GB2174429A

GB2174429A - Rood heat insulation and energy-saving air-conditioning of agricultural buildings

Info

Publication number: GB2174429A
Application number: GB08509724A
Authority: GB
Inventors: Pal Gal
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-04-16
Filing date: 1985-04-16
Publication date: 1986-11-05
Also published as: GB8509724D0

Abstract

The roof comprises spaced layers 1,2 bounding an air-space I. Heat radiation 4 is directed parallel to the layers from radiating surfaces 3. The air-space may comprise water- vapour 7 emanating from water streams 5 in channel 8, and the radiant heat absorbed by the vapour increases the enthalpy of the air in the space. Water may condense as dew 10 on the layers and prevent radiation passing through the layers. The layers 1 and 2 may also be cooled by evaporation of the condensation. A warm airstream 16 from the building may be cooled, and reduced in humidity, by contact with walls 3a of the air-space. Circulating water may act in conjunction with a heat-exchanger, e.g. in the soil, to regulate the building temperature. <IMAGE>

Description

SPECIFICATION A process for the energy-saving operation of multi-purpose agricultural buildings The invention concerns a process for the energy-saving operation of multi-purpose agricultural buildings. The invention is particularly applicable to buildings having a multi-layer covering, whether light-transmitting or not, where the individual layers are thin-walled and may be stiff or flexible and/or sheet-like; the process according to the invention enables the air conditioning or climatic regulation of the closed spaces between the layers, in spite of the low heat enertia of such layers, in an improved manner, with reduced power consumption to maintain the state or condition of the atmosphere between the layers independently of whether the ambient temperature is colder or warmer, and which process can also assure the required relative humidity of the atmosphere between the layers as well as the maintenance of the covering layer surfaces in a clean or clear condition.

During operation of single-aisle or multi-aisle greenhouses, mushroom cultivation houses or livestock houses the internal atmosphere frequently passes through a variety of changes of state, one after the other or even simultaneously, as a result of changes in the environment or due to technological requirements relating to cultivation and breeding. Such changes of state may include e.g. heating, cooling, watering, wetting, drying, ventilation, mixing, conditions of lighting or illumination etcetera. This is why it is desirable that there should be provided a simple process which can effectively and in given cases in an automatable manner partly or wholly solves the climatic requirements of a stucture or of a building at relatively low investment costs and low power requirements.

Hitherto no solution existed which could effectively solve the various above-mentioned tasks which frequently involve mutually antagonistic requirements.

Research and development have resulted in numerous solutions put into practice but all of them suffered from some disadvantage or other preventing them from becoming widely used. Such a disadvantage is the large investment costs or a restricted scope of applicability. In the solutions known hitherto a given aim was sought to be accomplished and the parameters sought to be perfected could be achieved only at the cost of another functional criterion or parameter. In this way the following exemplary anomalies occurred.

1. In the interests of reducing the heating power consumption of greenhouses the light parameters of the latter became worse. These solutions involved causing a. liquid streaming over or sprayed over the covering layer of the structure or over the forced trajectory on the structure but the salts precipitating from the liquid or algae establishing themselves in the liquid tended to contaminate the lighttransmitting surface areas of the covering and in the light-scarce winter season the shadowing caused by these contaminations restricted one of the most important and biological needs of hot house plants, namely the light.

Moreover, if the covering layer became damaged or faulty, the liquid (water) flowing thereon could seep into the working or cultivation space.

2. In the case of mushroom cultivation houses of light structure, mushrooms have a high-intensity air exchange requirement and they have a poor tolerance to carbon dioxide, hence such buildings must be continuously vented and fresh air ingested from the outside. For productive and efficient mushroom growing it is necessary to maintain the air temperature and humidity to a high accuracy.

These air or atmospheric parameters are mutually antagonistic hence they could be assured only exclusively by artificial means and through purpose-built air-conditioning apparatus; or alternatively the production had to be restricted to such seasons in which the external environmental conditions enabled productive growing. This of course is an undesirable restriction to cultivation.

3. In animal husbandry buildings the number of animals per unit area is high and therefore the accurate maintenance of the humidity and internal temperature of the atmosphere is imperative; hence a simple air-conditioning system is very important. The attainment of the required purity of the atmosphere and its humidity necessitates the use of ventilation but keeping the temperature of the fresh air at a desired value requires an energy input and hence increased power consumption.

4. Similarly, it is imperative to reduce the high relative humidity of the atmosphere of greenhouses and this has hitherto been solved exclusively by ventilation. Ventilation means the discharge of hot air in the Winter and cool air in the Summer which in both cases can be achieved only by using extra power, or alternatively one had to abandon the accurate acclimatisation of the technological prescriptions of cultivation or breeding.

The present invention seeks to provide a process which eliminates or at least reduces the above-mentioned disadvantages and drawbacks and which provides a novel, simple, reliably operable, energy-sparing process requiring only low investment.

A special advantage of the process according to the invention is that in its operation the atmospheric parameters of the building or structure can be maintained at the designed or planned level and they do not change during operation. The use of the process improves the climatic and energetic properties of the building or structure.

A process according to the invention may be utilised for all structures where one can assure the separated or combined streaming of air and water in a purpose-built flow duct or channel having a free water surface, and where the flow-conveying channel is expediently built on or into the frame structure of the building and where the frame structure is capable of carrying a covering consisting of at least two layers which may be light-transmitting or light-impermeable, expediently made of glass, a foil material or various synthetic materials.

Apparatus suitable for carrying out the process according to the invention in the form of a building has been described in Hungarian Patent Application No. GA-1136 entitled "Single or Multi-Aisle Agricultural Building Air-Conditionable in an Energy-Saving Manner".

However, this Patent Application does not provide adequate teaching for users for performing the energy-saving process but merely provides expedient embodiments of structural constructions.

The present invention eliminates the above shortcoming and provides adequate teaching for the exploitation of a wholly new effectmechanism arising in the operation of the above and similar buildings either as an independent process or as one that supplements in an energy saving manner pre-existing heating/cooling, i.e. acclimatising systems. In the latter case the process influences in an advantageous direction and manner the output requirement of the basic air-conditioning system.

The choice between the two possibilities is determined always by the energy level of the heat carrier means present, and the heat requirement of the covered-over air space as well as the agrotechnical prescriptions. The present invention regards as known the socalled "greenhouse effect" arising in covered spaces and exploits it.

The process according to the invention is based on numerous novel and unexpected discoveries, among which the more important and characteristic ones are listed below: 1. It is an inventive discovery that the internal space or interior is expediently delimited from the ambient environment by means of a thin covering material of low thermal inertia arranged in a double layer such that the spacing between the two covering layers should be less than the buoyant force arising from the different temperature conditions of the air layer (I) between the layers, and that the frictional inertia of the air particles should be greater than the force causing the air movement and resulting from the density of the particles of differing temperatures.

In this way a relatively steady state will be formed between the covering layers and this layer has good heating insulating properties because no heat transfer by convection can be formed and mainly only molecular heat displacement is possible.

2. Another discovery on which the invention is based is that the air space (I) bounded by the two foil layers can only be heated up effectively with long wavelength radiant heat if the heating radiation is directed at an angle deviating from the surfaces of the planes of the foils, bearing in mind that the foils otherwise are permeable to thermal radiation. With such a direction of the radiant heating, the radiation cannot penetrate through the otherwise radiation-permeable foil surfaces. The most expedient embodiment of this concept is to direct the radiation in parallel with the planes of the foils which in turn can be realised by locating the heat transfer surface perpendicularly to the plane of the foil in question.

The size of the radiant structural part amounts expediently to 3 to 6% of the surface area of the covered space. Because of its directionality, this relatively small radiant unit significantly increases the heat insulation of the whole covering layer, reduces the heat "step" or gradient between the ambient environment and the covered space and reduces the heat loss by radiation from the space.

3. A further discovery on which the invention is based is that the natural heat content and enthalpy of the various media may be exploited for acclimatising the covered space by ensuring that the heat exchange and changes in state of the media take place on expediently constructed statical constructions.

The power required for causing the media to flow is provided by the most efficient form of energy investment, namely by transforming electricity into mechanical work.

4. A further discovery of the invention is that the air layer may only be heated effectively by means of long-wave heat radiation if the air contains a sufficient quantity of radiation-absorbent energy-accumulating particles.

An expedient medium for this is water vapour in the air. The enthalpy of air saturated with water vapour increases under the effect of irradiation, for the same energy transfer, compared to the maximum achievable value for dry air.

5. Yet another discovery underlying the invention is that the expediently employed water vapour can be passed into the covered air space (I) in the simplest manner by arranging the free liquid surface in contact with the air space to function also as a heat carrier medium which, flowing in the ducts/channels of the framework, maintains the surface parts of the heat-radiating body at the desired and appropriate energy level.

6. The next inventive discovery is that the changes in air conditions are self-regulating and prevail to an increased extent in extreme conditions in the environment. Hence the extreme peaks of weather are attenuated towards the covered air space, whereby the temperature conditions of the latter are rendered more uniform.

The air space (I) between the two covers becomes warmer than the environment under the effect of the measures taken and based on the above discoveries and becomes warmer by more than might have been expected, hence it is capable of dissolving or containing more water vapour. Should there be an inrush of cold air this extra vapour precipitates onto the inner surfaces of the covering layers and increases the heat insulation of the cover while also preventing or significantly reducing the radiant heat emission of the covered internal space. The water vapour precipitating and changing state on the surface of the cover assures an exothermic process to take place.

When sleet or snow falls, the extra heat energy available by radiation or conduction prevents the external precipitation from depositing on the external covering layer.

When normal temperature conditions are attained the air space (I) between the covers is restored to its equilibrium condition and the precipitation evaporates as vapour back into the air space or drips or trickles down from the surface.

7. A further inventive discovery is that the process according to the invention is capable of insulating the covered air space (II) against rising to an undesirably high temperature, if in the flow channel of free surface water at a temperature colder than the environment is caused to flow and the heat absorbed by the water as it warms up as well as its heat of evaporation, serve to cool the interior of the covered space.

The moisture from the over-saturated vapour content of the air precipitates onto the two interior surfaces of the covering which will provide heat insulation against inwardly directed heat radiation and in the case of a light-permeable covering the light rays are scattered, absorbed and heat is extracted from the surface by re-evaporating the precipitate. This is an endothermic process embodied in the process according to the invention.

8. The heated up, covered space may be cooled by a forced circulation of the warm air from higher points or regions of the space through the channel of the plane structure to transfer its enthalpy directly or indirectly to the cold liquid also flowing through the channels in the frame structure. This process is reversible. In another part of the day the stored warm water can be used to heat the air space with the heat flow in the opposite direction. This represents a heat-storing or accumulating process embodied in the process of the invention.

9. A recognition forming part of the invention is that the vapour content or humidity of the covered structure may be reduced to a desired value by causing water of a temperature colder than the environment to flow in the free-streaming channel (in the case of a greenhouse, e.g. the water of irrigation) while causing at the other side of the cooled metal surface the vapour containing warm air to flow in forced circulation. In this process the air is cooled, its relative vapour content increases and hence the water vapour is precipitated. In this way the water can be dehumidified without the need to resort to ventilation/blowing. The water of condensation can be collected and mixed to the water of irrigation which may also mean a saving of water. This is the condensation process embodied in the process according to the invention.

10. When the task is to provide the covered space with vapour-enriched fresh air, then the blowing-in of air takes place via a flow duct at the bottom of which free-surface water flows at a temperature which is warmer or colder than the environment in accordance with the requirement of the atmosphere of the covered space. The flowing air makes contact with the water and dissolves or takes up the necessary amount of vapour and simultaneously by convective heat transfer from the water and the boundary surfaces of the duct its temperature changes to the desired value.

The undesired carbon dioxide and ammonia can be absorbed from the air by the water current and so purification of the air is also solved. This is the air purification and evaporation portion of the process according to the invention.

The flow channel in the frame structure may be extended or lengthened by means of a perforated foil or muslin cloth air channel, whereby the air is caused to flow in forced circulation, after adjustment to the required parameters thereof, directly to the vicinity of the cultivated plants or the breed stock. This discovery is particularly significant for acclimatising mushroom cultivation houses (beds) because it eliminates pockets of still air and other dead, non-circulating air spaces.

11. The acclimatising or air-conditioning media do not contaminate the surfaces of the covering layers because they flow in separate channels. When the covering layers are lightpermeable, then in the whole cultivation season or period maximal air transmission is assured. By regulating the climate in the air space between the two covering layers the quality of the radiated light may be influenced so as advantageously to affect the agrotechnical results. This is the light-regulating portion of the process according to the invention.

The process according to the invention will now be described with reference to the accompanying purely schematic drawings wherein: Figure 1 diagrammatically illustrates the mode of carrying into practice the inventive concepts numbers (1) and (2) described above, namely the disposition and direction of the covering and of the radiation of heat; Figure 2 diagrammatically illustrates a mode of realising the inventive concepts listed under numbers 3 to 5 above, showing the covering, the radiation of heat, the conduction of water and the formation of vapour; Figure 3 diagrammatically illustrates a mode of realising inventive concepts numbers 6 and 7 listed above, namely precipitation of moisture, evaporation, drying and heat transfer; Figure 4 diagrammatically illustrates a mode of realising inventive concept number 9 illustrated above, with a condensation process;; Figure 5 diagrammatically illustrates a mode of carrying into practice inventive concept number 10 with contact between flowing and air currents and the taking up or dissolution of vapour; and Figure 6 diagrammatically illustrates inventive concept number 8 listed above, schematically showing the accumulation and storage of heat by means of water flow.

Referring first to Fig. 1 illustrating the first two of the inventive concepts listed above there is shown a covering for a structure or building consisting of an external covering layer (1), an internal covering layer (2), a surface portion (3) of a heat radiator, an air space (I) bounded by the mentioned parts, (1), (2) and (3), and wherein (4) designates the direction of radiation of heat, which direction is parallel with the planes of the covering layers (1) and (2). X designates the height of the heat-radiating surface portion and in choosing this height is expedient to have regard to the magnitude or extent of sagging by the external covering layer (1) into the air space (I) and the heat output of the radiating surface part (3). Expediently the layers (1) and (2) are made of foil.In order to improve the heat emissivity of the heat-radiating surface part (3) it is expedient to colour it black.

Fig. 2 illustrates the third, fourth, and fifth inventive concepts and wherein again the external layer, the internal covering layer, the heat radiating surface portion, the coveredover air space and the direction of heat radiation have all been designated by the same reference number as before. A flow channel 8 is provided to conduct a stream 5 of water having a free surface 5a from which, along the arrow 6, vapour particles evaporate into the air space (I) wherein the enthalpy of the air space (I) is increased by the absorption by the vapour particles 7 of the heat radiation.

One effect is demonstrated on the right hand side of Fig. 2, as viewed: When snow 9 or a layer of ice 9a adheres to the outer surface of the outer covering layer 1, the vapour particles 11 adjacent thereto and containing an increased amount of energy by the absorption of radiation from the direction 4 transfer their heat content to the internal surface of the outer layer 1 whereby to melt the snowy or icy precipitation 9, 9a.

This effect or mechanism is continuous. The energy containing vapour particle 11 gives off its heat of evaporation to the layer 1 and this is greater than the latent heat of fusion of the snow 9 or ice 9a. The vapour particle 11 precipitates on the surface of the covering layer 1 and then trickles away and is replaced by further vapour particles 7 which have risen from the free surface 5a of the water, absorb energy from the heat radiation 4 to be activated thererby and rise as vapour particles 11 to the surface 1. The process or cycle then repeats.

In Fig. 3 similar parts again designate identical or functionally similar parts and this Figure illustrates the sixth and seventh inventive concepts. The vapour particles 7 absorb heat from the radiation 4 and become energy-enriched vapour particles, whereby the temperature of the air space I becomes warmer than that of the ambient atmosphere. The warmer air space I is capable of absorbing or dissolving more vapour and so the relative humidity increases. The vapour particles 10 adjacent the boundary surfaces or covering layers 1 and 2 are cooled and are precipitated as dew on those surfaces. The vapour particles 10 precipitating as dew increase the heat insulation of the covering layer and the radiation 13 from the covered-over internal space of the structure cannot pass through the layer 2 and is reflected back as scattered heat diagrammatically designated as 13a.The analogously formed insulating layer of dew formed by precipitated vapour particles 10 on the outer covering layer 1 analogously protects the airspace I from colder radiation 12 and hence the effective or actual heat loss 14 is smaller than the energy of the radiation 13 from the covered-over space.

This process can also be employed with all directions reversed when the covered-over space is colder than the ambient atmosphere; all above-described effects then take place in the reverse direction.

Similarly to the process above, it is also possible to cool the covering layers 1 and 2 when the precipitate on the covering layer extracts the latent heat of evaporation from the covering layer surfaces as it dries and reverts to being a vapour layer 10. The arrows in the diagram attached to the particles show that since no cyclonic air flow can arise in the airspace I, the vapour particles dissolved in the air have a mutual effect on each other.

The directed changes in enthalpy taking place in the airspace I equalise or damp down the peaks of extreme ambient temperature changes.

Fig. 4 illustrates the principle of the ninth inventive concept. Reference numbers 3a and 4a, respectively illustrate a surface portion that absorbs heat radiation and the direction of the heat rays.

Arrow 16 indicates the flow of an appropri ately warmed up airstream of high humidity; as it flows in the flow channel bounded by the heat-absorbing surface portions 3a and the temperature of the water 5 is colder than that of the ambient atmosphere. The cold water cools the surfaces 3a, and the humid warm air 16 transfers its heat by convection and by heat radiation 4a to the surface parts 3a while the heat is transferred from there by metallic conduction and condensation to the flowing water 5 to raise the temperature of the latter.

As the airstream 16 cools, and its enthalpy decreases, the excess vapour content 15 condenses on the surface layers 3a and this condensation flows along the direction of arrow 17 in the form of water or condensation 18 to a water discharge channel 19. As the flowing water 5 warms up due to the heat exchange, vapour particles 7 evaporate from its free surface 5a into the airspace I.

With this solution, any undesirably high air temperature in the covered-over space can be reduced. The unfavourably high humidity content can be reduced without ventilation to the appropriate level, whereby to save energy.

The water of condensation 18 obtained by recooling can be used up as water of irrigation. Insofar as the water 5 taking part in the recooling of the air is itself water of irrigation, then in this way it is preheated.

Fig. 5 illustrates the tenth inventive concept in which 3b designates a heat-radiating, as well as heat-absorbing, convective surface portion; 4a and 4b designate respectively the outward and inward heat radiation and in which 16 again designates the flowing air which is flowing in the same space as the space defined by the flow channel 8 bounded on two sides by the surface portions 3b.

From the free surface 5a of the liquid vapour particles 7 pass along the direction of arrow 6 into the airstream 16 so that the relative humidity of the latter increases. Setting the desired air temperature takes place by way of the regulatable heat-exchange with the temperature of the flowing liquid or water 5 at the liquid surface 5a and the surface parts 3b along the directions indicated by arrows 4a and 4b depending on whether the flowing air 16 is to be heated or cooled.

Since the free liquid surface 5a makes contact with the airstream 16 over an extended path or section, it is suitable for removing dust and other water-soluble contaminants in the air as well as to purify the air from undesired enrichment of gaseous contaminants such as carbon dioxide.

The flow channel between the surface portions 3b and the outer covering layer 1 has a tap or bleed-off so that the air 16a passing into the airspace I receives vapour particles 11 of increased energy to regulate the climate in the airspace I in accordance with the description already given.

It is possible to flush or ventilate the airspace I by blowing in air along 16a which is an expedient embodiment or solution n the case where the covering layers 1 and 2 are not light-permeable.

Fig. 6 illustrates and explains the eighth inventive concept. The covered-over airspace II is maintained at the desired temperature or in the vicinity of the desired temperature by positioning an air flow channel 20 at a suitable height through which air 24 flows and is intermittently bled off to be brought into contact with an arrangement according to either one of those shown in Figs. 4 and 5 i.e. with cold or warm water, indicated by the arrow 25, whereby heat exchange will take place between the water and the air to adjust the temperature. After heat-exchanger, the air with the required parameters flows along the arrow 16 into the covered airspace II.Thereafter, the water 5 is caused by forced circulation to flow under the cultivation soil 26 into a canal system, indicated by parallel inclined lines, wherein it effects heat exchange via a heatexchanger 22 with the volume or body of the soil acting as a heat accumulator or storage medium 28. In this way, the accumulator 28 will assure the required heat capacity and should the air temperature require to be adjusted in the opposite sense, then the water may be passed through it at 5 and 25 to condition the air 16 to the required value.

This preferred embodiment, based on a soil accumulator idea is particularly advantageous because practically any magnitude of heat may be stored in the soil. The midday and afternoon heat of the air 16 can be used for overcoming the nocturnal and dawn cold while conversely the latter can be used for attenuating the midday, mid-afternoon heat; all the while, the air remains clean, the closed system in the soil does not wash the soil out, the water is not contaminated and is not enriched by any particular ingredient. A special advantage is that the water flow circulating in a closed system and designated by 5 and 25 assures the heat transfer with a relatively small quantity of water and can be used for any covering layers and for all structures, whether single aisle or multi-aisle.

The following are some possible areas of application of the invention: -Frost-free cold stores by employing the process according to the invention; -Greenhouses and moderate temperature buildings, by employing the prowess according to the invention and utilising waste water and thermal water; -For operating greenhouses by providing supplementary heating in peak periods of vegetative heating; --Air-conditioning of lightweight mushroom beds with closed structures; --Air-conditioning structures for breeding small domestic animals; -Operating buildings with one or more naves or aisles and for air-conditioning structures with covered surfaces of any desired magnitude; ; -Combining the process with other methods or processes, other ways of heattransfer and any desired method of operation so as to save heating energy.

Advantages of the invention include the following: -its realisation requires low investment costs; -the efficiency of power or energy utilisation is high; it is economic in its usage of water because it warms the water or irrigation and obtains water of condensation; -good heat stability; -the process may be automated; -protects against loads and stresses due to ice and snow; -moderates extreme weather peaks; -is suitable for accumulating energy due to diurnal heat changes; and -is versatile in its applicabiity.

Claims

1. A process for the heat insulation of the coverings or roofs, including at least two spaced-apart covering layers with an insulating air space therebetween, of agricultural buldings and for the energy-saving air conditioning of the internal spaces covered thereby, the process comprising circulating water, thermal energy and air and changing the state of the circulated water, thermal energy and air, and increasing the heat content of a heat-insulating space defined between said covering layers is increased by means of heat radiation directed along planes generally parallel with the planes of the layers while allowing or causing vapour to pass into the air space from a free liquid surface provided within the covered heat insulated space so that the vapour absorbs the heat radiation and increases the overall enthalpy of the air in said space, and causing the air and vapour to release or to take up energy by way of precipitation and evaporation, respectively, in dependence on external environmental factors while the climate of the covered space is wholly or partially protected against temperature fluctuations and other external factors.

2. A process according to claim 1, wherein ventilating air is caused to flow in forced circulation to contact the free liquid surface so that by way of convective heat transfer, the temperature of the air reaches equilibrium with the temperature of the liquid while the relative humidity of the air increases beyond its normal maximum.

3. A process according to claim 1 or 2, wherein any excess relative humidity of the covered space is allowed or caused to condense and flow along or on the surface of a cooled channel of the frame structure of the building and expediently preheats water of irrigation and obtains water of irrigation from the moisture.

4. A process according to any preceding claim, wherein in the case of overheating or during periods of intense sunshine, the hot air accumulating near the top covering or roof of the building is brought into heat exchange with a liquid, expediently water, at that level and the cooled air is passed into the vicinity of e.g. growing plants, the heat content of the heated up water is stored and during colder parts of the day the available heat capacity is supplemented therefrom.

5. A process according to any preceding claim, wherein in the interest of maintaining the light-permeability of the covering layer(s), the heat-carrying medium or media e.g. water, is circulated in separate flow channels and the channels are decontaminated in cycles when cultivation is not in progress.

6. A process according to any preceding claim, wherein the temperature and enthalpy of natural heat carriers are increased or decreased by direct or indirect interaction via radiation, conduction and mixing while the heat carriers are caused to flow in forced circulation.

7. A process according to any preceding claim wherein the heat transfer is assured to the covered air space wholly or partly by means of radiating heat-transfer surfaces while heat transfer is assured to the cultivation or breeding space wholly or partly by convective surfaces, the proportion of the radiating surfaces to the convective surfaces being in the ratio of 1:3 while the radiating surface portions amount to 3-6% of the whole of the covered surface.

8. A process according to claim 1 substantially as herein described with reference to and as shown in Fig. 1 in combination with any of Figs. 2 to 6 of the accompanying drawings.