Note: Descriptions are shown in the official language in which they were submitted.
CA 02358337 2001-10-02
Matter no.: V80012CA
Filename: 28452 v1
Greenhouse Climate Control System
FIELD OF THE INVENTION
The invention relates generally to a climate control system for a greenhouse.
BACKGROUND OF THE INVENTION
A greenhouse is an enclosure for cultivating and protecting plants inside the
greenhouse from the outside environment. Greenhouses are designed to control
the
balance oftemperature, moisture, COZcontent, and light to suit the growth
requirements
for plants, and particularly, for tender plants or plants grown out of season.
The temperature conditions inside the greenhouse will depend on the type of
plant grown in the greenhouse. Some plants require substantially the same
temperature to be maintained 24 hours a day, while other plants will require
very
specific temperature changes at different times of the day. The temperature
outside the
greenhouse of course affects the temperature inside. Further, solar radiation
during a
sunny day can heat the greenhouse, dramatically increasing the inside
temperature.
Typical energy sources used to heat greenhouses include natural gas, propane,
wood, coal, solar radiation, and electricity. Some of the energy sources can
be used
directly to heat the greenhouse, wherein others such as propane or natural gas
are
burned in a gas-fired boiler to heat water. The heated water is distributed
through heat-
conductive pipes that typically are located near the plants to be heated. The
heat
radiated by these pipes is typically distributed around the greenhouse by a
series of
fans that are used to circulate air.
Cooling the greenhouse may be achieved via a number of ways. For example,
wall and roof vents may be provided that are opened to allow outside ambient
air inside
the greenhouse and inside hot air to escape. Fans may be provided to assist in
this air
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exchange. Roof vents in particular can be configured to open small or large
portions
of the roof. A shading system may be provided on the roof and walls that
during the
day block incoming solar radiation from entering the greenhouse. The shading
system
may also serve as thermal barriers, and as such be used at night to reduce
heat loss
out of the greenhouse when the outside is cooler than the inside. Typical
shades are
made of a porous fabric that allow for some limited air flow through the
fabric. Other
cooling systems include fog systems that include high pressure pumps that are
used
to distribute a fine mist of high pressure water (often in excess of 1000psi)
via a
plurality of very small nozzles. The water molecules tend to absorb some of
the heat
inside the greenhouse, but will fall to the ground and increase relative
humidity (RH).
Therefore, fog systems are best used for temporary cooling.
Another important consideration for greenhouse design is the control of
humidity
within the greenhouse. The relative humidity inside a greenhouse usually
builds up
during the night while the plants are transpiring, and by evaporation of any
liquid water
that is left on the floor during the day from irrigation cycles, fog cooling,
etc. Overly high
RH will prevent a plant from cooling itself adequately, while an overly low RH
will cause
the plant to dry out. Therefore, precise control of the RH in a greenhouse is
important
to prevent the plants within from suffering.
Typically, greenhouse operators vent the greenhouse early in the morning, e.g.
by opening roof vents, to reduce the RH that has built up inside the
greenhouse over
the night. Also, exhaust fans typically used for cooling can be turned on to
increase the
air exchange rate into and out of the greenhouse. When internal RH is lower
than
desired, systems typically used for cooling can be activated to increase the
RH, e.g.
by turning on the fog mist system and/or pad cooling system, provided that
appropriate
conditions exist for such operation. Many of these known humidity controlling
techniques require the exchange of outside and inside air; if the RH or the
temperature
of the outside air is not at an appropriate level, then such techniques are
less effective,
or even dangerous to the health of the plant. For example, venting moisture
from a
greenhouse on a cold damp day may not appreciably reduce the RH inside the
greenhouse, may cause a dramatic temperature change-related shock to the
plants,
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and may increase operating costs by requiring additional heat to be supplied
to warm
the greenhouse back to its pre-venting temperature.
Other factors that are considered in greenhouse design include plant
irrigation
and carbon dioxide supply. It has been long recognized that elevated levels of
C02
enhances crop growth, and as such, growers try to maintain C02 levels at
higher than
ambient conditions inside the greenhouse. Typically, C02 introduced into the
greenhouses is produced by one or more of open air natural gas or propane
burners,
flue gas recovery systems, or supplied from liquid C02 tanks. If C02 is
introduced via
a combustion process, unwanted water, carbon monoxide and nitrous oxides are
typically also introduced with the C02 into the greenhouse. C02 is typically
introduced
into the greenhouse during the day. Unfortunately, other climate control
techniques
used during the day compromise the effectiveness of COZ injection. For
example,
periodic venting of moisture from the greenhouse tends to also vent a
substantial
amount of the injected CO2.
Various factors must be controlled to maintain an ideal environment for plant
growth. The traditional methods and systems for controlling one factor are
often not
compatible with controlling another factor, and thereby results in high
operating costs
and reduced plant growth. A typical day and night cycle illustrates the
difficulty of
controlling such factors. During the night, plants give off moisture and C02.
By the end
of the night, the RH and C02 will tend to be relatively high. As the sun
rises, and the
plants awaken to their day cycle, they requires moisture which is provided to
them by
the greenhouse irrigation system, which further raises the RH inside the
greenhouse.
The RH must be reduced quickly to avoid damaging the plants. Air exchange
methods
are thus undertaken to replace the RH-heavy greenhouse airwith lower RH
outside air.
As the internal air is discharged, accumulated COZthat would be usefully used
during
the day is also flushed out of the greenhouse. The vents are often left open
for
extended periods to cool and reduce the moisture content inside the
greenhouse,
forcing the operator to pump a relatively high amount of COZ into the
greenhouse to
compensate for the amounts lost by venting. As the sun falls and evening sets
in,
venting may also occur to lower the RH prior to nightfall. Such venting often
prevents
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the use of the greenhouse's shading system that would normally be used for
heat
retention. Heaters must therefore be run at a relatively high level to
compensate for the
heat lost by venting.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided an air processing
unit
for a greenhouse comprising a main body having a greenhouse return air inlet,
a
greenhouse supply air outlet, and an air flow path between the inlet and
outlet. Further,
inside the main body in the air flow path there is: an air temperature
modifier, an air
humidity modifier; and a COZ injector. Greenhouse return air fed into the air
processing
unit is processed to modify one or more of its temperature, relative humidity,
or C02
content before being discharged from the air processing unit as supply air
back into the
greenhouse.
The air temperature modifier may comprise an air cooler and an air heater, and
the humidity modifier may comprise a dehumidifier and a humidifier. The
dehumidifier
and cooler may comprise dehumidification and cooling coils that flow cooling
fluid
therethrough so that heat in the air path passing by the coils is transferred
to the cooling
fluid, and moisture in the air path is condensed inside the unit. The
humidifier may
comprise at least one water jet for spraying a mist of water into the air
path. The heater
may comprise primary heating heat exchanger coils that flow hot water
therethrough so
that heat is radiated from the hot water and into the air stream.
The air processing unit may further comprise reheating heat exchanger coils
that
are fluidly connected to the dehumidification and cooling coils, such that
return cooling
fluid from the dehumidification and cooling coils is flowable through the
reheating heat
exchanger coils to transfer some of the heat extracted during cooling and
dehumidification back into the air stream.
According to another aspect of the invention, a climate control system for a
greenhouse is provided that comprises the air processing unit as described
above, a
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greenhouse return air collector inside the greenhouse, a return air duct
fluidly
connected to the return air collector and the inlet of the processing unit; a
greenhouse
supply air distributor inside the greenhouse, and, a supply air duct fluidly
connected to
the supply air distributor and outlet of the processing unit.
$
Distribution tubes may be provided that are fluidly connected to the supply
air
distributor and mounted to the floor of the greenhouse, and have a plurality
of spaced
openings for discharging supply air into the greenhouse.
The climate control system may further comprise temperature, humidity and
carbon dioxide sensors mounted inside the greenhouse. The climate control
system
may further comprise a control unit communicatively linked to the temperature,
humidity
and carbon dioxide sensors, and the processing unit. The computer system has
stored
therein at least one reference plant climate profile; the control unit is
configured to
1$ measure the temperature, humidity and carbon dioxide levels inside the
greenhouse,
compare the measured levels against the reference plant climate profile, and
adjust the
settings of the processing unit to modify the greenhouse air to conform to the
reference
plant climate profile.
The climate control system may further comprise a boiler and a main radiant
heating water loop fluidly connected to the boiler, and wherein the primary
heating coils
are fluidly connected to the main radiant heating water loop. A floor heating
system
may_also be fluidly connected to the main radiant heating water loop. The
floor heating
system may comprise a heat exchanger thermally connected to the floor heating
system
2$ and to a cooling fluid return conduit connected to the processing unit,
such that some
of the heat absorbed by cooling fluid in the unit is transferred via the heat
exchanger
to the floor heating system.
The climate control system may further comprise an irrigation heating system
that is fluidly connected to the main radiant heating water loop. The
irrigation heating
system may comprise a heat exchanger thermally connected to the irrigation
heating
system and to a cooling fluid return conduit connected to the processing unit,
such that
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some of the heat absorbed by cooling fluid in the unit is transferred via the
heat
exchanger to the irrigation heating system.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic perspective view of an air processing unit of a
greenhouse climate control system according to an embodiment of the invention;
Figure 2 is a schematic top view of the processing unit of Figure 1;
Figure 3 is a schematic perspective view of a greenhouse incorporating the
climate control system;
Figure 4 a schematic top view of a greenhouse supply air distribution array of
the
greenhouse climate control system;
Figure 5 is a schematic piping diagram of an another embodiment of the
greenhouse climate control system; and,
Figure 6 is schematic piping diagram of yet another embodiment of the
greenhouse climate control system.
DETAILED DESCRIPTION
Referring to Figures 1 and 2 and according to one embodiment of the invention,
there is provided a greenhouse climate control system 10 for controlling the
temperature, relative humidity (RN) and COZ levels in a greenhouse. The system
10
has an air processing unit 12 that receives return air from the greenhouse via
a return
air duct 14 connected to an inlet 16 of the unit 12. The unit 12 discharges
processed
supply air back to the greenhouse via a supply air duct 18 connected to an
outlet 20 of
the unit 12. The unit 12 is preferably fluidly sealed to prevent or at least
significantly
impede air from escaping from the unit 12.
Inside the unit 12 are a number of components for processing the greenhouse
air, including primary dehumidication and cooling coils 22, airfilters 24, re-
heat coils 26,
heating coils 28, a COZ injector 30, a humidifier 32, and a fan 38. All of
these
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components are arranged in-line with the air flow so that air passing through
the unit
12 will encounter each of these components in sequential downstream order.
Return air from the greenhouse is typically warm and saturated with water. The
air entering the unit 12 first passes by air filters 24 to remove any unwanted
particulates
that may damage the unit 12, as well as to provide cleaner air back into the
greenhouse. The filters 24 per se are of a conventional design and may be for
example, disposable fibre filters commonly used in the HVAC industry.
Having passed through the filters 24, the air then passes by the primary
dehumidification and cooling coils (PDC coils) 22. The PDC coils 22 are made
from thin
copper tubing and have an inlet and an outlet for the inflow and outflow of a
cooling
fluid, such as water, or a suitable refrigerant fluid. The coil pattern can be
based on one
of many known heat exchanger coil designs in the refrigeration industry. The
PDC coils
22 are preferably made of copper but may be made with any material having a
suitably
high degree of thermal conductivity. In a system using cooling water as the
cooling
fluid, cooling water is pumped through the PDC coils 22 from a cold water
source via
cooling water conduit 40 connected to the inlet of the PDC coils 22. As warm
greenhouse return air passes by the PDC coils 22, heat will be transferred
from the air
to the cooling water, thereby lowering the temperature of the air and raising
the
temperature of the cooling water. As the air cools, its RH will reach 100% and
the air
will reach its dew point and will not be able to hold any more water; as the
air is cooled
further, some of the water vapour will condense inside the unit 12 and
particularly on
the PDC coil 22. This condensed water is drained from the unit 12 through a
drain (not
shown) at the bottom of the unit 12. The recovered water can then be stored
for reuse
by other systems, such as the irrigation and fog systems.
The cooling water warmed during the cooling and dehumidification of the
greenhouse air can be immediately removed from the unit 12 for discharge via a
cooling
water return conduit 42 connected to the outlet of the PDC coils 22, or can be
directed
through the reheat coils 26 to return some of the heat back to the greenhouse
air
stream, before being removed from the unit 12. The removed heat can be stored
in a
heat sink (not shown) such as a pond or an irrigation storage tank, such that
the heat
can be usefully used later. The path of the cooling water is controlled by a
diversion
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valve 44. If the greenhouse requires cooling, then the diversion valve 44 is
set to
bypass the re-heat coils 26 and to direct the water immediately to the return
conduit 42
for removal from the unit 12. If however, the temperature of the greenhouse is
at or
about nominal levels, or requires heating (e.g. at night, or during the
winter), the
diversion valve 44 can be set to direct water through the reheat coils 26 to
return some
of the heat back to the greenhouse air. The re-heat coils 26 are a heat
exchanger
having a construction similar to the PDC coils 22, and in particular has an
outlet that is
fluidly connected to the return conduit 42.
The heating coils 28 are a heat exchanger and are constructed similarly to the
PDC coils 22 and the reheat coils 26. Heated water is transmittable through
the
heating coil 28 via a heated water inflow conduit 46 fluidly connected to an
inlet of the
heating coil 28, and a heated water return conduit 48 fluidly connected to an
outlet of
the heating coil 28. On occasions requiring heating of the greenhouse air, the
heating
coil 28 is activated by flowing hot water through the heating coil 28 so that
heat from the
heating water can be transferred to the greenhouse air stream.
COZ can be introduced into the air stream by one or more COZ injectors 30
located downstream of the heating coil 28. The C02 injectors 30 have an
injection port
36 which is fluidly connected to a COZ supply (shown as 49 in Figure 3). The
C02
supply may be a propane or natural gas burner located remote from the unit 12.
If the PDC coils 22 lowered the RH of the greenhouse air stream below a
desired
level, or the return air is low in RH (e.g. during high solar periods when
internal air
temperatures rise), water can be reintroduced into the air stream by the
humidifier 32,
which may suitably be a series of water jets that are controllable to emit a
fine spray of
water into the air stream. The humidifier 32 has an injection port 33 that is
fluidly
connected to a water supply (not shown).
The fan 38 is provided downstream of the humidifier 32 to move the greenhouse
air stream through the system 10, and particularly, from the air return
ducting 14,
through the unit 12, and back into the greenhouse via air supply ducting 18.
After the greenhouse air stream has been processed by the unit 12, it is
returned
as supply air to the greenhouse. In particular, the supply air is discharged
through the
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supply air ducting 18 and into the greenhouse through a supply air
distribution array 50.
Referring to Figure 3, the distribution array 50 is located inside and along
the floor at
one end of the greenhouse. Referring to Figure 4, the distribution array 50 is
a series
of branching tubes that distribute air from a main supply tube 51 to a
plurality of branch
tubes 52 and then to a plurality of outlets 54 of each branch tube 52. An air
damper
may be provided at each branching point to balance the air flow between each
of the
downstream branches; such air dampers are conventional devices known in the
HVAC
industry to serve such a purpose.
Each branch tube outlet 54 is connected to a distribution tube 56 that has a
plurality of small apertures along its length to discharge processed air back
into the
greenhouse. A plurality of distribution tubes 56 are shown in Figure 3 to
extend from the
distribution array 50 at one end of the greenhouse, along the floor of the
greenhouse,
and to the opposite end of the greenhouse. With such a configuration,
processed supply
air is discharged relatively uniformly from the ground of the greenhouse.
Mounted near the top of the greenhouse at the end opposite the end having the
distribution array 50, is a greenhouse air collector array 60. Hot air rising
towards the
roof of the greenhouse is sucked into the collector array 60 for delivery via
return air
return ducting 14 to the processing unit 12.
One or more C02 sensors, thermometers and hygrometers (not shown) are
provided in the greenhouse nearthe distribution tubes 56 to measure the
respective C02
level, RH and temperature of the processed supply air. Additional C02 sensors,
thermometers and hygrometers (not shown) are located above the plants and/or
near
the air collector array 60 to measure the RH and temperature of the return
air. A
computer (not shown) is programmed with a climate control program, and is
communicatively linked to the COZ sensors, thermometers and hygrometers and
the
processing unit 12. In the computer system, the program has stored a number of
reference climate profiles for different plants. For each plant's climate
profile there is
included a number of parameters such as preferred temperature range, RH range,
and
C02 range for different times of the day, and for different seasons in the
year. The
parameters in each reference profile are adjustable by operator, enabling the
operator
to fine tune the reference profile to the particular plant he is growing; or,
the operator
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may input his own parameters and create his own unique climate profile. In
operation,
the computer compares the actual climate conditions inside the greenhouse as
measured by the thermometers and hygrometers against the reference levels, and
controls the processing unit 12 to process air to conform to the reference
levels.
Alternatively, such control may be performed manually by an operator, who can
monitor the measured climate conditions, e.g. via a computer monitor at a
station inside
the greenhouse, and make the necessary adjustments to the unit 12.
According to a second embodiment of the invention, and referring to Figure 5,
a
climate control system 100 is provided that includes the climate control unit
12 as
described above, as well as components for providing hot water radiant heating
to the
greenhouse interior. The system includes a pair of boilers B1 and B2, a main
water
distribution loop 102 fluidly connected to the boilers B1 and B2, a primary
pump P3 for
pumping water through the main water distribution loop 102, an expansion tank
E1
fluidly connected to the distribution loop 102 for accepting increased water
volume
resulting from thermal expansion, a make-up water source MU1 fluidly connected
to the
distribution loop 102 for providing a uniform water pressure inside
distribution loop 102,
a roof heating system A fluidly connected to the distribution loop 102, a
floor heating
system C thermally connected to the distribution loop 102, and an irrigation
system D
thermally connected to the distribution loop 102.
Roof heating system A comprises a loop of metal roof piping 104 mounted near
the roof of the greenhouse, and serves to heat the roof by hot water radiant
heating, to
melt any snow that may have accumulated on the roof. The roof piping 104 has
an inlet
and an outlet connected to the main water distribution loop 102 such that
supply water
heated by the boilers B1, B2 is delivered to the roof piping 104, and return
water cooled
from the heat transfer to the roof is returned to the boilers B1 and B2 for
reheating. Flow
of heating water through the roof piping can be controlled by controlling a
control valve
Z.
Floor heating system C comprises a heat exchanger HA, a closed loop of floor
piping 106 mounted to the floor of the greenhouse and having a portion passing
through
the heat exchanger HA, heat transfer piping 108 having an inlet and outlet
fluidly
connected to the main water distribution loop 102 and having a closed portion
passing
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through the heat exchanger HA, control valves V1A and V1B located at the inlet
and
outlet of the heat transfer piping 108, a pump P7 located in the heat transfer
piping 108,
pumps P8 and P9 located in the floor piping 106, a make-up water source MU2
fluidly
connected to the floor piping 106, and an expansion tank E2 fluidly connected
to the
floor piping 106. In heating operation, valves V1A and V2A are opened and hot
water
heated by boilers B1, B2 is pumped through the heat transfer piping 108 by
pump P7.
Heat is radiantly transferred from the heat transfer piping 108 to the floor
piping 106
inside heat exchanger HA, and the heated water in the floor piping 106 is
pumped
through the floor piping 106 by the pumps P8 and P9. Water flow inside the
main water
distribution loop 102 is fluidly isolated from the water flow inside the floor
system C.
Irrigation system D comprises a heat exchanger HB, a loop of irrigation piping
110
mounted to the floor of the greenhouse and having a closed portion of the loop
passing
through the heat exchanger HB, heat transfer piping 112 having an inlet and an
outlet
fluidly connected to the main water distribution loop 102 and having a closed
portion
passing through the heat exchanger HB, a control valves V2A and V2B located at
the
inlet of the heat transfer piping 112, a pump P10 located in the heat transfer
piping 112,
and pumps P11 and P12 located in the irrigation piping 110. In heating
operation,
irrigation water to be delivered to the plants inside the greenhouse receives
heat from
boiler in a manner similar to the heat transfer to the floor heating system C.
That is,
heated water from the boilers B1, B2 is pumped through heat transfer piping
112 by
pump P10, and heat is radiantly transferred to the irrigation piping 110
inside heat
exchanger HB. Water flow inside the main water distribution loop 102 is
fluidly isolated
from the water flow inside the irrigation system D.
Heating coils 28 of the unit 12 are fluidly connected to the main water
distribution
loop 102 by the heating water inflow conduit 46 and the heating water return
conduit 48.
In this embodiment, heating coils 28 can also serve as cooling coils: control
valve X is
provided upstream of heating water inflow conduit, and can be closed to stop
flow of
heating water from the boilers B1, B2 to the heating coils 28; cold water from
the cold
water source is fluidly connected to the heating water inflow conduit 46 by
cold water
supply pipe 120; a control valve Y is provided between the inflow conduit 46
and cold
water supply pipe 120. In heating operation, control valve Y is closed and
control valve
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X is opened, so that hot water from boilers B1, B2 are pumped by a pump P5
through
the heating coils 28. In cooling operation, control valve Y is opened, and
control valve
X is closed so that cold water from cold water source is pumped through the
heating
coils 28.
According to third embodiment of the invention, and referring to Figure 6, a
climate control system 200 is provided that includes the climate control unit
12 as
described above, the components of the second embodiment, as well as
components
to direct heat captured during the dehumidification and cooling operation of
the unit 12
back into the greenhouse at an appropriate time.
l0 The additional components of the third embodiment include:
a heat exchanger HP;
floor heating supply conduit 202 having an inlet connected to the heat
transfer piping
108 of floor heating system C downstream of the heat exchanger HA, an outlet
connected to the heat transfer piping 108 upstream of the heat exchanger HA,
and a
closed portion passing through heat exchanger HP;
a control valve V3 in floor heating supply conduit 202 upstream of heat
exchanger HA;
a irrigation heating supply conduit 206 having an inlet connected to heat
transfer piping
112 of irrigation heating system D downstream of heat exchanger HB, an outlet
connected to the heat transfer piping 112 upstream of the heat exchanger HB,
and a
closed portion passing through heat exchanger HP;
a control valve V4 in irrigation heating supply conduit 206 upstream of heat
exchanger
HB;
a heat exchanger pump 204 for pumping water in the floor heating supply
conduit 202
and the irrigation heating supply conduit 206 and,
a cooling water return conduit 208 fluidly connected to the outlet of the PDC
coils 22 and
having a portion passing through the heat exchanger HP.
On occasions where greenhouse heating is required, e.g. at night or during the
winter, the boilers B1 and B2 are operated to provide heat to the greenhouse
interior via
the radiant heating water loop and via heating coils 28. Additional heating
can also be
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provided to the greenhouse interior using heat extracted from the greenhouse
return air
by the processing unit 12, as follows: Valves V1A, V1 B and V2A, V2B are
closed to stop
radiant heating water from flowing into heating loops HA and HB (boilers B1
and B2
may be shut off or turned down at this time to save energy). Then, valves V3
and V4 are
opened and pump 204 is operated to pump water through heat transfer piping
108, 112
to heat exchangers HA and HB.
Cooling water that has absorbed heat during the greenhouse air cooling process
is directed through the conduit 208 and through the heat exchanger HP; heat is
then
radiantly transferred from the cooling water to the water in heat transfer
piping 108, 112.
In all embodiments, a system is provided to process the internal air of a
greenhouse and provide simultaneous control of various climate parameters,
namely
RH, temperature and carbon dioxide content. These climate parameters are
monitored
and adjusted as needed by a computer or operator. Recovered heat can be reused
in
the greenhouse to reduce energy costs associated with operating the
greenhouse.
Recovered water (condensate) can be reused by the greenhouse to reduce water
usage. By controlling the climate using climate using system 10, the use of
venting or
other conventional energy or resource wasting measures can be minimized. For
example, studies have shown that carbon dioxide usage is reduced by up to 54%
by
using system 10, i.e. a reduction of 81 kg/hour/? of carbon dioxide lost to
the
atmosphere.
While the present invention has been described herein by the preferred
embodiments, it will be understood to those skilled in the art that various
changes may
be made and added to the invention. The changes and alternatives are
considered
within the spirit and scope of the present invention.
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