Heat pump external unit

Abstract

Provided is a heat pump or heat pump external unit contained within a housing of plastics material, the heat pump external unit including an evaporator, a compressor, and a motor driven axial fan with blades to move ambient air over the heat exchanger, wherein the evaporator, the compressor, and the motor-driven fan are mounted to and carried by the plastics housing, optionally without use of a metal chassis, wherein the housing provides a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the fan blades to the exhaust grille, the exhaust grille defining a second area at least 10 percent smaller than the first area; the duct being substantially devoid of obstructions (and optionally of constant cross-sectional area sections) between the evaporator and the fan blades, the duct being shaped to draw air effectively from across the area of the evaporator, and optionally the duct having a generally circular section.

Description

[0001] Heat Pump External Unit

[0002] Technical field

[0003] The present invention relates to a heat pump external unit, in particular an air source heat pump external unit, to a method of constructing a heat pump external unit in particular an external unit for an air source heat pump.

[0004] Background

[0005] According to Directive 2012 / 27 / EU buildings represent 40 % of the final energy consumption and 36% of CO2 emissions. The EU Commission report of 2016 “Mapping and analyses of the current and future (2020 - 2030) heating / cooling fuel deployment (fossil / renewables)” concluded that in EU households, heating and hot water alone account for 79% of total final energy use (192.5Mtoe). The EU Commission also report that, “according to 2019 figures from Eurostat, approximately 75% of heating and cooling is still generated from fossil fuels while only 22% is generated from renewable energy. To fulfil the EU’s climate and energy goals, the heating and cooling sector must sharply reduce its energy consumption and cut its use of fossil fuels. Heat pumps, with energy drawn from the air, the ground or water, have been identified as potentially significant contributors in addressing this problem. Because only a small percentage of domestic households have access to a body of water to support the use of a heat pump that draws energy from water, and because the cost and space requirements for installing a ground source heat exchanger are very significant, it is generally cheaper and more convenient to install an air source heat pump. It is also generally recognised that an air source heat pump is the better replacement for an existing gas central heating boiler.

[0006] A significant barrier to the wholesale adoption of air source heat pumps as replacements for boilers that burn fossil fuels is cost. The UK’s Energy Saving Trust reports that the average cost of installing an air source heat pump as a replacement for a gas boiler is around £14,000, whereas the average cost of replacing an existing gas boiler with a modern condensing gas boiler is around £4,000. While much of the difference in price is attributable to the need to increase the size of radiators and possibly to increase insulation standards, in general air source heat pumps themselves cost significantly more than a gas boiler of comparable power output, in part because of the complexity of the construction. If more users of existing fossil fuelled boilers are to be encouraged to switch to air source heat pumps it will be necessary to reduce the cost of the heat pumps themselves.

[0007] As more users turn to heat pumps for domestic heating to replace fossil fuel-based systems, efficiency in design has become increasingly important. Improving the airflow paths and overall efficiency of heat pumps can lead to cost savings for individual users and contribute to significant global energy savings.The present invention seeks to provide an air source heat pump or heat pump external unit suitable for providing heat to a domestic dwelling. The unit comprises a housing in which an axial fan mounted, optionally in an upper portion of a curved front wall, with the fan’s rotational axis angled between a vertical and horizontal direction, may be positioned to exhaust air in a generally forward direction with an upward component through an exhaust grille. The axial fan’s motor may be suspended forward (i.e. downstream) of the fan blades. The evaporator lies generally in a plane and the axis of rotation of the fan is tilted with respect to a normal to the plane, with the housing providing a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the fan blades to the exhaust grille, the exhaust grille defining a second area at least 10 percent smaller than the first area. The duct is substantially devoid of obstructions between the evaporator and the fan blades and is shaped to draw air effectively from across the area of the evaporator.

[0008] This arrangement, particularly with the fan motor mounted forward of the blades and the duct substantially unobstructed and converging, improves airflow efficiency. This reduces the compressor and / or fan power required for a given heat output. Additionally, the duct’s construction from plastics material helps absorb noise, while the converging shape of the duct further reduces resonances and noise.

[0009] The present invention also seeks to provide various air source heat pump external units, and air source heat pumps in which at least some of the drawbacks of existing air source heat pumps are mitigated in whole or in part.

[0010] Summary

[0011] According to a first aspect there is provided a heat pump or heat pump external unit contained within a housing, the heat pump or heat pump external unit including an evaporator and a motor driven axial fan with blades to move ambient air over the heat exchanger, wherein: the evaporator lies generally in a plane and the axis of rotation of the fan is tilted with respect to a normal to the plane; the housing providing a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the fan blades to the exhaust grille, the exhaust grille defining a second area at least 10 percent smaller than the first area; the duct being substantially devoid of obstructions between the evaporator and the fan blades, and the duct being shaped to draw air effectively from across the area of the evaporator.

[0012] The fan’s motor is preferably suspended forward (i.e. downstream) of the fan blades. This arrangement, particularly with the fan motor mounted forward of the blades and the duct substantially unobstructed and converging, improves airflow efficiency. This reduces thecompressor and / or fan power required for a given heat output. Additionally, the duct’s construction from plastics material helps absorb noise, while the converging shape of the duct further reduces resonances and noise.

[0013] According to a second aspect there is provided an air source heat pump or heat pump external unit having a housing and within the housing an evaporator, a compressor, a motor driven axial fan to move ambient air over the heat exchanger, and a processor to control the operation of the fan and the compressor, wherein the housing comprises a base portion and an upper portion that together define a first chamber to contain the compressor, a second chamber to contain the processor, and a third chamber to contain the evaporator and the fan, and the base portion and the upper portion each being a moulded or printed plastics component, wherein the housing provides a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the blades of the fan to an exhaust grille, the exhaust grille having a second area at least 10 percent smaller than the first area; the fan blades optionally being positioned in a converging section of the duct, the duct being substantially devoid of obstructions between the evaporator and the fan blades, the duct being shaped to draw air effectively from across the area of the evaporator, and the fan’s motor preferably being suspended forward (i.e. downstream) of the fan blades.

[0014] According to a third aspect there is provided an air source heat pump or heat pump external unit having a housing of plastics material and within the housing an evaporator, a compressor, a motor driven axial fan to move ambient air over the heat exchanger, wherein the housing is structural and comprises a base portion and an upper portion that together support and contain the evaporator, compressor and motor driven fan without reliance on an internal metal chassis, wherein the housing provides a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the blades of the fan to an exhaust grille, the exhaust grille having a second area at least 10 percent smaller than the first area; the duct being substantially devoid of obstructions between the evaporator and the fan blades, the duct being shaped to draw air effectively from across the area of the evaporator, and the fan’s motor preferably being suspended forward (i.e. downstream) of the fan blades, and optionally the duct having a generally circular section.

[0015] According to a fourth aspect there is provided an air source heat pump or heat pump external unit having a housing and within the housing an evaporator, a compressor, and a motor driven axial fan to move ambient air over the heat exchanger, the housing comprises a base portion and an upper portion, wherein: the upper portion co-operates with the base portion; the evaporator is received within a recess or other receiving arrangement within the base portion, the compressor is secured to the base portion; and the fan motor is secured to and supported by theupper portion, wherein the housing provides a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the blades of the fan to an exhaust grille, the exhaust grille having a second area at least 10 percent smaller than the first area; the duct being substantially devoid of obstructions between the evaporator and the fan blades, the duct being shaped to draw air effectively from across the area of the evaporator, and the fan’s motor preferably being suspended forward (i.e. downstream) of the fan blades.

[0016] According to a fifth aspect there is provided an air source heat pump or heat pump external unit having a housing of plastics material and within the housing an evaporator, a compressor, a motor driven axial fan to move ambient air over the heat exchanger, wherein: the housing is structural and comprises a base portion, to which the compressor is secured, and an upper portion which carries the fan and its drive motor, the evaporator being supported in a groove or recess in the base portion and located between the upper portion and the base portion; the base portion and the upper portion together defining a first chamber to contain the evaporator and the fan, the first chamber including an air flow conduit to guide air flow from the evaporator to the fan, the air flow conduit being defined at least in part by the upper portion, wherein the conduit forms, or forms part of, a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the blades of the fan to an exhaust grille, the exhaust grille having a second area at least 10 percent smaller than the first area; wherein the duct is substantially devoid of obstructions between the evaporator and the fan blades, the duct being shaped to draw air effectively from across the area of the evaporator, and the fan’s motor preferably being suspended forward (i.e. downstream) of the fan blades, and optionally the duct having a generally circular section.

[0017] According to a sixth aspect there is provided an air source heat pump having a housing and within the housing an evaporator, a compressor, and a motor driven axial fan to move ambient air over the heat exchanger, wherein the housing comprises an assembly of three principal body portions each being a moulded or printed plastics component, wherein the housing provides a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past blades of the fan to an exhaust grille, the exhaust grille having a second area at least 10 percent smaller than the first area; the duct being substantially devoid of obstructions the evaporator and the fan blades, the duct being shaped to draw air effectively from across the area of the evaporator, the fan’s motor preferably being suspended forward (i.e. downstream) of the fan blades, and optionally the duct having a generally circular section.

[0018] According to a seventh aspect there is provided a heat pump external unit comprising:a housing having a substantially planar, substantially vertical rear wall section in which a generally planar evaporator is located, a curved front wall, and an axial fan mounted at an upper portion of the curved front wall, the axial fan having a motor and fan blades with the motor suspended forward of the blades, wherein the fan axis is angled between vertical and horizontal directions and positioned to exhaust air in a generally forward direction with an upward component through an exhaust grille; wherein the housing defines a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the fan blades to the exhaust grille, the exhaust grille having a second area at least 10 percent smaller than the first area; wherein the duct is substantially devoid of obstructions between the evaporator and the fan blades, the duct being shaped to draw air effectively from across the area of the evaporator, and optionally the duct having a generally circular section.

[0019] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the axis of rotation is tilted at least 25 degrees (e.g. 30 to 60 degrees) away from a normal to the plane of the evaporator.

[0020] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the evaporator is disposed generally vertically and the fan’s axis of rotation is angled between 0 and 60 degrees from the vertical.

[0021] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the housing is a plastics housing, and the evaporator and the motor driven fan are mounted to and carried by the housing without the use of a metal chassis.

[0022] In such a heat pump or heat pump external unit the fan motor may be supported by the exhaust grille.

[0023] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the fan blades may be positioned at a point in the duct where the duct has its smallest cross sectional area.

[0024] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects a converging section of the duct may be provided just upstream of the fan blades.

[0025] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the fan blades may be positioned at a point in the duct where the duct converges.

[0026] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the fan blades may be positioned in a converging section of the duct.In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the fan motor may located between the fan blades and the exhaust grille.

[0027] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the housing may comprise a substantially planar, substantially vertical rear wall section in which the evaporator is located, and a curved front wall, the axial fan being mounted at an upper portion of the curved front wall.

[0028] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the plastics material of the duct is preferably selected to absorb noise and reduce vibration.

[0029] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the angle of the fan’s rotational axis relative to the vertical may be between 30 and 60 degrees.

[0030] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the duct may be configured to have a converging shape that reduces noise resonances during operation.

[0031] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the fan blades may be positioned at a section of the duct where the cross-sectional area transitions from a generally rectangular shape to a generally circular shape.

[0032] An air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects may further comprise a display mounted coaxially on the exhaust grille, wherein the display is connected to the control logic and configured to indicate operational status, modes, and diagnostic information.

[0033] An air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects may further comprise control logic coupled to an indoor control unit, the indoor control unit being configured to allow users to set operational parameters and modes and monitor the status of the external unit remotely.

[0034] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the fan motor may be positioned forward of the fan blades so as to create an unobstructed and efficient converging duct pathway.

[0035] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the housing may comprise a base portion and an upper portion that together define, at least in part, a first chamber to contain the compressor, a second chamber to contain the evaporator and the fan, and the base portion and the upper portion each being a moulded or printed plastics component. With such a configuration:i) Such a heat pump or heat pump external unit may further comprise a processor to control the operation of the heat pump, the processor being accommodated within a third chamber that is defined at least in part by the base portion and optionally the upper portion; ii) Optionally the third chamber may be in part defined by a liquid cooled heat transfer plate that is thermally coupled to an inverter that is used to power electronics of the heat pump;

[0036] iii) Such a heat pump or heat pump external unit may further comprise at least one cover for one or both of second and third chambers to provide access to components or systems within the relevant chamber - and optionally the or each cover is a moulded or printed plastics component;

[0037] iv) In such a heat pump or heat pump external unit the fan and its motor may be carried by the housing upper portion, and optionally the housing upper portion is demountable from the base portion to provide access to the compressor and to the evaporator.

[0038] v) In such a heat pump or heat pump external unit the duct may be defined at least in part by the upper portion, and optionally the duct is at least partly defined by the base portion.

[0039] vi) In such a heat pump or heat pump external unit the evaporator may be received within a recess or other receiving arrangement within the base portion, and optionally the base portion may include an air flow guiding surface that flares at an angle away from the recess and towards the upper portion, and optionally the upper portion may include an air flow guiding surface that together with the air flow guiding surface of the base part defines a wall of the duct.

[0040] vii) In such a heat pump or heat pump external unit the base portion and the upper portion may be configured to couple together to define the second chamber.

[0041] viii) In such a heat pump or heat pump external unit the base portion may include features to receive pipework to carry refrigerant, wherein optionally the included features are moulded-in features.

[0042] ix) In such a heat pump or heat pump external unit the base portion may include antirotation features to hold captive and prevent the rotation of threaded pipework couplings, unions or components, wherein optionally the included anti-rotation features are moulded-in features.

[0043] x) In such a heat pump or heat pump external unit the upper housing portion may be in the form of a hollow plastics moulding containing thermal and / or noise insulation, and optionally the thermal and / or noise insulation is a foamed plastics material, also optionally the foamed plastics material may have been foamed in situ or the foamed plastics material may be in the form of beads or the like.

[0044] x) In such a heat pump or heat pump external unit the base portion may include a recess to receive a lower end of the air heat exchanger.xi) In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the plastics housing may be structural and comprises a base portion and an upper portion that together support and contain the evaporator, compressor and motor driven fan without reliance on an internal metal chassis.

[0045] xii) In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the housing may structural and comprises a base portion, to which the compressor is secured, and an upper portion which carries the fan and its drive motor, the evaporator being supported in a groove or recess in the base portion and located between the upper portion and the base portion; the base portion and the upper portion together defining a first chamber to contain the evaporator and the fan, the first chamber including an air flow conduit to guide air flow from the evaporator to the fan, the air flow conduit being defined at least in part by the upper portion, the air flow conduit defining at least part of the length of the duct, and optionally the air flow conduit is at least partly defined by the base portion.

[0046] Preferably the housings of air source heat pumps and heat pumps according to aspects of the invention are formed without reliance on internal metal chassis. By avoiding the requirement for an internal metal chassis it is possible to design a more efficient air flow path from the evaporator to the fan, improving efficiency and possibly reducing the amount of noise generated.

[0047] In an air source heat pump, or heat pump external unit according to any variant of the first through seventh aspects the duct is preferably also substantially devoid of constant cross-sectional area sections between the evaporator and the fan blades.

[0048] Brief description of the drawings

[0049] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures, in which:

[0050] Figure 1 is a schematic diagram showing the main components of an air source heat pump in heating mode;

[0051] Figure 2 corresponds to figure 1 but shows the heat pump in cooling mode;

[0052] Figure 3 A is a three quarter perspective view of a heat pump external unit according to an aspect of the invention;

[0053] Figure 3b is a three quarter perspective view of a heat pump external unit, corresponding to Figure 3A, including an optional status display indicator, according to an aspect of the invention; Figures 4A to 4D are exploded views of the housing of figures 3 A and 3B;

[0054] Figures 5A, 5B and 5C are three quarter perspective views of the lower housing portion of the heat pump of figures 3 A and 3B;

[0055] Figures 6A and 6B are perspective views of the upper housing part of the heat pump of figures 3 A and 3B;Figure 7A and 7B are perspective views of a front cover of the heat pump of figures 3 A and 3B; Figure 8A is a vertical section showing the arrangement of the fan and evaporator of the heat pump of figures 3 A and 3B;

[0056] Figure 8B is perspective view showing a possible arrangement of internal components of the heat pump of figures 3 A and 3B;

[0057] Figure 9 is a plan view corresponding to figure 8B;

[0058] Figure 10 is a front elevation corresponding to figure 9 with the front cover removed;

[0059] Figure 11 is a schematic showing a typical domestic heat pump installation, according to an aspect of the invention, for premises in the form of a house; and

[0060] Figures 11A to 11D illustrate details of a status display arrangement according to various aspects of the invention.

[0061] Specific description

[0062] Before describing in detail the features of the new heat pump that contribute to reducing the cost of construction it may be helpful to describe the operation and main components that are typical of an air source heat pump according to aspects of the invention.

[0063] Figure 1 shows schematically an air source heat pump 10 operating in heating mode. The main mechanical components of the heat pump are shown, but for the sake of clarity the electrical, sensing, and control elements and connections, including the controller or processor of the heat pump, have been omitted. Starting in the bottom right-hand corner of the Figure, cold liquid refrigerant is forced from a liquid receiver 12, under the action of the compressor 32, along a conduit 14, which passes through the lower portion of the air heat exchanger 20, to a heating expansion valve 16. The conduit 14 has an open end 15 which in use is submerged within liquid refrigerant - so that refrigerant liquid rather than refrigerant vapour is supplied to the conduit 14 from the reservoir 12.

[0064] In the heating expansion valve 16 the refrigerant passes through a small opening, resulting in a reduction in pressure which in turn reduces the boiling point of the refrigerant. Depending on the temperature of the refrigerant at the expansion valve inlet and the pressure of the refrigerant at the expansion valve outlet, a portion of the refrigerant may spontaneously vaporise, resulting in a reduction in temperature of the refrigerant, such that the refrigerant leaves the expansion valve as a mixture of liquid and vapour. From the expansion valve 16 the refrigerant passes into a distributor 18 in which a single input conduit is coupled to a plurality of output conduits each of which supplies a conduit of the air heat exchanger 20.

[0065] A one-way valve 50 is provided in parallel with the heating expansion valve 16, but this is oriented to permit flow from the distributor 18 to the conduit 14 (the direction in which refrigerant flows during the cooling mode of operation) and to prevent flow of refrigerant fromthe conduit 14 to the distributor - so that in heating mode the refrigerant must pass through the heating expansion valve 16 to reach the distributor 18. As the skilled person will understand, the heating expansion valve 16 (like other expansion valves in the heat pump) is controlled by the heat pump’s processor to achieve a target value of refrigerant superheat as appropriate to the prevailing operating conditions.

[0066] A filter-drier 51 may be provided in the flow path to the heating expansion valve 16, and if present this too is bypassed by flow through the one-way valve 50 during cooling and defrosting.

[0067] In one variant, the distributor 18 may include 3 flow paths - a single input conduit 17 with a small internal fixed orifice (not shown), a plurality of output conduits (indicated with reference numeral 19) and an internal bypass conduit. In heating mode, the refrigerant flows through the heating expansion valve 16 to the single input conduit 17 of the distributor 18, through the small internal fixed orifice and out of the plurality of output conduits 19. In heating mode there is no flow via the internal bypass conduit. Expansion of the refrigerant is achieved through the heating expansion valve and fixed orifice. In cooling mode, the refrigerant is able to flow from the plurality of output conduits 19 and out of the internal bypass conduit and through the one-way valve 50, bypassing the internal fixed orifice and heating expansion valve 16 such that the heating expansion valve 16 and internal fixed orifice of the distributor 18 have negligible effect in cooling mode. In another variant, the distributor may be formed without the small internal fixed orifice and the internal bypass conduit.

[0068] The air heat exchanger 20 is shown schematically as comprising just four conduits traversing the air heat exchanger, but in reality, many more such conduits are provided, and each is typically provided with thermally conductive fins to improve heat transfer from the air to the refrigerant inside the conduits. The air heat exchanger 12 includes (or is coupled to) a fan 24 which causes ambient air to move over the air heat exchanger 20.

[0069] In heating mode, refrigerant inside the air heat exchanger 20 is warmed by energy absorbed from the ambient air and this causes it to change state into vapour, and the vapour may itself be further heated by absorbing energy from the air so that the vapour may be superheated. The vapourised refrigerant leaves the air heat exchanger 20 via a collector (or manifold) 26 which feeds a return conduit 28 which supplies a first port, port 1, of a 4- way valve 30. The vapourised refrigerant exits the 4-way valve 30 via port 2 from where it flows to a compressor 32. In the compressor the warmed vapourised refrigerant, which is received at low pressure, is compressed to become high pressure vapour, and in the process of being compressed the refrigerant further increases in temperature. From the compressor 32 the refrigerant passes back through the 4-way valve 30, entering via port 3 and exiting via port 4 which feeds a heatexchanger matrix, not shown, in heating system heat exchanger 34. The heating system heat exchanger 34 may be, as shown here, a heating system heat exchanger in which energy from the hot refrigerant is transferred to water (or some other suitable operating fluid in the case of space heating, although hereinafter we will for simplicity simply refer to water), e.g., for space heating via a central heating system, or to provide hot water for domestic or industrial use. Hot refrigerant enters the heat exchanger 34 at port 36, condenses and then exits as cooled refrigerant at port 38. Water for heating enters the heat exchanger 34 at port 40, on the cooler side of the heat exchanger 34, and exits at port 42 on the hotter side of the heat exchanger 34. Within the heating system heat exchanger 34 the refrigerant condenses from a vapour to a liquid, giving up heat to water in the water circuit of the heat exchanger 34. From port 38 the cooled liquid refrigerant passes to a one-way valve 54 that is oriented to permit flow from the heating system heat exchanger 34 to the liquid reservoir 12. This one way valve 54 therefore serves as a bypass for another expansion valve 44 which is provided to expand refrigerant as it flows from the liquid reservoir 12 towards the heating system heat exchanger 34 in the cooling mode of operation (and hence also during defrosting of the air heat exchanger). In heating mode, the refrigerant is able to flow through the one-way valve 54, bypassing the cooling expansion valve 44 with minimal restriction such that the cooling expansion valve 44 has negligible effect in heating mode. The liquid refrigerant then passes back into the liquid reservoir 12 at which we started the process. It will be appreciated that the heating system heat exchanger 34 may, instead of using the refrigerant to heat water, use the refrigerant to heat air - for example for warm air space heating, but the principal remains the same.

[0070] Figure 1 also includes a further heat exchanger 46 which is fed from the refrigerant conduit 14 via a further expansion valve 48. This further heat exchanger 46, which may also be referred to as a cooling plate, is optional but is preferably provided as a means of cooling (and controlling the temperature of) an electrical inverter (not shown) that powers the compressor and various other of the heat pump’s electrical components and systems. The further heat exchanger 46 may include a heat sink that is thermally coupled to the inverter and optionally other of the heat pump’s electronics and power components. The cooling provided by the further heat exchanger 46 helps to ensure correct operation of the inverter and other electronics, extending their lifetimes, and also captures what would otherwise be waste heat and feeds this into refrigerant which is then fed into the compressor 32 - thus further contributing to the efficiency of the heat pump. The function of, and flow direction through, the inverter cooling expansion valve and inverter cooler heat exchanger is independent of and regardless of operating mode (i.e., heating, cooling, defrost). The inverter cooling expansion valve is again controlled by theprocessor of the heat pump to regulate the refrigerant conditions through the inverter cooler heat exchanger to achieve a desired cooling effect, e.g. a target value of inverter drive temperature.

[0071] If the heat pump of Figure 1 is run in a temperate climate on a cool day (e.g., less than about 10 degrees Celsius) water vapour in the ambient air may condense on the air heat exchanger 20, and then turn to ice. The build-up of ice on the air heat exchanger 20 both restricts the flow of air through the air heat exchanger and also reduces the efficiency of energy transfer from the ambient air to the refrigerant. The heat pump will typically include either a mechanism to detect the build-up of ice, or to detect climatic conditions when ice build-up is to be expected, or have some other mechanism to ensure timely defrosting, and have a processor configured (e.g., programmed) to cause the heat pump to enter a defrost mode as appropriate. Throughout this specification, references to the processor are references to a processor or controller (e.g., a microcontroller or microprocessor) configured or programmed to perform the relevant functions and operations. The processor or controller will typically include, and or be coupled to, a memory arrangement that stores relevant code, instructions, programs, algorithms, and data to enable the processor to perform the relevant operations, functions, methods, and procedures.

[0072] Although not shown in Figure 1, a drip tray is preferably provided beneath the air heat exchanger 20 to collect condensate when the heat pump is running in defrost or heating mode, for the reasons given above.

[0073] At the inlet of the compressor 32 sensors 31 may be provided to measure the temperature and pressure of the refrigerant. Based on values obtained from these sensors 31 the processor or controller of the heat pump is able to determine the state of the refrigerant, and in particular the degree of superheating, at or just upstream of the compressor inlet.

[0074] Figure 2 corresponds to Figure 1, but shows the heat pump operating in a cooling mode (e.g., for cooling premises served by the heat pump), rather than in a heating mode, which is also used as the defrost mode. In the cooling mode the flow of refrigerant is reversed compared to that of the heating mode, and this reversal is achieved by controlling the 4-way valve 30 so that the output from the compressor 32, which is received on port 3, flows to port 1 rather than port 4. So instead of refrigerant heated by the compressor 32 passing next to the heat exchanger 34, it passes to the collector (or manifold) 26 and thence to the air heat exchanger 20. By supplying hot refrigerant to the air heat exchanger, ice build-up can be thawed. Cooled refrigerant leaves the air heat exchanger 20 via the distributor 18 and then passes via one-way bypass valve 50 and the sub-cooler back to the liquid receiver 12.

[0075] From the liquid receiver 12 the expanded refrigerant flows out along conduit 52. The conduit 52 has an open end 53 which in use is submerged within liquid refrigerant - so that refrigerant liquid rather than refrigerant vapour is supplied to conduit 52 from the reservoir 12.Refrigerant from the reservoir 12 flows along conduit 52 through the cooling expansion valve 44, and thence to port 38 of the heating system heat exchanger 34. In cooling mode, there is no flow via the bypass conduit due to the position and orientation of the one-way valve 54.

[0076] Expansion of the refrigerant is achieved through the cooling expansion valve 44. In the expansion valve the refrigerant passes through a small opening, resulting in a reduction in pressure which in turn reduces the boiling point of the refrigerant. Depending on the temperature of the refrigerant at the expansion valve inlet and the pressure of the refrigerant at the expansion valve outlet, a portion of the refrigerant may spontaneously vaporise, resulting in a reduction in temperature of the refrigerant, (such that the refrigerant leaves the expansion valve as a mixture of liquid and vapour). The expansion valve may be controlled by the heat pump’s processor based on data from the pressure and temperature sensors 31 at the input side of the compressor 32.

[0077] Flowing through the heating system heat exchanger 34 the expanded refrigerant absorbs heat from the hot water in the heat exchanger (water flowing, in use, from port 40 to port 42) and is vaporised. Warmed vaporised refrigerant leaves the heat exchanger by port 36 and passes to port 4 of the 4-way valve 30 and exits via port 2. From port 2 of the 4-way valve 30 the refrigerant vapour passes to the compressor 32. It is important that the refrigerant arrives at the compressor in the form of a vapour because the compressor can be damaged if it receives liquid refrigerant. The compressor compresses the refrigerant, further increasing its temperature, and supplies the refrigerant to port 3 of the 4-way switch 30. The refrigerant leaves the 4-way switch via port 1. Because the input side of the compressor 32 is always at a lower pressure when the compressor is running, in cooling mode refrigerant continues to flow through the heat exchanger 46 of the inverter towards the compressor 32, as it did in heating mode, under the control of the processor of the heat pump.

[0078] As the skilled person will be aware, defrosting techniques other than that just described may be used to defrost an air heat exchanger 20 - for example using electrically powered heaters associated with the heat exchanger 20. Such a technique, or others, may be used as alternatives to or in addition to the technique described with reference to Figure 2.

[0079] Having described the operation and main functional components of heat pumps according to examples of aspects of the invention we will now describe examples of a housing for the heat pump that may permit cost reduction both during manufacturing and assembly, also may improve energy efficiency, and may also reduce costs incurred through “wastage” due to damage to the heat pump during transport, storage, and installation.

[0080] Figure 3 A is a three quarter perspective view showing the front and one side of an example of a heat pump 300 according to an aspect of the invention in the new housing. Thehousing may conveniently be formed of a plastics material, for example a material such as medium density polyethylene. The main housing components may each be formed by a moulding process, for example roto-moulding, blow moulding, or injection moulding. The mouldings may be formed as hollow mouldings and the cavities within the mouldings may be filled with a thermal and / or sound-absorbing material such as a foamed plastics material (e.g., polyurethane foam), plastics beads (optionally of foamed plastics), or other suitable material. By thermally insulating the housing the efficiency of the heat pump may be improved. The provision of a plastics outer case or housing, in place of the more conventional sheet metal construction is likely to lead to reduced wastage and expense caused by the damage that sheet metal cases / housings all too commonly suffer in storage, transit and on site before installation. Plastics housings are also less likely to resonate during operation of the heat pump, potentially reducing the heat pump’s noise footprint. Unlike typical sheet metal housings, plastics housing will not corrode under the influence of the wind borne salt that may be experienced in installations near the sea.

[0081] Some air source heat pumps may have been provided with housings made of plastics materials, typically where the heat pump is used for heating a swimming pool, but these are believed to have been based on the use of an internal metal chassis or framework to which the heat pump’s functional parts must be attached prior to the addition of the plastics cover or housing. Such a structure is time consuming and therefore expensive to construct. Conversely, embodiments of the present invention use the housing as a structural element which secures the heat pump’s internal components, some of are secured directly to the housing while others rest on or in supports provided by the plastic housing itself. By moulding (or printing) pipe-retaining features into the housing, pipework of the heat pump may be positioned, supported and held in place by the material of the housing itself. Such pipework holding / supporting features may also be used to provide a jigging function to enable pipework to be held in place prior to connection of adjoining pipe ends (for example by brazing using inductive brazing). Threaded inserts may be moulded (or otherwise included) into portions of the housing during manufacture of the housing, facilitating accurate positioning of components and speedier assembly - which may lead to further cost savings.

[0082] In this example the housing is formed of three main components. In this example the main components are an upper housing part 302, a lower housing part 304, and a front panel 306. In this example the upper housing part 302 houses the axial fan, mounted beneath an exhaust grille or louvre arrangement 308 in an opening 310. The axial fan, which has a motor and fan blades, is preferably mounted with the motor suspended forward of the blades. Positioning thefan motor forward (i.e. downstream) of the fan blades helps to create an unobstructed and efficient converging duct pathway - which helps with efficiency and hence with noise reduction.

[0083] In this example the opening 310 serves as an outlet for the air that the fan induces to flow over the air heat exchanger. In the configuration shown, the air outlet or exhaust 310 is formed in a portion of the upper housing that is angled away from the vertical, so that expelled air is directed at least partially upwardly and not just horizontally (potential benefit of reducing the noise pollution suffered by neighbours). The fan axis is preferably angled between vertical and horizontal directions and positioned to exhaust air in a generally forward direction with an upward component through the exhaust grille 308. As will be seen, the axis of rotation of the fan may be arranged to be inclined about 30 to 60, e.g., 33 to 45 degrees to the horizontal.

[0084] It will be noted that the housing has a curved front wall with the axial fan mounted at an upper portion of the curved front wall. Figure 3B corresponds to figure 3A but additionally illustrates provision of an optional status display indicator 315, here located within the centre of the annulus formed by the exhaust grille 308. That is, the heat pump external unit according to aspects of the invention may further comprise a display mounted on or within an the exhaust grille, optionally coaxially with the grille. The display indicator 315 may be connected to heat pump control logic and configured to indicate operational status, modes, and diagnostic information of the heat pump or heat pump external unit. The function, construction, uses and other aspects of the status display indicator 315 will be described with reference to figures 11 to 11D.

[0085] Figures 4A and 4B are three quarter views from the front and rear respectively, showing the heat pump of figure 3, with the three main components separated, revealing their individual forms. Figures 4a and 4b also reveal the location of the air heat exchanger 20, but apart from this and the fan, which is positioned in the upper part 302 beneath the grille 308, the heat pump’s internal components are not shown. The air heat exchanger 20 may be disposed generally vertically as shown. The air heat exchanger’s conduits or pipework that carry refrigerant may extend generally transversely between the two generally vertically extending sides. The air heat exchanger may also include cooling fins thermally coupled to the refrigerant-carrying conduits and these may be arranged generally transverse to the conduits - for example also extending generally vertically.

[0086] The air heat exchanger be received in a receiving structure, such as a trough or channel, not shown, in the lower housing part 304. The trough or channel may include or communicate with a drip tray arranged to catch condensate that falls from the air heat exchanger 20. The rear face of upper housing part 302 includes an opening, defined by sidewalls 400, which in theassembled state exposes the air heat exchanger, the periphery of the opening framing the air heat exchanger 20 on three sides (as shown) or optionally on all four sides.

[0087] Internally, to either side of the opening, the upper housing part 302 may include a channel 402 into which the air heat exchanger 20 may be received or slotted. Between the mounting location for the air heat exchanger 20 and the air outlet 310 the upper housing includes an air flow conduit or duct 406. The conduit or duct is shaped to guide the air flow that the fan induces through the air heat exchanger the fan angled upwards. The walls of the conduit 406 may together define a generally straight path or may define a curved path, although a more compact arrangement is likely to require the use of a curved path. The conduit 406 forms part of a moulded, generally converging duct of plastics material that curves to direct airflow from a first generally rectangular area across the evaporator past the fan blades to the exhaust grille 308. The fan blades may be positioned at a section of the duct where the cross-sectional area transitions from a generally rectangular shape to a generally circular shape, although such a transition may also be positioned upstream of the fan - so that the duct provides a generally circular bore upstream of the fan.

[0088] In some variants the fan blades may be positioned at a point in the duct where the duct has its smallest cross sectional area.

[0089] In some variants a converging section of the duct may be provided just upstream of the fan blades.

[0090] In some variants the fan blades may be positioned at a point in the duct where the duct converges.

[0091] In some variants the fan blades may be positioned in a converging section of the duct. The area of the opening 310, within which grille 308 is located, may be 10% smaller than the area occupied by the face of the evaporator. That is, the duct of which the conduit forms part may comprise a first generally rectangular area that is occupied by the evaporator, the duct leading to the exhaust grille, the exhaust grille having a second area at least 10 percent smaller than the first area. The converging nature of the duct helps to reduce resonance and hence noise during operation. Noise reduction / minimisation can also be facilitated by an appropriate choice of plastics material for the principal mouldings.

[0092] It will be noted that the evaporator lies generally in a plane and the axis of rotation of the fan is tilted with respect to a normal to the plane. In particular, the fan’s axis of rotation is tilted at least 25 degrees (e.g. 30 to 60 degrees) away from a normal to the plane of the evaporator. Moreover, in the illustrated embodiment, the evaporator is disposed generally vertically and the fan’s axis of rotation is angled between 0 and 60 degrees from the vertical. Such arrangements permit compact construction while also helping to reduce the effects of noise pollution from theheat pump external unit’s exhaust. Orientating the exhaust in this way also provides a convenient support surface for a an optional status display indicator 315 with near certainty that the display indicator will be visible from a distance of at least several metres.

[0093] Figures 4C and 4D correspond generally to Figures 4A and 4B but additionally show the fan assembly 408 removed from within the upper housing part 302. The fan assembly 408 includes the fan and its drive motor mounted inside a casing that is mounted within, and secured to, the upper housing part 302 for example using screws fastened from within the upper housing part. As shown, the fan assembly casing includes on the exhaust side a cylindrical sleeve portion 410, sized to fit snuggly within the opening 310, which at its inner end abuts against a laterally extending flange 412 that mates to the underside of the upper housing part 302. The fan motor is centrally located in the inner sleeve portion, behind the stationary “boss” 312 that can be seen externally in the middle of the fan grille 308. The fan is largely contained within the enlarged inner end 414 of the fan assembly 408 where the casing widens.

[0094] It will be noted that the housing has a substantially planar, substantially vertical rear wall section in which a generally planar evaporator is located, a curved front wall, and an axial fan mounted at an upper portion of the curved front wall.

[0095] In an alternative arrangement the fan assembly may be arranged to be mounted and demounted from the upper housing from outside the housing, so that the upper housing does not first need to be removed or “opened” before installing or removing the fan. Thus, rather the enlarged flange portion 412 on the entry side of the fan assembly could be dispensed with and there may be no sleeve 41O.Figure 5 shows in greater detail the lower housing part 304. Figure 5A is a three quarter perspective view from the back left of the heat pump from which can clearly be seen the recess 500 within which the lower end of the air heat exchanger is received. The base of this recess may be in the form of a drip tray 502, as shown. The drip tray is provided with a drainage outlet 504 through which gathered condensate can escape. The floor of the drip tray to either side (left and right when viewed from the rear of the heat pump) preferably slopes downwards to the drainage outlet 504. To the front, back, and sides of the drip tray 502 a ledge or shelf 506 is provided, onto which the lower end of the air heat exchanger is placed during assembly of the heat pump. At either end of the recess 500 are upstanding flanges 508 spaced to accommodate the air heat exchanger snugly therebetween. A back wall 510 of the recess 500 may provide the lower edge 512 of the opening (otherwise defined by sides 400 of the upper housing part) through which air is, in use, sucked into the air heat exchanger by the fan. On the opposite, innermost, side of the recess 500 the lower housing part provides an air guiding feature in the form of a sloping surface 514 which is designed to match with a corresponding sloping surface, in the upper housing part 304, that in part defines the air flow conduit 406. Togetherthese sloping surfaces are designed to guide air flow smoothly from the inner side of the air heat exchanger to the fan to reduce energy wastage and noise generation. The two sloping surfaces are preferably formed integrally with the upper and lower housing parts during the moulding (or printing) of these components. In order to facilitate manufacture of the housing parts, the sloping surfaces may each comprise multiple generally flat surfaces that angle together to define the required surface shape - rather than, for example, being in the form of curved arcuate shapes 514. This may help to reduce the cost of mould making and also possibly simplify the moulding process. Of course a suitable streamlined air flow conduit may be formed from the sloping surfaces of the upper and lower housing parts can be designed and made using curved / arcuate surface shapes albeit possibly with a consequent increased cost of mould creation. If the housing parts are to be made by printing the use of curved / arcuate surfaces may be accommodated without significant cost increase. Figures 5A and 5B show an example in which the sloping surface 514 is defined by three sections, with an inner section flanked on either side by a side section, although of course more or fewer sections could be used. More detail about the possible configuration of the air flow conduit 406 will be discussed with reference to Figure 8.

[0096] A ledge 516 may be provided at the upper edge of the sloping surface 514, and an upstanding flange 518 may be provided around at least a portion of the ledge 516, to co-operate with corresponding features on the upper housing part. These co-operating parts, which may take other forms, enable the upper and lower housing parts to abut in such a way that there is little disruption of air flow through the composite air flow conduit, and preferably also in such a way that an effective seal can be provided between, on the one hand, the compartment that will contain the air heat exchanger and the fan, and on the other the compartment that will respectively contain the heat pump’s electronics and the compartment that will contain the compressor and its associated refrigerant pipework. Preferably a substantially gas-tight (or at least weather tight) seal is provided between the first compartment containing the compressor and the second compartment containing the fan and air heat exchanger, and between the second compartment and the third compartment containing the heat pump’s electronics, without the need to use an intermediate sealing component between the upper and lower housing parts. But in practice it may be necessary to use a suitable sealing strip or sealant in order to achieve a sufficiently good seal(e.g. a weather tight seal).

[0097] In general we want the housing to be weather tight, and care in design and assembly, particularly with respect to elements 516, 518, 534, 550, 552, (and 602 and 604 which will be mentioned later) to provide weather tight seals where surfaces meet is desirable.

[0098] Other features may be provided to enable the upper and lower housing parts to couple together and to provide structural stability to the assembled housing. One such feature, shown inFigures 5 A and 5B, is an upstanding frame portion 520 provided in what will become the compartment containing the compressor. The frame portion may include at its upper end a socket 522 to receive a corresponding boss that is formed in a lower surface of the upper housing part. In the example shown, the upper end of the frame part 520, and the socket 522, are each square in section, to mate with a corresponding square section boss on the upper housing part. The socket may also be provided with one or more pairs of holes 524 to receive a bolt or the like which may pass through the paired holes and through a corresponding hole or holes in the boss on the upper housing part. The bolt or bolts being used to secure the upper and lower housing parts together.

[0099] Figure 5A shows a pair of openings 526 and 528 on the back face of the heat pump. Opening 526 communicates with what will become the chamber that houses the processor and other electronics (e.g. the inverter) of the heat pump, and is provided to accommodate electrical (and potentially optical) cables for powering the heat pump and for providing communication and control features. Conversely, opening 528 communicates with what will become the chamber that houses the compressor and the refrigerant and water pipework, to accommodate the pipes (e.g. pair of flow and return) by means of which the heat pump will be connected to a heating installation. The opening 528 preferably includes suitable sized and located channels 530 to accommodate the relevant pipework, and these channels may each include anti -rotation features (e.g. formations configured to mate to 4 sides of a 6-sided union or connector) by means of which the unions (or bodies) of compression (or other) pipework fittings may be held in place to facilitate installation. These anti-rotation features may again be formed in situ during the moulding or printing process, saving further manufacturing and labour costs.

[0100] Cover plates may be provided for each of the openings 526 and 528. Cover plate 526 may be provided with suitable glands for sealing around wiring conduit, and wiring, as appropriate to provide a weatherproof seal and to prevent ingress of rodents and other pests and also to protect the cables / pipework from human interference. The cover plate 528 for pipework may include factory-made circular openings for the male union fittings to poke through.

[0101] To the left of figure 5B can be seen an upstanding wall 532 at the top of which are channels 534 through which will pass the pipes which carry refrigerant to and from the evaporator 20 and wiring to the sensors and valve(s) within the evaporator. Also to the left of the figure a zone 535 is marked out to receive the compressor 32 and the liquid receiver 12. This zone 535 may be distinguished from the surrounding portions of the upper face (or floor) of the lower housing part 304, for example by having a flat and level base whereas the surrounding portions (or the rest) of the upper face may slope downwards towards the leading edge of the lower housing part. - a feature that is useful for ventilating the refrigerant and electricalchambers in the event of refrigerant leakage, particularly if a flammable refrigerant is being used. The zone 535 preferably includes captive nuts 536 / 537 or other fastening features to permit the ready securing of the compressor and the liquid reservoir to the lower housing part.

[0102] To the right of the zone 535 is the frame portion 520 which includes at its lower front edge a flange 538 that is spaced from the floor surface of the lower housing part to accommodate water and refrigerant pipes. The upper surface provides a support or abutment surface 540 for the condenser or water heat exchanger 34 as will be seen in Figures 8 to 10.

[0103] Somewhat to the right of the frame portion one or more features 542, 543 such as grooves or flanges, may be provided to accommodate the cooling plate 46 on which the inverter will be mounted. The grooves or other features 542, 543, may be provided in the back wall and floor of the lower housing part. The cooling plate may form a partition that will separate the two compartments 544 and 546 that will house on the one hand the compressor and other refrigerant circuit, and on the other the heat pump’s processor and other electronics.

[0104] Figure 5C is another perspective view showing the base part 304 with the front panel 306 in place, viewed from above and to the right. As can be seen, the front panel 306 has at its upper edge a structure 550 to mate with the corresponding surface of a lower edge of the upper housing part 302. The structure preferably includes one or more features to aid alignment of the two parts during assembly and these alignment features, or others, preferably also provide an effective seal between the upper part and the lower part. For example the structure 550 may comprise a ledge and one or more upstanding flanges. At its back edge on either side the front panel 306 may couple at 552 with corresponding surfaces on front edges of the base part 304, again preferably to provide a substantially gas tight (or at least weather tight) seal (with or without the use of intermediate sealing members, but preferably without). Adjacent portions 554 of the back edge of the front panel 306 are also designed to mate with corresponding edges / surfaces of the upper housing part, again preferably providing a substantially gas tight (or at least weather tight) seal.

[0105] Figures 6A and 6B are perspective views showing the upper housing part 304 with the fan assembly removed. Figure 6A shows a view looking into the aperture 310 into which the fan assembly is mounted. The aperture 301 opens into a generally cylindrical space which, once the fan assembly is installed, surrounds the cylindrical housing part 410. In the side wall that defines this space are formed channels 600 which serve to accommodate and guide the wiring that feeds the motor (and motor controller) of the fan assembly.

[0106] Figure 6B shows the generally vertical mating surface 602 that will abut the portions 554 of the back edge of the front panel 306, and the generally horizontal mating surface 604 that will abut with the upper edge 550 of the front panel, when the housing is assembled. The upperhousing part includes a floor (behind sloping surface 406, and between the two horizontal mating surfaces 604) which serves as a roof to the compartment housing the compressor and the compartment housing the processor and other electronics. This helps to keep heat within these compartments so that it can be harvested using the cold plate 46, as will later be described.

[0107] Figures 7A and 7B show the front panel 306 from behind and from in front. It will be appreciated that rather than using a single housing element to cover the fronts and the sides of the chambers that house the compressor and the electronics it would be possible to provide one or more separate covers for each of these chambers. The use of a one piece cover, generally as shown, does have the advantages of reducing parts count and also eliminating the need to seal more joints between panels or housing elements. The boss that can be seen on the rear face of the cover is an artefact of the moulding process used.

[0108] Figure 8A is a vertical cross section through the centre line that bisects the front and rear faces of the housing. The fan motor 800 can be seen as part of the fan assembly 408, along with the fan 802. The condenser or heating heat exchanger 34 can be seen being supported by the abutment surface 540 on the flange 538. The drip tray 804 to collect condensate that falls from the air heat exchanger 20 is also shown.

[0109] Figure 8A also illustrates the smooth and largely unobstructed air flow path between the evaporator 20 and the fan, due to the fact that the fan is mounted to and carried by the upper housing cover 302 and that no chassis needs to be provided between the evaporator and the fan. Indeed the fan is preferably entirely supported structurally by the upper housing. The contouring of the air flow conduit 406, formed between the housing base part 304 and the housing upper part 306, which may contribute to improving efficiency and reducing noise generation, can clearly be seen in the figure. The fan assembly 408 may be in the form of a “cassette” that fits snugly between the inner walls provided in the opening 310, the opening 310 typically defining the ’’throat” of the duct which carries air past the evaporator and out through the exhaust grille -the throat being the part of the duct that has the smallest cross sectional area. The duct may converge substantially continuously from the evaporator to the throat portion. It will be appreciated that the fan assembly may include a generally cylindrical outer wall, which in use is received in what may generally be a cylindrical passage leading from within the housing to opening 310. If the fan assembly does have such a generally cylindrical outer wall, the throat of the duct will generally be defined in fact by the bore defined by the inner sides of that cylindrical outer wall. In this way the fan blades can be positioned at a point in the duct where the duct has its smallest cross sectional area and hence where the air flow velocity is highest in use. The fan blades may also be positioned at a point in the duct where the duct converges, that is the duct may converge just upstream of the position of the fan assembly. The fan blades may bepositioned in a converging section of the duct, for example the duct cross section may reduce between the upstream side of the fan and the downstream side of the fan (e.g. the fan “cassette” may have a tapering conical inner bore - whether or not the outer sidewall is cylindrical).

[0110] The fan assembly (e.g. in particular the blades) may be positioned at a section of the duct where the cross-sectional area transitions from a generally rectangular shape to a generally circular shape, although such a transition may also be positioned upstream of the fan - so that the duct provides a generally circular bore upstream of the fan.

[0111] The fan assembly 408 may be provided just downstream of a converging section of the duct (e.g. such a converging section may be provided just upstream of the fan blades).

[0112] The lower end of the evaporator 20 may include the sub-cooler 100 through which refrigerant is arranged to pass on route from the liquid receiver 12 to the heating expansion valve 16. The sub-cooler may consist of just a few vertically displaced rows of conduit (say one to four), and all or most of these may be shielded from the air flow induced by operation of the fan by an upstand 806 formed as part of the base part 304. This upstand may be on the upstream or downstream (i.e. left or right) of the sub-cooler as viewed in Figure 8A, or there may be a formation on both sides.

[0113] A peg or boss 808 extending downwardly from the lower surface of the upper housing part 302 is shown as engaging with the socket 522 on the integrally formed frame portion 520. A bolt or screw may be used to secure the boss 808 within the socket 522, thereby securing the upper and lower housing parts. The previously mentioned floor 80 of the upper housing part, that provides a roof or ceiling to the two compartments below is also shown.

[0114] Note that in Figures 8 and 10 the evaporator 20 is represented as having two featureless surfaces separated by a feature rich region, but this is merely a CAD artefact and it is without technical significance.

[0115] Figure 8B is a near three quarter view from the left front, with the front cover removed, of the heat pump that is partially populated with its internal components. The compressor 30 can be seen secured to the floor of the lower housing part. To the right of the compressor is the fluid reservoir 12 also secured to the floor of the lower housing part 304. To the right of the fluid reservoir 12 is the condenser 12 supported on the flange 538 that forms part of the lower housing part. The four way valve arrangement 32 is carried by the metal pipework that carries refrigerant and which may be clipped into place in features moulded or printed into the lower housing part. Also shown is the optional, but preferred, pump 810 that serves to pump heating fluid through the condenser 34.

[0116] To the right of the condenser 34 is the cold plate 46 to which is attached the heat pump’s electrical inverter. The cold plate 46 may be fed with refrigerant taken from the fluid reservoir12, the refrigerant passing through expansion valve 48 before entering the cold plate. The expansion valve 48 may be controlled based upon the temperature of an IGBT in the inverter, for example targeting an IGBT temperature of 25C. Although not shown in the drawings, a cover may be provided over the cold plate and a fan provided to draw air in from towards the top of the chamber housing the compressor and to expel the air from around the lower end of the cold plate - in this way harvesting energy from warm air in the chamber housing the compressor, as well as recovering energy from the inverter. Warmed refrigerant from the cold plate then passes back into the inlet side of the compressor 32.

[0117] The thermal insulation properties of the plastics housing, which may be double skinned (hollow) and which may include insulation between the outer and inner skins, mean that harvesting heat internally in this way may make a worthwhile contribution to improving the efficiency of the heat pump. It also means that the pipework within the heat pump does not need to be separately lagged or insulated, further saving construction labour costs.

[0118] The lower housing part 304 preferably includes one or more grooves (e.g. a groove in the generally vertical wall and another in the floor) to receive and hold the cold plate 46, again doing away with the need for an internal chassis. The processor and other electronics of the heat pump may be located in the chamber to the right of the cold plate 46. The cold plate 46 acts as a barrier to separate the compartment housing the electronics from the compartment housing the compressor and most other refrigerant-handling components.

[0119] Preferably the cold plate, the lower housing part 304 and the front cover 306 are so configured that an effective gas seal is provided between the chamber containing the electronics and that containing the compressor. If the refrigerant is flammable it is useful to have such a substantially gas tight (some leakage of refrigerant gas into the electronics chamber may be permitted by the relevant technical standards, the acceptable threshold depending upon the explosion risk posed by the electronics) barrier between the two chambers because it can reduce the need to ensure that all the electronics / electrics in the second chamber are certified flame proof. If the refrigerant is flammable it may also be necessary to provide some form of ventilation for the chamber that houses the compressor and the refrigerant circuits, but otherwise it may be preferable to ensure that the chamber is gas tight or at least weather tight (and draft proof) to reduce energy losses.

[0120] The pipework that runs close to the floor of the compartment housing the compressor may clip into place in features integrally formed (moulded or printed) in the plastics material of the lower housing part. In this way the lower housing may act as a jig for use when connecting the various refrigerant and water pipes, for example by soldering or brazing. In addition, moreanti-turn features may be provided to hold captive threaded fasteners / coupling components / valves, etc. to facilitate speedier assembly of the heat pump.

[0121] An expansion vessel for the heating circuit (pumped by pump 810) may be located in the gap between the condenser and the cooling plate 46.

[0122] Figure 9 is a plan view looking down on the lower housing part and front cover after the heat pump has been assembled. Here we see the PCB 900 that carries the heat pump’s processor, and coupled to this a wiring loom or harness 902 that is wrapped for protection and that passes from the chamber that houses the processor to the chamber that houses the compressor 30.

[0123] Suitable gas sealing (and sealing to provide weather tightness) precautions may be implemented, as just discussed. The inverter 903is mounted to the cold plate 46 whose temperature is regulated to ensure optimum performance of the inverter. The temperature of the processor may also be monitored and using by the processor in controlling operation of the heat pump and the flow of refrigerant through the cold plate 46 in order to prevent thermal damage to the processor.

[0124] Figure 10 corresponds generally to Figure 9, but shows the heat pump after assembly but with the front cover and upper housing portion removed. The space between the condenser 34 and the cold plate 46, to receive the expansion vessel for the heating system can clearly be seen. Element 1000 is a cover for the pipework-receiving opening 528.

[0125] Constructing a heat pump according to aspects of the invention starts with a bare lower housing part 304 which is then populated with the compressor and fluid reservoir, which are bolted to the floor of the lower housing part for example using captive nuts incorporated during the moulding or printing of the lower housing part. The condenser may be mounted on the flange 538 on the integrally formed frame portion, and may be held in place with a strap that secures the condenser to the lower housing part. As previously mentioned, pipework to carry refrigerant and pipework to carry water may be clipped into place in formations pre-formed on the floor of the lower housing part and elsewhere. The evaporator may be slotted into place in the receiving recess 500, and the pipework connected. The inverter may be mounted to the cooling plate 46, and the assembly then inserted into the receiving grooves (or other features) 542, 543. The electronics may then be mounted to the body of the inverter, and the wiring loom connected to the various valves, sensors, etc. The fan assembly, which may be pre-wired with cabling for fan power and control (e.g. MODBUS), is mounted to the upper housing part 302. Once assembly and charging of the components on the lower housing part is completed the wiring from the fan is connected to the electronics and power feed on the lower housing part, and the upper housing part is placed on the lower housing part and the two connected. The front cover may then be put in place, with the heat pump awaiting despatch and installation. Such an assembly process may be significantly simpler and faster than with heat pumps of conventional construction.Figure 11 is a schematic showing a typical domestic heat pump installation 1100 for premises in the form of a house 1102, according to an aspect of the invention. The heat pump, in this case an air source heat pump, includes a heat pump external unit 1104 which is coupled, by pipework 1105, to a space heating (and optionally cooling) arrangement and a domestic hot water system, together indicated as arrangement 1106. The heat pump external unit 1104 comprises a housing that encases and protects the main components of the system. The housing is designed to withstand environmental conditions and provide structural support for the components of the heat pump. Inside the housing, the heat pump may include an evaporator, a condenser integrated with a heat exchanger, a fan motor, a fan, a compressor, and an electrical drive unit that controls both the fan motor and the compressor. The evaporator absorbs heat from the surrounding environment (air or another heat source), facilitating the evaporation of a refrigerant that circulates through the system. Positioned in the airflow path, the evaporator serves to maximize the efficiency of heat absorption. Downstream from the evaporator, the condenser with its heat exchanger releases the absorbed heat. The heat exchanger transfers heat to either the indoor or outdoor environment, depending on whether the heat pump is in heating or cooling mode. The fan motor drives the fan, which is mounted adjacent to the condenser, ensuring airflow across the heat exchanger to enhance heat dissipation.

[0126] The compressor increases the pressure and temperature of the refrigerant before it enters the condenser. The electrical drive unit supplies power to both the fan motor and the compressor, managing their operation based on control signals from the system's control logic.

[0127] The control logic is connected to the drive unit and oversees the operation of the heat pump, including regulating fan speed, compressor activity, and monitoring system performance through various sensors. It is also linked to a remote indoor control unit 1110, which allows for the setting and reading of operational parameters and modes. This control unit 1110 enables users or technicians to adjust the system and monitor its status without needing physical access to the external unit. That is, the heat pump external unit may further comprise control logic coupled to an indoor control unit, the indoor control unit being configured to allow users to set operational parameters and modes and monitor the status of the external unit remotely.

[0128] The heat pump external unit 1104 includes a compressor and an evaporator, not shown, which during a heating mode of operation together extract energy from ambient air, the energy then being supplied to the heating and / or hot water supply parts of the arrangement 1106. The heat pump external unit 1104 also includes a processor 1108 (and associated control logic) to control the functioning of the heat pump. The processor 1108 is arranged to communicate with a control panel 1110 located within the premises, by means of which occupants of the premises 1102 can control the heat pump. That is, the heat pump external unit includes control logic forcontrolling the fan and a compressor connected to the evaporator, the control logic being arranged to operate with the control panel to display information on the operation of the unit and to set one or more parameters relating thereto.

[0129] Additionally, the heat pump may feature a display 315 which may be mounted coaxially within the grille 308 of the fan. The display 315 is connected to the control logic and provides visual indicators of the unit’s status, operational mode, and diagnostic information. This display 315 may be illuminated and configured to show various patterns or colours, enhancing visibility in low-light conditions and improving the user’s ability to determine system status at a glance. Also, the arrangement of these components optimizes the airflow through the evaporator and condenser and maximizes the efficiency of heat exchange. The control logic, in combination with the indoor control unit and the (coaxial) display, ensures that the heat pump operates efficiently and that its status is easily discernible, even from a distance.

[0130] The control panel 1110 may include or be associated with a display 315 by means of which status, settings, and optionally other operational parameters may be displayed. The control panel may incorporate a thermostat for setting a threshold temperature for activating the heating, and / or may be coupled to one or more thermostats each of which permits the setting of a threshold temperature for a different room or zone within the premises. The heat pump external unit 1104 may include at least one RF transceiver 1110, and such a transceiver may be used for bidirectional communication with the control panel 1110, additionally or alternatively there may be a wired connection between the two devices. One or more of the transceivers 1110 may be used to receive weather information and / or power tariff information, either or both of which may be used by the processor 1108 in controlling and optionally optimising the performance and / or operation of the heat pump installation. The heat pump external unit 1104 also has a fan, which may be located at or adjacent an upper or front or angled face for exhausting air from the unit. A generally circular cover grille 308, may be provided, to prevent interference with the fan, and for the passage of air exhausted from the unit by the fan. The cover grille is typically in the form of an annulus so configured that exhaust air passes through the annulus but not through a “blind” central portion. The location of the central portion may correspond generally with the location of the motor that drives the fan, the rotational axis of the fan also extending through the central portion. The heat pump external unit further comprises a status display indicator 115 that may be located at, on or adjacent the upper or front or angled face that includes the vent opening for the exhaust from the fan as will be described in more detail later. Optionally the status display indicator 115 is located within the central portion of the cover grille 308. In this position the status display indicator 115 may overlie the fan’s drive motor while leaving the annular grille part substantially unobstructed. An advantage of positioning the status display indicator 115 inthis way is that, if the heat pump external unit is correctly situated, the exhaust grille will be unobstructed and facing towards an open space of some kind - so that the exhaust from the unit is able to dissipate without significant restriction - which in turn means that there is a high likelihood that the status display indicator will be unobscured and visible from at least a few metres distance, and typically from as far as away as 5 to 10 metres. This is advantageous in that it is possible to carry out status checks without the need to visit the external unit, and that awareness of the heat pump’s status can be maintained without special effort, and in particular without the need to visit and inspect the external unit.

[0131] Figure 11A illustrates an arrangement of the annular grille 308 located in an aperture 1120 in a panel 1122 of the cabinet of the external unit 1104. The centre portion 1124 of the grille 308 underlies the status display indicator 115. The position of the fan 1126 behind the grille 308 is shown schematically in outline - although in reality an aerodynamically efficient fan blade design is chosen both to improve the overall efficiency of the heat pump, but also to help minimise the sonic footprint of the heat pump. The axis of rotation of the fan is shown nominally as 1128. It will be noticed that this axis lies within the area occupied by the status display indicator 115.

[0132] Figure 1 IB shows schematically, in partial cross section, an arrangement of a status display indicator 115 and its relationship with the fan, motor, and adjacent housing portions of a heat pump external unit, for example as shown in figure 11A. The axial fan comprises a central hub or boss 1126 from which extend fan blades 1130. The fan hub 1126 may be coupled to a drive shaft 1132 of a fan motor 1134 - although as will be appreciated the motor may be provided within the fan hub rather than being coupled to the latter via a drive shaft. Other configurations are also possible, of course. The rotational axis of the fan is indicated by the broken line 1133. As previously mentioned, the fan may be received in aperture 1120 of the housing 1122 - although it may also be located upstream of the opening rather than being located within the opening 1120 proper. Covering the opening 1120, and the fan blades 1130 is grille 308. The grille may be annular, for example as shown in Figure 1 la, with a central region 144 which does not serve as an exhaust for air ejected from the housing by the fan. In the arrangement shown, the central region 1144 within the centre of the annular grille 308 supports the status display indicator 115. The central region 1144 may also house a bearing to support the shaft 1132.

[0133] The fan may be supported by the grille arrangement that comprises the louvred part 308 and the central region 1144. The grill arrangement may include suitable strengthening ribs by means of which the central region 1144 and the fan are supported by the housing part 1122.

[0134] In the arrangement shown, the status display indicator 115 comprises a layered structure.A first layer 1150 may comprise a plurality of addressable illumination elements. This first layer is overlaid by a second layer 1152 which comprises a diffuser and / or an image or logo (e.g. a printed, etched, moulded, or cast). The diffuser and / or the image / logo at least partially obscures or blurs the individual addressable illumination elements. The diffuser may be translucent, for example a translucent plastics material. The addressable elements are controllable (under control of the heat pump’s processor) to illuminate the diffuser and / or printed image or log. The effect of this may be to render the fan exhaust visible in darkness. The addressable illumination elements may include at least one element of selectable colour and / or the plurality of addressable illumination elements may include elements of multiple different colours. The intensity of either or both of illumination (brightness) and colour (saturation) of at least some of the plurality of addressable illumination elements may be variable in multiple steps or substantially continuously. The second layer may be overlaid by a third, protective layer, 1154 through which light from the first layer may pass when the latter is illuminated, although the presence of this layer is optional.

[0135] Figure 11C illustrates schematically another example of a status display indicator 115, wherein the display comprises a central element 1160, a first radial array of elements 1162, and a second outer array 1164 of radial elements. The central element 1160 may comprise a plurality of individually addressable illumination elements whose colour (e.g. hue and optionally saturation), and / or illumination (e.g. light intensity) can be controlled by control logic of the heat pump. Likewise, each of the elements of the two arrays 1162 and 1164 may comprise plurality of individually addressable illumination elements whose colour (e.g. hue and optionally saturation), and / or illumination (e.g. light intensity) can be controlled by control logic of the heat pump.

[0136] Figure 1 ID illustrates schematically a further example of a status display indicator 115, wherein the display comprises a plurality of central elements 1170, a first radial array of elements 1172, and a second outer array 1174 of radial elements. Each of the plurality of central elements 1170 may comprise a plurality of individually addressable illumination elements whose colour (e.g. hue and optionally saturation), and / or illumination (e.g. light intensity) can be controlled by control logic of the heat pump. Likewise, each of the elements of the two arrays 1172 and 1174 may comprise plurality of individually addressable illumination elements whose colour (e.g. hue and optionally saturation), and / or illumination (e.g. light intensity) can be controlled by control logic of the heat pump.

[0137] Preferably the heat pump (e.g. the heat pump external unit) includes control logic (e.g. which may be run on the processor of the heat pump external unit) which is controllable to send one of a plurality of static patterns or animation sequences to control the addressable illumination elements based on both a status of operation of the heat pump external unit andbased on one or more stored configuration parameters so that different states of operation of the device are discernible from observation of the collective arrangement of the addressable illumination elements.

[0138] Although the described embodiments have focused on a particular housing design in which the ceilings of the refrigerant and electrics chambers are provided by a floor of the upper housing part, it should be appreciated that these ceilings could be provided instead by the lower housing part, as could the majority or the whole of the lower surface of the airflow path (instead of this being split between the upper and lower housing parts). That is, it is not necessary for both housing parts to contribute to both the refrigerant chamber and the electronics chamber. The upper housing part could still contain and support the fan and its motor, and cap off the evaporator.

Claims

Claims1. A heat pump external unit contained within a housing, the heat pump external unit including an evaporator and a motor driven axial fan with blades to move ambient air over the heat exchanger, wherein:the evaporator lies generally in a plane and the axis of rotation of the fan is tilted with respect to a normal to the plane;the housing provides a moulded, generally converging duct of plastics material curving and directing airflow from a first generally rectangular area across the evaporator past the fan blades to the exhaust grille, the exhaust grille defining a second area at least 10 percent smaller than the first area;the duct being substantially devoid of obstructions between the evaporator and the fan blades, and the duct being shaped to draw air effectively from across the area of the evaporator.

2. The heat pump external unit as claimed in claim 1, wherein the axis of rotation is tilted at least 25 degrees (e.g. 30 to 60 degrees) away from a normal to the plane of the evaporator.

3. The heat pump external unit as claimed in claim 1 or claim 2, wherein the evaporator is disposed generally vertically and the fan’s axis of rotation is angled between 0 and 60 degrees from the vertical.

4. The heat pump external unit as claimed in any one of the preceding claims, wherein the housing is a plastics housing, and the evaporator and the motor driven fan are mounted to and carried by the housing without the use of a metal chassis.

5. The heat pump external unit as claimed in claim 4, wherein the fan motor is supported by the exhaust grille.

6. The heat pump external unit as claimed in any one of the preceding claims, wherein the fan blades are positioned at a point in the duct where the duct has its smallest cross sectional area.

7. The heat pump external unit as claimed in any one of claims 1 to 6, wherein a converging section of the duct is provided just upstream of the fan blades.

8. The heat pump external unit as claimed in any one of the preceding claims, wherein the fan blades are positioned at a point in the duct where the duct converges.

9. The heat pump external unit as claimed in any one of the preceding claims, wherein the fan blades are positioned in a converging section of the duct.

10. The heat pump external unit as claimed in any one of the preceding claims, wherein the fan motor is located between the fan blades and the exhaust grille.

11. The heat pump external unit as claimed in any one of the preceding claims, wherein the housing comprises a substantially planar, substantially vertical rear wall section in which the evaporator is located, and a curved front wall, the axial fan being mounted at an upper portion of the curved front wall.

12. The heat pump external unit as claimed in any one of the preceding claims, wherein the plastics material of the duct is selected so as to absorb noise and reduce vibration.

13. The heat pump external unit as claimed in any one of the preceding claims, wherein the angle of the fan’s rotational axis relative to the vertical is between 30 and 60 degrees.

14. The heat pump external unit as claimed in any one of the preceding claims, wherein the duct is configured to have a converging shape that reduces noise resonances during operation.

15. The heat pump external unit as claimed in any one of the preceding claims, wherein the fan blades are positioned at a section of the duct where the cross-sectional area transitions from a generally rectangular shape to a generally circular shape.

16. The heat pump external unit as claimed in any one of the preceding claims, further comprising a display mounted coaxially on the exhaust grille, wherein the display is connected to the control logic and configured to indicate operational status, modes, and diagnostic information.

17. The heat pump external unit as claimed in any one of the preceding claims, further comprising control logic coupled to an indoor control unit, the indoor control unit beingconfigured to allow users to set operational parameters and modes and monitor the status of the external unit remotely.

18. The heat pump external unit as claimed in any one of the preceding claims, wherein the fan motor is positioned forward of the fan blades so as to create an unobstructed and efficient converging duct pathway.

19. The heat pump external unit as claimed in any one of the preceding claims, wherein the housing comprises a base portion and an upper portion that together define, at least in part, a first chamber to contain the compressor, a second chamber to contain the evaporator and the fan, and the base portion and the upper portion each being a moulded or printed plastics component.

20. The heat pump external unit as claimed in claim 19, wherein the heat pump comprises a processor to control the operation of the heat pump, the processor being accommodated within a third chamber that is defined at least in part by the base portion and optionally the upper portion.

21. The heat pump external unit as claimed in claim 20, wherein the third chamber is in part defined by a liquid cooled heat transfer plate that is thermally coupled to an inverter that is used to power electronics of the heat pump.

22. The heat pump external unit as claimed in claims 20 or claim 21, further comprising at least one cover for one or both of second and third chambers to provide access to components or systems within the relevant chamber.

23. The heat pump external unit as claimed in claim 22, wherein the or each cover is a moulded or printed plastics component24. The heat pump external unit as claimed in any one of claims 19 to 23, wherein the fan and its motor are carried by the housing upper portion.

25. The heat pump external unit as claimed in claim 24, wherein the housing upper portion is demountable from the base portion to provide access to the compressor and to the evaporator.

26. The heat pump external unit as claimed in any one of claims 19 to 25, wherein the duct is defined at least in part by the upper portion.

27. The heat pump external unit as claimed in claim 26, wherein the duct is at least partly defined by the base portion.

28. The heat pump external unit as claimed in any one of claims 19 to 27, wherein the evaporator is received within a recess or other receiving arrangement within the base portion.

29. The heat pump external unit as claimed in claim 28 as dependent on claim 27, wherein the base portion includes an air flow guiding surface that flares at an angle away from the recess and towards the upper portion.

30. The heat pump external unit as claimed in claim 29, wherein the upper portion includes an air flow guiding surface that together with the air flow guiding surface of the base part defines a wall of the duct.

31. The heat pump external unit as claimed in any one of claims 19 to 30 wherein the base portion and the upper portion are configured to couple together to define the second chamber.

32. The heat pump external unit as claimed in any one of claims 19 to 31, wherein the base portion includes features to receive pipework to carry refrigerant, wherein optionally the included features are moulded-in features.

33. The heat pump external unit as claimed in any one of claims 19 to 32 wherein the base portion includes anti-rotation features to hold captive and prevent the rotation of threaded pipework couplings, unions or components, wherein optionally the included anti-rotation features are moulded-in features.

34. The heat pump external unit as claimed in any one of claims 19 to 33, wherein the upper housing portion is in the form of a hollow plastics moulding containing thermal and / or noise insulation, and optionally the thermal and / or noise insulation is a foamed plastics material.

35. The heat pump external unit as claimed in claim 34, wherein the foamed plastics material has been foamed in situ.

36. The heat pump external unit as claimed in claim 34, wherein the foamed plastics material is in the form of beads or the like.

37. The heat pump external unit as claimed in any one of claims 19 to 36, wherein the base portion includes a recess to receive a lower end of the air heat exchanger.

38. The heat pump external unit as claimed in claim 1, wherein the housing is a plastics housing that is structural and comprises a base portion and an upper portion that together support and contain the evaporator, a compressor of the heat pump and the motor driven fan without reliance on an internal metal chassis.

39. The heat pump external unit as claimed in claim 1, wherein the housing is a plastics housing that is structural and comprises a base portion, to which a compressor of the heat pump is secured, and an upper portion which carries the fan and its drive motor, the evaporator being supported in a groove or recess in the base portion and located between the upper portion and the base portion;the base portion and the upper portion together defining a first chamber to contain the evaporator and the fan, the first chamber forming part of the duct to guide air flow from the evaporator to the fan, the duct being defined at least in part by the upper portion.

40. The heat pump external unit as claimed in claim 39, wherein the duct is at least partly defined by the base portion.

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