Optimization study of a novel district heating system based on large temperature-difference heat exchange

•A novel district heating system based on the absorption heat pumps is proposed.•The return water temperature of the heat network can be greatly decreased.•The comprehensive exergy efficiency of the system is improved by 29.2%.•The heating capacity of the combined heating and power plant is improved by 47.5%.•The comprehensive costs per unit heat output are decreased by 18.6%