A piping cleaning system switches over a four-way switching valve 43 of a heat pump circuit 200 so that two transfer heat exchangers 25, 26 are operated alternately as a cooling device and a heating device, by which a cleaning refrigerant in a cleaning circuit 2 is circulated through a gas line 3 and a liquid line 5. During this cleaning operation with the cleaning refrigerant circulated, when the cleaning refrigerant runs short in amount, a solenoid valve SV3 is opened so that cleaning refrigerant of the refrigerant cylinder 71 is resupplied through a refrigerant resupply line 72 to either one of the transfer heat exchangers 25 or 26 that is cooling. On the other hand, when the cleaning refrigerant is excessive, a solenoid valve SV4 is opened so that the cleaning refrigerant is returned to the refrigerant cylinder 71 through a refrigerant bleed line 73. Thus, the amount of cleaning refrigerant can be maintained at an appropriate level.
This application is the national phase under 35 U.S.C. .sctn.371 of PCT International Application No. PCT/JP98/04020 which has an International filing date of Sep. 8, 1998, which designated the United States of America.
Disclosed herein is a control method for a multiple heat pump. In the control method, when one of multiple indoor units operates in the heating mode and the other indoor units shut down, electronic expansion valves of the shutdown indoor units are controlled to have an opening degree higher than a standard opening degree if an outlet temperature of compressors is higher than a preset temperature, so as to permit a liquid refrigerant, remaining in the shutdown indoor units, to be more readily recovered to the compressors. This eliminates a refrigerant shortage phenomenon of the compressors and prevents deterioration of heating performance as well as reduction of life-span of the compressors.
An air conditioning system is disclosed which takes advantage of low ambient temperature conditions so as to activate a refrigerant flow that bypasses the compressor. The activation of the refrigerant flow is achieved by the intelligent control of a pump positioned between the outlet of the condenser and the inlet of an expansion device upstream of the evaporator. The refrigerant flow produced by the pump does not require any particular positioning of the condenser and evaporator components with respect to each other. The evaporator preferably absorbs heat from water circulating in a secondary loop which is used to remove heat from a building by one or more fan coil units.
