Study On The Energy-saving Potential Of Air Conditioning System With Variable Chilled Water Temperature Optimization Operation Based On Thermal Comfort

Usually,the air-conditioning system operates most of its life time at part-load conditions,deviating from the design conditions,resulting in energy waste.Optimization of chilled water temperature is a simple and effective operation regulation method to achieve the purpose of energy-saving operation.But the higher the chilled water temperature,the lower the dehumidification ability of the end facility,which could result in sacrificing occupants’ thermal comfort.At present,due to the difficulty of predicting the impact on comfort during the operation of the air conditioning system,the variable chilled water temperature adjustment is mainly set based on experience,which makes it difficult to fully realize its energy-saving potential.Therefore,it is of great significant to conduct search on the upper limit of chilled water temperature setpoint and the optimal chilled water temperature setting strategy,which could take full advantage of reduce power consumption in chiller plant without compromising the thermal comfort of human.An office building was chosen as the research object in this study.And a simulation model of the air-conditioning system was established based on the feature recognition method.The model was used to quantitatively analyze the impact of the increased temperature of the chilled water on the operation performance of the air-conditioning system and indoor comfort,so as to obtain the setting regulation between the room load rate and the best chilled water temperature.In addition,optimized operation strategies for variable chilled water temperature of air conditioning system that meets different comfort requirements were proposed,the feasibility of these strategies was verified and energy-saving analysis was carried out on typical weather days to explore the most optimal variable chilled water temperature operation strategy.Mainly carry out the following research work:(1)The simulation model of air conditioning system is constructed based on feature recognition method.A novel modeling method which makes unknown structure parameters lumped and obtains them(i.e.the characteristic parameters,which are unique for each device)with measured data is adopted,based on which the air-conditioning system models are established including chiller,cooling coil,cooling tower,fluid conveying equipment.The comparison between the measured data and the simulation results under variable chilled water temperature shows that the simulation error is within 7%,which can be used to characterize the performance change of the air conditioning system under variable chilled water temperature.(2)Explore the changes in the performance of air-conditioning systems with varying chilled water temperatures.Analyze the variation of the coefficient of performance with the chilled water temperature under different load rates for the chiller,and compare the performance of different types of fan coils under variable air handling capacity,variable chilled water volume and variable return air parameter conditions.The results show that when the load rate of screw chiller is 70%,the energy efficiency of the chiller increases by 25.65% if the supply temperature of chilled water increases from 7 ℃ to 15 ℃.When the return air parameter is 27 ℃ and 50%,and the fan coil unit turns to dry operation when the chilled water temperature is 14 ℃ and 12 ℃ when the fan coil unit handles 55% and 100% of the air volume respectively;When processing 100% air volume,change the return air temperature to 28 ℃,the fan coil can still dehumidify when the chilled water temperature is increased to 12 ℃.(3)Study the indoor environment affected by the temperature increase of the chilled water.Based on the PMV-PPD thermal comfort index,the indoor temperature and humidity setting range that meets human comfort was determined,and the De ST software is using to simulate load variation of the object building in cooling season,the load change of the most unfavorable room is used as the model input parameter to study chilled water under different load rates.Simulation results indicate that in order to ensure that the indoor hourly parameters that meet the comfort requirements,when the room load rate is lower than 60% at all times,the chilled water supply temperature can be increased to 15～17 ℃;when the maximum room load rate is about 75%,the chilled water temperature should not exceed 11 ℃.However,when the room load rate is higher than 85% for a long time,the chilled water temperature can only be maintained at 7 ℃.(4)According to the correlation analysis between the influencing factors and the chilled water supply temperature,the optimal regulation law of the chilled water temperature set point at different load rates in each period was determined,and the optimal operation strategy of variable water temperature for the air conditioning system that meets the comfort requirements and energy saving is proposed.The result found that,on the premise of meeting the thermal comfort requirement,the best optimal operation strategy proposed in this study can increase the unit energy saving rate to over 12.16%,and the air-conditioning system can save 7.40%～9.35%energy consumption.