Abstract
Night-time ventilation has been used in non-residential buildings to enhance indoor air quality before occupied periods. However, many hypotheses exist on how this ventilation should be used. A typical choice has been to shut down the ventilation after occupancy and restart the ventilation again 2 hours before occupancy. Another option has been to ventilate the buildings continuously. In this study, the shut-down, continuous, and intermittent ventilation strategies were compared by evaluating indoor air quality. The daily occupied-hour ventilation was kept as usual. Each test case lasted for 2 weeks. Indoor air quality was assessed by measuring TVOC concentrations. Also, the thermal conditions, carbon dioxide, and pressure differences over the building envelope and over the air distribution devices were measured. The results show that the averaged TVOC concentrations were at the same level in the mornings with all those ventilation strategies. The evening concentrations reached a minimum level after a 2-hour purging period. TVOC concentrations were higher during the day than at night. This reveals that space usage had the largest effect on TVOC concentrations. The results indicate that a 2-hour purging is enough to cleanse indoor air before occupancy, and therefore the continuous night-time ventilation is not necessary.
Highlights
Ventilation plays a central role while improving wellbeing indoors [1]-[3]
The chosen indoor environments were a classroom in primary school that was measured in winter (Figure 1a), a playroom in kindergarten (Figure 1b) measured in winter, a playroom in kindergarten measured in autumn (Figure 1c), and a classroom in secondary school measured in autumn (Figure 1d).The primary and secondary schools had a variable air volume system (VAV) and both the kindergartens had a constant air volume system (CAV)
The results show that the average total amount of volatile organic compounds (TVOC) concentration on weekday mornings was at the same level for all the studied night-ventilation strategies
Summary
Ventilation plays a central role while improving wellbeing indoors [1]-[3]. This is important in schools and kindergartens because indoor air quality has effects on learning [4]-[7]. The European standard 15251:2007 recommends using pre-started or continuous minimum ventilation during the unoccupied hours to guarantee good indoor air quality at the beginning of the occupied periods [8]. A typical choice has been to turn off the ventilation after occupancy and restart the ventilation 2hours before occupancy. Another strategy has been to ventilate continuously 24 hours per day by using demand-controlled ventilation. A third option could be to ventilate intermittently during those unoccupied hours by operating the ventilation couple of hour intervals
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