Air valve heat pump refrigeration systems may be included in air conditioners so that air in the enclosure to be conditioned may be either heated or cooled for comfort. During the cooling operation, the air valves are positioned to cause indoor air to be circulated through the evaporator and outdoor air circulated through the condenser. Conversely, during the heating operation, the air valves cause indoor air to be circulated through the condenser and outdoor air circulated through the evaporator.
During the summer cooling operation or cycle, there is a considerable temperature differential between the evaporator and its surrounding atmosphere, the room air, whereas during the winter heating operation or cycle, there is ordinarily a much smaller differential between the evaporator and its surrounding atmosphere, the cold outside air. Thus, the evaporator subjected to outdoor temperatures and, in some instances, to frost accumulation during the heating cycle cannot pick up as much heat as is absorbed during the cooling cycle. As a result, the system cannot be operated with good efficiency at the same rate of refrigerant flow for both operations. A rate of refrigerant flow which allows substantially complete vaporization of refrigerant in the evaporator operating under indoor ambient during cooling results in a "flooding through" of the evaporator operating under outdoor ambient during the heating operation. In other words, with the most efficient rate of flow for the cooling cycle flowing during the heating cycle, the evaporator operating under outdoor ambient would be unable to vaporize all the refrigerant flowing therethrough so that liquid refrigerant would pass or "flood through" to the compressor.
In reverse cycle heat pumps, refrigerant flow is reversed through the system when changing from cooling to heating modes of operation.
By employing one way flow check valves and a capillary of different flow characteristics in parallel with each of the check valves one of the capillaries is bypassed depending on the direction of refrigerant flow. Accordingly only the capillary having the proper flow characteristics for the selected mode of operation monitors flow from the heat exchanger functioning as a condenser to the heat exchanger functioning as the evaporator.
In air valve heat pump systems the refrigerant flow is not reversed since air is selectively directed over the heat exchangers between the heating and cooling modes of operation. This means that the capillaries cannot be substituted as of function of the direction of refrigerant flow.
Accordingly, it is an object of the present invention to provide means for modulating restriction as needed to maintain a fixed level of liquid in the condenser.