Apparatus for heating a greenhouse

An apparatus for heating a greenhouse and supplying carbon dioxide gas thereto, including a heater burning a hydrocarbon fuel arranged to at least indirectly heat the atmosphere of the greenhouse when required; a cooler for cooling the carbon dioxide produced by operation of the heater; a storage device connected by a gas flow mechanism to receive combustion gas from the heater and to hold the combustion gas having carbon dioxide produced by the operation thereof; a distribution mechanism supplying the stored carbon dioxide gas containing combustion gas from the storage device to the greenhouse atmosphere, and a distribution control mechanism for allowing a supply of the carbon dioxide gas at a predetermined time and flow rate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an apparatus for heating a greenhouse and 
enriching its atmosphere with carbon dioxide. 
More particularly, the invention provides means to capture and store the 
carbon dioxide contained in the combustion gases of a hydrocarbon-fueled 
greenhouse heater, and to supply said carbon dioxide from a storage vessel 
or envelope to the greenhouse atmosphere at the optimum time, as 
determined by horticultural considerations. 
2. Dicussion of the Background 
Greenhouses are a well-known means for improving agricultural plant yields, 
and for allowing cultivation of crops which would not develop as well in 
open fields. Greenhouses have transparent roofs which trap incoming solar 
radiation. While the daytime temperature inside the greenhouse enclosure 
is usually sufficiently high for optimum plant development, greenhouse 
heaters are commonly used to boost nighttime temperatures so as to prevent 
crop damage during the winter season. 
As is known, plant growth can be very substantially accelerated when such 
plants are grown in an atmosphere provided with an enhanced carbon dioxide 
content. For industrial purposes, carbon dioxide gas is readily supplied 
through the use of commercially-available compressed gas cylinder. 
However, although it is not expensive, this form of gas supply is not 
economically viable for use in agriculture, even after making allowance 
for the advantage of supplying the gas at no higher than ambient 
temperature. 
Greenhouse heating systems of the type having a heater burning hydrocarbon 
fuels are known. Such systems have arrangements with heat exchangers and 
secondary media, e.g., air or water, for heating the greenhouse while 
venting the exhaust gases of said heater to the atmosphere, since the 
exhaust gases of heavy fuels normally used to power said systems are known 
to be dangerous to plants. Systems using this principle are described in 
U.S. Pat. Nos. 3,357,088; 4,830,276 and 5,228,303. 
Small carbon dioxide generators based on small combustion systems are also 
known. However, high temperatures can be harmful to plants and can cause 
undesirable water evaporation and loss, and therefore, operation of such 
carbon dioxide generators during the day is problematic in warm climates. 
Carbon dioxide, however, should be supplied to plants during the day, as 
sunlight is used in the basic photosynthesis reaction: 
EQU CO.sub.2 +H.sub.2 O+Chlorophyll+light=(H.sub.2 CO)+O.sub.2 +Chlorophyll. 
If the heater is not operated during the day, the carbon dioxide in these 
systems is not available when it is needed. 
SUMMARY OF THE INVENTION 
It is therefore one of the objectives of the present invention to obviate 
the disadvantages of the prior art heating and carbon-dioxide enrichment 
systems, and to provide an apparatus which allows operation of the heater 
when required, typically at night, and yet supply carbon dioxide to the 
greenhouse atmosphere when required by the plants, primarily during the 
day and in sunlight, which combination of nighttime heating, carbon 
dioxide generation and storage, and subsequent daytime supply of cooled 
carbon dioxide to the greenhouse, is neither taught nor suggested in the 
prior art. 
It is a further objective of the present invention to provide the required 
carbon dioxide at a cost substantially lower than that of 
commercially-supplied gas. 
The present invention achieves the above objectives by providing an 
apparatus for heating a greenhouse and for supplying carbon dioxide gas 
thereto, comprising: a heater for burning a hydrocarbon fuel arranged to 
at least indirectly heat the atmosphere of said greenhouse when required; 
cooling means for cooling the carbon dioxide produced by operation of said 
heater; storage means connected by gas flow means to receive combustion 
gas from said heater and to hold carbon dioxide produced by the operation 
thereof; distribution means for supplying the stored carbon dioxide gas 
from said storage means to said greenhouse atmosphere, and distribution 
control means for allowing the supply of said carbon dioxide gas at a 
predetermined time and flow rate. 
In a preferred embodiment of the present invention, there is provided an 
apparatus for heating a greenhouse and for supplying carbon dioxide gas 
thereto, further comprising piping inside said greenhouse arranged to 
allow hot combustion gases from said heater to be circulated within said 
greenhouse at the time when heating thereof is required, said gases then 
being transferred after partial cooling for compression and storage. 
In a most preferred embodiment of the present invention, an apparatus is 
provided for heating a ventilated greenhouse and supplying carbon dioxide 
gas thereto, said heater supplying sufficient carbon dioxide to maintain 
the carbon dioxide level within said greenhouse substantially above the 
carbon dioxide level of the outside atmosphere, despite carbon dioxide 
losses resulting from ventilation due to the excess of carbon dioxide 
supplied by the heating, which is an order of magnitude higher than 
necessary for carbon dioxide enrichment. Thus, e.g., there is needed and 
desired about 30-50 kg carbon dioxide per enclosed dunam per day, while 
consumption of 150 kg fuel per dunam per night provides 450 kg carbon 
dioxide per dunam per day. 
Therefore, the present system can produce three times as much carbon 
dioxide as is necessary for providing even 100-150 kg carbon dioxide per 
dunam per day, for a ventilated greenhouse system. 
It will be realized that, in accordance with the present invention, in warm 
climates and/or when heating is not necessary, the heating system can be 
run at low load or for only a partial time at night, to generate 
sufficient carbon dioxide for storage for daytime use, and said generated 
heat, instead of being directed to the greenhouse, can be simply 
dissipated to the atmosphere. 
It will also be realized that many greenhouses are provided with their own 
cooling systems, and these cooling systems can be arranged for effecting 
the cooling of the carbon dioxide produced by operation of said heater. 
The invention will now be described in connection with certain preferred 
embodiments with reference to the following illustrative figures so that 
it may be more fully understood.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
There is seen in FIG. 1 apparatus 10 for heating a greenhouse 12 and for 
supplying carbon dioxide gas thereto, either simultaneously or 
subsequently. 
A heater 14 is arranged to burn a hydrocarbon fuel, typically in gaseous 
form, and thereby to heat the interior of the greenhouse when necessary. 
The heater 14 shown heats air which is blown into the center of the 
greenhouse by means of a conduit 16. Other forms of heat distribution are 
shown in the following embodiments of the invention. The arrangement shown 
in FIG. 1 is intended to serve a small greenhouse; to serve a large 
greenhouse, a plurality of conduit branches are provided. Distribution of 
hot air into the greenhouse 12 will provide ventilation. However, a closed 
hot air circuit having an air inlet inside the greenhouse, as shown in 
FIG. 6, may be used when such ventilation is undesirable. 
A horizontal plane partition 18 is positioned between the plants 20 and the 
transparent greenhouse roof 22. Partition 18 is made of a transparent 
sheet, to allow the passage therethrough of solar radiation. Part of 
partition 18 is composed of a thin metal foil, to reflect incoming 
radiation by acting as a thermal curtain when excessive greenhouse 
radiation is to be prevented. A series of fogger valves 21 are optionally 
provided, to spray water mist into storage means 24 and thereby to effect 
evaporative cooling. 
The upper volume between plane 18 and roof 22 forms storage means 24, which 
is connected by gas flow means 26 to receive combustion gas from heater 14 
and thereby to hold carbon dioxide produced by its operation. Due to the 
large size of storage means 24, storage pressure need only be slightly 
above atmospheric, thus saving compression energy. A light-duty blower 27 
drives exhaust gases through the pipe 26 and into the atmosphere of the 
greenhouse. 
Heater exhaust gases which are in excess of carbon dioxide requirements are 
vented to the atmosphere from the chimney 25. An exhaust control baffle 29 
is provided to selectively alter the ratio of gas supplied to the chimney 
25 and to the pipe 26. 
The lower volume 28 of the greenhouse, formed between the ground 30 and 
partition 18, receives hot air from conduit 16 and is also provided with a 
blower 27. Air pressure in volume 28 is lower than the gas pressure in 
storage means 24. Distribution means 32, in the form of a plurality of 
short, vertical-axis tubes 34, are provided for supplying the stored 
carbon dioxide gas from storage means 24 to the greenhouse atmosphere, 
i.e., to lower volume 28. Control valves 36 in tubes 34 serve as 
distribution control means, and allow the supply of carbon dioxide gas at 
a predetermined flow rate, e.g., at a constant flow, for example, via 
valve means independent of storage pressure and positioned in appropriate 
spaces above different planted areas of said greenhouse, for predetermined 
periods of time during the day. 
With reference now to FIG. 2, there is shown a further embodiment 38 of 
apparatus for heating a greenhouse 39 and for supplying carbon dioxide gas 
to same. Carbon dioxide is held, until required, in at least one 
elastomeric container 40. Container 40, as shown, is a butyl rubber hollow 
torus. Gas blower 42 is arranged to force said carbon dioxide gas into 
container 40. 
While not shown, container 40 can alternatively be placed inside the 
greenhouse to facilitate carbon dioxide distribution during use and to 
provide internal heating of the greenhouse while the carbon dioxide 
collected therein cools to the greenhouse temperature. 
Embodiment 38 is provided with cooling means 44 for cooling the carbon 
dioxide produced by the operation of heater 14. The carbon dioxide passes 
through heat exchanger 46 before entering container 40, the gas to be 
stored thereby taking up a smaller storage volume at a moderate storage 
pressure of about 0.1-0.5 atmospheres, which is suitable for container 40. 
Distributor tube 48 connects container 40 to greenhouse 39, and a control 
valve 50 in tube 48 allows supply of carbon dioxide when required. The 
heat exchanger 46 shown is water-cooled in a circuit 52, which includes an 
evaporation pool 54 and circulation pump 56. 
FIG. 3 shows an embodiment 58, which is similar to embodiment 38 except 
that the carbon dioxide is stored at a higher pressure and in smaller 
volume. Embodiment 58 has storage means comprising a steel pressure vessel 
60. A gas compressor 62 is arranged to force the carbon dioxide into 
vessel 60, storage pressure typically being above 5 atmospheres. 
High-pressure storage is particularly advantageous where gas storage space 
is expensive or unavailable. A heat exchanger 64 comprises cooling means, 
and is positioned within flow path 66 of the carbon dioxide, arranged to 
cool the carbon dioxide before it enters into compressor 62, thus 
facilitating compression and allowing storage of a larger quantity of 
carbon dioxide gas than would be possible without cooling. A water 
separator 67 is provided downstream from the heat exchanger 64, to remove 
water formed in the cooled gas before the gas enters the compressor 62. 
In FIG. 4, there is shown apparatus 68, which uses heater exhaust gases for 
additional heating of the greenhouse 70 when the heater 72 is in 
operation. A first piping array 74 inside greenhouse 72 is arranged to 
allow the circulation of hot combustion gases from heater 72 at a time 
when heating of the greenhouse is required. A second piping array 76 is 
provided for distributing hot air from furnace 72. The air inlet 78 of 
array 76 is inside greenhouse 70, which is intended to be unventilated. 
Heating fuel economy is thereby improved, while at the same time the 
combustion gases are cooled and are therefore more easily compressed and 
stored in container 40. 
Referring now to FIG. 5, there is seen an apparatus 76, which is similar to 
apparatus 10 but has arrangements for the even distribution of heat 
throughout the large greenhouse 78. The greenhouse heater comprises a hot 
water boiler 80, piping 82 and water circulation pump 84, which circulates 
hot water in greenhouse 78 at the time when heating is required. 
FIG. 6 illustrates apparatus 86, which has arrangements to distribute heat 
evenly throughout a large greenhouse 88. Apparatus 86 is similar to 
apparatus 68 shown in FIG. 4, but has several additional improvements 
which will be described below. 
Greenhouse heater 72 comprises a hot air furnace, hot air piping 90, and an 
air preheater 92, which extracts unwanted heat from the exhaust gases and 
uses this heat to warm the air used to heat the greenhouse 88. Piping 90 
includes a blower 27. Exhaust control baffle 94 is provided to selectively 
alter the amount of exhaust gas going to discharge chimney 96, the 
remainder thereof being used in the carbon dioxide system. An additional 
circuit 98 passes hot exhaust gases through greenhouse 88 to heat the same 
when required. Two futher baffles 100, 102 control the hot gas flow 
through circuit 98. A blower 42 slightly compresses the exhaust gases 
before they are transferred to storage in flexible container 40. A cooling 
circuit 104 cools the gases both before and after compression, but 
requires only a single fan-cooled radiator 106 to disperse the extracted 
heat into the atmosphere. 
FIG. 7 depicts a ventilated greenhouse 108, provided with apparatus 38, as 
described above with reference to FIG. 2. Heater 14 provides sufficient 
carbon dioxide to the greenhouse 108 to maintain the carbon dioxide 
content of the greenhouse interior substantially above the carbon dioxide 
content of the outside atmosphere, despite carbon dioxide losses resulting 
from ventilation. 
Greenhouse 108 is naturally ventilated by allowing the escape of hot air 
through roof vents 110 and allowing ingress of cold air through low wall 
vents 112. When the apparatus 10 is in use for heating, the hot air driven 
into greenhouse 108 through conduit 16 provides adequate ventilation. At 
other times, additional ventilation is available by use of 
through-the-wall, electrically-powered ventilators 114. 
It will be evident to those skilled in the art that the invention is not 
limited to the details of the foregoing illustrated embodiments and that 
the present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof. Thus, e.g., in 
the figures described hereinabove, the secondary media for effecting 
heating of the greenhouses is air; however, it will be realized that water 
can also be used by methods known per se. The present embodiments are 
therefore to be considered in all respects as illustrative and not 
restrictive, the scope of the invention being indicated by the appended 
claims rather than by the foregoing description, and all changes which 
come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.