Hetmanchuk H. Assessment of the decentralized level of natural air exchange in buildings, taking into account the variability of internal and external conditions

In the dissertation, a review and analysis of the influence of the air exchange rate as a ventilation component on the energy efficiency of buildings of various purposes was carried out. A literature review on approaches to determining the air exchange rate is presented, where the main factors that influence the provision of comfortable conditions from the point of view of air quality are outlined. Including attention paid to the CO2 indicator in the premises as an indicator of air quality. An empirical method of calculating the hourly natural multiplicity of air exchange in multi-story buildings in conditions of variability of the external and internal environment is presented. The experiment plan and the method of determining the natural multiplicity of air exchange on the basis of experimental measurements of the CO2 level in representative rooms with a step of 1 minute are also given. Determination of CO2 concentration was carried out on the basis of the mass balance of selected rooms, taking into account key parameters: natural air exchange, background (external) concentration of CO2, initial concentration of CO2 in the room, presence of people and geometric dimensions of the room. As part of the study, the change in the concentration of CO2 in the room was analyzed depending on a number of parameters, namely: secretions from people, changes in the concentration of CO2 in the supply air and the volume of supply air. Based on the results of the analysis, it was established that regulating the air exchange rate according to the CO2 level is a better approach than simply observing the normative values, since this approach allows for more accurate and effective regulation of air exchange in buildings, taking into account the real conditions and needs of users. The dissertation presents the results of experimental studies of CO2 concentration and determined the frequency of natural air exchange in the classrooms of the educational building of National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”. It was established that without taking into account ventilations, the air exchange rate is 0.41 ACH, with ventilations, the average air exchange rate is 0.48 ACH. On the basis of several series of measurements carried out in the winter period in the premises of a residential building, it was established that the phenomenon of infiltration is characteristic. With this air circulation mechanism, the air exchange rate was 0.74 ACH for the living room, 0.73 ACH for the corridor, and 3.4 ACH for the kitchen. Under exfiltration conditions, the air exchange rate for the living room was at the level of 0.37 ACH, 1.06 ACH for the corridor, and 0.57 ACH for the kitchen. Experiments have confirmed that the actual air exchange rate, when fresh air enters through windows and doors, exceeds the minimum regulatory values. However, with the reverse air flow, it does not meet the normative values. A series of experimental studies was also carried out in the representative rooms of the apartment in the summer period. During the summer period, it was found that the number of cases of infiltration and exfiltration is almost the same, but, as for the heating period, the directions of air movement in the premises depend on the direction of the wind. For infiltration conditions, the air exchange rate was 0.57 ACH for the living room, 2.34 ACH for the corridor, and 2.41 ACH for the kitchen. For exfiltration conditions, the air exchange rate was 0.24 ACH for the living room, 0.94 ACH for the corridor, and 0.52 ACH for the kitchen. As part of the experimental study, experimental measurements of CO2 concentration were also carried out in the auditorium of the educational building of the National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute" No. 22 in the cooling mode in the summer. The obtained results show that the value of the natural multiplicity of air exchange depends on wind and stack effects. As the temperature difference between the indoor and outdoor air increases, there is an increase in the air exchange rate from 0.37 to 0.9 ACH. In the fourth chapter of the dissertation, an analysis of the energy indicators of the researched premises is carried out based on models created in the EnergyPlus software environment, which allow determining the building's energy consumption for heating needs, taking into account the variability of the actual natural air exchange in residential buildings. According to the results of energy modeling, the annual energy saving, taking into account the actual values of the natural multiplicity of air exchange in different areas of the building, is 5.4% compared to the standard DSTU B EN 15251:2011, and compared to the standard DBN B.2.2-15:2019 – 7.7%.