Design and Optimization of an Integrated Bathhouse Wastewater-Solar Heat Pump System

Yongji Wang; Xiaolei Yuan; Cheong Peng Au-Yong; Bee Teng Chew; Mingyuan Qin

doi:10.53941/ubs.2025.100003

Abstract

Public bathhouse wastewater exhibits significant waste heat recovery potential due to its high-temperature and high-flow characteristics. However, the temporal mismatch between wastewater availability cycles and bathing demand necessitates supplementary heat sources, with solar energy emerging as a critical renewable solution. Current research gaps persist in understanding multi-factor synergy mechanisms and parameter optimization in solar-wastewater source heat pump (WSHP) coupled systems. This study focuses on a university bathhouse in Changchun, China, designing a solar-WSHP hybrid heating system integrated with an air-source heat pump (ASHP) as auxiliary backup, tailored to academic calendar-driven operational cycles and bathing load characteristics. Utilizing the Transient System Simulation Tool (TRNSYS), a dynamic simulation model was developed to analyze annual performance, while a five-level orthogonal experimental design optimized four key parameters: solar collector area, storage tank volume, WSHP heating capacity, and ASHP heating capacity. Results demonstrate that the optimized system not only meets the hot water load demand, but also improves energy performance, with solar heat collection increased by 13.22% and the coefficient of performance (COP) of the wastewater source heat pump improved by 3.16%. In terms of economy, the initial investment of the system is reduced by 11.40%, and the annual operation cost is decreased by 1.80%. The composite system can reduce carbon dioxide emissions by 706.15 tons each year. This study provides theoretical and technical foundations for multi-objective optimization of waste heat recovery systems in public buildings, particularly addressing the operational demands of educational institutions.

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