Project Title:

Operable Windows, Personal Control, and Thermal Comfort

Evaluating the influence of personal control in allowing building occupants to be comfortable in a wider range of conditions than prescribed by existing standards.

Status (updated 08/01/2013): Complete

Funding sources: CBE Industry Consortium, ASHRAE 1161

Project Objective

Determine how the use of operable windows in office buildings affects occupants’ thermal comfort and acceptance of variable thermal environments. Previous work developing the adaptive model of thermal comfort showed that occupants prefer a wider range of temperatures than in sealed buildings. This project investigated the extent to which this difference is related to the amount of control that occupants have over their environment.

Significance to Industry

Thermal environments in buildings with operable windows are typically more variable and less predictable than those in fully air-conditioned buildings. In naturally ventilated buildings, occupants prefer a wider range of temperatures than in sealed buildings. If this is because of increased personal control, it may be more appropriate for standards such as ASHRAE 55 to segregate their requirements based on the level of occupant control instead of simply the type of ventilation. This would save energy by allowing the adaptive comfort standard to apply to many mixed-mode buildings.

Research Approach

We conducted a field study to quantify the degree to which personal control of operable windows influences local thermal conditions and occupant response. Test methods included physical measurements and online occupant questionnaires that addressed personal control of operable windows, thermal variability, comfort, and window use patterns.

Our findings offer strong empirical confirmation for the role of shifting expectations in the adaptive model of thermal comfort. We found that occupants experienced similar thermal environments, independent of proximity to and level of control over operable windows. Despite the similarity of conditions, the reactions of the high and low personal control groups were significantly different. Occupants who had greater control preferred a wider range of temperatures. These findings reinforce the adaptive comfort model.

Publications and Reports

Brager, G.S., G. Paliaga, and R. de Dear, 2004. Operable Windows, Personal Control and Occupant Comfort. ASHRAE Transactions, 110 (2), June.

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Office with operable windows. © Pete Eckert/Eckert & Eckert, courtesy of ZGF.

Operable windows provide building occupants with multiple benefits including personal control of the indoor environment.

Berkeley Civic Center

Subject building for operable windows and comfort study in Berkeley, California.

Berkeley Civic Center

The study building’s cooling strategies included exposed thermal mass, stack and cross ventilation, and ceiling fans.