IL177688A

IL177688A - Method of maintaining temperature in a chamber within a structure

Info

Publication number: IL177688A
Application number: IL177688A
Authority: IL
Original assignee: Uri Drori; Trio Energy Systems Ltd
Priority date: 2006-08-24
Filing date: 2006-08-24
Publication date: 2012-03-29
Also published as: WO2008023377A2; IL177688A0; WO2008023377A3

Description

foa» 71Π3 i r»-i mitnoao iitt ¾/ nv A method of maintaining temperature in a chamber within a structure Trio Energy Systems Ltd. *» K> »'>UN C. 169013.0 A METHOD OF MAINTAINING TEMPERATURE IN A CHAMBER WITHIN A STRUCTURE FIELD OF THE INVENTION This invention relates to heating and energy conservation methods, in particular, for use in greenhouses.

BACKGROUND OF THE INVENTION In the field of agriculture, greenhouses are usually used for growing plantations throughout the year. The greenhouse, apart from providing desired climatic and temperature conditions, also protects the plantations from environmental damages such as rain, wind, hail etc.

In greenhouses, it is required to maintain a certain temperature that will be kept steady throughout the year, regardless of the seasons and the temperature of the outside environment. It is known that in greenhouses it normally has to be relatively warm for the plants to grow properly, and efforts are made to maintain them at an average temperature not lower than 12-18°C.

The design of a greenhouse is such that absorbs solar energy in order to maintain that required temperature, while excess heat is released to the environment and/or removed from the greenhouse by conventional means such as ventilation and/or evaporative cooling system.

When the temperature of the outside environment is lower than the desired temperature within the greenhouse, and heat escapes from the greenhouse, the temperature within the greenhouse drops below the desired temperature, requiring the supply of heat thereto. This may be achieved by an air conditioning system, heating the greenhouse to compensate for the loss of heat as known per se.

It is further known the use of thermal screens or similar means adapted to divide the space of the greenhouse in order to create a buffer zone between the space 01690130X9-02 containing the plantations and the outside environment to reduce the emission of heat to the outside. One such example is disclosed in GB 2,176,590.

Another problem in greenhouses is the humidity. High humidity may increase the incidence of plant disease, such as Botrytis (a plant disease). Therefore, it is required to constantly reduce the humidity level within the greenhouse and remove water vapor therefrom. This dehumidification may be achieved in a variety of ways, for example a system of heat exchangers as disclosed in US 4,739,627.

SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided, for use in a closed structure surrounded by an environment, the structure having a surface through which heat from the structure tends to escape to the environment when the temperature of the environment is lower than that within the structure, a method for maintaining in a chamber within said structure a temperature higher than that of the environment, said method including: 1. providing within the structure a thermal screen which separates said chamber from most of said surface and from the remainder of the structure that is contiguous with said surface, the thermal screen being located so as to ensure that most of the heat escaping from said chamber passes through said thermal screen into said remainder of the structure; 2. withdrawing heat from the remainder of the structure, thereby reducing temperature difference between the remainder of the structure and said environment, due to which heat transfer from said remainder of the structure to said environment is at least reduced; and 3. releasing into said chamber the heat withdrawn from the remainder of the structure, thereby at least partially compensating for the loss of heat associated with its escape from said chamber into the remainder of the structure.

In operation, the thermal screen functions so that, when the outside environment has a relatively low temperature T0 and said chamber has a temperature Tj higher than To, the remainder of the structure will have a temperature T2 meeting the condition T0 < T2 < Tj. Heat from said chamber tends to escape to the remainder of the structure through the thermal screen and heat from the remainder of the structure tends to escape to the outside environment. When, according to the present invention, heat is withdrawn 01690130X9-02 from the remainder of the structure so that its temperature T2 lowers to T2' which is close to T0, there will be no significant heat transfer from the remainder of the structure to the outside environment. Thus, the heat which could escape to the outside environment from the remainder of the structure, were the temperature T2 higher than T0, is withdrawn from the remainder of the structure and released into said chamber thereby maintaining its temperature essentially constant in spite of the heat escape from said chamber to the remainder of the structure via said thermal screen.

If the remainder of the structure is cooled down to temperature T2" < To < Ti, this will cause condensation of water vapor on the outside of said surface, forming thereon a layer of condensate. This condensation will generate latent heat energy that will be absorbed into the structure. In addition, the condensate layer reduces the heat transfer coefficient between the structure and the outside environment along said surface. This effect becomes beneficial when the temperature in remainder of the structure is allowed to return to . its normal state above the temperature of the environment, because it reduces heat loss to the environment and power consumption of the system.

The above process turns out to be surprisingly effective since the heat escaping from the chamber to be heated, into the remainder of the structure is constantly returned thereto so that the overall heat losses from the structure to the outside environment are substantially reduced while an additional insulation is created by the condensate outside the structure.

The structure may be a greenhouse, a large pavilion, or the like, or a part thereof required to be maintained at a predetermined temperature, usually exceeding that of the outside environment.

The structure may have a bottom, a top or a cover constituting said surface through which heat from the structure tends to escape to the environment when the temperature of the environment is lower than that in the structure, and side walls extending between the top and the bottom. In such a structure the thermal screen may extend between the side walls essentially parallel to the bottom of the structure, thereby dividing the structure into said chamber confined by the side walls and bottom of the structure and the thermal screen, which will hereinafter be referred to as a chamber, and to the remainder of the structure, which may be confined by the cover, the side walls of the structure and the thermal screen. 01690130X9-02 The structure may be outfitted with one or more additional thermal screens, mounted in conjunction with the thermal screen mentioned above, dividing the remainder of the structure into two or more sub-chambers. This method may be useful when the outside environment has a temperature which is substantially lower than that of the required temperature within the first chamber.

The method of the present invention may use a heat pump comprising a condenser and an evaporator, wherein the condenser is mounted in said chamber and the evaporator is mounted in the remainder of the structure. If more than one thermal screen is used, the condenser may be mounted in one of the sub-chambers.

The method may be adapted to be performed automatically to maintain a desired relationship between the temperatures of said chamber, the remainder of the structure and said outside environment based on economical considerations such as the cost of energy and/or system requirements.

A by-product of the method of the present invention is that it dehumidifies said chamber is achieved. In a greenhouse, lowering humidity also reduces the incidence of plant disease, such as botrytis. Dehumidification is achieved since the water vapor in the remainder of the structure is removed by means of condensation on the evaporator. When water vapor is removed from the air in the remainder of the structure, the water vapor from the chamber passes into the remainder of the structure in order to equalize the vapor pressure.

This condensation also produces a considerable amount of water, which may be used in various ways. In case of hydroponics it may be simply redirected back to a main water bed on which plantation is grown.

According to a second aspect of the present invention, there is provided a controller adapted to operate at least one heat pump to perform the method as described above.

According to a third aspect of the present invention there is provided a structure for the implementation of the method described above.

The method of the present invention is intended for use during periods when natural heating of the structure, i.e. by solar energy or means using such energy, is not available or not sufficient, and the temperature of the outside environment is substantially lower than the desired temperature of the first chamber, and it may thus be 01690130\9-02 particularly advantageous for use in cold regions and/or during cold seasons and/or cold periods of the day.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, several embodiments will now be described, by way of a non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic perspective view of a conventional greenhouse; Fig. 2 is a schematic cross-sectional view taken along plane I-I of the greenhouse unit of Fig. 1 , adapted for the implementation of a method according to one embodiment of the present invention; and Fig. 3 is a schematic cross-sectional view of a greenhouse unit according to another embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS As shown in Fig. 1, a conventional greenhouse 1 comprises several gables 10 having pillars 23, mounted on the ground G adjacent each other, and a transparent cover 12 supported by the pillars 23 of the gables 10, thereby forming a structure bounded by the ground G, side walls 16 (shown Fig. 2) and a top 18, the latter having an inner surface 18a and an outer surface 18b. The greenhouse 1 further comprises gutters 19 between each two gables 10. The bottom 14 of the greenhouse 1 is used for growing thereon plantations P normally organized in furrows F.

It is known that in greenhouses it normally has to be relatively warm for the plants to grow properly, and efforts are made to maintain them at an average temperature Tj not lower than 12-18°C, even when the temperature T0 of the environment E is substantially lower than Tj. For this purpose, it is known to use within a greenhouse a heating means (not shown) and a thermal screen 30 mounted parallel to the ground G so as to divide the greenhouse into a lower chamber 26 where the heating means is deployed to heat this chamber, when required, in order to raise its temperature Ti, and a remainder of the greenhouse, hereinafter referred to as an upper chamber 28, separating the lower chamber 26 from the top 18 via which heat from the greenhouse tends to escape to the environment E, when the temperature T0 of the environment is lower than Tj. In this case, the upper chamber 28 has a temperature T2 01690130X9-02 lower than Ti but higher than To since it on the one hand receives heat which escapes from the lower chamber 26 via the thermal screen 30, and on the other hand heat escapes this chamber 28 via the top 18. Examples of materials from which thermal screens are made include polyethylene and woven polyester, sometimes with aluminum strips.

In Fig. 2, a partial cross-section of the greenhouse 1 is shown adapted for maintaining the temperature Ti in the lower chamber 26 by a method of the present invention. For this purpose, the greenhouse 1 comprises a heat pump generally designated as 40, which includes an evaporator 42 mounted in the upper chamber 28, a condenser 44 and compressor (not shown) mounted in its lower chamber 26, and piping 32 and 34 therebetween. It should be noted that the heat pump 40 does not necessarily need to be deployed in each gable 10; rather one such pump may serve several gables 10 with the appropriate piping extending therealong.

The greenhouse 1 further comprises a controller 45 connected to the heat pump 40 and adapted to operate it as follows.

When the temperature T0 of the environment E drops to a predetermined value, the temperature Tj in the lower chamber 26 tends to fall due to the heat flux Fl, from the lower chamber 26 to the upper chamber 28. At this stage, the controller 45 operates the heat pump 40 so that heat is withdrawn from the upper chamber 28 by working fluid in the evaporator 42 absorbing the heat and thereby causing the temperature of the upper chamber 28 to lower to the temperature T2'. The heated working fluid is then forwarded via the piping 32 to the condenser 44 in the lower chamber 26, where it is condensed and its heat is released, preventing the temperature Ti in the lower chamber 26 from falling in spite of the heat transfer therefrom to the upper chamber 28 (heat flux Fl and latent heat from condensation). The condensed working fluid from the condenser 44 is then forwarded via the piping 34 back to the evaporator 42 and the above process is repeated as long as needed. The temperature T2' may be close or equal to the temperature T0 of the environment E, in which case heat from the upper chamber 28 will not escape to the environment E via the top 18 of the greenhouse 1.

If desired, the temperature T2' may be lowered below the temperature To of the environment E, causing water vapor contained in the air of the environment E to condense on the outer surface 18b of the top 18 of the greenhouse and turn into water drops, i.e. condensate 54. As a result, heat flux 50 will be delivered to the upper 01690130X9-02 chamber 28 as latent heat, so that the upper chamber 28 actually gains heat from the outside environment E. In addition, in certain cases the temperature in the upper chamber 28 may be permitted to become higher than the temperature of the environment after the aforementioned condensation. It is then that the condensate 54 may serve as an insulation layer, preventing the heat from the upper chamber 28 from escaping to the environment E. This insulation is achieved since the condensate layer lowers both the conduction heat transfer coefficient with the environment E as well as IR radiation losses from the greenhouse to the sky. Furthermore, the condensate 54 may be collected in the gutters 19 and reused for various purposes, such as irrigation.

Another byproduct of the operation of the heat pump 40 is dehumidification of the lower chamber 26. Humid air may have a number of damaging effects on plantations in a greenhouse, such as botrytis. Dehumidification is achieved since the water vapor in the upper chamber 28 is removed by means of condensation on the evaporator 42. Once the water vapor is removed from the air in the upper chamber 28, the water vapor from the lower chamber 26 passes into the upper chamber 28 in order to equalize the vapor pressure, thereby dehumidifying the lower chamber 26.

The controller 45 is adapted to monitor the temperature within the greenhouse 1 and in the environment E and regulate the operation of the heat pump 40 to maintain the desired temperature in the lower chamber 26 in the most economical way.

Compared to other systems known in the trade, the system according to the present invention may provide energy conservation of up to 70% of the energy required to conventionally heat the greenhouse.

It should be noted here, that the heat pump 40 may, apart from its functions listed above, be used as a cooler for the greenhouse 1 when the temperature T0 of the environment E is substantially greater than the temperature Ti in the lower chamber 26, and the removal of heat from the chamber 26 is required.

Fig. 3 illustrates an alternative embodiment of a greenhouse unit 110, which is similar to the greenhouse unit 10 described above and has the same thermal screen 30 dividing the unit into the lower chamber 26 and the upper chamber 28. However, the greenhouse unit 110 comprises one additional thermal screen 130 dividing the greenhouse unit's upper chamber 28 into two sub-chambers, lower sub-chamber 132 and an upper sub-chamber 134. The additional thermal screen 130 is positioned such that it completely separates the lower sub-chamber 132 from the top 18 of the unit 110, i.e. the 01690130\9-02 lower sub-chamber 132 is confined between the thermal screen 30 and the additional thermal screen 130. This embodiment is especially suitable for cold regions where the temperature T0 of the environment E is substantially lower than Tj.

In the greenhouse unit 110, the evaporator 42 is mounted in the lower sub-chamber 132 and the condenser 44 is mounted in the lower chamber 26, and they operate in the same manner as in the greenhouse unit 10, to maintain the desired temperature Tj in the lower chamber 26 by withdrawing heat from the lower sub-chamber 132 and thereby lowering its temperature to become close or equal to that in the upper sub-chambers 134.

Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations and modifications can be made without departing from the scope of the invention mutatis mutandis. 01690130X9-02

Claims

1. For use in a closed structure surrounded by an environment, the structure having a surface through which heat from the structure tends to escape to the environment when the temperature of the environment is lower than that within the structure, a method for maintaining in a chamber within said structure a temperature higher than that of the environment, said method including: a. providing within the structure a thermal screen which separates said chamber from most of said surface and from the remainder of the structure that is contiguous with said surface, the thermal screen being located so as to ensure that most of the heat escaping from said chamber passes through said thermal screen into said remainder of the structure; b. withdrawing heat from the remainder of the structure, thereby reducing temperature difference between the remainder of the structure and said environment, due to which heat transfer from said remainder of the structure to said environment is at least reduced; and c. releasing into said chamber the heat withdrawn from the remainder of the structure, thereby at least partially compensating the loss of heat associated with its escape from said chamber into the remainder of the structure.

2. A method according to Claim 1, wherein the temperature of said remainder of the structure is approximately equal to the temperature of said environment.

3. A method according to Claims 1 or 2, wherein the temperature of said remainder of the structure is lower than that of said environment.

4. A method according to any one of Claims 1 to 3, wherein said thermal screen extends between side walls of said structure, essentially parallel to the ground.

5. A method according to Claim 4, wherein additional thermal screens are positioned within said structure, adapted to divide said remainder of the structure into additional sub-chambers. 01690130\9-02

6. A method according to Claims 4 or 5, wherein said thermal screen and additional thermal screens are made of polyethylene, woven polyester with aluminum strips, or the like.

7. A method according to any one of Claims 1 to 6, wherein said a heat pump is positioned within said structure, said heat pump comprising a condenser mounted in said chamber and an evaporator mounted in said remainder.

8. A method according to any one of Claims 1 to 7, wherein said method is adapted to be performed automatically to maintain a desired relationship between the temperatures of said chamber, said remainder and said outside environment based on economical considerations such as the cost of energy and/or system requirements.

9. A method according to any one of the preceding Claims, wherein said method further includes: d. reducing the temperature of said remainder to a temperature lower than said environment to allow formation of a condensate on the outside of said structure. e. using said condensate as an insulator when the temperature of the remainder is permitted to rise above the temperature of the environment.

10. A method according to all of the preceding Claims wherein said method is used for dehumidification of said chamber.

11. 1 1. A method according to any one of the preceding Claims, wherein said structure is a greenhouse.

12. For use with a closed structure surrounded by an environment, the structure having a surface through which heat from the structure tends to escape to the environment when the temperature of the environment is lower than that within the structure, and comprising a thermal screen, a chamber, and a heating system, said chamber being separated by said thermal screen from most of said surface and from the remainder of the structure that is contiguous with said surface, the thermal screen being located so as to ensure that most of the heat escaping from said chamber passes through said thermal screen into said remainder of the structure; said controller being adapted to control said heating system to perform: 01690 l 30\9-02 a. withdrawing heat from the remainder of the structure, thereby reducing temperature difference between the remainder of the structure and said environment, due to which heat transfer from said remainder of the structure to said environment is at least reduced; and b. releasing into said chamber the heat withdrawn from the remainder of the structure, thereby at least partially compensating for the loss of heat associated with its escape from said chamber into the remainder of the structure.

13. A controller according to Claim 12, wherein the temperature of said remainder of the structure is approximately equal to the temperature of said environment.

14. A controller according to Claims 12 or 13, wherein the temperature of said remainder of the structure is lower than that of said environment.

15. A controller according to any of Claims 12 to 14, wherein said thermal screen extends between side walls of said structure, essentially parallel to the ground.

16. A controller according to Claim 15, wherein additional thermal screens are positioned within said structure, adapted to divide said remainder of the structure into additional sub-chambers.

17. A controller according to Claim 15 or 16, wherein said thermal screen and additional thermal screens are made of polyethylene, woven polyester with aluminum strips etc.

18. A controller according to any of Claims 12 to 17, wherein said heat pump is positioned within said structure, said heat pump comprising a condenser mounted in said chamber and an evaporator mounted in said remainder.

19. A controller according to any of Claims 12 to 18, wherein said method is adapted to be performed automatically to maintain a desired relationship between the temperatures of said chamber, said remainder and said outside environment based on economical considerations such as the cost of energy and/or system requirements.

20. A controller according to any one of Claims 12 to 19, wherein said method further includes: 01690130\9-02 c. reducing the temperature of said remainder to a temperature lower than said environment to allow formation of a condensate on the outside of said structure. d. Using said condensate as an insulator when the temperature in the remainder is permitted to rise back above the temperature of the environment.

21. A controller according to any one of Claims 12 to 20, wherein said method is used for dehumidification of said chamber.

22. A controller according to any one of Claims 12 to 21, wherein said structure is a greenhouse.

23. A closed structure surrounded by an environment, the structure having a surface through which heat from the structure tends to escape to the environment when the temperature of the environment is lower than that within the structure, and comprising a thermal screen, a chamber, a heating system and a controller, said chamber being separated by said thermal screen from most of said surface and from the remainder of the structure that is contiguous with said surface, the thermal screen being located so as to ensure that most of the heat escaping from said chamber passes through said thermal screen into said remainder of the structure; said controller being adapted to control said heating system to perform: a. withdrawing heat from the remainder of the structure, thereby reducing temperature difference between the remainder of the structure and said environment, due to which heat transfer from said remainder of the structure to said environment is at least reduced; and b. releasing into said chamber the heat withdrawn from the remainder of the structure, thereby at least partially compensating for the loss of heat associated with its escape from said chamber into the remainder of the structure.

24. A structure according to Claim 23, wherein the temperature of said remainder of the structure is approximately equal to the temperature of said environment. 01690130\9-02

25. A structure according to Claims 23 or 24, wherein the temperature of said remainder of the structure is lower than that of said environment.

26. A structure according to any of Claims 23 to 25, wherein said thermal screen extends between side walls of said structure, essentially parallel to the ground.

27. A structure according to Claim 26, wherein additional thermal screens are positioned within said structure, adapted to divide said remainder of the structure into additional sub-chambers.

28. A structure according to Claims 26 or 27, wherein said thermal screen and additional thermal screens are made of polyethylene, woven polyester with aluminum strips etc.

29. A structure according to any of Claims 23 to 28, wherein said a heat pump is positioned within said structure, said heat pump comprising a condenser mounted in said chamber and an evaporator mounted in said remainder.

30. A structure according to any of Claims 23 to 29, wherein said method is adapted to be performed automatically to maintain a desired relationship between the temperatures of said chamber, said remainder and said outside environment based on economical considerations such as the cost of energy and/or system requirements.

31. A structure according to any one of Claims 23 to 30, wherein said method further includes: c. reducing the temperature of said remainder to a temperature lower than said environment to allow formation of a condensate on the outside of said structure. d. Using said condensate as an insulator when the temperature of the remainder is allowed to rise back above the temperature of the environment.

32. A structure according to any one of Claims 23 to 31 , wherein said method is used for dehumidification of said chamber.

33. A structure according to any one of Claims 23 to 32, wherein said structure is a greenhouse.

34. A method substantially as described herein with reference to the accompanying drawings 01690130\9-02

35. A controller substantially as described herein with reference to the accompanying drawings.

36. A closed structure substantially as described herein and/or as shown in the accompanying drawings. For the Applicants, REINHOLD COHN AND PARTNERS 0 1690130X9-02