Low energy school design : a study of factors affecting energy use in New Zealand primary schools

Abstract

The energy consumption patterns of 247 Wellington Education Board schools and a pilot sample of 15 Auckland, 16 Christchurch and 17 Dunedin schools were analysed. In addition, case studies of 26 Wellington schools were carried out as well as detailed analysis and measurements of the thermal and lighting environments in four Wellington city schools. 73 schools were surveyed and the principals, teachers and caretakers were interviewed. Results from the analysis of the data along with the review of results from overseas research were then applied to put up a set of design recommendations for low energy school buildings. 70 percent of the Wellington Education Board schools had AEUI in the range between 100 and 500 MJ/m2/year with an average of about 310 MJ/m2/year. The Auckland, Canterbury and Otago schools had 80 percent of energy consumed in schools was for space heating purposes, the rest being for lighting, domestic hot-water and swimming pool pumps and heating. The differences in the total energy consumption per unit floor area between schools were found to be due mostly to differences in the space heating energy consumption. The schools with higher AEUI tended to have a higher proportion of their energy use for space heating. Climate was found to be a significant factor affecting this, with the number of heating degree days showing very close correlation to the space heating energy requirement. A set of performance analysis computer programs were developed to assess heat losses and gains. It was found that solar gains contributed to about 30 percent of a building's space heating requirement. Wind related losses, which are mostly through infiltration, can constitute between 3 and 70 percent of a building's total heat loss. On average, the wind induced heat losses amounted to about 34 percent of total heat loss. In the monitoring of the thermal environment in the four pilot Wellington city schools, it was observed that more than half of a typical day's space heating energy was consumed between 0600 and 0900 hours to warm up the buildings and very little energy consumed for space heating after 1200 hours. Thus the heavy buildings which have to be heated up earlier were found to have higher space heating energy requirements. The monitoring also revealed the importance of night sky rediation losses, which is aften overlooked. In the study of heating systems it was found that the average energy requirement of central heating systems were nearly twice those for unit heating systems. The survey of the central heating systems also revealed some serious problems in many of the installed coal boiler systems.