Power-based energy grade study of Chinaʹs on-grid distributed combined heating and power systems

China has been vigorously developing natural-gas-based urban district heating (UDH) to reduce the severe impact of emissions from coal-based UDH. China has strict regulations concerning the energy utilization efficiency and heat-to-power ratio of combined heating and power (CHP) according to national conditions. These regulations determine the particularities of Chinaʹs CHP. This study proposes a distributed energy system (DES) with heat pump heating (DES + HPH) and power-based energy grade methodology. The equivalent power consumption of steam and hot water consumed for heating is calculated according to the resulting reduction in the power output of the DES by providing steam and hot water. The comparable coefficient of performance (CCOP, i.e., the ratio of the heat output to the sum of heating equivalent power consumption and electricity consumption of HPH) can be applied to directly evaluate various heating systems because the denominator of CCOP has the same energy grade as power consumption. When the maximum heat load of HPH accounts for 40% of the maximum heat load of UDH, the average CCOP of the DES + HPH for conditions in Beijing reaches a maximum value of approximately 4.4, and its natural gas consumption corresponding to heating is approximately 64% lower than that of gas-fired heating boilers.