AU2002347197A1 - Energy efficient heat pump systems for water heating and air conditioning - Google Patents

Description

WO 03/050457 PCT/AU02/01683 TITLE: ENERGY EFFICIENT HEAT PUMP SYSTEMS FOR WATER HEATING AND AIR CONDITIONING FIELD OF THE INVENTION This invention relates to heat pump systems, and is particularly concerned with 5 energy efficient heat pump systems for providing year-round water heating with year round air cooling, or with seasonal air cooling, or with seasonal air cooling and heating. BACKGROUND OF THE INVENTION Any discussion of the prior art throughout the specification should in no way 10 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 this system, United States Patent No. 5,050,394 describes an improved heat pump system for air 15 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 20 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 enters the hot water heat exchanger first and then passes to the outdoor heat exchanger. It is stated in US 5,050,394 that such a system may be 25 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 assumed 30 desuperheating mode, partial condensing may occur in the hot water heat exchanger. That means the condenser temperature of the system will be raised to an unnecessarily WO 03/050457 PCT/AU02/01683 -2 high level (higher than the temperature of the hot water) which makes the system work in an inefficient way. 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, 5 the higher the temperature of the compressor which is detrimental to the compressor. It is therefore desirable to overcome the above-mentioned problem and make the heat pump systems for water heating and air conditioning operate in a more energy efficient and reliable manner. It is also desirable to provide heat pump systems for water heating and air 10 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. 15 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 year-round water heating and air cooling, year-round water heating and seasonal air cooling, year-round water heating and seasonal air cooling and heating. 20 It is 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. DISCLOSURE OF THE INVENTION The invention provides a heat pump system for providing water heating and air conditioning, comprising one or more compressors for circulating a refrigerant in the 25 system, a hot water tank having a heat exchanger for heating and storing the hot water, an outdoor heat exchanger and a 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 indoor heat exchanger with a fan for conditioning and supplying air to an indoor space. 30 According to one aspect of the invention, when the water 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 WO 03/050457 PCT/AU02/01683 -3 liquid or subcooled liquid state, and then to the outdoor heat exchanger to be cooled further. After the water is heated to the preset value, the refrigerant vapour exhausted from the compressor is passed to the outdoor heat exchanger directly to exhaust the heat to the ambient air. By this way, a low condenser temperature can be achieved. 5 According to another aspect of the invention, the outdoor fan is turned on when the temperature of the refrigerant exiting the coil is a certain amount higher than that of the ambient air, with the speed of the outdoor fan preferably being variable in direct proportion to the amplitude of the temperature difference. In this way, the refrigerant can be cooled to a relatively constant temperature thus no matter how the 10 heating load varies, there will be little impact to the cooling side. Preferably the supply fan and/or compressor also operate at variable speeds corresponding to the cooling load, eg., the difference between the indoor thermostat setpoint and the temperature of the space being conditioned. Advantageously, the system is particularly suitable in applications which 15 require water heating and house cooling all year round. The system may also be adapted to other situations such as year-round water heating with seasonal air cooling, or year-round water heating with seasonal air cooling and heating, etc., and used for different applications, eg., space heating and cooling simultaneously. According to one aspect of the invention, there are two ways for the refrigerant 20 to go upon being exhausted from the compressor. When the water needs to be heated, the refrigerant exhausted from the compressor first enters the water heat exchanger to heat the water, and then passes to the outdoor heat exchanger to be cooled further. After the water is heated to a predetermined temperature, the refrigerant exhausted from the compressor is bypassed/diverted to the outdoor heat exchanger directly, with 25 the path of the refrigerant being controlled by a control unit and one or more associated valves. Preferably the predetermined temperature is within the range of 60 0 C to 65 0 C. Since the temperature of the outdoor environment is significantly lower than that of the hot water a low condenser temperature can be achieved. For a given evaporator temperature, the lower the condenser temperature the greater the efficiency 30 of the system. Therefore, this arrangement provides an energy efficient working mode. If the outdoor heat exchanger is a coil, the outdoor fan is turned on when the WO 03/050457 PCT/AU02/01683 -4 temperature of the refrigerant exiting the coil exceeds that of the ambient air by a certain amount. According to another aspect of the invention, the speed of the exhaust outdoor fan is preferably variable in direct proportion to the magnitude of the temperature 5 difference between the refrigerant exiting the coil and the ambient air. In this way, the refrigerant is almost cooled down in the same magnitude with an economic fan power consumption. In comparison to the water being heated, the temperature of the outdoor air changes little, so the temperature of the refrigerant cooled changes little, and even though the water heating load changes (with the condenser temperature) there is little 10 impact on the cooling side. 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 speed of the exhaust outdoor fan may be provided by 15 the controller according to the signals of the temperature sensors of the refrigerant exiting the outdoor coil and of the ambient air. Experimental testing shows that the temperature of the refrigerant exhausted from the water heater exceeds the temperature of the ambient air within a relatively short time frame (typically a couple of minutes after the unit starts). When temperature difference is larger than a certain 20 predetermined value, the outdoor fan starts running. The greater the temperature difference, the faster the fan operates. 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 25 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.

WO 03/050457 PCT/AU02/01683 -5 PREFERRED EMBODIMENT OF THE INVENTION The preferred embodiment of the heat pump system depicted in Figure 1 comprises a compressor 1, a hot water tank 2, a heat exchanger 3 to heat the water (water heat exchanger) connected to the compressor 1 by pipeline 21, 22 and valve 12 5 in the pipeline 22, an outdoor heat exchanger 4 connected to the water heat exchanger 3 by pipeline 23 and a valve in the pipeline and pipeline 25, and also connected to the compressor 1 by pipeline 24 and valve 14 in the pipeline and pipeline 25, a filter/drier/accumulator 6 connected to the outdoor heat exchanger 4 by pipeline 26, an indoor heat exchanger 8 connected to the filter/drier/accumulator 6 by pipeline 27, 10 expansion means 7, and the pipeline 28, and to the compressor 1 by pipeline 29 and maybe a suction filter/receiver 10 in the pipeline to complete the circuit. The outdoor heat exchanger 4 is preferably of a finned coil type and has a fan 5 for blowing or drawing air across the finned coil if air is used as the heat source or heat sink. The operating speed of the fan 5 is variable in response to signals from the 15 controller 11. It should be noted that whilst the outdoor heat exchanger 4 is typically located outdoor, it may also be located in some indoor space but it should not exhaust the thermal energy (heat or cold air) to the same space conditioned by the so-called 'indoor heat exchanger', or to the space where the warm or cool air from the heat exchanger is objectionable. 20 Preferably the indoor heat exchanger 8 is 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 25 which are incorporated herein by reference. The compressor 1 may be driven by electric power. In use, the compressor 1 is arranged to circulate a refrigerant fluid in the heat pump system. The compressor withdraws refrigerant from the indoor heat exchanger 8 (or from a filter/receiver 10) via pipeline 29. The way the refrigerant exhausted from the compressor 1 goes 30 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 21 and 22 to heat the water while the refrigerant vapour is cooled to WO 03/050457 PCT/AU02/01683 -6 liquid or subcooled liquid state, and then to the outdoor heat exchanger 4 via pipeline 23 and 25 to be cooled further (valve 12 and 13 open, valve 14 closed). After the water is heated to the preset value (eg. 60 0 C), the water heat exchanger is isolated by closing the valve 12 and 13 and the refrigerant vapour exhausted from the compressor 5 1 is passed to the outdoor heat exchanger 4 directly to exhaust the heat to the ambient air (valve 12 and 13 closed, valve 14 open). Since the temperature of the outdoor environment (water or air) is much lower than that of the hot water, 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 10 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 14 for sensing the temperature of the water or the tank wall. 15 If the outdoor heat exchanger 4 is a coil, the outdoor fan 5 is turned on when the temperature of the refrigerant exiting the coil 4 exceeds that of the ambient air a certain amount, and the speed of outdoor fan 5 is preferably variable in direct proportion to the amplitude of the temperature difference, ie. the larger the difference, the speedier the fan runs. By this way, the refrigerant is almost cooled down in the 20 same magnitude (as it is designed) with an economic fan power consumption. Compared to the water being heated, the temperature of the outdoor air changes little, so the temperature of the refrigerant cooled changes little, and even though the water heating load changes (with the condenser temperature), there is little impact on the cooling side. The outdoor fan 5 is controlled by controller 11 in response to the 25 signals sensed by the refrigerant temperature sensor 16 and the outdoor temperature sensor 17. The cooled refrigerant liquid is then forced to expand by the expansion means 7, which may comprise a throttling restriction or an expansion valve or other means. After the expansion means 7, the pressure and thus the temperature of the refrigerant 30 drop. The temperature of the refrigerant is below the temperature of the heat source, eg, the indoor air to be conditioned, now, and heat is transferred from the heat source (eg, indoor air) to the refrigerant in the indoor heat exchanger 8. The refrigerant is WO 03/050457 PCT/AU02/01683 -7 vaporised or even superheated while the air is cooled down. The fan 9 forces the air go through the coil 8 with some velocity to enhance the heat transfer effect and blows the cooled air to further space to make the temperature distribution in the space to be conditioned evenly. To make the system respond the air conditioning load efficiently, 5 the compressor 1 is also 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. The heat pump system of the present invention is particularly suitable for use in applications which require daily hot water and house cooling year-round. The 10 system may also be adapted to other situations such as year-round water heating with seasonal air cooling, or year-round water heating with seasonal air cooling and heating. 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 15 buildings 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 20 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.

Claims (12)

1. A heat pump system for providing water heating 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 5 heat exchanger and a 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 indoor heat exchanger with a fan for conditioning and supplying air to an indoor space.

2. The heat pump system as claimed in claim 1 wherein when heating water high 10 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 to be cooled further.

3. The heat pump system as claimed in claim 2 wherein after the water is heated to a predetermined temperature, the refrigerant vapour exhausted from the compressor 15 is passed to the outdoor heat exchanger directly to exhaust the heat to the ambient air.

4. The heat pump system as claimed in claim 3 wherein the predetermined temperature in the range of 60 0 C to 65C.

5. The heat pump system as claimed in claim 1 wherein the outdoor fan is activated when the temperature of the refrigerant exiting the coil is higher than that of 20 the ambient air by a predetermined amount.

6. The heat pump system as claimed in claim 5 wherein the speed of the outdoor fan is variable in direct proportion to the amplitude of the temperature difference between the refrigerant exiting the coil and the ambient air.

7. The heat pump system as claimed in any one of the preceding claims wherein 25 the speed of operation of the supply fan is variable speed depending upon the cooling load.

8. The heat pump system as claimed in any one of the preceding claims wherein said one or more compressors operate at a variable speed depending upon the cooling load. 30

9. The heat pump system as claimed in any one of the preceding claims wherein said outdoor heat exchanger is a finned coil type. WO 03/050457 PCT/AU02/01683 -9

10. The heat pump system as claimed in any one of the preceding claims wherein said indoor heat exchanger is a finned coil type.

11. The heat pump system as claimed in any one of the preceding claims wherein a signal to control the path of the refrigerant exhausted from the compressor is provided 5 by a controller in response to a signal from a thermal sensor or thermostat.

12. The heat pump system as claimed in any one of the preceding claims wherein a signal to control the speed of the exhaust outdoor fan is provided by a controller in response to a signal from temperature sensors measuring the temperature of the refrigerant exiting the outdoor coil and the ambient air. 10