Abstract
Night ventilation methods have been used in educational buildings to guarantee indoor air quality at the beginning of occupied periods. A typical method has been to pre-start ventilation 2 h before the space usage. Another selection has been to ventilate a building continuously during the night with a minimum airflow rate that can dilute material emissions. In this study, the pre-started, continuous, and intermittent ventilation methods were compared by assessing indoor air quality in field measurements. The daytime ventilation was operating normally. The test periods lasted for 2 weeks. Indoor air quality was assessed by measuring the total volatile organic compounds and microbial concentrations using the quantitative polymerase chain reaction method. Additionally, the thermal conditions, carbon dioxide, and pressure differences over the building envelope were measured. The results show that the night ventilation strategy had negligible effects on microbial concentrations. In most cases, the indoor air microbial concentrations were only a few percent of those found outdoors. The averaged concentration of total volatile organic compounds was at the same level with all the night ventilation methods at the beginning of the occupied periods in the mornings. The concentrations reached a minimum level after 2-h ventilation. The concentrations of total volatile organic compounds were higher during the day than at night. This reveals that space usage had the largest effect on the total volatile organic compounds. Generally, the results show that continuous night ventilation does not significantly affect the biological and chemical contaminants. Consequently, a 2-h flushing period is long enough to freshen indoor air before occupancy.
Highlights
The results support the hypothesis of the effect of night ventilation methods on indoor air quality over a two-week collection period
The results support the hypothesis of the effect of night ventilation methods on indoor air quality in the mornings and the effect of daily activities on TVOC concentration
The pre-started, continuous, and intermittent ventilation strategies were compared by assessing indoor air quality in field measurements
Summary
Research literature has shown that poor ventilation is usual in schools, worsening the health symptoms of individuals [3,4,5,6]. Taking care of health and wellbeing has caused additional ventilation use which rises the energy consumption of buildings. The European standard 15251:2007 recommends using pre-started or continuous minimum ventilation in unoccupied hours to remove material emissions before space usage [10]. In Nordic countries, a usual method has been to stop mechanical ventilation after the building usage and pre-start the ventilation around 2 h before the occupied periods. An alternative ventilation method has been to use night ventilation at 30–50% partial power that can remove material emissions. A third method has been to use intermittent ventilation during unoccupied periods, and in this way, achieve a minimum night-time ventilation level in spaces on average
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