ASHRAE-Standard-55 - Page 050

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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 H COMFORT ZONES DEFINING SATISFACTORY THERMAL CONDITIONS  IN OCCUPIED SPACE

H1. INTRODUCTION

This standard generates comfort zones within the ranges of environmental and personal conditions likely to be found indoors. The boundaries of comfort zones enclose sets of conditions that are considered satisfactory by their occupancies. They are based on predicted values of how occupants on average evaluate their thermal sensation—specifically, their sense of the environment being warm or cool. Thermal sensation is individually measured by point-in-time survey questionnaires using the ASHRAE seven-point thermal sensation scale.

+3 Hot +2 Warm +1 Slightly warm 0 Neutral –1 Slightly cool –2 Cool –3 Cold

Because groups of people in a given environment exhibit considerable variance in their thermal sensation votes, the mean thermal sensation vote is needed to characterize each combination of environmental and personal conditions. In the standard, this mean vote is predicted using the predicted mean vote (PMV) model given in Normative Appendix B. The PMV model calculates the heat balance of a specified occupant and relates their thermal gains or losses to their predicted mean thermal sensation.

H2. COMFORT ZONE BOUNDARIES

The boundaries of the comfort zone are defined by equal contours of PMV values. The boundary value is set at ±0.5 PMV in thermal sensation scale units. In field studies of actual buildings, environmental conditions within comfort zones bounded by this ±0.5 value were found satisfactory by roughly 80% of occupants. This percentage varies depending on additional confounding circumstances beyond the PMV model of an occupant’s heat balance. Sources of local discomfort are thought to add to dissatisfaction, as are other factors such as occupants’ sense of personal control over their thermal environment. This effect is described in Informative Appendix L, Sections L1, L2, and L3. The measurement and evaluation methods for determining satisfaction are described in Sections 7.3.1 and 7.4.1 of the standard.

Comfort zones with the ±0.5 PMV boundaries are generated by the Thermal Comfort Tool [ 3.] They are plotted in psychrometric chart format with air temperature ta or operative temperature to on the abscissa, or in temperature vs. relative humidity format. In evaluating comfort zones, it is usually most useful to use the operative temperature parameter, as surface temperatures within indoor environments will shift along with air temperature across the width of the comfort zone.

The comfort zones are seen to shift continuously with changes to the environmental and personal input parameters that are not plotted on the two chart axes. The presence of solar radiation on the occupant is shown to shift the comfort zone toward the cool side. Elevating the air speed is shown to shift the comfort zone toward the warm side. Note that there is an additional comfort attribute to elevated air speed, that of whether occupants have control of it or not. The presence or absence of group control over air speed produces a subzoning as identified in Figure 5-4. This is also included in the output of the Thermal Comfort Tool [ 3] .

Impacts of personal factors: The outer comfort zone boundaries shift toward the left or right, depending on clo and met level. An increase of 0.1 clo or 0.1 met corresponds approximately to a 0.8°C (1.4°F) or 0.5°C (0.9°F) reduction in operative temperature to ; a decrease of 0.1 clo or 0.1 met corresponds approximately to a 0.8°C (1.4°F) or 0.5°C (0.9°F) increase in operative temperature.

The computer code in Normative Appendix B was developed for use with this standard and is incorporated into the Thermal Comfort Tool [ 3] . If any other software is used, it is the user’s responsibility to verify and document that the version used yields the same results as the code in Normative Appendix B or the Thermal Comfort Tool for the conditions for which it is applied.

48 ANSI/ASHRAE Standard 55-2023