Theoretical And Expreimental Study Of District Heating Systems With Distributed Variable Frequency Drive Pumps

The increasing of energy efficiency and decreasing the transportation powerconsumption of District Heating (DH) systems have been increasingly focused due tothe need to save energy. DH system with Distributed Variable Frequency DrivePumps (DVFDP) is considered a technology with good potential of saving energy,lowering transportation power consumption and upgrading the heating services. Byemploying theoretical analysis and experimental research, a new DH system withDVFDP and the approach to analyze the dynamic hydraulic characteristics, thedynamic thermal characteristics and the stability in the operation of the systems arepresented in this paper.DH system with DVFDP, as a multi-pumps system, is of quite a difference onprinciples and hydraulic characteristics with the traditional central pumping DHsystems. The main task to analyze the DH system with DVFDP is to research thepressure and flow rate distribution. The working characteristic of the distributedvariable frequency drive pumps is especially the key point for the hydraulic analysis.The model of the DH system with DVFDP is presented in the paper. In the hydraulicmodel, the branches in which there is feedback water pump is mainly considered aswell as its solving approach. The model is also a foundation of the experimentalresearch.DH system with DVFDP has an obvious advantage on using energy sufficientlyand efficiently which is the purpose of DH system. The analysis of thermalcharacteristic of DH system is carried out in this paper which is aiming to understandthe mechanism of energy distribution in the DH system and build a theoreticalanalysis tool for the design of DH system with DVFDP.The experimental system includes two parts: One is mainly used to validate thehydraulic method, in which a network with2substations is set up to study thedistribution of flow rate and pressure. The results of a series of dynamic hydraulicexperiments show that the method presented in this paper can correctly describe thedynamic hydraulic characteristics of the DH systems with DVFDP. The other one isan engineering demonstration project in which a network with10substations is set upto study the distribution of flow rate and pressure but mainly to study the energy distribution and the principles of regulation which is based on the understand of thedynamic thermal characteristic.The stability of the DH system with DVFDP is very important for the operation insafe and high efficiency. According to the characteristic of the DH system withDVFDP, the method of offset coeficiency and sensitivity are adopted to analyze themain factors of the stability of DH system with DVFDP, which can be used for theoptimization of the system design and operation strategy.