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Though heat balance approach of thermal comfort have a significant breaking in the thermal comfort research field, it also with certain limits. It is now widely accepted that though laboratory studies offer static and corresponding conditions for measurement not possible in the field studies (Djongyang 2010), the previously used climate chambers fail to provide the participants with so-called “experimental realism” in determining their thermal comfort (Schiavon 2008). Since in the normal life style, people live in the changeable, unstable and inconsistent environments, which may cause a deviation when the standards are applied on the occupants living in real-world situation (Han et al. 2007). Fanger’s climate chamber work and Humphreys’s field study in 1976 have been compared (McIntyre 1978). It indicated that certain intervening variables that occur in the “real” world might not be reproducible in the climatic chamber. It is reported on the significant inconsistency between predicted mean votes (PMV) and actual mean votes (AMV) values (Oseland 1995). This result

obtained in offices and homes as compared with climate chamber studies, which attribute the difference to contextual and adaptation effects as follows: “since the

development of the PMV equation, many field studies have shown differences between the occupants’ reported thermal sensation and those predicted by PMV and the corresponding neutral temperatures’’ (Djongyang 2010). Thus, the situation of field

studies closer to the “real” world may be more desirable to climate chambers (Ealiwa 2001). So the adaptive approach is used frequently in the research correlated to thermal comfort.

The adaptive comfort theory was first proposed in the 1970s in response to the huge increase in oil price (Brager 1998). Adaptive approach is based on a variety of field studies all over the world, the purpose of adaptive approach is to analyze the real acceptability of thermal environment, which strongly depends on the behavior of occupants, their experience and expectations. The adaptive approach to thermal comfort proposing that people can take actions to ease their comfort conditions by adjusted their activity levels and clothing insulation or by interacting with the built environment (Sugawara et al. 2008). The concepts of “adaptive model” is based on this propose and which indicates the level to which people can thermally adapt to their ambient. When the adaptive opportunity is insufficient, deviate from thermal neutrality leads to thermal discomfort (Baker and Standeven 1996).

As Brager and de Dear (1998) suggested that adaptive models are linear regression model relate indoor design temperatures or acceptable ranges of temperature to outdoor meteorological or climatological parameters. Thus thermal neutrality became a significant element of adaptation approach. Thermal neutrality is defined as the temperature which gives a neutral thermal sensation, neither warm nor cool, in the environment (Humphreys 1975) or the thermal index value (temperature) corresponding with a maximum number of building occupants voting neutral on a thermal sensation scale (Brager 1998). There are three adaptive categories: behavior adaptation, physiological adaptation and psychological adaptation (De Dear 2004). As used in ASHRAE RP-884, adaptation included all physiological mechanisms of acclimatization, in addition to all behavioral and psychological processes which

building occupants experience in order to improve the adapt of the indoor environment to their personal or group requirements. Within this wide definition it is possible to clearly distinguish three categories of adaptation (Prosser 1958, Folk 1974, 1981, Goldsmith 1974, Clark and Edholm 1985).

a. Behavior adaptation

Behavior adaptation includes all consciously or unconsciously modifications people make to modify heat and mass fluxes governing the body’s thermal balance. It defined adjustment in terms of three subcategories as Figure 3.2 (de Dear and Brager 1997).

Figure 3.2 The three components of adaptation to indoor climate (Source: de Dear and Brager 1997).

Personal adjustment: adjusting to the ambient by changing personal variables, such as take on/off clothing, adjusting activity and posture, drinking /eating some hot/cold food or beverages, or moving to a different location. Among these parameters, activity level and clothing insulation are the individual parameter of the six basic parameters of decides thermal comfort. Activity level influences energy production in human body and can considerably affect the comfort level. Activity level is expressed by met: each met is the metabolic rate of a seated relaxed adult and equals 58 W/m2 (Clark and Edholm 1985). Clothing influences human thermal sensation by offering thermal

insulation that is suitable to one’s environment. It is expressed by m2_{K/W or in CLO}

units that equals 0.155 m2_K/W.

Environmental or technological adjustment: modifying the surroundings themselves, when control is available, for instance, opening/closing windows or shades, turning on/off fans or heating, blocking air diffusers, or operating other HVAC controls, etc.; Cultural adjustments: including scheduling activities, siestas, dress codes etc. b. Physiological adaptation

To define the physiological adaptation comprehensively, it would include all of the changes in the physiological responses, which result from exposure to thermal environmental factors, and which lead to a gradual decrease in the strain induced by such exposure. Two subcategories of physiological adaptation are genetic adaptation and acclimation or acclimatization:

Genetic adaptation: alterations were became part of the genetic heritage of an individual or group of people, but the development of the time scales beyond that of an individual’s lifetime.

Acclimation or Acclimatization: changes in the establishment of the physiological thermoregulation system over a period of days or weeks, which is the way of response to the exposure to a variety of thermal environmental stressors. The physiological adaptation is not of fundamental importance in this context because it is caused by exposure to a stimulus, leading to a gradually declining strain from such exposure (Clark and Edholm 1985).

c. Psychological adaptation

The psychological adaptation of indoor climates refers to an altered perception of sensory information and the reaction of it. Thermal perceptions are directly and significantly elongated by people’s experiences and expectations of the indoor climate. This form of adaptation involves building occupants’ “comfort set points” which may vary across time and space. Relaxation of indoor climatic expectations can be likened to a psychophysics notion of habituation-chronic or repeated exposure to an

environmental stressor leading to a decrease of the evoked sensation’s intensity (Glaser 1966, Frisancho 1981).

Naturalness: people tend to have more tolerance to non-artificial changes occur in their physical environments (Griffiths et al. 1987). Therefore, the comfort temperature range in natural ventilated space is wider than in air-conditioned space (ASHRAE 2005). It also found by scholars that people in outdoor spaces tolerate a wide range of air temperatures the changes (Nikolopoulou and Lykoudis 2006).

Expectations and experience: People’s perceptions are notably influenced by they think what the environment should be like, rather than what it truly is like (Nikolopoulou and Lykoudis 2006). Expectations and experience also can explain the difference in comfort temperature between the transitional seasons (autumn and spring). Autumn is preceded by warmer temperatures therefore people tend to be less tolerant to cold, hence the temperature in which people feel comfortable is higher than that in spring (Zrudlo 1988).

Time of exposure: Nikolopoulou and Steemers (2003) claimed that thermal perception of people in outdoor spaces influences the period of their stay. This issue is of particular importance when related to the level of activity in outdoor public spaces because level of activity can be stimulated by both large amount of people and by longer individual stays (Gehl 1996). People are able to tolerate thermal discomfort if they anticipate that their exposure to it will be brief (Aljawabra 2014).

Perceived control: Perceived control as opposed to actual control advises available choice. It is a state of being in control over a source of discomfort and according to Evans (1984) this increases tolerance and reduces people’s annoyance. Therefore, when an space offers seats in the shade and others in the sun, people are expected to stay longer than if only one option was available, regardless of whether they use the other option or not. Nikolopoulou and Steemers (2003) use this theory to the research of outdoor thermal comfort and claimed that since actual control over thermal discomfort source is limited in outdoor spaces, perceived control is important in such

places.

Environmental stimulation: Environmental stimulation is always has an influence in external space. It is one of the main reasons why people spend time outdoors, breaking the boredom and seeking satisfaction. When outdoor spaces offer various types of environmental stimulations, people tend to have higher tolerance to weather conditions in them (Aljawabra 2014). This leads to more people visiting the outdoor space and more time being spent in it. The reason is that neutrality does not necessarily lead to satisfactory; however, environmental stimulations such as sun or fresh air after being in the office for a long time on a warm day do (Nikolopoulou 2011b).