ASHRAE-Standard-55 - Page 044

Extracted Content

(This appendix is not part of this standard. It is merely informative and does not contain requirements necessary for conformance to the standard. It has not been processed according to the ANSI require- ments for a standard and may contain material that has not been subject to public review or a consen- sus process. Unresolved objectors on informative material are not offered the right to appeal at ASHRAE or ANSI.)

INFORMATIVE APPENDIX E CONDITIONS THAT PROVIDE THERMAL COMFORT

E1. INTRODUCTION

Thermal comfort is that condition of mind that expresses satisfaction with the thermal environment. Because there are large variations, physiologically and psychologically, from person to person, it is difficult to satisfy everyone in a space. The environmental conditions required for comfort are not the same for everyone. Extensive laboratory and field data have been collected that provide the necessary statistical information to define conditions that a specified percentage of occupants will find thermally comfortable.

Note that the pairs of terms “satisfaction”/“acceptability,” “satisfactory”/“acceptable,” and “are satisfied with”/“accept” are each considered synonymous in the standard, though the standard uses “satisfaction” as its standard nomenclature.

E2. THERMAL COMFORT FACTORS

Six primary factors must be addressed when defining conditions for thermal comfort. A number of other, secondary factors affect comfort in some circumstances. The six primary factors are as follows:

a. Metabolic rate b. Clothing insulation c. Air temperature d. Radiant temperature e. Air speed f. Humidity

The first two factors are characteristics of the occupants, and the remaining four factors are conditions of the thermal environment. Detailed descriptions of these factors are presented in Section 3 and Informative Appendix E through Informative Appendix G. These must be clearly understood in order to use the methods of Section 5 effectively.

E3. VARIATION AMONG OCCUPANTS

For each occupant, the activity level, represented as metabolic rate M in mets, and the clothing worn by the occupants, represented as insulation Icl in clo, must be considered in applying this standard. When there are substantial differences in physical activity and/or clothing for occupants of a space, these differences must be considered.

In some cases, it will not be possible to achieve a satisfactory thermal environment for all occupants of a space due to individual differences, including activity and/or clothing. If the requirements are not met for some known set of occupants, then the standard requires that these occupants be identified.

E4. TEMPORAL VARIATION

It is possible for all six primary factors to vary with time. This standard only addresses thermal comfort in a steady state (with some limited specifications for temperature variations with time in Section 5.3.6).

As a result, people entering a space that meets the requirements of this standard may not immediately find the conditions comfortable if they have experienced different environmental conditions just prior to entering the space. The effect of prior exposure or activity may affect comfort perceptions for approximately one hour.

E5. LOCAL THERMAL DISCOMFORT

Nonuniformity is addressed in Section 5.3.5. Factors 1 through 6 may be nonuniform over an occupant’s body, and this nonuniformity may be an important consideration in determining thermal comfort.

E6. VARIATION IN ACTIVITY LEVEL

The vast majority of the available thermal comfort data pertain to sedentary or near-sedentary physical activity levels typical of office work. This standard is intended primarily for these conditions. However, it is acceptable to use the standard to determine appropriate environmental conditions for moderately elevated activity. It does not apply to sleeping or bed rest. The body of available data does not contain significant

42 ANSI/ASHRAE Standard 55-2023