Modeling and optimization for hydraulic performance design in multi-source district heating with fluctuating renewables

Hydraulic performance of a district heating system is a significant aspect in designing. In the context of multiple heat sources and looped topology layout, severe non-linear hydraulic characteristics have markedly impacts on the hydraulic performance design of a district heating network. Design or select variable-speed circulating pumps with suitable capacities and hydraulic characteristics can be a rather difficult issue especially when there are fluctuating renewable heat sources. In this paper, an optimization model is proposed to achieve the lowest power consumption of all pumps and still fulfill the hydraulic head demands of all substations simultaneously. Based on the proposed model, a holistic design method is presented for optimal hydraulic design of the variable speed pumps in each heat source. Then a case study is illustrated to validate the proposed method. With consideration of fluctuating heat load of a renewable heat source, the optimal rated capacities of all pumps and variable speed hydraulic characteristic curves are obtained in the designed heating schemes from 100% to 40% of full heat load. Moreover, when all pumps operating on their optimal regime, there always exists one substation branch whose excess head would reach the preset minimum value. The sensitivity analysis results show that the variation of total work of pumps can be from 0.16% to 7.56% when the heat load of the renewable heat source fluctuated 1.0% in different designed heating schemes.