Description of Invention

The present invention is concerned with the transfer of heat and is primarily concerned with the transfer of heat from an airstream, in order to cool the airstream. It is common to cool a stream of air supplied to the interior of a building. It is also common to cool a stream of air, in order to reduce the water vapour content of that stream.

According to a first aspect of the invention, there is provided a method of effecting the transfer of heat wherein low grade heat is converted to a higher grade heat, a portion of the higher grade heat is converted to a second form of energy and the energy in the second form is used to promote the transfer.

By low grade heat, we mean heat at a relatively low temperature, for example the ambient temperature. Higher grade heat is heat which can be extracted from a medium which is at a higher temperature. After such extraction, a part of the heat will remain as low grade heat.

The energy in the second form may be used to drive a compressor for converting the low grade heat to higher grade heat. Additionally or alternatively, the energy in the second form may be used to promote flow through a heat exchanger of air or another medium from which the heat is to be transferred and/or to promote the flow through a further heat exchanger of the ambient air or other medium to which the low grade heat is to be transferred.

Energy in the second form may be converted to energy in a third form, before being used to promote the transfer of heat. For example, the higher grade heat may be converted to electrical energy, which is converted to mechanical energy and applied to a heat transfer medium to compress that medium and raise the grade of heat carried by the heat transfer medium.

Conversion of the higher grade heat to energy in the second form may be effected by means of a heat engine to which a heat transfer medium is conveyed from a compressor. Alternatively, the heat transfer medium may be passed from the compressor through a heat exchanger where higher grade heat is transferred to a second heat transfer medium, that second medium being conveyed to the heat engine. Thus, there may be two separate circuits,

one including the compressor and a first side of the heat exchanger and the other circuit including the heat engine and a second side of the heat exchanger.

According to a second aspect of the invention, there fs provided a compressor for compressing a heat transfer medium to raise the grade of the heat carried thereby, a heat engine, means for delivering the heat transfer medium from an outlet of the compressor to the heat engine or to a heat exchanger associated therewith, cooling means for transferring heat to the heat transfer medium, a first duct for leading the heat transfer medium from the heat engine or associated heat exchanger to the cooling means, the duct including a pressure-reducing orifice, and a second duct for leading the heat transfer medium from the cooling means to an inlet of the compressor.

In a case where the heat transfer medium is conveyed from the outlet of the compressor to the heat engine, the apparatus may have a single circuit for the heat transfer medium. In a case where the heat transfer medium is conveyed from the outlet of the compressor to a heat exchanger associated with the heat engine, the apparatus may comprise two, separate circuits, one including the compressor and a first side of the heat exchanger and the other circuit including the heat engine and a second side of the heat exchanger.

The apparatus preferably includes means for transferring power from the heat engine to the compressor.

There may be associated with the cooling means means for inducing flow of air in thermal communication with the cooling means and means may be provided for transmitting power from the heat engine to the flow-inducing means.

There may be provided further flow-inducing means for inducing a flow of ambient air into thermal communication with a further heat exchanger through which the heat transfer medium is caused to flow, in order to transfer low grade heat to the ambient atmosphere. Means may also be provided for transferring power from the heat engine to this further flow- inducing means.

Apparatus in accordance with the second aspect of the invention may be adapted to transfer heat from a low grade source to a space which is to be occupied by people. The source may be the ambient atmosphere or another medium at ambient temperature, for example water. The heat may be transferred to the space which is to be occupied by the people by means of air fed into that space or by means of a heat transfer medium which is passed

through radiators or other heat-emitting devices associated with that space. In a case where the source is the ambient atmosphere and heat is transferred to the space to be occupied by people by means of air delivered to that space, the air from which heat is extracted may be discharged to the ambient atmosphere whilst a further supply of air is drawn from the ambient atmosphere to be heated and delivered to the space to be occupied by people. Two examples of apparatus embodying the present invention, and which are used in methods according to the present invention, will now be described, with reference to the accompanying drawings, wherein:-

FIGURE I is a diagram representing a circuit of the first apparatus ; and

FIGURE 2 is a diagram representing the circuit of a second apparatus.

The apparatus represented in Figure I is suitable for transferring heat from an airstream represented by the arrow 10 to a current of air represented by the arrow I I . The heat carried by the airstream 10 is relatively low grade heat, that is to say that the temperature of the airstream 10 is similar to the ambient temperature. Typically, the air of the stream 10 is ambient air which is to be supplied to the interior of a building or some other space occupied by people. The temperature of the airstream 10 is typically within the range 20 to 45 C. The air is required to be cooled, for example to a temperature of 15 C. This achieved by drawing the current of air over a heat exchanger 12 disposed within a housing 13. The housing also contains a fan 14 for drawing the air through the housing and an electrically energisable motor 15 for driving the fan. The airstream 10 may be withdrawn from the space to which the air leaving the housing 13 is directed, the air being circulated through the housing for cooling.

The heat exchanger 13 may be in the form of one or more pipe coils and forms a part of a fluid circuit containing a heat transfer medium. The heat transfer medium may be a vapour which can readily be condensed to a liquid by the application of pressure at ambient temperature. The circuit also includes a compressor 16 for compressing the heat transfer medium, a condenser I 7,a restrictor 18 defining a pressure-reducing orifice and ducts connecting the other components of the circuit. Such circuits and the components thereof are well known.

The condenser 17 is enclosed in α jacket 20 containing a second heat transfer medium which is a volatile liquid. An electrically energϊsable motor 19 is provided for driving the compressor 16. When the compressor is driven, the first heat transfer medium is drawn from the heat exchanger 12 by the compressor and is compressed to a pressure which is typically within the range 10 to 20 bar. This raises the grade of the heat carried by the heat transfer medium, the temperature of the heat transfer medium being raised to a value in excess of 75 C. From the compressor, the heat transfer medium flows through the condenser 17, where a portion of the heat is transferred to the second heat transfer medium contained within the jacket 20. In consequence of this loss of heat, the first heat transfer medium condenses in the condenser 17. The resulting liquid heat transfer medium, carrying lower grade heat, but still under high pressure, flows from the condenser 17 through the pressure reducing orifice of the restrϊctor 18. Downstream of the orifice, the pressure of the heat transfer medium is less than 10 bar and is typically in the region of 5 bar. The heat transfer medium flows, under this low pressure, through the heat exchanger 12, where the liquid heat transfer medium evaporates and extracts heat from the airstream 10.

The jacket 20 forms a part of a second circuit which also Includes a heat engine 21, a second condenser 22 and a pump 23 which includes non¬ return valve, together with ducts connecting these components in the second circuit. The heat engine is a known heat engine, for example a turbine, and has an output shaft drivingly connected with an electrical generator 24. The second condenser 22 comprises a jacket 25 containing a pipe coil 26 through which a third heat transfer medium circulates. The pipe coif is connected in a third circuit with a radiator 27 or other means for delivering heat to the current of air I I . The third circuit may Include a pump for circulating the third heat transfer medium. The third heat transfer medium is typically water.

Alternatively, the current of air 1 1 may flow in direct contact with the second condenser, in which case the latter would have an alternative form, for example a pipe coil or an array of finned tubes. Furthermore, heat may be transferred to a heat storage medium before being transferred to the current of air 1 1 or the third circuit may be used to provide a supply of hot water, rather than heated air.

By extracting heat from the current of air 1 1 in the heat exchanger 12, water vapour contained in the air can be caused to condense. By subsequently transferring heat to the current of air, the temperature of the latter can be raised to a required value, thereby reducing the relative humidity of the air.

The heat carried from the jacket 20 by the second heat transfer medium is relatively high grade heat, the second heat transfer medium being heated to a temperature in excess of 75 C in the jacket 20. The condenser 17 may be a two-stage condenser, each stage having a respective jacket connected in series with the jacket of the other stage. With this arrangement, one stage may serve as a pre-heater and the other stage as a super heater for the second heat transfer medium. Since the heat carried to the heat engine is relatively high grade heat, the heat engine is able to convert a part of the thermal energy to mechanical energy with reasonable efficiency.

To promote the flow of air past the radiator 27, there may be provided a further fan 28 having an electrically energisable motor at 29. The motor 29, the pump 30 (if any) incorporated in the third circuit, the motor 1 and the motor 15 are connected electrically with a controller 3 1 by suitable leads 32. The controller 31 controls the supply of electrical energy from the generator 24 and from a mains electrical supply 32 to the electrically energisable components of the apparatus. For the purpose of illustration, a simplified electrical circuit is represented in Figure I but it will be appreciated that a more complex electrical circuit would normally be provided, in order that the electrically energisable components of the apparatus can be controlled independently of one another, if required.

When the apparatus is required to be brought into operation, electrical energy is drawn from the mains supply 32. However, when the apparatus is operating under at least approximately steady state conditions, at least some of the power required by the electrically energisable components of the apparatus will be provided by the generator 24 and either less power or no power wil l be drawn from the mains supply.

In some cases, the generator 24 may provide electrical energy at a rate higher than that required to operate the electrically energisable parts of the apparatus. In this case, the power controller 31 may make electrical energy available to other apparatus or to storage means, from which energy may be drawn subsequently, for example during start-up of the apparatus of Figure 1 .

The apparatus may be used simply for cooling the airstream 10. Alternatively, the apparatus may be used for reducing the water vapour content of the airstream 10. This is achieved by reducing the temperature sufficiently to cause the required proportion of water vapour to condense In the heat exchanger 12, and draining away the resulting water. If necessary, the cool air may then be reheated, for example by heat exchange with the airstream 10. The apparatus may alternatively be used for heating a fluid, for example air or water. Heat transferred for this purpose may be waste heat extracted from air, water or other fluid being discharged after use.

Whilst it Is convenient to convert heat energy to electrical energy by means of the heat engine 21 and generator 24, It will be understood that energy extracted from the second heat transfer medium could be utilised in some other form. For example, a mechanical drive could be provided for transmitting energy from the heat engine 2! to the compressor 16 and/or other energisable components of the apparatus.

The apparatus of Figure I may be modified by the omission of certain components. Such modified apparatus is illustrated in Figure 2 where corresponding parts are identified with like reference numerals having the prefix I . Except for differences hereinafter mentioned, the preceding description is deemed to apply to such corresponding parts.

In the apparatus of Figure 2, the first heat transfer medium flows from the compressor 1 16 directly to the heat engine 121. From the heat engine, this heat transfer medium flows through a pipe coil 126 to an expansion valve 1 18, from which it returns to the heat exchanger 1 12. A flow of air I I I may be directed over the outside of the coil 126 to extract heat therefrom. Alternatively, water or some other heat transfer medium may be directed over the outside of the coil 126.

High grade heat energy is converted by the heat engine info mechanical energy which is applied to the generator 124. Electrical energy produced by the generator is applied by the power controller 131 to the compressor 1 16, to the fan motor 1 15 and to the fan motor 129.

The features disclosed in the foregoing description, or the accompanyi ng drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.