WO2012005608A1

WO2012005608A1 - Heat pump system

Info

Publication number: WO2012005608A1
Application number: PCT/NZ2011/000125
Authority: WO
Inventors: John Percival Cavill
Original assignee: Black Diamond Technologies Limited
Priority date: 2010-07-07
Filing date: 2011-07-01
Publication date: 2012-01-12
Also published as: AU2011274655A1; GB2493888B; JP2013530375A; GB2493888A; AU2011274655B2; JP6072682B2; NZ603962A

Abstract

A heat pump system 10 for raising a temperature of a load to at least a desired temperature. A first working fluid circuit 12 is arranged to receive heat energy from a heat energy source, the first working fluid circuit arranged to directly transfer some of its heat energy to the load to raise the temperature of the load to at least an intermediate temperature, if the temperature of the load is less than the intermediate temperature. A second working fluid circuit 14 is arranged to directly receive some of the heat energy from the first working fluid circuit, the second working fluid circuit arranged to directly transfer some of its heat energy to the load to raise the temperature of the load from the intermediate temperature to at least the desired temperature, if the temperature of the load is less than the desired temperature.

Description

HEAT PUMP SYSTEM

FIELD OF THE INVENTION

The present invention relates to a heat pump system. In one embodiment, the invention relates to a heat pump system for use in heating water.

BACKGROUND

Safety standards/regulations for hot water storage tanks require temperature of water in a domestic water tank to be above a desired temperature to eradicate or prevent the growth of harmful bacteria in the water. In New Zealand, the required temperature is at least 60°C to eradicate bacteria, such as legionella bacteria.

Hot water heat pump systems use a working fluid to collect heat energy from a source (ambient air) and transfer that energy to a hot water tank. The working fluid is circulated in a closed circuit and heat energy is transferred to the working fluid circulating in the circuit. A compressor increases the pressure of the working fluid and raises its internal energy. The high pressure working fluid transfers the energy in the working fluid to water using a heat exchanger. The working fluid from the heat exchanger is then passed to an expander. The working fluid circulates to back to the heat source and the cycle continues.

R22 refrigerant is an example of a working fluid that is used in refrigeration circuits. R22 refrigerant has moderate performance characteristics and is an ozone-depleting refrigerant that is harmful to the environment. R410a refrigerant has replaced R22 and is a non-ozone depleting working fluid with zero global warming potential and a proven track record for low cost reliable and efficient non-potable hot water heat pump applications. R410a refrigerant offers high efficiency in the form of improved heat transfer rates because of its high density, good surface heat transfer rates and high enthalpy of evaporation.

A circuit using R410a refrigerant requires smaller capacity compressors, smaller heat exchangers and smaller pipe sizes than a circuit using R22 and other similar refrigerants. These features can result in a compact plant which is capable of delivering a strong coefficient of performance (COP) over a wide range of ambient temperatures. Circuits using R410a refrigerant are capable of producing COP values of 5 or greater when condenser temperatures are limited to 55°C.

The high COP values normally associated with R410a refrigerant are not achievable at condensing temperatures of R410a refrigerant over 55°C, when the ambient temperature of the heat source is low. R410a refrigerant has a low critical temperature of 72.1°C. At condensing temperatures of R410a refrigerant approaching the critical temperature, for example 65°C, the enthalpy of evaporation climinishes and the level of superheat (sensible temperature rise) increases. Under these conditions, discharge temperatures are high and pressure ratios become excessive resulting in high power consumption and decreasing compressor efficiency.

R134a refrigerant is another non-ozone depleting working fluid. R134a refrigerant does not offer the high COP values that are possible with the R410a refrigerant. However, the R134a refrigerant has a critical temperature of 101.2°C and is capable of handling higher condensing temperatures in the order of 70"C without loss of performance.

Some existing hot water heat pump systems use two working fluid circuits in a fully cascaded arrangement. A first working fluid circuit collects energy from a heat source. Heat from the first working fluid circuit is transferred directly to a second working fluid circuit. Heat from the second working fluid circuit is transferred directly to a load circuit in which water circulates and that is in communication with a water storage tank. Existing cascaded systems provide an improved COP over single lift systems for low ambient temperature conditions. Cascaded systems do not normally heat water directly from the first circuit. Further, cascaded systems do not provide the desired level of sub-cooling to R410a refrigerant required for optimizing COP.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art. It is an object of at least preferred embodiments of the present invention to provide a system that addresses at least one of the issues outlined above, or to at least provide the public with a useful alternative. SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a heat pump system for raising a temperature of a load to at least a desired temperature, the system comprising:

a first working fluid circuit arranged to receive heat energy from a heat energy source, the first working fluid circuit arranged to directly transfer some of its heat energy to the load to raise the temperature of the load to at least an intermediate temperature, if the temperature of the load is less than the intermediate temperature; and

a second working fluid circuit arranged to directly receive some of the heat energy from the first working fluid circuit, the second working fluid circuit arranged to directly transfer some of its heat energy to the load to raise the temperature of the load from the intermediate temperature to at least the desired temperature, if the temperature of the load is less than the desired temperature.

The term "comprising" as used in this specification means "consisting at least in part of; that is to say when interpreting statements in this specification which include "comprising", the features prefaced by this term in each statement all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in a similar manner.

The system may comprise a first heat exchanger arranged to directly transfer heat energy from the first working fluid circuit to the load. Preferably, the system further comprises a second heat exchanger arranged to directly transfer heat energy from the first working fluid circuit to the second working fluid circuit. Preferably, the system further comprises a third heat exchanger arranged to directly transfer heat energy from the second working fluid circuit to the load.

In one embodiment, the first working fluid circuit contains a working fluid that has a substantially stable coefficient of performance at temperatures of the load in the first heat exchanger up to at least the intermediate temperature. Preferably, the second working fluid circuit contains a working fluid that has a substantially stable coefficient of performance at temperatures of the load in the third heat exchanger up to at least the desired temperature. Preferably, the working fluid in the first working fluid circuit is any one of R410a refrigerant, R407 refrigerant, R438 refrigerant, or M099 refrigerant. Preferably, the working fluid in the second working fluid circuit is any one of R134a refrigerant, R600 refrigerant, or C0₂. Any other suitable refrigerant(s) could be used. The working fluid used in the first working fluid circuit and the working fluid used in the second working fluid circuit may be the same.

Preferably, the first working fluid circuit is arranged to receive heat energy from an external heat energy source. Preferably, the external heat energy source is ambient air. Preferably, the first working fluid circuit is in communication with or may comprise an outdoor inverter unit which collects heat energy from the ambient air. Preferably, the first working fluid circuit may be in communication with or comprise a ground sourced outdoor unit.

Preferably, the first working fluid circuit is arranged to directly exchange heat energy with the second working fluid circuit before directly exchanging heat energy with the load. Alternatively, the first working fluid circuit is arranged to directly exchange heat energy with the load before directly exchanging heat energy with the second working fluid circuit. Preferably, the first working fluid circuit is arranged to directly exchange a major part of its heat energy with the load, and a minor part of its heat energy with the second working fluid circuit.

In one embodiment, the system comprises a load circuit for circulating a load fluid to be heated. Preferably, the load circuit is in communication with or comprises a fluid storage tank for storing the heated load fluid. Additionally or alternatively, the load circuit is in communication with or comprises one or more domestic and/ or light commercial space heating elements or equipment circulating a fluid. Additionally or alternatively, the load circuit is in communication with or comprises domestic high temperature radiator(s). Additionally or alternatively, the load circuit is used in light industrial process applications requiring temperatures of about 65 to 80°C. Examples of industrial process applications include manufacture of grease, resins, adhesives and the like. Preferably, the load fluid is any fluid that needs to be heated to a higher temperature than is efficiently possible using a single lift. Preferably the load fluid is water, such as potable water. In one embodiment, the load circuit comprises a pump to control flow rate of the load fluid in the load circuit to assist with controlling the temperature of the load fluid in the load circuit.

Preferably, the pump is located before the load fluid passes through the first heat exchanger to control the flow rate of the load fluid through the first and third heat exchangers. In one embodiment, the load circuit is arranged to sub-cool the working fluid in the first working fluid circuit. In one embodiment, the load circuit is arranged to desuperheat, condense and sub- cool the working fluid in the second working fluid circuit. In one embodiment, the second working fluid circuit comprises a working fluid compressor that is arranged to be cooled by transferring heat energy from the working fluid in the second working fluid circuit to load fluid in the load circuit. The compressor may be a fixed speed compressor or a variable speed compressor. Preferably, a heat transfer coil or cooling jacket, such as a copper pipe for example in which the load fluid is adapted to circulate before the load fluid circulates through the first heat exchanger, is wrapped around the compressor in the second working fluid circuit.

In one embodiment, the second working fluid circuit comprises a working fluid expander that is adjustable to optimise the second working fluid circuit. Preferably, the expander is a linear expansion valve (LEV) that is adjustable to optimise the second working fluid circuit. Alternatively, the expander is a capillary tube.

In one embodiment, the load circuit is in communication with or comprises a fluid storage tank for storing the heated load fluid, and the system is arranged to monitor load fluid temperature before the load fluid passes through the first heat exchanger, load fluid temperature after the load fluid passes through the first heat exchanger, and load fluid temperature after the load fluid passes through the third heat exchanger, to determine when load fluid in the fluid storage tank is fully heated. Preferably, the system is arranged to control compressors and/ or expanders of the first and/ or second working fluid circuits based on load fluid temperatures. Preferably, the load circuit comprises a fluid pump that is configured to run so that heated load fluid in the heat exchangers and load circuit is transferred into the fluid storage tank before turning off the pump, to minimise wastage of heated load fluid.

The load fluid in the fluid storage tank may be stratified forming a thermocline with a distinct upper region of relatively high temperature and a lower region of cooler load fluid of relatively low temperature. Preferably, the system is configured to maintain the load fluid in at least the upper region of the fluid storage tank at the desired temperature or above, and is configured to remove cooler load fluid from the lower region of the fluid storage tank and circulate the cooler load fluid around the load fluid circuit, to elevate that cooler load fluid to at least the desired temperature and return that heated load fluid to the upper region of the fluid storage tank. Preferably, the system is configured to substantially maintain the stratification in the fluid storage tank as the cooler fluid is removed from the tank.

Preferably, the system comprises a load fluid supply oudet in communication with the upper region of the fluid storage tank. Preferably, the system comprises a load fluid supply inlet in

communication with the lower region of the fluid storage tank. Preferably, the system comprises a diffuser located at a load fluid supply inlet adapted to maintain stratification within the fluid storage tank and to minimise or prevent mixing/ stirring of hot and cold water in the fluid storage tank. In one embodiment, the system further comprises a controller to control heat being exchanged with the load circuit. Preferably, the controller is adapted to be in communication with a control unit of an outdoor inverter unit. Preferably, the load circuit comprises three temperature sensors to monitor the temperature of the load before receiving heat from the first working fluid circuit, the temperature after receiving heat from the first working fluid circuit and the temperature after receiving heat from the second working fluid circuit, with all three temperature sensors in communication with the controller. Preferably, the system comprises a fluid storage tank sensor to determine the volume of fluid in the fluid storage tank, the fluid storage tank sensor being in communication with the controller. Preferably, the system comprises an outdoor temperature sensor in communication with the controller. Preferably, the system comprises an electronic variable speed control circuit to control the pump in the load circuit and thereby the flow rate in the load circuit, the speed circuit being in communication with the controller. Preferably, the system comprises a mains relay for turning on/off the compressor in the second working fluid circuit in communication with the controller. Preferably, the system comprises a compatible electronic interface to communicate with the first working fluid circuit in communication with the controller. Preferably, the system comprises a seven-day timer with customer feedback, the timer being in communication with the controller. Preferably, the system comprises a smart power control interface in communication with the controller. Preferably, the system comprises an external LAN interface for smart home control in communication with the controller.

In accordance with a second aspect of the present invention, there is provided an apparatus for use in a heat pump system for raising temperature of a load to at least a desired temperature, the apparatus being operably connectable to an existing heat exchanger that is arranged to collect heat energy from a heat energy source, the apparatus comprising:

a first heat exchanger arranged to receive some heat energy collected by the existing heat exchanger and to directly transfer heat energy to the load to raise the temperature of the load to an intermediate temperature, if the temperature of the load is less than the intermediate temperature; a second heat exchanger arranged to receive some heat energy collected by the existing heat exchanger; and

a third heat exchanger arranged to receive heat energy collected by the second heat exchanger and to directly transfer heat energy to the load to raise the temperature of the load from the intermediate temperature to at least the desired temperature, if the temperature of the load is less than the desired temperature.

In one embodiment, the apparatus comprises a load circuit for circulating a load fluid to be heated. Preferably, the load circuit is in communication with or comprises a fluid storage tank for storing the heated load fluid. Additionally or alternatively, the load circuit is in communication with or comprises one or more domestic and/or light commercial space heating elements or equipment circulating a fluid. Additionally or alternatively, the load circuit is in communication with or comprises domestic high temperature radiator(s). Additionally or alternatively, the load circuit is used in light industrial process applications requiring temperatures of about 60 to 80°C. Examples of industrial process applications include manufacture of grease, resins, adhesives and the like. Preferably, the load fluid is any fluid that needs to be heated to a higher temperature than is efficiently possible using a single lift cycle using only one refrigerant stage. Preferably the load fluid is water, such as potable water. Preferably, the apparatus further comprises a load fluid pump to control flow rate of the load fluid in the load circuit to assist with controlling the temperature of the load fluid in the load circuit.

In a preferred embodiment, the existing heat exchanger, the first heat exchanger and the second heat exchanger are components in a first working fluid circuit. Preferably, the first working fluid circuit contains a first working fluid that has a substantially stable coefficient of performance at temperatures of the load in the first heat exchanger of up to at least the intermediate temperature. Preferably, the working fluid in the first working fluid circuit is any one of R410a refrigerant, R407 refrigerant, R438 refrigerant, or M099 refrigerant. Any other suitable refrigerant(s) could be used. In a preferred embodiment, the second heat exchanger and the third heat exchanger are components in a second working fluid circuit. Preferably, the second working fluid circuit contains a second working fluid that has a substantially stable coefficient of performance at temperatures of the load in the third heat exchanger of up to at least the desired temperature. Preferably, the working fluid used the second working fluid circuit is any one of R134a refrigerant, R600 refrigerant, or C0₂. Any other suitable refrigerant(s) could be used. Preferably, the second working fluid circuit comprises an expander that is adjustable to optimise the high temperature circuit. Preferably, the expander is a linear expansion valve (LEV) which is adjustable to optirmze the second working fluid circuit. Alternatively, the expander is a capillary tube. In one

embodiment, the second working fluid circuit comprises a working fluid compressor that is cooled by transferring heat energy from the working fluid in the second working fluid circuit to load fluid in the load circuit. Preferably, the compressor is a fixed speed compressor. Alternatively, the compressor is a variable speed compressor. Preferably, a heat transfer coil, such as a copper pipe in which the load fluid is adapted to circulate before the load fluid circulates through the first heat exchanger, is wrapped around the compressor in the second working fluid circuit.

Preferably, the apparatus is arranged to control compressors and/ or expanders of the first and/ or second working fluid circuits based on load fluid temperatures. Preferably, the apparatus of the second aspect is retrofittable to an existing air-to-air heat pump system.

The apparatus of the second aspect may have any one or more features outlined in relation to the first aspect above.

In" accordance with a third aspect of the present invention, there is provided a method for adjusting a temperature of a load fluid to a desired temperature within a heat pump system, the heat pump system having a first working fluid circuit arranged to receive heat energy from a heat energy source, a second working fluid circuit arranged to directly receive some of the heat energy from the first working fluid circuit, and a load circuit arranged to directly receive heat energy from the first working fluid circuit and/ or the second working fluid circuit, the method comprising:

measuring the temperature of the load fluid; and

adjusting a flow rate of load fluid within the load circuit based at least partly on the measured temperature to adjust the heat energy that is transferred to the load fluid from the first working fluid circuit and/ or the second working fluid circuit, to adjust the temperature of the load fluid to the desired temperature.

In one embodiment, the load comprises a load fluid circulating in a load circuit. Preferably, the load circuit is in communication with a fluid storage tank for storing the heated load fluid.

Additionally or alternatively, the load circuit is in communication with or comprises one or more domestic and/ or light commercial space heating elements circulating a fluid. Additionally or alternatively, the load circuit is in communication with or comprises domestic high temperature radiators. Additionally or alternatively, the load circuit is used in light industrial process applications requiring temperatures of about 60 to 80°C. Examples of industrial process applications include manufacture of grease, resins, adhesives and the like. Preferably, the load fluid is any fluid that needs to be heated in higher temperature than is efficiently possible using a single lift. Preferably the load fluid is water, such as potable water. The system may comprise a first heat exchanger arranged to direcdy transfer heat energy from the first working fluid circuit to the load fluid. Preferably, the system further comprises a second heat exchanger arranged to directly transfer heat energy from the first working fluid circuit to the second working fluid circuit. Preferably, the system further comprises a third heat exchanger arranged to directly transfer heat energy from the second working fluid circuit to the load fluid.

Preferably, the load circuit comprises a fluid pump, and the method comprises adjusting the fluid pump to adjust the flow rate of the load fluid. Preferably, the pump is located before the load fluid passes through the first heat exchanger and controls the flow rate of the load fluid through the first and third heat exchangers. Preferably, the method comprises running the fluid pump so that heated load fluid in the first and third heat exchangers and load circuit is transferred into the fluid storage tank before turning off the pump, to minimise wastage of heated load fluid.

In one embodiment, the step of measuring the temperature of the load fluid comprises measuring a temperature before the load passes through the first heat exchanger, a temperature after the load fluid passes through the first heat exchanger, and a temperature after the load fluid passes through the third heat exchanger.

Preferably, the method comprises increasing the flow rate of the load fluid through the first and third heat exchangers if the measured temperature is above the desired temperature. Preferably, the method comprises decreasing the flow rate of the load fluid through the first and third heat exchangers if the measured temperature is below the desired temperature.

The method may comprise increasing the flow rate of the load fluid through the first and third heat exchangers from zero if the measured temperature is below the desired temperature.

In one embodiment, the method further comprises the step of adjusting compressors and/ or expanders of the first and second working fluid circuits based at least partly on the measured temperature to adjust the temperature of the load fluid. Preferably, an expander of at least one of the working fluid circuits is an adjustable linear expansion valve (LEV). Alternatively, an expander of at least one of the working fluid circuits may be a capillary tube.

The load fluid in the fluid storage tank may be stratified forming a thermocline with a distinct upper region of relatively high temperature and a lower region of cooler load fluid of relatively low temperature. Preferably, the load fluid is maintained in at least the upper region of the fluid storage tank at at least the desired temperature, and the method comprises removing cooler load fluid from the lower region of the fluid storage tank and circulating the cooler load fluid around the load fluid circuit, to elevate that cooler load fluid to at least the desired temperature, and returning that heated load fluid to the upper region of the fluid storage tank. Preferably, the stratification is maintained in the fluid storage tank as the cooler fluid is removed from the tank. Preferably, a diffuser is provided for maintaining stratification within the fluid storage tank and for rninimising or preventing mixing/ stirring of hot and cold water in the fluid storage tank.

Preferably, the method is implemented by a controller.

The third aspect may have any one or more of the features outlined in relation to the first or second aspects above.

In accordance with a fourth aspect of the present invention, there is provided a computer readable medium having stored thereon computer-executable instructions that, when executed by a processor, cause the processor to perform a method for adjusting a temperature of a load fluid to a desired temperature within a heat pump system, the heat pump system having a first working fluid circuit arranged to receive heat energy from a heat energy source, a second working fluid circuit arranged to directly receive some of the heat energy from the first working fluid circuit, and a load circuit arranged to directly receive heat energy from the first working fluid circuit and/ or the second working fluid circuit, the method comprising:

measuring the temperature of the load fluid; and

The fourth aspect may provide or have any one or more of the features outlined in relation to the third aspect above.

As used herein the term "(s)" following a noun means the plural and/or singular form of that noun. As used herein the term "and/or" means "and" or "or", or where the context allows both.

The invention consists in the foregoing and also envisages constructions of which the following gives examples only. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of non-limiting example only and with reference to the accompanying drawings in which:

Figure 1 shows a schematic diagram of a system of a first embodiment of the present invention;

Figure 2 shows a schematic diagram of a system of a second embodiment of the present invention;

Figure 3 shows a block diagram of a control system used in an embodiment of the present invention; and

Figure 4 shows a flow chart of a method implemented by the controller of an embodiment of the present invention

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION An embodiment of the present invention provides a heat pump system 10 for exchanging heat with a load. The system 10 comprises a first closed working fluid circuit 12 for circulating a first working fluid, a second closed working fluid circuit 14 for circulating a second working fluid, and a load circuit 16. The load circuit 16 is a circuit in which a load to be heated circulates.

The load is a fluid to be heated, and is generally a liquid. In the example of a hot water heat pump system, the load is potable water, to be heated. The load circulates in the load circuit 16. The load circuit 16 is in communication with a fluid storage tank 18 for storing the heated load fluid. The load circuit has a load fluid supply inlet 16a for receiving fresh cool fluid from a fluid source and a load fluid supply outlet 16b for distributing heated fluid. The outlet 16b is in fluid communication with the upper region of the fluid storage tank 18, to deliver fluid from the upper region of the storage tank, or from the third heat exchanger 26 (described below). Fresh cool fluid enters the load circuit 16 via inlet 16a and is heated using the system of the present invention. The inlet 16a is in fluid communication with the lower region of the fluid storage tank 18. The fluid that is heated is circulated into the fluid storage tank 18 from above and can be output to a consumer via outlet 16b.

The load circuit 16 includes a fluid pump 21 to control flow rate of the fluid in the circuit 16 through heat exchangers 23 and 26 of the first and second working fluid circuits 12 and 14. The flow rate of fluid in the load circuit 16 can be adjusted to optimize the temperature of the heated fluid. The placement of the fluid pump 21 in the load circuit 16 is flexible, and supplementary water circulation pumps may be placed anywhere in the load circuit to minimise possible noise and vibration.

As the fluid may remain in the fluid storage tank 18 over an extended period of time, as the fluid loses heat it is circulated around the load circuit 16 to be heated by the system again.

The first working fluid circuit 12 is in communication with a heat energy source. In the form shown, the heat energy source is an external heat source, and heat energy from the external source may be collected by an outdoor inverter unit 25. The outdoor unit 25 comprises a compressor 27 and an expander 29 such as an expansion valve, a heat exchanger (not shown) to extract heat from airflow AF, and a fan (not shown) to control airflow AF. The outdoor inverter unit 25 is positioned outside E a building such as a consumer's residence. The outdoor unit 25 could be any suitable device that is capable of extracting heat energy from the external heat source. The heat source could be ambient air. The unit 25 extracts heat from the ambient air that is flowing AF through the heat exchanger in the unit 25, and transfers the extracted heat to the working fluid circulating in the first working fluid circuit 12.

By way of example, the outdoor inverter unit could be an R410a inverter unit, for example a Mitsubishi GE35 or FB25 inverter unit supplied by Mitsubishi Electric of Japan or an FB35 inverter unit supplied by Mitsubishi Electric of Japan. These units are capable of operating over a wide range of ambient conditions. While these units are typically used for home air-to-air heating, the system of the present invention enables these outdoor units to be used for other applications such as water heating.

The first working fluid circuit 12 contains and circulates a first working fluid that includes any suitable refrigerant such as R410a refrigerant, R407 refrigerant or M099 refrigerant for example. The first working fluid circuit 12 comprises insulated piping that extends through the wall W to the interior of the building I. The first working fluid circuit 12 is in communication with a first heat exchanger 23 and a second heat exchanger 28.

The second working fluid circuit 14 comprises a compressor 30, and an expander 32 that is adjustable to optimise the second working fluid circuit 14. Preferably, the expander 32 is a linear expansion valve (LEV) which is adjustable to optimise the second working fluid circuit 14.

The second working fluid circuit 14 contains and circulates a second working fluid that includes any suitable refrigerant such as R134a refrigerant, R600 refrigerant, or C0₂ refrigerant. The working fluid in the first working fluid circuit could be the same as the working fluid in the second working fluid circuit. The use of the same working fluid in both first and second working fluid circuits is not excluded as it offers the same thermodynamic advantages as using different working fluids. The second working fluid circuit 14 is in communication with a third heat exchanger 26. The compressor 30 of the second working fluid circuit 14 can use a low cost R134a fixed speed

300W compressor similar to the compressor used in a domestic dehumidifier. The compressor 30 hermetic case and other components can be cooled using the cold load fluid input prior to the R410a first heat exchanger 23. In operation, the heat exchanger (not shown) in the outdoor unit 25 extracts heat energy from ambient air AF and transfers the extracted heat energy to working fluid circulating in the first working fluid circuit 12. The compressor 27 in the outdoor unit 25 compresses the working fluid. The working fluid that exits the compressor 27 becomes superheated.

The heated working fluid in the first working fluid circuit 12 is passed through the second heat exchanger 28, where some of the energy including superheated and partially condensed working fluid is directly transferred to the working fluid passing through the second heat exchanger in the second working fluid circuit. The first working fluid that exits the second heat exchanger 28 is then passed through a first heat exchanger 23, where some of the heat energy remaining in the first working fluid is directly transferred to the load passing through the first heat exchanger in the load circuit 16.

The second heat exchanger 28 transfers some heat from the first working fluid in the first working fluid circuit 12 to the second working fluid in the second working fluid circuit 14. The heated second working fluid in the second working fluid circuit is compressed using the compressor 30. The working fluid that exits the compressor 30 is superheated. The superheated working fluid is passed through the third heat exchanger 26, where some heat from the superheated working fluid is directly transferred to the load from the first heat exchanger passing through the third heat exchanger in the load circuit 16.

The amount of heat that is transferred from the working fluids to the load using the first and third heat exchangers 23 and 26 depends on the working fluids that are used. The working fluids are able to operate with a substantially stable coefficient of performance up to certain temperature limits in the load. The heat that is transferred to the load from the first working fluid circuit 12 should be sufficient to raise the temperature of the load circulating through the first heat exchanger 23 to an intermediate temperature, where the intermediate temperature is less than or equal to the temperature limit of the first working fluid in the first working fluid circuit. Similarly, the heat that is transferred to the load from the second working fluid circuit 14 should be sufficient to raise the temperature of the load from the first heat exchanger 23 passing through the third heat exchanger 26 from an intermediate temperature to at least a desired temperature, where the desired temperature is less than or equal to the temperature limit of the second working fluid in the second working fluid circuit 14. A second embodiment of the present invention is shown in Figure 2. The embodiment shown in Figure 2 is similar to the embodiment shown in Figure 1, with the addition of a recovery jacket 31 for the compressor 30 of the second working fluid circuit 14. The recovery jacket 31 improves the efficiency of the compressor 30 and reduces heat loss from the compressor 30. The reference numerals used in Figure 1 are used in Figure 2 to denote like parts of the system, and other than as described here the features and functioning are as the first embodiment.

Load fluid at low temperatures in the load circuit 16 circulates through the recovery jacket 31 on the compressor 30 of the second working fluid circuit 14 before being circulated through the first heat exchanger 23. The recovery jacket 31 could be a cooling coil, such as copper pipe wrapped around the compressor 30. In the embodiment shown, load fluid exiting the load fluid storage tank 18 at a low temperature (such as about 2-25°C, preferably about 12°C) circulates through the load fluid pump 21 then through the cooling coil 31 around the compressor 30 before circulating through heat exchanger 23.

A compressor 30 without the jacket recovery gives off heat energy as a loss (typically around 150W). Wrapping a number of turns of copper pipe around the compressor 30 and feeding the cold load fluid through the copper pipe allows for recovery of 50 to 200W, preferably about 140 Watts of waste energy before entering the R410a-water first heat exchanger 23.

A controller 34 is also provided to control the operation of the system of Figure 1 or the system of Figure 2. The controller 34 is shown in Figure 3 and implements the method shown in Figure 4. While Figure 3 schematically shows a system corresponding to Figure 1, the functioning of the controller will generally be the same for either the system of Figure 1 or the system of Figure 2. The controller 34 sits indoors with the fluid storage tank 18 and can control the delivery of energy at the required levels for efficient operation through smart control. The controller can be any suitable type, such as a programmable logic control (PLC) unit or embedded controller for example. The controller 34 monitors the performance of the system based on the measurements of temperatures in the load circuit 16 in step 201. Three temperature sensors A, B and C are placed in the load circuit 16 to monitor the temperature of the load circulating in the circuit. A first temperature sensor A is placed in any suitable position to measure the temperature of the load fluid before entering first heat exchanger 23. The temperature sensed by temperature sensor A is the lowest temperature in the load circuit 16 of the system of Figure 1. Alternatively, for the system of Figure 2, the first temperature sensor A could be positioned as shown in that figure, to measure the lowest temperature of that load circuit 16. For either embodiment, a second temperature sensor B is placed to measure the temperature of the load fluid after exiting the first heat exchanger 23 (before entering the third heat exchanger 26). The temperature sensed by temperature sensor B is the intermediate temperature of the fluid that is obtained from the first working fluid circuit. For either embodiment, a third temperature sensor C is placed to measure the temperature of the load fluid after exiting the third heat exchanger 26. The temperature sensed by temperature sensor C measures if the fluid has reached the desired temperature.

Based on the temperatures in the load circuit, the controller 34 calculates and optimises the energy requirements of the system by controlling the outdoor unit 25, the second working fluid circuit 14 and the load circuit 16. Sets of computer executable instructions are executed within the controller 34 that cause the controller 34 to perform the methods described above and below. The controller may also include any other computing device capable of executing a set of instructions that specify actions to be taken by that device. These instructions can be sequential or otherwise. The term "computing device" also includes any collection of devices that individually or jointly execute a set or multiple sets of instructions to perform any one or more of the methods described above.

The processor 34 includes or is interfaced to a machine readable medium on which is stored one or more sets of computer-executable instructions and/or data structures. The instructions implement one or more of the methods or functions described above and below.

The computer-executable instructions may also reside completely or at least partially within the processor 34 during execution. In this case the processor 34 comprises machine-readable tangible storage media.

The computer-readable medium is described in an example embodiment to be a single medium. This term should however be taken to include a single medium or multiple media. The term "computer-readable medium" should also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the processor and that cause the processor to perform any one or more of the methods described above. The computer-readable medium is also capable of storing, encoding or carrying data structures used by or associated with these sets of instructions.

The outdoor inverter unit 25 contains a smart controller 33 that is the master control unit of the outdoor inverter unit which is designed to communicate with a controller of a standard inverter indoor unit. The smart controller 33 controls the fan speed, expander 29 and/ or compressor 27 in the outdoor unit 25. In the system of the present invention, the outdoor inverter unit 25 also feeds back important information to the controller 34. The sorts of important information include fault conditions, when the unit 25 starts to supply heat and when the outdoor unit 25 is in defrost mode.

The controller 34 of the present invention emulates a controller of a standard inverter indoor unit from a control protocol perspective and communicates with the master control unit 33 in the outdoor unit 25 using the same protocol. The controller 34 calculates and optimises the energy requirements of the system by controlling the outdoor unit 25 using this control protocol.

The controller 34 keeps the superheat and condenser temperatures stable indoors by keeping the discharge temperatures as low as possible, while maintaining the first working fluid (e.g. R410a refrigerant) at a suitable temperature to cause the desired load fluid temperature lift. The controller 34 optimises the COP that can be gained from the outdoor unit 25 while giving the desired intermediate temperature lift from heat exchanger 23.

The controller 34 keeps this process optimised by continually fine tuning but will have limits in place so that the outdoor unit 25 will not stray outside the ideal design operating limits.

The controller 34 maintains the most efficient temperature lift from the low temperature first working fluid (e.g. R410a) circuit 12 before getting any significant loss of performance caused by an excessively high first working fluid (e.g. R410a refrigerant) condensing temperature lift. The controller 34 determines the temperature difference between the two refrigerants exchanging heat energy in the second heat exchanger 28. The controller 34 may also control the mass flow rate of the working fluid in the second working fluid circuit 14 by means of a linear expansion valve (LEV) 32 in the second working fluid circuit 14. A capillary tube may be used in lieu of the LEV. In the form shown, the controller 34 emulates five different variables which are communicated to the master controller 33 in the outdoor unit 25 to maintain the desired energy levels. These are:

1. the indoor first working fluid (e.g. R410a) condensing temperature

2. the indoor first working fluid (e.g. R410a) evaporator temperature

3. the indoor room sensor temperature

4. the indoor fan speed

5. the indoor room set temperature

This data including when to start/ stop is sent to the outdoor unit 25. The ratios are predefined in the controller in look-up tables to achieve the desired indoor energy levels.

The controller 34 controls the operation of and interaction between the first working fluid circuit 12, the second working fluid circuit 14 and the load circuit 16. The two key drivers are the water flow which directly controls the system load and the total free energy input controlled by telling the outdoor inverter to supply more or less energy. The controller 34 of the present invention looks up set limits in look-up tables to ensure optimum performance efficiency. There may be multiple look-up tables depending on the inlet water temperature to initially set the flow rates and limits in each circuit. The fluid pump 21 circuit adjusts the fluid flow to keep the fluid delivery temperature at a chosen set point. If the fluid flow is too slow, the controller 34 sends a signal to the controller 33 of the outdoor inverter 25 to provide more energy. In this case, sub-cooling of the first working fluid 12 may not be optimised. The controller 34 can only control the expander LEV 32 in the second working fluid circuit 14 which is tuned to give the biggest temperature rise at heat exchanger 26. If the lift of temperature of fluid in the load circuit 16 is too small, then the outdoor unit 25 is backed off to reduce energy input and the fluid flow rate is reduced. The look-up table sets limits so the whole system cannot get too far out of balance and will operate within defined limits.

Fine adjustment is achieved by adjusting the difference between 1 & 2 above. Coarse adjustment is achieved by changing the ratio between 3 & 5 above.

The controller 34 communicates with the master controller 33 in the outdoor inverter unit 25 to provide sufficient heat to get the intermediate temperature out of heat exchanger 23 as low as possible while maintaining the desired set point temperature from heat exchanger 26. The outdoor unit 25 is kept at the lowest possible energy input to achieve the desired fluid output temperature thus allowing for the highest possible COPs.

The outdoor R410a inverter unit 25 feeds back important information to the controller 34. The sorts of important information include fault conditions, when the unit 25 starts to supply heat and when the outdoor unit 25 is in defrost mode.

The controller 34 will turn on the fixed speed compressor 30 before the R410a compressor 27 starts up to allow the lower powered compressor 30 to heat up the circuit 14 and any residual water in the third heat exchanger 26. It is important that this circuit 14 maintains as high a COP as possible because that governs how much lift is required from the first working fluid circuit 12. The second working fluid (e.g. R134a) circuit 14 can be optimised using a linear expansion valve (LEV) 32. The controller 34 adjusts the LEV 32 to vary the second working fluid (e.g. R134a refrigerant) flow based on the R410a condenser 27 and evaporator temperatures.

The controller 34 electronically controls the load fluid pump 21 to maintain the desired fluid temperature to feed to the fluid storage tank 18. The controller 34 controls the flow rate of fluid based on measurements from the three temperature sensors A, B, C located at the fluid inlet of the R410a heat exchanger 23, the fluid outlet of R410a heat exchanger 23, and the fluid oudet of R134a heat exchanger 26.

Referring to Figure 4, if the load fluid at the outlet of the R134a heat exchanger 26 exceeds a desired temperature (step 202), the fluid pump 21 is sped up (step 204). If the fluid at the outlet of the R134a heat exchanger is less than a desired temperature (step 203), the pump 21 is slowed down (step 206) provided that the flow rate of the fluid pump 21 is not at zero (step 205). Because the R134a circuit 14 has a fixed speed compressor 30 there is very little adjustment of the top up lift except for load fluid flow. Alternatively, a variable speed compressor could be used in place of the fixed speed compressor 30. Monitoring the intermediate load fluid temperature at B gives an advance warning of when the load fluid flow will require coarse adjustment as it takes several seconds for that load fluid to pass through heat exchanger 26. The control of the intermediate load fluid temperature from the heat exchanger 23 in the R410a circuit 12 is carefully monitored and the outdoor unit 25 instructed (at steps 207 and 208) to adjust the energy input to give the optimum COP. Turning off the heating process

The input fluid temperature at temperature sensor A is carefully monitored to identify when the fluid in the fluid storage tank is fully heated. As shown in Figure 1, the fluid in the tank is stratified, with a distinct upper region 18a of relatively high temperature and lower region of relatively low temperature 18c, separated by a 'membrane' 18b. Using fluid stratification in the fluid tank 18 means that the inlet fluid will stay cold and sharply increase when the tank is heated. This is the trigger to turn off the two compressors 27, 30 and then the fluid pump 21. The fluid pump 21 is caused to run so that the estimated hot water in the heat exchangers 23, 26 and pipe work is transferred into the fluid tank before turning off the pump so no hot load fluid is wasted. Fluid storage tank top up feature

The fluid inlet temperature setting at temperature sensor A is also used if the tank requires a top up. The controller 34 knows that in this case the outdoor unit 25 needs to run at a very low energy level and the R134a top circuit 14 is used to extract most of the R410a energy to be put into the lifting the load fluid temperature. In this state there is no sub-cooling from the load fluid hence the outdoor unit has to be backed off to a low energy input to keep the overall COP as high as possible.

In this case, where the temperature of the load after the third heat exchanger 26 is not significantly less than the desired temperature (desired temperature range: 60 to 80°C, preferably about 62°C), the compressor of the outdoor unit will not need to do much work to top-up the temperature of the load. The outdoor unit will need to produce sufficient energy to be used in the second working fluid circuit. Most of the heat in R410a refrigerant is transferred to the R134a refrigerant. Heat from the R134a refrigerant is subsequently transferred to the load needing a top up using heat exchanger 26.

Start the load fluid heating process

A temperature probe is placed at the top of the fluid storage tank 18 with a thermal mass. The mass is calibrated at installation by draining off 1 litre of load fluid and the controller measuring how hot the sensor gets and how long it stays hot for. The fluid storage tank capacity is also entered and the controller 34 will estimate how much load fluid has been drained off and decide when the unit needs to start heating the tank again.

If there has been no load fluid drawn for an extended period of time, then the system will start up operating in the "fluid storage tank top up" mode described above.

Normal start up process

Start is triggered based on any one of the following:

^■ via the 7 day timer built in the controller

■ when 80% (or another value set by the customer) of the available load fluid capacity has been used or

^■ when a temperature sensor in the fluid storage tank 18 detects cooled fluid

^■ via external smart control from intelligent building power meters that allow power supply companies to switch on and off water cylinder heating. This is more efficient during the day time when the ambient temperatures are higher

^■ based on weekly load fluid (e.g. water) demand patterns where a heating period is

automatically decided based on best outdoor ambient temperature while maintaining enough hot load fluid. The Rl 34a compressor 30 is started immediately to give time for this small compressor to warm heat exchanger 26. The R4 0a outdoor unit 25 is told to start up which takes several minutes.

The heat exchangers 23 and 26 are allowed to heat up past the desired output load fluid temperature.

Once this occurs the load fluid pump 21 is started at full speed for several seconds to get load fluid moving then slowed down to the previous operating speed or the factory ideal speed if the first time. Defrost

When the outdoor R410a unit 25 decides that it is time to defrost, the load fluid flow is stopped by controlling load fluid pump 21. The R134a compressor 30 is kept on to provide extra energy for a faster defrost recovery. The temperature sensor on heat exchanger 26 is monitored. If the temperatxire gets too hot the R134a compressor 30 will be turned off. Alternatively, if the R134a compressor 30 gets too hot it will be turned off by the controller until it comes back within limits.

Operational parameters of a system in accordance with an embodiment of the invention A system according to an embodiment of the present invention comprises an outdoor R410a inverter unit 25 which collects heat from ambient air AF. The outdoor unit may be a FB25 inverter unit, having a COP of 4.89. The heat exchanger of the outdoor inverter unit collects about 2.7kW of heat energy from the outside ambient air which is transferred to the R410a refrigerant in the first working fluid circuit 12. The compressor 27 compresses the R410a refrigerant to produce a high pressure working fluid carrying 2.5 to 6.5 kW, preferably about 3.4 kW of energy. R410a refrigerant circulates in the first working fluid circuit 12 in the direction of the arrows shown. The flow rate of R410a in the first working fluid circuit 12 is kept constant at about 0.016 kg/ s.

The first working fluid circuit 12 carries the fluid from the exterior of the building E, through the wall of the building W, to the interior of the building I. In this example, some of the heat collected from the outdoor unit 25 and carried by the first working fluid is initially passed through the second heat exchanger 28 to directly transfer some of its heat to the second working fluid circuit 14, before being passed through the first heat exchanger 23 to directly transfer some of its remaining heat to the load circuit 16. Energy in the R4 0a refrigerant is split between the second working fluid circuit 14 and the load circuit 16. The output of the first heat exchanger 23 is about 2.4kW. The output of the second heat exchanger 28 is about IkW. Therefore, it can be seen that the first working fluid transfers a major part of its heat/ energy with the load, and a minor part of its heat/ energy with the second working fluid. Higher outputs could be provided for light industrial applications. The R410a refrigerant is at a temperature of about 70°C and is slightly superheated before entry to the second heat exchanger 28. The R410a refrigerant is at a condensing temperature of about 45°C after passing through the second heat exchanger 28 and before passing through the first heat exchanger 23. The R410a refrigerant is at a temperature of about 23°C after passing through the first heat exchanger 23. This provides substantial sub-cooling of the R410a which cannot be easily achieved by full cascade systems.

The load circuit 16 is arranged to sub-cool the working fluid in the first working fluid circuit 12. Cold water entering the first heat exchanger 23 is at a lower temperature than would be the case if exchanging heat energy with a second working fluid in a full cascade system. The incoming water lowers the exit temperature of the condensed refrigerant in the first circuit 12 (sub-cooling) thus increasing the heat energy uptake from the air heat energy source.

The first heat exchanger lifts the temperature of the load fluid from about 12°C at the inlet 16a, to an intermediate temperature, with the intermediate temperature being less than a desired temperature for storing in the fluid storage tank 18. By way of example, the intermediate temperature may be between about 35°C and about 55°C, preferably between about 35°C and about 45°C, and preferably about 40°C. The intermediate temperature selected will be dependent on the working fluids used in the first and second working fluid circuits 12, 14, and the desired final temperature of the load fluid.

The second working fluid circuit 14 circulates R134a refrigerant. The flow rate of R134a is kept constant at about 0.0071kg/s. In the second working fluid circuit 14, an R134a compressor 30 is used to lift the lkW heat energy in the R134a refrigerant to produce 1.25kW of superheated vapour at 75 to 80°C that condenses at 67°C. The energy in the R134a refrigerant is used to lift the load in the load circuit 16 from the intermediate temperature up to at least the desired temperature of about 62°C using the third Rl 34a- water heat exchanger 26.

The desired temperature will depend on the requirements of the load fluid, and on local standards. For example, in New Zealand the desired temperature is about 62°C, but needs to be at least about 60°C. The 2"C difference allows for minor heat losses in the pipes. For other countries or regions, the desired temperature may be lower or higher. The system is preferably configured to provide the load fluid with a desired temperature of between about 60°C and about 70"C.

Temperatures of up to 80°C are possible by adjustments to the LEV valve and water flow rate. The flow rate of fluid in the load circuit is in the order of 0.8 to 1.8 Htres per minute, for example, and preferably 0.9 to 1 litre per minute. By using a low flow rate, the system of the present invention can elevate the cool fresh water to at least the desired temperature in the first and third heat exchangers 23 and 26. By placing the second R134a circuit 14 close to the hot water storage cylinder, slow water flow rates cause minimal losses that would otherwise be significant if the secondary circuit is placed outdoor along with the outdoor unit (FB25) 25.

In this example, the coefficient of performance (COP) of the system is around 3.2-3.6 at an ambient outside temperature of 7°C. Actual heat recovery from the R134a jacket cooler 31 and actual power input to the R134a compressor 30 may vary significantly with each make/model tested.

Alternative configurations of system

The system could be provided and installed from new with all of the components shown in the attached figures, including an outdoor unit 25, first working fluid or refrigerant circuit 12, second working fluid or refrigerant circuit 14, load circuit 6, and optionally the fluid storage tank 18.

Alternatively, parts of an existing installed heat pump system and hot water tank could be used, and the apparatus of the present invention could be retrofitted to the existing system. The apparatus could be retrofitted to an existing air-to-air heat pump system. In that configuration, the apparatus of a preferred embodiment would have the components shown in the broken line box in Figure 1; namely the first heat exchanger 23, second heat exchanger 28, third heat exchanger 26, load fluid pump 21, the other components of the second working fluid circuit 14, and the controller 34. The system may be provided in a housing form that can be connected to the piping and electronics of the existing heat pump system and of the hot water storage system, and positioned in the vicinity of the hot water tank to minimise losses.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

Systems of at least some embodiments of the present invention provide the following advantages. It will be understood that not all embodiments of the invention need to provide all of the stated advantages.

This system is able to take full advantage of using a low cost outdoor unit. For example, a Mitsubishi GE35 or FB25 inverter could be used in most areas of New Zealand and for extra cold areas the FB35 could be used. The same system could be adapted to work with split system compressors and city multi installations. The R410a outdoor unit can operate at maximum efficiency without any stress or overloading. The R410a outdoor unit exhibits excellent low ambient performance. There will be saving in costs by using a mass produced R410a outdoor unit.

The first working fluid circuit 12 can be applied to existing unmodified outdoor unit 25 to produce water at an intermediate temperature of, for example, about 35-55°C while operating much the same as it does in its designed air-to-air application. This greatly reduces the compressor stress and increases the COP. The outdoor unit is designed to produce excellent results over a wide range of operating conditions for air-to-air applications and will not need to be modified for the air-to- water applications. This provides substantial subcooling of the R410a refrigerant which cannot be easily achieved by full cascade systems.

Some outdoor inverter units do not communicate the outdoor power consumption to the indoor unit, as the outdoor units are typically the master control units. In a conventional air-air system, the outdoor unit is typically connected to a power supply, and the power transferred from the outdoor unit to the indoor unit. In the preferred embodiments of the present invention, the controller is part of the indoor unit. As most cylinder cupboards are fitted with a substantial power supply to deliver energy to electric elements, that existing power supply will typically be used to power the preferred embodiment systems. The indoor unit may have a mains relay to disconnect power to the outdoor unit and current sensing so that the power consumption of the outdoor unit can be accurately measured and optimised to ensure an optimal COP.

The R134a circuit operates in relatively fixed conditions allowing for a simple boost of the intermediate temperature to the desired temperature. The Rl 34a circuit allows the condensing temperature of the R4 0a circuit to be lowered with significant improvement in COP. Using an electrical resistance heating element offers only a 4 to 6°C temperature rise in the water compared to a 15 to 20°C temperature rise from the secondary Rl 34a circuit.

The system increases the COP when raising water to over 60°C when ambient temperature conditions are 7°C or lower

Only a small water circulation pump 21 is required to physically circulate the water as the system is closed with an effective head equivalent to the height of the water tank 18. Water tank stratification gives near instant heat availability of hot water by feeding water at the desired temperature of 60° to 80°C, preferably about 62°C gendy into the upper region of the tank.

It is possible to use one outdoor compressor for space heating during the day and switch to hot water heating at night. That is, the apparatus of an embodiment the present invention could be connected into an existing air-to-air heat pump system, so that the system can heat indoor air during the day and water at night.

As the temperature of the water in the tank will diminish over time, it is possible to efficiendy reheat water that has cooled in the tank by running the R410a system at very low power and running the R134a circuit to lift the water back up to the desired temperature (60 to 80°C, preferably about 62°C).

The R410a stage runs efficiendy using the full benefits possible from that working fluid. By heating water direcdy to a low intermediate temperature via the first heat exchanger 23, the R410a cycle retains a high COP and also gains the benefit of additional (free) source energy by sub- cooling the working fluid.

R134a provides a secondary temperature lift to the water using a small system with low power input. Thus it is possible to achieve water temperatures of up to 80°C with strong COP at low ambient conditions.

Hot water is generated by a high efficiency low-loss system that may be positioned direcdy adjacent to a hot water cylinder. Issues relating to delivery of hot water from outside to indoors, through up to 8m of pipe are eliminated. Sensible heat loss in long runs of small bore low flow rate hot water can be significant and a very inefficient means of transferring energy. The system overcomes the water transfer issues from the outdoor unit and frost issues and could be installed by a refrigeration engineer rather than a plumber. A conventional installation of the R410a outdoor unit is possible with normal runs of working fluid piping to the indoor unit. This known technology that remains unaffected by the indoor unit. Energy is delivered in the normal way. Installation is simple requiring only one tradesman. Freezing of external water pipes when the system is shut down is not an issue in areas subject to below zero conditions. Especially if the system is not running (owners on holiday, water up to temperature, and water use is negligible) The second working fluid circuit 14 using R134a refrigerant is designed and controlled to work in a fixed environment, which greatly reduces the need for inverter compressors and complex control. An FB25 outdoor unit can run as designed, sensing no difference between the standard indoor fin/coil heat exchanger unit heating air in the range 20° to 50°C and the heat exchangers 23 and 28 which are giving up heat to R134a refrigerant and water respectively. COP capability is preserved. The second working fluid circuit 14 is therefore unaffected by outdoor ambient conditions and operates in a fully controlled environment.

As the system is compact and can be placed substantially close to the water tank, more sensors can be used to more accurately monitor usage and optimise when the water needs to be heated.

This method should enable optimum performance over a large range of climate conditions with maximum reliability. With 3.2kW input and the water being lifted directly to 62°C, the useable recovery time will be faster than an electric element allowing smaller fluid storage tanks to be used. Preferred embodiments of the invention have been described by way of example only and modifications may be made thereto without departing from the scope of the invention.

For example, the system is described as a hot water heat pump system. However, the system also has other applications, such as domestic and light commercial space heating using circulating water and high temperature radiator (s). Other applications may also include light industrial process applications requiring temperatures of 65 to 80°C, or where any fluid needs to be efficiendy heated during manufacturing or testing. The system may be especially useful in hazard areas where the maximum heat can be limited. In some embodiments, a second expander, such as a linear expansion valve, may be provided in the first working fluid circuit 2 in series with expander 29, but in the indoor unit. This may slow down the flow of the working fluid in the first working fluid circuit. As an alternative, a sub- controller could be installed in series with the expander 29 of the outdoor unit, to control the expander 29. The sub-controller would have two temperature sensors on the gas discharge and liquid return lines within the outdoor unit to override the outdoor control of the expander 29 to optimise subcooling.

In some embodiments, the second working fluid circuit 14 could be modified to operate as a suction/liquid circuit. Referring to Figure 2 for example, an additional heat exchanger could be provided to transfer heat energy between the left side of the second working fluid circuit (with the additional heat exchanger positioned between the heat exchanger 28 and the compressor 30), and the right side of the second working fluid circuit (with the additional heat exchanger positioned between the heat exchanger 26 and the expander 32). Alternatively, the pipe on the left side of the circuit that runs between the heat exchanger 28 and the compressor 30 could be clamped to the pipe on the right side of the circuit that runs between the heat changer 26 and the expander 32, so heat energy can be directed transferred between the two pipes. The heat exchanger/ clamping is represented schematically by broken line HX in Figure 2. This configuration provides additional subcooling, that in turn may enhance the COP of the second working fluid circuit.

While specific components and parameters have been described, it will be appreciated that these could be varied will still working within the scope of the present invention.

As shown, the system has two circuits in a partial cascaded arrangement where each working fluid circuit directiy transfers heat energy directiy to the load. For certain applications, additional working fluid circuits could be provided in partial cascade arrangement. For example, a third working fluid circuit could be provided for directly receiving heat energy from the first or second working fluid circuits 12 or 14 and directiy transferring the heat energy to the load circuit 16. Other example modifications are described in the "Summary of the Invention" section.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Claims

1. A heat pump system for raising a temperature of a load to at least a desired temperature, the system comprising:

a second working fluid circuit arranged to direcdy receive some of the heat energy from the first working fluid circuit, the second working fluid circuit arranged to directly transfer some of its heat energy to the load to raise the temperature of the load from the intermediate temperature to at least the desired temperature, if the temperature of the load is less than the desired temperature.

2. A heat pump system as claimed in claim 1 , comprising a first heat exchanger arranged to direcdy transfer heat energy from the first working fluid circuit to the load.

3. A heat pump system as claimed in claim 2, wherein the first working fluid circuit contains a working fluid that has a substantially stable coefficient of performance at temperatures of the load in the first heat exchanger up to at least the intermediate temperature. 4. A heat pump system as claimed in claim 2 or 3, comprising a second heat exchanger arranged to direcdy transfer heat energy from the first working fluid circuit to the second working fluid circuit.

5. A heat pump system as claimed in claim 4, comprising a third heat exchanger arranged to directly transfer heat energy from the second working fluid circuit to the load.

6. A heat pump system as claimed in claim 5, wherein the second working fluid circuit contains a working fluid that has a substantially stable coefficient of performance at temperatures of the load in the third heat exchanger up to at least the desired temperature.

7. A heat pump system as claimed in claim 6, wherein the working fluid in the first working fluid circuit and the working fluid used in the second working fluid circuit are the same.

8. A heat pump system as claimed in claim 3, wherein the working fluid in the first working fluid circuit is any one of R410a refrigerant, R407 refrigerant, R438 refrigerant, or M099 refrigerant.

9. A heat pump system as claimed in claim 6, wherein the working fluid in the second working fluid is any one of R134a refrigerant, R600 refrigerant, or C0₂.

10. A heat pump system as claimed in any one of claims 1 to 9, wherein the first working fluid circuit is arranged to receive heat energy from an external heat energy source. 11. A heat pump system as claimed in any one of claims 1 to 10, wherein the first working fluid circuit is arranged to directly exchange a major part of its heat energy with the load, and a minor part of its heat energy with the second working fluid circuit.

12. A heat pump system as claimed in any one of claims 1 to 11, comprising a load circuit for circulating a load fluid to be heated.

13. A heat pump system as claimed in claim 12, wherein the load circuit comprises a pump to control flow rate of the load fluid in the load circuit to assist with controlling the temperature of the load fluid in the load circuit. 4. A heat pump system as claimed in claim 2 or 13, wherein the load circuit is arranged to sub-cool the working fluid in the first working fluid circuit.

15. A heat pump system as claimed in any one of claims 12 to 14, wherein the load circuit is arranged to desuperheat, condense and sub-cool the working fluid in the second working fluid circuit.

16. A heat pump system as claimed in claim 15, wherein the second working fluid circuit comprises a working fluid compressor that is arranged to be cooled by transferring heat energy from the working fluid in the second working fluid circuit to load fluid in the load circuit.

17. A heat pump system as claimed in any one of claims 1 to 16, wherein the second working fluid circuit comprises a working fluid expander that is adjustable to optimise the second working fluid circuit.

18. A heat pump system as claimed in claim 5, wherein the load circuit is in communication with or comprises a fluid storage tank for storing the heated load fluid, and wherein the system is arranged to monitor load fluid temperature before the load fluid passes through the first heat exchanger, load fluid temperature after the load fluid passes through the first heat exchanger, and load fluid temperature after the load fluid passes through the third heat exchanger, to determine when load fluid in the fluid storage tank is fully heated.

19. A heat pump system as claimed in claim 18, wherein the system is arranged to control compressors and/or expanders of the first and/or second working fluid circuits based on load fluid temperatures.

20. A heat pump system as claimed in any one of claims 12 to 15, wherein the load circuit is in communication with or comprises a fluid storage tank for storing the heated load fluid, and wherein load fluid in the fluid storage tank is stratified forming a thermocline with a distinct upper region of relatively high temperature and a lower region of cooler load fluid of relatively low temperature.

21. A heat pump system as claimed in claim 20, wherein the system is configured to maintain the load fluid in at least the upper region of the fluid storage tank at the desired temperature or above, and is configured to remove cooler load fluid from the lower region of the fluid storage tank and circulate the cooler load fluid around the load fluid circuit, to elevate that cooler load fluid to at least the desired temperature and return that heated load fluid to the upper region of the fluid storage tank.

22. A heat pump system as claimed in any one of claims 12 to 15, 20, or 21, further comprising a controller to control heat being exchanged with the load circuit.

23. An apparatus for use in a heat pump system for raising temperature of a load to at least a desired temperature, the apparatus being operably connectable to an existing heat exchanger that is arranged to collect heat energy from a heat energy source, the apparatus comprising:

a first heat exchanger arranged to receive some heat energy collected by the existing heat exchanger and to direcdy transfer heat energy to the load to raise the temperature of the load to an intermediate temperature, if the temperature of the load is less than the intermediate temperature; a second heat exchanger arranged to receive some heat energy collected by the existing heat exchanger; and

a third heat exchanger arranged to receive heat energy collected by the second heat exchanger and to direcdy transfer heat energy to the load to raise the temperature of the load from the intermediate temperature to at least the desired temperature, if the temperature of the load is less than the desired temperature.

24. An apparatus as claimed in claim 23, wherein the existing heat exchanger, the first heat exchanger and the second heat exchanger are components in a first working fluid circuit.

25. An apparatus as claimed in claim 24, wherein the first working fluid circuit contains a first working fluid that has a substantially stable coefficient of performance at temperatures of the load in the first heat exchanger up to at least the intermediate temperature. 26. An apparatus as claimed in claim 25, wherein the working fluid in the first working fluid circuit is any one of R410a refrigerant, R407 refrigerant, R438 refrigerant, or M099 refrigerant.

27. An apparatus as claimed in any one of claims 23 to 26, wherein the second heat exchanger and the third heat exchanger are components in a second working fluid circuit.

28. An apparatus as claimed in claim 27, wherein the second working fluid circuit contains a second working fluid that has a substantially stable coefficient of performance at temperatures of the load in the third heat exchanger of up to at least the desired temperature. 29. An apparatus as claimed in claim 28, wherein the working fluid in the second working fluid is any one of R134a refrigerant, R600 refrigerant, or C0₂.

30. An apparatus as claimed in any one of claims 27 to 29, wherein the apparatus is arranged to control compressors and/or expanders of the first and/or second working fluid circuits based on load fluid temperatures.

31. Any one of claims 23 to 30, wherein the second working fluid circuit comprises a working fluid compressor that is arranged to be cooled by transferring heat energy from the working fluid in the second working fluid circuit to load fluid in the load circuit.

32. A heat pump system as claimed in any one of claims 23 to 31, which is retro fittable to an existing air-to-air heat pump system. 33. A method for adjusting a temperature of a load fluid to a desired temperature within a heat pump system, the heat pump system having a first working fluid circuit arranged to receive heat energy from a heat energy source, a second working fluid circuit arranged to direcdy receive some of the heat energy from the first working fluid circuit, and a load circuit arranged to direcdy receive heat energy from the first working fluid circuit and/ or the second working fluid circuit, the method comprising:

measuring the temperature of the load fluid; and

adjusting a flow rate of load fluid within the load circuit based at least partiy on the measured temperature to adjust the heat energy that is transferred to the load fluid from the first working fluid circuit and/or the second working fluid circuit, to adjust the temperature of the load fluid to the desired temperature.

34. A method as claimed in claim 33, wherein the load circuit comprises a fluid pump, and the method comprises adjusting the fluid pump to adjust the flow rate of the load fluid. 35. A method as claimed in claim 34, wherein the system comprises a first heat exchanger arranged to direcdy transfer heat energy from the first working fluid circuit to the load fluid, a second heat exchanger arranged to directly transfer heat energy from the first working fluid circuit to the second working fluid circuit, and a third heat exchanger arranged to direcdy transfer heat energy from the second working fluid circuit to the load fluid.

36. A method as claimed in claim 35, wherein the step of measuring the temperature of the load comprises measuring a temperature before the load fluid passes through the first heat exchanger, a temperature after the load fluid passes through the first heat exchanger, and a temperature after the load fluid passes through the third heat exchanger, and wherein the method comprises increasing the flow rate of the load fluid through the first and third heat exchangers if the measured temperature is above the desired temperature or decreasing the flow rate of the load fluid through the first and third heat exchangers if the measured temperature is below the desired temperature.

37. A method as claimed in claim 36, comprising increasing the flow rate of the load fluid through the first and third heat exchangers from zero if the measured temperature is below the desired temperature. 38. A method as claimed in any one of claims 35 to 37, wherein the load circuit is in

communication with a fluid storage tank for storing the heated load fluid.

39. A method as claimed in claim 38, comprising running the fluid pump so that heated load fluid in the first and third heat exchangers and load circuit is transferred into the fluid storage tank before turning off the pump, to minimise wastage of heated load fluid.

40. A method as claimed in claim 38 or 39, wherein the load fluid in the fluid storage tank is stratified forming a thermocline with a distinct upper region of relatively high temperature and a lower region of cooler load fluid of relatively low temperature, and wherein the load fluid is maintained in at least the upper region of the fluid storage tank at at least the desired temperature, and the method comprises removing cooler load fluid from the lower region of the fluid storage tank and circulating the cooler load fluid around the load fluid circuit, to elevate that cooler load fluid to at least the desired temperature, and returning that heated load fluid to the upper region of the fluid storage tank.

4 . A method as claimed in claim 40, comprising maintaining the stratification in the fluid storage tank as the cooler fluid is removed from the tank.

42. A method as claimed in any one of claims 33 to 41 , further comprising the step of adjusting compressors and/ or expanders of the first and/ or second working fluid circuits based at least partly on the measured temperature to adjust the temperature of the load fluid.

43. A method as claimed in any one of claims 33 to 42, wherein the method is implemented by a controller.

44. A computer readable medium having stored thereon computer-executable instructions that, when executed by a processor, cause the processor to perform a method for adjusting a

temperature of a load fluid to a desired temperature within a heat pump system, the heat pump system having a first working fluid circuit arranged to receive heat energy from a heat energy source, a second working fluid circuit arranged to directly receive some of the heat energy from the first working fluid circuit, and a load circuit arranged to direcdy receive heat energy from the first working fluid circuit and/ or the second working fluid circuit, the method comprising:

measuring the temperature of the load fluid; and

adjusting a flow rate of load fluid within the load circuit based at least pardy on the measured temperature to adjust the heat energy that is transferred to the load fluid from the first working fluid circuit and/or the second working fluid circuit, to adjust the temperature of the load fluid to the desired temperature.

45. A computer readable medium as claimed in claim 44, having stored thereon computer- executable instructions that, when executed by a processor, cause the processor to perform the method as claimed in any one of claims 33 to 43.