Reuse of Thermal Energy in Municipal Reclaimed Water: Assessment for Transmission Distance

Abstract

With the aim of energy-saving and environment protection, Chinese government and energy consumers are focusing on energy recovery from municipal reclaimed water using the heat pump during building heating and cooling. Municipal reclaimed water assembled in treatment units need to be transmitted to satisfy remote heating and cooling demands in large-scale utilization projects, and transmission distance between treatment units and energy consumers is an important problem greatly affecting the efficient and economic performance of a municipal reclaimed water source heat pump system. Three key problems depending on transmission distance were analyzed. Reclaimed water temperature variation along the delivering pipeline was discussed in consideration of the mutual influence between the transmission medium and the circumjacent soil. Energy consumption of the transmission process was calculated based on pipeline frictional resistance, transmission energy consumption ratio was proposed as an evaluation index reflecting the system energy-saving rate; the transmission distance influence on economic performance was evaluated by dynamic investment payback period and internal return rate. A comprehensive model to determine the transmission distance was presented, which can provide a theoretical analysis tool for system design.