Comfort Zones

In general, when a person is thermally comfortable, the person’s thermal sen­sation for the whole body is at or near neutral as depicted in Fig. 5.7a. As we have seen, the thermal conditions necessary for comfort are affected by cloth­ing insulation. Figure 5.7b shows the range of temperatures and humidities

Comfort Zones

Indicate that temperature has a much stronger effect than humidity on the hu­man thermal response. That is, the ET* lines show that for the same thermal sensation at a higher humidity the temperature must be lower. On average, for an 11 °C increase in dew point the temperature would need to be 1 °C lower to have the same thermal sensation. In terms of human response the bound­aries are not hard and sharp as indicated in Fig. 5.7b but instead are more soft and fuzzy in nature.

Optimum comfort would be in the center of each zone. Moving away from the center, some people would be expected to have thermal sensations ap­proaching — 0.5 and +0.5 at the cooler and warmer ET* borders. The zones of Fig. 5.76 are for sedentary or slightly active (M ^ 1.2 met) people. If the activ­ity level is higher than that, then the ET* line borders can be shifted about 1.4 K lower per met of increased activity. Similarly, if the clothing is different than the 0.9 and 0.5 clo vales of Fig. 5.7a, the temperature boundaries can be de­creased about 0.6 K for each 0.1 clo increase in clothing insulation. Another, similar way to adjust the comfort zone for both different activity levels and do values is to shift the zone centered on the optimum temperature at

50% RH as ~

^active = Sedentary ~ 3 ( 1 + do) • ( met — 1.2 ) ° C. (5.13)

Conditions that are warmer than the applicable still-air comfort zone of Fig. 5.7b can often be made comfortable by increasing the air speed. If the condi­tions are 1 to 6 °C warmer than the still-air comfort zone of Fig. 5.7b, the necessary air speed (v) to restore thermal balance and comfort can be esti­mated from Fig. 5.8, where T — Tcomf is the temperature difference between the environment and the still-air comfort temperature. Though the increased air speed will bring the whole-body thermal sensation to the comfort level, air motions above 0.8 m/s or so may cause other kinds of discomfort from

Comfort Zones

-a

1>

A

подпись: -a
1>
a

Comf

подпись: comf

(°C)

подпись: (°c)

FIGURE 5.8 Air speed necessary at temperature T for the same thermal response as air environment (Ј0.2 m/s).

подпись: figure 5.8 air speed necessary at temperature t for the same thermal response as air environment (ј0.2 m/s).

R~rr

подпись: r~rr,in a still —

Comfort Zones

Temperature

Ra

Time

If P < 15 min. and AT> J.1 JC thei: dfidt < 2.2 °C/K

Comfort Zones

98

подпись: 
98

FIGURE 5.9 Nonuniformity limits to avoid discomfort.

Moving papers, hair, and other light objects, and the pressure of the air speed itself may affect some people.

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