A ventilation intervention study in classrooms to improve indoor air quality: the FRESH study

BACKGROUND: Classroom ventilation rates often do not meet building standards, although it is considered to be important to improve indoor air quality. Poor indoor air quality is thought to influence both children’s health and performance. Poor ventilation in The Netherlands most often occurs in the heating season. To improve classroom ventilation a tailor made mechanical ventilation device was developed to improve outdoor air supply. This paper studies the effect of this intervention. METHODS: The FRESH study (Forced-ventilation Related Environmental School Health) was designed to investigate the effect of a CO(2) controlled mechanical ventilation intervention on classroom CO(2) levels using a longitudinal cross-over design. Target CO(2) concentrations were 800 and 1200 parts per million (ppm), respectively. The study included 18 classrooms from 17 schools from the north-eastern part of The Netherlands, 12 experimental classrooms and 6 control classrooms. Data on indoor levels of CO(2), temperature and relative humidity were collected during three consecutive weeks per school during the heating seasons of 2010–2012. Associations between the intervention and weekly average indoor CO(2) levels, classroom temperature and relative humidity were assessed by means of mixed models with random school-effects. RESULTS: At baseline, mean CO(2) concentration for all schools was 1335 ppm (range: 763–2000 ppm). The intervention was able to significantly decrease CO(2) levels in the intervention classrooms (F (2,10) = 17.59, p < 0.001), with a mean decrease of 491 ppm. With the target set at 800 ppm, mean CO(2) was 841 ppm (range: 743–925 ppm); with the target set at 1200 ppm, mean CO(2) was 975 ppm (range: 887–1077 ppm). CONCLUSIONS: Although the device was not capable of precisely achieving the two predefined levels of CO(2), our study showed that classroom CO(2) levels can be reduced by intervening on classroom ventilation using a CO(2) controlled mechanical ventilation system.