Applied Energy, Vol.236, 690-699, 2019
Experimental performance evaluation of a novel anti-fouling wastewater source heat pump system with a wastewater tower
Using wastewater source heat pumps to recover heat from the sewage discharged from buildings could help improve building energy utilization efficiency remarkably, which is a promising technology in near-zero energy buildings and should be widely used. However, fouling deposit would occur on a heat exchanger surface due to the poor water quality of wastewater, which would affect the heat transfer performance and may even block the heat exchanger, reducing the reliability of a wastewater source heat pump unit. Fouling poses a challenge for the wider application of wastewater source heat pumps. A novel anti-fouling wastewater source heat pump system with a wastewater tower was proposed in this work and its operational performances were experimentally investigated based on a long-term test of 41 days (492 h). Experimental results showed that the heat transfer rate in the evaporator of the novel wastewater source heat pump was stable during the 41-day test at an average of 3.80 kW. Unlike in the evaporator of a conventional wastewater source heat pump unit, the total thermal resistance in the evaporator of the novel wastewater source heat pump unit was not increased but only fluctuated around an average of 0.0267 K m(2)/W throughout the entire 41 days test. The evaporating temperature of the refrigerant stayed stable around an average of 2.74 degrees C. Furthermore, the coefficient of performance of the unit was also stable at an average of 3.32 and the coefficient of performance of the system maintained an average of 2.13. The condensate drained away from the bottom of the evaporator did not contain any foulant. In addition, the photos for the evaporator showed that its surface was still clean after the 41-day test. Therefore, the experimental results suggested that the novel wastewater source heat pump system not only had superior performance of heat recovery but also achieved effective anti-fouling on its evaporator surfaces.