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FIELD OF THE INVENTION The present invention relates a solar powered cooling system used in HVAC (Heat Ventilation and Air Conditioning) system of buildings. More particularly, the present invention relates to absorption or adsorption based refrigeration system integrated in the outside envelope of any construction to cool the inside using solar energy. The solar cooling system is made compact so that it can be easily integrated in the building envelope.
BACKGROUND OF THE INVENTION The absorption or adsorption based cooling system uses heat to provide air-conditioning. These are popular air-conditioning systems, wherever waste heat is available (like in process plants, power plants etc.). Absorption based chillers mostly use Lithium Bromide (LiBr)-Water system or Water-Ammonia as absorber-refrigerant for absorption cycle. Adsorption based chillers usually use Silica Gel-Water or Zeolite-Water as adsorber-refrigerant pair. The adsorption/absorption cycle (FIG. 1) is similar to a vapor compression cycle, but instead of a mechanical compressor, the compression of the refrigerant vapor is achieved via adsorption/absorption process. FIG. 1 illustrates the working of an adsorption/absorption cooling cycle. The refrigerant enters the evaporator as a saturated liquid. The pressure of the evaporator chamber is such that the corresponding saturation temperature of the refrigerant is below the temperature of the region to be cooled. Let the region to be cooled be termed as region C. Inside the evaporator, the refrigerant evaporates. The latent heat of vaporization is extracted from the region C. The extraction of heat of vaporization causes the region C to cool down. After evaporation, the refrigerant converts into saturated or super-heated vapor. In case of absorption cooling system, the refrigerant is absorbed in a substance which has high affinity to absorb water (for example, a concentrated solution of LiBr). The substance is called an absorbent. The absorbent chamber is connected to a Generator chamber. In the Generator chamber, the absorbent is heated from a heat source. The increase in temperature of the absorbent leads to release of the refrigerant. The refrigerant is released from the absorbent in the vapor phase at higher pressure than the evaporator. The refrigerant then goes to a condenser wherein it is condensed to liquid state by removal of heat. The refrigerant comes out of the condenser as a saturated liquid. The refrigerant then passes through a throttle valve, which leads to a sudden decrease in the pressure of the refrigerant. Because of this sudden drop in the pressure, a small amount of refrigerant evaporates, and the remaining refrigerant cools down to the saturation temperature associated with the low pressure in the evaporator. In an adsorption cooling cycle, instead of an absorption chamber, the refrigerant is adsorbed in an adsorber. In the Generator chamber, the adsorber is regenerated by heat, which releases the refrigerant. In FIG. 1, the Desorption/Generator (D) is the energy consuming chamber and it consumes heat energy instead of electric energy in compressors. The Condenser (Qout) and Absorber/Adsorber (A) reject heat to environment. The Evaporator (Qin) takes the heat from the occupied space. The coefficient of performance (COP) of the system is defined as:
COP=Qin/Generator(D)heat consumed
In FIG. 1,
-
- Qin=Heat absorbed by evaporator from the occupied space,
- Absorber=Absorber or Adsorber chamber
- Desorber=Generator chamber taking heat as energy input and separating refrigerant from adsorber/absorber
- Pump=Pump for flow of absorber (Not required in adsorption cycle)
The simplified process of absorption is explained in FIG. 2. The absorber has affinity toward the refrigerant and hence the refrigerant in the evaporator chamber evaporates and gets absorbed in the absorber chamber. The process of evaporation cools down the evaporator chamber. In order to regenerate the absorber and the refrigerant, heat is provided to the absorber chamber, due to which the refrigerant gets separated from the absorber. This refrigerant is then replenished in the evaporator chamber using an expansion valve and then the process is repeated.
The working of adsorption cycle is similar to absorption cycle, the only difference being that instead of liquid absorber, solid adsorber is used to evaporate refrigerant. The capacity of absorption chillers is available in various sizes varying from 10 KW to 10,000 KW. Numerous conventional chiller companies like York, Trane, Johnson-Control, Thermax etc. have absorption and adsorption chillers in their product range. These chillers typically use waste heat available in process plants and power plants. There have been efforts to power these chillers using solar energy. There have been recent innovations related to reflectors to concentrate the solar heat to attain the required temperature and energy to power these chillers. However the usage of such chillers using solar energy is still not cost effective and there have been very limited installations of such systems, especially in residential buildings.
OBJECTS OF THE INVENTION The main object of the present invention is to provide a miniature version of absorption and adsorption cooling system so that it can be used as a building material.
Another object of the present invention is to design a passive system which can run solely on the solar energy.
Yet another object of the present invention is to design building material which can be retrofitted to existing construction, providing cooling using solar energy.
Yet another object of the present invention is to design the system such that its cooling capacity increases with increase in available solar energy, hence it cools less when solar energy is less and cools more when solar energy is more.
DETAILED DESCRIPTION OF THE INVENTION FIG. 3 is a schematic drawing of the 1st embodiment of the refrigeration system. 301 is the evaporation chamber which is in thermal contact with the region to be cooled (denoted by region C). Let the target temperature of region C be denoted by Tc. The temperature in chamber 301, denoted by Te should be such that Te<Tc. From the thermodynamic properties of the refrigerant, the pressure inside the chamber 301, denoted by Pe is determined so that Te is the saturation temperature of the refrigerant in chamber 301. Chamber 301 absorbs heat from region C because of thermal contact between then causing the refrigerant to evaporate. On evaporation, refrigerant absorbs heat. Chamber 302 is the absorber chamber containing concentrated absorber, which is capable of absorbing refrigerant vapour. Presence of concentrated absorber also promotes evaporation of the refrigerant in chamber 301. Evaporated refrigerant from chamber 301 gets absorbed to the absorber in chamber 302. Absorption of refrigerant is accompanied by release of heat. This heat is removed via cooling tubes 308. In one embodiment, the fluid in cooling tubes 308 is cooled via capillary evaporation. The diluted absorber is pumped from chamber 302 to chamber 303 using a micro-pump 309. Chamber 303 is the generator chamber. Dilute absorber in chamber 303 is heated using a heat source. In the embodiment shown in FIG. 3, the heat source is sun's radiation. In another embodiment, the heat source can be waste heat from an internal combustion engine, or waste heat from a chemical or nuclear reaction. The pressure in chamber 303, denoted by Pg is higher than Pe. Upon getting heated, refrigerant is released from the absorber and concentrated absorber flows back to chamber 302. The tube bringing the absorber from chamber 303 to chamber 302 is connected to tube 310, which is filled with a high density liquid, such as mercury to ensure the pressure difference between the chamber 302 and chamber 303 is maintained. The desorbed refrigerant in vapour state in chamber 303 flows to chamber 304, which is called the condenser chamber. In chamber 304, the refrigerant is cooled and condensed. In one embodiment of the invention, cooling in chamber 304 is achieved via capillary evaporation of cooling fluid flowing in cooling tubes 307. The condensed refrigerant in chamber 304 at pressure Pg passes through a throttle valve 305 to chamber 301, which is at lower pressure, Pe. Upon sudden decrease in pressure, a small fraction of the refrigerant evaporates, thereby cooling the remaining refrigerant to the temperature Te in the evaporation chamber 301. From chamber 301, the above described cycle continues. Different chambers of the system are thermally insulated from each other using insulating material 306 (represented in FIG. 4 by broad lines). The chamber 310 in FIG. 4 also acts like an insulating region.
FIG. 4 shows another design of the invention. The basic process cycle of this design is the same as the design in FIG. 3. Chamber 101 is the evaporation chamber, chamber 102 is the absorption chamber, chamber 103 is the generator chamber, chamber 104 is the condenser chamber, 105 is the throttle valve, 106 is insulation material which is represented in the diagram as thick lines. 107 and 108 are cooling tubes for chamber 102 and chamber 104 respectively. In this design, a reverse osmosis (RO) membrane 109 separates the absorber chamber 102 and the generator chamber 103. The RO membrane allows only the refrigerant to pass through it. When the unit is not in operation, the refrigerant in chamber 103 remains in equilibrium with the refrigerant in chamber 102. That is, the high pressure Pg in chamber 103 plus the fluid pressure due to gravity is balanced by the osmotic pressure plus Pe across the RO membrane 109 because of the lower concentration of absorbent in chamber 102. Contrary to the traditional absorption based refrigerators, in this design the absorption chamber 102 is maintained at lower absorbent concentration than the generator chamber 103 in order to trap overhead sun rays. During normal operation of the unit, as refrigerant is absorbed in chamber 102, the pressure differential will develop across the RO membrane 109 because of which the refrigerant will flow into chamber 103. In chamber 103, using heat, refrigerant is separated from the absorbent. The remaining functioning of this design is similar to one described in FIG. 3. The working conditions (temperature, pressure) of different chambers is similar to the design in FIG. 3.
FIG. 5 shows another design of the invention. The basic process cycle of this design is the same as the design in FIG. 3. Chamber 201 is the evaporation chamber, chamber 202 is the absorption chamber, chamber 203 is the generator chamber, chamber 204 is the condenser chamber, 205 is the throttle valve, 206 is insulation material which is represented in the diagram as thick lines. 207 and 208 are cooling tubes for chamber 202 and chamber 204 respectively. In this design, a reverse osmosis (RO) membrane 209 separates the absorber chamber 202 and the generator chamber 203. The RO membrane allows only the refrigerant to pass through it. Similar to the design in FIG. 3, the absorber in chamber 202 is at slightly lower concentration than in chamber 203 in order to balance the higher pressure in chamber 203 (Pg) with osmotic pressure.
The design of the system is made such that miniature version of vapor absorption or adsorption cycle is packed in to a small chamber. The various possible embodiments of this design are shown in FIGS. 1, 2(a), 2(b), 2(c), 3(a), 3(b) and 4.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS In the drawings accompanying the specification,
FIG. 1 shows the cycle diagram for absorption or adsorption refrigeration system used in this invention.
FIG. 2 shows the mechanism of absorption/adsorption and regeneration process used in this invention.
FIG. 3 shows the 1st embodiment of design and arrangement of absorption based system proposed in this invention.
FIG. 4 shows the 2nd embodiment of design and arrangement of absorption based system proposed in this invention.
FIG. 5 shows the 3rd embodiment of design and arrangement of absorption based system proposed in this invention.
Although the description of this invention has been given with reference to a particular embodiment, it is not to be construed in a limiting sense. Many variations and modifications will now occur to those skilled in the art. For a definition of the invention reference is made to the appended claims.
