U.S. patent application number 14/245157 was filed with the patent office on 2015-10-08 for climate control system and method for a greenhouse.
The applicant listed for this patent is GREENHOUSE HVAC LLC. Invention is credited to F. Mack Shelor.
Application Number | 20150282440 14/245157 |
Document ID | / |
Family ID | 54208515 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150282440 |
Kind Code |
A1 |
Shelor; F. Mack |
October 8, 2015 |
CLIMATE CONTROL SYSTEM AND METHOD FOR A GREENHOUSE
Abstract
A greenhouse environment control system generates a
CO.sub.2-enriched air which is supplied to a greenhouse at a
controlled temperature suitable for plant growth. An absorption
chiller reduces temperature of a CO.sub.2-containing stream of
processed gasses from an engine. A mixing and blending unit
maintains CO.sub.2 at an acceptable concentration for enhanced
plant growth and human occupation. An HVAC system modulates
temperature and positively pressurizes the greenhouse with the
CO.sub.2-enriched air to reduce risk of contaminant intrusion.
Misting further controls temperature. Retractable shades regulate
light supplied to plants and solar gain.
Inventors: |
Shelor; F. Mack; (Palm
Coast, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GREENHOUSE HVAC LLC |
Jacksonville |
FL |
US |
|
|
Family ID: |
54208515 |
Appl. No.: |
14/245157 |
Filed: |
April 4, 2014 |
Current U.S.
Class: |
47/17 |
Current CPC
Class: |
A01G 9/246 20130101;
A01G 9/18 20130101; Y02A 40/25 20180101; Y02A 40/268 20180101 |
International
Class: |
A01G 9/18 20060101
A01G009/18 |
Claims
1. A greenhouse environment control system comprising a greenhouse
for growing plants, said greenhouse comprising a substantially
enclosed structure comprised of a transmissive material that allows
passage of sunlight, said substantially enclosed structure defining
an interior in which plants may be grown; said environment control
system comprising a plurality of subsystems, said plurality of
subsystems including a generator subsystem, a gas cooling
subsystem, a mixing subsystem, and an HVAC subsystem; said
generator subsystem comprising a natural gas fueled engine
producing a stream of exhaust gases and an exhaust gas treatment
module converting the stream of exhaust gases to a gas stream
comprised of nitrogen gas, water vapor and carbon dioxide; said gas
cooling subsystem being in fluid communication with the generator
subsystem and comprising a plurality of fluidly coupled heat
transfer units, said plurality of fluidly coupled heat transfer
units reducing the temperature of the gas stream to about
200.degree. F. to 100.degree. F.; said mixing subsystem comprising
an inlet fluidly coupled to the gas cooling system, an outlet, a
fresh air duct through which fresh air flows, a particle filter
associated with the fresh air duct, the fresh air flowing through
the fresh air duct being filtered by passing through the particle
filter, a mixing chamber in which the gas stream is mixed with
filtered fresh air to produce CO.sub.2-enriched air, said CO.sub.2
enriched air having a concentration of CO.sub.2 from about 800 ppm
to 2000 ppm, said CO.sub.2 enriched air flowing out of the outlet;
said HVAC subsystem comprising a plurality of fan coil units, each
fan coil unit including a housing defining an interior compartment,
a gas inlet being fluidly coupled to the outlet of the mixing
subsystem and leading to the interior compartment, a gas outlet
leading from the interior compartment, a coil contained in the
interior compartment, said coil having an inlet and an outlet, and
a fluid flowing through said coil, said fluid being at a
temperature effective for cooling the CO.sub.2 enriched air, and
said interior compartment defining a flow path from the gas inlet
of the fan coil unit, over the coil, and out of the gas outlet,
said gas outlet being in fluid communication with the interior of
the greenhouse.
2. A greenhouse environment control system according to claim 1,
said generator subsystem including a urea supply in fluid
communication with the stream of exhaust gases and a nozzle
introducing urea from the urea supply into the stream of exhaust
gas.
3. A greenhouse environment control system according to claim 2,
said generator subsystem further including a selective catalytic
reduction catalyst downstream of the nozzle introducing urea from
the urea supply into the stream of exhaust gas, the selective
catalytic reduction catalyst comprising a metal zeolite catalyst
effective for reduction of NOx.
4. A greenhouse environment control system according to claim 3,
said metal zeolite catalyst comprising a catalyst from the group
consisting of an iron zeolite and a copper zeolite.
5. A greenhouse environment control system according to claim 1,
said gas cooling subsystem comprising an absorption chiller, said
absorption chiller including a condenser-generator, an
evaporator-absorber containing a desiccant, and a refrigerant
comprised of water, said condenser generator being fluidly coupled
to the generator subsystem and receiving the gas stream comprised
of nitrogen gas, water vapor and carbon dioxide from the generator
subsystem at an inlet temperature, said gas stream transferring
heat to evaporate the refrigerant from the desiccant, the desiccant
being chemically stable at the inlet temperature, and said
transferred heat reducing the temperature of the gas stream.
6. A greenhouse environment control system according to claim 5,
said desiccant comprising lithium bromide salt (LiBr).
7. A greenhouse environment control system according to claim 6,
said absorption chiller including a first stage and a second stage,
said first stage containing refrigerant and said second stage
containing evaporated refrigerant from the first stage absorbed by
the desiccant.
8. A greenhouse environment control system according to claim 5,
said gas cooling subsystem further comprising a heat exchanger
downstream of and fluidly coupled to the absorption chiller, said
heat exchanger comprising a gas flow chamber with an inlet and an
outlet, and a coil through which a water refrigerant flows, said
gas stream from the absorption chiller flowing through the gas flow
chamber from the inlet of the gas flow chamber over the coil of the
gas flow chamber to the outlet of the gas flow chamber , and said
gas stream transferring heat to the water refrigerant in the coil
of the gas flow chamber.
9. A greenhouse environment control system according to claim 1,
said mixing subsystem comprising a mixing receptacle with a first
inlet and a second inlet for combining two fluid streams in the
mixing receptacle including a first fluid stream comprised of the
gas stream from the gas cooling subsystem at a first volumetric
flow rate and a second fluid stream comprised of fresh air at a
second volumetric flow rate, and an outlet, the combined fluid
streams being expelled through the outlet.
10. A greenhouse environment control system according to claim 9,
said mixing subsystem further comprising an adjustable damper in
the mixing receptacle, said adjustable damper regulating the second
volumetric flow rate of fresh air comprising the second fluid
stream supplied to through the second inlet of the mixing
receptacle to the mixing receptacle thereby regulating a ratio of
the first fluid stream to the second fluid stream.
11. A greenhouse environment control system according to claim 10,
said first fluid stream containing CO.sub.2 and said regulating a
ratio of the first fluid stream to the second fluid stream includes
regulating concentration of CO.sub.2 in the combined fluid
streams.
12. A greenhouse environment control system according to claim 11,
further comprising a particulate filter associated with the second
inlet, said particulate filter being upstream of the mixing
receptacle and filtering all of the second fluid stream flowing
through the second inlet into the mixing receptacle.
13. A greenhouse environment control system according to claim 9,
said HVAC subsystem comprising a manifold fluidly coupling the
outlet of the mixing receptacle to the gas inlet of each of the
plurality of fan coil units.
14. A greenhouse environment control system according to claim 1,
said fan coil units of the HVAC subsystem being at a determined
height, and said greenhouse environment control system further
comprising: a plurality of retractable shade curtains disposed in
the interior of the greenhouse adjacent to the transmissive
material that allows passage of sunlight at a height above the
determined height of the fan coil units.
15. A greenhouse environment control system according to claim 14,
each of said plurality of retractable shade curtains including a
first retractable shade and a second retractable shade, the first
retractable shade and second retractable shade providing different
amounts of shading, about 30% shading for the first shade and about
60% shading for the second shade.
16. A greenhouse environment control system according to claim 1,
said fan coil units of the HVAC subsystem being at a determined
height, and said greenhouse environment control system further
comprising: a misting system including a plurality of misting
nozzles in the interior of the greenhouse at a height above the
determined height of the fan coil units, each of the misting
nozzles emitting a water mist.
17. A greenhouse environment control system according to claim 1,
said greenhouse including a vent and a vent screen, an exterior
environment surrounding the greenhouse, said vent providing a fluid
flow path from the interior space of the greenhouse to the exterior
environment, and said vent screen being disposed in the fluid flow
path.
18. A greenhouse environment control method comprising steps of:
running a natural gas fueled engine to produce a stream of exhaust
gases; converting the stream of exhaust gases to a gas stream
comprised of nitrogen gas, water vapor and carbon dioxide; reducing
the temperature of the gas stream to about 200.degree. F. to
100.degree. F. using a cooling subsystem including an absorption
chiller; mixing the gas stream with filtered fresh air to produce
CO.sub.2-enriched air, said CO.sub.2 enriched air having a
concentration of CO.sub.2 from about 800 ppm to 2000 ppm; supplying
the CO.sub.2-enriched air to a plurality of fan coil units;
modulating the temperature of the CO.sub.2-enriched air using the
fan coil units; supplying the temperature modulated
CO.sub.2-enriched air from the fan coil units to the greenhouse at
a pressure greater than ambient pressure, said supplied temperature
modulated CO.sub.2-enriched air positively pressurizing the
greenhouse.
19. The greenhouse environment control method of claim 18, wherein
said step of converting the stream of exhaust gases to a gas stream
comprised of nitrogen gas, water vapor and carbon dioxide comprises
supplying urea through a nozzle to the stream of exhaust gases and
providing a selective catalytic reduction catalyst downstream of
the nozzle, the selective catalytic reduction catalyst comprising a
metal zeolite catalyst effective for reduction of NOx.
20. The greenhouse environment control method of claim 18, further
comprising a step of cooling the CO.sub.2-enriched air supplied to
the plurality of fan coil units to remove water vapor via
condensation before supplying the temperature modulated
CO.sub.2-enriched air from the fan coil units to the greenhouse.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to horticulture, and, more
particularly, to a greenhouse with a controlled climate, including
temperature, humidity and carbon dioxide concentration.
BACKGROUND
[0002] Commercial greenhouses are high tech production facilities
for vegetables and flowers. Heretofore, such greenhouses have been
adapted for use in regions with cold winters and arid summers. In
such climates, the greenhouse interior may be heated in winter
months such as by using boilers, heat pumps, or heat transferred
from hot engine exhaust. Such greenhouses may be cooled during hot
summer months through evaporative cooling systems. One example of
such a cooling system is a pad and fan, which draws dry outside air
through a wet porous pad to cool the air via evaporative cooling.
To work, the fan must continuously draw ambient air through the pad
and exhaust the cooled air to the outside. Fogging and misting
systems are also widely used to cool greenhouses in arid
environments.
[0003] In warm humid environments, cooling systems that depend upon
evaporation for cooling are marginally effective at best. When
considering water evaporating into air, the wet-bulb temperature
which takes both temperature and humidity into account is a measure
of the potential for evaporative cooling. The amount of heat
transfer depends on the evaporation rate, which depends on the
temperature and humidity of the air. As humidity increases, the
actual air temperature approaches the wet bulb temperature. The
less the difference between the wet bulb and actual air
temperature, the less the evaporative cooling effect. Thus, in hot
humid climates, the evaporative cooling effect is typically
insufficient to maintain a greenhouse at a temperature favorable to
plant growth.
[0004] Photosynthesis depends on a series of external and internal
factors. The internal factors are the characteristics of the leaf
(structure, chlorophyll content), the accumulation of products
assimilated in the chloroplasts of the leaves, the availability of
water, mineral nutrients and enzymes, among others. Among the most
relevant external factors are the radiation incident on the leaves
(quantity and quality), temperature, the ambient humidity and the
concentration of CO.sub.2 and oxygen in the surrounding air.
Excessive heat and humidity, or insufficient CO.sub.2, are
non-limiting examples of factors that may stifle
photosynthesis.
[0005] The concentration of CO.sub.2 in ambient outside air
commonly varies from 300 to 500 parts ppm or more by volume
depending on the season, time of day and the proximity of CO.sub.2
producers such as combustion or composting, or CO.sub.2 absorbers
such as plants or bodies of water. Plants growing in greenhouses,
particularly sealed structures, can reduce CO.sub.2 levels to well
below ambient levels, greatly reducing the rate of photosynthesis.
Conversely, enriching the concentration of CO.sub.2 above ambient
levels can significantly increase the rate of photosynthesis.
Consequently, many commercial greenhouses include CO.sub.2
enrichment systems to augment photosynthesis. Such systems
typically supply CO.sub.2 from storage vessels or as a product of
combustion of carbon-based fuel. The ideal concentration depends on
the crop, light intensity, temperature and the stage of crop
growth. However, 1000 to 1200 ppm is considered effective for many
flowers and vegetables, with some exceptions. At this level, worker
exposure should fall far below the 5,000 ppm permissible exposure
limit for an 8-hour shift (measured as a time weighted average), as
set by the U.S. Occupational Safety & Health Administration
(OSHA).
[0006] In greenhouses with fan and pad evaporative cooling systems,
it is difficult to maintain an elevated CO.sub.2 concentration,
notwithstanding enrichment efforts. Such greenhouses continuously
vent injected CO.sub.2 to the atmosphere. A vigorous stream of air
must be maintained to provide cooling. The stream captures injected
CO.sub.2. Venting releases it to the atmosphere with the air
stream. This attenuates any benefit to photosynthesis while
increasing production costs and compromising the outside
environment.
[0007] An improved greenhouse climate control system that is
capable of controlling temperature, providing heating and cooling
as desired, and providing CO.sub.2 enrichment for optimal plant
growth, in all ambient environments, including hot, cold, arid and
humid, is needed. The invention is directed to overcoming one or
more of the problems and solving one or more of the needs as set
forth above.
SUMMARY OF THE INVENTION
[0008] To solve one or more of the problems set forth above, in an
exemplary implementation of the invention, a greenhouse system is
provided that maintains (1) a positively pressurized
CO.sub.2-enriched air environment with a CO.sub.2 concentration of
about 1,200 ppm, (2) an air temperature of between 60 F and
75.degree. F., (3) a relative humidity of between 50% and 70%
except under extreme summer conditions, and (4) lighting between
about 200 micro mols/square meter/sec and 600 micro mols/square
meter/sec during lighted conditions. An exemplary system according
to principles of the invention uses urea and selective catalytic
reduction (SCR) to reduce pollutants in exhaust gases from
combustion of natural gas. Ammonia produced by hydrolysis of urea
reacts with nitrogen oxide emissions and is converted into nitrogen
and water. An exemplary system according to principles of the
invention uses direct heat double effect absorption chillers as a
primary heat recovery device to provide both heating and cooling.
Direct contact condensing heat exchangers reduce exhaust gas
temperature from about a nominal 300.degree. F. to approximately
130.degree. F. in order to more efficiently use the heat in a
greenhouse. A mixing and blending unit maintains positive control
of entering outside air. Outside air is drawn through a fine
particle filter to prevent insects and other airborne foreign
matter from entering the mixing and blending unit and greenhouse.
Using a fan and optional damper, the mixing and blending unit
controls the intake of outside air to constantly maintain both the
oxygen and CO.sub.2 level within an acceptable range of setpoint
values.
[0009] Ductwork leads from an outlet of the mixing and blending
unit to fan and coil units. The fan and coil units have outlets
within the greenhouse. The fan and coil units maintain a positive
pressure in the greenhouse which will continually expel air from
the greenhouse out of one or more vents, such as a screened roof
vent, and return ductwork, allowing for additional cooled and
dehumidified air to enter the greenhouse through the fan and coil
units. Concomitantly, the fan and coil units provide a negative
pressure to the mixing and blending Unit to assist in drawing in
the outside air, without imposing a back pressure on the generator
that is providing CO.sub.2.
[0010] During warm days chilled water (i.e., water at about 40 to
50.degree. F., preferably about 44 to 45.degree. F.) may run
through coils of the fan coil units to cool and condense water
vapor in the CO.sub.2-enriched air before it enters the greenhouse.
This provides a low temperature and humidity CO.sub.2-enriched air
entering the greenhouse. By way of example and not limitation, the
entering CO.sub.2-enriched air may be at about 60.degree. F. and
30% relative humidity, even during hot humid summer days. Plants
inside the greenhouse will aspirate water through leaves, which
will evaporate, thereby cooling the plants to further off-set some
of the solar gain. Depending upon the level of natural aspiration
by plants inside the greenhouse, a misting system may be utilized
to regulate temperature and humidity. Plants generally perform best
with humidity levels between 50% and 70% but are not at serious
risk unless the humidity approaches 100% and the temperature inside
the greenhouse exceeds 95.degree. F. for a sustained period.
[0011] The misting system employs sensor data, for both temperature
and humidity, to control the temperature inside of the greenhouse
through evaporative cooling to maintain the best possible growing
temperature. The misting system may be used to reduce temperature
until the relative humidity reaches about 90%. The misting system
may also provide some irrigation. The greenhouse is also equipped
with two retractable shading curtains. One shading curtain, which
reduces the light by 30%, is deployed when the light intensity at
the plant tips exceeds 400 micro mols/square meter/sec and the
space temperature reaches more than 75.degree. F. If the space
temperature continues to rise and the light intensity remains above
400 micro mols/square meter/sec, the first shade curtain will be
displaced by a second curtain that reduces the light by 60%.
Optionally, both curtains may be deployed to provide enhanced
shading.
[0012] The greenhouse may be equipped with a screened roof
ventilation system. The screen prevents ingress by pests and
particulate. Air and CO.sub.2 in the greenhouse that has become hot
and humid is continually displaced by fresh cooled dry CO.sub.2
enriched air. The displaced hot humid gasses are expelled from the
greenhouse through the vents. A positive pressure is maintained in
the greenhouse to prevent airborne and gaseous contaminants and
unconditioned ambient air from flowing through the vent.
[0013] If the temperature inside of the greenhouse continues to
rise, the outside air fan and damper in the mixing and blending
unit and the fan and coil units fans will be brought to maximum
ventilation levels to increase the number of air displacements to
the maximum design level for the system. This may result in reduced
CO.sub.2 concentrations but will reduce the risk of
over-heating.
[0014] A system according to principles of the invention may
recover fuel-generated water and water condensate from the outside
air as a part of the overall water supply. This reduces the overall
dependence on other available water sources, which may be limited
or costly in many locations. Recovered water may be combined with a
harvested rain water to minimize overall water requirements.
[0015] During the winter, the mixing and blending unit will bring
in cool outside air which will be blended with the relatively hot
exhaust gases leaving the direct contact heat exchanger. The
exhaust gases will be entering the mixing and blending unit at
approximately 130.degree. F. and will serve to temper the colder
outside air that will be entering through the filter system. The
tempered air from the mixing and blending unit will be drawn to the
fan and coil units where it will pass over the heating coils
containing hot (e.g., 180.degree. F.) water to maintain a nominal
temperature inside the greenhouse of 75.degree. F. As moisture will
not have been removed from the gases/outside air by condensation,
the plants along with the misting system will be enabled to
maintain an average relative humidity in the greenhouse of about
70%.
[0016] The CO.sub.2 level is maintained at 1,200 ppm during the
winter by modulation of the intake outside air fans.
[0017] In addition to the fan and coil units, with their
heating/cooling coils, the greenhouse may be provided with a heated
pipe system in areas that are designed for vine type products. This
system may circulate hot (e.g. 180.degree. F.) water through pipes.
Solenoid valves may control flow to the pipes. A heating control
system (e.g., programmable logic controller with a thermostat and
one or more temperatures sensors) may modulate water between the
fan and coil system and the pipes to maintain an even distribution
of the heat.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The foregoing and other aspects, objects, features and
advantages of the invention will become better understood with
reference to the following description, appended claims, and
accompanying drawings, where:
[0019] FIG. 1 is a high level block diagram showing subsystems for
an exemplary greenhouse environment control system according to
principles of the invention;
[0020] FIG. 2 is a high level schematic of a generator subsystem
with exhaust gas processing for an exemplary greenhouse environment
control system according to principles of the invention;
[0021] FIG. 3 is a high level schematic of a generator subsystem
with exhaust gas processing for an exemplary greenhouse environment
control system according to principles of the invention;
[0022] FIG. 4 is a high level schematic of a cooling subsystem for
an exemplary greenhouse environment control system according to
principles of the invention;
[0023] FIG. 5 is a high level schematic of a mixing subsystem for
an exemplary greenhouse environment control system according to
principles of the invention;
[0024] FIG. 6 is a high level schematic of an HVAC subsystem for an
exemplary greenhouse environment control system according to
principles of the invention;
[0025] FIG. 7 is a high level schematic of a misting and shading
subsystem for an exemplary greenhouse environment control system
according to principles of the invention;
[0026] FIG. 8 is a high level schematic of a cooling tower
subsystem for an exemplary greenhouse environment control system
according to principles of the invention;
[0027] FIG. 9 is a high level schematic of a HVAC water loop for an
exemplary greenhouse environment control system according to
principles of the invention;
[0028] FIG. 10 is a high level flow chart for an exemplary
greenhouse environment control methodology according to principles
of the invention; and
[0029] FIG. 11 is a high level flow chart for a programmable logic
control methodology according to principles of the invention.
[0030] Those skilled in the art will appreciate that the figures
are not intended to be drawn to any particular scale; nor are the
figures intended to illustrate every embodiment of the invention.
The invention is not limited to the exemplary embodiments depicted
in the figures or the specific components, configurations, shapes,
relative sizes, steps, ornamental aspects, parameters or
proportions as shown in the figures.
DETAILED DESCRIPTION
[0031] A climate control system for a greenhouse according to
principles of the invention provides electricity, water, heating,
cooling, dehumidification and CO.sub.2 enriched air to the interior
of a greenhouse for purposes of facilitating plant growth. With
reference to the high level block diagram of FIG. 1, the system is
comprised of a number of operably coupled subsystems that supply
the aforementioned utilities and provide the functionality. The
greenhouse 125 is substantially closed, excepting screened vents,
and positively pressured to prevent intrusion by contaminants,
pests and ambient air, it is not suitable for fan and pad
evaporative cooling which requires an open path for rapid airflow
to facilitate evaporative cooling. The subsystems include one or
more generator subsystems 100 which simultaneously produce
electricity for lighting and/or sale to a local grid, hot water for
heating, and CO.sub.2 for enhanced photosynthesis. Nox from the
generator exhaust is removed by reaction with urea and catalytic
reduction. Exemplary generator subsystems are illustrated in FIGS.
2 and 3 and discussed below.
[0032] One or more exhaust gas cooling subsystems 105 substantially
reduce the temperature of the hot exhaust gasses from the generator
subsystems. In an exemplary embodiment, one or more single or
multi-stage LiBr absorption units are employed. An exemplary
exhaust gas cooling subsystem is illustrated in FIG. 4 and
discussed below. Water from cooling towers 125 is supplied to the
gas cooling subsystems 105.
[0033] One or more air mixing subsystems 110 mix filtered fresh air
from a fresh air duct and CO.sub.2 from exhaust gas to meet a
setpoint for the greenhouse that is conducive to both
photosynthesis and human occupancy. A return duct within the
greenhouse 125 may supply greenhouse air and CO.sub.2 to the air
mixing subsystems 110 for mixing with the fresh air and exhaust
CO.sub.2 to enhance efficiency. A programmable logic controller 130
may control fans and valves of the air mixing subsystem 110 to
achieve a desired ratio of CO.sub.2 to air in the greenhouse 125,
as determined using one or more CO2 sensors 135 in the greenhouse
125. An exemplary air mixing subsystem is illustrated in FIG. 5 and
discussed below.
[0034] One or more HVAC subsystems 115 feed hot or cold water to
coils in fan coil units in a closed loop. Air and CO.sub.2 from the
mixing subsystem 110 pass over the coils to enter the greenhouse
125. The programmable logic controller 130 may control fans and
valves in the fan coil units to control temperature of water
supplied to the coils. Coil temperature may be controlled to
achieve a temperature in the greenhouse 125 within a determined
range of a setpoint value, as monitored via one or more temperature
sensors 135 in the greenhouse 125. In this manner temperature and
humidity of the greenhouse are controlled. An exemplary HVAC
subsystem is illustrated in FIG. 6 and discussed below.
[0035] One or more temperature regulation subsystems 120 are
provided for controlling shading and misting, which may be employed
in addition to fan coil units. Shading is applied primarily to
limit the temperature rise in the greenhouse. Misting is applied to
provide an evaporative cooling effect. Retractable shading and
misting may be controlled manually or by a programmable logic
controller 130 based upon temperature and humidity sensor readings
135. An exemplary temperature regulation subsystem is illustrated
in FIG. 7 and discussed below. A cooling tower subsystem 125
transfers heat from process water to the atmosphere via evaporative
cooling. An exemplary cooling tower subsystem is illustrated in
FIG. 8 and discussed below.
[0036] A closed water loop subsystem 140 provides water to fan
coils units for heating or cooling. An exemplary closed water loop
subsystem is illustrated in FIG. 9 and discussed below.
[0037] Together, the subsystems comprise an exemplary climate
control system for a greenhouse according to principles of the
invention. Natural gas generators produce exhaust which is treated
via urea reaction and catalytic reduction to yield CO.sub.2 and
water. Absorption units cool the high temperature exhaust gasses to
prevent excessive temperature increases in the greenhouse. A mixing
unit mixes exhaust CO.sub.2 with filtered fresh air. The filtered
CO.sub.2-enriched air enters the greenhouse at a controlled
temperature conducive to plant growth and low humidity that
substantially facilitates evaporative cooling via misting.
Unfiltered ambient air and contaminants are substantially blocked
from entry into the greenhouse.
[0038] Referring to FIG. 2, a schematic of a natural gas generator
subsystem for use in a climate control system for a greenhouse
according to principles of the invention is conceptually
illustrated. A natural gas generator 200 simultaneously produces
electricity for lighting and/or sale to a local grid, hot water for
heating, and CO.sub.2 for enhanced photosynthesis. In one
non-limiting exemplary embodiment, the generator 200 comprises a
Caterpillar CG170-16 generator set, which includes a 16 cylinder
natural gas fueled internal combustion piston engine. Coolant
(e.g., water) heated to approximately 200.degree. F. flows from the
generator through coolant outlet line 205 to a jacket accumulator
tank. The flow rate for the exemplary generator 200 is
approximately 200 to 250 gpm at full load. Exhaust from the
generator 200 is heated to about 800.degree. F. and communicated
through exhaust outlet line 210 at a rate of about 18,500 to 19,000
lb/hr at full load.
[0039] Urea CH.sub.4N.sub.2O and air are supplied to reduce NOx
emissions in the exhaust from the generator 200. Urea
CH.sub.4N.sub.2O is supplied from a storage tank 215 by pump 220.
An air compressor 225 supplies pressurized air to a tank 230 which
supplies air to the exhaust. Optionally, the urea CH.sub.4N.sub.2O
may be diluted in water. Under heat, urea CH.sub.4N.sub.2O
decomposes to ammonia (NH.sub.3) and carbon dioxide
(.sub.CO.sub.2). Ammonia (NH.sub.3) reacts with NOx in the presence
of a catalyst. Urea and air are supplied to the exhaust in a mixing
tube 235 via an injector. Heat from the exhaust evaporates any
water and decomposes the urea, releasing ammonia (NH.sub.3) and
carbon dioxide (CO.sub.2). The ammonia (NH.sub.3) uniformly mixes
with the NOx contained in the exhaust in the mixing tube. The
ammonia (NH.sub.3) and NOx mixture in the exhaust stream enters a
selective catalytic reduction (SCR) catalyst 240, such as a copper
(or iron) zeolite catalyst. The SCR catalyst 240 causes a chemical
reaction between the ammonia (NH.sub.3) and NOx. The products are
nitrogen (N.sub.2) gas and water vapor (H.sub.2O), from the
reaction between the ammonia (NH.sub.3) and NOx, and (CO.sub.2) and
air. Th SCR catalyst may be provided in honeycomb, plate or
corrugated geometries to provide ample surface area for catalytic
reduction while reducing risk of plugging. Additional air may be
introduced through fan 245. A diverter 250 allows some or all of
the exhaust to be exhausted through a silencer 255. The silencer
may comprise a muffler with baffles to attenuate the noise from
exhaust. The un-diverted exhaust gasses (i.e., N.sub.2, H.sub.2O,
CO.sub.2 and air) flow to an absorption chiller.
[0040] Coolant returns from the jacket accumulator to the generator
200 via a return line 260. The fluid may pass through one or more
heat exchangers 265 on return to the generator 200.
[0041] An aftercooler associated with the generator 200 at the end
of a supercharger or turbocharger chain reduces compressed air
temperature to prevent premature ignition. Coolant from the
aftercooler is circulated via fluid circuit 275 through a heat
exchanger 270 to a cooling tower and back to the aftercooler.
[0042] A system according to principles of the invention is
scalable. The principles of the invention are not limited to
systems with one or two generators. Rather one or more generators
may be utilized in systems within the scope of the invention.
Additional generators may be provided to increase electric,
heating, and CO.sub.2 capacity. Larger generators with increased
output may be used. For small scale greenhouses, smaller or fewer
engines may be used. By way of example and not limitation, in the
exemplary embodiment, two generators are shown.
[0043] Referring to FIG. 3, a second natural gas generator
subsystem is conceptually illustrated. The second natural gas
generator subsystem is substantially similar in structure,
configuration and function to the first generator subsystem.
Exhaust and coolant output from the second generator subsystem
merges with output from the first generator subsystem to supply
utilities to the greenhouse. More specifically, a second natural
gas generator 300 simultaneously produces electricity for lighting
and/or sale to a local grid, hot water for heating, and CO2 for
enhanced photosynthesis. In one non-limiting exemplary embodiment,
the generator 300 comprises a Caterpillar CG170-16 generator set.
Coolant (e.g., water) heated to approximately 200.degree. F. flows
from the generator through coolant outlet line 305 to a jacket
accumulator tank. The flow rate for the exemplary generator 300 is
approximately 200 to 250 gpm at full load. Exhaust from the
generator 300 is heated to about 800.degree. F. and communicated
through exhaust outlet line 310 at a rate of about 18,500 to 19,000
lb/hr at full load.
[0044] Urea CH.sub.4N.sub.2O and air are supplied to reduce NOx
emissions in the exhaust from the generator 300. Urea
CH.sub.4N.sub.2O is supplied from a storage tank 315 by pump 320.
An air compressor 325 supplies pressurized air to a tank 330 which
supplies air to the exhaust. Optionally, the urea CH.sub.4N.sub.2O
may be diluted in water. Under heat, urea CH.sub.4N.sub.2O
decomposes to ammonia (NH.sub.3) and carbon dioxide (CO.sub.2).
Ammonia (NH.sub.3) reacts with NOx in the presence of a catalyst.
Urea and air are supplied to the exhaust in a mixing tube 335 via
an injector. Heat from the exhaust evaporates any water and
decomposes the urea, releasing ammonia (NH.sub.3) and carbon
dioxide (CO.sub.2). The ammonia (NH.sub.3) uniformly mixes with the
NOx contained in the exhaust in the mixing tube. The ammonia
(NH.sub.3) and NOx mixture in the exhaust stream enters a selective
catalytic reduction (SCR) catalyst 340, such as a copper zeolite
catalyst. The SCR catalyst 340 causes a chemical reaction between
the ammonia (NH.sub.3) and NOx. The products are nitrogen (N.sub.2)
gas and water vapor (H.sub.2O), from the reaction between the
ammonia (NH.sub.3) and NOx, and (CO.sub.2) and air. Additional air
may be introduced through fan 345. A diverter 350 allows some or
all of the exhaust to be exhausted through a silencer 355. The
silencer may comprise a muffler with baffles to attenuate the noise
from exhaust. The un-diverted exhaust gasses (i.e., N.sub.2,
H.sub.2O, CO.sub.2 and air) flow to an absorption chiller.
[0045] Coolant returns from the jacket accumulator to the generator
300 via a return line 360. The fluid may pass through one or more
heat exchangers 365 on return to the generator 300.
[0046] An aftercooler associated with the generator 300 at the end
of a supercharger or turbocharger chain reduces compressed air
temperature to prevent premature ignition. Coolant from the
aftercooler is circulated via fluid circuit 375 through a heat
exchanger 370 to a cooling tower and back to the aftercooler.
[0047] Whether used for cooling or heating, high temperature
exhaust gasses from the generator subsystems must be cooled before
being introduced into the greenhouse. A cooling subsystem provides
the desired cooling. In an exemplary implementation, the cooling
devices of the cooling subsystem operate on available heat energy.
The invention uses high temperature exhaust gasses to cool a fluid
to a desired temperature. Temperature of exhaust gasses is then
reduced to a desired temperature by heat transfer through one or
more heat exchangers with coils filled with the chilled fluid.
Substantial water vapor in the exhaust gasses condenses upon
adequate cooling, resulting in a relative dry (low humidity)
exhaust gas stream. The invention thus avoids reliance on
conventional fan and pad or misting cooling systems to provide
temperature control in the greenhouse, while also controlling
humidity and providing a water supply. Conventional misting cooling
systems may still be utilized in the greenhouse to provide
additional cooling and irrigation. However, such a misting system
is not a required component of a system according to principles of
the invention. Thus, the invention provides cooling even in humid
climates where evaporative cooling effects from fan and pad or
misting cooling systems would be insufficient.
[0048] Referring now to FIG. 4, an exemplary cooling subsystem is
conceptually illustrated. High temperature exhaust gasses from the
generator subsystems described above with reference to FIGS. 2 and
3 are supplied to one or more absorption units of the cooling
subsystem. Each absorption unit may be single or multiple stage.
Single stage systems operate under two pressures--one corresponding
to the condenser-generator (high pressure side) and the other
corresponding to the evaporator-absorber. In multi-stage systems a
series of condenser-generators operating at progressively reducing
pressures are used. Heat is supplied to the highest stage generator
operating at the highest pressure. The enthalpy of steam generated
from this generator is used to heat and generate more refrigerant
vapor in the lower stage generator and so on. In a cooling
subsystem with more than one absorption unit, such as the subsystem
illustrated in FIG. 4, conduit, manifolds and valves may be
provided to selectively utilize one or more of the absorption units
as may be needed to cool the hot exhaust gasses to a desired
temperature.
[0049] With reference to FIG. 4, each absorption unit 405, 410 uses
a heat source (e.g., heat from generator exhaust) to provide the
energy needed to drive the cooling system. The auxiliary absorption
unit is a single stage unit. The primary absorption unit 410 is a
multi stage unit having first and second stages 415, 417. A liquid
refrigerant evaporates in a low pressure environment, thus
extracting heat from its surroundings. The gaseous refrigerant is
then absorbed--dissolved into another liquid--reducing its partial
pressure in the evaporator and allowing more liquid to evaporate.
The refrigerant-laden liquid is then heated, causing the
refrigerant to evaporate out. It is then condensed through a heat
exchanger to replenish the supply of liquid refrigerant in the
evaporator. In one exemplary embodiment, a solution of lithium
bromide salt LiBr as the absorbent and water H.sub.2O as the
refrigerant are used in the primary absorption unit 410. Water
under low pressure is evaporated from coils that are being chilled.
The evaporated water vapor is absorbed by a lithium bromide/water
solution. Being extremely hygroscopic, lithium bromide readily
absorbs the evaporated water vapor. The water is then driven off
the lithium bromide solution using heat. Condensed water from the
absorption units 405, 410 is supplied to one or more cooling towers
440, 450. Each absorption unit 405, 410 is cooled by condensed
water from wet cooling towers 435, 444 to avoid the possibility of
crystallization of the lithium bromide. Exhaust from an absorption
unit 410 passes through a silencer 420 (e.g., a baffled muffler) to
attenuate noise before release to the atmosphere.
[0050] Accumulator 400 is a pressure storage reservoir in which a
non-compressible fluid (i.e., water) is held under pressure. The
accumulator includes an inlet 455 and outlet 460. The accumulator
400 enables the cooling subsystem to cope with extremes of demand
using a less powerful pump, to respond more quickly to a temporary
demand, and to smooth out pulsations.
[0051] Chilled water from the cooling subsystem is supplied via
outlet line 425 to heat exchangers, i.e., fan coil units, to
further cool the exhaust gasses to a desired temperature before
introduction into the greenhouse. As exhaust gasses pass through
the heat exchangers, heat is transferred from the exhaust gasses to
the supplied chilled water. The heated water is then recirculated
back to the cooling subsystem via return line 430 where it is
chilled again, as described above. This loop continues while the
system operates.
[0052] Referring now to FIG. 5, an air mixing subsystem is
conceptually illustrated. This subsystem adjusts a mix of fresh air
and CO.sub.2 from exhaust gas to meet a setpoint for the
greenhouse. Output from this subsystem is CO.sub.2 enriched air
having a CO.sub.2 concentration that maintains a greenhouse
environment that is conducive to both photosynthesis and human
occupancy.
[0053] Exhaust gasses are cooled and water condenses before the
gasses are mixed with air. Cooling is achieved in primary 515 and
auxiliary 500 cooling units. While two units 500, 515 are
illustrated, the invention is not limited to any particular number
of cooling units. One or more fans and/or pumps 505 propels the
exhaust gasses through the air mixing subsystem.
[0054] An adjustable outlet vent 510 selectively diverts some of
the exhaust gas to the atmosphere. The vent may be opened, closed
or partially opened. The vent may be driven from 0% open (i.e.,
closed) to 100% open. When closed, none of the exhaust gas is
diverted. When opened, all of the exhaust gas may be diverted. When
partially opened, the portion of diverted gas depends upon the
extent the vent is opened. Venting helps maintain a desired
concentration of CO.sub.2 in the gasses that are introduced into
the greenhouse.
[0055] Excessive CO.sub.2 is not desired for photosynthesis and
poses a health risk to human occupants of the greenhouse. A
CO.sub.2 concentration setpoint may be from 750 to 2000 ppm, more
preferably from 800 to 1500 ppm, and most preferably about 1200
ppm. Maintaining 1,200 ppm of CO.sub.2 will increase the growth
rate of most plants by as much as 40% compared to plants grown
in
[0056] greenhouses using only outside air. Such a CO.sub.2-enriched
greenhouse environment will be safe for human occupancy.
[0057] Concentration of CO.sub.2in the greenhouse may be monitored
using CO.sub.2sensors. A programmable logic controller (PLC) may
receive sensor input and adjust an actuator coupled to the vent 510
to control the state of the vent. The vent 510 may be continually
or periodically adjusted in an effort to maintain a setpoint
concentration of CO.sub.2in the greenhouse.
[0058] Each cooling unit in the air mixing subsystem 500, 515 may
comprise a heat exchanger configured for efficient heat transfer
from exhaust gasses to water. In a shell and tube heat exchanger, a
set of tubes contains the hot exhaust gasses. Lower temperature
water from an inlet 530 fluidly coupled to an outlet of a cooling
tower runs over the tubes to absorb the heat required. The set of
tubes may be plain or finned, e.g., longitudinally finned. As the
exhaust gas is cooled below its water dew point, heat is
transferred from the hot exhaust to the water, and water vapor in
the exhaust gas condenses. The heated water may recirculate to a
cooling tower via an outlet 535.
[0059] A mixing box 520 or plenum combines two fluid streams, the
exhaust gas stream and a fresh air stream. The mixing box 520 may
contain dampers or baffles to enhance mixing of the exhaust and
air. The output 525 from the mixing box 520 is CO.sub.2 enriched
air. Air and CO.sub.2 from one or more return ducts 725 within the
greenhouse may be supplied into the mixing box 520 for combination
with the fresh air and exhaust CO.sub.2. The return duct 725 thus
supplies previously conditioned air and CO.sub.2 to reduce the
cooling or heating demands of the system while improving efficiency
and temperature stability in the greenhouse.
[0060] Fresh air is filtered before being mixed with exhaust gasses
in the mixing box 520. Filtration removes contaminants and prevents
intrusion by pests. In one nonlimiting example, fresh air is drawn
through a particulate filter 540, such as a HEPA filter, by a fan
or blower. The filter 540 may be placed at or upstream of the fresh
air inlet to the mixing box 520. Air and Referring now to FIG. 6,
an HVAC subsystem is conceptually illustrated. Hot or cold water is
fed to coils in one or more fan coil units in a closed loop. Air
and CO.sub.2 passes over the coils to enter the greenhouse. In this
manner temperature and humidity are controlled. All, or the vast
majority, of the air and CO.sub.2 in the greenhouse are supplied
through the units of the HVAC subsystem, with the exception of
emissions from plants, organic matter, personnel, and air entering
through doors and any vents and gaps in the greenhouse structure.
This configuration allows precise management of the internal
environment of the greenhouse, including air quality, CO.sub.2
concentration, temperature and humidity.
[0061] Filtered CO.sub.2-enriched air from the mixing box 520
enters a manifold 620. The manifold 620 comprises a main pipe 620,
or channel, from which, branch pipes or channels lead 625, 630.
Each branch 635, 640 supplies the CO.sub.2-enriched air to a fan
coil unit 635, 640. Each fan coil unit is comprised of one or more
coils for heating and cooling, a fan and a chamber. The coils
receive hot or cold water from a central supply 605, and removes
heat from or adds heat to the CO.sub.2-enriched air through heat
transfer. The CO.sub.2-enriched air flows over the coils in the
chamber. The fan coil units are supplied hot or cold water for
heating or cooling from one or more central supplies such as the
absorption units and cooling towers described herein, via an input
line 605. A fan draws the CO.sub.2-enriched air through the chamber
and expels it into the greenhouse 645. The fan speed may be
constant or variable. In the former case, a damper may be provided
in each fan control unit to regulate flow. The fan and damper may
be controlled by a programmable logic controller. In the latter
case, fan speed may be controlled by a climate control system with
a programmable logic controller. Each fan coil unit 635, 640 may
contain an internal thermostat or may be wired to operate with a
remote thermostat. Depending upon the selected chilled water
temperatures and the relative humidity of the space, it is likely
that the cooling coil will dehumidify the entering air stream, and
as a by product of this process, it will at times produce a
condensate which will may be carried to a drain. Each fan coil unit
may contain a drip tray with drain connection for this purpose. The
drain connection may lead to a water storage vessel for use in
irrigation or use with the system described herein. Water flowing
through the coils returns to the system described above via a
return line 610, forming a closed loop.
[0062] The fans of the fan coil units 635, 640 maintain a positive
pressure in the greenhouse. The positive pressure exceeds ambient
air pressure. The greenhouse it is a substantially closed
structure, excepting screened vents, which may be opened and
closed. Air and CO.sub.2 will be expelled from the greenhouse
through any leak in the greenhouse, preventing ingress of
unfiltered ambient air and contaminants. Thus, the greenhouse is a
substantially closed positively pressurized structure containing
CO.sub.2-enriched air.
[0063] The fan coil units may be sized and configured to provide a
determined amount of air changes per time period. In an exemplary
embodiment, the fan coil units change the greenhouse air about once
per twenty minutes, or three times per hour. To achieve the
requisite volumetric flow for the determined number of changes, the
number and size of the fan coil units will depend upon the size of
the greenhouse as well as the volumetric flow rate of each fan coil
unit. Referring now to FIG. 7, a temperature regulation subsystem
is conceptually illustrated. Shading and misting are employed, in
addition to fan coil units 635, 640. Shading is applied primarily
to limit the temperature rise in the greenhouse (i.e., limit solar
gain). Misting is applied to provide an evaporative cooling
effect.
[0064] The amount of energy that comes from the sun is high from
late spring until early autumn. This energy increases air and plant
temperature. The quality of some crops decline when temperature is
excessively high. In addition, photosynthesis peaks for many high
light greenhouse crops at about half the intensity of full
sunlight. Plants require light intensities between 200 micro
mols/square meter/sec and 600 micro mols/square meter/sec. Plants
have a maximum number of mols of light that they can effectively
utilize each growing period. Therefore, the extra light simply is
not needed and potentially detrimental. Even for many high-light
crops, the shading percentage should be about 40 percent, and
perhaps slightly higher (50 percent) for transparent greenhouses
from late spring until early autumn. When light becomes limited
once again in the autumn, shading may be reduced so that crop
quality is not marginalized.
[0065] In an exemplary embodiment, retractable shade curtains 705
are installed inside the greenhouse above the crop. In a particular
preferred embodiment the shading system includes both 30% and 60%
light reducing shade curtains. Individually and in combination the
retractable curtains enable several grades of shading (0%, 30%, 60%
and 90%) that are suitable for a wide range of plants at all times
of year. The fan coil units are below the shade curtains. Solar
energy is allowed to enter the greenhouse before it is reflected by
the curtains 705. This allows heat to accumulate above the shading
material, which provides additional insulation during cooler
evening hours. The shade curtains may be deployed in the evenings
to maintain the heated air space above the shading material during
evening hours. The ability to selectively retract shade curtains
705 during periods of low light is an important attribute of the
shading device. Deployment and refraction of the shade curtains is
controlled by a programmable logic controller.
[0066] As discussed above, a system according to principles of the
invention removes water vapor as condensate from the air and
CO.sub.2 mixture that is blown in through the fan coil units 635,
640. Thus, the CO.sub.2-enriched air blown into the greenhouse is
relatively dry and conducive to evaporative cooling, even when the
greenhouse is located in a region with high ambient humidity.
[0067] It is recognized that the plants can endure temperatures and
humidity levels above this point, and that the greenhouse may reach
conditions that are above the ideal levels. Additional misting may
be employed as the temperatures rise to keep from harming the
plants.
[0068] A fogging or misting system 700 generates a fog or fine mist
to help cool the interior of the greenhouse and provide irrigation,
as solar gain increases. A pump 720 supplies water, from a storage
vessel 715, to nozzles of the misting system 700. The storage
vessel 715 may receive water from any available source of clean
water, including, but not limited to, captured condensate from the
system. The nozzle emit a mist of water droplets. The water
droplets are small enough so they do not saturate the plants, to
avoid the development of diseases and limit deposit of salts
contained in the water, when the water evaporates from the surface
of the leaves between fogging or misting episodes. The droplets are
emitted at a height above the fan coil units and above the plant
canopy, so that evaporation may commence before reaching the
plants, absorbing energy and decreasing the air temperature. The
current of air and CO.sub.2 from the fan coil units 635, 640
facilitates such evaporation. Plants aspirate water and will work
in conjunction with the misting system to maintain an average
relative humidity of between about 50% and 70%, and an ideal
temperature of between about 55.degree. F. to 85.degree. F.,
preferably about 75.degree. F.
[0069] One or more return ducts 725 direct air and CO.sub.2 from
the greenhouse to the mixing box 520, where it can be combined with
fresh air and exhaust CO.sub.2. The return duct 725 thus supplies
previously conditioned air and CO.sub.2 to reduce the cooling or
heating demands of the system while improving efficiency and
temperature stability in the greenhouse.
[0070] Such evaporative cooling via misting would not be efficient
or even effective in humid environments without the greenhouse
being substantially closed and supplied with relatively dry air. In
such environments, where fan and pad cooling systems have been
used, the cooling achieved is predominantly from drenching in water
rather than evaporation. Such drenching can be detrimental to plant
health. Additionally, the openness of a fan and pad cooling system
allows ambient air, contaminants and pests to infiltrate the
system.
[0071] Referring now to FIG. 8, a cooling tower subsystem for use
in a climate control system for a greenhouse according to
principles of the invention is conceptually illustrated. The
cooling tower subsystem includes a cooling tower 800 and a sump
405. The cooling tower is a heat removal device used to remove the
heat absorbed in the circulating cooling water system by
transferring the heat to the atmosphere. In an exemplary
embodiment, the cooling tower uses the evaporation of water to
remove the absorbed heat and cool the working fluid to near the
wet-bulb air temperature. However, other cooling towers such as
closed circuit dry cooling towers may be utilized. In a particular
embodiment, the cooling tower may comprise a mechanical draft tower
using either single or multiple fans to provide flow of a known
volume of air through the tower to achieve stability and reduce the
affect of psychrometric variables. The fans also provide a means of
regulating air flow, to compensate for changing atmospheric and
load conditions, by fan capacity manipulation and/or cycling. A
collection basin is a vessel below and integral with the tower 800
where water is transiently collected and directed to the sump 805.
The sump 805 is a depressed chamber either below or alongside (but
contiguous to) the collection basin of the cooling tower 800. Water
from the basin 800 flows into the sump 805.
[0072] Hot fluid from the engines and their water-cooled
accessories, flue gas cooling vessel and primary and auxiliary
absorption units 810-840 enter the sump 805, where it mixes with
cooled water from the cooling tower 800. Collected fluid from the
sump is pumped into the cooling tower 800, where it is cooled and
returns to the sump 805. Cooled water from the sump 805 is returned
to the engines and their water-cooled accessories, flue gas cooling
vessel and primary and auxiliary absorption units 845-875. A fresh
water makeup supplies fresh water to the sump 805 to replenish
water lost due to evaporation. The fresh water may be supplied from
any fresh water source including harvested rainwater, water
collected from engine exhaust gasses, wells and utility supplied
water.
[0073] Referring now to FIG. 9, a closed water loop 900 provides
condenser water to coils of interior zone HVAC units for heating or
cooling. The water loop 900 temperature may be maintained and
regulated from about 60.degree. F. to 100.degree. F. and more
preferably from about 65.degree. F. to 95.degree. F. to provide
adequate heating and cooling year round in all climates. Water
flows to and from the absorption units, heat exchangers, one or
more optional boilers, and chillers, via inlet and outlet lines
905-975 to supply the warm or cool water desired from achieving a
targeted greenhouse indoor temperature. Supplied water flows to the
units of the HVAC system via supply line 980. Return from the HVAC
system is received via return line 985.
[0074] With reference to the flowchart of FIG. 10, an exemplary
method of controlling climate for a greenhouse according to
principles of the invention entails providing a greenhouse that
receives substantially all air and CO.sub.2 through a plurality of
fan coil units, as in step 1000. Unlike conventional greenhouses
which maintain a stream of air from an inlet to an opposite outlet
for fan and pad cooling, a greenhouse according to principles of
the invention is substantially closed. Air and CO.sub.2 are
introduced through fan coil units. Also, unlike a conventional
greenhouse, a greenhouse according to principles of the invention
receives dehumidified air and CO.sub.2 within a setpoint
temperature range through the fan coil units. This obviates fan and
pad cooling. It also allows greater control over the gasses and
contaminants that enter the greenhouse. It also enables use of the
greenhouse in humid environments, where conventional evaporative
cooling methods would be inadequate.
[0075] In the vicinity of the greenhouse, but external to the
greenhouse, a natural gas fueled internal combustion engine is
operated to produce high temperature exhaust, as in step 1005. Urea
CH.sub.4N.sub.2O and air are supplied to the hot exhaust to reduce
NOx emissions, as in step 1010. Under heat, urea CH.sub.4N.sub.2O
decomposes to ammonia (NH.sub.3) and carbon dioxide (CO.sub.2).
Ammonia (NH.sub.3) reacts with NOx in the presence of a catalyst.
Urea and air are supplied to the exhaust in a mixing tube via an
injector. Heat from the exhaust evaporates any water and decomposes
the urea, releasing ammonia (NH.sub.3) and carbon dioxide
(CO.sub.2). The ammonia (NH.sub.3) uniformly mixes with the NOx
contained in the exhaust in the mixing tube. The ammonia (NH.sub.3)
and NOx mixture in the exhaust stream enters a selective catalytic
reduction (SCR) catalyst, such as a copper zeolite catalyst, as in
step 1015. The SCR catalyst causes a chemical reaction between the
ammonia (NH.sub.3) and NOx. The products are nitrogen (N.sub.2) gas
and water vapor (H.sub.2O), from the reaction between the ammonia
(NH.sub.3) and NOx, and (CO.sub.2) and air. These products are
supplied to an absorption chiller for cooling, as in step 1020.
[0076] Temperature of the exhaust products is reduced by passing
the exhaust gasses through one or more absorption units, as in step
1020, where heat from the exhaust causes a liquid refrigerant to
evaporate in a low pressure environment. The gaseous refrigerant is
then absorbed--dissolved into another liquid--reducing its partial
pressure in the evaporator and allowing more liquid to evaporate.
The refrigerant-laden liquid is then heated, causing the
refrigerant to evaporate out. It is then condensed through a heat
exchanger to replenish the supply of liquid refrigerant in the
evaporator. In one exemplary embodiment, a solution of lithium
bromide salt LiBr as the absorbent and water H.sub.2O as the
refrigerant are used in an absorption unit. Water under low
pressure is evaporated from coils that are being chilled. The
evaporated water vapor is absorbed by a lithium bromide/water
solution. Being extremely hygroscopic, lithium bromide readily
absorbs the evaporated water vapor. The water is then driven off
the lithium bromide solution using heat. Condensed water from the
absorption units is supplied to one or more cooling towers. Each
absorption unit is cooled by condensed water from the cooling
towers to avoid the possibility of crystallization of the lithium
bromide.
[0077] One or more heat exchangers may be used to further reduce
the temperature of the exhaust products, as in step 1025. Cooled
water from the cooling towers may be supplied to the heat
exchangers. Heat from the exhaust gas is transferred to the cooled
water from the cooling tower.
[0078] Filtered fresh air and CO.sub.2 from the cooled exhaust gas
from the absorption unit are mixed with air and CO.sub.2 drawn
through a return duct from inside the greenhouse to produce
CO.sub.2 enriched air having a CO.sub.2 concentration that
maintains a greenhouse environment that is conducive to both
photosynthesis and human occupancy, with a CO.sub.2 concentration
setpoint from 750 to 2000 ppm, more preferably from about 800 to
1500 ppm, as in step 1030. The CO.sub.2 concentration is measured
inside the greenhouse at one or more locations using CO.sub.2
sensors. Using a programmable logic controller, the mixture of air
and CO.sub.2 may be adjusted to achieve and maintain the CO.sub.2
concentration within a determined range of the setpoint.
[0079] The fresh air and CO.sub.2 mixture are passed over the coils
of the fan coil units leading into the greenhouse, as in step 1035.
In this manner temperature and humidity are controlled. All, or the
vast majority, of the air and CO.sub.2 in the greenhouse are
supplied through the fan coil units. This configuration allows
precise management of the internal environment of the greenhouse,
including air quality, CO.sub.2 concentration, temperature and
humidity. The coils receive hot or cold water from a supply source,
and remove heat from or adds heat to the CO.sub.2-enriched air
through heat transfer. Depending upon the water temperature and the
relative humidity of the CO.sub.2-enriched air, the coils may
dehumidify the entering stream, and as a by product of this step
produce a condensate. The fresh air and CO.sub.2 mixture that has
passed over the coils is at a temperature suitable for plant growth
and human occupancy when it enters the greenhouse. Air and CO.sub.2
in the greenhouse are drawn through a return duct, as in step 1040,
and then mixed with filtered fresh air and CO.sub.2 from the cooled
exhaust gas from the absorption unit as in step 1030.
[0080] Referring now to FIG. 11, a programmable logic controller,
such as but not limited to a proportional-integral-derivative
controller (PID controller), calculates an "error" value 1110 as
the difference between a measured process variable (e.g.,
temperature, pressure, light, humidity, CO2 concentration, etc . .
. ) 1100 and a desired setpoint 1105. The process variable 1100 is
determined from sensor input for the measured variable. The
controller attempts to minimize the error by adjusting the process
control variables 1115 which are analog and/or digital logic level
signals output to controlled devices. By way of example and not
limitation, controlled devices may include valves, dampers, motors,
solenoids, actuators, switches, microcontrollers, etc. . . .
Adjustment of the controlled devices via the control variables 1115
influence the sensed process variables. For example, a damper may
be opened or closed fully or partially and/or fan's speed may be
increased or decreased to adjust CO2 concentration, or pressure or
temperature. As another non-limiting example, a shade may be
deployed or retracted to adjust light intensity. As yet another
example, misting may cease to limit humidity or commence to reduce
temperature. In the interest of achieving a gradual convergence to
the desired setpoints, the controller may damp oscillations by
tempering its adjustments, or reducing the loop gain, thereby
avoiding or minimizing overshoot.
[0081] While an exemplary embodiment of the invention has been
described, it should be apparent that modifications and variations
thereto are possible, all of which fall within the true spirit and
scope of the invention. With respect to the above description then,
it is to be realized that the optimum relationships for the
components and steps of the invention, including variations in
order, form, content, function and manner of operation, are deemed
readily apparent and obvious to one skilled in the art, and all
equivalent relationships to those illustrated in the drawings and
described in the specification are intended to be encompassed by
the present invention. The above description and drawings are
illustrative of modifications that can be made without departing
from the present invention, the scope of which is to be limited
only by the following claims. Therefore, the foregoing is
considered as illustrative only of the principles of the invention.
Further, since numerous modifications and changes will readily
occur to those skilled in the art, it is not desired to limit the
invention to the exact construction and operation shown and
described, and accordingly, all suitable modifications and
equivalents are intended to fall within the scope of the invention
as claimed.
* * * * *