Publication date: Available online 5 February 2014
Source:Building and Environment
Author(s): Li Huang , Edward Arens , Hui Zhang , Yingxin Zhu
In ASHRAE Standard 55-2010, the comfort effects of elevated air movement are evaluated using the SET index as computed by the Gagge 2-Node model of whole-body heat balance. Air movement in reality has many forms, which might create heat flows and thermal sensations that cannot be accurately predicted by a simple whole-body model. This paper addresses two of such potential inaccuracies: 1) indoor airflows may affect only a portion of the body surface (e.g., above desktop), and the affected body surface might be variably nude (e.g. face) or clothed, 2) the turbulence intensity (TI) in some typical airstreams (e.g., those created by fans) might have a different impact on heat transfer than the TI implicit in 2-Node’s single convective heat transfer coefficient. For both these issues, can a whole-body index like SET represent such a wide range of possible exposures to airflow? Measurements of thermal sensation were obtained from human subjects using face-level fans in warm environments. Previous laboratory studies of a range of airstream sources were also analyzed. The effects of turbulence intensity were examined with manikin tests. The results show that indices derived from the 2-Node model of whole-body heat balance are effective at predicting thermal sensation under most non-uniform air movement. In contrast, the PMV index underestimates cooling in warm conditions. Turbulence increases the cooling effect of air movement, but by amounts that might be neglected for most design purposes.
Source:Building and Environment
Author(s): Li Huang , Edward Arens , Hui Zhang , Yingxin Zhu