Experimental investigation on the thermal performance of a domestic gas boiler for space heating with different heating load ratio

Abstract

This study explores the effects of heating demand and hot water temperature on energy efficiency in a domestic gas boiler (DGB). Mock-up experiments were conducted using two types of boilers with different capacities (i.e., 11.6 kW and 23.3 kW of non-condensing boilers, 16.3 kW of condensing boiler) for comparative analysis. As results, for space heating, the efficiencies of non-condensing boilers (i.e., 11.6 kW and 23.3 kW) and condensing boiler (i.e., 16.3 kW) decreased by 12-44%, 15-46%, and 2-22% respectively as the heating load ratios were changed from 100%-25%. When the supply hot water temperature settings decreased from 55℃ to 45℃, the efficiencies were reduced by 13.6% (11.6 kW) and 53.3% (23.3 kW). For the condensing boiler, an efficiency reduction rate was 16.7% as the hot water temperatures dropped from 45℃ to 35℃. Also, since the boiler capacity depends on domestic hot water (DHW) load, the daily heating demands of space heating and DHW load were analyzed. In the results, reducing the lower limit of heating output could be more effective in improving the boiler efficiency for space heating. To provide sufficient DHW demand, it is required to maintain the upper limit of the heating output.