ASHRAE-Standard-55 - Page 049
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Tables 5-2 and 5-3 are for a standing person. A sitting posture results in a decreased thermal insulation due to compression of air layers in the clothing. This decrease can be offset by insulation provided by the chair. Table 5-4 shows the net effect on clothing insulation Icl for typical indoor clothing ensembles that result from sitting in a chair. These data may be used to adjust clothing insulation calculated using any of the above methods. For example, the clothing insulation for a person wearing Ensemble 3 from Table 5-2 and sitting in an executive chair is 0.96 + 0.15 = 1.11 clo. For many chairs, the net effect of sitting is a minimal change in clothing insulation. For this reason, no adjustment to clothing insulation is needed if there is uncertainty as to the type of chair and/or if the activity for an individual includes both sitting and standing.
Tables 5-2 and 5-3 are for a person that is not moving. Body motion decreases the insulation of a clothing ensemble by pumping air through clothing openings and/or causing air motion within the clothing. This effect varies considerably, depending on the nature of the motion (e.g., walking versus lifting) and the nature of the clothing (stretchable and snug fitting versus stiff and loose fitting). Because of this variability, accurate estimates of clothing insulation Icl for an active person are not available unless measurements are made for the specific clothing under the conditions in question (e.g., with a walking manikin). An approximation of the clothing insulation for an active person is
Icl, active = Icl × (0.6 + 0.4/ M ) for M 1.2
where M is the metabolic rate in met units and Icl is the insulation without activity. For metabolic rates less than or equal to 1.2 met, no adjustment for motion is required. This clothing adjustment for an active person is applied automatically as part of the PMV code as described in Normative Appendix B.
When a person is sleeping or resting in a reclining posture, the bed and bedding provide considerable thermal insulation. It is not possible to determine the thermal insulation for most sleeping or resting situations unless the individual is immobile. Individuals adjust bedding to suit individual preferences. Provided adequate bedding materials are available, the thermal environmental conditions desired for sleeping and resting vary considerably from person to person and cannot be determined by the methods included in this standard.
Clothing variability among occupants in a space is an important consideration in applying this standard. This variability takes two forms. In the first form, different individuals wear different clothing due to factors unrelated to the thermal conditions. Examples include different clothing style preferences for men and women and offices where managers are expected to wear suits while other staff members may work in shirtsleeves. In the second form, the variability results from adaptation to individual differences in response to the thermal environment. For example, some individuals wear sweaters while others wear short-sleeve shirts in the same environment if there are no constraints limiting what is worn. The first form of variability results in differences in the requirements for thermal comfort between the different occupants, and these differences should be addressed in applying this standard. In this situation, it is not correct to determine the average clothing insulation Icl of various groups of occupants to determine the thermal environmental conditions needed for all occupants. Where the variability within a group of occupants is of the second form and is a result only of individuals freely making adjustments in clothing to suit their individual thermal preferences, it is correct to use a single representative average clothing insulation value for everyone in that group.
For near-sedentary activities where the metabolic rate is approximately 1.2 met, the effect of changing clothing insulation Icl on the optimum operative temperature to is approximately 6°C (11°F) per clo.
For example, Table 5-3 indicates that adding a thin, long-sleeve sweater to a clothing ensemble increases clothing insulation Icl by approximately 0.25 clo. Adding this insulation would lower the optimum operative temperature to by approximately 6°C/clo × 0.25 clo = 1.5°C (11°F/clo × 0.25 clo = 2.8°F).
ANSI/ASHRAE Standard 55-2023 47