Selecting the optimum pressure drop per unit length of district heating piping network based on operating strategies

A mathematical model used to obtain the optimum pressure drop per unit length (PDPUL) and the minimum annual cost (MAC) of a district heating (DH) piping network based on operating strategies was established. A case study based on a DH system in Hebei Province, China, was carried out. Four operating strategies were used respectively. Sensitivity analysis method was used to investigate the impact of pump overall efficiency, electricity price, heat price and interest rate on the optimum PDPUL and the MAC of the DH piping network. Results showed that the optimum PDPUL and the MAC of the DH piping network could be obtained by using the mathematical model. The MAC of the DH piping network for variable mass flow rate (VMFR) operating strategies was lower than that for constant mass flow rate (CMFR) operating strategies. Also, the decrease of the design supply temperature in the primary side caused the reduction of the optimum PDPUL. But the MAC increased with the decrease of the design supply temperature in the primary side. Among all the parameters, the pump overall efficiency had the greatest impact on the optimum PDPUL and the MAC of the DH piping network.