1. Field of the Invention
The present invention relates to refrigeration/air conditioning equipment, and particularly to refrigeration/air conditioning equipment in which the heating capacity at low outdoor temperature is improved by gas injection, and a defrosting operation is performed efficiently.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2001-304714 discloses refrigeration/air conditioning equipment including a gas-liquid separator in an intermediate-pressure portion between a condenser and an evaporator. A gas refrigerant separated by the gas-liquid separator is injected into an intermediate-pressure portion of a compressor to increase the heating capacity.
Japanese Unexamined Patent Application Publication No. 2000-274859 discloses another conventional refrigeration/air conditioning equipment without a gas-liquid separator. In this equipment, part of a high-pressure liquid refrigerant is bypassed, is decompressed, is vaporized through heat exchange with the high-pressure liquid refrigerant. The vaporized refrigerant is injected into a compressor to increase the heating capacity.
Japanese Unexamined Patent Application Publication No. 2001-263882 discloses still another conventional refrigeration/air conditioning equipment, in which a heater for heating a refrigerant is provided to improve the efficiency in a defrosting operation.
However, these pieces of conventional refrigeration/air conditioning equipment have the following problems.
First, as described in the Japanese Unexamined Patent Application Publication No. 2001-304714, when the injection is performed with the gas-liquid separator, the fluid volume in the gas-liquid separator varies with the amount of the injection. This variation causes fluctuations in the distribution of a liquid refrigerant level in a refrigeration cycle and makes the operation unstable.
When the flow rate of a gas refrigerant to be injected is substantially equal to the flow rate of a gas refrigerant in a two-phase refrigerant flowing into the gas-liquid separator, only the liquid refrigerant flows out to an evaporator and therefore the liquid refrigerant level in the gas-liquid separator is substantially constant. However, when the flow rate of the gas refrigerant to be injected is smaller than that of the gas refrigerant flowing into the gas-liquid separator, the gas refrigerant also flows out to the evaporator from the bottom of the gas-liquid separator. Thus, most of the liquid refrigerant in the gas-liquid separator flows out. Conversely, when the flow rate of the refrigerant to be injected increases and the gas refrigerant becomes deficient, the liquid refrigerant is also injected into the compressor. Thus, the liquid refrigerant flows out from the top of the gas-liquid separator, and the gas-liquid separator is almost filled with the liquid refrigerant.
The injection flow rate tends to vary, for example, with the pressure of the refrigeration cycle, the pressure of the gas-liquid separator, or the operation capacity of the compressor. Thus, the injection flow rate hardly balances with the flow rate of the gas refrigerant flowing into the gas-liquid separator. Actually, the liquid refrigerant level in the gas-liquid separator tends to vary with the operation and be almost zero or full. This variation often causes fluctuations in the distribution of the refrigerant in the refrigeration cycle, making the operation unstable. Furthermore, the heater as in the Japanese Unexamined Patent Application Publication No. 2001-263882 is only used in a defrosting operation and does not contribute significantly to the increase in the capacity during a heating operation.