To sewage treatment plants, the sewage is plenteous and costless. If the sewage is utilized for air conditioning purpose, it will achieve more value. The temperature of sewage is basically constant in summer or winter. The treated sewage can be used for absorbing the condensing heat in summer and releasing heat to the building space in winter through the sewage heat exchanger. Especially the heating coefficient of the sewage source heat bump is higher in winter, which is an advantage to heating. In this paper the cooling and heating theory of the sewage source heat bump is briefly introduced, the advantages and disadvantages of sewage source heat bump system is explained. With an example in Beijing, China, compared with the boiler/ductless split air conditioner system, the initial investment and annual operating cost are calculated and the economics of the sewage source heat pump system is analyzed. At last the impact of fossil fuel rate and electric rate on the annual operating costs is analyzed. The calculating results showed that under the present rates of fossil fuel and electricity in China, the initial investment of the sewage source heat pump system is higher, the annual operating cost is lower than that of the boiler/ductless split air conditioner system. All these above will be good references for the actual applications of sewage source heat pump systems.

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