Patent Application
20230074965
Various aspects of the invention relate to heat pumps and fluid pumps and various components and methods therefor. Some aspects of the invention are applicable beyond the context of such pumps.
Spaced about the fluid circuit 3 are a compressor 5, a heat exchanger in the form of condenser 7, an expansion valve 9 and a heat exchanger in the form of evaporator 11. The compressor receives and increases the pressure and temperature of refrigerant vapor. The refrigerant is then cooled through the condenser. An exterior fan 7a is employed to drive air through the condenser to accept heat.
The compressor 5 is a form of fluid pump. For the avoidance of doubt ‘fluid’ and similar terminology is used herein in its broadest sense to refer to flowable substances such as liquids and gases, and mixtures thereof.
Liquid high-pressure refrigerant emerges from the condenser. As such the portion of the fluid circuit 3 from the compressor 5 to the expansion valve 9 is known as the high-pressure side of the circuit. The other side of the circuit, from the expansion valve 9 to compressor 5, is known as the low-pressure side of the circuit.
The expansion valve reduces the pressure of the refrigerant. The low-pressure refrigerant emerging from the expansion valve is typically a mixture of liquid and vapor.
Through the evaporator 11 the refrigerant is heated. An interior fan 11a drives air through the evaporator 11 to reject heat to the refrigerant. The air conditioner may be either a recirculating system, wherein the fan 11a recirculates air within the cabin, or a fresh air system wherein the fan 11a draws air from outside the cabin and drives the air into the cabin of the vehicle. Refrigerant vapor is conveyed from the evaporator to the compressor to complete the circuit 3.
The tubing is supported by support structure 223 and carries a set of horizontal, approximately planar aluminium fins. Typically a fan is arranged to convey air through the evaporator 11 in a direction normal to the page.
Air conditioners are often thermostatically controlled whereby they are periodically activated and deactivated based on a measured temperature relative to a desired temperature.
A respective piston-cylinder arrangement 17 sits at each end of the housing 13. Each piston-cylinder arrangement 17 incorporates a sleeve 19 pressed into the body 15 and defining a cylinder 21. The arrangement 17 further includes a piston 23 and a head portion 25. The piston 23 is mounted to slide within the cylinder 21. The cylinder 21, piston 23 and head portion 25 together define a pumping chamber 27.
The sleeves 19 also form parts of the housing.
A crank member 29 is mounted within the housing 13. The crank member includes an input shaft 31 mounted to rotate within bearings 33. The crank member 29 further includes a crank pin 35 eccentric to the input shaft 31. The housing 13 further includes a tubular drive-adaptor 37 embracing the input shaft 31 and sealingly engaging the body 15. A seal 39 is mounted within the adaptor 37 and sealingly engages the input shaft 37. The housing 13 and pistons 23 together house the crank member 29 in an interior 41 that is sealed to capture blow-by.
For the avoidance of doubt, ‘blow-by’ is used herein in its ordinary sense in this art to refer to the leakage of fluid from a pumping chamber and past a piston.
The adaptor 37 includes a mounting flange co-operable with an electric motor. The input shaft 31 is fitted with a coupling 43 to connect the input shaft 31 to the output shaft of the electric motor. The electric motor is a 12V DC motor sold by Allied Motion™ under the part no. PJ2P021Q.
A connection arrangement 45 connects the crank shaft 29 to the pistons 23. The connection arrangement 45 includes a pair of conrods (i.e. connecting rods). One end of each of the conrods is journaled to the crank pin 35 with suitable roller bearings. The other end of each of the conrods is connected to a respective one of the pistons 23 via a respective gudgeon pin.
Head portion 25 incorporates a main body 25a machined from aluminium billet and a stainless steel valve plate 25b (see
A pair of simple holes 25c, 25d open through the plate 25b in register with the pumping chamber 27. A respective simple hole 25e passes through each corner of the plate 25b and a pair of holes 25f, 25g open through the plate towards the rear of the compressor 5.
The holes 25e accommodate head bolts 25h (
A petal 46 (
The petal 46 has an opening 46d positioned to sit in register with the opening 25c so as not to occlude the opening 25c.
A petal (now shown) similar to the petal 46 is clamped between the main body 25a and the plate 25b to co-operate with the port 25c to define an outlet from the chamber 27. The petal of the outlet is positioned so as not to overlie the port 25d such that there is no need for an opening akin to the opening 46d.
The main body 25a has a contoured interior surface shaped to sealingly engage the plate 25b to define a flow path from the outlet 25c to the hole 25f and another flow path from the hole 25g to the inlet 25d, 46. The holes 25f, 25g sit in register with galleries running the full length of the body 15. At the other end of the body 15 is a head portion 25′ similar to the head portion 25 and including apertures akin to the apertures 25f, 25g opening to the same galleries. The lower gallery (in register with the 25g) is tapped at the rear of the body 15 to define an inlet of the compressor 5. The gallery in register with the hole 25f is tapped at a rear of the body 15 to define an outlet of the compressor 5.
Reverse cycle air conditioners are heat pumps that can pump heat in either direction. The heat pump of
In the first mode of
The shuttle 51 resides within the tubular housing 49 and has a respective piston 51a, 51b at each of its ends defining end chambers 51c, 51d. The end chambers 51c, 51d are alternately connected to the high-pressure half of the fluid circuit 3 via a small three-way solenoid valve (now shown) and capillary lines. In the first operating mode, the chamber 51d is connected to the high-pressure refrigerant whilst the chamber 51c is isolated therefrom whereby the refrigerant drives the shuttle 51 towards the left as illustrated in
To change modes, i.e. to reverse the direction in which the pump 1 pumps heat, the position of the three-way solenoid valve (now shown) is reversed to switch the high-pressure refrigerant from the chamber 51d to the chamber 51c whereby the refrigerant drives the shuttle 51 towards the right (as drawn) to the position of
To the inventor's knowledge, all commercially available reverse cycle heat pumps incorporate this style of reversing valve. Such valves are widely regarded as simple and effective and also cost-effective in that the only electromechanically-driven valve element is the valve element of the small solenoid valve. The larger valve element, the shuttle 51, is driven by the refrigerant. In effect, the shuttle 51 is moved by the compressor 5 which makes efficient use of the available resources.
The inventor's compressor 5 is significantly more efficient than comparable compressors that dominate the market. To the inventor's knowledge, the most popular comparable compressor (at least in the Australian market) is sold by Danfoss™ under the part number BD350GH. When the inventor tested that compressor in a heat pump, the heat pump pumped 979 watts of heat and drew 32.5 amps of current corresponding to a power draw of 391 watts and a coefficient of performance of about 2.5. A compressor similar to the Danfoss™ BD350GH compressor sold under the BOYARD trade mark was also tested with similar results. When a variant of the compressor 5 having a bore of 16 mm and stroke of 8 mm was tested, the heat pump pumped 950 watts of heat and drew 14 amps corresponding to a power draw of 185 watts and a coefficient of performance in excess of 5.
Nonetheless, the present inventor has recognised that further improvements are possible. In particular, the present inventor has recognised scope a) for further efficiency gains, b) to reduce the risk of leakage, and c) to improve the reliability of the compressor. Likewise, whilst the reversing valves 47 are widely accepted in the art, the present inventor has recognised that in certain contexts they are a source of unreliability. Some of the inventor's advantageous developments may be usefully applied in other contexts.
With the foregoing in mind the present invention in its various aspects aims to provide improvements in and for valves, fluid pumps and/or heat pumps, or at least to provide alternatives for those concerned with valves, fluid pumps and/or heat pumps.
One aspect of the invention provides a fluid pump including one or more piston-cylinder arrangements each including a respective piston portion and
a respective pumping chamber;
a crank member;
a housing; and
a transmission;
the housing together with the respective piston portion of each of the one or more piston-cylinder arrangements defining an interior in which the crank member is housed;
the interior being sealed to capture blow-by; and
the transmission being arranged to transmit power, for rotating the crank member, into the housing at least one of magnetically and electrically.
The transmission may be a magnetic coupling including a rotatable portion outside the housing and a portion inside the housing magnetically co-operable with, to be rotated by, the rotatable portion. The fluid pump may include an electric motor for driving the rotatable portion.
Alternatively the fluid pump may include an electric motor having inside the housing each of a stator and a rotor. The transmission may include at least one wire for the electric motor and entering the housing via a sealed aperture.
Alternatively the transmission may include an electric motor having a stator outside of the housing and a rotor inside the housing.
The fluid pump preferably includes two or more of the piston-cylinder arrangements. Optionally the crank member and one or more connecting arrangements, connecting the crank member to the respective piston portions, are configured to move the respective piston portions of the two or more of the piston-cylinder arrangements in unison to hold substantially constant a volume of the interior. The one or more connecting arrangements may include a member having two ends and a respective one of the piston portions at each of the ends.
Preferably the fluid pump includes an electric drive motor. Preferably the pump has a total weight, including the electric drive motor, not exceeding 10 kg. Most preferably the total weight does not exceed 6 kg
Another aspect of the invention provides a reed valve including
a port;
a ridge surrounding the port; and
a petal arranged to bear against the ridge to close the reed valve.
The ridge is preferably shaped to contact the petal along a line of contact not more than 0.5 mm thick.
Another aspect of the invention provides a fluid pump including
one or more pumping chambers;
each of the pumping chambers having
Preferably each respective one of the pumping chambers has a second reed valve defining the other of the inlet to the respective pumping chamber and the outlet from the respective pumping chamber.
Another aspect of the invention provides a reverse cycle heat pump having a first mode of operation and a second mode of operation and including
a fluid circuit; and
a pump-and-valve arrangement including
The reversing valve arrangement may include a pair of electromechanical three-way valves. Preferably the first-mode flow paths include
Preferably the fluid pump has a displacement of not more than 10 cc (0.61 ci), most preferably it is not more than 5 cc (0.31 ci).
Another aspect of the invention provides a heat pump including
a fluid circuit; and
a fluid pump for pumping fluid about the fluid circuit;
wherein
the heat pump is configured for evaporation of the fluid when the heat pump is in at least one operating mode of the heat pump;
the fluid circuit includes a fluid circuit portion;
the fluid circuit is configured for at least most of the evaporation to occur along the fluid circuit portion; and
the fluid circuit portion is arranged for the fluid to flow upwardly, or at least horizontally, along substantially all of the fluid circuit portion when the heat pump is in the at least one operating mode of the heat pump.
The fluid circuit is preferably configured for at least 90% of the evaporation to occur along the fluid circuit portion. The fluid circuit portion may include a serpentine conduit along which the fluid flows. The serpentine conduit may include horizontal portions and bends connecting the horizontal portions.
Preferably at least most of the fluid circuit portion is within a finned portion of an evaporator.
The heat pump may include a control arrangement configured to vary, between non-zero values, a speed of the fluid pump.
The fluid pump and the reversing valve arrangement may be mechanically connected so that they may be handled as a single unitary body, i.e. to form a pump-and-valve unit. This aspect of the invention also provides the pump-and-valve unit. Alternatively, the components of the pump-and-valve arrangement may be distributed with suitable fluid connections therebetween.
Another aspect of the invention provides a heat pump including
a fluid circuit; and
a sensor to sense at least one of pressure and temperature of the fluid on a high-pressure side of the fluid circuit; and
a control arrangement configured to vary, between non-zero values, a speed of the fluid pump in response to the sensor and in positive relation to the at least one of pressure and temperature.
‘Between non-zero valves’ and similar wording are used herein to distinguish the varying the speed from the trivial case of the varying the speed being simple activation or deactivation.
The control arrangement may be configured to vary the speed in positive relation to a load on the heat pump.
The heat pump preferably includes a sensor to sense at least one of pressure and temperature of the fluid on a high-pressure side of the fluid circuit. The control arrangement may be configured to vary the speed in response to the sensor and in positive relation to the at least one of pressure and temperature.
The heat pump may include a refrigerant-cooling fan for driving air through a heat exchanger downstream of the fluid pump. The control arrangement may be configured to vary a speed of the refrigerant-cooling fan in response to the sensor and in positive relation to the one of pressure and temperature.
Preferably the heat pump includes
a refrigerant-heating fan for driving air through a heat exchanger upstream of the fluid pump;
a temperature sensor for providing an indication of a temperature of the material to be cooled by the heat pump;
the control arrangement being configured to vary a speed of the refrigerant-heating fan in response to the temperature sensor and in positive relation to the temperature of the material to be cooled by the heat pump.
Another aspect of the invention provides a heat pump including a fluid pump and a control arrangement configured to operate the fluid pump at an idle speed.
Another aspect of the invention provides a method of operating a heat pump including operating a fluid pump of the heat pump at an idle speed.
Another aspect of the invention provides a vehicle, e.g. self-propelling land vehicle, having an occupant-carrying interior heated by a heat pump.
Advantageously the vehicle may be fitted with a solar panel to power the pump. The sun roof of some vehicles may be a convenient point to place the solar panel.
Another aspect of the invention provides a transportable container, e.g. a shipping container or smaller refrigerated unit, including
an interior;
a heat pump to at least one of heat and cool the interior; and
a battery for powering the heat pump.
The inventor's earlier compressor 5 includes a mechanical transmission for transmitting power into the housing 13. Shaft power is conveyed by the input shaft 31. The sealing arrangement 39 incorporates a lip seal acting on the shaft 31 to prevent the escape of refrigerant from the interior 41 to atmosphere. The inventor's studies have shown that:
Accordingly, a compressor having a magnetic transmission in the form of the magnetic coupling 49 in place of a mechanical transmission is proposed. The magnetic coupling 49 incorporates an external rotor 51 and an internal rotor 53 separated by housing portion 55. The housing portion 55 includes a radial mounting flange carrying an array of bolt holes and by which the housing portion 55 is mounted and sealingly engaged with a front of the body 15. The housing portion 55 defines a closed cup including a cylindrical wall 55b extending from the flange 55a, and an end face 55c.
The external rotor 51 is shaped to embrace the cup 55b, 55c and includes magnets 51a positioned to revolve about and in close proximity to the cylindrical wall 55b. The internal rotor 53 includes magnets 53a positioned to revolve within and in close proximity to the cylindrical wall 55b.
The internal rotor 53 forms part of a crank member 29′ (
The coupling 49 includes both external magnets 51a and internal magnets 53a. Other variants are possible. By way of example, the magnets 51a might be replaced with steel (or other material) magnetically co-operable with the magnets 53a. For the avoidance of doubt, ‘magnetically co-operable material’ and similar terms as used herein take in both magnets and non-magnets.
The coupling 49 incorporates rotationally-driven external magnets 51a to create a rotating magnetic field by which the internal rotor 53 is rotated. In another variant of the compressor, the external rotor 51 is replaced by a stator co-operable with the rotor 53 to form an electric motor whereby the stator electrically creates a rotating magnetic field by which power is magnetically transmitted into the housing 13.
Another possibility is to place the stator inside the housing 13, in which case a magnetic transmission in the form of a wireless power transfer may be employed to transmit power into the housing 13. Alternatively, an electrical transmission in the form of simple wires (or other conductor(s)) may be employed. Of course, sealing about one or more wires is simpler than sealing about the input shaft 31 and does not entail the friction losses associated with the seal 39.
The improved sealing offered by an electrical and/or magnetic transmission helps to minimise the weight of the compressor. Some existing compressors are mounted within a sealed canister to capture any refrigerant leaking therefrom. The improved sealing allows for the elimination of the canister and its weight. It also contributes to the reliability of the heat pump, particularly on hot days when the pump is working hardest. On hot days, refrigerant pressure can built up within the canister of canister-sealed systems such that refrigerant is effectively lost from the fluid circuit, reducing the performance and reliability of the system.
The addition of a sealant, such as LOCTITE™, to the metal-to-metal interfaces between the body 15, plate 25b and head portion 25 is another possible precaution against leakage.
Preferred forms of the compressor, including the electric drive motor, weigh less than 6 kg. To the inventor's knowledge, this is much lighter than commonly available compressors delivering comparable output.
For the avoidance of doubt, as various terminology is used herein:
One advantage of the connection arrangement 57 over the connection arrangement 45 is that it enables the cylinders 21′ to be moved into coaxial alignment to enable the sleeve-receiving bores to be machined in a single operation from one end of the block 15. This reduces manufacturing costs. The block 15 may be formed by metal injection moulding. The co-axial alignment is advantageous in this context because it enables the sleeve-receiving bores to be cored from one end of the block.
Whilst, in principle, the member 59 and pistons 23′ could be parts of a common integrally formed member, preferably they are separate members. In this example, each piston 23′ is connected to the connecting member 59 via a respective gudgeon pin. Whilst there is no need for the gudgeon pin to work through a range of angles associated with the movement of a conventional conrod, a very small degree of movement is desirable in that it enables each of the pistons 23′ to self-align within its respective cylinder bore 21′ to account for any misalignment between the bores 21′ as a result of manufacturing tolerances and/or deformations in use resulting from thermal and/or mechanical stresses.
Separately forming the components also enables different materials to be used. The pistons 23′ and cylinders 21′ are preferably formed of substantially the same material, or at least of materials selected to have substantially identical thermal coefficients, so as to expand at the same rate as the components heat up in operation.
In this case, the components 19′, 23′ are formed of cast iron selected for its self-lubricating properties. The cylindrical surfaces of these components are ground to form accurate finishes to provide a satisfactory compromise between sealing and friction without the need for piston rings or any similar sealing arrangements. In one variant, the cylinder is ground to a diameter in the range of 16.002 mm to 16.005 mm (0.63 in to 0.63012 in) and to a surface roughness not greater than 0.8. The exterior of the piston is ground to a diameter in the range of 15.997 mm to 16.000 mm (0.62980 in to 0.62992 in) and within the same roughness tolerance.
The connecting member 59 has at its centre an oval-shaped aperture 61 in which the pin 35′ is mounted. The pin 35′ is mounted eccentrically (relative to the axis about which the crank member 29′ rotates) to describe a circular path. Whilst following the circular path, the pin 35′ races around the periphery of the oval-shaped opening 61 to drive the member 59 and pistons 23′ connected thereto to reciprocate.
The shape of the hole 61 and the shape and eccentricity of the pin 35′ may be varied to vary the stroke and acceleration curves of the pistons. The crank members 29, 29′ and connection arrangements 45, 57 are but two examples of a range of possibilities. ‘Crank member’ is used herein to refer to a rotationally-driven member having at least one eccentric portion by which the piston(s) is/are driven to reciprocate. By way of example, the crank member could be a cam and the connection arrangement could be a cam-following arrangement.
In each of the described arrangements, the crank member and the connection arrangement co-operate to drive the pistons in unison so as to hold substantially constant the internal volume 41. Other arrangements are possible. By way of example, with reference to
The present inventor has recognised that most refrigerants have lubricating properties adequate to lubricate the pistons and cylinders and provide some resistance to blow-by. Blow-by into the interior 41 provides sufficient lubrication for the crank member 29′ to operate without additional lubricating oils. Accordingly, preferred forms of the compressor 5 operate without an additional volume of oil within the housing 13 and as such losses associated with moving this oil are avoided. R134A and HR30 are the preferred refrigerants.
The inventor has also found room to significantly improve the efficiency of the reed valves. In the inventor's earlier variants, the petals 46 sealed against the planar face of the valve plate 25b in conventional fashion. The inventor's studies suggested that the petals 46 adhere to the planar surface and that, with each stroke of the compressor, work is required to break the petals away from this adherence. The studies also suggest that some petals twisted along their long axes rather than fully lifting away from their ports and therefore imposed some restriction to flow.
To address this issue, the modified valve seats illustrated in
The valve plate 25b is formed of 3 mm thick stainless steel and the ports 25c′, 25d′ have finished internal diameters of 6 mm. The plate is laser-cut. The holes for the ports are initially cut undersized and then subject to a drilling operation. The drill is operated at a slow rpm and rapid rate of advance whereby consistent burrs respectively surrounding each end of each hole are formed. This drilling operation takes the holes to their finished size(s). The resultant downstream burr is then lapped to define a consistent sealing edge for the petal 46.
The burr is then removed from the upstream edge of the outlet port 25c′ so as not to interfere with the petal 46 for the inlet port 25d′. The burr may also be removed from the upstream side of the inlet port 25d′.
Another possibility, instead of the described drilling and lapping operations, is to fit the plate with suitable ridge-defining inserts. This may be preferable for mass production. Metal injection moulding is another possibility for the valve plate. Optionally, the apexes of the ridges may be subject to a post-moulding material-removal operation (e.g. lapping).
The inventor's testing identified the petal 46 as a potential failure point and it has been discovered that this can be addressed by taking advantage of the anisotropic properties of the spring steel. Early failures of the petal were associated with cracking in the vicinity of the root portion of the petal. Preferably the petals are cut so that their long axis (which is perpendicular to the axis of bending) is at least approximately parallel to the axis along which the steel is rolled. The axis along which the steel is rolled is believed to be coincident with the orientation of the steel's grain structure.
Testing suggests that the disclosed sealing ridges also improve the reliability of the petals by at least reducing torsional loads on the petals associated with twisting about their long axes.
The inventor's early testing has focused on two variants of the compressor both of which have a stroke of 8 mm (0.31 in). One variant has a bore of 16 mm (0.63 in) corresponding to a displacement of 3.2 cc (0.20 ci) for the compressor. The other variant has a bore of 17.5 mm (0.69 in) corresponding to a displacement of 3.9 cc (0.24 ci). Both variants are configured to operate at about 2,100 rpm.
The pump 5 is an example of a positive displacement pump. Other positive displacement pumps are possible. Indeed, some aspects of the invention may be implemented with non-positive displacement pumps such as centrifugal pumps.
The inventor has discovered that conventional reversing valves (such as the reversing valve 47) are not reliable when used with small compressors (say up to 10 cc). Practical design considerations dictate a less than perfect seal between the pistons 51a, 51b and the interior of the housing 49 such that the valve does not reliably change mode when driven by such a small compressor. By way of example, with reference to
To address this non-obvious problem, the inventor proposes to replace the refrigerant-driven valve element 51 with one or more electromechanically-driven valve elements, e.g. a solenoid could be added to the valve 47 to electromechanically drive the shuttle 51. This would allow the small three-way solenoid and the associated capillary tubes to be eliminated.
The valve arrangement 67 incorporates ports 5in′, 5out, 7″ and 11″. The ports 5in′, 5out′ are respectively connected to the compressor's inlet and the outlet. Plumbing 69 in the form of copper tubing defines a T-piece connecting the port 5out′ to each of the ports 7″, 11″. One arm of the T-piece carries a first first-mode solenoid SFM1 which, when open, defines a first first-mode flow path akin to the flow path FPFM1 and mutually connecting the ports 5out, 7″. The other arm of the T-piece carries a first second-mode solenoid SSM1 which, when open, defines a first second-mode flow path akin to the flow path FPSM1 and mutually connecting the ports 5out′, 7″.
The unit 65 further includes further plumbing 71 defining another T-piece equipped with solenoid valves SFM2, SSM2 for alternately connecting the port 5in′ with one or the other of the ports 7″, 11″.
This arrangement advantageously thermally separates the first-mode flow paths from each other and the second-mode flow paths from each other, to avoid heat exchange therebetween (as may occur within the valve 47) to lead to further efficiency gains.
In operation, only a diagonally-opposed two of the four solenoid valves are open at any one time. All four valves change state to change the operating mode. By way of example, to switch from the first operating mode to the second operating mode, the first-mode solenoid valves SFM1, SFM2 are closed and the second-mode solenoid valves SSM1, SSM2 are opened.
The valve arrangement 67 incorporates four two-way solenoid valves. Another possibility entails one or more three-way valves. Any adjacent two of the four two-way solenoid valves could be replaced by a suitable three-way valve.
The described arrangements of one or more electromechanically-driven valve elements enables smaller than conventional heat pumps to reliably reverse cycle.
The solenoid valves are preferably 12V solenoid valves to operate from the same power supply as is the compressor. For the avoidance of doubt, the movable fluid-contacting portion of a conventional solenoid valve is an electromechanically-driven valve element as those words and similar words are used herein.
The present inventor has also discovered that, in the context of extraordinarily small heat pumps, the evaporator can be a source of inefficiency.
The inventor has recognised that as the refrigerant evaporates along the path 217 it becomes relatively buoyant, and that along the downward runs 219b this buoyancy provides a resistance against which the compressor must work.
In the heat exchanger 311 the buoyancy of the vapor urges the refrigerant to flow in the same direction as it is urged to flow by the fluid pump 5. More specifically:
In the illustrated example, a single serpentine path connecting the inlet 313 to the outlet 315 is disclosed. Other options are possible. By way of example, the relevant portion of the fluid circuit may be made up of two parallel flow path portions.
Preferably all mixed-phase portions of the low-pressure side of the fluid circuit are upward or at least horizontal. Likewise, preferably there are no downward portions in the fluid path portion within the evaporator, although it is possible that a downward run of conduit might be added to a single-phase portion of the flow path within the evaporator, e.g. for more convenient connection to the expansion valve or the compressor, without a dramatic reduction in efficiency.
The inventor's studies into the reliability of heat pumps have also revealed that many failures occur at start-up as opposed to when the heat pump is pumping heat. Many of these failures have been found to relate to the torque necessary to start the compressor. In an inactive heat pump, significant pressure can build in the fluid circuit, including in the pumping chamber, such that the torque required to move the piston is more than the electric motor is capable of, e.g. the current draw from the motor may exceed an enforced current limit, e.g. may blow a fuse. As such, automotive air conditioners are notorious for being least reliable when they are most needed, i.e. on the hottest days.
The present inventor's adoption of two smaller pistons (having their compression and suction strokes out of phase to each other) as opposed to a single larger piston is a first step to addressing the start-up problems. Having a variable-speed drive unit (e.g. electric motor) dedicated to the compressor is another step in the right direction and is in stark contrast to the conventional approach of driving a compressor by selective engagement with a vehicle's combustion engine. The dedicated drive allows the compressor to be driven at a speed that is most efficient for the particular operating conditions rather than to be driven at a speed corresponding to the combustion engine, which may well lead to sub-optimal operation of the compressor and the heat pump.
Providing a dedicated variable-speed drive allows for the convenient implementation of new control strategies to improve the performance of the compressor and/or heat pump and to address the risk of failure at start-up.
The present inventor has recognised that the start-up problems can be largely avoided by operating the compressor at an idle speed rather than allowing the compressor to shut down completely (e.g. at the whim of a thermostatic controller). The inventor's prototypes have been tested at an idle speed of 1,000 rpm at which their electric motors each draw about 5 amps at about 12 volts (i.e. at about 60 watt). When the compressor is operated at this speed, the heat pump 1 provides negligible heating performance. The fans 7a, 11a may be deactivated or at least slowed or operated on a low-duty cycle.
Whilst the about 60 watt idle-speed power draw results in some waste relative to simply deactivating the system, the inventor has found that under typical automotive operating conditions this waste is more than offset by the other efficiencies of the disclosed methods and apparatus.
The 60 watt/1000 rpm idle speed is achieved using Allied Motion's PJ2P021Q electric motor. Of course, other electric motors (and indeed other drive arrangements more generally) are possible. Direct current 12V, 36V or 48V drives are preferred to suit automotive applications.
The inventor's studies have shown that many existing 12V vehicle electrical systems are capable of supplying the compressor with 20 amps for a sustained period. Preferred variants of the disclosed heat pumps have a coefficient of performance of at least 4 whereby utilising the available 20 amps at 12V (240 watt) they are capable of delivering about 900 watts or more of heating and/or cooling within the 20 amp current limit.
The start-up problems are most significant on hot days during which the heat pump may well operate almost continuously. Accordingly, to suit some applications, it may be appropriate to enter the idle-speed mode based on an indication of the ambient temperature. By way of example:
To implement these control strategies, the heat pump 1 may include a controller 71, an ambient temperature sensor 73, a cabin (or other target) temperature sensor 75 and a pressure sensor 77. The control arrangement 71 is configured to receive data from the sensors 73, 75, 77 and to send control signals to the components 5, 7a, 11a. The various components are preferably connected by suitable wired links, although wireless connections are also possible. Various of the components may be integrated and/or commonly housed.
On hotter days, the control arrangement moves on to increment a counter at step 107, and then to check whether the counter is above the threshold corresponding to, for example, 15 minutes. Whilst the counter remains below the threshold, the controller moves on to operation in an overspeed mode at step 111.
In the overspeed mode, the compressor is operated faster than its components are intended for continuous operation, to maximise the cooling effects. For the same reason, the condenser fan 7a is also operated at about 20% above its typical operating speed. The internal fan is also operated at about 10% more than its peak efficiency speed. The peak efficiency speed is the speed at which the air it moves rejects the most heat (as measured by power) to the refrigerant for a given temperature of the air being moved.
Overspeeding the fan serves to stir the air within the truck cabin. In particular, the hottest pools of air around the ceiling of the cabin, which can be as hot as 80° C. (176° F.) are moved. When the air is recirculated within the truck cabin, the displacement of these hot pools of air leads to hotter air moving through the evaporator 11 and thereby to improved cooling. The illustrated cycle continues to iterate until the end of the preset period for the overspeed mode, whereupon (at step 109) the control 71 moves on to the pressure control mode at step 105.
Other variants are possible. By way of example, between steps 107 and 111 the sensor 75 may be rechecked. The control arrangement may move to the pressure control mode if the cabin temperature drops below a threshold which may or may not be the same threshold as the overspeed mode entry threshold (at step 103).
The pressure control mode is so named because the speed of the condenser is controlled in positive relation to the pressure on the high-pressure side of the fluid circuit 3, e.g. in response to the sensor 77. This control arrangement advantageously leads to efficient steady-state operation of the heat pump, in stark contrast to conventional stop-start thermostatic control and sub-optimal compressor speed.
The pressure on the high-pressure side of the fluid circuit provides an indication of the load on the heat pump. Other indicators of load may be relied upon to control the heat pump.
For the avoidance of doubt, ‘in positive relation’ means ‘to increase with’. Over the domain of positive real numbers, y=ax, y=ax2, y=ax and y=log x are examples of positive relationships.
The speed of the external fan 7a is also controlled in positive relation to the pressure of the high-pressure refrigerant. In other examples of the invention, the air flow to a heat exchanger may be controlled in other ways, e.g. in the context of a truck, instead of accelerating the fan 7a, a vent may be opened to allow for more air movement as a result of movement of the truck.
The speed of the internal fan 11a is controlled in positive relation to the cabin temperature, e.g. controlled in positive relation to an amount that that temperature exceeds a set desired temperature. The desired temperature is 22° C. in this example. Preferably the speed of the fan 11a is also limited to the peak efficiency speed.
The described heat pump is particularly advantageous in and for the context of vehicles wherein its compact size, light weight and reliability are particularly advantageous.
As noted, electrically-driven variants of the heat pump allow for the compressor to be operated at speeds independent of the crank speed of the vehicle. It also enables the heat pump to be moved away from the engine. The costly and often problematic drive belt for driving the compressor can be eliminated.
The conventional placement of automotive air conditioners towards the front of the engine bay presents other problems. Since the compressor is positioned to be driven off the engine's crank shaft, it typically follows that the condenser is positioned foremost in the engine bay in front of the engine's radiator. At this location, the condenser is typically in prime position to be damaged during minor road accidents. Vast quantities of refrigerant are lost to atmosphere in this way. This causes environmental damage. The damage to the air conditioner also adds to the cost of the crash repair. The adoption of an electrically-driven compressor enables the entire heat pump to be conveniently relocated to a safer position, e.g. towards the rear of the vehicle whereto suitable cooling air may be ducted.
The overall efficiency of the heat pump also lends itself to the ongoing operation of the heat pump whilst the vehicle's combustion engine is deactivated. In many parts of the world, it is not uncommon to see unoccupied vehicles idling simply to run the air conditioner. This is of course grossly inefficient and thus expensive. It also leads to unnecessary pollution.
Whilst the invention is particularly advantageous in the context of self-propelling land vehicles, it may also be advantageously applied elsewhere, such as in the context of yachts and other water-going vessels. In the context of some water-going vessels, using existing technologies, it is not uncommon for the vessel's large diesel engines to be idling simply to power the air conditioners. Of course, this is especially inefficient.
The application of the described heat pump, and in particular reverse-cycle variants of the disclosed heat pump, to heat the occupant-carrying interior of a vehicle is particularly advantageous. At present, many vehicles have essentially separate heating and cooling systems. The heating systems have a ‘water core’ through which heat is transferred from the water of the combustion engine to air to heat the interior. Of course, these cores entail some cost, some weight and some risk of failure. Advantageously these cores (and the associated fans, etc) can be eliminated by adopting the disclosed heat pumps. As described, the same heat exchanger that cools the cabin can be employed to heat it when the vehicle is exposed to colder weather.
Early variants of the compressor 5 were developed to provide air conditioning to the helmets of race-car drivers racing at an elite level whereat high performance, minimum weight and absolute reliability are essential under very challenging conditions. As such, the compressor 5 has been proven to inertial loadings up to 8G. With the continued development of the concept disclosed herein, the pump's performance continues to surprise and impress. A test of a variant of the heat pump powered by a N70ZZ battery and a 250 watt solar panel to cool a 5.5 m (18 ft) caravan was highly successful.
The integration of the described heat pump with battery solar systems is particularly advantageous. In such systems, the efficiency of the disclosed heat pump is a clear advantage. The improved start-up characteristics of the compressor are also important. Many such systems which cannot supply the electrical current necessary to start a conventional heat pump of similar scale (or can only do so when their batteries are in good condition and fully charged) can reliably start up the disclosed heat pump over a wide range of battery conditions. This is particularly advantageous in the context of water-going vessels and dwellings that are not connected to a mains power supply.
Some vehicles may be equipped with two or more of the disclosed heat pumps. By way of example, a limousine may be fitted with separate heat pumps for the driver and each of two or more passengers in the rear of the vehicle to enable each of the occupants to have separately controlled heating and cooling.
Optionally, a vehicle may be connected to mains power whilst it is stationary, to operate the heat pump as required. By way of example, in colder climates the heat pump may be operated overnight to provide a comfortable interior for the driver in the morning.
Various examples have been described. The invention is not limited to these examples. Rather, the invention is defined by the claims. By way of example, the disclosed heat pump may be employed for heating substances other than air. Likewise, whilst a fluid pump for pumping fluid about the fluid circuit of a heat pump has been described, the disclosed fluid pumps may find application elsewhere. In particular, the compressor 5 is particularly advantageous when used as a vacuum pump to evacuate the fluid circuit of a heat pump.
For the avoidance of doubt, a typical combustion engine is an example of a fluid pump, driven by the release of chemical energy from fuel, as ‘fluid pump’ and similar terminology is used herein albeit that preferred forms of the disclosed fluid pumps are driven by sources of more organized power, such as sources of shaft or electrical power.
The term ‘comprises’ and its grammatical variants has a meaning that is determined by the context in which it appears. Accordingly, the term should not be interpreted exhaustively unless the context dictates so.
| Number | Date | Country | Kind |
|---|---|---|---|
| 779984 | Sep 2021 | NZ | national |
