Actual performance of naturally ventilated and air-conditioned Green Star certified office buildings in New Zealand

In the last decade, environmental imperatives have found their way into New Zealand’s debate on the quality and performance of the built environment. The New Zealand Green Building Council launched Green Star Office Design in 2007, soon complemented by the Office Built tool. However, the actual performance of Green Star rated buildings seldom has been verified after occupation. Most are not dissimilar to common-practice office buildings, with high proportions of unshaded glazing, lightweight structures and air-conditioning systems. This raises legitimate questions about their overall indoor air quality and comfort, and about the efficacy of the rating tool in actually delivering the assessed quality. This paper examines the overall features of Green Star rated office buildings in Auckland, and discusses the measured performance of two case study buildings, one naturally ventilated and one air-conditioned, comparing their indoor air quality and comfort. Results of the first research phase reveal clear discrepancies between predicted and measured performance, with localized thermal comfort issues in the naturally ventilated building due to both design failures and human behaviour. They also indicate the need for further adjustments of the rating tool in order to increase its sensitivity to different ventilation systems.