BACKGROUND OF THE INVENTION Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

United States Patent No. 4,766, 734 describes a heat pump system for air conditioning, comfort zone heating, and water heating. Based on the same principle, United States Patent No. 5,050, 394 describes an improved heat pump system for air conditioning and water heating. Conventionally, the heat pump for air conditioning and water heating consists of a compressor for circulating a refrigerant in the system, a hot water heat exchanger for heating water, an indoor heat exchanger for conditioning and supplying air to the space to be conditioned, and an outdoor heat exchanger having an outdoor fan for dissipating or extracting heat to or from the outdoor ambient. The novel aspect of the system disclosed in United States Patent No. 5,050, 394 is that it also includes a means for controlling the compressor speed in accordance with the cooling load. In conventional systems, the refrigerant exhaust from the compressor initially enters the hot water heat exchanger and then passes to the outdoor heat exchanger. It is stated in United States Patent No. 5,050, 394 that such a system may be operated in a full condensing mode in which the outdoor fan is switched off and most of the heat released from the refrigerant is used for water heating, and in a desuperheating mode in which the outdoor fan is turned on so that most of the heat released from the refrigerant is transferred by the outdoor heat exchanger to the outdoor air. However, one of the problems of such a system is that in the desuperheating mode, partial condensing may occur in the hot water heat exchanger. As a consequence the condenser temperature of the system will be raised to an unnecessarily high level (higher than the temperature of the hot water) which has a detrimental effect on the operating efficiency of the system.

On the other hand, more heat than that required to maintain the temperature of the water may be continuously transferred to the water which makes the water hotter than the set value, and the higher the water temperature, the higher the temperature of the compressor which is detrimental to the compressor.

It is desirable to overcome the above-mentioned problems and provide a heat pump systems for water heating and space heating or cooling which operates in a more energy efficient and reliable manner.

It is also desirable to provide heat pump systems for water heating and air conditioning which can be adjusted to meet different heating and cooling loads both economically and with little impact on each other. That is when the heating load changes, the system should be able to be adjusted correspondingly with little impact on the cooling side, and when the cooling load changes, the system should be able to be adjusted correspondingly with little impact on the heating side.

It is further desirable to provide energy efficient heat pump systems for water heating and air conditioning which can be adjusted to work in different demanded modes such as hot water and/or space cooling, hot water and/or space heating, and only hot water in mild seasons.

It is therefore an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

SUMMARY OF THE INVENTION The invention provides a heat pump system for providing hot water and air conditioning, comprising one or more compressors for circulating a refrigerant in the system, a hot water tank having a heat exchanger for heating and storing the hot water, an outdoor heat exchanger (usually a finned coil with fan), for rejecting or extracting heat to or from the outdoor environment in air cooling, or water heating and/or air heating modes of operation respectively, an air conditioning heat exchanger for heating or cooling the air conditioning media (water or air), an expansion device (such as a TX valve) for the refrigerant expansion from high temperature to low temperature, a four- way valve (or a set of valves) to change the passes of the refrigerant.

According to one aspect of the invention, when the water in the tank needs to be heated, the high-temperature refrigerant vapour exhausted from the compressor enters

the water heat exchanger first to heat the water while the refrigerant vapour is cooled to liquid or subcooled liquid state, and then to the outdoor heat exchanger or to the air conditioning heat exchanger, depending on the requirement for space cooling or space heating. After the water in the tank is heated to a preset value (e. g. in the range of 60°C to 65°C), the refrigerant vapour exhausted from the compressor is passed to the outdoor heat exchanger directly to exhaust the heat to the ambient or to the air conditioning heat exchanger to heat the air conditioning media, in hot water and space cooling, or hot water and space heating model, respectively. In this way, a lower condenser temperature can be achieved.

Advantageously, this arrangement provides a more energy efficient working mode than the desuperheating model. Another advantage is the water temperature can be controlled under the preset value, while the water temperature in the desuperheating model could climb to an undesirably high (e. g. 80°C) which could damage the linings of the tank and may be not safe for some users (e. g. elderly persons).

If the outdoor heat exchanger is a coil, the outdoor fan is turned on when the temperature of the refrigerant exiting the coil exceeds that of the ambient air by a certain amount.

The signal to control the path of the refrigerant exhausted from the compressor may be provided by the controller according to the signal of the thermal sensor or thermostat of the water or the tank wall.

The signal to control the compressor and the pump or fan for air conditioning may be provided by the controller according to the signals of the temperature sensor in the conditioned space, or the temperature sensor in the outlet of the water exiting the heat exchanger.

According to another aspect of the invention, the system includes at least one four-way valve (or a combination of valves which, in combination, achieves the same function). When the space heating is needed, the refrigerant exhausted from the sanitary water tank or the compressor is lead to the air conditioning heat exchanger to heat the air conditioning media. When the space cooling is needed, the refrigerant exhausted from the sanitary water tank or the compressor is switched to the outdoor heat exchanger to reject the heat, and the low temperature refrigerant coming from the expansion valve is

lead to the air conditioning heat exchanger to absorb the heat from the air conditioning media.

Advantageously, the system is suitable for many applications, such as the provision of hot water and space heating, hot water and space cooling, and hot water only (i. e. no space heating or cooling). With the corresponding air conditioning heat exchangers, the space could be conditioned via water, ducted air, or refrigerant. The system may also be adapted to other situations such as space heating and cooling simultaneously.

It is to be noted that, unless the context clearly requires otherwise, throughout the description and the claims, the words'comprise','comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense ; that is to say, in the sense of"including, but not limited to".

BRIEF DESCRIPTION OF THE DRAWING A preferred embodiment of the invention will now be described, by way of example only, with reference to Figure 1, which is a schematic diagram of a heat pump system in accordance with the invention.

PREFERRED EMBODIMENT OF THE INVENTION A preferred embodiment of the heat pump system according to the present invention is depicted in Figure 1. The system comprises a compressor 1, a hot water tank 2, a heat exchanger 3 to heat water (water heat exchanger) connected to the compressor 1 by pipeline 31,32 and valve 13 in the pipeline 32, a four-way valve 4, an outdoor heat exchanger 5 connected to the water heat exchanger 3 by pipeline 33,35 and 36 via the four-way valve 4, and also connected to the compressor 1 by pipeline 31,34 and valve 14 in the pipeline and pipeline 35 and 36 via four-way valve 4, a filter/drier or a filter/drier/accumulator 7 connected to the outdoor heat exchanger 5 by pipeline 37,38 and a one-way valve or a solenoid valve 15, a sight glass 8 connected to the filter/drier 7 by pipeline 39, an air conditioning heat exchanger 11 connected to the sight glass 8 by pipeline 40, a one-way valve or a solenoid valve 16, expansion device 9, and the pipeline 41, and to the compressor 1 by pipeline 42, the four-way valve 4, pipeline 43, preferably a suction accumulator 12, and pipeline 44 to complete the circuit.

If air is used as the heat sink in summer and heat source in winter, the outdoor heat exchanger 5 is preferably of a finned coil type and has a fan 6 for drawing (or blowing) air across the finned coil. Fan 6 could be switched on/off in response to signals from the controller 11.

If air is used as the media for air conditioning system, the heat exchanger 11 is preferably also of a finned coil type having a fan for blowing or drawing air across the finned coil. Examples of fan-forced finned coil heat exchangers which may be used in the present invention are described in Australian Patent Application No. PN9202 filed on 10 April, 1996 and Australian Complete Patent Application No. 17803/97 filed on 9 April, 1997, the contents of which are incorporated herein by reference.

If water is used as the media for air conditioning system, the heat exchanger 11 could be any kind of refrigerant-to-water heat exchanger, and a pump normally needs to be employed to circulate the water in the air conditioning system.

The compressor 1 is normally driven by electric power. In use, the compressor 1 is arranged to circulate a refrigerant fluid in the heat pump system. In hot water and cooling model, the compressor withdraws refrigerant from the air conditioning heat exchanger 11 via pipeline 42,43, and 44. The way the refrigerant exhausted from the compressor 1 goes follows the following fashion. When the water needs heat, the high- temperature refrigerant vapour exhausted from the compressor 1 enters the water heat exchanger 3 first via pipeline 31 and 32 to heat the water while the refrigerant vapour is cooled to liquid or subcooled liquid state, and then to the outdoor heat exchanger 5 via pipeline 35 and 36 to be cooled further if necessary (valve 13 open, valve 14 closed).

After the water is heated to a preset value (e. g. 60°C), the water heat exchanger is isolated by closing the valve 13 and the refrigerant vapour exhausted from the compressor 1 is passed to the outdoor heat exchanger 5 directly to reject the heat to the ambient air (valve 13 closed, valve 14 open). Since the temperature of the outdoor environment (water or air) is much lower than that of the hot water being heated in the tank, the refrigerant coming from the water heat exchanger 3 can be cooled further, and when the water is heated, the refrigerant is cooled by the low-temperature outdoor ambient directly, so a low condenser temperature can be achieved. At the same evaporator temperature, the lower the condenser temperature, the higher the efficiency of the system. Therefore, this arrangement results in a high energy efficient mode. The

valves are controlled by controller 11 connected to the thermal sensor or thermostat 19 for sensing the temperature of the water or the tank wall.

If the outdoor heat exchanger 5 is a coil, the outdoor fan 6 is turned on when the temperature of the refrigerant exiting the coil 5 exceeds that of the ambient air a certain amount. Fan 6 is controlled by controller 11 in response to the signals sensed by the refrigerant temperature sensor 20 and the ambient temperature sensor 21.

The cooled refrigerant liquid is then forced to go through the filter/drier 7 and expand by the expansion device 9, which may comprise a throttling restriction or an expansion valve or other means. After the expansion device 9, the pressure and thus the temperature of the refrigerant drop. The temperature of the refrigerant is below the temperature of the heat source, the air conditioning media, e. g. water or air, so heat is transferred from the heat source to the refrigerant in the air conditioning heat exchanger 11. The refrigerant is vaporised or even superheated while the air conditioning media is cooled down. The fan or pump 27 forces the water or air go through the heat exchanger or the air coil 11 with some velocity to enhance the heat transfer effect and pumps the chilled water or blows the cooled air to the space to be conditioned.

In hot water and heating model, the compressor withdraws refrigerant from the outdoor heat exchanger 5 via pipeline 36,43, and 44. The way the refrigerant exhausted from the compressor 1 goes follows the following fashion. When the water needs heat, the high-temperature refrigerant vapour exhausted from the compressor 1 enters the water heat exchanger 3 first via pipeline 31 and 32 to heat the water while the refrigerant vapour is cooled to liquid or subcooled liquid state, and then to the air conditioning heat exchanger 11 via pipeline 35 and 42 to be cooled further if necessary (valve 13 open, valve 14 closed). After the water is heated to the preset value (e. g. 60°C), the water heat exchanger is isolated by closing the valve 13 and the refrigerant vapour exhausted from the compressor 1 is passed to the air conditioning heat exchanger 11 directly to reject the heat to the air conditioning media (water or air) (valve 13 closed, valve 14 open). Since the temperature of the air conditioning media is normally lower than that of the hot water being heated in the tank, the refrigerant coming from the water heat exchanger 3 can be cooled further, and when the water is heated, the refrigerant is cooled by the air conditioning media directly, so a low condenser temperature can be achieved. Therefore, this arrangement results in a high energy efficient mode. The valves are controlled by

controller 11 connected to the thermal sensor or thermostat 19 for sensing the temperature of the water or the tank wall.

The cooled refrigerant liquid is then forced to go through the filter/drier 7 and expand by the expansion device 10, which may comprise a throttling restriction or an expansion valve or other means. After the expansion device 10, the pressure and thus the temperature of the refrigerant drop. The temperature of the refrigerant is below the temperature of the heat source, e. g. the ground water or the ambient air, so heat is transferred from the heat source to the refrigerant in the outdoor heat exchanger 11. The refrigerant is vaporised or even superheated in the outdoor heat exchanger. The fan or pump 27 forces the water or air go through the heat exchanger or the air coil 11 with some velocity to enhance the heat transfer effect and pumps and to refresh the source water or air.

In pure hot water model, the compressor withdraws refrigerant from the outdoor heat exchanger 5 via pipeline 36,43, and 44. The way the refrigerant exhausted from the compressor 1 goes follows the following fashion. When the water needs heat, the high- temperature refrigerant vapour exhausted from the compressor 1 enters the water heat exchanger 3 first via pipeline 31 and 32 to heat the water while the refrigerant vapour is cooled to liquid or subcooled liquid state, and then to the air conditioning heat exchanger 11 via pipeline 35 and 42 to be cooled further if necessary (valve 13 open, valve 14 closed). The cooled refrigerant liquid is then forced to go through the filter/drier 7 and expand by the expansion device 10. After the expansion device 10, the pressure and thus the temperature of the refrigerant drop. The temperature of the refrigerant is below the temperature of the heat source, e. g. the ground water or the ambient air, so heat is transferred from the heat source to the refrigerant in the outdoor heat exchanger 11. The refrigerant is vaporised or even superheated in the outdoor heat exchanger. The fan or pump 27 forces the air or water go through the air coil or the heat exchanger 11 with some velocity to enhance the heat transfer effect and pumps and to refresh the source water or air.

To make the system respond the air conditioning load efficiently, the compressor 1 is also preferably to be configured to run at variable speeds with its operating speed being related to the cooling load; e. g. , the difference between the indoor thermostat setpoint and the temperature of the space being conditioned.

It should be noted that whilst the outdoor heat exchanger 5 is typically located outdoor, it may also be located in some indoor space but it should not exhaust heat or cold to the same space to be cooled or heated to offset the air conditioning effect, or to the space where the warm or cool air from the heat exchanger is objectionable.

The heat pump system of the present invention may also be used to year-round water heating, and cooling and heating simultaneously. For example, in some buildings even in winter the interior zones need cooling while the exterior zones need heating. By using the heat otherwise rejected to the outdoor ambient, the heating can be supplied.

There are also other variations in using the system. For example, intake air from the outdoor may also be pre-cooled or pre-heated by the air exhausted from the conditioned space, and the air exhausted from the conditioned space or from the intake air/exhaust air heat exchanger may also be fed to the outdoor heat exchanger.

Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.