Research On The Modeling Of Customer Side Chilled Water Systems In Air-conditioning Systems

Refrigeration station and chilled water system are paly a key role inair-conditioning systems, and its design and operation effect the energy consumption ofair-conditioning systems directly. A large number of literature studies and fieldinvestigations indicated that many unsolved problems and disputes exist in design, suchas chilled water systems operating with “large chilled water flow and low temperaturedifference”, the selection of water system type and so on. As it is very complex indesigning refrigeration station and chilled water system due to many effecting factors,we have to analyze the operating performance of chilled water system all conditionswith simulation tools. Although building energy simulation tools in the world, such asDOE-2, EnergyPlus, DeST and so on, can simulate the all-year conditions ofrefrigeration station and chilled water system hour by hour, the simulation results cannotreflect the real operating performance, which implies that models of refrigeration stationand chilled water system ignore some key influencing factors. In fact, the operatingperformance of the customer side chilled water system has a large effect on theperformance of refrigeration station and simulation tools now available do not havereasonable models for this part. Based on the literature studies, few research findingsare achieved about the characteristics and modeling method about customer side chilledwater systems. Thus, the research purpose of this paper is to build the model ofcustomer side chilled water systems by comparing the real operating results andsimulation results, applied in the combined calculation of refrigeration stations.Firstly, the real operating data and the simulation result of heat exchanger model ofone cooling coil was compared to determine the key influencing factors of the heatexchanger model, which is the base of the paper. Secondly, two types of cooling coilwere analyzed respectively, as the control method of water valves determines thecharacteristics of customer side chilled water systems. The two types are cooling coilswith continuous control and on-off control. Compared with the real operating results byBuilding Monitoring System and simulation results of cooling coil systems, keyinfluencing factors on the characteristics of customer side chilled water systems weredetermined, and then the models of the customer side chilled water systems were built. The chilled water flow rate and return water temperature could be calculated accordingto the supply water temperature and the chilled water pressure difference by the models.Thirdly, the combined calculation method of refrigeration station and chilled watersystem were achieved. Finally, the all condition performance and energy consumptionof the refrigeration station and chilled water system with VAV system or Fan Coilsystem in customer side were simulated. Based on the simulation results, we couldevaluate different design scheme and also help us to size the capacity of equipment andoptimize operations.The efforts of this paper help us understand the characteristics of customer sidechilled water systems, and also support effective models applied to the combinedcalculation of the refrigeration station and chilled water system, which is verysignificant for design work.