Abstract In the quest towards energy conservative building design thermal comfort must not be sacrificed. This paper explores energy conservation strategies and their impact on the thermal environment. Parametric variations in envelope design and HVAC operation on energy performance and thermal comfort of a typical commercial office building in Singapore are investigated. With proper plant operation, the resulting internal environment suffers no loss in comfort level, and the savings in energy arising from the various conservation measures are realistic. These measures are ranked according to their effectiveness, and provides valuable knowledge for achieving energy conservation without introducing occupant discomfort.