Study On The Thermal Response Modeling And Duty Cycling Control Strategies For Central Air Conditionings In The Public Buildings

Central air conditioning(CAC)in public buildings,especially commercial buildings,is the main factor of peak load of urban power grid in summer.So,peak clipping control of central air conditioning load is of great significance for solving the contradiction between power supply and demand in summer,for improving the efficiency of power grid operation and for avoiding the risk of power investment.The duty cycling control(DCC)is a kind of peak clipping control method for central air conditioning in public buildings.In the light that the research of DCC is quite limited so far,this thesis focuses on the peak clipping control strategies of DCC for central air conditioning in public buildings.The thermal response model(TRM)describes the dynamic function relationship between the synthesized room temperature and air conditioning control parameters,the refrigerator start/stop state and the corresponding cooling capacity in DCC.The thermal response modeling is the basis of the research on the control strategy of air conditioning peak clipping.In view of the problem that the existing equivalent thermal parameter(ETP)model does not include the new wind load,the sunshine heat gain and indoor heat source,this thesis proposed a thermal response model for central air conditioning(TRM-CAC)including the characteristics of the central air conditioning firstly.Based on the two stage least square method,the practical parameter identification method was established for the proposed model secondly.The parameter observation and identification of the thermal response of a shopping mall in Shanghai city was carried out lastly.The comparative analysis showed that,compared with ETP model,TRM-CAC model can more accurately describe the dynamic variation of the room temperature in the shopping mall.Compared with cooling space of residential air conditioning,the cooling capacity and the equivalent heat capacity for cooling space of the shopping mall were far higher than residential air-conditioning,with the thermal resistance of surrounding structures opposite.Therefore,it is necessary to carry out the measurement of thermal response parameters in the cooling space of public buildings,which is the basis of the decision making of the control scheme.In view of the current lack of theoretical research on the demonstration of the control period of DCC,a control period demonstration model was proposed,which was based on a single controlled end to minimize the average load of the air conditioning in the load clipping period.Based on the thermal response parameters of the same shopping mall in Shanghai,the optimal control period of the refrigerator unit was calculated.The comparative analysis showed that,in order to obtain the maximum hourly peak clipping,the optimal control period should not include the maintained period,the size of which was determined by the allowable fluctuation range of room temperature and the thermal response parameters of the controlled end.When DCC was applied to the scattered air conditionings,it was a pair of contradiction to get the benefit of load clipping and to reduce the complexity of the control scheme.In order to avoid significant air conditioning load fluctuations,the former requested maintaining the diversity of the refrigeration status of controlled ends as far as possible,while the latter required reducing the number of aggregates and giving the same control signal to the same grouping controlled ends.In view of the above problem,a clustering and peak-staggering(CPS)control strategy was presented in this thesis.It started with defining a temperature variation exponent,a coefficient of sunshine heat gain and a coefficient of indoor heat source based on the thermal response model for central air conditioning.The controlled ends were then clustered into several aggregates by these three indices.Lastly,in order to keep the diversity of the refrigeration units,avoid significant load fluctuation and get corresponding temperature range for the peak clipping,the staggering effects among the controlling aggregates were produced by optimizing the standby time of each of the aggregates,which showed the time interval between the beginning time of the peak clipping period and the aggregate’s controlling period.To take typical values of thermal response parameters in the shopping malls for example,the numerical example reveals the characteristics and peak-clipping regulation mechanism of the CPS control,which is compared with various other grouping control strategies from the aspects of peak-clipping regulation performance,thermal comfort requirements and load waveform.The results show that CPS control can meet thermal comfort requirements greatly and the peak-clipping requirements with a small group number by unearthing peak-staggering effectiveness.The above research achievements can provide reference of theory and method for central air-conditioning DCC in public buildings in our country.