Page 224 - Industrial Ventilation Design Guidebook

5. i THERMAL COMFORT 1 85

that are considered comfortable by ASHRAE Standard 55-94 for the typical
summer and winter clothing levels of Fig. 5.7a.
In Fig. 5.76, the comfort zone at 50% RH for the 0.9 clo winter clothing
is from 20 °C to 23.5 °C and for the 0.5 clo summer clothing is from 22.5 °C
to 26 °C. The temperature boundaries on the right and left sides of the com-
fort zones have constant ASHRAE Effective Temperature (ET*) levels. An
ET* line is the locus of conditions that are calculated to have the same heat
loss from the skin, skin temperature, and skin moisture levels. Since the physi-
ology of the skin is the same for a constant ET* line, the thermal sensation
and comfort judgments are also generally constant along the line. The temper-
ature value of this line is the temperature where the relative humidity is 50%.
Along an ET* line the environment feels the same as it feels for air at temper-
ature T at 50% RH. The ET* lines are not vertical but are affected by humid-
ity and the human's physiological responses to the environment. Thus on the
warm side of a comfort zone the humidity has more of an effect than on the
cool side of the zone. But the differences in the slopes are not large and both

FIGURE 5.7 (a) Comfort and thermal sensations of a comfort zone. (6) Conditions for comfort on
pyschometric chart for sedentary persons ( ^ 1.2 met). 14