Carbon dioxide (CO2) demand-controlled ventilation in university computer classrooms and possible effects on headache, fatigue and perceived indoor environment: an intervention study

To study the effects of a CO2 demand-controlled ventilation system (variable flow) in computer classrooms on perceived air quality and sick building syndrome. University students (27 % women) participated in a blinded study. Two classrooms had variable flow (mean 5.56 ac/h); two others had constant ventilation flow (mean 5.07 ac/h). After one week, ventilation conditions were shifted. The students reported symptoms/perceptions during the last hour on rating scales. Temperature, air humidity, CO2, PM10 and number concentration of particles were measured simultaneously. Cat (Fel d 1), dog (Can f 1), horse (Equ cx) and house dust mites (Der f 1 and Der p 1) allergens were measured in dust. Those participating twice in the same classroom (N = 61) were analysed longitudinally. Mean CO2 was 784 ppm (9 % of time > 1,000 ppm) with variable flow and 809 ppm with constant flow conditions (25 % of time > 1,000 ppm). Mean temperature (22.6 A degrees C), PM10 (18 mu g/m(3)) and number concentration (1,860 pt/cm(3)) were unchanged. The median levels of cat, dog, horse and Der f 1 allergens were 10,400 ng/g, 4,900 ng/g, 13,700 U/ng and 260 ng/g dust, respectively. There were slightly less headache (p = 0.003), tiredness (p = 0.007) and improved perceived air quality (p = 0.02) with variable flow. Use of a CO2-controlled ventilation system, reducing elevated levels of CO2, may slightly reduce headache and tiredness and improve perceived air quality. The high levels of pet allergens, due to track in of allergens from the home and possible accumulation due to electrostatic forces, illustrate a need for improved cleaning.