A field study of a wastewater source heat pump for domestic hot water heating

Abstract

An experimental heat pump utilizing wastewater discharged from the common bathroom in a SPA center as a heat source was built. In this article, the field measured operating performance of the wastewater source heat pump is reported. An analysis based on the collected field data under various operating conditions is included. It was shown that the temperature of wastewater greatly affected the evaporating temperature and the coefficient of performance of the wastewater source heat pump. Circulating wastewater from the bottom to the top of the wastewater storage tank could weaken even out the vertical wastewater temperature distribution inside the wastewater storage tank and improve the coefficient of performance and compressor suction pressure of the wastewater source heat pump accordingly. The daily averaged coefficient of performance of the wastewater source heat pump was monitored for over an entire month. It was shown that the measured coefficient of performance gradually reduced, suggesting the need for regular cleaning of the heat exchangers used in a wastewater source heat pump system. In addition, the recorded maximum transporting capacity of the wastewater pipe reduced by 16.9% over the 1 month operation and by 20.1% after ∼5 months due to the bio-fouling build-up. Finally, an analysis comparing the economics of operating a wastewater source heat pump system with that of operating conventional water heating systems is presented.

Practical application: The use of heat pump to recover heat from wastewater is significant to energy conservation and environmental protection. A number of researches and projects on wastewater source heat pumps using urban sewage or treated sewage as a heat source have been carried out. However, field measured results on a heat pump, which recovered heat from waste bath water, was not previously reported. As the quality of waste bath water was different from that of sewage in terms of temperature, amount, and the degree of cleanliness, the experiences on designing and operating urban sewage source heat pumps previously obtained could not be used as a full reference for designing a waste bath water source heat pump. In this article, field experiment work of designing and operating a heat pump which used waste bath water as a heat source for hot water heating is presented, and the results can be used as a key reference for designing and operating waste bath water source heat pump systems in the future.