Feasibility study on solar coupled gas-fired boiler heating system retrofit in residential buildings in the HSCW zone of China

Residential buildings in the hot summer and cold winter (HSCW) zone rely on gas-fired boiler for heating have a certain application basis, but high operating costs and limited gas consumption seriously limit the promotion of gas-fired boiler. To reduce domestic gas consumption in Wuhan, two solar auxiliary gas-fired boiler heating systems formed in parallel and series are proposed and explore the feasibility of coupled heating system retrofit. The simulation models of two solar coupled gas-fired boiler heating systems are established by TRNSYS, and the results indicate that the indoor thermal environment of the two systems is good and the temperature of the tank is stable. The solar fraction of the parallel system reaches 24.40%, which has better energy saving. The optimization analyses display that the system has the best economy when the collector area ratio is 10.0%, and the collector area and tank volume ratio is 8/0.7. The solar-assisted parallel heating system retrofit can save 2.02 × 104 MJ over the entire life cycle, and the increased initial investment can be recovered within 4.75 years. The research results can provide a basis and new ideas for the heating retrofit of the gas-fired boiler in residential buildings in the HSCW zone.