FIELD OF THE INVENTION

This invention relates to heating and cooling of habitable spaces, as well as water heating. In particular, the invention relates to heat pump apparatus and methods suitable for air conditioning and water heating.

BACKGROUND TO THE INVENTION

It is common practice in many parts of the world to heat and/or cool habitable spaces such as the insides of houses, offices, shops or the like (referred to as a

"building" herein) and one of the ways in which this can be done conveniently, is with the use of a system commonly referred to as an air conditioning system, which comprises a reversible heat pump using vapor-compression refrigeration and including a reversing valve and two heat exchangers. The reversing valve can switch the flow directions of refrigerant and heat through the cycle and therefore the heat pump may deliver either heating or cooling to a building, with the one heat exchanger acting as an evaporator and the other heat exchanger acting as condenser - and the functions of the two heat exchangers reversing if the heat pump is switched between heating and cooling modes. Heat pumps of this type can thus transfer heat in either direction between the inside and outside of a building.

Similar heat pumps, albeit not reversible, have also been used to heat water, e.g. to heat swimming pools and the water in hot water cylinders, transferring ambient heat from inside or outside buildings, to the water.

Attempts have been made to combine some of the functions of these devices, but systems suitable for multiple functions are expensive due to the additional equipment required, are not efficient and/or do not reach operational goals. In particular, systems that combine cooling the insides of buildings with water heating, often do not heat water adequately. The present invention seeks to provide cost effective, efficient and convenient heating or cooling of the inside of a building, optionally in combination with water heating. SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided heat pump apparatus for heating water, said apparatus comprising:

a compressor having an inlet and a discharge;

a first heat exchanger connected by a conduit to the compressor's discharge and configured to transfer heat to the water;

a second heat exchanger and a third heat exchanger, with a fan configured to force air to flow over the second heat exchanger;

an expansion valve connected by conduits between said second and third heat exchangers, in series;

a valve configuration connected by conduits to the first, second and third heat exchangers and to the inlet of the compressor, said valve configuration being configured to connect the outlet of the first heat exchanger to flow through the second and third heat exchangers, in series and to flow from the second and third heat exchangers to the inlet of the compressor; and said valve

configuration being configured to reverse the connection of the second and third heat exchangers; and

at least one switch that is configured to control operation of the fan to maintain pressure in the conduit extending between the compressor and the first heat exchanger.

The switch may be configured to switch the fan on and off or to vary the speed of the fan continuously.

The switch may be configured, when the second heat exchanger is connected to the first heat exchanger and the third heat exchanger is connected to the compressor, to increase the speed of the fan if pressure in the conduit extending between the compressor and the first heat exchanger increases, e.g. if the pressure exceeds a predetermined high pressure, and to reduce the speed of the fan if pressure in the conduit extending between the compressor and the first heat exchanger decreases, e.g. if the pressure drops below a predetermined low pressure. For the purposes of determining increases and decreases in pressure, the switch may be configured to react to related increases or decreases in temperature. Further, the terms

"increasing" and "decreasing" fan speed are used broadly and include continuous increases or decreases, but also include switching on and switching off. The switch may be configured, when the third heat exchanger is connected to the first heat exchanger and the second heat exchanger is connected to the

compressor, to decrease the speed of fan the if pressure in the conduit extending between the compressor and the first heat exchanger increases and to increase the speed of the fan if pressure in the conduit extending between the compressor and the first heat exchanger decreases.

The heat pump apparatus may include two of the switches, each being configured to control the fan when the second and third heat exchangers are connected in a particular order.

According to another aspect of the present invention there is provided a method of heating water, said method comprising the steps of:

compressing a fluid in a compressor;

passing the compressed fluid to a first heat exchanger to transfer heat from the fluid to the water in the heat exchanger, whether directly or indirectly, e.g. via a heating fluid,

passing the fluid from the first heat exchanger to a series arrangement, said series arrangement including a second heat exchanger, expansion valve and third heat exchanger, in series and said fluid flowing through the series arrangement in any either direction;

reducing pressure of the fluid in the expansion valve; absorbing heat in at least one of the heat exchangers in the series arrangement; passing the fluid from the series arrangement to the compressor; and

controlling the operation of a fan that is configured to force air to flow over the second heat exchanger to maintain pressure in of the fluid in a conduit extending between the compressor and the first heat exchanger.

The method may include controlling operation of the fan, when the fluid in the series arrangement flows in a direction from the second heat exchanger via the expansion valve to the third heat exchanger, to increase the speed of the fan if the fluid pressure in the conduit extending between the compressor and the first heat exchanger increases and to reduce the speed of the fan if the fluid pressure in the conduit extending between the compressor and the first heat exchanger decreases.

The method may include controlling operation of the fan when the fluid in the series arrangement flows in a direction from the second heat exchanger via the expansion valve to the third heat exchanger, to reduce the speed of the fan if the fluid pressure in the conduit extending between the compressor and the first heat exchanger increases and to increase the speed of the fan if the fluid pressure in the conduit extending between the compressor and the first heat exchanger decreases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which:

Figure 1 shows a schematic diagram of apparatus operating in a first mode, to cool the inside of a building and heat water, in accordance with the present invention; and

Figure 2 shows a schematic diagram of the apparatus of Figure 1 , in a second

mode, to heat the inside of the building. DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, heat pump apparatus or a system in accordance with the present invention is generally indicated by reference numeral 10. The system 10 includes a unit 12 housing a number of components and shown in the drawings in broken lines. The unit 12 is typically installed on the outside of a building where the system 10 is to be used.

The system 10 further includes a hot water cylinder (HWC) 14 installed in any position, although elevated positions are typical. The HWC 14 includes an internal coil 16 making good thermal contact with water inside the HWC and can be of the type of HWC suitable for use with a solar collector. If preferred, the system 10 can be used in conjunction with a solar collector. The coil 16 in HWC 14 is connected via conduits to one side of a heat exchanger 18 inside the unit 12 in a closed heating loop 17, which may be filled with water or other heating fluid. In other embodiments, the HWC 14 does not include an internal coil 16, but the water from the HWC is circulated directly through the heat exchanger 18 and thus fulfils the purpose of the heating fluid. A heat exchanger pump 19 is provided in the closed loop and is configured to circulate the heating fluid. The heat exchanger 18 can of various suitable types, but in a preferred embodiment, it is a tube heat exchanger with the shell-side of the heat exchanger forming part of the closed loop with the coil 16. The system 10 includes a second heat exchanger inside the unit 12 in the form of a coil, to which reference will be made herein as the outdoor coil 20 (referring to the typical outdoor location of the unit 12) and a motor driven outdoor fan 22 configured to blow ambient air across the outdoor coil and increase heat transfer between the outdoor coil and ambient air.

The unit 12 also includes a bi-flow thermostatic expansion valve (TXV) 24, a compressor 26 and a valve configuration in the form of a four-way valve 28, connected together and to the outdoor coil 20 by conduits. Instead of the TXV 24, the unit 12 may include a capillary or electronic expansion valve. Further, the compressor 26 may be a conventional compressor or may be driven by an inverter or a variable frequency drive to vary compressor speed.

For ease of reference, the respective openings of the four-way valve are identified by alphabetic suffixes. Opening 28a is connected by a conduit to an outlet on the tube-side of heat exchanger 18, opening 28b is connected by a conduit to the outdoor coil 20, opening 28c is connected by a conduit to an inlet of the compressor 26, and opening 28d is connected by a conduit to an indoor coil (see below). The use of a four way valve 28 is preferred, but the same functionality can be achieved with other valve arrangements, e.g. with a combination of three-way valves. Three sensors in the form of pressure switches 30,32 and 34 are connected to a conduit extending between an outlet of the compressor 26 and an inlet of the tube- side of heat exchanger 18. However, instead of pressure switches 30, 32 and 34, other sensors such as temperature switches, or transducers may be used. Inside the building where heating and/or cooling may be required, the system 10 includes a third heat exchanger in the form of an indoor coil 36 and a motor driven indoor fan 38 configured to blow indoor air across the indoor coil and increase heat transfer between the indoor coil and indoor air. The indoor coil 26 is connected by conduits to the TXV 24 and to opening 28d of the four-way valve 28. The TXV 24 is connected in series between the outdoor coil 20 and the indoor coil 36.

The conduits connecting the components inside the unit 12 and the indoor coil 36 are filled with a suitable fluid such as refrigerant in a closed system. Many refrigerants may be suitable for use in the system 10, but refrigerant R22 has been used in experiments and if use of refrigerant R22 is not permitted, refrigerant 41 OA may be used (at higher pressures). The operations of the heat exchanger pump 19, four-way valve 28, compressor 26 and indoor and outdoor fans 22,38 are controlled by a controller (not shown) and by the pressure switches 30, 32 and 34, as described below.

Referring to Figure 1 , when the system 10 is operating in cooling mode, the four-way valve connects openings 28a and 28b and connects 28c and 28d, the heat exchanger pump 19 and indoor fan 38 are switched on and the outdoor fan 22 initially remains off.

Refrigerant gas is compressed by the compressor 26 to an elevated pressure and temperature (typically up to a temperature of about 106°C in a preferred

embodiment) and flows from a discharge of the compressor to the tube-side of the heat exchanger 18, where heat is transferred from the refrigerant to the heating fluid on the shell-side, which is pumped by the pump 19 to dissipate its heat to water in the HWC 14 in the coil 16 and thus to heat the water in the HWC. The refrigerant flows from the heat exchanger 18 via the four-way valve 28 to the outdoor coil 20 where further heat is dissipated from the refrigerant to the ambient air, but since the outdoor fan 22 is initially switched off, the heat dissipated in the outdoor coil may be little. The heat exchanger 18 and, to a lesser degree, the outdoor coil 20, causes heat to be dissipated from the refrigerant and thus serve the same purpose as a "condenser" in a conventional air conditioning system and the refrigerant condenses as a result of the heat loss and is in a liquid phase when it exits the outdoor coil 20. The refrigerant's pressure and temperature are reduced as it flows through the TXV 24 and the cold liquid flows through the indoor coil 36 where it absorbs heat and evaporates with increased hear transfer through forced convection from the indoor fan 38. The indoor coil 36 functions in the same way as an evaporator in a conventional air-conditioning system and the refrigerant exits the indoor coil as a gas, which is fed via openings 28d and 28c to the inlet of the compressor 26. The heating fluid in the closed heating loop 17 and the water in the HWC 14 are heated by the refrigerant in the heat exchanger 18 until it reaches a temperature of about 55°C and at this point, heat transfer to the heating fluid and water reduces and the pressure and temperature of the refrigerant in the system 10 begin to rise. When the refrigerant pressure in the system has risen to a pressure corresponding to a temperature of about 58°C at the discharge of the heat exchanger 18, pressure switch 30 switches on the outdoor fan 22, which increases heat dissipation from the refrigerant to ambient air in the outdoor coil 20 and thus reduces refrigerant temperature and pressure in the system 10. When the refrigerant pressure in the system has dropped to a pressure corresponding to a temperature of about 55°C at the discharge of the heat exchanger 18, pressure switch 30 switches off the outdoor fan 22 again and the system pressure and temperature begin to rise again.

Pressure switch 30 causes the outdoor fan 20 to cycle on and off and thus to maintain a safe refrigerant pressure in the system 10, and in the meantime, heat dissipated in the heat exchanger 18 heats the heating fluid and water in the HWC 14 to temperatures of about 62°C. This is a suitable temperature for domestic hot water supplies and is much higher than water temperatures achieved in prior art heat pumps combining indoor cooling and water heating.

In alternative embodiments, the outdoor fan 22 may be a variable speed fan, which may optimise system efficiency.

Referring to Figure 2, when the system 10 is operating in water heat pump mode, the controller energises the four-way valve to connect openings 28a and 28d and to connect 28b and 28c, the heat exchanger pump 19 is switched on and the indoor fan 38 remains off. Pressure switch 32 switches outdoor fan 22 on.

The compression of refrigerant in the compressor 26 and heat transfer to the heating fluid and water in the heat exchanger 18 and coil 16 are as described with reference to Figure 1 . However, condensed refrigerant flowing from the heat exchanger 18 is directed by the four-way valve to flow to the indoor coil 36, where little heat exchange takes place, because the indoor fan 38 is off. Refrigerant from the indoor coil 36 flows through the TXV 24, where its pressure and temperature are reduced and it flows to the outdoor coil 20, which serves as evaporator, resulting in heat transfer from the ambient air to the refrigerant (with forced convection from the outdoor fan 22), causing the refrigerant to evaporate and flow via the four-way valve 28 to the inlet of the compressor 26.

The heating fluid in the closed heating loop 17 and the water in the HWC 14 are heated by the refrigerant in the heat exchanger 18 until it reaches a temperature of about 55°C and at this point, heat transfer to the heating fluid and water reduces and the pressure and temperature of the refrigerant in the system 10 begin to rise. When the refrigerant pressure in the system has risen to a pressure corresponding to a temperature of about 58°C at the discharge of the heat exchanger 18, pressure switch 32 switches off the outdoor fan 22, which reduces heat absorption from the ambient air to the refrigerant in the outdoor coil 20 and thus reduces refrigerant temperature and pressure in the system 10. When the refrigerant pressure in the system has dropped to a pressure corresponding to a temperature of about 55°C at the discharge of the heat exchanger 18, pressure switch 32 switches on the outdoor fan 22 again and the system pressure and temperature begin to rise again.

Pressure switch 32 causes the outdoor fan 20 to cycle on and off and like in the case of cooling mode, a safe refrigerant pressure is maintained in the system 10 and heat dissipated in the heat exchanger 18 heats the heating fluid and water in the HWC 14 to temperatures of about 55°C.

In alternative embodiments, an extra control may be added in water heat pump mode to cycle the indoor fan 38 to de-superheat the refrigerant to improve efficiency and reduce refrigerant pressure. If the indoor fan 38 is cycled, the water in the HSC 14 can be heated to temperatures of about 62°C. The system 10 can also be operated in a space heater mode, in which its operation is similar to that of water heat pump mode described with reference to Figure 2, except that the heat exchanger pump 19 is off, so no heat is transferred from the refrigerant to the heating fluid in the heat exchanger 18 and the indoor fan 38 is on, so that heat is transferred from the refrigerant in the indoor coil 36 to the inside of the building. The refrigerant condenses inside the indoor coil 26 and evaporates in the outdoor coil 20.

Pressure switch 34 is a high pressure cut-out and protects the system 10 by stopping the compressor in the event of a high pressure in any mode.