Research On Pre-cooling Optimal Control And Energy Conservation Potential In Variable Air Volume Air-conditioning System

Since the global energy crisis in20thcentury, more and more concern aboutenergy issue is received from the national energy sectors, and energy saving andemission reduction has been a basic state policy in china. Air-conditioning energyconsumption has been main building energy consumption, when air condition isgradually becoming a necessity in our lives. Thereby, improving the energy efficiencyof air conditioning system is the most effective approach of energy saving.The paper proposed several energy-saving ways for the pre-cooling of airconditioning system, such as an accurate estimate of the pre-cooling time of airconditioning system, improving the operation and management level, adopting theenthalpy value control to optimize the fresh air, using variable static pressure andalterable temperature control of supply air to regulate fan speed for changing the airflow, so as to reduce energy consumption of air conditioning system.At first, with the purpose of lessening the pre-cooling energy consumption of airconditioning system, the paper propose that the application of improved Elman neuralnetwork algorithm model to accurately forecast the pre-cooling time of airconditioning system based on the collected operation data of the office building inHong Kong. In the paper, correlation coefficient and root mean square error of themeasured values and predicted values are applied to assess the well reliability andpredictable performance. Furthermore, the optimal pre-cooling time of airconditioning system is determined by the statistics pre-cooling time in winter and theforecast pre-cooling time in more seasonal patterns.The paper has built the energy consumption model of fan in view of fanperformance curve and similarity law, and air conditioning system is frequentlyoperating under the circumstance that variable resistance characteristics result fromchanging valve opening at all times. Therefore, it is very necessary to ensure thestatus point of fan operation. In order to make sure the status of fan working, themathematical models of supply air duct, VAV Box, mixed air duct, cool coil and PIDcontroller are established to calculate the outlet total pressure drop of fan, then energyconsumption of fan is simulated based on TRNSYS.The energy consumption model of a chilled water pump is established wellbecause there are a lot of similarities between fan and pump, at the same time, the parallel connection problem of the pumps are also taken into account in the paper.Through the analysis of the relationship both load rate and coefficient of performanceof chillers, energy consumption of chillers are modeled.Based on the operation data of air conditioning system, we can simulate energyconsumption of fan, chiller, chilled water pump and system under the controls ofconstant and variable static pressure in the TRNSYS platform and compare energysaving rate and energy efficiency ratio so as to evaluate energy consumption ofair-conditioning equipments and system under both controls in typical workingcondition.