Reversible heat pump system

0001This invention relates to a reversible heat pump system suitable for heating and air conditioning use in motor vehicles.

0002Vehicle air conditioning systems are well established. Conventionally, the air conditioning system is used only to cool the passenger compartment, with heating being separately provided using waste engine heat.

0003It is also known, although less common, for such systems to be reversible so as to be usable for cooling or heating the passenger compartment. In the present application, the cooling mode is referred to as "air conditioning" or "A/C", while the heating mode is referred to as "heat pump" operation. This is desirable, for example, where the available engine heat is limited, as with high efficiency diesel engines. Examples of reversible systems are shown in GB 2,375,596A, US 4,991,405, and EP 1,247,670.

0004There are, however, situations in which it would be desirable to provide both air conditioning and heat pump operation simultaneously, especially for simultaneous heating and de-fogging of the passenger compartment.

0005Accordingly, the present invention provides a reversible heat pump system for use in heating and cooling a given space, comprising: <ul id="ul0001" list-style="none" compact="compact"><li>a compressor;</li><li>an outside heat exchanger which, in use, is positioned outside said space;</li><li>an inside heat exchanger positioned, in use, inside said space; and</li><li>a reversing valve connected to the compressor such that the outside heat exchanger can be connected to act as a condenser or an evaporator;</li><li>and is characterised in that: <ul id="ul0002" list-style="none" compact="compact"><li>the inside heat exchanger comprises an evaporator and a condenser or gas cooler;</li><li>a control valve is positioned such that closure of the control valve prevents flow through the outside heat exchanger; and</li><li>further valve means are provided which are operable, when said control valve is fully or partially closed, to permit refrigerant to flow through the condenser or gas cooler and the evaporator sequentially.</li></ul></li></ul>

0006In this way, the system can be selectively operated in a heat pump mode, an A/C mode, or a de-fogging mode.

0007Preferred features and advantages of the invention will be apparent from the claims and the following description.

0008An embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which: <ul id="ul0003" list-style="none" compact="compact"><li>Figure 1 is a schematic of one form of reversible heat pump system in accordance with the invention;</li><li>Figure 2 shows the system of Figure 1 in operation in air conditioning (cooling) mode;</li><li>Figure 3 shows the system of Figure 1 in operation in heat pump (heating) mode; and</li><li>Figure 4 shows the system of Figure 1 in operation in a defogging mode.</li></ul>

0009Referring to Figure 1, the system comprises a compressor 10 having an inlet 12 connected to a reversing valve 14 via an accumulator-drier 16, and an outlet 18 also connected to the reversing valve 14. The inlet 12 is also connected to an air conditioning evaporator 20.

0010The AC evaporator 20 is positioned in the vehicle interior along with a heat pump condenser 22. A heating ventilating and air conditioning air flow 36, produced by a suitable fan, can be directed across the AC evaporator 20 and subsequently the HP condenser 22 and thence into the vehicle interior. An outside heat exchanger 24 is positioned exteriorly of the vehicle cabin.

0011One side of the HP condenser 22 is connected to the reversing valve 14, and the other side via an orifice tube 26 and check valve 28 to a control valve 30. The AC evaporator 20 is connected between the accumulator drier 16 and the control valve 30 via an orifice tube 32 and a valve 34. The outside heat exchanger 24 is connected between the opposite side of the control valve 30 and the reversing valve 14.

0012The system is thus similar to prior art reversible systems except for the addition of the control valve 30.

0013Figure 2 shows the system operating in air conditioning (cooling) mode. The control valve 30 is open, as is the AC evaporator valve 34. Refrigerant circulates as shown, with the outside heat exchanger 24 acting as a condenser. Flow through the HP condenser 22 is prevented by the check valve 28.

0014Figure 3 shows the system operating in heat pump (heating) mode. The control valve 30 is open, and the AC evaporator valve 34 is closed. Refrigerant circulates as shown, with the outside heat exchanger 24 acting as an evaporator.

0015Figure 4 shows the system operating in defogging mode. With the AC evaporator valve 34 open and the control valve 30 closed, refrigerant circulates as shown in full lines. In this condition, the AC evaporator 20 acts as the system evaporator, the HP condenser 22 acts as the system condenser, and the outside heat exchanger 24 is inoperative.

0016The air flow 36 passes first through the AC evaporator 20 which cools the air below its dew point thereby removing moisture. This air is then reheated by passing through the HP condenser 22. In this condition the heat extracted from the air by the AC evaporator 20 plus that supplied by the compressor 10 is supplied to the air at the HP condenser 22.

0017Alternatively, the control valve 30 can be partially opened, giving the refrigerant flow indicated in dashed lines. In this condition, additional heat is added to the system from the outside heat exchanger 24.

0018The AC evaporator 20 may be provided with a sensor (not shown) for detecting freezing of the evaporator, the control valve 30 being partially opened in response to evaporator freezing to provide additional heat.

0019An automatic control may be added to produce gradual opening of the control valve 30 accompanied by gradual closing of the AC evaporator valve 34, in order to achieve a gradual transition from defogging to heat pump mode.

0020The foregoing embodiment is suitable for use with conventional refrigerant. If a gas such as carbon dioxide is sued as the refrigerant, the condenser would be replaced by a gas cooler.

0021The invention is particularly useful in vehicles such as cars, but may also be used in other forms of HVAC systems. Modifications may be made to the foregoing embodiment within the scope of the appended claims.