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Mean clothing insulation values (including the incremental insulation of the chairs) varied seasonally in both building types. Summer vs. winter mean values were 0.70-0.92 clo in the HVAC buildings, compared to 0.66–0.93 in the naturally ventilated buildings. Although the buildings didn’t differ significantly in terms of their mean clothing values, the total range of clothing worn was much wider in the naturally ventilated buildings. Occupants of these buildings also demonstrated a stronger relationship between their clothing patterns and indoor temperature, with mean clothing insulation decreasing by an average of 0.1 clo unit for every 2°C (3.6°F) increase in mean indoor temperature.
Air velocity is considered a form of behavioral adaptation when people are able to make the environmental adjustments themselves, such as opening or closing a window, turning on a local fan, or adjusting an air diffuser. Mean air speeds recorded in the HVAC buildings generally were confined to the region below 0.2 m/s (39.4 fpm), as prescribed in Standard 55-1992. In a naturally ventilated building, speeds above this limit were recorded when indoor temperatures extended beyond the upper temperature limit of 26°C (78.8°F) in Standard 55-1992. As will be shown later, however, these forms of behavioral adaptation could account for only part of people’s acceptance of higher temperatures in the naturally ventilated buildings.
How do people react as conditions deviate from the optimum? A weighted linear regression model of the relationship between mean thermal sensation (TS) and mean indoor operative temperature (Top) was used to judge how quickly people felt too warm or too cool as temperatures deviated from the optimum:
(Centralized HVAC buildings)
TS=0.51 × Top - 11.96(Top in °C) (1)
TS=0.28 × Top - 21.03(Top in °F)
(Naturally ventilated buildings)
TS= 0.27 × Top - 6.65(Top in °C) (2)
TS= 0.15 × Top - 11.45(Top in °F)
In these equations, TS represents a vote on the familiar ASHRAE seven point thermal sensation scale, where TS=0 is“neutral.”This analysis revealed that occupants of centralized HVAC buildings were twice as sensitive to deviations in temperature as were occupants of naturally ventilated buildings. Such a finding suggests that people in air-conditioned buildings have higher expectations for thermal consistency, and quickly become critical if thermal conditions perge from these expectations. In contrast, people in naturally ventilated buildings seem to demonstrate a preference for a wider range of thermal conditions, perhaps due to their ability to exert control over their environment, or because their expectations match the more variable conditions they are used to experiencing in such buildings.
How does one define a “comfort temperature?” Does everyone always prefer to feel “neutral?” The traditional method of defining a comfortable temperature is to assume that a “neutral thermal sensation” represents ideal conditions, and then to solve a linear regression equation such as those in Equations 1 and 2 for the “neutral temperature” at which TS=0. However, when surveys include a question about preference (usually expressed as “do you prefer to feel warmer, no change, or cooler?”), one can also calculate a “preferred temperature” in a similar way, assuming that a preference for “no change” represents ideal conditions.
Both types of analyses were conducted in this project, with the result that generally no difference existed in neutral vs. preferred temperatures for occupants of naturally ventilated buildings. However, in the HVAC buildings, the analysis revealed that people preferred slightly warmer-than-neutral temperatures in cold climates, and cooler-than-neutral temperatures in warmer climates(the difference being up to 1°C (1.8°F) at either extreme end).Since we viewed “preference” as being a more appropriate indicator of optimum thermal conditions than the traditional assumption of “neutral thermal sensation,” we developed a correction factor to modify calculations of neutral temperatures in HVAC buildings to more accurately reflect preference.