Usage of wastewaters as a heat source for a heat pump operation

Abstract

A significant improvement in economic and environmental performance of production thermal energy can be achieved by using heat pumps. Whereas ground waters, an air and a ground itself are well-known and explored heat sources, the heat that residents return to the ground with sewage remains mostly unused. Meanwhile, sewages possess necessary characteristics (such as relatively high temperatures, widespread availability and an absence of necessity in costly drilling works) to serve as a low-potential heat source. Investigated technologies are interesting for a large number of customers: from the private-house owners, who use local treatment facilities, to the water treatment plants. Difference in initial conditions such as effluents temperatures, their flow rates and quality leads to variety of technical decisions.

The main aim of submitted thesis is to estimate the potential of utilizing wastewater as a source of low-potential heat for the heat pump operation in scale of a one-family house. The thesis starts with a technical review of existing technologies, which is based on results of the literature analysis. In the practical part, the feasibility analysis of implementation the wastewater source heat pump system for heating and hot water preparing systems in a one-family house is performed. Calculated and compared values of thermal energy that could be extracted from effluents by heat exchanger and the energy demand of heating and hot water systems in the building. Performed a simulation of heat pump operation with use of CoolPack program. Its results demonstrate which part of required low-potential heat could be obtained from sewage. Finally, assessed an energy efficiency of pro-posed wastewater source heat pump system and its economic validity.

Obtained results indicate that wastewater can be considered only as an additional source of low-grade heat for a heat pump operation into a heating mode in scale of a one-family house. The main precondition is unevenness of water use. Meanwhile, the heat of sewage is sufficient for preparing hot water for domestic use (with a heat pump application). Evaluation of the payback period of the proposed sewage source heat pump system revealed the inexpediency of its application in case of existing connection to the gas pipeline. From the standpoint of energy efficiency, the heat pump system proved to be the most efficient converter of primary fuel energy (with using natural gas as the main fuel on the power station).