Operational analysis of a newly untreated sewage source heat pump with a plate heat exchanger

Urban untreated sewage is widely used as a heat source in the heat pump system. Sewage energy has typically been extracted indirectly, i.e., by setting up a heat exchanger before the units. Among sewage heat exchangers, the shell-and-tube heat exchanger is widely applied, while the untreated sewage source heat pump system using a plate heat exchanger is less common owing to its special structure requiring a higher quality of sewage treatment and a superior cleaning method. To solve this problem, a specially designed, sewage source heat pump system was developed and tested. It consists of a kind of pretreatment device, i.e. self-designed spiral-flow type sewage filter and automatic backwashing plate sewage heat exchanger. The model of the heat transfer coefficient of the plate heat exchanger is validated through the comparison between the actual operation data and the theoretical value, and then the influence of the sewage flow velocity on the exchanger is analyzed. Finally, the COP value is calculated, and an energy conservation performance evaluation of the complete system is performed. The test results of actual operation show that the COP value of the new sewage source heat pump system proposed in this paper is 3.02. The filter device has good anti-clogging effect, and the heat exchanger runs stably, achieving the expected energy saving effect.