The Optimization Of The Temperature Difference Between The Chilled Water Supply And Return In District Cooling System

DCS has caused great attention to its economic analysis due to its largescale,enormous investment and high operating costs. The optimization of thetemperature difference between the chilled water supply and return is an economicand energy-saving technology, which can cut down the transport costs of the chilledwater pump, pipe network investment and maintenance costs by raising thetemperature difference between the chilled water supply and return to reduce thechilled water flow rate. According to different economic temperature difference interms of different scale DCS, this paper establishes an optimization model for thetemperature difference between the chilled water supply and return.Constrained by the cold source and terminal devices,bigger is not always betterfor the temperature difference between the chilled water supply and return, for thelower chilled water supply temperature will decrease the evaporation temperature,which results in the decrease of the coefficient of performance of the chiller, while ahigher chilled water return temperature can not meet the indoor comfort requirements.Therefore, the optimization of the temperature difference must be considered from theeconomy of DCS primaryly based on the indoor comfort requirements. This paperanalyzes the impact of the chilled water supply and return temperature on theperformance of the FCU under all kinds of operating conditions, when it is assumedthat the flow rate was consistent with the loading rate and we could obtain therelationship between the temperature difference and the chilled water supplytemperature in demand of the total heat load, which can be applied to the theoptimization model for the selection of the chilled water supply and returntemperature.Then, in order to obtain COP for the calculation of energy consumptionof Chillers,this paper also analyzes the impact of the chilled water supply and returntemperature on the performance of in order to ensure the chillers’safe and stableoperation,the chilled water supply temperature must be higher than3℃, and thetemperature difference must be below than9.4℃.Different temperature rise and cooling loss of pipe network corresponds toDifferent chilled water supply and return temperature, in order to accurately calculatethem, this paper adopts temperature rise factor to establish a calculation model of thepipe section and branched pipe network, and analysis cooling loss of the pipe section and branched pipe network and the worst user’s temperature rise of the pipe section.Compared with the conventional computing model, the impact of the temperature riseon the cooling loss can be ignored in the practical engineering applications.Meanwhile, analysis of a branched pipe network shows that heat dissipation of thecirculating pump is the main factor of the pipe section temperature rise and coolingloss, while pipe section heat transfer can be ignored.On this basis, this paper establishes an optimization model for the temperaturedifference between the chilled water supply and return of DCS under the condition ofminimum annual equivalentent cost. And the result of the analysis to a project showsthat economic temperature difference is6.3°C and the corresponding design chilledwater supply temperature is5.9°C. Based on the project, the analysis of the influenceson the economy temperature difference shows that economic temperature differencereduces by the increase of electricity price and rises by the increase of the friction,cooling distance and air conditioning load level.