ASHRAE-Standard-55 - Page 047
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(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 F USE OF METABOLIC RATE DATA
The data presented in Table 5-1 are reproduced from ASHRAE Handbook—Fundamentals [ 1], Chapter 9. The values in the table represent typical metabolic rates per unit of skin surface area for an average adult (DuBois area = 1.8 m [2] [19.6 ft [2] ]) for activities performed continuously. This Handbook chapter provides additional information for estimating and measuring activity levels. General guidelines for the use of these data follow.
Not every activity that may be of interest is included in this table. Users of this standard should use their judgment to match the activities being considered to comparable activities in the table. Some of the data in this table are reported as a range and some as a single value. The format for a given entry is based on the original data source and is not an indication of when a range of values should or should not be used. For all activities except sedentary activities, the metabolic rate for a given activity is likely to have a substantial range of variation that depends on the individual performing the task and the circumstances under which the task is performed.
It is permissible to use a time-weighted average metabolic rate for individuals with activities that vary over a period of one hour or less. For example, a person who typically spends 30 minutes out of each hour “lifting/packing,” 15 minutes “filing, standing,” and 15 minutes “walking about” has an average metabolic rate of 0.50 × 2.1 + 0.25 × 1.4 + 0.25 × 1.7 = 1.8 met. Such averaging should not be applied when the period of variation is greater than one hour. For example, a person who is engaged in “lifting/packing” for more than one hour and then “filing, standing” for more than one hour should be treated as having two distinct metabolic rates.
As metabolic rates increase above 1.0 met, the evaporation of sweat becomes an increasingly important factor for thermal comfort. The PMV method does not fully account for this factor, and this standard should not be applied to situations where the time-averaged metabolic rate is above 4.0 met.
Rest breaks (scheduled or hidden) or other operational factors (get parts, move products, etc.) combine to limit time-weighted metabolic rates to about 2.0 met in most applications.
Time averaging of metabolic rates only applies to an individual. The metabolic rates associated with the activities of various individuals in a space may not be averaged to find a single, average metabolic rate to be applied to that space. The range of activities of different individuals in the space, and the environmental conditions required for those activities, should be considered in applying this standard. For example, the customers in a restaurant may have a metabolic rate near 1.0 met, while the servers may have a metabolic rate closer to 2.0 met. Each of these groups of occupants should be considered separately in determining the conditions required for comfort. In some situations, it will not be possible to provide an acceptable level or the same level of comfort to all disparate groups of occupants (e.g., restaurant customers and servers).
The metabolic rates in Table 5-1 were determined when the subjects’ thermal sensation was close to neutral. It is not yet known the extent to which people may modify their metabolic rate to decrease warm discomfort.
ANSI/ASHRAE Standard 55-2023 45