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1、Thermal comfort in the future - Excellence and expectationP. Ole Fanger and Jrn ToftumInternational Centre for Indoor Environment and EnergyTechnical University of DenmarkAbstractThis paper predicts some trends foreseen in the new century as regards the indoor environment and thermal comfort. One tr
2、end discussed is the search for excellence, upgrading present standards that aim merely at an “acceptable” condition with a substantial number of dissatisfied. An important element in this connection is individual thermal control. A second trend is to acknowledge that elevated air temperature and hu
3、midity have a strong negative impact on perceived air quality and ventilation requirements. Future thermal comfort and IAQ standards should include these relationships as a basis for design. The PMV model has been validated in the field in buildings with HVAC systems that were situated in cold, temp
4、erate and warm climates and were studied during both summer and winter. In non-air-conditioned buildings in warm climates occupants may sense the warmth as being less severe than the PMV predicts, due to low expectations. An extension of the PMV model that includes an expectancy factor is proposed f
5、or use in non-air-conditioned buildings in warm climates. The extended PMV model agrees well with field studies in on-air-conditioned buildings of three continents.Keywords: PMV, Thermal sensation, Individual control, Air quality, AdaptationA Search for ExcellencePresent thermal comfort standards (C
6、EN ISO 7730, ASHRAE 55) acknowledge that there are considerable individual differences between peoples thermal sensation and their discomfort caused by local effects, i.e. by air movement. In a collective indoor climate, the standards prescribe a compromise that allows for a significant number of pe
7、ople feeling too warm or too cool. They also allow for air velocities that will be felt as a draught by a substantial percentage of the occupants.In the future this will in many cases be considered as insufficient. There will be a demand for systems that allow all persons in a space to feel comforta
8、ble. The obvious way to achieve this is to move from the collective climate to the individually controlled local climate. In offices, individual thermal control of each workplace will be common. The system should allow for individual control of the general thermal sensation without causing any draug
9、ht or other local discomfort. We know the range of operative temperatures required in a workplace to satisfy nearly everybody (Wyon 1996; Fanger 1970) and we know the sensitivity to draught from a wide range of studies. A search for excellence involves providing all persons in a space with the means
10、 to feel thermally comfortable without compromise.Thermal Comfort and IAQPresent standards treat thermal comfort and indoor air quality separately, indicating that they are independent of each other. Recent research documents that this is not true (Fang et al. 1999; Toftum et al. 1998). The air temp
11、erature and humidity combined in the enthalpy have a strong impact on perceived air quality, and perceived air quality determines the required ventilation in ventilation standards. Research has shown that dry and cool air is perceived as being fresh and pleasant while the same composition of air at
12、an elevated temperature and humidity is perceived as stale and stuffy. During inhalation it is the convective and evaporative cooling of the mucous membrane in the nose that is essential for the fresh and pleasant sensation. Warm and humid air is perceived as being stale and stuffy due to the lack o
13、f nasal cooling. This may be interpreted as a local warm discomfort in the nasal cavity. The PMV model is the basis for existing thermal comfort standards. It is quite flexible and allows for the determination of a wide range of air temperatures and humidities that result in thermal neutrality for t
14、he body as a whole. But the inhaled air would be perceived as being very different within this wide range of air temperatures and humidities. An example: light clothing and an elevated air velocity or cooled ceiling, an air temperature of 28C and a relative humidity of 60% may give PMV=0, but the ai
15、r quality would be perceived as stale and stuffy. A simultaneous request for high perceived air quality would require an air temperature of 20-22oC and a modest air humidity. Moderate air temperature and humidity decrease also SBS symptoms (Krogstad et al. 1991, Andersson et al. 1975) and the ventil
16、ation requirement, thus saving energy during the heating season. And even with air-conditioning it may be beneficial and save energy during the cooling season.PMV model and the adaptive modelThe PMV model is based on extensive American and European experiments involving over a thousand subjects exposed to well-controlled environments (Fanger 1970). The studies showed that the thermal sensation is closely related to the thermal load on the effector mechanisms of the h
