Tuesday, April 14, 2009

ASHRAE Comfort Zones

ASHRAE Comfort Zones
Based on results of research conducted at Kansas State University and at other institutions,
ANSI/ASHRAE Standard 55-1992 specified winter and summer comfort zones to provide for the
selection of the indoor parameters for thermal comfort . This chart is based upon an
occupant activity level of 1.2 met (69.8 W/m2). For summer, typical clothing insulation is 0.5 clo,
that is, light slacks and short-sleeve shirt or comparable ensemble; there is no minimum air speed
that is necessary for thermal comfort. Standard 55-1992 recommended a summer comfort zone with
an effective boundary temperature ET*  73 to 79°F (22.5 to 26°C) at 68°F (20°C) wet-bulb as its
upper-slanting boundary and dew-point temperature 36°F (2.2°C) as its bottom flat boundary. If the
clothing insulation is 0.1 clo higher, the boundary temperatures both should be shifted 1°F (0.6°C)
lower. Rohles et al. (1974) and Spain (1986) suggested that the upper boundary of the summer
comfort zone can be extended to 85 or 86°F (30°C) ET* if the air velocity of the indoor air
can be increased to 200 fpm (1 m/ s) by a ceiling fan or other means.
The winter comfort zone is based upon a 0.9-clo insulation including heavy slacks, long-sleeve
shirt, and sweater or jacket at an air velocity of less than 30 fpm (0.15 m/s). Standard 55-1992 recommended
a winter comfort zone with an effective boundary temperature ET*  68 to 74°F (20 to
23.3°C) at 64°F (17.8°C) wet-bulb as its slanting upper boundary and at dew-point 36°F (2.2°C) as
its bottom flat boundary.
Indoor air parameters should be fairly uniform in order to avoid local discomfort. According to
Holzle et al., 75 to 89 percent of the subjects tested found the environment within this summer
comfort zone to be thermally acceptable.
ASHRAE comfort zones recommend only the optimal and boundary ET* for the determination
of the winter and summer indoor parameters. For clothing insulation, activity levels, and indoor air
velocities close to the values specified in Standard 55-1992, a wide range of indoor design conditions
are available.

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