Research On The Distribution Of Indoor CO₂ Concentration And The Relationship Between Fresh Air Volume That Meets The Pre-warning Value Of Breathing Area And Personal Density

For the past few years,building energy consumption and indoor air quality have been two significant concerns in the field of HVAC.Air conditioning system energy consumption accounts for about 65% of the building energy consumption,while in which the energy consumption to deal with the fresh air energy accounts for 25% to 30%,or even up to 60% in the winter.Although the increase in fresh air volume can effectively dilute indoor pollutants and improve indoor air quality,at the same time,it will increase the system energy consumption.For buildings where people activities are mainly CO₂-based,it is possible to effectively improve the indoor air quality and reduce the building energy consumption by adjusting the fresh air volume in line with the people density on the basis that the CO₂ concentration does not exceed the pre-warning value.Therefore,the study of the relationship between the fresh air volume and personal density to enhance the technical level of HVAC industry has important engineering value and academic significance.In this paper,theclosed computer in summer is firstlytaken as the case to analyze the distribution of CO₂ concentration when there is no fresh air entering the room,and utilizes the numerical simulation method to study the time required for CO₂ concentration in the computer room with the change of people size to reach the pre-warning value.The results show that the indoor CO₂ concentration distribution is related to the indoor flow field,while the temperature field haslittle impact on it.The time for mean value of CO₂ concentration to reach the pre-warning value,900 ppm,is related to the number of indoor people.The relationship between the pre-warning time and the per capita occupancy volume can be formulated as t=-36.12+95.69 x.The formula can be used to determine the interval time between replacement ventilation to ensure the CO₂ concentration in the room below 900 ppm.Secondly,the paper studies the relationship of fresh air with the change of personal density by CO₂ pre-warning value,esignsand constructs the “Up-supply Up-return” air distribution multi-coupling physical experimental table,analyzes the effect of different fresh air volume on the distribution of CO₂ concentration by the combination of experiment and numerical simulation methods.The results show that the change of fresh air volume has an important effect on the steady state ofindoor CO₂ distribution,and the CO₂ concentration in thearea with Z = 1.2m is higher than that of other parts in the room.In the experimental table that is constructed in the paper and in the premise of constant air outlet,area and number of return air outlet,the amount of fresh air volume required for the CO₂ concentration in the breathing area to reach 900 ppm is researched.The relationship between the fresh air volume and the staff density that satisfies the pre-warning value of the breathing area can be formulated as Q=-252.35546(1-e^3.17985x .This formula can be used to adjust the fresh air volume according to personal density in the room during the operation of the air conditioning system,achieving the comfortable and energy-efficient environmental protection operation.On the basis of the research of this paper,it is possible to change the airflow distribution and return air outlet size and relative position to form different airflow distribution,and obtain the minimum fresh air volume to achieve energy saving operation in the air conditioning system.