| Modern people spend most of their time in an indoor environment,and a comfortable thermal environment not only makes people physically and mentally healthy,but also improves their learning efficiency.In summer time,air conditioning is often turned on indoors to solve the problem of indoor thermal environment and thermal comfort of personnel.Since entering the 21 st century,epidemic diseases have been frequent,such as SARS in 2002,influenza A in 2009,and the COVID-19 in 2019,which have brought great inconvenience to people’s lives.A large number of experts and scholars recommend that indoor environments should be strengthened with open windows and ventilation to dilute the concentration of indoor pollutants and reduce the risk of infection,especially for more densely populated public places like school classrooms.In summer,due to the large temperature difference between indoor and outdoor,opening windows and ventilation can easily disturb the indoor thermal environment,causing discomfort to personnel and easily increase the energy consumption of air conditioning.Therefore,maintaining the balance of prevention and control requirements,personnel thermal comfort and energy consumption has become an urgent problem for HVAC systems.In this paper,the indoor thermal environment and the thermal comfort of the personnel in a classroom of a university in Zhejiang province were studied under the conditions of 0 and 10% window opening ratio using experimental and questionnaire methods,and the environmental characteristics of the classroom under the conditions of different air supply parameters were investigated by CFD numerical simulation method,and the optimal air supply conditions were obtained by comprehensive evaluation of each condition using TOPSIS method with thermal comfort and energy utilization coefficient(EUC)as indicators.For the presence of infection sources at different locations in the classroom under the optimal working conditions,the discrete phase model(DPM)in Fluent was used to simulate the droplet dispersion,and an improved Wells-Riley model was used to predict the infection risk in each area of the classroom.The details of the study and the results are as follows:(1)By analyzing and summarizing the existing studies,it was found that when the window opening ratio is 10%,it not only conforms to people’s window opening habits but also has better indoor air quality,better removal of indoor virus particles and lower risk of infection.In the air conditioning design temperature of 26℃,the average temperature at the height of 1.1m in the classroom was 26.9℃ and 26.1℃ under the10% window opening ratio and 0 window opening ratio condition respectively,which was 0.8℃ higher.The thermal sensory voting value was slightly higher than that of the0 window opening ratio condition,while the perceived air quality voting value was slightly higher than that of the 0 window opening ratio condition,and the work efficiency of the subjects was lower than that of the 0 window opening ratio condition.(2)For the classroom with top diffuser air supply,the effect of changing the air supply angle on the temperature field is greater than that of changing the air supply speed and air supply angle,and the increase of air supply angle is beneficial to reduce the indoor PMV value,but will increase the DR value.For the vertical cabinet air conditioner air supply method classroom,the change of air supply temperature on the indoor temperature field is linear,while the air supply speed and air supply angle on the indoor temperature field is not a linear relationship,when the air supply angle is 30 °,the indoor work area PMV value is better.(3)For both air supply methods,the impact of air supply angle on the energy utilization factor is larger,while the impact of air supply temperature and air supply speed is smaller.And for the top diffuser air supply mode classroom,increasing the air supply angle will reduce the energy utilization coefficient.The energy utilization coefficient of the classroom with vertical cabinet air conditioner air supply method under the same air supply condition is generally larger than that of the classroom with top diffuser air supply method.(4)Through TOPSIS method to evaluate the advantages and disadvantages of all working conditions,the best air supply working condition for the classroom of central air conditioning system is: air supply temperature is 14℃,air supply speed is3m/s,and air supply angle is 60°.The best air supply condition for the classroom of vertical cabinet air-conditioning system is: air supply temperature is 16℃,air supply speed is 5m/s,and air supply angle is 30°.(5)For classrooms with top diffuser air supply,the risk of infection exceeded0.5 in 5 cases,or 10%: the risk of infection was less than or equal to 0.1 in 21 cases,or42%.The overall risk of infection for personnel is low.For the classroom with vertical cabinet air conditioners,the risk of infection was less than or equal to 0.1 in 10 cases,accounting for 20%.The overall risk of infection for personnel was relatively high.(6)For the indoor environment represented by the classroom environment,in order to ensure indoor thermal comfort,energy consumption and infectious disease prevention and control requirements,10% of the windows should be opened in summer,for the top diffuser air supply method classroom,the air supply conditions should be selected: air supply temperature of 14 ℃,air supply speed of 3m / s,air supply angle of 60°.For vertical cabinet air conditioning air supply method classroom,should choose the air supply conditions: air supply temperature of 16 ℃,air supply speed of 5m / s,air supply angle of 30°.And in the best air supply condition top diffuser air supply method classroom overall infection probability is lower than the vertical cabinet air conditioning air supply method classroom. |
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