A Relationship between Room User and Carbon Dioxide in Air-Conditioned Classroom

Abstract

This study aimed to determine a relationship between room users and carbon dioxide (CO2)
in an air-conditioned classroom. The CO2 concentration was measured in three air-conditioned
classrooms in the Department of Civil Architecture, Faculty of Technology, Udon Thani Rajabhat
University, which had different physical characteristics and different activities, using an air quality
meter ‘Air meter Fluke 975’. The standard criteria (ASHRAE) determines that the CO2 concentration
should not exceed 1,000 parts per million (ppm). The measurement results showed that in
classrooms with 30 or fewer users, the CO2 concentration ranged from 393 to 5,314 ppm. All
classrooms are equipped with 2 split-type air conditioners and no exhaust fan. When the rooms
were in use for 45 to 60 minutes, CO2 concentrations exceeded 1,000 ppm, indicating insufficient
ventilation because many people use the room, and no air exchange system is installed. Therefore,
students should take a break during use and open the windows and doors for ventilation every
45 to 60 minutes. And after being in the room for 3 hours continuously, the concentration of carbon
dioxide would always exceed 1,800 ppm, which may cause dizziness, headache, exhaustion,
lack of concentration, and throat and nose irritation. The classrooms in the afternoon had the
accumulation of CO2 from the morning exceed the standard. Even without people in the classroom
during the one-hour lunch break, CO2 concentrations could not be reduced below 1,000 ppm.
The study found that the number of classroom users that do not cause CO2 to exceed
1,000 ppm during a continuous 3-hour class period is 3 to 6 persons per classroom, which is not
practical. The ventilation rate should be increased by the flow of fresh air outside into the room
and sucks the air inside the room out during use, such as installing an exhaust fan with an inlet-out
system if installing an exhaust fan two machines in opposite positions will make the air flow faster.
The study also found that studying in the same room without air conditioning but opening windows
and doors in opposite positions. Let the air ventilate naturally in conjunction with turning on the
ceiling fan. The CO2 concentration average value is only 459.5 ppm, which does not adversely affect
the health of the room users.