WO2005114056A1

WO2005114056A1 - Heat pump installation

Info

Publication number: WO2005114056A1
Application number: PCT/IB2005/001348
Authority: WO
Inventors: Jacob Rorvik
Original assignee: Abk A/S
Priority date: 2004-05-19
Filing date: 2005-05-18
Publication date: 2005-12-01
Also published as: EP1766295A1

Abstract

A heat pump installation comprises a circuit through which a working fluid may circulate. The circuit is formed by an evaporator in which heat may be supplied to the working fluid to cause evaporation thereof, a first heat exchanger capable of removing substantially all the available heat from the working fluid to heat a first product fluid to a first temperature; and a second heat exchanger capable of removing substantially all the available heat from the working fluit to heat a second product fluid to a second temperature. The first and second heat excangers may be connected in parallel or in series.

Description

Heat Pump Installation

The present invention relates to heat pumps and in particular to heat pump installations for the supply of heat over different temperature ranges.

Various forms of heat pump are presently known. In general terms, such heat pumps make use of a working fluid to extract heat from a first environment at a first low temperature and to supply the heat to a second environment at a higher temperature. The working fluid may be pumped around a cycle comprising a number of stages: Firstly, in liquid form, the cold fluid is passed through a first heat exchanger where it absorbs heat from the first environment by evaporation to form a vapour; Secondly, the vapour passes through a compressor where it is compressed until it is supersaturated; Thirdly, the vapour is passed through a second heat exchanger or condenser, where it condenses. The latent heat of condensation is transferred to the second environment. Fourthly, the condensed working fluid returns to the first heat exchanger through an orifice or expansion valve, returning its pressure to the starting value The principle of operation of a heat pump is thus substantially similar to that of a refrigerator or air conditioning unit and in the past similar working fluids have been used, in particular Freon.

The main advantage of heat pumps over conventional heating systems is the coefficient of performance or CoP. Under normal operating conditions, the energy input to drive the compressor and circulate the fluid is substantially less than the total heat delivered to the second environment. The energy removed from the first low temperature environment is effectively concentrated and supplied to the second high temperature envkonment. Since the first environment is usually external ambient air or water, this heat is supplied "free-of-charge". The total heat supplied to the second environment may then be considered as a factor of the energy input to power the pump, this ratio is known as the CoP. For a CoP value of 3.0, for each 1K of input (electrical) energy a total of 3KW of thermal heat output to the second environment is achieved. For this reason heat pumps are becoming increasingly popular forms of heating, due to the savings in energy that they can provide.

Heat pumps are also becoming popular in combination with air conditioning units. Since a heat pump is effectively an air conditioning unit operating in reverse, it has become increasingly common in regions having hot summers and cool or cold winters to install combined units. The unit may then provide cooling in summer and then provide primary or backup heating in the wintertime.

As sources of external heat, current heat pumps usually use either external ambient air or ground water. The working fluid may circulate through a heat exchanger in direct heat exchanging relation with the air or water. Alternatively an intermediate fluid such as water may be used to bring the heat from outside or underground, to the heat pump. Similarly, the second environment may be provided by e.g. a circulation of air within a building or by a further liquid such as water within a domestic hot water or heating system. Depending upon the medium for heat transfer to and from the working fluid, a heat pump installation may be designated as air/air, air/water, water/air or water/water. Of course other alternatives exist using other media although these are not at present common in conventional systems.

In the past, heat pumps have been limited by their low temperature operation. Early heat pumps were unable to operate effectively when the external temperature dropped much below 0°C. This made them unsuitable as a source of primary heating in colder climates in particular, since the requirement for heating increases as the external temperature falls. They were thus often combined with existing systems e.g. as an energy saving alternative for spring and autumn, but could not replace such existing systems.

Even in climates where extremely low temperatures were rarely encountered, early heat pumps could only provide effective quantities of heat at up to about 35°C. They were thus found ideal for supplying water directly to underfloor type heating systems or for providing ambient air heating. For providing domestic hot water or for supplying a radiator type central heating system, this temperature is insufficient and the heat pump could only be used for preheating. Dual systems are also known, providing preheating for domestic hot water and also supplying warm water for underfloor heating. The water is supplied to both systems at substantially the same temperature. In all these configurations, additional sources of heat are required to complete the installation.

Other systems are known in which so-called "desuperheaters" are used in combination with a condenser. A desuperheater extracts a first f action of the heat from the working fluid without allowing it to fully condense. Such desuperheaters allow a high temperature of the product fluid to be achieved but cannot extract a large quantity of the total available heat. Typical desuperheaters may remove only about 15% of the heat from the working fluid. The remaining 85% available heat is removed at a lower temperature in the condenser.

Recent improvements in working fluids now allow domestic type heat pumps to operate efficiently from temperatures as low as -25°C, while providing heat to the second environment at up to as much as 80°C. A particularly advantageous working fluid is R-410A which is a 50/50 mixture of difluoromethane and pentaflouroethane. Carbon dioxide (CO ) has also been found to operate successfully. Such advances in the performance of heat pumps have increased considerably their possible applications. While this high temperature may now be ideal for domestic hot water systems, for other situations such as underfloor heating, this temperature is too high. The increased temperature performance of modern working fluids have thus generated additional problems in providing heat at different temperatures from a single heat pump to meet the different requirements of different systems. Furthermore, for extracting heat from the working fluid at different temperatures, different condenser or heat exchanger constructions may be advantageous to allow e.g. for different flow rates of the product fluids.

According to the present invention there is provided a heat pump installation for providing domestic hot water and underfloor heating comprising a circuit through which a working fluid may circulate, the circuit comprising: an evaporator in which heat may be supplied to the working fluid to cause evaporation thereof; a first heat exchanger capable of removing substantially all the available heat from the working fluid and designed to allow a relatively low flow rate of a first product fluid to heat it to a first relatively high temperature; a second heat exchanger capable of removing substantially all the available heat from the working fluid and designed to allow a relatively high flow rate of a second product fluid to heat it to a relatively low temperature; the heat pump installation further comprising: a domestic hot water system connected to the first heat exchanger for circulation of the first product fluid; an underfloor heating system connected to the second heat exchanger for circulation of the second product fluid; and a control unit, the control unit controlling operation of the installation to allow selective circulation of the first and second product fluids. In this way, by providing separate heat exchangers for each product fluid, each heat exchanger may be separately optimised.

Although low and high may be considered as indefinite relative terms, in the present context they are understood to clearly differentiate the first heat exchanger from the second heat exchanger. Thus, the relatively high temperature achieved in the first heat exchanger may be close to the maximum temperature achievable from the working fluid for a given pressure e.g. about 40 bar for most common compressors. Preferably, it should be greater than 80% of the maximum temperature achievable. In the case of R-410A at 40 bar, the first temperature may be greater than 60 C, preferably greater than 70 C and more preferably greater than 80 C.

In a preferred embodiment of the present invention, the first heat exchanger is a counter flow small bore heat exchanger. Various different arrangements may be used to achieve such a heat exchanger but a preferred embodiment comprises a pair of small bore tubes joined together in heat conducting relation over substantially their entire length. The tubes may have an internal diameter of between 4mm and 8mm, preferably around 6mm. The tubes may be wound as a coil such that the working fluid runs downwards in a spiral. In this way, the condensed working fluid may flow under gravity through the coil. Preferably, the heat exchangers are arranged in parallel and a valve arrangement is provided for switching the flow of working fluid to flow either through the first heat exchanger or through the second heat exchanger. A pulse-modulating valve may also be provided at an outlet of each of the first and second heat exchangers for closing the respective outlet when flow through the respective heat exchanger is not required. Operation of these valves may be controlled by the control unit.

Alternatively, the heat exchangers may be arranged in series and the first heat exchanger may be located above the second heat exchanger such that the condensed working fluid may then flow under gravity through the second heat exchanger.

Preferably, the second heat exchanger is distinct in design from the first heat exchanger to allow a relatively higher flow rate of the second product fluid with respect to the first product fluid. For use with water as the second product fluid, the design of the second heat exchanger may allow a flow of second product fluid that is more than five times the flow rate of the first product fluid and preferably as much as ten times the flow rate. A preferred form of the second heat exchanger is a plate type heat exchanger in which water is the product fluid. The water may then be provided either via a buffer storage tank or directly to an underfloor heating system.

Alternatively, the second heat exchanger may be a convector type heat exchanger provided with fins and the second product fluid may be air e.g. for domestic warm air heating. In such an arrangement, when the flow of first product fluid through the first heat exchanger is stopped, a relatively higher flow of the second product fluid can flow through the second heat exchanger. The second product fluid will then be heated to a relatively lower temperature than the first product fluid. In this context, relatively low may be understood to be a temperature that is substantially lower than the effective maximum temperature that could be achieved from the chosen refrigerant for a given pressure. Preferably the second product fluid is heated to a second temperature lower than 50° C. Preferably, the second temperature will be between about 25° C and 45° C. According to the present invention, there is also provided a method of operating such a heat pump installation by circulating a first product fluid through the first heat exchanger at a first volumetric flow rate to heat the first product fluid to a first temperature; and circulating the second product fluid at a second volumetric flow rate to heat the second product fluid to the second temperature.

The first and second product fluids may both circulate simultaneously. Preferably, the first and second product fluids may circulate alternately such that when the first product fluid flows, the second product fluid is stopped and vice versa. Preferably, when used to supply both domestic hot water and ambient (interior) heating, the installation is controlled to normally provide both supplies under thermostatic control with the hot water overriding the heating when both supplies are required simultaneously.

An embodiment of the invention will now be described by way of example only with reference to the accompanying description and figures, in which:

Figure 1 is a schematic view of a heat pump installation according to the present invention;

Figure 2 is a schematic view of a coil heat exchanger;

Figure 3 is an exploded view of a plate heat exchanger; and

Figure 4 is an exemplary control module for use in the installation.

Figure 1 shows a heat pump installation 1 comprising an outdoor unit 2 for mounting on the exterior of a building, an indoor unit 4, a hot water system 6 and a heating system 8. While reference is hereby made to individual elements and systems, it will be understood that these elements and systems are at least partially integrated with one another. The outdoor unit 2 contains an evaporator 10 and may be a standard split heat exchanger/ air- conditioning unit suitable for use outdoors. Exemplary devices for use as an outdoor unit 2 are the Dai Sei Kai, digital inverter and super digital inverter outdoor units available from Toshiba Corporation. The outdoor unit 2 also includes a number of other standard components such as compressor 3, electronically controlled pulse modulating expansion valve 5, control circuitry (not shown) etc. The inclusion of these elements within the outdoor unit has been found advantageous in reducing noise disturbance within the building. While in the following, reference will be made to an evaporator 10, it is noted that this device is effectively a heat exchanger, which may also operate as a condenser should flow reversal be used or if the installation is operated as an air- conditioner. Likewise, the following description will relate primarily to the operation of the installation 1 as a heat pump, it being understood that operation as an air-conditioner is also possible. The evaporator 10 is preferably a standard convoluted tube provided with fins, through which the refrigerant may flow and over which air may be directed. A fan 11 is included in the outdoor unit 10 to effect forced convection of air over the evaporator 10.

According to the present invention, the indoor unit 4 comprises a first condenser 12 and a second condenser 14. The first and second condensers 12, 14 are effectively heat exchangers through which the refrigerant may flow in thermal contact with a product fluid. They are in the present case referred to as condensers to indicate that they are each designed to allow complete condensation of the refrigerant. Further constructional details of the first and second condensers 12, 14 will be provided below. A refrigerant circuit 16 connects the evaporator 10 with the first condenser 12 and the second condenser 14 in series. The refrigerant circuit 16 contains a quantity of a commercially available refrigerant or heat exchange medium such as R-410A, which operates as the working fluid.

To control flow to the first and second condensers 12, 14, a valve arrangement is provided comprising a pair of inlet valves 13, 15 and a pair of pulse modulating outlet valves 17, 19. The first condenser 12 also forms a part of the hot water system 6. The hot water system 6 additionally comprises a hot water storage tank 18, a hot water pump 22 and a hot water back-up heater 24.

The second condenser 14 forms part of the heating system 8. The heating system further comprises buffer tank 26, an underfloor circuit 28, heating backup heaters 30, a circulation pump 32 and a heating pump 34.

Temperature sensors 20 are provided at various locations throughout the system.

Operation of the installation will now be explained with reference to figure 1.

1. Operation for hot water supply

According to the normal principle of operation of a heat pump, low-pressure refrigerant in the circuit 16 absorbs heat from the outside air as it flows through the evaporator 10. The heat causes the refrigerant to evaporate. The evaporated refrigerant is then compressed by a compressor (not shown) to a pressure of up to about 40 bar and directed to the indoor unit 4. With valves 15 and 19 closed and valves 13 and 17 open, the high-pressure refrigerant enters the first condenser 12 where it flows downwards in close heat exchanging contact with water from the hot water system 6. Operation of the hot water pump 22 causes the water in the hot water system 6 to also flow through the first condenser 12 in counter flow to the refrigerant. In doing so, available latent heat from the refrigerant is transferred to the water causing the refrigerant to condense and the water to be heated. The heated water is circulated by the pump 22 to the top of the hot water storage tank 18. As hot water is supplied to the top of the hot water storage tank 18, cooler water is removed from the bottom of the tank 18. This water is then returned through the hot water pump 22 to the first condenser 12.

After passing through the first condenser 12, the condensed refrigerant flows around the refrigerant circuit 16 and is returned as liquid refrigerant to the outdoor unit 2. In the outdoor unit 2, it is passed through the pulse modulating expansion valve 5 allowing the refrigerant to return to its initial low pressure. At this point, the circuit is complete and it can commence to evaporate again.

2. Operation for heating

For operation of the heating system 8, the installation operates in a substantially similar way to that described above. In this case however valves 15 and 19 are open, while valves 13 and 17 are closed. The high-pressure refrigerant enters the second condenser 14, the refrigerant is in heat exchanging contact with the water of the heating system 8. The thermostatic control of heating pump 34, on detection of the rise in temperature, causes operation of the pump and circulation of the water in the heating system 8. The second condenser 14 is designed for a significantly greater flow rate of water than the first condenser 12. As a consequence of the greater flow rate and the condenser design, the water passing through the second condenser 14 will be heated to a substantially lower temperature than the hot water that exits from the first condenser 12.

According to the heating requirements of the heating system 8, the pump 34 may be controlled to operate slower or faster. Likewise, the refrigerant may also be caused to circulate at an increased rate by control of the compressor 3. The condensed refrigerant exiting the second condenser 14 is returned to the outdoor unit 2 as described above.

The water exiting from the condenser 14 is supplied to the head of the buffer tank 26. Warm water from the head of the buffer tank 26 is also drawn off and supplied to the underfloor circuit 28 at a temperature of between 25° C and 45° C. Because of the nature of underfloor heating, the water must circulate at a flow sufficient to prevent excessive cooling thereof which could lead to local cold spots. The water leaving the underfloor circuit returns via the heating pump 34 to the condenser 14 at a temperature of between 20° C and 40° C.

According to the disclosed embodiment of Figure 1, the heating system 8 is still able to operate if the heat pump itself is non operational, if its heating capacity is exceeded or during extended periods of operation of the hot water system 6. If the heating requirement is not fulfilled by heat transfer from the refrigerant, the heating backup heater 30 may be operated in combination with the circulation pump 32. The circulation pump 32 causes circulation of water from the head of the buffer tank 26 through the underfloor circuit 28 and back to the base of the buffer tank 26 without passing through the second condenser 14. The heating backup heater 30, which may be a standard multi-step electrical resistance heater, heats the circulating water to the required temperature.

A design of the first condenser 12 according to Figure 2 will now be described in greater detail. In order to achieve an effective supply of water at the highest possible temperature, the first condenser 12 is designed as a small bore counter-flow exchanger in which the refrigerant and product flow channels are connected over substantially their entire lengths. Figure 2 indicates a spiral coil 102, comprising a product channel 104 and a refrigerant channel 106. The channels 104, 106 are formed of a good heat conducting material such as copper or aluminium and are joined over their entire length at a seam 108. The coil 102 is optionally provided with an insulating outer layer 110. Alternatively it may be located in an insulated housing.

The relatively small bore of the product channel 104 ensures good heat transfer from the refrigerant at low flow rates. The product channel 104 has a cross-section of 15 - 60 mm². It is noted in this context, that while the product channel 104 is ideal for heat transfer at a high temperature to the hot water system 6, it is unsuitable for fulfilling the heating requirements of the heating system 8 due to the excess flow resistance to greater flow rates. In the embodiment of Figure 2, the refrigerant channel 106 has a slightly smaller bore than product channel 104.

Other arrangements of the channels 104, 106 may also be used to achieve a similar effect. Such arrangements may include e.g. concentric tubes or a single tube with a central partition. For reasons of security, it is however presently preferred to use separate tubes joined at a seam according to Figure 2 in situations where there could be a danger of contaminating a domestic supply in the event of leakage of refrigerant. Furthermore, although a single heat exchange coil 102 is shown, the first condenser 12 may comprise a number of such coils arranged in parallel with one another according to the heat transfer and flow rate required. In a preferred embodiment of the invention, a pair of spiral coils 102 may be used in parallel, each having a product channel 104 with a bore of around 7 mm and a refrigerant channel 106 having a bore of around 5 mm. The combined flow area for the water through the first condenser 12 is thus approximately 80 mm².

The second condenser 14 as shown in Figure 3 may be a standard plate heat exchanger of the type available from Alfa Laval. As can be seen from the figure, the second condenser 14 comprises a plurality of parallel heat exchanger plates 112. A first series of spaces 114a-c between the plates 112 form flow channels for the refrigerant. A second series of spaces 116a-c form flow channels for the water. The plates 112 are located within an outer housing 118 provided with a manifold plate 120 and a rear plate 122. The manifold plate has a first inlet 124 for water from the heating system 8 and a first outlet 126 for water to return to the heating system 8. It also has a second inlet 128 for refrigerant leaving the first condenser 12 and a second outlet 130 for condensed refrigerant to return to the outdoor unit 2. The first inlet is located below the second inlet such that the water rises through the channels 116a-c in counter flow with refrigerant descending through channels 114a-c. The plates 112 may be brazed together or joined by any other conventional means and the inlets and outlets may be provided with appropriate connections (not shown). For use in the preferred embodiment referred to above, a plate heat exchanger may be used having a total cross-sectional area available for flow of water through the second condenser 14 of approximately 700 mm . This is approximately nine times greater than the flow area through the first condenser 12 and allows a higher flow rate of water without substantial pressure drop. According to this preferred embodiment it is believed that for outdoor temperature of 8°C, flow rates of 50 to 100 litres per hour in combination with an outlet temperature of 80° C may be achieved through the first condenser while flow rates of 400 to 1300 litres per hour in combination with an outlet temperature of 35° C may be achieved through the second condenser. In order to optimise performance of the heat pump installation for use in a typical domestic situation a control module may be provided to control operation. An exemplary control module is shown in Figure 4 , in which: 51 power supply indicator light. 52 hot-water supply or heating operation indicator light

53 indicator of preset hot water storage temperature for hot-water supply: 40, 65, 80°C

54 indicator of preset hot water storage temperature for heating operation:35, 40, 45°C, AUT - light is on "AUT" during auto operation

55 indicator light for night-time hot water supply operation - temperature is set lower by 10°C .

56 indicator light for night-time heating operation - temperature is set lower by 5°C

57 Clock function - indicates current time. Indicates failure mode in event of failure. 58 ON/OFF button for hot- water supply 59 ON/OFF button for heating.

60 Preset temperature button of stored hot water for hot-water supply. Temperature may be preset at 40, 65, 80°C. Additional heater is switched on when the temperature does not reach the setting temperature by heat pump operation

61 Preset temperature button of stored hot water for heating operation. Temperature is set at 40, 65, 80°C, AUT. Additional heater is switched on when the temperature does not reach the setting temperature by heat pump operation. For AUT operation, outside temperature is detected, and the tank temperature changes automatically.

62 Night-time saving button for hot- water supply. e.g. Temperature is automatically set lower by 10°C from 24:00 to 5:00. 63 Night-time saving button for heating e.g. Temperature is automatically set lower by 5°C from 24:00 to 5:00. 64 Clock set button Presets as the same system as the current remote controller A proposed method for implementation by the control module will now be described:

A) In order to achieve the best possible performance factor, the temperature lift for the heat pump should be minimized. The heat pump may be set to only produce hot water to a required maximum temperature.

B) This means an unshunted system (no blending of hot and cold water), and water temperature is determined by the outdoor temperature. (The heating curve may be adjustable in order to match different houses and different preferences from house residents)

C) A timer may be provided with programmable functions for utilizing differences in electricity tariffs and also for adapting the desired times for production of heat. An anti legionnaires disease program may also be incorporated to ensure adequate heating to above the required temperature for bacteria prevention.

D) For cold periods where the heat pump is unable to fulfil all the heating requirements additional heat may be made available, controllable by the heat pump control module.

E) Safety, protection and monitoring may also be included in the controller.

F) Individual room temperature control may be provided by the control module or by separate local (room) thermostats.

In operation, the heat pump switches to hot water supply when a temperature sensor in the bottom of hot water storage tank 18 goes below e.g. 40 degrees. This value is programmable.

When hot water storage tank 18 is fully loaded with hot water, the heat pump switches to supply the heating. Backup heating by the electrical heating backup heater 30 may be provided as follows: a) if the desired temperature in floor/radiators is not met within e.g. 30 minutes, a first step of heating backup heater 30 is connected (2 kW). b) step two of heating backup heater 30 is added if a) is not reached after e.g. 30 minutes (4 kW). c) step three of heating backup heater 30 is added if b) is not reached after e.g. 30 minutes (6kW).

If the heat pump must reduce speed in order to maintain desired temperature the heating backup heater 30 can be switched off in steps, e.g. after 15 minutes with reduced speed one step of the heating backup heater 30 is switched off and so forth.

When the heat pump is working with the heating backup heater 30 for heating, hot water supply production from the heat pump may be blocked and the electrical backup heater 24 in the hot water storage tank 18 is made available. In this way, when insufficient total heat is available from the heat pump, lower temperature heating in the heating system 8 is prioritised. The present invention is not limited to specific condenser or heat exchanger configurations. It is thus noted that the second condenser may form part of a warm air heat exchanger for heating a flow of air into a building interior. Alternatively, or additionally, further heat exchangers or condensers may be arranged in the refrigerant circuit 16 either in series with the first or second condensers or in parallel therewith. Such a third heat exchanger could be used to undercool the refrigerant prior to returning it to the outdoor unit and could be used for e.g. low grade heating to a driveway. During the night, or in the absence of demand from other systems, the full capacity of the heat pump could be directed to a high flow rate low temperature rise driveway heating system which in the context of the present invention may be understood to also fall within the definition of an underfloor heating system.

While the above example illustrates a preferred embodiment of the present invention it is noted that various other arrangements may also be considered which fall within the spirit and scope of the invention as set out in the appended claims.

Claims

1. A heat pump installation for providing domestic hot water and underfloor heating comprising a circuit through which a working fluid may circulate, the circuit comprising: an evaporator in which heat may be supplied to the working fluid to cause evaporation thereof; a first heat exchanger capable of removing substantially all the available heat from the working fluid and designed to allow a relatively low flow rate of a first product fluid to heat it to a first relatively high temperature; a second heat exchanger capable of removing substantially all the available heat from the working fluid and designed to allow a relatively high flow rate of a second product fluid to heat it to a relatively low temperature; the heat pump installation further comprising: a domestic hot water system connected to the first heat exchanger for circulation of the first product fluid; an underfloor heating system connected to the second heat exchanger for circulation of the second product fluid; and a control unit, the control unit controlling operation of the installation to allow selective circulation of the first and second product fluids.

2. The installation according to claim 1, wherein the first and second heat exchangers are arranged in parallel and the installation further comprises a valve arrangement for switching the flow of working fluid to flow either through the first heat exchanger or through the second heat exchanger.

3. The installation according to claim 2, further comprising a pulse-modulating valve at an outlet of each of the first and second heat exchangers for closing the respective outlet when flow through the respective heat exchanger is not required.

4. The installation according to claim 1, wherein the first and second heat exchangers are connected in series, the first heat exchanger being located upstream of the second heat exchanger.

5. The installation according to any preceding claim, wherein the first heat exchanger is a counter flow small bore heat exchanger.

6. The installation according to any preceding claim, wherein the first temperature is greater than 60° C, preferably greater than 80° C.

7. The installation according to any preceding claim, wherein the second heat exchanger is a plate type heat exchanger.

8. The installation according to any preceding claim, wherein the second temperature is lower than 50° C.

9. The installation according to any preceding claim, wherein the first and second product fluids are water, wherein the first heat exchanger has a first product fluid flow channel and the second heat exchanger has a second product fluid flow channel and wherein a cross-sectional flow area of the second product fluid flow channel is at least five times greater than a cross-sectional flow area of the first product fluid flow channel.

10. The installation according to any preceding claim, further comprising an indoor housing in which the first and second heat exchangers are located.

11. The installation according to any preceding claim, further comprising an outdoor housing in which the evaporator is located, the outdoor housing further comprising a compressor for compression of the working fluid.

12. The installation according to any preceding claim, wherein the domestic hot water system comprises a hot water storage tank for heating by the first product fluid.

13. The installation according to any preceding claim, wherein the underfloor heating system comprises a hot water storage tank for heating by the second product fluid.

14. A method of operating a heat pump installation according to any preceding claim comprising: circulating the first product fluid through the first heat exchanger at a first volumetric flow rate to heat the first product fluid to the first temperature; and circulating the second product fluid at a second volumetric flow rate to heat the second product fluid to the second temperature.

15. The method according to claim 14, further comprising supplying the first product fluid to a hot water storage tank at a temperature greater than 60° C.

16. The method according to claim 14 or claim 15, further comprising supplying the second product fluid to an underfloor heating system at a temperature between 35° C and 45° C.

17. A heat pump installation substantially as hereinbefore described with reference to Figures l to 5.

18. A method of operating a heat pump installation substantially as hereinbefore described with reference to Figures 1 to 5.