Perceptual and adaptational basis for the management of indoor climate : a study in warm Australian environments.

Abstract

The study examines thermal perception in office buildings and the potential for energy conservation in the practice of air conditioning. The specific objective of the study was to assess the degree of control that the body-environment heat balance exerts on thermal sensation, comfort, acceptability and preference. The setting also provided the opportunity to explore affective, cognitive and behavioural aspects of indoor-climate-related attitudes and their relationships with processes of thermal perception.

Six separate field studies were conducted in a total of 23 air-conditioned and 8 non-air-conditioned buildings, involving 1163 respondents and 3290 complete sets of data. Two surveys in air-conditioned buildings were conducted in tropical Darwin; one in the "Dry" season, the other in the build-up to the "Wet" season. There were two surveys in sub-tropical Brisbane's summer; one in air-conditioned, the other in non-air-conditioned buildings, while there were also air-conditioned and non-air-conditioned building surveys conducted in mid-latitude Melbourne's summer. Subjective thermal assessments were recorded from each respondent on three separate occasions, and these were accompanied by full sets of microc1imatological data necessary to define the body-environment heat balance. These measurements were used in two mathematical models of thermal comfort; 1) Predicted Mean Vote (PMV), and 2) Standard Effective Temperature (SET), which were used to standardise thermal environments for between-group comparisons.

Each respondent on their first interview was also questioned on various aspects of their thermal history. Attitudes and beliefs were assessed by means of free-answer questions, checklists, rating scales and successive interval attitude scales.

Mean levels of standardised warmth were generally similar in all four air-conditioned surveys, whereas the mean thermal sensations, comfort and temperature preference assessments elicited by those envionments were significantly different between these surveys. Furthermore, the standard effective temperatures associated with optimal comfort and 20% warmth dissatisfaction were both found to vary significantly between the six surveys; the highest values being recorded in the Darwin "Dry" air-conditioned and Brisbane non-air-conditioned surveys, while the lowest values were observed in Melbourne. These data are broadly consistent with the notion of thermal experience, comprising both indoor and outdoor components, exerting an influence on thermal perceptual set points, as predicted by adaptation level theory. Further suppcrt for this interpretation was obtained from the between-survey comperisons of thermal sensitivity, with the highest values being obse'ved in the surveys where microc1imatological parameters were most homogeneous. Also, respondents who had recently arrived in Darwin from cooler locations had significantly cooler comfort set points than did long-term residents of the tropics, and exposure to home air conditioning in Dirwin lowered comfort set points further.

The attitudinal data indicated that indoor climatic factors were ranked by occupants among the most important determinants of buil;-environmental quality. All air-conditioned buildings surveyed had exteisive concern among their occupants that mechanical air cooling had adverse health effects. The "sick building" syndrome possibly represents an exagerated form of this background malaise. Belief in adverse health effects was closely associated with disaffection for air conditioning, and a preference for passive designs. A majority of non-air-conditioned building occupants preferred such buildings, while the reverse was true of the air-conditioned building occupants. Preference for mechanical cooling was highest in the build-up to Darwin's "Wet" season, but for six months of the year, a majority preferred non-air-conditioned buildings in that city. Overall thermal impressions of indoor seasonal conditions, and the general level of thermal satisfaction with the survey buildings were both dissociated from prevailing mean microc1imatological Conditions.

The notion of a universally optimal climate, advanced originally by climatic determinists, and subsequently promulgated by the HVAC industry, ignores both the physiological and psychological adaptability of building occupants. Recognition of this perceptual plasticity facilitates energy conservation in HVAC sytem operation by reductions of outdoor/indoor thermal gradients, temperature drifts and ramps, and broadened set temperature control deadbands. Furthermore, a greater reliance on human adaptation instead of mechanical adjustment, combined with widespread concern about the side-effects of air conditioning, enhance the viabili