Thermal and Hydraulic Performance Analysis of a Waste Heat Recovery Device for Domestic Furnace Exhaust Gases

This study experimentally investigates the steady-state thermal and hydraulic performance of a Waste Heat Recovery Device (WHRD) designed to extract heat from non-condensed domestic heating furnaces to preheat the main water supply. The device was tested under varying water flow rates (0.5; 2.5 GPM), while maintaining a constant hot gas flow rate of 34 m3/hr (20 CFM) at 90 degrees Celsius. Single and multi-pass hot gas flow configurations were examined within the same external dimensions of the WHRD. The performance was analyzed using the effectiveness and total pressure drop. Results showed that the WHRD effectiveness decreases with increasing water flow rate, following trends typical of a standard counterflow heat exchanger. A maximum effectiveness of 38% was achieved at 1 GPM in the four-pass configuration. The hydraulic analysis of the WHRD found a maximum pressure drop of about 1.49 kPa at 30 CFM hot gas flow rate in the 4-passes flow configurations. This performance underscores how waste-heat recovery technologies could accelerate building sector decarbonization by demonstrating substantial potential for annual energy savings and CO2 emission reduction in residential heating applications. The findings equip valuable insight into optimizing WHRD designs for residential energy efficiency and support sustainable building practices.