Practices

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Adaptive Thermal Comfort and Ventilation

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Existing thermal comfort standards and methods cover mainly thermal comfort conditions under steady state conditions. Most of the thermal comfort studies have been carried out in laboratories and are based on evaluations of the heat transfer between the human beings and their environment and of the required physiological conditions for thermal comfort. Given the thermal interaction between the building envelope, the occupants and the heating and cooling system, it is very rare to encounter steady state conditions in real buildings, and it is evident that the temperature in free running buildings is far less likely to be steady. Field comfort studies carried out around the world have shown that the so called adaptive approach describes comfort conditions in non air conditioned buildings better. The fundamental assumption of the adaptive approach is expressed by the ‘adaptive principle’ that stipulates: “If a change occurs such as to produce discomfort, people react in ways which tend to restore their comfort”. This principle codifies the behaviour of building occupants which takes two basic forms: * Adjustments to the optimal comfort temperature by changes in clothing, activity, posture, etc. so that the occupants are comfortable in prevailing conditions; * Adjustment of indoor conditions by the use of controls such as windows, blinds, fans and in certain conditions mechanical heating or cooling. Occupants may also migrate around the room to find improved conditions. The VIP on adaptive comfort offers the basic scientific and practical information on adaptive comfort and discusses the impact of air speed on thermal comfort.
Ventilation Information Paper (VIP) No12 of AIVC (Air Infiltration and Ventilation Center)