key: cord-0701694-jxhir3j8
authors: Niu, Run ping; Chen, Xiaoyi; Liu, Hua
title: Analysis of the impact of a fresh air system on the indoor environment in office buildings
date: 2022-05-11
journal: Sustain Cities Soc
DOI: 10.1016/j.scs.2022.103934
sha: f85de3184cc35f6c01d714582657f9c381575a5d
doc_id: 701694
cord_uid: jxhir3j8

In this paper, objective physical tests and subjective questionnaire surveys were used to study an office building in Beijing during the operation of the fresh air system in the summer before the coronavirus disease 2019 (COVID-19). This paper conducted long-term tests on indoor environmental parameters: air temperature, relative air humidity, air velocity, CO(2) concentration, PM(2.5) concentration, fresh air volume, and conducted a questionnaire survey on the satisfaction of indoor office workers with the indoor environment. The results showed that the indoor environmental parameters conformed to the design values specified in the relevant design standards, but the satisfaction of the indoor personnel with the indoor environmental parameters was generally low. The risk probability of infection of indoor personnel with the COVID-19 under two existing fresh air system operation modes was calculated and compared, and the results showed that the probability of infection was less than 5%. Gray correlation analysis of the measured data with the questionnaire results identified indoor air temperature and indoor air quality as the main factors affecting the subjective satisfaction of indoor personnel, which was consistent with the results of the questionnaire analysis. A new operation and maintenance method of the fresh air system was proposed for the regular epidemic prevention and control to ensure the normal operation of the office building and the health of the indoor personnel.

As a place where people live and work, architecture provides a healthy and comfortable environment for people. People spend more than 90% of their time indoors. A large number of studies have pointed out that the quality of the indoor environment has an important impact on the comfort, health, productivity of indoor personnel [1] [2] [3] . With the rapid development of China's economy urbanization is speeding up, living standards continue to improve at the same time the northern region in recent years haze pollution frequently, building interior decoration pollution, and outdoor environmental pollution caused by the building indoor environment in the situation of internal and external problems, long-term exposure to the polluted environment seriously affects the health of personnel. The COVID broke out at the end of 2019 and spread rapidly across the globe, posing a huge threat to the lives and health of people around the world. The virus is highly transmissible from person to person and is significantly more infectious than SARS-CoV and MERS-CoV [4, 5] ，At present, it is generally believed that the COVID-19 can be transmitted through droplet transmission, contact transmission, aerosol transmission in relatively confined environments with high concentrations of aerosol environment, the building indoor environmental health problems gradually become the focus of attention, A large number of studies [6] [7] [8] pointed out that mechanical ventilation fresh air system to dilute harmful substances, filter dust, bacteria to improve the indoor environment, to ensure the health of indoor personnel has an important role [9, 10] .

The indoor environment of a building is affected by a combination of four factors: thermal, acoustic, light, and indoor air quality [11, 12] . A large number of scholars conducted objective and practical inspections of indoor environmental parameters and thoroughly analyzed the indoor environmental quality of office buildings [13] [14] [15] . Geng Yang [16] Mechanical ventilation can effectively reduce the indoor carbon dioxide concentration below the standard reference value. Under the combined effect of natural ventilation and air purifiers, the indoor air quality of residential buildings is significantly improved. In addition to the parameters that meet the design standards, the indoor environment of the building should also focus on the subjective feelings and satisfaction of the indoor personnel on the indoor environment [18] . Zhang

Zhubai [19] adopted a questionnaire survey method to conduct a questionnaire survey on the university library from the four aspects of the building's interior design, interior environment, performance, user satisfaction, and later established a structural equation model based on the theory of evaluation. The interrelationships between the influencing factors were analyzed for the feelings of the staff in the library. D.O.Sant'Anna [20] takes Brazil's green office buildings and traditional office buildings as a case study, conducts a questionnaire survey on the interior staff and visitors of the building, and analyzes the subjective indoor environment of different types of office buildings and different interior staff There are differences between feelings and satisfaction.

The results show that the visitors have no significant difference in the indoor environment of different types of office buildings, but the staff's satisfaction with the indoor environment of green office buildings is much higher than that of traditional buildings. M.M.Agha-Hossein [21] conducted a questionnaire on the subjective satisfaction of the indoor environment personnel in new and old office buildings, and found that indoor office workers are more satisfied with the indoor environment of new buildings, and also calculated the energy consumption of air conditioning systems in old buildings The analysis shows that the new building consumes less energy, and enhancing the indoor personnel's regulation of the indoor environment will not reduce the indoor personnel's satisfaction with the environment and can effectively reduce the energy consumption of the air conditioning system.

Lou [12] LEED or BREEAM certification. The difference between satisfaction, the results show that LEED or BREEAM certified office building interior staff satisfaction is not higher than the three-star certification. Wang [24] et al. researched two hospitals in China from both objective and subjective aspects and conducted objective tests of indoor environmental parameters and subjective questionnaire surveys of indoor staff satisfaction. The results show that the indoor air humidity in summer and the indoor temperature in winter are both lower than the design standard, and there is no obvious correlation between the indoor objective physical environment and the subjective satisfaction of the indoor personnel in Chinese medical buildings. Pei [25] and others used a combination of subjective and objective methods to study green office buildings and traditional office buildings in two different climatic regions in China. The results show that the indoor office satisfaction of green office buildings is higher than that of traditional office buildings.

Based on the above studies, we can find that a large number of scholars have conducted a lot of research on the indoor environment from the objective and subjective aspects: thermal environment, air quality, acoustic environment, and light environment. However, there are relatively few studies on the influence of fresh air systems on the indoor environment. In this paper, through the actual testing of indoor environmental parameters: air temperature, relative humidity, CO 2 concentration, PM 2.5 concentration, indoor air velocity, the fresh air volume in an office building in Beijing during the summer fresh air system operation before the COVID-19, indoor environmental satisfaction questionnaires were conducted on indoor office personnel during the testing period. The results were statistically analyzed by SPSS, and the influence of indoor environment parameters on the satisfaction of indoor personnel was analyzed by the grey correlation method. According to the existing fresh air system operation mode, the probability of virus infection of indoor personnel is calculated, and because of the problems and shortcomings in the operation of the existing fresh air system and the development of the regular epidemic prevention and control to ensure the normal operation of office buildings and people's life and health, the operation management methods and suggestions of the fresh air system under the future regular epidemic prevention and control mode are given. It provides a theoretical basis for improving the indoor environment and enhancing the operational efficiency of the fresh air system.

This article focuses on the long-term actual monitoring of the indoor environment parameters of an office building in Beijing during the summer fresh air system operation, such as temperature, relative humidity, CO 2 concentration, PM 2.5 concentration, air velocity, and fresh air volume to analyze the fresh air system operation impact on the indoor environment during the process. The research object selected an office building in Beijing for research. The air-conditioning system in the building's interior was a fan coil and fresh air system. Table 1 lists the basic information of the tested office. Investigator's satisfaction with indoor temperature, relative humidity, air quality, and indoor air velocity of the building; 3) Whether the respondent has physical discomfort in the building's interior and satisfaction with the overall indoor environment when completing the questionnaire.

The questionnaire used Likert's five-scale method to measure the satisfaction and physical condition of indoor personnel in office buildings during the operation of the fresh air system. Satisfaction is measured by the size of the score. The Likert scale is divided into five orders of magnitude [19] .

Select three questionnaires during the normal working day to distribute questionnaires to conduct actual surveys on the satisfaction of indoor environment personnel. Each time, more than 30 questionnaires were issued, a total of 115 questionnaires were returned, 105 questionnaires were valid, and the questionnaire recovery rate was 91.5%, including 56 men. People, 49 women.

The questionnaire used SPSS version 24.0 to analyze the data, using the Cronbach's coefficient to test the consistency of the questionnaire, the partial correlation Bartlett test, and the Kaiser-Meyer-Olkin (KMO) test to determine the effectiveness of the questionnaire degree.

Pearson correlation coefficient was used to analyze the correlation between each factor and the overall satisfaction of indoor environment personnel.

The thermal comfort level and related parameter design standards for buildings under summer cooling conditions specified in the Design Code for Heating Ventilation and Air Conditioning of Civil Buildings (GB 50736-2012) are shown in Table 3 [31, 32] . In the subsequent actual detection of the indoor temperature of the office building, an objective evaluation of the indoor temperature of the office building will be made concerning the recommended values of the standard. As the normal working day working hours in office buildings are from 9: 00 to 18: 00, the data of August and September are screened and daily data samples from 9: 00 to 18: 00 are retained for analysis and research. This time the data analysis uses box plotting to present the test data. Boxplots have the advantage of displaying the median value and overall distribution of the data intuitively. The median value is used to represent the overall situation of the indoor environment of the building.

At the same time, the abnormal values in the data batch can be identified, and the hot and humid environment and air quality in the building should be analyzed through the areas where the abnormal values appear. The indoor air temperature is an important index for evaluating the indoor thermal environment.

Fanger takes the indoor air temperature as an important factor affecting the thermal comfort of the human body to conduct a theoretical analysis of human thermal balance. Human body temperature is a dynamically changing process. The human body maintains the balance and stability of body temperature through convection and radiant heat exchange with the surrounding air. The indoor air temperature of a building has a direct impact on the heat production and heat dissipation of the human body. it can be seen that the indoor air temperature fluctuations of various office buildings in summer are small and meet the design requirements. The indoor air temperature can be distributed in a more comfortable temperature range, to that ensure the comfort and health of indoor office staff. there is no significant effect on the comfort of the indoor personnel [32] . If the indoor is in a high temperature and high humidity environment in summer, it will cause the indoor humidity to easily breed mold, which will pollute the air and affect the health of indoor personnel. If the relative humidity of the indoor air is too low, it will cause indoor dust and excessive suspended particles, which will cause respiratory diseases to indoor personnel, especially children.

The statistical results of indoor relative humidity in the summer test office are shown in Fig. 5 .

The comparison of the test results in the box chart with the standard requirements requires that the relative humidity of the indoor air at each measurement point remains between 30% and 70%, and the average relative humidity of the indoor air at each measurement point fluctuates between 35% and 45%. From the distribution percentages of the measured values of air relative humidity at different measurement points shown in Fig. 6 , it can be seen that the measured values of indoor air relative humidity at each measurement point are distributed in the 30% -40% and 40% -60%

intervals. Point 01 and measurement point 11 indicate that the proportion of the measured indoor air relative humidity distribution in the 40% -60% interval is slightly greater than the numerical proportion in the 30% -40% interval. From the overall data, the measured summer indoor air relative humidity in the office tested is distributed within the recommended range of relative humidity. This test building's summer indoor air relative humidity meets design requirements and meets human comfort requirements. A more comfortable working environment. Table 3 , the median indoor CO 2 concentration in the tested office is constantly lower than 700 ppm when fresh air is continuously sent indoors. Figure   8 shows the percentage distribution of indoor measured CO 2 concentration at different measurement points. It can be seen from the figure that the measured CO 2 concentration at different measurement points is distributed in the range of 400ppm -600ppm and 600ppm -800ppm. The above areas account for the smallest proportion. According to China's -Indoor Air Quality Standards‖, the indoor CO 2 concentration does not exceed 1000 ppm. It can be known that during the operation of the fresh air system in the test office building in summer, the indoor CO 2 concentration was controlled below 1000 ppm. For some measurement points, the measured CO 2 concentration exceeded the standard According to the current investigation, it is found that the CO 2 concentration exceeding the standard is greatly affected by the change of indoor personnel density [33] . Besides, the air conditioning system operation and maintenance department have problems such as shortening the opening time of the fresh air system to reduce operating energy consumption. In response to the indoor PM 2.5 concentration exceeding the standard, through actual investigation, it was found that the indoor PM 2.5 concentration is closely related to the outdoor environmental quality. Besides, as indoor personnel travel between indoors and outdoors, there will be clothing to carry, and PM 2.5 will be adsorbed on clothing outdoor. 5th class of particulate matter is brought into the room. And through actual investigation, it is found that the presence of printers and other equipment in offices with severe PM 2.5 concentrations and the incomplete filtering of the fresh air system are the main reasons for the indoor PM 2.5 concentrations being seriously exceeded. The indoor air velocity needs to be measured with the help of a Testo anemometer. Fig. 11 shows the line graph of the change in indoor air velocity in the office during a randomly selected test period of three working days. Combined with Table 1 , it can be seen that the indoor air velocity in the office is less than or equal to 0.3m/s to meet the design requirements of indoor air velocity in air-conditioned office buildings in summer. The office buildings tested all used fan coils plus fresh air systems to regulate the indoor environment, and the pre-test research revealed that the indoor air conditioning panel parameters were set the same in summer. During the test period, the indoor air velocity of an office during the time of 9:00-18:00 on a normal working day was selected for testing. It can be seen from Fig. 11 that the indoor air velocity in the office during each time of normal working days meets the design requirements of Class Ⅰ and Class Ⅱ for indoor air velocity under the cooling condition of the Design Code for Heating, Ventilation, and Air

Conditioning of Civil Buildings.

In this paper, we measure the indoor fresh air quantity in office buildings concerning the indoor ambient air quality measurement parameters and then provide a reference for improving indoor air quality. Indoor CO 2 concentration is an important index used to characterize the amount of fresh air, and the standard GB/T 18883-2002 stipulates that the indoor fresh air per capita is not less than 30 m 3 /h and the indoor CO 2 concentration is not more than 1000 ppm.

When there is no CO 2 emitting source in the room, the formula for calculating the fresh indoor air volume, as shown in Eq. (1):

At that time, there was a stable source of CO 2 dispersion in the building, and since the indoor personnel of the building was the main source of CO 2 dispersion, the indoor fresh air volume was calculated according to the environmental quality balance equation as shown in Eq. (2):

Based on the measured indoor CO 2 concentration, the fresh indoor air volume can be calculated by the difference method. The calculation accuracy of the different method is closely related to the indoor CO 2 dispersion rate and the divided time interval, the smaller the time interval, the more the change tends to be transient and the more accurate [35] , as shown in Eq. (3):

Where, C is the indoor CO 2 concentration (mg/m3); out C is the outdoor CO 2 concentration (mg/m 3 ); 0 C is the indoor starting CO 2 concentration (mg/m 3 ); 0 Q is the CO 2 emission, the amount of human exhaled CO 2 is 18L/h/person, which is about 549 (mg/min); q is the fresh air volume (m 3 /h); V is the room volume (m 3 ); t is the change time; A is the air exchange volume Fig. 12 , it can be seen that when the fresh air system is running from 9: 00 to 18: 00 on weekdays, the indoor CO 2 concentration in the office mainly fluctuates within the range of 600ppm -700ppm, and according to the standard indoor CO 2 concentration does not exceed 1000ppm, it can be seen that the indoor air quality in the office is relatively good. The indoor air quality of the office is good. According to the operation control strategy of the fresh air system in this office building in summer, the fresh air system was turned on at 9: 00-11: 00 am and 2: 00-4: 00 pm respectively to regulate the indoor air quality. As shown in Fig. 12 , the indoor CO 2 concentration in the office was increasing from the time the fresh air system was turned on to the time the fresh air system was turned off, and the indoor CO 2 concentration gradually tended to stabilize over time from the time the fresh air system was turned off to the next time it was turned on. After the new air system was turned on in the afternoon, the indoor CO 2 concentration gradually decreased and was maintained at a low concentration level, and the indoor CO 2 concentration increased again after the new air system was turned off at 16: 00.

On the premise that the indoor CO 2 concentration is known, this paper uses the differential method to measure the fresh air volume in the office room. The data between the test intervals of 30 minutes were selected, and the fresh air volume in the operation of the fresh air system was calculated according to Equation 2-3. The calculation results are shown in Table 4 . According to the calculation results of indoor fresh air volume shown in Table 4 , the fresh air volume per capita is 40.5m 3 /h when the indoor CO 2 concentration is maintained at 600-700ppm during the whole working day and 35.7m 3 /h when the fresh air volume per capita is maintained at 600-800ppm during part of the time when the fresh air system is turned on. The per capita fresh air volume is higher than the standard 30m 3 /h.

If the indoor and outdoor ambient air temperature and humidity parameters are unchanged, the fresh air volume per capita is 26.5m 3 /h when the indoor CO 2 concentration is maintained at 800-1000ppm during the whole time the fresh air system is turned on, and the fresh air volume per capita is 28m 3 /h when the indoor CO 2 concentration is maintained at 700 -1000ppm during part of the time, which is slightly lower than the standard fresh air volume per capita 30m 3 Table 5 . The histogram of fresh air volume and the line graph of fresh air volume per capita for the fresh air outlets tested during the test period are shown in Fig. 13 The results of the fresh air volume testing and per capita, fresh air volume calculation for each new air outlet using the combination of Testo 405i anemometer and air volume hood is shown in the above figure. The analysis found that the indoor fresh air volume detection value meets the design requirements, and the error of the per capita fresh air volume and the standard 30m3/h is within the allowed range to meet the design requirements.

When the indoor CO 2 concentration is maintained at the standard 1000ppm, the required fresh air volume is 30m 3 /h. According to the results of the differential method, when the CO 2 concentration is maintained at 600-700ppm, the required fresh air volume per person is 40.5m 3 /h, which is higher than the standard 30m 3 /h. At present, due to the outbreak of new coronavirus infectious diseases, public buildings adopt cleaning and disinfection of ventilation systems, increase the amount of fresh air and all fresh air operation to ensure the indoor environment; CO 2 concentration is easy to detect so it can be used to characterize whether the amount of fresh air in the room meets the standard and whether it can meet the demand of indoor personnel for fresh air. Comparing the calculation results of the fresh air volume differential method and the actual measurement results, we can see that the fresh air volume per capita of 30m 3 /h can ensure that the indoor CO 2 concentration of office buildings does not exceed 1000ppm [38] . If the indoor CO 2 concentration is required to be maintained at 600ppm -700ppm or even lower, the fresh air volume per capita will be higher than the standard 30m 3 /h.

The increase in fresh air volume will lead to a significant increase in system energy consumption, but in the current serious epidemic situation, increasing the fresh air volume is the most effective way to ensure the health of indoor personnel.

The Cronbach's coefficient was used to test the reliability of the collected questionnaires, the According to the data in Table 6 , it can be seen that the overall satisfaction of indoor personnel on the subjective feelings of the indoor environment is 3.69, followed by indoor air quality 3.66, indoor air temperature 3.61, fresh air volume 3.59, indoor air velocity 3.32, and indoor air relative humidity 3.51. The average satisfaction rate of indoor office workers for indoor odor is 3.30.

Therefore, it can be known that the office building during the operation of the summer fresh air system investigated has the highest overall satisfaction with the subjective feelings of the indoor environmental personnel, and the indoor office personnel has the highest satisfaction with the indoor air temperature and indoor air quality. The average satisfaction value of subjective feelings is closer to the expression of neutral feelings, rather than a very satisfactory value 5. Therefore, the indoor environment of the building still needs to be improved, and the subjective satisfaction of indoor environment personnel is relatively poor. This shows that the two environmental parameters of indoor air temperature and indoor air quality have a greater impact on indoor staff satisfaction than other environmental parameters.

According to the comparison and analysis of the average satisfaction score of the subjective feelings of indoor personnel in Table 4 , it can be known that the indoor personnel of the office building under investigation have a high degree of attention to indoor air temperature and indoor air quality. Key factors for overall evaluation. Also, environmental parameters that affect indoor personnel's satisfaction with the indoor environment, such as indoor air relative humidity, indoor air velocity, fresh air volume, and odor, are closely related to indoor environment personnel satisfaction and cannot be ignored. Therefore, the design of air conditioning and fresh air systems in office buildings should fully consider the close relationship between various environmental parameters and personnel satisfaction. On the premise of meeting the design requirements, increase the indoor personnel's satisfaction with the indoor environment as much as possible to create a healthy comfortable indoor environment.

Since the 1960s, the ideas and methods of uncertainty research have been successively proposed.

Professor L.A.Zadeh proposed the fuzzy mathematical theory in 1965, and Professor Deng Julong of China proposed the gray system theory in 1982. These results have had a profound impact on the systematic research of uncertainty from different levels. Grey system theory provides effective solutions and new ideas for solving small data, uncertainty, and poor information problems.

Through the analysis of some known data, effective information is extracted to grasp the change law of system behavior and achieve the expression and control of the system [41, 42] . 

, which constitute the reference sequence, as shown in Table 8 . 

Find the absolute value sequence of the difference between the corresponding components. This is the first difference between the reference sequence and the comparison sequence, as shown in Eq. (6): 

M is the maximum range and m is the minimum range. When calculating the maximum range, ) ( △ i k is the value with the largest absolute difference between the comparison sequence and the reference sequence, and when calculating the minimum range, ) ( △ i k is the value with the smallest absolute value of the difference between the comparison sequence and the reference sequence.

(3)Find the correlation coefficient, as shown in Eq. (8): People's perception of carbon dioxide is more sensitive than PM 2.5 , so CO 2 is often used as an index to evaluate indoor air quality, but the harm caused by PM 2.5 to the human body is not denied.

Long-term tests to analyze changes in indoor air quality in office buildings. It can be known from Fig. 7 and Fig. 8 that the measured values of the CO 2 concentration at each measurement point of the office building, except for some data higher than 1000 ppm specified in the standard, have the largest proportion of the measured data distribution between 400 ppm and 1000 ppm. It can be known from Fig. 9 and Fig. 10 that the median measured value of indoor PM 2.5 concentration is mainly distributed between 10 μg/m 3 and 75 μg/m 3 , and there is a phenomenon of data exceeding the standard at individual measurement points. The subjective questionnaire survey results show that the average indoor staff's satisfaction with indoor air quality is 3.66/5.

As shown in Fig. 12 , the measured fresh air volume during the operation of the fresh air system meets the design requirements. The indoor carbon dioxide concentration in the office building was tested for 8 hours of fresh air operation during a normal working day and 4 hours of fresh air system operation during part of the working day, and the required fresh air volume values at different concentrations were calculated using the steady-state difference method. It is found that when the indoor carbon dioxide concentration is maintained at 600 -800ppm, the required fresh air volume per capita is higher than the standard value of fresh air volume per capita, and when the concentration is maintained at 1000ppm, the required fresh air volume per capita fluctuates around the standard value of 30m 3 /h. Therefore, it can be seen that under the condition of relatively stable indoor personnel and workload in the office building, the size of the fresh air volume can be appropriately adjusted according to the changes in indoor carbon dioxide concentration, to achieve the purpose of energy-saving under the premise of fully ensuring indoor air quality. The current research found that there are a large number of different models of printers and other photocopying equipment in the office building, Such equipment is used more frequently in the daily office environment, due to ink volatilization and other factors leading to relatively poor air quality in local locations, and due to the lack of reasonable design of the location of the air outlet in some rooms resulting in poor local airflow organization can not send fresh air to the work area and breathing area where office workers are located.

Combined with Fig. 11 , it can be seen that the indoor air velocity of a certain three normal working days during the test period is less than or equal to 0.3m/s to meet the design requirements of indoor air velocity of air-conditioned office buildings in summer. The results of the subjective questionnaire analysis show that the average satisfaction value of indoor office workers with indoor air velocity is 3.32/5. In response to the problem of low satisfaction of indoor personnel with the air velocity, the current research found that some personnel feedback on the existence of indoor blowing sensation, causing discomfort. Also, the satisfaction level of air velocity of office workers in air-conditioned rooms is largely inseparable from the noise generated by air velocity at the air outlet. Office buildings with the air conditioning or fresh air indoor air outlets exist to varying degrees of noise, newly renovated offices in the wind noise situation and the renovation of a long time in the office is relatively better less noise. Building indoor air conditioning or fresh air outlet velocity in varying degrees determines the degree of noise reverberation, that is, the velocity is greater when the general air outlet noise is relatively large, and vice versa is smaller. Some indoor personnel chooses to reduce the velocity to reduce the generation of noise because low velocity leads to poor indoor air circulation caused by local thermal comfort and air quality, which in turn affects the indoor personnel's satisfaction with the environment.

Based on the above analysis, it can be seen that before the outbreak of the epidemic, the new air conditioning system of the office building could ensure the quality of the indoor environment by running for 4 hours a day. With the outbreak of the COVID-19, it is now generally believed that maintaining the operation of the air conditioning system and increasing the amount of ventilation in the building can effectively reduce the probability of personnel being infected [43] .

The air conditioning system of this office building is a fan coil unit and fresh air system. 

In this paper, the indoor environmental parameters of an office building in Beijing during the summer were tested and the satisfaction of the indoor personnel was investigated from both objective and subjective aspects.

(1)Through the actual testing of indoor environmental parameters air temperature, relative humidity, CO 2 concentration, PM 2.5 concentration, air velocity, and fresh air volume, it can be seen that the environmental parameters are maintained within the range of air conditioning interior design parameters required by the Design Code for Heating, Ventilation and Air Conditioning in Civil Buildings, but there are still a large number of data deviating from the recommended values of design standards. At the same time, the analysis of the subjective survey of indoor environmental personnel satisfaction shows that the average value of indoor personnel satisfaction with each environmental parameter is generally low.

(2)The article collated the questionnaires of indoor personnel's subjective feelings about the indoor environment, analyzed the Spearman correlation between indoor environmental parameters and indoor environmental personnel's subjective satisfaction, and conducted a gray correlation analysis by combining the actual measured data of indoor environmental parameters with indoor personnel's satisfaction with the indoor environment. It was found that the results of Spearman correlation analysis and gray correlation analysis were consistent, and it was determined that indoor air temperature and indoor air quality were some of the most important factors affecting indoor personnel's satisfaction with the indoor environment.

(3)Through the calculation of the probability of indoor personnel being infected under the two modes of operation of the fresh air system, it can be seen that the probability of infection under both modes of operation is more than 5%, but because the COVID-19 is extremely infectious and pathogenic, it is necessary to pay attention to the danger of the virus to ensure the health of life and normal work under the normalization of the epidemic.

(4)To cope with the COVID-19 and the regular epidemic prevention and control, the fresh air system in office buildings should increase the amount of fresh air during operation, extend the running time of the fresh air system, and the operation and maintenance management department of the air conditioning system should develop a more scientific and reasonable operation and maintenance management mechanism, strengthen the maintenance of all kinds of air conditioning equipment for overhaul and timely cleaning and disinfection to fully ensure the health needs of indoor personnel. Besides, office workers should strengthen their protection and wear masks at all times to maintain a safe distance, and the management department should strictly control the body temperature of people entering the room to ensure the health and safety of the working environment during the epidemic.

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Declaration of Interest Statement