Impact on primary school classrooms temperature and ventilation from using a roof-mounted solar air heater: a winter case study in New Zealand

Classrooms that rely on natural ventilation are often under ventilated in winter. However, conventional mechanical ventilation is prohibitively expensive for schools. This study investigates the impact on temperature and ventilation in New Zealand (NZ) primary classrooms in winter, with the intervention of operating a roof-mounted solar air heater (SAH). This study was carried out in NZ school Term 3 (from end July to end September) in 2013 and 2014. Two adjacent classrooms (Room 1 and Room 2) from one school participated. These two classrooms had very similar construction characteristics and population characteristics. In 2013, baseline monitoring was conducted. In 2014, Room 1 was the control, Room 2 was the treatment. Ambient air is heated by the SAH, and this heated air was delivered to the treatment classroom. Heater use hours, temperature levels and carbon dioxide (CO2) concentrations in both classrooms were measured. The ventilation rate was estimated using traces gas decay techniques. In 2013, the temperature levels in Room 1 (21.8 ºC ± 1.4 ºC) were statistically significantly lower (P < 0.01) than in Room 2 (23.9 ºC ± 1.5 ºC), with the temperature difference of 2.1 ºC. In 2014, the temperature difference between Room 2 (treatment) and Room 1 (control) increased to 2.7 ºC. However, the ratio of total daily heater use (Room2/Room1) reduced from 2.3 (227 hours difference) in 2013 to 1.9 (191 hours difference) in 2014. In 2013, CO2 levels in Room 1 were statistically significantly lower (P < 0.01) than in Room 2. In 2014, CO2 concentrations had no differences between these two classrooms. Between both classrooms, mean (±sd) ventilation rate was from 1.7 (± 1.5) to 2.6 (± 2.4) h-1, or from 3.0 (± 2.4) to 4.2 (± 3.9) l/s/person. This study indicates that operating a SAH played a positive role in increasing room temperature and ventilation rate, while reducing the consumption of purchased energy.