Sewage source heat pump is to rely on the internal circulation of the refrigerant heat pump cycle changes in the winter to absorb heat from the sewage heat pump after heating the building in summer through the heat pump unit to the building's heat transfer to the sewage in order to achieve cooling. Sewage instead of the cooling tower to solve the cooling tower noise, drift and other issues, with high efficiency and energy saving, green, safe and reliable, a multi-purpose machine and other prominent advantages. Sewage source heat pump to achieve the recycling of urban waste heat, turning waste into treasure, is a new renewable clean energy use of technology, in line with the sustainable development and building a resource-saving and environment-friendly society requirements. The combination of water source heat pump system technology and urban sewage has far-reaching significance in expanding the scope of urban sewage utilization and expanding the benefits of urban sewage treatment. There are three forms of urban sewage: sewage raw water, secondary water, water. The city has a wide range of sources of sewage and large confluence area, with the features of large water flow, stable water volume, suitable temperature and relatively stable water temperature. Details are as follows: a) Water temperature characteristics Monitoring data in Beijing show that in winter, the temperature of urban sewage is between 12-20 ℃, the water contains a lot of low-temperature heat, heat pump system is a good low-temperature heat source; summer urban sewage temperature between 20-25 ℃, and small daily variation, it can be used as a heat pump condensing heat radiator body. The temperature characteristics of urban sewage can well meet the needs of stable and efficient operation of sewage heat pump system. Therefore, urban sewage as a heat pump system, heat sink has great value. b) Characteristics of water Municipal wastewater treatment plant effluent water volume and stability, large flow, stable flow rate can make the heat pump unit stable operation, the normal operation of the unit performance, have better energy-saving effect and utilization prospects. With the improvement of residents' living standards, the increase of water quota and water use standard, especially the increase of domestic hot water consumption, urban sewage discharge and heat discharge show an increasing trend year by year. The potential of urban sewage heat utilization also will show a trend of increasing year by year. The application prospect of urban sewage heat pump is broad. c) Water Quality Characteristics There are mainly three kinds of water quality in city sewage affected by heat pump system: corrosion, scale and blockage, microbial deposition and growth. If the sewage directly enters the heat exchanger, it will still affect the system to a certain extent. The usual practice is to set up a heat exchanger between the city sewage and the heat pump circulating water to set up a filtering and cleaning device before the urban sewage inlet heat exchanger so as to ensure that the heat exchanger works efficiently and stably and the heat pump unit only absorbs heat from the urban sewage Or to release heat to the water, the exchange of energy after the city sewage from the return pipe back to the urban sewage discharge system. Since the 1980s, the United States, Japan, Australia, Norway, Switzerland, Sweden and the former Soviet Union and other countries have used urban sewage to establish a number of large-scale sewage source heat pump systems. Starting from a few megawatts of stand-alone capacity, up to 30 megawatts of stand-alone capacity and a total installed capacity of 160 megawatts in a single project are now available. With the increasing awareness of environmental protection, the introduction of measures to control air pollution, the adjustment of building energy structure, sewage source heat pump technology has been rapid development in our country.