WO2020012182A1

WO2020012182A1 - A vehicle air conditioning system

Info

Publication number: WO2020012182A1
Application number: PCT/GB2019/051947
Authority: WO
Inventors: Michael TOMLIN
Original assignee: Dyson Automotive Research And Development Limited
Priority date: 2018-07-11
Filing date: 2019-07-11
Publication date: 2020-01-16
Also published as: GB201811344D0; GB2575629A

Abstract

A vehicle air conditioning system and a vehicle comprising the air conditioning system are disclosed. The air conditioning system comprises a heat exchanger (107'); a blower for blowing air over the heat exchanger; and a circulation system for supplying coolant to the heat exchanger, the circulation system comprising: a first coolant circuit (402) comprising a first thermal exchanger (evaporator 115') for cooling coolant in the first coolant circuit, a second coolant circuit (403) comprising a second thermal exchanger (405) for heating coolant in the second coolant circuit, and a valve (407) for controlling the combination of coolant from the first coolant circuit with coolant from the second coolant circuit. The valve is controllable to control the combination of cooled coolant from the first coolant circuit (402) with heated coolant from the second coolant circuit (403)to thereby control the temperature of coolant supplied to the heat exchanger (107).

Description

A VEHICLE AIR CONDITIONING SYSTEM

Field of the Invention

The present invention relates to a vehicle air conditioning system.

Background of the Invention

Vehicles such as passenger cars are usually equipped with an air conditioning (AC) system for heating and cooling air blown into the passenger cabin.

Such AC systems typically include a pair of heat exchangers arranged successively in the cabin air inlet over which air is blown to the cabin by an electric fan, a“blower”. Each of the heat exchangers is typically operable in a single mode to either heat or cool the influent air. The heating heat exchanger is usually supplied with heated coolant from a combustion engine cooling circuit. The cooling heat exchanger is usually supplied with refrigerant as the evaporator stage of a vapour-compression cycle heat pump.

Conventional vehicle AC systems suffer a number of disadvantages. The requirement for two heat exchangers to heat and cool influent air is disadvantageous as it increases the overall volume occupied by the air conditioning system. Further, two heat-exchangers may present a greater restriction to the through-flow of air than a single heat exchanger, thus requiring a more powerful blower to maintain a desired flowrate. Further, where the pair of heat exchangers operate at hot and cold temperature extremes, to obtain heated air at a temperature between the two extremes requires controlled balancing of the airflow over each of the heat exchangers. Furthermore, the cooling heat exchanger presents a hazard inasmuch that, in the event of a leak, refrigerant circulating through the heat exchanger may escape directly into the influent air stream, which may be noxious to persons occupying the passenger cabin.

Summary of the Invention

A first aspect of the present invention provides a vehicle air conditioning system comprising: a heat exchanger, a blower for blowing air over the heat exchanger, and a circulation system for supplying coolant to the heat exchanger, the circulation system comprising: a first coolant circuit comprising a first thermal exchanger for cooling coolant in the first coolant circuit, a second coolant circuit comprising a second thermal exchanger for heating coolant in the second coolant circuit, and a valve for controlling the combination of coolant from the first coolant circuit with coolant from the second coolant circuit, wherein the valve is controllable to control the combination of cooled coolant from the first coolant circuit with heated coolant from the second coolant circuit to thereby control the temperature of coolant supplied to the heat exchanger.

Because the circulation system may controllably supply heated and cooled coolant to the heat exchanger, the heat exchanger may be used for both heating and cooling air supplied to a vehicle passenger cabin. The dual heating/cooling function of the single heat exchanger may thus avoid the need for two heat exchangers to separately heat and cool cabin air.

Advantageously this may simplify temperature control of the influent air to the passenger as controlled balancing of the airflow over two heat exchangers and subsequent recombination of the air streams is not required. Further, that two heat exchangers are not required may advantageously reduce the space occupied by the air conditioning system. Further, the single heat exchanger may advantageously tend to present a lesser restriction to the through-flow of air into the passenger cabin than would be presented by two heat exchangers. Advantageously this may allow a less powerful blower to be used to provide a given flow rate than would be possible for two heat exchangers.

Furthermore, a circulation system supplying coolant to the heat exchanger is advantageous in many applications for the reason that a coolant is a relatively flexible medium for transporting thermal energy between distributed thermal sources and influent air to the passenger cabin. For example, the circulation system may circulate a coolant across a plurality of thermal exchangers distributed about a vehicle, each component exchanging thermal energy with the coolant. This is compared in particular to refrigerant in a vapour compression cycle for which thermal exchange between the refrigerant an external thermal source is generally achieved through phase transition of the refrigerant.

The circulation system comprises first and second coolant circuits each comprising a thermal exchanger for cooling or heating coolant in the respective circuit, and coolant from the first and second coolant circuits may be controllably combined by the valve for supply to the heat exchanger. This configuration allows coolant heated or cooled to different temperatures in the coolant circuits to be combined, that is to say blended, and supplied to the heat exchanger. Advantageously this enables coolant to be supplied to the heat exchanger at a temperature intermediate the temperature of the coolant in each of the circuits. This is particularly advantageous where the only sources of heat available to the circulation system are at hot and cold extremes of temperature, in which circumstance it may be desirable to combine coolant from the two heat sources to obtain coolant at an intermediate temperature. For example, coolant in the first coolant circuit may be cooled to a first temperature by the first thermal exchanger, and coolant in the second coolant circuit may be heated to a second temperature by the second thermal exchanger. Coolant from the first and second circuits may then be combined to supply coolant to the heat exchanger at a temperature intermediate the first circuit and second circuit temperatures.

The valve allows control of the combination of the coolant from the first and second coolant circuits and thus allows control of the temperature of the combined coolant supplied to the heat exchanger. For example, the valve may be controllable to adjust the relative proportions of cooled coolant from the first coolant circuit and heated coolant from the second coolant circuit that is supplied to the heat exchanger.

The valve may be common to the first coolant circuit and the second coolant circuit. In this arrangement the common valve thus receives both cooled coolant from the first coolant circuit and heated coolant from the second coolant circuit. This has the advantage that the valve component itself is less likely to be damaged through being excessively heated or cooled by the coolant flows. For example, the valve may be a three-way valve, having first and second fluid inlets fluidly coupled to the first and second coolant circuits respectively, and having a fluid outlet fluidly coupled to the heat exchanger.

The first thermal exchanger of the first coolant circuit and the second thermal exchanger of the second coolant circuit may be in fluid parallel with respect to the heat exchanger. In this arrangement, because coolant is not required to flow sequentially across the two thermal exchangers, the restriction presented to the flow of coolant around the circulation system may be relatively low. Consequently, the work required to pump coolant around the circulation system is reduced.

The first thermal exchanger of the first coolant circuit and the second thermal exchanger of the second coolant circuit may be operable simultaneously to cool coolant in the first coolant circuit and heat coolant in the second coolant circuit. In this arrangement sustained cooling and heating of the flows of coolant is possible. Accordingly, it is possible to sustain a supply of coolant to the heat exchanger at a temperature intermediate that of the two thermal exchangers.

The first coolant circuit may comprise a first coolant pump for pumping coolant in the first coolant circuit and the second coolant circuit may comprise a second coolant pump for pumping coolant in the second coolant circuit. In this arrangement, the relative rates of coolant flow around each of the coolant circuits may be conveniently varied. The air conditioning system may further comprise an electronic controller for independently controlling the operation of the first coolant pump and the second coolant pump.

The coolant supplied by the coolant circuit to the heat exchanger may be a liquid coolant, and may be a water or glycol based liquid coolant, i.e. a coolant with a major proportion of water or glycol respectively. Water or glycol based coolants are relatively safe coolants for circulating through the heat exchanger, in particular as they will tend to remain in liquid phase in normal ambient temperature and pressure conditions. Advantageously this means that a coolant leak is less likely to result in formation of a potentially flammable or noxious gas. In contrast refrigerants used in vapour-compression cycle refrigerant circuits, such as certain chlorofluorocarbons, will typically tend to boil readily in ambient temperature and pressure conditions. Such refrigerants thus present a hazard inasmuch that, in the event of a refrigerant leak into the passenger cabin, the boiling refrigerant may tend to displace oxygen from the cabin. Furthermore, water or glycol based coolants advantageously tend to have a relatively high specific heat capacity. Advantageously this may improve transfer of thermal energy.

The coolant may be formulated to have a boiling point (in ambient pressure conditions, i.e. approximately 100 kPa) of approximately 100 degrees Celsius (°C), preferably at least 90 °C, more preferably at least 100 °C. This may allow the coolant to be heated to a relatively high temperature in the coolant circuit without boiling. Advantageously this may allow the heat exchanger to heat the influent air to a relatively high temperature.

The circulation system may control the temperature of the coolant supplied to the heat exchanger by controlling the temperature of the one or more thermal exchangers. Advantageously precise temperature control of the coolant may be achieved by controlling the temperature of the thermal exchanger(s). Moreover, controlling the temperature of the thermal exchangers may be an energy efficient way of controlling the temperature of the coolant.

Alternatively or additionally, the circulation system may control the temperature of the coolant supplied to the heat exchanger by, for example, controlling the flow of coolant around the circulation system between the one or more thermal exchangers and the heat exchanger. For example, the circulation system may alternatively comprise a valve for throttling the flow of coolant through the heat exchanger.

The circulation system may comprise a vapour-compression cycle heat pump including a further heat exchanger supplied with refrigerant, wherein the one or more thermal exchangers comprises the further heat exchanger. A vapour-compression cycle heat pump may advantageously provide an efficient source of heating and/or cooling to the coolant. The refrigerant may be selected from: halons, chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HFC) and hydrofluoro-Olefms (HFO). These refrigerants may have desirable thermodynamic characteristics. Advantageously this may enable efficient heating or cooling of the coolant.

The refrigerant may have a boiling point (in ambient pressure conditions i.e. approximately 100 kPa) of below 0 °C, or below -10 °C, or even below -20 °C. This may have thermodynamic advantages. The refrigerant may be tetrafluoroethane (HFC-l34-a) or tetrafluoropropene (HFO-l234yf). These refrigerants may have desirable thermodynamic characteristics. In particular, HFO-l234yf has a desirably low global warming potential (GWP) rating.

The vapour-compression cycle heat pump may be operable in a first mode of operation such that said further heat exchanger heats the coolant and in a second mode of operation such that said further heat exchanger cools the coolant. This allows a single heat pump to be used for both heating and cooling the coolant. This has the first advantage that the cost and complexity associated with providing and controlling separate cooling and heating systems is avoided. Secondly, because only the single heat exchanger is required to exchange thermal energy with the coolant to achieve both heating and cooling, advantageously excessive restriction to the flow of coolant that might result from two or more such thermal exchangers is avoided.

The heat exchanger may be installed in a passenger cabin of a vehicle and the further heat exchanger may be installed in a compartment sealed from the passenger cabin. It is generally desirable that the heat exchanger, which is exposed to the influent cabin air, is installed in the passenger cabin of a vehicle so as to minimise the distance air treated by the heat exchanger must be ducted following heating/cooling by the heat exchanger. It is desirable to reduce this distance to minimise thermal losses resulting from thermal exchange between air in the ducting and ambient air which may result in undesirable heating or cooling of the air in the ducting. Installing the heat exchanger in the passenger cabin thus advantageously reduces the distance the heated/cooled air must be ducted before being discharged, and so may reduce thermal losses. It is desirable for reason of safety however that the further heat exchanger of the vapour compression cycle heat pump is sealed from the passenger cabin, in order that refrigerant circulating through the further heat exchanger is prevented from leaking into the passenger cabin. Thus, installing the further heat exchanger in a compartment sealed from the cabin advantageously reduces the risk of refrigerant leaked from the further heat exchanger entering the passenger cabin.

The system may further comprise ducting for ducting air from a vehicle exterior to a vehicle passenger cabin via the blower and the heat exchanger. Advantageously this allows air in the passenger cabin to be replaced with atmospheric air, thus improving air quality in the cabin.

According to a second aspect of the present invention, there is provided a vehicle having a passenger cabin for accommodating passengers and comprising an air conditioning system, according to any one of the preceding statements, for ventilating the passenger cabin. This is advantageous for the aforementioned reasons.

The vehicle may comprise ducting for ducting air from outside of the passenger cabin to inside the passenger cabin via the blower and the heat exchanger. As already noted, this advantageously allows air in the passenger cabin to be replaced with atmospheric air, thus improving air quality in the cabin

In the context of this specification the term“coolant” is used consistent with its ordinary use in the field of the invention, and thus should be understood to define a substance which heats or cools by temperature change through exchange of sensible heat. Thus, a “coolant circuit” or similar should be understood to define a system which normally operates such that circulating coolant absorbs or rejects heat primarily by temperature change rather than through phase transition. Examples of coolants according to this definition are water or glycol based liquids. Such coolants typically have boiling points (in ambient pressure conditions) well above 0 °C, and usually approximately 100 °C or greater. Conversely, again consistent with its ordinary use in the technical field, the term “refrigerant” should be understood to define a substance which heats or cools by phase transition through exchange of latent heat, and for which exchange of thermal energy accompanies a phase change of the substance, for example, from liquid to gaseous phase. Thus, a“refrigerant circuit” or similar should be understood to define a system which normally operates such that circulating refrigerant absorbs or rejects heat primarily by phase change. Examples of refrigerants according to this definition are halons, chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HFC) and hydrofluoro-Olefms (HFO). Such refrigerants typically have boiling points (in ambient pressure conditions) well below 0 °C, usually below -10 °C, or even below -20 °C.

Thus, coolants and refrigerants are typically distinguished by their different boiling temperatures.

An aspect of the invention provides a vehicle air conditioning system comprising: a heat exchanger; a blower for blowing air over the heat exchanger; and a circulation system comprising a coolant circuit for supplying a coolant to the heat exchanger, the circulation system comprising one or more thermal exchangers operable to heat and cool the coolant; wherein the circulation system is controllable to control the temperature of coolant supplied to the heat exchanger.

The coolant supplied by the coolant circuit to the heat exchanger may be a liquid coolant, and may be a water or glycol based liquid coolant.

The coolant may be formulated to have a boiling point (in ambient pressure conditions, i.e. approximately 100 kPa) of approximately 100 degrees Celsius (°C), preferably at least 90 °C, more preferably at least 100 °C. The circulation system may control the temperature of the coolant supplied to the heat exchanger by controlling the temperature of the one or more thermal exchangers. Advantageously precise temperature control of the coolant may be achieved by controlling the temperature of the thermal exchanger(s). Moreover, controlling the temperature of the thermal exchangers may be an energy efficient way of controlling the temperature of the coolant. Alternatively or additionally, the circulation system may control the temperature of the coolant supplied to the heat exchanger by, for example, controlling the flow of coolant around the circulation system between the one or more thermal exchangers and the heat exchanger. For example, the circulation system may alternatively comprise a valve for throttling the flow of coolant through the heat exchanger.

The circulation system may comprise first and second coolant circuits each comprising one or more thermal exchangers for heating or cooling coolant in the circuit, and coolant from the first and second coolant circuits may be combined for supply to the heat exchanger.

The circulation system may comprise a valve operable to control the combination of coolant in the first and second coolant circuits.

The circulation system may comprise a vapour-compression cycle heat pump including a further heat exchanger supplied with refrigerant, wherein the one or more thermal exchangers comprises the further heat exchanger.

Brief Description of the Drawings

In order that the present invention may be more readily understood, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic side view of a vehicle in the form of a passenger car comprising an air conditioning system; Figure 2 is a schematic representation of the example air conditioning system previously identified in Figure 1;

Figures 3a and 3b are partial schematic representations of the air conditioning system showing the heat pump circuit in first and second modes of operation respectively; and

Figure 4 is a schematic representation of a second example of an air conditioning system embodying the invention. Detailed Description of the Invention

Referring firstly to Figure 1, passenger car 101 comprises a body structure 102 defining internally a passenger cabin 103 in a central area for accommodating passengers, and a utilities compartment 104 at a front end of the vehicle that is sealed from the passenger cabin.

Utilities compartment 104 is used for housing functional equipment such that it is sealed from the passenger cabin for reason of safety and refinement. In conventional internal- combustion (IC) engine vehicles utilities compartment 104 may be used for housing, inter alia, the IC engine and transmission, in which use it may be referred to as an“engine- bay”. In the specific example however car 101 is an electric vehicle, an“EV”, in which motive power is provided by one or more electric motors coupled to the wheels and driven by an on-board rechargeable battery. Thus, in the example, utilities compartment 104 may primarily be employed for housing power systems and other ancillaries associated with the electric motor. Utilities compartment 104 is sealed from the passenger cabin 103 by partition wall 105 which serves to substantially prevent ingress of pollutants such as noxious fumes or noise from the utilities compartment to the passenger cabin. In the example partition 105 provides structural rigidity to the vehicle body structure, and may thus be referred to as a‘bulkhead’. Car 101 further comprises an air conditioning system, an exemplary embodiment of which is indicated generally at 106, operable to supply heated and cooled air to the passenger cabin 103 to increase the passengers’ comfort.

Air conditioning system 106 comprises a heat exchanger 107 interposed in an influent airflow to the passenger cabin 103 for exchanging thermal energy with the airflow, and a circulation system, indicated generally at 108, for supplying a heated or cooled liquid coolant to the heat exchanger 107.

Heat exchanger 107 is housed in an air handling unit 109 installed in the passenger cabin 103. Air handling unit 109 comprises a blower in the form of radial fan 110 operable to blow air over the heat exchanger 107, and ducting for ducting air from the vehicle exterior to the passenger cabin space 103 across the blower 110 and the heat exchanger 109. A first duct 111 is provided with an inlet end open to an exterior of the vehicle and an outlet end in communication with an inlet of the blower 110 for ducting air from an exterior of the vehicle to the blower. A second duct 112 is provided with an inlet end in communication with an outlet of the blower 110 via the heat exchanger 107, and an outlet end open to the passenger cabin space, such that air discharged by the blower passes over the heat exchanger 107 and is admitted to the passenger cabin space.

In the example, the circulation system 108 comprises principally a coolant circuit, indicated generally at 113, and a refrigerant circuit functioning as a vapour-compression cycle heat pump, indicated generally at 114. The refrigerant circuit 114 comprises first and second further heat exchangers 115, 116, which, in use, as will be described in further detail with reference to Figures 3a and 3b, function interchangeably as the condenser and evaporator of the heat pump circuit.

Heat exchanger 115 is a coolant-refrigerant heat exchanger, which thermally couples the refrigerant circuit 114 to the coolant circuit 113. Heat exchanger 116 is a refrigerant-air heat exchanger, which thermally couples the refrigerant circuit to atmospheric air. In the example heat exchanger 116 is installed in the utilities compartment 104 across a frontal opening to the compartment 104, such that as the car moves air will tend to flow over the heat exchanger 116 into the compartment 104.

Thus, as coolant in the coolant circuit 113 circulates through the heat exchanger 107 and the heat exchanger 115, thermal energy may be transferred between the refrigerant in the refrigerant circuit 114 and the influent airflow to the cabin via the coolant in the coolant circuit 113. Air conditioning system 106 may thus be operated to draw in fresh-air from the exterior of the vehicle, which may then be heated or cooled by the heat exchanger 107, before being admitted to the passenger cabin 103 to ventilate the cabin.

Referring secondly to Figure 2, as previously described, in the example air conditioning system 106 comprises a heat exchanger 107 arranged in the path of influent air to the passenger cabin, and a circulation system, indicated generally at 108, for supplying coolant to the heat exchanger 107.

In the example, heat exchanger 107 is a microchannel coolant-air heat exchanger, in which coolant is ducted between the inlet and the outlet through a plurality of spaced- apart narrow-gauge channels provided with radiating fins on their external surface. As the influent air flows between the channels and over the fins thermal energy is exchanged between the coolant circulating in the heat exchanger and the influent airflow.

As previously described, in the example, circulation system 108 comprises coolant circuit 113 and refrigerant circuit 114.

Coolant circuit 113 comprises a plurality of coolant-carrying pipes 201, 202, 203 forming a closed circuit through the heat exchanger 107 and the heat exchanger 115, and a pump 204 operable to pump the coolant around the circuit.

The coolant circuit 113 is configured such that the circulation of coolant through the heat exchangers is a constant-phase cycle, that is to say where the absorption or rejection of thermal energy by the coolant does not accompany a change of phase of the coolant, or indeed a significant change in pressure. Rather the liquid coolant in the coolant circuit remains in its liquid phase at a relatively constant pressure throughout the cycle, with the temperature of the coolant changing as heat energy is absorbed or rejected.

Coolant circuit 113 uses a liquid coolant. A water or glycol based liquid coolant, that is a coolant comprising a major proportion of water or glycol, is favoured for this purpose in particular because of its relatively high specific heat capacity and relatively low toxicity. Advantageously this reduces the potential for harm to passengers in the event that coolant is leaked into the passenger cabin, for example, from the heat exchanger 107. Typically such a water-based coolant will further include minor proportions of additives aimed at lowering the freezing point and/or increasing the boiling point of the liquid, for example, a glycol antifreeze additive. In the example the water-based coolant used has a relatively conventional chemical composition, comprising by weight approximately 50 percent water, and approximately 50 percent ethylene glycol, and further includes minor proportions of various other additives and corrosion inhibitors. Alternatively a glycol based‘water-less’ liquid coolant, or another liquid coolant, may be used.

In the example pump 204 is an electrically operated centrifugal pump. A number of suitable alternative pump types which may be used in substitute are however well known in the prior art, for example, diaphragm or screw pumps.

Refrigerant circuit 114 comprises first and second heat exchangers 115, 116, refrigerant compressor 205, four-way valve 206, expansion valve 207, and refrigerant-carrying pipes 208, 209, 210, 211, 212 and 213, which form a closed circuit through the heat exchangers 115, 116. In the example the refrigerant employed by the vapour-compression cycle heat pump is a hydrofluorocarbon (HFC) refrigerant, specifically tetrafluoroethane, commonly referred to by the technical designation HFC-l34a. A number of alternative suitable refrigerants are well known in the prior art. As an example, a hydrofluoro-olefm refrigerant, specifically tetrafluoropropene, commonly referred to by the designation HFO-l234yf, may alternatively be used. HFO-l234yf may be a preferred refrigerant in certain applications for its relatively lower global warming potential (GWP) rating. Heat exchanger 116 is a refrigerant-air micro-channel heat exchanger that is similar in construction to heat exchanger 107. As illustrated in Figure 1, heat exchanger 116 is arranged in an influent airflow into the utilities compartment 104 of the vehicle such that the refrigerant flowing through the heat exchanger may exchange thermal energy with the airflow. Thus, heat exchanger 116 allows refrigerant in the refrigerant circuit to absorb or reject thermal energy to atmospheric air.

Heat exchanger 115 is a refrigerant-coolant heat exchanger which thermally couples refrigerant in the refrigerant circuit 114 to coolant in the coolant circuit 113. In the example, heat exchanger 1 15 is a plate type heat exchanger, in which the refrigerant carrying channels are thermally coupled to the coolant carrying channels by thermally conductive plates.

Compressor 205 and expansion valve 207 are substantially conventional in construction and operation, and, as will be understood, function to compress and throttle respectively the flow of refrigerant around the refrigerant circuit.

As will be described in detail with particular reference to Figures 3a and 3b, in the specific example heat pump 114 is reversible in operation, such that the direction of refrigerant flow around the circuit may be reversed to thereby reverse the functions of the heat exchanger 115 and the heat exchanger 116. Thus, in the example, four-way valve 206 is provided to allow reversal of the direction of flow of refrigerant around the circuit.

In operation, pump 204 circulates liquid coolant around the coolant circuit 113 through the heat exchanger 107 and through coolant carrying channels in the heat exchanger 115. Compressor 205 likewise circulates refrigerant around the refrigerant circuit 114 through the heat exchanger 116 and through refrigerant carrying channels in the heat exchanger 115. Thermal exchange between coolant in the coolant circuit and refrigerant in the refrigerant circuit will occur in the heat exchanger 115 if a temperature gradient exists between the coolant and refrigerant. As will be understood, if coolant in the coolant circuit is warmer than refrigerant in the refrigerant circuit, the coolant may reject thermal energy to the refrigerant, thus cooling the coolant. Conversely, if coolant in the coolant circuit is colder than refrigerant in the refrigerant circuit, the coolant may absorb thermal energy from the refrigerant, thereby warming the coolant. The coolant in the coolant circuit may thus be heated or cooled by the heat pump circuit 114. The heated or cooled coolant may then similarly exchange thermal energy with the airflow to the passenger cabin via the heat exchanger 107.

It should be understood that a variety of alternative thermal exchangers for heating and cooling coolant in the coolant circuit are well known in the prior art. Thus, as an alternative to said refrigerant circuit/vapour-compression cycle heat pump 114, the circulation system 108 may alternatively comprise, for example, one or more thermoelectric devices or resistive heater elements in thermal contact with the coolant in the coolant circuit, for example, in the place of heat exchanger 115. As a further alternative, instead of dedicated thermal exchangers, the coolant circuit may exchange thermal energy with, for example, vehicle motor, drivetrain or battery components to heat or cool the coolant in the coolant circuit. A vapour compression cycle heat pump, such as refrigerant circuit 114, may however be preferred to such alternatives in many applications for its relatively high efficiency and operational flexibility.

Referring next to Figures 3a and 3b, as previously described, in the example said heat pump 114 is reversible in operation, such that the function of heat exchangers 115 and 116 may be changed to allow selective heating and cooling of cooling in the coolant circuit.

Referring firstly to Figure 3a, the heat pump circuit 114 is shown in a first,‘cooling’, mode of operation in which the heat pump is being used to cool coolant in the coolant circuit.

In this mode of operation circulating refrigerant enters the compressor 205 in the gaseous phase, and its pressure and temperature are increased. The superheated vapour is directed by the four-way valve 206 through the heat exchanger 116, which in this mode operation functions as the condenser. As the refrigerant travels through the condenser it is cooled by the through flow of ambient air, rejecting heat from the refrigerant to the atmosphere, and condensed into a liquid. The condensed liquid refrigerant is next routed through expansion valve 207, where it undergoes an abrupt reduction in pressure, resulting in adiabatic flash evaporation of a part of the liquid refrigerant greatly lowering its temperature. From the expansion valve the cold refrigerant is routed through the heat exchanger 115, which in this mode functions as the evaporator. As the blower 111 blows relatively warmer air across the heat exchanger 115 the liquid part of the refrigerant is evaporated, further lowering the refrigerant temperature and cooling the flow of air to the passenger cabin. To complete the cycle the refrigerant vapour is then routed back through the four- way valve into the compressor.

Thus, in this mode of operation the heat exchanger 116 functions as the condenser, rejecting heat from the refrigerant to the atmosphere, and the heat exchanger 115 functions as the evaporator absorbing heat from the coolant circuit to thereby cool the coolant. The cooled coolant may subsequently be circulated through the heat exchanger 107 to cool the airflow into the passenger cabin.

Referring secondly to Figure 3b, it will be noted that the configuration of the four-way valve 206 is changed such that direction of refrigerant flow through the heat exchanger 116, the expansion valve 207, and the heat exchanger 115, is reversed from the configuration shown in Figure 3a. Consequently, in this second configuration, superheated vapour refrigerant from the compressor firstly enters the heat exchanger 115 where the superheated gaseous phase refrigerant may reject heat to the relatively cooler coolant in the coolant circuit to thereby warm the coolant, and secondly, via the expansion valve 207, the refrigerant enters the heat exchanger 116, where the part-liquid refrigerant evaporates and absorbs heat from the atmosphere. Thus, in this second mode of operation the heat pump may be used to warm coolant in the coolant circuit and so warm the airflow to the passenger cabin. Thus, by suitable control of the heat pump system 114, and in particular by providing means for control of the four-way valve 206, the air conditioning system may be controlled to selectively heat and cool influent air to the passenger cabin.

An exemplary alternative embodiment of an air conditioning system embodying the invention is depicted schematically in Figure 4. Air conditioning system 401 shares many components with air conditioning system 114 previously described with reference to Figures 1 to 3b, and in the Figure like components are identified by like reference numerals.

Similar to air conditioning system 114, air conditioning system 401 comprises heat exchanger 107’ and a circulation system, indicated generally at 108’, for supplying coolant to the heat exchanger 107’ . Circulation system 108’ comprises principally of first and second coolant circuits 402, 403, and a refrigerant circuit 404, similarly functioning as a vapour compression cycle heat pump. Refrigerant circuit 404 comprises first and second further heat exchangers 115’, 116’, adapted to function as the evaporator and condenser of the heat pump respectively.

Coolant circuit 402 is arranged to circulate coolant through the heat exchangers 107’ and 115’ by operation of pump 204’. Accordingly, similarly to coolant circuit 113, coolant circuit 402 functions to thermally couple the heat exchanger 107’ to the heat exchanger 115’ of the refrigerant circuit 404.

Coolant circuit 403 is provided with a heating device 405, which in the example is an electrical resistive heater element, operable to heat coolant in the coolant circuit 403, and a further pump 204” operable to circulate coolant across the heater element 405 and through the heat exchanger 107’. Accordingly, coolant circuit 403 thermally couples the heater 405 to the heat exchanger 107’.

Coolant circuits 402 and 403 each form a closed loop arranged in parallel with respect to the heat exchanger 107’, arranged on a branch 406 common to the circuits. Branch 406 is provided with a three-way valve 407, operable to throttle or shut-off the flow of coolant around each of the coolant circuits 402, 403 to thereby control the degree of combination of coolant from the coolant circuit 402 with coolant from the coolant circuit 403 prior to circulation through the heat exchanger 107’ . Thus, valve 407 may be operated to vary the proportion of coolant from the circuit 402 compared to the proportion of coolant from the circuit 403 that enters the branch 406 and is circulated through the heat exchanger 107’.

Refrigerant circuit 404 is substantially similar to refrigerant circuit 114, excepting that refrigerant circuit 404 is configured to be operable only in a single, cooling, mode of operation, to cool coolant in the coolant circuit 402, rather than being reversibly operable to both heat and cool the coolant.

Heat exchanger 107’ may thus be supplied with cooled coolant by coolant circuit 402 which exchanges thermal energy with the evaporator function heat exchanger 115’ of refrigerant circuit 404, and with heated coolant by coolant circuit 403 comprising resistive heater element 405.

In this embodiment, air conditioning system 401 further comprises an electronic control unit 408 in electrical communication with each of the first and second coolant pumps 204’, 204” and the valve 407. The electronic control unit 408 is operable to control the operation of the pumps 204’, 204”, for example, by controlling the speed of the pumps and so the pumping rate. The electronic control unit 408 is further operable to control the state of the valve 407, for example, to control the restriction presented by the valve to coolant flow around each of the first and second coolant circuits 402, 403 respectively, and thereby control the relative proportions of coolant from each of the circuits 402, 403 that is supplied to the heat exchanger 107’. As an alternative to the common electronic control unit 408, the pumps 204, 204”, and the valve 407 could each be provided with individual controllers.

Valve 407 may thus be operated to control the flow of coolant from each coolant circuit through the heat exchanger, and so control the temperature of the coolant circulated through the heat exchanger 107’. For example, in a first configuration, valve 407 may shut-off the circulation of heated coolant in the coolant circuit 403 through the heat exchanger 107’, whilst permitting circulation of cooled coolant from the coolant circuit 402. Thus, in this first configuration the heat exchanger 107’ may be supplied with cold coolant to enable cooling of the influent airflow to the passenger cabin. In a second exemplary configuration the valve 407 may shut-off circulation of cooled coolant in the coolant circuit 402 through the heat exchanger 107’, while permitting circulation of heated coolant in coolant circuit 403. Thus, in this second configuration the heat exchanger 107’ may be used to heat the influent airflow to the cabin. In a third exemplary configuration the valve 407 may be operated to throttle the circulation of coolant from each coolant circuit through the heat exchanger 107’, such that a combination of heated coolant from the coolant circuit 403 and cooled coolant from the coolant circuit 402 may be circulated through the heat exchanger 107’. In the latter mode of operation valve 407 may thus operate to adjust the temperature of the coolant circulated through the heat exchanger 107’ between the temperature extremes of coolant in each of the coolant circuits 402, 403.

Claims

1. A vehicle air conditioning system comprising:

a heat exchanger,

a blower for blowing air over the heat exchanger, and

a circulation system for supplying coolant to the heat exchanger, the circulation system comprising:

a first coolant circuit comprising a first thermal exchanger for cooling coolant in the first coolant circuit,

a second coolant circuit comprising a second thermal exchanger for heating coolant in the second coolant circuit, and

a valve for controlling the combination of coolant from the first coolant circuit with coolant from the second coolant circuit,

wherein the valve is controllable to control the combination of cooled coolant from the first coolant circuit with heated coolant from the second coolant circuit to thereby control the temperature of coolant supplied to the heat exchanger.

2. A vehicle air conditioning system as claimed in claim 1, wherein the valve is common to the first coolant circuit and the second coolant circuit.

3. A vehicle air conditioning system as claimed in claim 1 or claim 2, wherein the first thermal exchanger of the first coolant circuit and the second thermal exchanger of the second coolant circuit are in fluid parallel with respect to the heat exchanger.

4. A vehicle air conditioning system as claimed in any one of the preceding claims, wherein the first thermal exchanger of the first coolant circuit and the second thermal exchanger of the second coolant circuit are operable simultaneously to cool coolant in the first coolant circuit and heat coolant in the second coolant circuit.

5. The vehicle air conditioning system as claimed in any one of the preceding claims, wherein the first coolant circuit comprises a first coolant pump for pumping coolant in the first coolant circuit and the second coolant circuit comprises a second coolant pump for pumping coolant in the second coolant circuit.

6. A vehicle air conditioning system as claimed in claim 5, comprising an electronic controller for independently controlling the operation of the first coolant pump and the second coolant pump.

7. The vehicle air conditioning system of any one of the preceding claims, wherein the coolant is water or glycol based.

8. The vehicle air conditioning system of any one of the preceding claims, comprising a vapour-compression cycle heat pump including a further heat exchanger, wherein the one or more thermal exchangers of the first coolant circuit comprises the further heat exchanger.

9. The vehicle air conditioning system of any one of the preceding claims, wherein the vapour-compression cycle heat pump is operable in a first mode of operation such that said further heat exchanger cools the coolant in the first coolant circuit and in a second mode of operation such that said further heat exchanger heats the coolant in the first coolant circuit.

10. The vehicle air conditioning system of claim 8 or claim 9, wherein the heat exchanger is installed in a passenger cabin of a vehicle and the further heat exchanger is installed in a compartment sealed from the passenger cabin.

11. The vehicle air conditioning system of any one of the preceding claims, further comprising ducting for ducting air from a vehicle exterior to a vehicle passenger cabin via the blower and the heat exchanger.

12. A vehicle having a passenger cabin for accommodating passengers and comprising an air conditioning system according to any one of the preceding claims for ventilating the passenger cabin.

13. The vehicle of claim 12, wherein the vehicle comprises a compartment sealed from the passenger cabin, and wherein the heat exchanger is installed in the passenger cabin and the further heat exchanger is installed in the compartment.

14. The vehicle of claim 12 or claim 13, further comprising ducting for ducting air from outside the passenger cabin to the passenger cabin via the blower and the heat exchanger.