Status (updated 7/18/2007): Complete
Funding sources: CBE Industry Consortium, Research Grants
Project Objective
Determine how the use of operable windows in office buildings affects occupants’ thermal comfort and the acceptance of variable thermal environments. An application of this research will be the development of industry comfort standards that addresses personal control, and thereby encourage energy-efficient building design strategies that respond to individuals’ preferences and adaptability.
Significance to Industry
Thermal environments in buildings with operable windows are typically more variable and less predictable than those in fully air-conditioned buildings. However, current comfort standards such as ASHRAE Standard 55 are universally applied across all building types, climates, and populations. This “one-size-fits-all” approach requires energy-intensive environmental control strategies to deliver stable, consistent temperatures, and can lead to excessive use of air-conditioning. Relaxed thermal standards for situations where people can open windows could result in greater energy efficiency.
Research over the last ten years clearly indicates that personal control affects people’s preferences, but we have no information on the extent to which such control affects the acceptability of varying thermal conditions. Research has also demonstrated that occupants of naturally ventilated buildings are comfortable over a wider range of conditions than occupants of air-conditioned buildings. This research explores whether thermal standards for situations where occupants have control of their environment should allow for a wider range of climatic conditions. This has particular relevance for encouraging widespread adoption of “mixed-mode” and natural ventilation strategies.
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. We selected a building with diverse conditions in terms of centrally-controlled HVAC, operable windows, and stable vs. variable thermal conditions. Test methods included physical measurements and on-line occupant questionnaires that addressed personal control of 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 they had over operable windows. Despite the similarity of conditions, their reactions were significantly different. Our findings reinforce the notion that the wider range of temperatures permitted under the new adaptive version of comfort standards will meet with occupant acceptance if those occupants have personal control of environmental conditions.
Publications and Reports
Olesen, B. W. and G.S. Brager, 2004. A Better Way to Predict Comfort: The New ASHRAE Standard 55-2004. ASHRAE Journal, August.
Brager, G.S., G. Paliaga, and R. de Dear, 2004. Operable Windows, Personal Control and Occupant Comfort. ASHRAE Transactions, 110 (2), June.
