Clothing

Thermal Insulation

Clothing affects heat and moisture loss. Increasing the thickness or num­ber of layers of clothing increases its insulating capability and reduces body heat loss. Clothing insulation is usually described with the clo unit. Originally, 1 clo was defined as the thermal resistance necessary for comfort while seden­tary in a uniform still air environment of 21 °C. In conventional SI nomencla­ture 1 clo has a thermal resistance of 0.155 K m2/W. Some ensembles’ clo values and associated comfort temperatures are shown in Fig. 5.4.

The clothing insulation necessary for comfort or a neutral thermal sensa­tion (TS = 0) in a thermally uniform 50% RH still-air environment is graphed in Fig. 5.5.9 The slope of the graph is such that comfort temperature is decreased about 0.6 °C for each 0.1 clo increase in clothing insulation. The

Th heat => Tc

—— 1 clo

Clothing insulation => clo unit: thermal resistance

0. 155 K m2/W

3 clo
N
0.1 clo	0.5 clo	1.0 clo
Comfortable at: 27 °C
24.5 °C	21 °C	5 °C

FIGURE 5.4 Some clothing ensembles with associated clo values and comfort temperatures.

Graph is for 1 met but the line can be shifted to cooler temperatures for in­creased metabolism at the rate of -1.4 K/met.

From Fig. 5.5, comfort is possible in still air from 18 to 27 °C by adjust­ing clothing insulation from 1.5 to 0 clo. This has significant building energy reducing potential with buildings only heated to 18 °C and cooled to 27 °C. However, personal, societal, and institutional preferences, norms, and codes usually limit the possible clo variation to a narrower range. For sedentary-

TABLE 5.4 Clo Values of Some Individual Clothing Items Item Clo, Item Do. Trousers (thin) 0.1 S Sweater (thin) 0.25 Trousers (thick) 0.24 Sweater (thick) 0.36 Sweat pants 0.28 Jacket (thin) 0.4 Overalls 0.30 Jacket (thick) 0.7 Coveralls 0.49 Sleeveless vest (thin) 0.13 Walking shorts 0.08 Sleeveless vest (thick) 0.22 Short-sleeved knit sport shirt 0.17 Sandals 0.02 Short-sleeved dress shirt 0.19 Shoes 0.03 I. ong-sleeved dress shirt 0.25 Boots 0.1 I ong sleeved flannel shirt 0.34 Ankle-length athletic socks 0.02 Long-sleeved sweatshirt 0.34 Calf-length socks 0.03 T-shirt 0.08 Long underwear (top) 0.2 Underwear 0.05 Long underwear (bottom) 0.15

Some clothing item clo values are listed in Table 5,4.9 For example, the do value of a person wearing a thin shirt, thin trousers, underwear, shoes, and socks estimated by this method would be: 0.17 + 0.25 + 0.05 + 0.05 = 0.52 clo. If the person were to add a T-shirt under the shirt, the clothing insulation would be expected to increase to 0.6 clo.

Effect of Chairs on Clothing Insulation

When a person is sitting, the chair generally has the effect of increasing clothing insulation (A2cl) by up to 0.15 clo depending on the contact area (CSAC) between the chair and body. Specifically,

Aicl = 7.48 • 105 • CSAC — O. lclo, (5.9)

Where CSAC is the chair surface area contact in cm2 or the surface area of the chair in contact with the human.6’12

For example, a desk chair with a body contact area of 2700 cm2 has a A/ci of 0.1 clo. This amount should be added to the insulation of the standing clothing ensemble to obtain the insulation of the ensemble when a person is sitting in the desk chair,

^^sitting dOstanding + ^t: ■ I5.10)

Effect Of Walking on Clothing Insulation

Body motion generally increases the ventilation of garments and thereby carries away heat and decreases the clothing ensemble’s effective insulation. The increased airflow between the garment and the skin is due to a combina­tion of increased air speed and the pumping action of the garment as it flexes during movement. As a result, walking decreases clo. The change in clothing insulation (AIc]w) can be estimated from the standing intrinsic insulation of the ensemble (clostanding) and the walking speed (S) in steps per minute:613

AJclw = 0.504 • Id + 0.0281 ■ 10~3 -5-0.24 clo (5.11)

Thus the insulation of the walking person is found by subtracting the walking effect from the insulation of the standing clothing ensemble,

DoWalking Clostanding“A/Clw • 5.12)

For example, the clothing insulation of a person wearing a winter business suit with a standing intrinsic insulation of 1 clo would decrease by 0.52 clo when the person walks at 90 steps per minute (about 3.7 km/h). Thus the en­semble’s intrinsic insulation when walking would be 0.48 clo. More complete clothing tables and figures are available in the literature, for example Chapter 8 of the ASHRAE Handbook of Fundamentals.6

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