Enhancing heat pump performance by drain water heat recovery and solar air heater–Experimental and numerical studies

This manuscript presents a hybrid numerical-experimental approach aimed at enhancing heat pump performance through the integration of a Drain Water Heat Recovery System (DWHRS) and solar air heating (S). In view of the significant energy consumption of domestic hot water and space heating, the proposed configurations combine drain water recovery with solar-assisted heating to improve heat pump efficiency, thereby reducing both energy use and greenhouse gas emissions. Four configurations of the combined system are scrutinized: solar upstream evaporator (SU-E-DWHRS), solar downstream evaporator (SD-E-DWHRS), solar downstream condenser (SD-C-DWHRS), and solar downstream mixed (SD-M-DWHRS) DWHRS. Simulation results indicate that the SD-M-DWHRS configuration achieved the highest performance gains, with a Coefficient of Performance (COP) increase of up to 1001 % and a 91 % reduction in compressor power at a drain water inlet temperature of 40 °C. The system also confirmed potential monthly energy savings of up to 410 kWh, cost savings of $53, and a reduction in CO₂ emissions of 291 kg per month. This hybrid heat recovery tactic presents a promising solution for reducing energy consumption in the building sector while advancing sustainable energy objectives. By exploring and optimizing multi-source systems that integrate solar energy with heat recovery, this research fills a critical gap and paves the way for more efficient, environmentally friendly energy systems.