A heat pump system economic operation of the basic requirements: 1, as far as possible the use of high temperature heat source. 2, the actual temperature difference between heat source and heat medium is the lowest. 3, the heat source should meet the following requirements: --- In the highest possible heating temperature to provide the required heat. --- The cost of using the heat source is lower. --- Whether in the chemical or physical, heat exchange equipment does not have a negative impact. --- Heat conditions change, better adaptability. --- Conveying equipment such as fans, pumps and other energy consumption as low as possible. Second, the heat pump system compressors should meet the following requirements: 1, for the air source heat pump, tz = -35 ~ +15 oC and tl ≤ 65 oC range should be able to operate normally; compression ratio up to 9, there should be satisfactory Efficiency; the same time, there should be no excessive temperature overheating. 2, the inhalation of steam in the superheated and unsaturated state, the compressor is not affected by the quality of inhalation. 3, can withstand the rapid changes in work pressure, does not produce oil foam; oil should be returned to the crankcase with steam, and in the box with immersion heaters. 4, there should be good, reliable over-temperature, over-voltage protection device. Trouble-free operation time in more than 25000h. 5, Larger heat pump, should be equipped with a smooth and without loss of energy mediator. 6, Compressor equipped with motor, with a flat efficiency curve. Based on the above requirements, put forward the following recommendations: Heating Q = 0.5 ~ 500KW, the use of positive displacement. Heating Q> 500KW, the use of centrifugal. Third, the refrigerant flow control to the use of thermal expansion valve is appropriate, and should be "balanced hole" type, in order to maintain the pressure does not change with the change, but in the case of smaller pressure normal operation. Economical judgments For a heat pump system with a certain performance, it is generally considered economical when used under the following conditions: There is a good source of heat, such as groundwater. The annual running time is not less than 2000h. COP values> 3 No heating is required for heating cycles based on summer cooling. Refrigeration equipment has been used in the occasion, such as cold storage, skating rink, supermarkets and so on. Waste heat available for use. Large internal waste heat within the building, it is possible to use the internal heat source to heat the building when the ambient temperature is below zero, such as department stores, theaters, computer rooms. Conversely, the economics of a heat pump in the following situations are not certain: for heating only. COP <3. Heat pump capacity is much larger than the heating load.