Retrofitting solar air heaters in New Zealand schools – A randomized crossover intervention study

Most New Zealand (NZ) schools rely on natural ventilation and are often inadequately ventilated in winter. NZ school hours typically span from 9 a.m. to 3 p.m. and are well aligned to optimum solar radiation. Existing classrooms could therefore be heated and ventilated using retrofitted solar energy applications. To investigate the suitability of a commercially available solar air heater (SAH) to improve ventilation, a randomized crossover study was conducted in 12 classrooms from six primary schools in Palmerston North, NZ, during the winter of 2014. Typical performance results showed a mean (sd) SAH outlet air temperature of 29.2 (10.4) °C at a mean (sd) velocity of 0.7 (0.3) m·s-1. During most school periods (64% to 99%) classrooms maintained required thermal comfort. The concurrent use of the extant heaters was reduced, and carbon dioxide levels were improved, lowering exposure for occupants. This study confirmed that retrofitting a commercially available SAH contributed to improved classroom ventilation, increased thermal comfort and reduced energy use. Optimising performance would require design improvements to improve airflow in order to comply with NZ ventilation and indoor air quality guidelines.