Predicted percentage dissatisfied with ankle draft

Abstract

Draft is unwanted local convective cooling. The draft risk model of Fanger et al. (Energy and Buildings 12, 21-39, 1988) estimates the percentage of people dissatisfied with air movement due to overcooling at the neck. There is no model for predicting draft at ankles, which is more relevant to stratified air distribution systems such as underfloor air distribution (UFAD) and displacement ventilation (DV). We developed a model for predicted percentage dissatisfied with ankle draft (PPD ) based on laboratory experiments with 110 college students. We assessed the effect on ankle draft of various combinations of air speed (nominal range: 0.1-0.6 m/s), temperature (nominal range: 16.5-22.5°C), turbulence intensity (at ankles), sex, and clothing insulation (<0.7 clo; lower legs uncovered and covered). The results show that whole-body thermal sensation and air speed at ankles are the dominant parameters affecting draft. The seated subjects accepted a vertical temperature difference of up to 8°C between ankles (0.1 m) and head (1.1 m) at neutral whole-body thermal sensation, 5°C more than the maximum difference recommended in existing standards. The developed ankle draft model can be implemented in thermal comfort and air diffuser testing standards.

Thermal comfort in environments with different vertical air temperature gradients

“…Test persons could not adjust their preferred mean room temperature. Liu et al and Schiavon et al have determined that the vertical temperature gradient has an insignificant effect and that test subjects are likely to accept gradients up to 8 K/m.…”

“…Regarding users’ comfort, critical body parts for local discomfort are the head and feet. Several authors have investigated the effect of thermal comfort in vertical temperature gradients: Eriksson and Domier, Olesen et al, Tanaka et al, Bohgaki et al, Wyon and Sandberg, Palonen et al, Ilmarinen et al, Mayer, Hori et al, Loveday et al, Hodder et al, Kawahara et al, Yu et al, Cheong et al, Melikov et al, Matsuo et al, Hashiguchi et al, Liu et al, and Schiavon et al . In the following chapters, we present a literature review on recent research on thermal comfort and the effect of vertical temperature gradients.…”

Ceiling fan air speeds around desks and office partitions

“…Since convective cooling is roughly proportional to the square root of air speed, the initial speed increases above 0.3 m/s are the most effective, e.g., 0.4 to 0.8 m/s. The comfort effects caused by this upward shift in localized cooling have not been addressed in the literature, although a study of ankle comfort under displacement ventilation provides preliminary insights [26]. Ultimately the cooling effects on the different body parts might be addressed by weighting the air speeds when averaging the three heights.…”

“…There are also amendments in progress within Standard 55 addressing how airflows that are not uniformly distributed across the body might affect comfort. Although some literature [7], [22], [26] has quantified the cooling under airstreams that only partially cover the body, there is no current guidance for translating such results into the metrics used in standards. One might identify three problems that need to be solved:…”

Experimentelle und numerische Untersuchung des Einflusses der Strahlungsasymmetrie auf die thermische Behaglichkeit am Beispiel temperierter Halbräume

“…Bild experimental and numerical investigation of the influence of radiation asymmetry on thermal comfort using the example of temperature-controlled half-spaces The influence of radiation asymmetry on thermal comfort is controversially discussed in the recent past among experts. In selected cases, the limit values laid down in current regulations such as DIN EN ISO 7730 [1] / DIN EN 16798-1 [2] can be significantly exceeded without being perceived as uncomfortable by the users, [3,4]. In other cases, however, the actual user acceptance is significantly lower than predicted.…”