Modelica Simulation And Experimental Study On Air Supply Parameters Control Of A Dual Cooling Source Fresh Air Unit

As a new trend in central air-conditioning systems in recent years,temperature and humidity independently controlled air-conditioning systems mainly use fresh air units to send in fresh outdoor air with lower moisture content to reduce the moisture content of indoor air and indoor CO₂ concentration,thus achieving better control of the building’s thermal and humidity environments and significant energy saving potential,but they generally use a single cooling source.However,as the proportion of fresh air load in the air-conditioning load is becoming higher and higher,and the state parameters of outdoor air and indoor temperature and humidity parameters change at any time during the day,the fresh air unit will also change its operation status with the changes of such indoor and outdoor air parameters,and the air supply parameters of fresh air will also directly affect the indoor air quality,to fully exploit the advantages of different gradient cold sources and achieve a more accurate to fully exploit the advantages of different ladder cooling sources.The dual cooling source fresh air unit is also gradually applied in the actual engineering field,which uses two different temperatures of high and low temperature chilled water for heat treatment of the new air,the sensible heat load and part of the wet load of the air conditioning system is mainly removed through the high temperature surface cooler heat exchange,while the low temperature cooling source is responsible for reducing the latent heat load of the air conditioning system,this new air treatment method can greatly improve the dehumidification capacity of the fresh air unit and save more energy than the traditional way.This method of fresh air treatment can greatly improve the dehumidification capacity of the fresh air unit and save more energy than traditional methods.If the fresh air unit operates according to the designed working conditions and provides a fixed cooling capacity,it is bound to cause energy wastage to a certain extent,so it is necessary for the fresh air unit to operate under different working conditions,for this reason,this paper firstly explored the influence characteristics of different water volumes on the air supply parameters when the high and low temperature surface coolers were used alone and at the same time by adjusting the opening degrees of the high and low temperature energy valves,and then,while keeping the flow rates of the high and low temperature surface coolers unchanged In these two cases,the indoor fresh air supply parameters were observed to change at the same time,and it was found that the temperature and humidity control effect was best and the system operation energy consumption was lower when the high and low temperature energy valves were opened at the same time and the high temperature valves were opened between 40%and10%and the low temperature valves were varied between 70%and 100%,in addition to that In addition,the energy consumption on the high and low temperature chilled water side and the overall energy consumption are about 17%less than the conventional operating condition in both the variable water volume parameter experiment and the variable air volume parameter experiment,which have high energy saving potential.To further investigate the characteristics of the dual cooling source fresh air unit,this paper uses Open Modelica and Mworks software to build a simulation model of the dual cooling source fresh air unit based on Modelica,and compares the inlet and outlet water temperature of high and low energy valves and indoor fresh air supply parameters according to the same variable water volume and variable air volume environment parameters as the experiment.This means that the model is more accurate for the low temperature side of the simulation,and the errors in the indoor fresh air supply temperature and humidity and moisture content are within10%,which is due to the fact that the high temperature side of the model does not take into account some of the heat dissipated by the external environment.In addition to this,a PID control module was added to this model to control the fresh air unit outlet air supply state parameters to certain values,and the changes in the respective outlet flow rates of the high and low temperature chilled water side were observed under changing air volumes and compared with the energy consumption of the experimental high and low temperature chillers under the variable air volume operation strategy,and it was found that the PID control based operation strategy could save a total energy consumption of 27.6 k Wh,with an energy saving of The PID-based operation strategy saves a total of 27.6 k Wh of energy,a saving of approximately 10.37%,and the low-temperature chiller is even more energy efficient compared to the high-temperature chiller,which saves 4.71%,with a saving of 15.21%.