Design and Operation Regulation of Combined Heating System with Gas-fired Boilers as Peak-load Heat Sources in Secondary Heating Network

Combined heating systems are regarded as the development trend of central heating in the near future. In China, combined heating systems using gas-fired boilers for peak-load compensation are starting to appear in some cities those are rich in natural gas resources. But there still exist some controversies in design and operation regulation of them. This paper developed a new method for designing the combined heating system. We firstly detailed a combined heating system with gas-fired boilers as peak-load heat source in Daqing city and demonstrated its connecting mode. Subsequently, we discussed the application of heat load duration curve in this heating system and developed a method to calculate basic heat load ratio when basic heat source provided the maximum full load heat supply. Then, we elaborated four design parameters, including critical peak heating temperature, duration running time of peak-load heat sources, design supply water temperatures of heat exchanger and peak-load heat sources. Finally, we analyzed the operation regulation of this kind of combined heating systems. In can be concluded that the critical peak heating temperature and duration running time of peak-load heat sources are only determined by basic heat load ratio. It is also suggested that two basic heat sources with different design heat load be applied in primary heating network, and thus to reasonably fulfill the economic requirements of a combined heating system.