Validity of CO2 based ventilation design

Abstract

The present ventilation design practice as well as the ventilation standards and building regulations are based on the assumption for complete mixing of air in occupied spaces. Required flow rate of outdoor air for dilution of metabolic CO2 generated by occupants is calculated to keep the CO2 concentration below certain required level. The CO2 concentration measured in the exhaust air or in the room but far from the occupants is assumed to be the same as the CO2 concentration in the air inhaled by the occupants. However, this assumption is seldom accurate, especially in spaces with closely seated occupants, such as classrooms, meeting rooms, etc. In such spaces the CO2 sources, i.e. the people, are close to each other and the CO2 concentration in the inhaled air may be much above the CO2 concentration level recommended as a limit in standards. This is because the upward free convection flow that exists around human body entrains the air with high CO2 concentration exhaled by seated people and move it to their breathing zone. Furthermore, the thermal flows generated by occupants’ body interact with the ventilation flow, which often results in insufficient dilution of the generated CO2 (as well as other pollution) and high levels of CO2 concentration at the breathing zone of occupants. This problem is discussed in the present paper in detail. The discussion is supported by results of measurements in a meeting room with mixing air distribution. People were used to generate metabolic CO2 and a breathing thermal manikin was used to measure accurately the CO2 concentration in the inhaled air. The results confirmed that inhaled CO2 concentration was much higher than the one at the exhaust and that there is need for changes in the present CO2 based ventilation design practice. Possible solutions are suggested.

Differences in temperature measurement by commercial room temperature sensors: Effects of room cooling system, loads, sensor type and position

“…Since the measured temperature serves as a control reference for the HVAC system, the uncertainties of the sensor measurements would influence the resulting thermal environment (e.g., compliance with comfort categories in standards such as [36]) and energy use. The same applies for other indoor environmental quality parameters [39,40]. Further numerical analyses such as those done by Kolarik and Olesen [29] would be necessary to quantify such an influence.…”

Fuzzy Logic Controlled Simulation in Regulating Thermal Comfort and Indoor Air Quality Using a Vehicle Heating, Ventilation, and Air-Conditioning System

“…The outside environment air was assumed to have a CO 2 concentration of 400 ppm [ 27 ]. The CO 2 concentration generated by the human body was a function of oxygen consumption level, respiratory system, and human metabolic rate [ 28 , 29 ]. The CO 2 exhaled by a passenger inside the vehicle cabin was assumed to be 0.01 g/s, as that in [ 28 , 29 ].…”

“…The CO 2 concentration generated by the human body was a function of oxygen consumption level, respiratory system, and human metabolic rate [ 28 , 29 ]. The CO 2 exhaled by a passenger inside the vehicle cabin was assumed to be 0.01 g/s, as that in [ 28 , 29 ]. An overview of the temperature and CO 2 models implemented in MATLAB Simulink is shown in Figure 4 .…”

Dynamic assessment of the risk of airborne viral infection

“…The second observation depends on external air ventilation. This can be of two types: natural ventilation 22 and forced ventilation. 23…”