GB1559318A

GB1559318A - Heat recovery

Info

Publication number: GB1559318A
Application number: GB3863976A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-08-12
Filing date: 1977-08-12
Publication date: 1980-01-16

Description

(54) HEAT RECOVERY (71) I, JOHN ALAN HAMMOND, a British Subject, of 67, Halton Road, Sutton Coldfield, West Midlands, B73 6NR, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the recovery of heat produced by compression refrigeration machines of the kind having an evaporator, a compressor, a condenser and an expansion valve, through all of which refrigerant circulates, and in which heat is extracted from one zone of the machine to evaporate liquid refrigerant by means of the evaporator, and is recoverable from another zone of the machine, where the refrigerant, vaporized by the evaporator, has heat removed from it by the condenser. Such machines will hereinafter be referred to as "of the kind specified".

There is known at present a system for heating a building by circulating around the building, water which is heated, by heat recovered by a compression refrigeration machine. In such a system the water is heated to a temperature of, typically, 100 F.

In the complete specification my copending British Patent Application Number 26284/75 (Serial No. 1558563) there is described and claimed a system for heating water for washing by means of heat recovered from a compression refrigeration machine. With the system described therein, the water can be heated to temperatures of approximately 1 303F, that is for example, up to the saturated refrigerant temperature.

The refrigerant leaving the compressor will contain a certain amount of super heat.

However, conventional condensers cannot collect such super heat efficiently.

The object of the present invention is to provide a method of recovering heat from a compression refrigeration machine in which said super heat is collected efficiently.

According to the present invention a method of recovering heat from a compression refrigeration machine of the kind specified is characterised in that the refrigerant and a liquid which extracts heat from the refrigerant flow in opposite directions through the condenser and said liquid passes only once through said condenser, thereby, in use, heating the liquid to a temperature higher than the saturated refrigerant temperature.

The invention will now be described by way of example with reference to the accompanying drawings which; Figure 1 is a diagrammatic view of a condenser for use in a system for recovering heat by a method in accordance' with the present invention Figure 2 is a graph showing the temperatures of refrigerant and water respectively flowing through the condenser of Figure 1 plotted against distance along the condenser.

Figure 3 is a temperature/enthalpy diagram for a normal refrigerant cycle for a compression refrigerator, Figure 4 is a diagrammatic layout of a heat recovery system constructed according to the present invention, Figure 5 is a diagrammatic layout of a heat recovery system similar to that shown in Figure 4 but including a heat exchanger in the form of a suction/liquid interchange, Figure 6 is a graph similar to that of Figure 2 but for a system fitted with a heat exchanger in the form of a suction/liquid interchange as in Figure 5, Figure 7 is a diagram similar to that of Figure 3 but for a system fitted with a heat exchanger in the form of a suction/liquid interchange as in Figure 5, Figure 8 is a graph of water temperature against percentage of total heat output for a system similar to that of Figure 6, and Figures 9, 10 and 11 show in a similar manner to Figure 1, alternative condensers.

It is known at present to recover the heat produced by a compression refrigeration machine by passing a liquid, particularly water, through a condenser of the refrigeration machine, through which condenser refrigerant is circulated. The refrigerant gives up some of its heat to the water flowing through the condenser, the water thus having its temperature raised.

With the condensers presently used to extract heat, from the refrigerant, the temp erature to which water flowing therethrough is raised is limited to less than the saturated refrigerant temperature, typically approximatelv 1200F.

The refrigerant contains a certain amount of superheat, that is, extra heat imparted to the refrigerant vapour in super-heating it from its dry and saturated condition. However, conventional condensers are too inefficient to use said super heat to raise the temperature of the water flowing therethrough above the saturated refrigerant temperature.

With conventional condensers, the pressure drop across the refrigerant path is kept as low as possible. Moreover known condensers are mostly of the multiple pass type, that is, the liquid flowing into the condenser to be heated passes more than once along the length of the condenser before flowing out of the condenser. With, for example. a four or five pass condenser, therefore, the liquid to be heated may follow a snake-like path within the condenser outer casing.

Thus, with a conventional condenser, its inlet and outlet are normally directly opposite one another to minimise the pressure drop, and at the centre of the condenser, and the liquid to be heated passes several times from one end of the condenser to the other before leaving it.

Although water flowing into such a condenser may at first be raised to a temperature above the saturated refrigerant temperature, the water cools as it passes within the condenser, so that on leaving the condenser its temperature will be below the saturated refrigerant temperature. Moreover, it is not possible significantly to increase the temperature of water leaving the condenser merely by making the condenser of the single pass type, if said minimum pressure drop arrangement of inlet and outlet is used.

However, Figure 1 shows, diagrammatically, a cylindrically-bodied condenser 10, constructed for use in the method of the present invention, which can be used to heat liquid flowing therefrom to a temperature above the saturated refrigerant temperature.

The condenser is of the single pass type and in the example illustrated, liquid flows, in this example. in four parallel pipes 11 from a header at one end of the condenser 10 to a header at the other end thereof. Any suitable number of pipes 11 may, however, be provided. At opposite ends of the condenser, the four pipes are connected to single inlet and outlet pipes 12 and 13 respectively. As shown in Figure 1 liquid flows from right to left through the condenser.

At the liquid outlet end of the condenser there is in the condenser body, an inlet 14 for refrigerant and at the liquid inlet end of the condenser there is in the condenser body, an outlet 15 for refrigerant. Thus, refrigerant passes through the condenser in the opposite direction to the flow of liquid to be heated in the condenser. Although the arrangement shown with the refrigerant inlet and refrigerant outlet spaced apart by the maximum possible amount is the optimum for heating the liquid flowing through the condenser, this spacing can be reduced if required.

Figure 2 is a graph showing refrigerant temperature in the direction x along the length of the condenser and also the temperature of water as it flows through the condenser from the inlet 12 to the outlet 13.

The refrigerant temperature graph is made up of a first region 16 which represents super heated refrigerant at a temperature above the saturated refrigerant temperature, and a second region 17 which is the latent heat region where the saturated refrigerant is at a constant temperature.

The heated water temperature graph shows that the temperature of the water rises steadily as the water flows through the condenser, the rise gradually levelling out so that at a position 18 corresponding to that where the regions 16 and 17 of the refrigerant graph meet, the water temperature is less than the saturated refrigerant temperature.

However, as the water to be heated reaches the end of the condenser at which the refrigerant inlet 14 is disposed, that is, the region of super heated refrigerant, the temperature of the water begins to rise sharply, as shown at 19. The temperature of the water leaving the condenser is somewhat above the saturated refrigerant temperature. This is due to the condenser being a single pass condenser and also because of the "contra flow" arrangement of the refrigerant and the water, that is, they flow in opposite directions. Although the refrigerant pressure drop is increased by having the inlet 14 and outlet 15 disposed at opposite ends of the condenser instead of directly opposite one another, the increase is more than compensated for by the heating of the water above the saturated refrigerant temperature.

The rise in water temperature above the saturated refrigerant temperature can only take place in the refrigerant super heat region, since the water temperature graph cannot meet or cross the refrigerant temperature graph.

Figure 3 is a temperature /enthalpy diagram for a normal refrigerant cycle of a com pression refrigeration machine, incorporating passage through a condenser as shown in Figure 1.

The region 20 is that where the refrigerant is a high pressure liquid/vapour and the region 21 where it is a low pressure liquid/vapour, after passing through the expansion valve of the refrigeration machine. The region 22 represents the super heated refrigerant gas.

The curve 23a represents the boundarv between the liquid/vapour (latent heat) region, and the liquid refrigerant region.

The curve 23h represents the boundary between the liquid/vapour (latent heat) region and the gaseous refrigerant region.

Figure 4 shows a system for recovering heat from a compression refrigeration machine in accordance with the method of the invention. The machine comprises an evaporator 30 from which refrigerant flows (as indicated by the dashed lines 31) to a compressor 32. From the compressor the refrigerant flows to four series connected condensers 33 to 36 inclusive and then to an expansion valve 37 before returning to the evaporator. The expansion valve 37 has a control 38.

The condensers 33 to 36 are all, in this example, single pass, contra-flow condensers like the condenser of Figure 1. As can be seen from Figure 4 the liquid to be heated, namely water, flows through the condensers in the opposite direction to the refrigerant. It is to be noted however, that the water flows through the condensers 33 and 35 in the opposite direction to that which it flows through condensers 34 and 36.

The evaporator 30 is connected in flow line 39 from a cooling circuit (not shown). A pump 40 in the line 39 pumps water through the evaporator 30. Although not shown as such, the flow line 39 is continuous, there being cooled water circuits in the line 39, downsteam of the evaporator 30. A thermostat 41 associated with a controller (not shown) monitors the temperature of the water flowing to the evaporator 30.

The cooled water can be used as required,, for example for circulation through a main cooling coil of an air conditioning apparatus.

A direct expansion cooling coil could be provided instead of the water cooled evaporator, as will be described with reference to Figure 5.

The condenser 33 is connected in a flow line 42. along which water to be heated is pumped by a pump 43 to the condenser. A by-pass line 44 is connected to the line 42 around the condenser 33. The by-pass line 44 and the line 42 meet, downstream of the condenser 33, at a valve 45. In the line 42 at a position downstream of the valve 45 is an auxiliary heater 46. A valve 47 in an outlet line from the heater 46 is. like the valve 45.

controlled by a controller 48. A thermostat 49 in the line 42 at a position downstream of the heater 46 monitors the water temperature for its associated controller 48.

The condenser 33 is the first condenser downstream of the compressor 32 and receives high pressure refrigerant containing some super heat. In a multi condenser arrangement as shown, this condenser is intended solely for the recovery of the super heat and thus the heating of the water flowing therethrough to a temperature well above the saturated refrigerant temperature.

The heater 46 can be brought into operation if the temperature of the water sensed by the thermostat 49 is too low. In the case of too much heat being rejected into the water circuit, the valve 45 is operated so that water by-passes the condenser and flows along the line 44. Thus heat would be conserved in the refrigerant system.

Condenser 34 is connected in a flow line 50 in exactly the same manner as the condenser 33 in line 42, the only difference being that, as already stated, flow through lines 42 and 50 is in opposite directions.

Condensers 35 and 36 are connected in respective flow lines 51, 52 and would not normally have either an auxiliary heater or a by-pass line, such as for the lines 42, 50.

These, however, could be provided if required.

With the system shown in Figure 4, the lead condenser 33 would heat water to the highest temperature with the other condensers heating the water flowing through them to correspondingly lower temperatures. By appropriate designing, at least condensers 33 and 34 could heat water to a temperature above the saturated refrigerant temperature.

The condensers 35, 36 could, if required, be replaced by conventional condensers which are not of the single pass, contra-flow type.

Moreover, the condensers 33 - 36 could be connected in parallel within the refrigerant circuit.

The system shown in Figure 4 can be used wherever water is required a temperature well above the saturated refrigerant temperature and also at one or more other lower temperatures. For example the system could be used in the confectionary and/or foods industry. The condenser 33 could supply water at, for example 200"F to melt jam, the condenser 34 could supply water at 1600F to melt a chewy centre and the condenser 35 could supply water at up to 1200F to melt chocolate. Each of the flow lines 42, 50 and 51 would lead to respective heat exchangers (not shown) where heat is extracted from the water to melt the various products mentioned.The flow line 52 would normally lead to a heat dissipation circuit including a cooling tower where any excess heat produced by the compression refrigeration machine could be dissipated. The water heated by the condenser 36 could, however, be used in other ways if required.

Although Figure 4 shows only one refrigeration machine in the system, it is of course possible to provide additional machines.

Each additional machine would have its evaporator connected in line 39 in series or parallel with evaporator 30, and its condensers, if it has four, connected in the lines 42, 50, 51, 52 in series or parallel with the condensers 33 to 36. Obviously additional machines could have as many condensers as necessary, at least the lead condenser of each additional machine being of the single-flow contra pass type.

In the Complete Specification of my British Patent Application Number 26284/75 Serial No. 1558563 there is described and claimed a system for heating water by means of heat recovered from a compression refrigeration machine. With the systems described therein, the condensers used to recover heat are of the conventional type. However it would be possible to use single pass. contraflow condensers of the present invention in their place. This would enable the water produced for washing to be raised to a temperature above the saturated refrigerant temperature of 1200F.

With such an arrangement, the condenser 33 would heat water up to a temperature of approximately 1603 F, for instance for use in a kitchen. condenser 34 would recover medium temperature water, both the high and medium temperature water being intended for washing. The water for washing could be led directly into a storage vessel or it could be led to a heat exchanger where its heat is extracted to heat water in a storage vessel.

The water heated by the condenser 35 would be of a lower temperature and used to heat the building in which the system is installed, whilst the condenser 36 would again be in a heat dissipation circuit.

Although water for showers, for example, would not normally be required at 200"F, water at such a temperature is required, for example as described for melting jam. It has been found that it is possible to increase the temperature to which water is heated by the lead condenser by incorporating into the system of, for example, Figure 4, a suction/liquid interchange 53.

The interchange is fitted in the refrigerant cycle of the refrigeration machine so that all the hot liquid refrigerant under high pressure, flowing from the final condenser passes through it. Moreover all the relatively cold, low pressure vaporised refrigerant leaving the evaporator 30 also passes through the interchange. Refrigerant flowing to the interchange from the condenser 36 flows thereto along the path denoted by the chain dotted lines 54, whilst refrigerant flowing to the interchange from the evaporator 30 flows thereto along the path denoted by the chain dotted lines 55. These paths 54, 55 are modifications of the path 31 of the refrigerant when no interchange is fitted.

The interchange is a contra-flow, heat exchanger in which heat is extracted from the hot liquid refrigerant flowing to the evaporator 30 and transferred to the cold gaseous refrigerant flowing to the condensers 33 to 36. The two refrigerant flows through the heat exchanger are in opposite directions, i.e. a contra-flow arrangement exists.

The effect of the suction/liquid interchange can be seen in Figures 6 and 7, which show certain differences, from the equivalent Figures 2 and 3 for a system without the interchange. Figure 6 shows that the point 18 at which the regions 16 and 17 of the refrigerant temperature graph meet, is moved along the length of the condenser towards the refrigerant outlet 15. This allows the region 19 of the water temperature graph to extend further with the result that a maximum water temperature of approximately 145"F can be attained, a rise of about 20"F above the maximum temperature attained without the interchange 53.

Figure 7 shows how heat from a region 56 of the temperature /enthalpy diagram is transferred by the suction liquid interchange to a region 57 prior to compression of the refrigerant to provide extra super heat in the refrigerant passing through the condensers.

A corresponding additional cooling at the evaporator 30 results, this being indicated by the region 57 in Figure 7.

The circuit of Figure 5 is similar to that of Figure 4 but shows only one condenser additional to condenser 33 in the water heating part of the circuit. As already mentioned, a direct expansion cooling coil can be provided instead of the evaporator 30 and this coil is shown at 56. A cooling fan is also provided.

An air-cooled condensing unit 57 is provided in the refrigerant flow line 31. A fan 58 of the unit 57 can be controlled with a thyristor or thermistor to dissipate any surplus heat from the refrigeration circuit. An air-cooled condenser is usually used on small to medium refrigeration plants, whereas a water cooled condenser is usually used on larger refrigeration machines.

The circuit of Figure 5 functions in a similar manner to that of Figure 4.

Figure 8 shows approximately how the heating provided by three condensers, such as the condensers 33, 34 and 35 is related to the total heat rejection of the compression refrigeration machine.

The super heat region 16 of the refrigerant lies within the range of less than 25% of the total heat rejected. The line 58 represents the temperature to which water passing through the condenser 33 is raised. As can be seen the quantity of the heat extracted by the condenser is less than said 25% and the water is heated in the condenser 33 to temperatures well above the saturated refrigerant temperature. This would be achieved by the use of a suction liquid interchange. The graph of Figure 8 does of course illustrate a situation where the saturated refrigerant temperature is equal to that of the Fig. 6 arrangement. With a higher saturated refrigerant temperature, water temperatures approaching 200"F could be achieved.

The line 59 represents the temperature rise of water passing through the condenser 34. This condenser extracts a larger percentage of total rejected heat than the condenser 34 but does not raise the water passing therethrough to such a high temperature. However it will heat water to above the saturated refrigerant temperature.

The line 60 represents the temperature rise of water passing through the condenser 35 and it can be seen that although extracting a large percentage of total rejected heat, the temperature of water is not raised above the saturated refrigerant temperature.

It will be appreciated that by altering the sizes and surface areas of the condensers used in the system their water, heating properties can be controlled as required. For example the condenser 33 could be modified to raise water from 800F up to 1600F instead of from 1500F to 1800F as shown.

Figure 9 shows an alternative single-pass contra-flow condenser 59 to that shown in Figure 1 which is quite long but has a small diameter. The condenser 59 is of serpentine form, but the liquid to be heated, for example, water, flows in the opposite direction to the refrigerant and the liquid passes only once through the condenser. The refrigerant flows into the condenser at inlet 60 and out of it at the outlet 61. The liquid inlet is 62 and the liquid outlet is 63. Two small diameter flow pipes, arranged in parallel, are provided for liquid flow in each of the three straight cylindrical sections of the condenser, a pair of U-shaped connecting tubes connecting adjacent straight sections together respectively.

Figure 10 shows a single-pass contra-flow condenser 64 similar to the condenser 59 of Figure 8. It is again of serpentine form, but is formed of a single piece of cylindrical tube bent into shape, with a pair of small-diameter flow pipes 65, 66 being provided therein. An inlet and an outlet 67, 68 respectively is provided for the refrigerant and an inlet 69 and an outlet 70 for the liquid is also provided.

Figure 11 shows an arrangement where a single-pass contra-flow condenser 71 of the present invention is connected in series with a conventional multi-pass heat exchanger 72.

The high temperature part of the heat recovery is achieved, in use, in the condenser 71, whilst the heat exchanger 72 is used to achieve heat recovery below the saturated refrigerant temperature in the conventional way. The condenser 71 is of similar form to the condenser 59 of Figure 9, having two straight portions 73, 74, the end of the portion 74 being connected by a U-shaped tube 75 to the liquid outlet end of the heat exchanger 72.

The liquid, e.g. water can flow from an inlet 76 in the heat exchanger along parallel small-diameter flow pipes 77, 78 to a junction region 79a at the opposite end of the heat exchanger from its water inlet 76. From the region 79a the water can flow in the reverse direction along flow pipes 79, 80 into the tube 75 and thence through the condenser 73 to its water outlet 81. The refrigerant flows from an inlet 82 in the condenser 73, through the condenser 73, tube 75 and heat exchanger 72 to the refrigerant outlet 83. Thus in the heat exchanger 72, but not in the condenser 71, the refrigerant flows in the same direction as the water for at least part of its travel and the water flows twice through the length of the heat exchanger 72.

It can thus be appreciated that the use of a single pass, contra-flow condenser enables super heat in the refrigerant of a compression refrigerant machine to be recovered very efficiently with the result that the temperatue of liquid, e.g. water heated by such a condenser can be raised to a value well above the saturated refrigerant temperature, this being a temperature to which many presently known condensers are unable to heat the liquid passing therethrough.

It will be appreciated that liquids other than water can be used as the medium to be heated. For example, oil could be used.

WHAT I CLAIM IS: 1. A method of recovering heat from a compression refrigeration machine of the kind specified characterised in that the refrigerant and a liquid which extracts heat from the refrigerant flow in opposite directions through the condenser and said liquid passes only once through said condenser, thereby, in use, heating the liquid to a temperature higher than the saturated refrigerant temperature.

2. A method as claimed in Claim 1 wherein opposite ends of the condenser respectively are provided with an inlet and an outlet for the liquid which extracts heat from the refrigerant, and an inlet and an outlet for the refrigerant are disposed adjacent the respective ends of the condenser at which said liquid outlet and said liquid inlet respectively are provided.

3. A method as claimed in Claim 2 in which said liquid flows, in use, from said liquid inlet to said liquid outlet through a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the temperature to which water passing through the condenser 33 is raised. As can be seen the quantity of the heat extracted by the condenser is less than said 25% and the water is heated in the condenser 33 to temperatures well above the saturated refrigerant temperature. This would be achieved by the use of a suction liquid interchange. The graph of Figure 8 does of course illustrate a situation where the saturated refrigerant temperature is equal to that of the Fig. 6 arrangement. With a higher saturated refrigerant temperature, water temperatures approaching 200"F could be achieved. The line 59 represents the temperature rise of water passing through the condenser 34. This condenser extracts a larger percentage of total rejected heat than the condenser 34 but does not raise the water passing therethrough to such a high temperature. However it will heat water to above the saturated refrigerant temperature. The line 60 represents the temperature rise of water passing through the condenser 35 and it can be seen that although extracting a large percentage of total rejected heat, the temperature of water is not raised above the saturated refrigerant temperature. It will be appreciated that by altering the sizes and surface areas of the condensers used in the system their water, heating properties can be controlled as required. For example the condenser 33 could be modified to raise water from 800F up to 1600F instead of from 1500F to 1800F as shown. Figure 9 shows an alternative single-pass contra-flow condenser 59 to that shown in Figure 1 which is quite long but has a small diameter. The condenser 59 is of serpentine form, but the liquid to be heated, for example, water, flows in the opposite direction to the refrigerant and the liquid passes only once through the condenser. The refrigerant flows into the condenser at inlet 60 and out of it at the outlet 61. The liquid inlet is 62 and the liquid outlet is 63. Two small diameter flow pipes, arranged in parallel, are provided for liquid flow in each of the three straight cylindrical sections of the condenser, a pair of U-shaped connecting tubes connecting adjacent straight sections together respectively. Figure 10 shows a single-pass contra-flow condenser 64 similar to the condenser 59 of Figure 8. It is again of serpentine form, but is formed of a single piece of cylindrical tube bent into shape, with a pair of small-diameter flow pipes 65, 66 being provided therein. An inlet and an outlet 67, 68 respectively is provided for the refrigerant and an inlet 69 and an outlet 70 for the liquid is also provided. Figure 11 shows an arrangement where a single-pass contra-flow condenser 71 of the present invention is connected in series with a conventional multi-pass heat exchanger 72. The high temperature part of the heat recovery is achieved, in use, in the condenser 71, whilst the heat exchanger 72 is used to achieve heat recovery below the saturated refrigerant temperature in the conventional way. The condenser 71 is of similar form to the condenser 59 of Figure 9, having two straight portions 73, 74, the end of the portion 74 being connected by a U-shaped tube 75 to the liquid outlet end of the heat exchanger 72. The liquid, e.g. water can flow from an inlet 76 in the heat exchanger along parallel small-diameter flow pipes 77, 78 to a junction region 79a at the opposite end of the heat exchanger from its water inlet 76. From the region 79a the water can flow in the reverse direction along flow pipes 79, 80 into the tube 75 and thence through the condenser 73 to its water outlet 81. The refrigerant flows from an inlet 82 in the condenser 73, through the condenser 73, tube 75 and heat exchanger 72 to the refrigerant outlet 83. Thus in the heat exchanger 72, but not in the condenser 71, the refrigerant flows in the same direction as the water for at least part of its travel and the water flows twice through the length of the heat exchanger 72. It can thus be appreciated that the use of a single pass, contra-flow condenser enables super heat in the refrigerant of a compression refrigerant machine to be recovered very efficiently with the result that the temperatue of liquid, e.g. water heated by such a condenser can be raised to a value well above the saturated refrigerant temperature, this being a temperature to which many presently known condensers are unable to heat the liquid passing therethrough. It will be appreciated that liquids other than water can be used as the medium to be heated. For example, oil could be used. WHAT I CLAIM IS:

1. A method of recovering heat from a compression refrigeration machine of the kind specified characterised in that the refrigerant and a liquid which extracts heat from the refrigerant flow in opposite directions through the condenser and said liquid passes only once through said condenser, thereby, in use, heating the liquid to a temperature higher than the saturated refrigerant temperature.

plurality of conduits.

4.A method as claimed in Claim 3 in which said conduits are mutually parallel.

5. A method as claimed in any one of the preceding claims in which said condenser is connected in a liquid heating circuit to heat the liquid to said temperature higher than the saturated refrigerant temperature.

6. A method as claimed in Claim 5 wherein at least one further condenser is connected in the refrigeration circuit of said refrigeration machine.

7. A method as claimed in Claim 6 wherein the refrigerant and a liquid which extracts heat from the refrigerant, flow, in use, in opposite directions through the or at least one of each further condenser, said liquid passing only once through the or said at least one of each further condenser, thereby, in use, heating said liquid to a temperature higher than the saturated refrigerant temperature.

8. A method as claimed in any one of the preceding claims wherein a heat exchanger is connected in the refrigeration circuit of the compression refrigeration machine, refrigerant flowing, in use, to the expansion valve passing through said heat exchanger and having heat extracted therefrom, and refrigerant flowing from the evaporator also passing through the heat exchanger and having heat imparted thereto.

9. A method of recovering heat from a compression refrigeration machine of the kind specified substantially as hereinbefore described with reference to the accompanying drawings. - - '.