GB2062215A

GB2062215A - Solar Powered Cooling System

Info

Publication number: GB2062215A
Application number: GB8032760A
Authority: GB
Original assignee: Agar Corp NV
Current assignee: Agar Corp NV
Priority date: 1979-10-12
Filing date: 1980-10-10
Publication date: 1981-05-20

Abstract

A solar powered cooling system comprises a closed conduit (10) adapted to contain a refrigerant, means (14) for expanding refrigerant in said closed conduit (10) so as thereby to cool the refrigerant, a duct (21) for passing a fluid to be cooled in heat exchange relationship with the said expanded refrigerant, and a compressor (15) for compressing the said expanded refrigerant. A solar heat absorber (11) is arranged to cause vaporisation by solar heat of liquefied refrigerant, and an engine (12) is driven by the said vaporised refrigerant and drives said compressor. A control arrangement (32) controls the supply of refrigerant to the solar heat absorber (11) so that the solar heat absorber (11) is supplied with refrigerant only when the level of the refrigerant in the solar heat absorber (11) is below a predetermined value. <IMAGE>

Description

SPECIFICATION Solar Powered Cooling System This invention concerns a solar powered cooling system and although the invention is not so restricted, it is more particularly concerned with a solar powered air-conditioning system.

Attempts have been made in the past to devise an air-conditioning system which is powered by solar energy, since the power for such a system would be at its maximum at the time when the need for such power would also be at its maximum.

For example, solar powered air conditioning systems are disclosed in U.S. Patent Specifications Nos. 3,960,322 and 4,018,581. Previous systems have, however, relied on high solar energy inputs and on direct solar radiation, and have therefore not been usable on warm but cloudy days.

According, therefore, to the present invention, there is provided a solar powered cooling system comprising a closed conduit adapted to contain a refrigerant, means for expanding refrigerant in said closed conduit so as thereby to cool the refrigerant, means for passing a fluid to be cooled in heat exchange relationship with the said expanded refrigerant, a compressor for compressing the said expanded refrigerant, a solar heat absorber arranged to cause vaporisation by solar heat of liquefied refrigerant, an engine which is driven by the said vaporised refrigerant and which drives said compressor, and control means for controlling the supply of refrigerant to the solar heat absorber so that the solar heat absorber is supplied with refrigerant only when the level of the refrigerant in the solar heat absorber is below a predetermined value.

Preferably the control means comprises a control valve which controls the flow of refrigerant to the solar heat absorber, one face of said control valve being open to the pressure of the refrigerant in the solar heat absorber. The control valve is preferably a float valve in a level control tank, the level control tank being disposed between the solar heat absorber and a storage tank.

There may be a condenser for liquefying the refrigerant in the closed circuit, there being means for extracting heat from the condenser and using the extracted heat to increase the temperature of the refrigerant entering the solar heat absorber.

Preferably, the means for passing the fluid to be cooled comprises means driven by the said engine for circulating said fluid past and in heat exchange with the closed conduit.

The engine is preferably a gas turbine engine although it could, if desired, be constituted by a reciprocating engine.

There is preferably a by-pass passage which communicates with the closed conduit to permit refrigerant flowing therethrough to by-pass the compressor, the by-pass passage having a by-pass valve therein and there being means for opening and closing the by-pass valve in dependence upon the mass flow of the refrigerant supplied to the compressor, whereby to avoid surging of the latter.

Heating may be provided adjacent to the solar heat absorber so that the latter may be heated when the solar heating thereof is inadequate.

The engine instead of, or in addition to, driving the means for circulating a fluid to be cooled, may drive an electric generator.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is a diagrammatic view of a first embodiment of a solar powered cooling system according to the present invention, and Figure 2 is a diagrammatic view of a second embodiment of a solar powered cooling system according to the present invention.

Referring first to Figure 1, a solar powered air-conditioning system comprises a closed conduit 10 which is adapted to contain a refrigerant, the refrigerant being capable of being expanded to vaporise it and of being compressed to liquefy it. A suitable refrigerant is one of low boiling point, such as that sold under the trade name R1 2. Connected successively in the closed conduit 10 are a solar heat absorber 1 a gas turbine engine 12, a condenser 13, an expansion chamber 14, a compressor 15, a check valve 16, the latter permitting flow of refrigerant therethrough only in the direction of an arrow 17, a storage tank 30, and a level control tank 31.

Liquefied refrigerant supplied to the solar heat absorber 11 is vaporised therein by the solar heat so that the pressure of the refrigerant is raised. The provision of the check valve 1 6 prevents flow of refrigerant in a direction opposite to that of the arrow 17, and consequently the so-pressurized refrigerant flows through the gas turbine engine 1 2 so as to drive the latter, the hot vaporised refrigerant thus losing much of its energy. Thus, if the vaporised refrigerant enters the gas turbine engine 1 2 at a temperature T, and a pressure P1, it may leave the gas turbine engine 12 at a reduced temperature T2 and reduced pressure P2.

The vaporised refrigerant then passes to the condenser 13 where its temperature is further reduced so as to convert it into a liquid. This may be achieved, as shown, by providing a conduit 20 opposite ends of which are respectively in heat exchange relationship with the condenser 13 and with the upstream side of the solar heat absorber 11. The fluid circulating through the conduit 20, therefore, will withdraw heat from the condenser 13 and will impart heat to refrigerant entering the solar heat absorber 11 so as to effect pre-heating of this refrigerant. If desired, the conduit 20 may be in heatexchange relationship with a domestic hot water supply conduit 1 9 which may lead to a hot water tank (not shown), such an arrangement promoting the cooling of the refrigerant passing through the condenser 1 3.

The liquefied refrigerant then enters the expansion chamber 14 where its temperature is yet further reduced to a value T3 by reason of the expansion of the refrigerant in the expansion chamber 14.

The closed conduit 10, on the downstream side of the expansion chamber 14, passes through an air duct 21 which forms part of a forced air cooler, the duct 21 having a fan 22 therein which is driven by the gas turbine engine 12. Warm air enters the duct 21 adjacent to the fan 22 and is circulated thereby past and in heat exchange with the expanded refrigerant so as to be cooled thereby. The refrigerant itself will thus have its temperature increased to a value T4.

The refrigerant then passes to the compressor 15, which is driven by the gas turbine engine 12 so as to compress the refrigerant, the refrigerant leaving the compressor 1 5 at a temperature T5.

A by-pass passage 23 communicates with the closed conduit 10 to permit refrigerant flowing therethrough to by-pass the compressor 15. The by-pass passage 23 has a by-pass valve 24 therein, the by-pass valve 24 being in operation opened and closed by a gauge 25 arranged to monitor flow through the closed conduit 10. The gauge 25 effects opening and closing as required of the by-pass valve 24 in dependence upon the mass flow of the refrigerant supplied to the compressor 15, whereby to avoid surging of the latter.

Thus although the solar heat absorber 11 may operate at temperatures of 400C and above, the temperature T3 may be as little as 15 OC, whereby to effect substantial cooling of the warm air supplied to the duct 21.

The enthalpy of the apparatus shown in Figure 1 is highest at the output of the solar heat absorber 11 as it is this unit which receives the outside energy. The mechanical work developed by the gas turbine engine 12, or by a reciprocating engine which may be used in substitution therefor, is larger than the mechanical energy required to compress the refrigerant in the compressor 1 5. The surplus energy may therefore be used to drive an electric generator 26.

If the air-conditioning and/or the electric generator 26 is required to operate at night, this may be achieved by operating heating means 27 disposed adjacent to the solar heat absorber 11 so that the latter may be heated when the solar heating thereof is inadequate. Such means may, for example, be constituted by L. P. G, (liquefied petroleum gas) burners.

The polytropic work developed at the gas turbine engine 12 is given by the equation:

N I IP2\ (N~I)/N inJoule/Mole (1) WI = N j (ZIRTI) I-/P2\ (N.I)/i in Joule/Mole (1) where: W,=Polytropic work in Joule/Mole N=Polytropic exponent Z1=lnitial super-compressibility factor R=Gas Constant=8.31 Joule/Mole OK T1=lnitial Absolute temperature in OK P1=lnitial Absolute Pressure in Newton/Sq.M P2=Final Absolute Pressure in Newton/Sq.M.

The above equation (1) can be approximated to: wl ss(ZIRTI) Jn(Pj/P2) (2) The polytropic work done by compressing one mole is

which can be approximated to: WC=RT4Z4 in (P1/P2) (4) For simplicity, it is assumed that the pressure P1 at the outlet of the compressor 1 5 is the same as the pressure P1 at the inlet of the gas turbine engine 12. Similarly, it is assumed for simplicity that the pressure P2 at the outlet side of the gas turbine engine 12 is the same as the pressure P2 on the inlet side of the compressor 1 5.

The ratio of W1/Wc gives the excess energy developed by the gas turbine engine 12 to drive the compressor 15 and the fan 22. From equations (2) and (4) it will be seen that: W1 RT1Z1 1n(P1/P2) T1Z1 (5) Wc RT4Z41 1n(P1/P2) T4Z4 The temperature T1 can easily reach 930C. Moreover, in the case of a really hot day, e.g. of 320C, the temperature T4 will be about 21 OC. Z1 is in the order of 0.95 and Z4 is in the order of 0.85, from which it may be deduced that: W, 0.95 (273+93) = =1.39 (6) Wc (273+21) 0.85 (6) Thus, the energy developed by the gas turbine engine 12 is about 40% greater than the energy required to drive the compressor 1 5, this energy being derived from the sun.As the ratio of energy consumed to energy transferred due to cooling is about 1.3 for this type of refrigeration, for every unit of heat energy transmitted to the gas turbine engine 12, three units of heat energy are removed from the air supplied to the duct 21.

As indicated above, the storage tank 30 and the level control tank 31 are connected in the closed circuit 10 between the check valve 1 6 and the solar heat absorber 11. Mounted in the level control tank 31 is a float valve 32 having a valve member 33 which controls flow from the storage tank 30 to the level control tank 31 and hence to the solar heat absorber 11. The level control tank 31 is disposed between the solar heat absorber 11 and the storage tank 30. The face 34 of the float valve 32 adjacent to the solar heat absorber 11 is open to the pressure of the refrigerant in the solar heat absorber 11.

Accordingly, if the pressure in the solar heat absorber 11 is low because there is little or no refrigerant therein, then the float valve 32 will fall and fresh refrigerant will enter the level control tank 31 from the storage tank 30 and will then flow into the solar heat absorber 11. If the solar heat absorber 11 is appropriately heated by the sun, the refrigerant therein will start to boil, the pressure in the solar heat absorber 11 will rise and this will cause the float valve 32 to rise so as to prevent any further quantity of refrigerant from passing from the storage tank 30 at this stage. The vaporised refrigerant produced in the solar heat absorber 11 will drive the gas turbine engine 12 until the solar heat absorber 11 has been substantially emptied of refrigerant.When this occurs, the float valve 32 will descend, a further quantity of refrigerant will pass from the storage tank 30 and so to the solar heat absorber 11, and the float valve 32 will then rise.

Accordingly, the provision of the storage tank 30, level control tank 31 and float valve 32 controls the supply of refrigerant to the solar heat absorber so that the solar heat absorber is periodically supplied with refrigerant only when the level of the refrigerant in the solar heat absorber is below a predetermined value. At the same time, the provision of the valve member 33 prevents reverse flow of refrigerant from level control tank 31 to the storage tank 30.

Thus, as long as there is refrigerant in the solar heat absorber 11 which is to be boiled, the pressure P1 thereof will be higher than the pressure P4 in the storage tank 30, whereby the valve member 33 will be closed. Once, however, all the refrigerant in the solar heat absorber 11 has been boiled off, the pressure P1 will drop below the pressure P4 and fresh refrigerant will enter the solar heat absorber 11, thus starting the cycle again.

The compressor 1 5 is therefore not required to compress the vaporised refrigerant to the same pressure as the pressure P1 prevailing at the input to the gas turbine engine 12, and this enables the system to operate at a lower solar heat absorption level than would otherwise be required. The construction shown functions in the form of bursts of activity with intermediate periods of inactivity during which time has to be provided for the refrigerant to evaporate from the solar heat absorber 11.

If, of course, sufficient solar heat is available, then the apparatus will operate on a continuous basis as the pressure of the refrigerant at the outlet from the compressor 1 5 will increase to the level P1 at which it enters the gas turbine engine 12.

The expansion chamber 14 may be a capillary tube expansion chamber.

In Figure 1 there is also shown a stand-by motor 35, e.g. an electric motor, to enable the airconditioning system to be operated when there is no solar heat available, as at night.

In one practical embodiment of the Figure 1 construction, the refrigerant employed may be that sold under the name R22.

In this embodiment, the temperature of the refrigerant in the storage tank 30, at the inlet to the gas turbine engine 12, at the condenser 13 and in the portion of the closed circuit 10 extending through the duct 21, may respectively be 270C, 820C,490Cand 40C.The pressure at these points may be respectively 1 1,39, 19 and 6 kg/sq.cm.

It will be appreciated that, since the conduit 10 is a closed conduit, the system is completely sealed and there is no loss of refrigerant. Moreover, the maximum energy if available for airconditioning at the time when this is most required, that is to say when the solar energy is at its greatest. Furthermore, the system shown permits the generation of mechanical energy at relatively low levels of temperature.

In Figure 2 there is shown a system which is generally similar to that of Figure 1 and which, for that reason, will not be described in detail, like reference numerals indicating like parts.

In the Figure 2 construction, the closed conduit 10 has connected therein the compressor 15, the condenser 13, and the expansion chamber 14. However, the closed conduit 10 does not have connected therein the solar heat absorber 11, the-gas turbine engine 12, the storage tank 30, and the level control tank 31, all these parts being connected in a further refrigerant conduit 40 which also has connected therein a pressure relief valve 41.

The further refrigerant conduit 40, which may contain the refrigerant sold under the trade name R1 1, is in heat exchange relationship with the closed conduit 10 on both the upstream and downstream sides of the compressor 1 5, the arrangement being such as to increase the heat at the inlet side of the gas turbine engine 12 and to decrease the heat at the outlet side thereof. For this purpose, the condenser 1 3 has coils 42 at its upstream end which are in heat exchange relationship with the further refrigerant conduit 40 adjacent the inlet of the gas turbine engine 12. Although for simplicity of illustration the coils 42 are shown as being spaced from the condenser 13, they are in fact part of the latter.

Similarly, the closed conduit 10 has coils 43 on the downstream side of the duct 21 , the coils 43 being in heat exchange relationship with the further refrigerant conduit 40.

Thus the waste heat from the condenser 13 is used to superheat the inlet to the gas turbine engine 12 and some of the cooling effect achieved by the expansion chamber 14 is used to subcool the outlet of the gas turbine engine 12. Thus the temperature difference, and hence efficiency, across the gas turbine engine 12 is increased by both raising its inlet and reducing its outlet temperature.

The pressure relief valve 41, which is connected in the further refrigerant conduit 40 between the solar heat absorber 11 and the gas turbine engine 12, prevents flow of refrigerant through the further refrigerant conduit 40 and towards the gas turbine engine 12 until the pressure of the refrigerant exceeds a predetermined value. This makes the system operate like a pressure cooker, forcing the solar heating not only to boil the liquid but to raise the vapour pressure as well.

The use of two separate refrigerant conduits 10, 40 as shown in Figure 2 enables different refrigerants (e.g. R22 and R1 1) to be used in the respective conduits, enables the two conduits 10, 40 to differ in size and flow rate, enables the two conduits to operate at different pressures and temperatures, and generally allows more flexibility and freedom in design.

Solar heating systems usually use direct solar radiation to achieve high temperatures. In the case of the present invention, however, the system can be run from the heat of the atmosphere itself. For example, if the temperature of the atmosphere is 270, which may be taken as the level when air conditioning becomes desirable, then the temperature and pressures at various points in the system may be as indicated in Figure 2. In the case of these particular temperatures and pressures, the compressor 1 5 raises the temperature of the refrigerant in the closed conduit 10 from 1 00C to 1 040C and the pressure of the refrigerant from 5.6 kg/sq. cm. to 21 kg/sq. cm.

The so-heated refrigerant flowing through the coils 42 of the condenser 13 causes the temperature of the refrigerant in the further refrigerant conduit 40 to rise from 32 OC to 820C. The latter refrigerant in passing through the gas turbine engine 12 has its pressure reduced from 5.6 kg/sq.

cm to 0.9 kg/sq. cm., while its temperature is reduced by heat exchange with the coils 43 to 1 60C. Its temperature then rises to 21 0C in the storage tank 30 due to the ambient temperature, and it is then heated by the solar heat absorber 11 so as to have a temperature at the pressure relief valve 41 of 320C.

Claims

Claims

1. A solar powered cooling system comprising a closed conduit adapted to contain a refrigerant, means for expanding refrigerant in said closed conduit so as thereby to cool the refrigerant, means for passing a fluid to be cooled in heat exchange relationship with the said expanded refrigerant, a compressor for compressing the said expanded refrigerant, a solar heat absorber arranged to cause vaporisation by solar heat of liquefied refrigerant, an engine which is driven by the said vaporised refrigerant and which drives said compressor, and control means for controlling the supply of refrigerant to the solar heat absorber so that the solar heat absorber is supplied with refrigerant only when the level of the refrigerant in the solar heat absorber is below a predetermined value.

2. A system as claimed in claim 1 in which the control means comprises a control valve which controls the flow of refrigerant to the solar heat absorber, one face of said control valve being open to the pressure of the refrigerant in the solar heat absorber.

3. A system as claimed in claim 2 in which the control valve is a float valve in a level control tank, the level control tank being disposed between the solar heat absorber and a storage tank.

4. A system as claimed in any preceding claim comprising a condenser for liquefying the refrigerant in the closed circuit, there being means for extracting heat from the condenser and using the extracted heat to increase the temperature of the refrigerant entering the solar heat absorber.

5. A system as claimed in any preceding claim in which the means for passing the fluid to be cooled comprises means driven by the said engine for circulating said fluid past and in heat exchange with the closed conduit.

6. A system as claimed in any preceding claim in which the engine is a gas turbine engine.

7. A system as claimed in any preceding claim in which there is a by-pass passage which communicates with the closed conduit to permit refrigerant flowing therethrough to by-pass the compressor, the by-pass passage having a by-pass valve therein and there being means for opening and closing the by-pass valve in dependence upon the mass flow of the refrigerant supplied to the compressor whereby to avoid surging of the latter.

8. A system as claimed in any preceding claim in which heating means are provided adjacent to the solar heat absorber so that the latter may be heated when the solar heating thereof is inadequate.

9. A system as claimed in any preceding claim in which the engine drives an electric generator.

1 0. A system as claimed in any preceding claim in which the solar heat absorber, the engine and the control means are all connected in the said closed conduit.

ii. A system as claimed in any of claims 1-9 in which the solar heat absorber, the engine and the control means are all connected in a further refrigerant conduit which is in heat exchange relationship with the closed conduit.

12. A system as claimed in claim 11 in which the further refrigerant conduit is in heat exchange relationship with the closed conduit on both the upstream and downstream sides of the compressor, the arrangement being such as to increase the heat at the inlet side of the engine and to decrease the heat at the outlet side thereof.

1 3. A system as claimed in claim 11 or 12 in which a pressure relief valve is connected in the further refrigerant conduit between the solar heat absorber and the engine, the pressure relief valve preventing flow of refrigerant towards the engine until the pressure of the refrigerant exceeds a predetermined value.

14. A solar powered cooling system substantially as hereinbefore described with reference to and as shown in Figure 1 or in Figure 2 of the accompanying drawings.

New Claims or Amendments to Claims filed on 6th March 1981.

Superseded Claim 1 New or Amended Claims

1. A solar powered cooling system comprising a closed conduit adapted to contain a refrigerant, means for expanding refrigerant in said closed conduit so as thereby to cool the refrigerant, means for passing a fluid to be cooled in heat exchange relationship with the said expanded refrigerant, a compressor for compressing the said expanded refrigerant, a solar heat absorber arranged to cause vaporisation by solar heat of liquefied refrigerant, an engine which is driven by the said vaporised refrigerant and which drives said compressor, and control means for controlling the supply of refrigerant to the solar heat absorber so that the solar heat absorber is supplied with refrigerant only when the solar heat absorber is substantially emptied of refrigerant.