U.S. patent application number 15/933019 was filed with the patent office on 2018-07-26 for contained growing space and environmental control system.
The applicant listed for this patent is Harvest Air, LLC. Invention is credited to Christopher Whaley, John Zimmerman.
Application Number | 20180206416 15/933019 |
Document ID | / |
Family ID | 58488475 |
Filed Date | 2018-07-26 |
United States Patent
Application |
20180206416 |
Kind Code |
A1 |
Zimmerman; John ; et
al. |
July 26, 2018 |
CONTAINED GROWING SPACE AND ENVIRONMENTAL CONTROL SYSTEM
Abstract
A controlled and closed agricultural system includes a growing
space and an air handling system having a heat exchanger and
cooling coil. The heat exchanger is capable of transferring
sensible and latent heat and is in fluid connection with a
recirculating air duct and an outside air duct. The recirculating
air duct is in fluid connection with the growing space and one or
more recirculation fans, while the outside air duct is in fluid
connection with one or more outside air fans positioned to cause
outside air to flow countercurrent to recirculating air through the
heat exchanger. A cooling coil is positioned within the
recirculating air duct, downstream of and in series with the heat
exchanger. The cooling coil circulates a heat transfer fluid to
remove additional heat from the recirculating air.
Inventors: |
Zimmerman; John; (Dallas,
TX) ; Whaley; Christopher; (Arlington, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Harvest Air, LLC |
Dallas |
TX |
US |
|
|
Family ID: |
58488475 |
Appl. No.: |
15/933019 |
Filed: |
March 22, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14878066 |
Oct 8, 2015 |
|
|
|
15933019 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A01G 9/246 20130101;
A01G 9/24 20130101; F24F 3/147 20130101; A01G 9/18 20130101; Y02A
40/268 20180101; F24F 3/1423 20130101; A01G 7/02 20130101; A01G
7/045 20130101; Y02A 40/25 20180101; A01G 9/20 20130101 |
International
Class: |
A01G 9/18 20060101
A01G009/18; A01G 9/24 20060101 A01G009/24; A01G 7/02 20060101
A01G007/02; A01G 9/20 20060101 A01G009/20; A01G 7/04 20060101
A01G007/04 |
Claims
1. A controlled agricultural system, comprising: a growing space;
and a heat exchanger capable of transferring sensible and latent
heat, the heat exchanger in fluid connection with both a
recirculating air duct and an outside air duct, the recirculating
air duct in fluid connection with the growing space and one or more
recirculation fans, the outside air duct in fluid connection with
one or more outside air fans positioned to cause outside air to
flow countercurrent to recirculating air through the heat
exchanger; and a cooling coil within the recirculating air duct,
downstream of and in series with the heat exchanger, the cooling
coil circulating a heat transfer fluid to remove heat from the
recirculating air.
2. The controlled agricultural system of claim 1, wherein the
growing space comprises a closed green house.
3. The controlled agricultural system of claim 1, wherein the
growing space is closed and comprises light impermeable outer walls
and grow lights positioned inside the closed growing space.
4. The controlled agricultural system of claim 1, wherein the
cooling coil comprises a direct expansion evaporation cooling
coil.
5. The controlled agricultural system of claim 4, further
comprising a compressor and a condensing coil external to the
recirculating air duct for removing heat from the heat transfer
fluid.
6. The controlled agricultural system of claim 1, further
comprising a recirculation damper within the outside air duct and
positioned to recirculate a portion of the outside air from
downstream of the heat exchanger to upstream of the heat
exchanger.
7. The controlled agricultural system of claim 1, further
comprising a heat source positioned to provide heat to the
recirculating air downstream of the heat exchanger.
8. The controlled agricultural system of claim 1, further
comprising a CO.sub.2 monitor positioned to monitor a CO.sub.2
content in the recirculating air duct.
9. The controlled agricultural system of claim 8, further
comprising a CO.sub.2 generator and CO.sub.2 controller in
communication with the CO.sub.2 monitor, the CO.sub.2 generator
having an outlet positioned to add CO.sub.2 to the recirculating
air duct.
10. A controlled agricultural system, comprising: a growing space;
and a first heat exchanger capable of transferring sensible heat,
the first heat exchanger in fluid connection with both a
recirculating air duct and an outside air duct, the recirculating
air duct in fluid connection with the growing space and one or more
recirculation fans, the outside air duct in fluid connection with
one or more outside air fans positioned to cause outside air to
flow countercurrent to recirculating air; and; a second heat
exchanger capable of transferring latent heat, the second heat
exchanger in fluid connection with the recirculating air duct in
series with the heat wheel such that recirculating air passes
through the second heat exchanger prior to passing through the
first heat exchanger; and a cooling coil within the recirculating
air duct, downstream of and in series with the first heat
exchanger, the cooling coil circulating a heat transfer fluid to
remove heat from the recirculating air.
11. The controlled agricultural system of claim 10, wherein the
growing space comprises a closed green house.
12. The controlled agricultural system of claim 10, wherein the
growing space is closed and comprises light impermeable outer walls
and grow lights positioned inside the closed growing space.
13. The controlled and closed agricultural system of claim 10,
further comprising a compressor and a condensing coil external to
the recirculating air duct for removing heat from the heat transfer
fluid, and wherein the cooling coil comprises a direct expansion
evaporation cooling coil.
14. A method for treating air within a growing space of a closed
agricultural system, the method comprising: recirculating air from
a contained growing space through an air handling system, the air
handling system comprising at least one heat exchanger to reduce
the energy content of the recirculating air; passing the
recirculating air exiting the at least one heat exchanger across a
cooling coil circulating a heat transfer fluid to further reduce
the heat content of the recirculating air; returning the
recirculating air passing the cooling coil to the contained growing
space; and passing outside air through the at least one additional
heat exchanger, the outside air passing counter-current to and
separated from the recirculating air.
15. The method of claim 14, further comprising circulating the heat
transfer fluid through a compressor and a condensing coil while
passing outside air across the condensing coil to cool and condense
the heat transfer fluid, and wherein the cooling coil comprises a
direct expansion evaporator cooling coil.
16. The method of claim 14, wherein the at least one heat exchanger
comprises an enthalpy wheel.
17. The method of claim 14, wherein the at least one heat exchanger
comprises a desiccant wheel and a heat wheel.
18. The method of claim 14, further comprising monitoring a
temperature and humidity of the recirculating air.
19. The method of claim 14, further comprising controlling the
temperature and humidity of the growing space by monitoring the
temperature and humidity of the recirculating air in the
recirculating air duct downstream of the cooling coil and
controlling operation of the at least one heat exchanger and the
cooling coil.
20. A controlled air system, comprising: a contained space; a heat
exchanger capable of transferring sensible and latent heat, the
heat exchanger in fluid connection with a bifurcated duct, the duct
having a recirculating air portion and an outside air portion, the
recirculating air portion in fluid connection with the contained
space and one or more recirculation fans, the outside air portion
in fluid connection with one or more outside air fans positioned to
cause outside air to flow countercurrent to recirculating air; and
a cooling coil within the recirculating air portion of the
bifurcated duct, downstream of and in series with the heat
exchanger, the cooling coil circulating a heat transfer fluid to
remove heat from the recirculating air.
Description
INCORPORATION BY REFERENCE STATEMENT
[0001] This application claims priority to U.S. application Ser.
No. 14/878,066 filed on Oct. 8, 2015, the content of which is
hereby expressly incorporated herein by reference in its
entirety.
BACKGROUND
1. Field of the Presently Disclosed and/or Claimed Inventive
Concepts
[0002] The inventive concepts disclosed and claimed herein relate
generally to systems and methods for controlling the interior
environment of an enclosure, and more particularly, but not by way
of limitation, to systems and methods for controlling the
temperature, humidity, and optionally CO.sub.2 levels in a
contained space.
2. Brief Description of Related Art
[0003] Greenhouses require temperature and humidity control to
maintain dry foliage and plant health. Lighting can cause excessive
heat and high humidity, especially free water on the plant foliage,
promotes the development of foliar diseases, such as tomato blight,
gray mold, and mildews in various crops. Such diseases
substantially reduce crop yield, impair product quality, and
require pesticides for control.
[0004] Replacing the greenhouse air with external air is a
customary method for decreasing the humidity in a greenhouse.
External cold air, with low absolute humidity, replaces the warmer
greenhouse air and absorbs the excess water that evaporates.
However, such methods are energy inefficient and can bring unwanted
contaminants into the growing space.
[0005] It would therefore be desirable to have a controlled and
contained growing space with recirculation of most or all of the
air. It would also be desirable to have a system to control the
temperature, humidity, and optionally the CO.sub.2 levels in the
contained growing space that does not require addition of outside
air. This disclosure proposes a method and system that accomplishes
this.
BRIEF SUMMARY
[0006] The inventive concepts disclosed and claimed herein relate
generally to systems and methods for controlling the environment,
including lighting, temperature, humidity, and optionally CO.sub.2
levels in an interior of an enclosure in which plants are grown. In
one embodiment, a controlled and closed agricultural system
includes a growing space and an air handling system having a heat
exchanger and a cooling coil. The heat exchanger is capable of
transferring sensible and latent heat and is fluid connection with
a recirculating air duct and an outside air duct. The recirculating
air duct is isolated from the outside air duct and is in fluid
connection with the growing space and one or more recirculation
fans, while the outside air duct is in fluid connection with one or
more outside air fans positioned to cause outside air to flow in a
predetermined manner, e.g., countercurrent to the recirculating air
though the heat exchanger. A cooling coil is positioned within the
recirculating air duct, downstream of and in series with the heat
exchanger. The cooling coil circulates a heat transfer fluid to
remove heat from the recirculating air.
[0007] In another embodiment, a controlled and closed agricultural
system includes a growing space and an air handling system having a
first heat exchanger, a second heat exchanger, and a cooling coil.
The first heat exchanger is capable of transferring sensible heat
and is in fluid connection with a recirculating air duct and an
adjacent outside air duct. The second heat exchanger is capable of
transferring latent heat and is positioned in series with the first
heat exchanger and is in fluid connection with the recirculating
air duct and the outside air duct. The recirculating air duct is
isolated from the outside air duct and is in fluid connection with
the growing space and one or more recirculation fans. The outside
air duct is in fluid connection with one or more outside air fans
positioned to cause outside air to flow in a predetermined manner,
e.g., countercurrent to the recirculating air. A cooling coil is
positioned within the recirculating air duct, downstream of and in
series with the first heat exchanger. The cooling coil circulates a
heat transfer fluid to remove heat from the recirculating air.
[0008] In yet another embodiment, a method for treating air within
a growing space of a closed agricultural system includes the
following steps. Air is recirculated from a contained growing space
through an air handling system having at least one heat exchanger
to reduce the energy content of the recirculating air. The
recirculating air exiting the heat exchanger(s) is passed across a
cooling coil circulating a heat transfer fluid to further reduce
the heat content of the recirculating air. The recirculating air
passing the cooling coil is returned to the contained growing space
of the closed agricultural system. Outside air is passed through
the heat exchanger (s) counter-current to and separated from the
recirculating air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Like reference numerals in the figures represent and refer
to the same or similar element or function. Implementations of the
disclosure may be better understood when consideration is given to
the following detailed description thereof. Such description makes
reference to the annexed pictorial illustrations, schematics,
graphs, and drawings. The figures are not necessarily to scale and
certain features and certain views of the figures may be shown
exaggerated, to scale or in schematic in the interest of clarity
and conciseness. All of the drawings are for the purpose of
describing selected versions of the present invention and are not
intended to limit the scope of the present invention. In the
drawings:
[0010] FIG. 1 illustrates an exemplary system for treating air
within a closed structure for growing plants in accordance with the
present disclosure.
[0011] FIG. 2 is an elevation view of an exemplary closed growing
space and air handling system in accordance with the present
disclosure.
[0012] FIG. 3 is a plan view of an upper deck of the air handling
system of FIG. 2.
[0013] FIG. 4 is a plan view of a middle deck of the air handling
system of FIG. 2.
[0014] FIG. 5 is a plan view of a lower deck of the air handling
system of FIG. 2.
[0015] FIG. 6 is a plan view of the air handling system described
in Example 1.
[0016] FIG. 7 is a flow diagram for the air handling system
described in Example 2.
[0017] FIG. 8 is a flow diagram for the air handling system
described in Example 3.
[0018] FIG. 9 is a flow diagram for the air handling system
described in Example 4.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0019] Before explaining at least one embodiment of the inventive
concepts disclosed herein in detail, it is to be understood that
the inventive concepts are not limited in their application to the
details of construction, exemplary data, and/or the arrangement of
the components set forth in the following description, or
illustrated in the drawings. The presently disclosed and claimed
inventive concepts are capable of other embodiments or of being
practiced or carried out in various ways. Also, it is to be
understood that the phraseology and terminology employed herein is
for purpose of description only and should not be regarded as
limiting in any way.
[0020] In the following detailed description of embodiments of the
inventive concepts, numerous specific details are set forth in
order to provide a more thorough understanding of the inventive
concepts. However, it will be apparent to one of ordinary skill in
the art that the inventive concepts within the disclosure may be
practiced without these specific details. In other instances,
well-known features have not been described in detail to avoid
unnecessarily complicating the instant disclosure.
[0021] As will be apparent to those of skill in the art upon
reading this disclosure, each of the individual embodiments
described and illustrated herein has discreet components and
features which may be readily separated from or combined with the
features of any of the other several embodiments without departing
from the scope or spirit of the present disclosure. Any recited
method can be carried out in the order of events recited as well as
any other order that is logically possible.
[0022] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus.
[0023] Further, unless expressly stated to the contrary, "or"
refers to an inclusive or and not to an exclusive or. For example,
a condition A or B is satisfied by anyone of the following: A is
true (or present) and B is false (or not present), A is false (or
not present) and B is true (or present), and both A and B are true
(or present).
[0024] In addition, use of the "a" or "an" are employed to describe
elements and components of the embodiments herein. This is done
merely for convenience and to give a general sense of the inventive
concept. This description should be read to include one or more and
the singular also includes the plural unless it is obvious that it
is meant otherwise.
[0025] Use of the term "plurality" is meant to convey "more than
one" unless expressly stated to the contrary.
[0026] As used herein any reference to "one embodiment" or "an
embodiment" means that a particular element, feature, structure, or
characteristic described in connection with the embodiment is
included in at least one embodiment. The appearances of the phrase
"in one embodiment" in various places in the specification are not
necessarily all referring to the same embodiment.
[0027] Reference to an energy wheel herein and in the appending
claims refers to a type of rotating air-to-air heat exchanger. An
energy wheel that transfers only sensible heat is referred to
herein and in the appending claims as a "heat wheel." An energy
wheel that transfers only latent heat is referred to herein and in
the appending claims as a "desiccant wheel." An energy wheel that
can transfer both sensible heat and latent heat is referred to
herein and in the appending claims as an "enthalpy wheel."
[0028] References to agricultural growing spaces are for example
only, and the inventive concepts disclosed herein can be used with
any closed, contained or nearly-closed and contained space.
[0029] Agricultural growing spaces generate high humidity due to
plant transpiration and high sensible heat loads due to either
sunlight or grow lights. To maintain a growing space with low
levels of contamination, it is desirable to remove the excess heat
and moisture without adding outside air to the contained growing
space.
[0030] Referring now to FIG. 1 and FIG. 2, a controlled
agricultural system 10 includes a growing space 12, and an air
handling system 13. The air handling system 13 includes an enthalpy
wheel 14, a cooling coil 16 and optionally a condensing coil 18.
The enthalpy wheel 14 is capable of transferring sensible and
latent heat and is positioned in and rotatable through a
recirculating air duct 22 and an outside air duct 24 adjacent the
recirculating air duct 22. The recirculating air duct 22 is in
fluid connection with the growing space 12 and one or more
recirculating air fans 26, while the outside air duct 24 is in
fluid connection with one or more outside air fans 28 positioned to
cause outside air to flow countercurrent to recirculating air. The
cooling coil 16 is positioned within the recirculating air duct 22,
downstream of and in series with the enthalpy wheel 14. The cooling
coil 16 circulates a heat transfer fluid through a heat transfer
fluid line 30 to remove heat from the recirculating air.
[0031] The controlled agricultural system 10 can be operated to
control the environment within the growing space 12 defined by side
walls 34 and an overhead wall 36. The side walls 34 and overhead
wall 36 can be made of glass as traditional greenhouses, with
louvers or the like to control the amount of sunlight entering the
growing space 12. In one embodiment, the side walls 34 and overhead
wall 36 are opaque to sunlight, and artificial light is provided to
plants growing in the growing space 12 by grow lights 38. The use
of grow lights 38 provides additional flexibility and energy
savings in that the environmental factors can be controlled and
therefore optimized in terms of plant yield and energy
efficiency.
[0032] For example, in some climates it may be advantageous to have
artificial light at night when the temperature of the growing space
exterior is cooler, and darkness during the day when the
temperature of the growing space exterior is much hotter, thereby
lessening the heat load that must be removed from the recirculating
air. Further, the use of grow lights 38 allows the duration of
light and darkness to be optimized for both plant yield and energy
costs.
[0033] In one embodiment, actual sunlight is completely replaced by
artificial light. In another embodiment, the light wavelengths,
light intensity, and light duration can be completely artificial
and controlled, thereby eliminating inefficiencies associated with
weather and seasonal conditions.
[0034] The growing space 12 can be conditioned year round and
outside air can be avoided thereby eliminating problems due to
variable seasons, pests, air contaminants such as molds, pollen,
etc. The constant cooling of the air within the growing space 12
can result in significant savings in energy use and resulting
costs.
[0035] In one embodiment, the air in the growing space 12 is
circulated such that it is not mixed with outside air, thereby
minimizing contamination of the growing space 12. Recirculating air
fans 26 draw air from the growing space 12 through the air handling
system 13, separated from and in counter current flow to the
outside air which is pulled from outside the air handling system 13
by the outside air fans 28 and may be controlled, at least in part,
by an outside air damper 39.
[0036] In one embodiment, the enthalpy wheel 14 is positioned in
and rotatable through a bifurcated duct 20. A separating wall 40
bifurcates at least a portion of the duct 20, such that the
separating wall 40 separates a recirculating air portion 22' from
an outside air portion 24'. The recirculating air portion 22' of
the bifurcated duct 20 is sometimes referred to as the
recirculating air duct 22. Likewise, the outside air portion 24' of
the bifurcated duct 20 is sometimes referred to herein as the
outside air duct 24.
[0037] The enthalpy wheel 14 can be positioned within the
bifurcated duct 20, or within the recirculating air duct 22 and the
outside air duct 24, such that warm moist air recirculated from the
growing space 12 passes though one portion of the enthalpy wheel 14
and outside air passes in the opposite direction through the
remaining portion of the enthalpy wheel 14. Brush seals and the
like may be used to maintain isolation between the recirculating
air and the outside air or at least minimize contamination of the
recirculating air with outside air.
[0038] Energy wheels are a type of air-to-air heat exchanger that
can not only transfer sensible heat but also latent heat. When both
temperature and moisture are transferred, the energy wheel is
considered an enthalpy wheel. The rotating energy wheel heat
exchanger is composed of a rotating cylinder filled with an air
permeable material resulting in a large surface area for the
sensible energy transfer. As the wheel rotates between the
recirculating air portion 22' and the outside air portion 24' of
the bifurcated duct 20, or through the recirculating air duct 22
adjacent the outside air duct 24, the wheel picks up sensible
energy (heat) and releases the sensible energy into a relatively
colder outside air stream. The driving force behind the exchange is
the difference in temperatures between the opposing air streams
which is also called the thermal gradient. Nonlimiting examples of
suitable material used includes polymer, aluminum, and synthetic
fiber.
[0039] The moisture or latent energy exchange in enthalpy wheels is
accomplished through the use of desiccants. Desiccants transfer
moisture through the process of adsorption which is predominately
driven by the difference in the partial pressure of vapor within
the opposing air streams. Nonlimiting examples of suitable
desiccants include silica gel and molecular sieves.
[0040] In some environments, modulating dampers can be used to
control the flowrate of outside air. Modulating the wheel speed,
preheating the air, and stop/jogging the system offer additional
means to control the energy transfer. Cross-contamination of the
contaminants via the desiccant can also be a concern but can be
avoided for example through the use of a selective desiccant like a
molecular sieve.
[0041] In one embodiment, a mixing damper 42 is positioned in the
outside air duct 24, or the outside air portion 24' of the
bifurcated duct 20, downstream of the enthalpy wheel 14, and can be
used to control the amount of outside air. For example, one or more
industry standard modulating damper(s) can be positioned in
parallel with the enthalpy wheel 14 and modulated in concert with
the outside air damper 39 to maintain a desired operation and
performance of the enthalpy wheel 14.
[0042] Temperature and relative humidity measurements can be taken
using, for example, industry standard temperature and humidity
sensors. Temperature and relative humidity measurements of the
outside air stream entering the enthalpy wheel 14, the
recirculating air entering the enthalpy wheel 14, and the
recirculating air exiting the enthalpy wheel 14 can be used to
control the speed of the outside air fans 28, the speed of the
enthalpy wheel, and control operation of the direct expansion
evaporator cooling coil 16.
[0043] The cooling coil 16 can further cool the recirculating air
exiting the enthalpy wheel 14. The cooling coil 16 can circulate
chilled water, a mixture of chilled water and glycol, refrigerant,
and the like.
[0044] In one embodiment, chilled water is produced in another
portion of the facility housing the controlled agricultural system
and is utilized to further cool recirculating air exiting the
enthalpy wheel 14.
[0045] In one embodiment, the cooling coil 16 is a direct expansion
evaporator cooling coil. A compressor 32 and condensing coil 18 are
external to the recirculating air duct 22, or the recirculating air
portion 22' of the bifurcated duct 20, and use outside air to
remove heat from the heat transfer fluid.
[0046] Design and operation of evaporator cooling coils are well
understood by those skilled in the art. Typically condensed and
pressurized liquid refrigerant is routed through an expansion valve
where it undergoes an abrupt reduction in pressure. That pressure
reduction results in flash evaporation of a part of the liquid
refrigerant, thereby lowering its temperature. The cold refrigerant
is then routed through the evaporator cooling coil. Air fans blow
the recirculating air across the evaporator, causing the liquid
part of the cold refrigerant mixture to evaporate as well, further
lowering the temperature. The recirculating air is therefore cooled
by heat transfer from the direct expansion evaporator cooling coil
16.
[0047] Circulating refrigerant vapor enters the compressor 32 and
is compressed to a higher pressure, resulting in a higher
temperature as well. The hot, compressed refrigerant vapor is at a
temperature and pressure at which it can be condensed and is routed
through the condensing coil 18 located in the outside air duct 24,
or the outside air portion 24' of the bifurcated duct 20. Outside
air fan(s) 28 causes outside air exiting the enthalpy wheel 14 to
flow across the condensing coil 18. The cooler outside air flowing
across the condensing coil 18 causes the refrigerant in the coil to
condense into a liquid. Thus, in summary, the circulating
refrigerant removes heat from the recirculating air and the heat is
carried away by the outside air.
[0048] In one embodiment, for example when weather or other
circumstances cause the recirculating air to be colder than
desired, the refrigeration cycle can be reversed and refrigerant is
pumped in the opposite direction. The overall effect is the
opposite, and the recirculating air is heated instead of
cooled.
[0049] In one embodiment, for example when the recirculating air
becomes cooler than desired for recirculating to the growing space
12, one or more heaters 44 in the recirculating air duct 22, or the
recirculating air portion 22' of the bifurcated duct 20, can be
utilized to control the temperature of the recirculating air and
the growing space 12. Non-limiting examples of suitable heaters
include electrical resistance heaters, hot water radiators, natural
gas furnaces, and the like.
[0050] A CO.sub.2 generator 46 can be used to add CO.sub.2 to the
recirculating air duct 22, or the recirculating air portion 22' of
the bifurcated duct 20. An associated CO.sub.2 sensor 48 can sense
and read the CO.sub.2 level in the recirculating air and input the
level to a CO.sub.2 controller 50. The CO.sub.2 generator 46 is
controlled by the CO.sub.2 controller 50 to maintain the CO.sub.2
content at a set point or set range.
[0051] In one embodiment, the CO.sub.2 generator 46 comprises a
natural gas burner located in the outside air duct 24, or the
outside air portion 24' of the bifurcated duct 20. Locating the
natural gas burner in the outside air portion allows a majority of
the heat related to combustion to exhaust directly outside. Flue
gas from the natural gas burner is delivered in controlled amounts
to the recirculating air. A flue gas fan 52 located in the
separating wall 40 can be utilized, for example to meter the flue
gas to the recirculating air portion 22' of the bifurcated duct 20
and thereby maintain the CO.sub.2 content at a set point or set
range.
[0052] In one embodiment, a control louver 54 is also used to purge
excess CO.sub.2 from the recirculating air duct 22, or the
recirculating air portion 22' of the bifurcated duct 20, to
maintain the CO.sub.2 content at a set point or set range.
[0053] In one embodiment, an industry standard CO.sub.2 sensor 48
is installed in the recirculating air duct 22, or in the
recirculating air portion 22' of the bifurcated duct 20. The
CO.sub.2 sensor 48 feeds back to the CO.sub.2 controller 50 within
a central control system 55 to determine if the natural gas burner
should fire and at what rate the CO.sub.2-containing flue gas
should be metered into the air handling system 13 to meet or
maintain a user-defined CO.sub.2 set point.
[0054] In one embodiment, the air handling system 13 includes a
separate desiccant wheel 56 for removing moisture from the
recirculating air. The desiccant wheel 56 is positioned in and
rotatable through both the recirculating air duct 22 and the
outside air duct 24 such that warm moist air recirculated from the
growing space 12 passes though one portion of the desiccant wheel
56 and heated outside air exiting the condensing coil 18 passes in
the opposite direction through the remaining portion of the
desiccant wheel 56. A separate heat wheel 57 capable of
transferring sensible heat also positioned in and rotatable through
both the recirculating air duct and the outside air duct. The heat
wheel 57 cools dried recirculating air exiting the desiccant wheel
56 and transfers the sensible heat to outside air upstream of the
desiccant wheel 56.
[0055] As described above for the enthalpy wheel 14, the desiccant
wheel 56 is composed of a rotating cylinder filled with an air
permeable material comprising desiccant. As the desiccant wheel 56
rotates between the recirculating air duct 22 and the outside air
duct 24, it picks up moisture from the moist recirculating air and
releases it into the drier outside air stream. Desiccants transfer
moisture through the process of adsorption which is predominately
driven by the difference in the partial pressure of vapor within
the opposing air streams. Suitable desiccants include silica gel,
and molecular sieves. The outside air with absorbed heat and
humidity is then discharged from the air handling system 13 and
returned to the atmosphere.
[0056] In one embodiment, a recirculating air filter 58 positioned
in the recirculating air duct 22 removes particulate from the
recirculating air before feeding it back to the growing space 12.
Design and operation of air filters are well understood by those
skilled in the art.
[0057] An outside air filter 60 can be positioned in the outside
air duct 24 to remove particulate from the outside air prior to
passing it through the enthalpy wheel 14 or the desiccant wheel 56
and heat wheel 57. Removal of particulate can aid in reducing the
maintenance of the wheels.
[0058] The central control system 55 can modulate the fans,
wheel(s), and optionally the compressor to minimize energy
consumption. Components of the system described above can be
variable speed. The fans can vary the volume of air moved and the
wheel speed(s) can vary to maximize efficiency. The mechanical
cooling system including the cooling coil 16 optimally provides
only the cooling necessary. Control logic for the components can be
housed in a common control cabinet.
[0059] In the embodiment shown in FIG. 2, the air handling system
13 is constructed adjacent to the growing space 12 with a
recirculating air outlet 62 originating from a far side of the
growing space 12, and a recirculating air intake 64 proximate the
air handling system 13. While numerous layouts can be used,
separation of the recirculating air outlet and intake 62 and 64,
respectively, improves efficiency of air replacement in the growing
space 12. FIG. 3 through FIG. 5 show possible equipment layouts in
three levels of the air handling system 13.
[0060] A method for treating air within a growing space of a closed
agricultural system includes temperature and moisture control
equipment as described above. Recirculating air from a contained
growing space is passed through an air handling system comprising
at least one energy wheel to reduce the energy content of the
recirculating air. The recirculating air exiting the energy
wheel(s) is passed across a cooling coil circulating a heat
transfer fluid to further reduce the heat content of the
recirculating air. The recirculating air passing the cooling coil
is then returned to the contained growing space. Outside air is
passed through the energy wheel(s) counter-current to and separated
from the recirculating air.
[0061] In one embodiment, the recirculating air exiting the energy
wheel(s) can be passed across a direct expansion evaporator cooling
coil circulating a heat transfer fluid to further reduce the heat
content of the recirculating air before returning the air to the
main portion of the closed structure. The heat transfer fluid is
cooled by circulating through a compressor and a condensing coil in
contact with the outside air.
[0062] In one embodiment the energy wheel comprises an enthalpy
wheel to reduce the temperature and the moisture content of the
recirculating air. In another embodiment, the energy wheels
comprise both a desiccant wheel to reduce the moisture content of
the recirculating air and a heat wheel to reduce the temperature of
the recirculating air.
[0063] The method for treating air within a growing space of a
closed agricultural system can additionally include monitoring the
CO.sub.2 content of air circulated from the growing space. CO.sub.2
is added if the CO.sub.2 content is below a desired value, and a
portion of the recirculating air is vented if the CO.sub.2 content
is above a level determined to be harmful.
[0064] In the following examples, specific controlled and closed
agricultural systems are described. However, the present inventive
concept(s) is not to be limited in its application to the specific
equipment, plant layout, and operating methods. Rather, the
Examples are simply provided as one of various embodiments and are
meant to be exemplary, not exhaustive.
Example 1
[0065] In some applications, the humidity level in the closed
agricultural system requires more extensive dehumidification than
normal. As shown in FIG. 6, a second desiccant wheel is installed
downstream of the recirculation fans and condensing coil. The
enthalpy wheel is replaced with a heat wheel (sensible heat-only
wheel, no desiccant). A condensing coil or a natural gas burner
acts as regeneration heat for the latent heat-only wheel. As the
desiccant wheel rotates from one air stream to the other it adsorbs
the moisture from the recirculation air. That moisture is then
released to the outside air stream. To aid in that release,
regeneration heat (condensing coil heat and/or optional natural gas
burner) is applied to the air entering the wheel in the outside air
stream. An additional set of temperature and relative humidity
sensors are installed downstream of the desiccant wheel. The
control system varies the speed of the desiccant wheel to meet the
user defined relative humidity set point. Similarly, the control
system varies the heat wheel to meet the user defined temperature
set point.
Example 2
[0066] The efficiency of the air handling system depends on the
outside air temperature and humidity. When conditions are favorable
(cooler dryer weather), the system is capable of transferring the
heat and humidity of the recirculation air through the enthalpy
wheel to the cooler and dryer outside air. As indicated in the flow
diagram shown in FIG. 7, 57.degree. F. outside air with 40.7 grains
of moisture is coming into the unit and into the enthalpy wheel.
The resulting recirculation air temperature and grain level off the
wheel (60.degree. F./45.1 grains) to provide 100% of the required
heating and dehumidification.
Example 3
[0067] As the outside air temperature and humidity go up, the
enthalpy wheel can still provide value by "pre-conditioning" the
recirculation air before the cooling coil. In the flow diagram
shown in FIG. 8, 57.degree. F. outside air with 60.6 grains is
entering the air handling unit and the enthalpy wheel. The
resulting recirculation air temperature and grain level off the
wheel (60.degree. F./63.2 Grains) is sufficient to cool the
recirculating air, but it is not sufficient to remove the moisture
from the recirculating air. As a result the air handling unit
control system shall enable the mechanical cooling to remove the
additional grains of moisture from the recirculation air, down to
the user defined set point of 48 grains. In order to remove the
moisture the cooling coil must over cool the air, 50.degree. F. The
over cooled air could potentially over cool the recirculating air,
therefore the air handling unit control system shall enable the
heat source to heat the recirculating air to the user defined set
point.
Example 4
[0068] At some point the outside air will be too hot and too wet
for the air handling system to be able to transfer heat and
humidity form the recirculating air stream to the outside air
stream. In the flow diagram shown in FIG. 9, when the control
system determines that there is no benefit from the enthalpy wheel,
the wheel shall stop. At this point the air handling unit is
capable of mechanically cooling all the recirculating air to meet
the user defined set point.
[0069] From the above description, it is clear that the inventive
concept(s) disclosed herein is well adapted to carry out the
objects and to attain the advantages mentioned herein as well as
those inherent in the inventive concept disclosed herein. While
exemplary embodiments of the inventive concept disclosed herein
have been described for purposes of this disclosure, it will be
understood that numerous changes may be made which will readily
suggest themselves to those skilled in the art and which are
accomplished without departing from the scope of the inventive
concept disclosed herein and defined by the appended claims.
* * * * *