Center for the Built Environment

Naturally ventilated buildings have been found to be comfortable over a wider range of indoor temperatures than in air-conditioned buildings, while using less energy. The mechanisms underlying this are not well understood. Through a longitudinal field study of a naturally ventilated office in Alameda, CA, we obtained insights into how occupants exercise various adaptive control opportunities to meet their comfort needs in the absence of a mechanical HVAC system. Continuous measurements were made of adaptive behaviors such as window state, ceiling fan usage, heater usage, and indoor and outdoor climate (dry-bulb air temperature, relative humidity, CO2, outdoor temperature). Over 1400 thermal comfort survey responses were collected, which showed that the building provided acceptable thermal conditions for 98% of the survey period, covering an indoor temperature range of 16–28°C. Occupants wore clothing between 0.5 and 0.6 clo in summer, and 0.7–0.8 in winter. Occupants opened windows when the outdoor temperature was above 15°C, with window opening often occurring at the occupant's arrival and proportional to outdoor temperature. Fan use was best explained by indoor temperature, typically being turned on during summer at indoor temperatures above 25°C. Heaters were turned on in winter more than an hour after arrival and commencement of sedentary activity. With these adaptive control behaviors, occupants were thermally neutral and satisfied from 18 to 27°C. Their satisfaction exceeded that predicted by ASHRAE Standard 55 or PMV-based ISO standards. Overall, our findings provide empirical support for adopting adaptive comfort model in office buildings.