Occupants' Habits and Natural Ventilation in a Hot Arid Climate

Introduction

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) defines thermal comfort as: “that condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation” (ASHRAE, 2017, p. 9.1). This definition emphasises that thermal comfort is a psychological state. Indeed, thermal comfort is greatly affected by psychological adaptation opportunities (Brager & de Dear, 1998). Thermal adaptation processes involve all actions taken by people to acclimatise themselves to the ambient thermal conditions (Brager & de Dear, 1998; Nicol et al., 2012; Nikolopoulou & Steemers, 2003). Defined by the available adaptive opportunities, these processes affect thermal comfort level (Nikolopoulou et al., 2001). Choosing a certain adaptive action is limited by effectiveness, ease, and related economic consequences (Mishra & Ramgopal, 2013).

Psychological adaptation opportunities include the natural appearance of internal spaces, known as naturalness, that increases the probability of accepting wide ranges of thermal conditions. Naturalness is widely achieved by vegetation presence and landscape viewing (Nikolopoulou & Steemers, 2003) and it is related to the expectation of designers’ responsibility in creating comfortable indoor environments. Expectation is another psychological adaptive action. It was found that people in mechanically ventilated buildings have less tolerance of temperature variations compared with those in naturally ventilated buildings (Brager & de Dear, 1998). People’s expectations are affected by their thermal experiences and usually assist them in accepting ambient conditions via decisions such as consuming cool or hot drinks, changing postures, or changing clothing. In this regard, a Chinese questionnaire explored the effect of thermal history on acceptability and comfort and revealed that adaptation to improved thermal conditions is relatively easy compared with lowering expectation of thermal ambience (Luo et al., 2016). Another study investigated the influence of participants’ thermal history through unifying clothing levels, which encourages psychological and physiological adaptation. Exposure to cool conditions resulted in higher sensitivity as participants maintained a narrow comfort range. The study concluded that the thermal history of cool experiences weakens thermal adaptation (Ning et al., 2016).

Furthermore, exposure time affects thermal perception as people tend to accept uncomfortable environments if they spend short periods in such spaces. This is obvious in outdoor spaces as people generally decide their stay time freely. This decision and other similar decisions such as switching on or off fans or air conditioning units, opening or closing windows, changing posture, or clothing level, are part of what is known as the perceived control that positively correlates to accepting thermal conditions (Nikolopoulou et al., 2001; Nikolopoulou & Steemers, 2003; Singh et al., 2011). As noticed, most psychological adaptation mechanisms affect people’s perception and, thus, their acceptance of thermal environment through adaptive actions or influencing tolerance.

Thermal adaptation is not limited to psychological adaptation. It besides involves physiological and physical processes. Physical or behavioural adaptation includes consuming food, closing or opening windows besides changing activity, posture, or clothing (Brager & de Dear, 1998; Nikolopoulou & Steemers, 2003; Singh et al., 2011). This type of adaptation is classified as interactive and reactive. The former involves altering the surrounding environment, whereas the latter deals with personal status alterations (Nikolopoulou & Steemers, 2003).