Field performance of a solar air heater used for space heating and ventilation – A case study in New Zealand primary schools

Abstract

New Zealand (NZ) primary schools are often inadequately ventilated in winter. The majority of NZ schools do not have mechanical ventilation systems. Surveys conducted prior to COVID-19 pandemic showed that only 30% of teachers were regularly opening windows in winter. Therefore there is a need to study an affordable alternative ventilation method. This research was conducted to investigate the space heating and ventilation performance of a roof-mounted solar air heater (SAH) in NZ primary schools in winter. Field experiments over two winters were carried out in Palmerston North, NZ. A SAH was installed on the sun-facing roof of four schools in winter 2013 and six schools in winter 2014. During the experiment, the air temperature and air velocity were measured inside the classroom at the SAH outlet. Ambient weather conditions were measured by a local climate monitoring station. Across all schools and two winters, when the SAH was operated at 75% of the maximum fan speed, a mean (standard deviation, SD) level of the air temperature difference between the SAH outlet and inlet was 16.6 (10.4) °C, the mean (SD) volumetric flow rate of the outlet air was 34.0 (12.9) m3·h-1, and the mean (SD) level of thermal efficiency was 16 (11)%. Results showed that operating a roof-mounted SAH increased the indoor temperature and was useful to supplement the natural ventilation flow rate. This is the first study to investigate the field performance of a roof-mounted SAH in NZ primary schools. Results of this study provide insights for the use of solar energy without need for energy storage to heat and ventilate the classrooms.