9,631,848. The air stream 251 flows counter to a cooling
fluid stream 254. Membranes 252 contain a liquid desiccant 253 that
is falling along the wall 255 that contains the heat transfer fluid
254. Water vapor 256 entrained in the air stream is able to
transfer through the membrane 252 and is absorbed into the liquid
desiccant 253. The heat of condensation of water 258 that is
released during the absorption is conducted through the wall 255
into the heat transfer fluid 254. Sensible heat 257 from the air
stream is also conducted through the membrane 252, liquid desiccant
253 and wall 255 into the heat transfer fluid 254.
[0028] FIG. 4 illustrates a schematic representation of another
prior art liquid desiccant air conditioner system operating in a
cooling mode, as disclosed in U.S. Pat. No. 10,323,867. Similar
liquid air conditioning systems are disclosed in U.S. Patent
Application Publication No. 20120125020 and U.S. Pat. Nos.
9,243,810 and 9,631,848. A three-way heat and mass exchanger
conditioner 503 (which is similar to the conditioner 101 of FIG. 1)
receives an air stream 501 from the outside ("OA"). Fan 502 pulls
the air 501 through the conditioner 503 wherein the air is cooled
and dehumidified. The resulting cool, dry air 504 ("SA") is
supplied to a space for occupant comfort. The three-way conditioner
503 receives a concentrated desiccant 527 in the manner explained
under FIGS. 1-3. It is preferable to use a membrane on the
three-way conditioner 503 to contain the desiccant and inhibit it
from being distributed into the air stream 504. The diluted
desiccant 528, which contains the captured water vapor is
transported to a heat and mass exchanger regenerator 522.
Furthermore, chilled water 509 is provided by pump 508, which
enters the conditioner module 503 where it picks up heat from the
air as well as latent heat released by the capture of water vapor
in the desiccant 527. The warmer water 506 is brought to the heat
exchanger 507 on the chiller system 530. The liquid desiccant 528
leaves the conditioner 503 and is moved through the optional heat
exchanger 526 to the regenerator 522 by pump 525. The chiller
system 530 comprises a water to refrigerant evaporator heat
exchanger 507, which cools the circulating cooling fluid 506. The
liquid, cold refrigerant 517 evaporates in the heat exchanger 507
thereby absorbing the thermal energy from the cooling fluid 506.
The gaseous refrigerant 510 is now re-compressed by compressor 511.
The compressor 511 ejects hot refrigerant gas 513, which is
liquefied in the condenser heat exchanger 515. The liquid
refrigerant exiting the condenser 514 then enters expansion valve
516, where it rapidly cools and exits at a lower pressure. The
condenser heat exchanger 515 now releases heat to another cooling
fluid loop 519 which brings hot heat transfer fluid 518 to the
regenerator 522. Circulating pump 520 brings the heat transfer
fluid back to the condenser 515. The three-way regenerator 522 thus
receives a dilute liquid desiccant 528 and hot heat transfer fluid
518. A fan 524 brings outside air 521 ("OA") through the
regenerator 522. The outside air picks up heat and moisture from
the heat transfer fluid 518 and desiccant 528 which results in hot
humid exhaust air ("EA") 523. The compressor 511 receives
electrical power 512. The fans 502 and 524 receive electrical power
505 and 529, respectively. Pumps 508, 520, and 525 have relatively
low power consumption.
[0029] Various embodiments disclosed herein relate to use of liquid
desiccant air-conditioning systems in greenhouses and growth
cells.
[0030] Greenhouses process recirculated air to maintain warm and
humid conditions (e.g., 30 C/80% RH). Liquid desiccant air
conditioning systems have the ability to manage heat and humidity
independently and can significantly improve greenhouse control over
growth cycles with sharply increasing humidification loads as
plants mature. Greenhouses tend to have a large sensible load from
lights.
[0031] Liquid desiccant air conditioning systems work most
efficiently at moderate concentrations of liquid desiccant (e.g.,
15-25%), which fits well with the target RH (relative humidity) of
about 70-80% in greenhouses, including the latent and sensible
loads.
[0032] Using regenerator air to maintain warm temperatures in the
greenhouse can further improve efficiency. A heat exchanger can be
used to preheat/postcool regenerator air during cold periods. One
heat exchanger can be used to do both using a set of dampers.
[0033] Greenhouses and growth cells operate at high temperatures
and high humidities, typically 30 C and an RH of 80%. Cooling loads
in greenhouses include significant solar heat, but in growth cells,
the heat supply is nearly completely from artificial lights. The
plants humidify and cool air. Air is refreshed to allow people to
operate inside. Greenhouses have high sensible loads from sunlight
and heating through low insulated walls. In the winter, the solar
loads are reduced and partially replaced with artificial lighting,
while heat losses through the walls require significant added heat.
In-building growth cells rely 100% on artificial light, but they do
have rest periods, which can be during the day while low cost night
rates are used for powering the lights. Using heat pipes and plate
heat exchangers for precooling and then reheating return air
reduces the temperature at which dehumidification takes place and
thus the liquid desiccant concentration required for effective
dehumidification. This allows the regenerator to maintain the
concentration at a much lower temperature. Thus, the chiller can
operate at lower temperatures with lower lift.
[0034] Urban agriculture uses closed growth cells with only LED
lighting to grow a variety of crops. Humidity loads differ over the
growth cycle, but optimal conditions tend to be stable at about 30
C and 80% RH. The ability of liquid desiccant air conditioning
systems to efficiently manage these different loads effectively
while maintaining a constant supply is significantly enhanced by
adding the ability to post cool or post heat conditioned air with
regenerator or unconditioned air.
[0035] With a damper, a single heat exchanger can support the
liquid desiccant air conditioning system during dehumidification
and either sensible cooling or sensible heating. Referring to FIG.
5, during the hot and humid outside air conditions 601 for the
regenerator, regeneration requires higher temperature at 602. At
the RH of 602, conditioning can be done from the return air
condition 603 to condition 604, which is warm and dry. Supply air
604 is humidified 612 and heated 613 because of the typical
conditions in a greenhouse/growth cell humidification results when
plants desorb large amounts of water to pump nutrients from the
roots to the plant and heating results from radiation in a
greenhouse or lights in a growth cell.
[0036] Typically, liquid desiccant at 30% or higher requires air
with an RH of less than 40% to regenerate 630. While liquid
desiccant at 20% can be regenerated at an RH of about 60% at
631.
[0037] However, typically compressor performance benefits from
dehumidifying and cooling air at the lower concentration 605. The
main driver for that is that the regenerator can fully
reconcentrate the liquid desiccant at 606. The disadvantage is that
the greenhouse air is dry and cool, while plants tend to prefer dry
and warm conditions for optimal growth. The heat exchanger 610/611
can be used to heat up the cool air from the conditioner with the
hot air from the regenerator.
[0038] As a result total lift of the system is only 620 rather than
621 with the higher concentration.
[0039] FIG. 6 shows a liquid desiccant air conditioning system for
a greenhouse (or growth cell) 700 that includes a heat exchanger
701, which takes the supply air 702 from the conditioner 703 and
warms the supply air 702 up with the regeneration air 704 from
regenerator 705 before returning it to the space 706 in the
greenhouse 700 to be air conditioned. Regenerator exhaust air is
expelled from the greenhouse at 707. Return air 708 from the space
706 is provided to the conditioner 703, and the outside air 709 is
used by the regenerator 705 to concentrate the liquid desiccant.
The water (i.e., heat transfer fluid) and desiccant circuits in and
between conditioner 703 and regenerator 705 are not shown. These
can be as described in prior art, e.g., in FIG. 4.
[0040] As depicted in FIG. 7, one advantage of the liquid desiccant
air conditioning systems is that they can dehumidify at low
concentrations of liquid desiccant while maintaining high
temperatures and controlling RH levels. By managing the flow of
regenerator air through the heat exchanger with the processed
conditioner air, temperature and RH can be managed in a narrow
bandwidth.
[0041] In winter conditions, outside air can be cold with a High
RH, the high humidity loads will need to be removed, while
significant heat needs to be added.
[0042] There are two possible approaches. One is to use highly
concentrated liquid desiccant that dehumidifies and warms the air.
This requires significant additional heat to regenerate the liquid
desiccant with the cold outside air. Part of that can be recovered
through an extra heat exchanger for the regenerator.
[0043] Alternatively, the heat exchanger can be used to precool and
then reheat the process air. Using a heat pump, the air can be
further cooled to reach the target DP at 80% RH and a cooler
temperature. This allows the regenerator to regenerate with just
the condenser heat of the heatpump. However, additional waste heat
or gas heat is then needed to post heat the process air.
Determining which is the lower cost solution depends not only on
starting conditions and loads in the greenhouse/growth cell and the
outside air conditions esp. HR, but also on the availability and
quality of waste heat, the cost of components, and the
effectiveness of the liquid desiccant heat exchanger.
[0044] Detailed thermodynamic models can be used to evaluate
alternative strategies and optimize control conditions.
[0045] FIGS. 8A and 8B are simplified block diagrams illustrating
liquid desiccant air-conditioning systems with energy recovery for
improved efficiency. In FIG. 8A, the air stream 720 in the
regenerator 705 is preheated and post cooled. Outside air flows
into a heat exchanger 701, which preheats the air stream 720 with
the air stream exiting the regenerator 705 before it is exhausted.
In FIG. 8B, the air stream 722 in the conditioner 703 is precooled
and post heated during the winter season. The air stream 722 flows
through a heat exchanger 701, which precools the air stream with
the airstream exiting the conditioner 703. The water (i.e., heat
transfer fluid) and desiccant circuits in and between conditioner
703 and regenerator 705 are not shown. These can be as described in
prior art, e.g., in FIG. 4.
[0046] FIG. 9 illustrates a liquid desiccant air conditioning
system in accordance with one or more embodiments used in a
greenhouse (or growth cell) 801. The greenhouse 801 has a
conditioner 802 that take air from a space 803 in the greenhouse
801 and returns it to the greenhouse space after dehumidifying it
to a DP of 45-60 F. The optimal humidity level is crop dependent,
with some crops preferring higher absolute humidity levels and
others requiring dryer conditions. For example, tomatoes grow best
at RH levels as high as 70% and temperatures above 75 F. For other
crops, the RH level should not exceed 50-60% for optimal quality.
RH levels are a combination of DB temperature and absolute humidity
levels. Optimal temperatures even differ by time of day, with
temperature during dark periods being lower than when light is
present to allow the plant to grow.
[0047] Maintaining the concentration of the liquid desiccant 804
used in the conditioner 802 is needed to maintain the RH of the air
stream 830 coming out of the conditioner 802. The liquid desiccant
804 is diluted in the conditioner 802 as humidity as absorbed in
the liquid desiccant 804. The regenerator 805 is used to
reconcentrate the liquid desiccant 804 before returning it to the
conditioner 802. Waste heat 806 is used to heat up the air flowing
through the regenerator 805 to a temperature of 40 to 60 C (110-150
F). The waste heat 806 can come from various sources such as, e.g.,
solar power or a power generator 807, which results in CO2
production 809. Cooling the generator 807 increases power
production 808.
[0048] The air stream 831 flowing through regenerator 805 is
enclosed in a space 810 and circulated by fan 811 to an air-to-air
heat exchanger 812 that uses greenhouse air to cool the air to a DP
equal to the DB condition in the greenhouse 801. This produces
water 820, which can either be used to water soil in the greenhouse
801 or to drive a cooling tower 821 that provide cooling water 822
to the conditioner 802. A small chiller 823 can be used to
accurately control cooling water conditions and thus DP depending
on plant conditions and the quality and the amount of waste heat
availability at any point during the day or year.
[0049] As noted above, the air-to-air heat exchanger 812 that uses
greenhouse air to cool the air in the regenerator space 810. The
greenhouse air can be provided to the air-to-air heat exchanger 812
in different ways. In one embodiment, the air stream 830 coming out
of the conditioner 802 is flowed through the heat exchanger 812 and
then returned to the greenhouse space 803. In another embodiment,
the air stream 830 coming out of the conditioner 802 flows directly
to the greenhouse space 803 as indicated at 840. Air from the
greenhouse space 803 is directly provided to the heat exchanger 812
as indicated at 832. In yet another embodiment, some of the air
stream 830 coming out of the conditioner 802 is provided to the air
space 803 and some of the air stream 830 coming out of the
conditioner 802 is flowed through the heat exchanger 812.
[0050] This results in a closed system that does not require extra
heat from either the sun or lamps to compensate for the cooling
linked to the evaporation by the plants. It also minimizes water
usage for use by the plant and the cooling tower. It uses the heat
needed to drive the lights through cogeneration and/or to produce
the CO2 that combined with water is used by the plant to build
carbohydrate molecules. This minimizes energy and water usage by
greenhouses, which has become a major concern during the growth of
high intensity and highly productive enclosed in-building
agriculture. One advantage of enclosed agro systems is a smaller
physical foot print as production per m2 can increase 10 to 100
fold. Use of liquid desiccant systems in accordance with various
embodiments can significantly reduce the energy foot print. Keeping
the greenhouse closed also reduces risk of contamination of the
crop as well as environmental concerns like odor from the growing
process.
[0051] 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.
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