ASHRAE-Standard-55 - Page 061

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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 L MEASUREMENTS, SURVEYS, AND EVALUATION OF COMFORT  IN EXISTING SPACES: PARTS 1 AND 2

L1. PHYSICAL MEASUREMENTS

L1.1 Overview of Comfort Prediction Using Physical Measurements. Measurements of indoor environmental parameters are converted to predictions of occupants’ thermal satisfaction through calculations and tests against comfort limits.

a. In the predicted-mean-vote-based (PMV) method (Section 5.3), environmental measurements are com bined with assumptions about clothing and activity level to calculate PMV, a measure of an average occupant’s thermal sensation. In Standard 55, comfort zone is defined as conditions falling within and including PMV levels from –0.5 PMV to +0.5 PMV.

At any given PMV level, a population’s proportion of dissatisfied members may be predicted via the predicted percentage dissatisfied (PPD) curve. This is an empirical probit fit of thermal sensation (TSENS) survey scores obtained in a range of test environments in which dissatisfaction was assumed to occur at TSENS absolute values of 2 or greater. With this method, a PMV of ±0.5 predicts 90% of a population satisfied, or a 10% PPD.

However, in most buildings this 90% satisfied rating is rarely obtained, with maximum satisfaction around 80%. The difference has been ascribed to discomfort perceived in local parts of the body. The probability of local discomfort is predicted by testing environmental parameters measured in sensitive locations against empirically determined limits. Rates of temperature change are also limited to avoid discomfort. Local discomfort effects are assumed to contribute an additional 10% PPD to the discomfort predicted by PMV, so that the total PPD expected in a building with PMV ±0.5 will be 20%. b. In the adaptive model, used for naturally ventilated spaces, environmental measurements are linked to

satisfaction through an empirical model in which the prevailing mean air outdoor temperature determines the position of percent satisfied contours bordering the comfort zone. Section 5.4 defines prevail- ing mean outdoor air temperature . Local discomfort limits are not used in the adaptive model.

L1.2 Environmental and Occupant Measurements. Environmental parameters are described in Section 5.1, and their measurement requirements are described in Section 7.3. For nonsteady conditions, the Section 7.3.3 prescribes measurement timing. The two personal parameters, activity level and clothing, must also be estimated for the occupants of the space. Estimation methods are presented in Informative Appendix F and Informative Appendix G. For evaluating a space, each of these parameters should be estimated in the form of mean values over a period of 0.25 to 1.0 hours immediately prior to measuring the indoor environmental parameters. If the occupants are not yet present, such as during design and commissioning, one may use clothing and activity values agreed upon by owners and designers as appropriate for the building’s function.

L2. SURVEYING OCCUPANTS

The use of occupant thermal environment surveys is an acceptable way of assessing comfort conditions for the satisfaction ranges discussed in this standard. With surveys, one may measure the percent who are “satisfied” or “comfortable” by putting those direct questions to a representative sample of the occupants. One may also obtain the percent satisfied using the ASHRAE thermal sensation scale, making the traditional assumption that satisfaction occurs when the seven-point scale is within TSENS = –1.5  satisfied  +1.5 (when using a scale unit resolution of 0.5 or less) or –2 < satisfied < +2 (when the scale resolution is limited to integers).

Surveys obtain occupants’ comfort perceptions directly, whereas measurements of the environment predict those perceptions indirectly through models. However, surveys cannot be administered in all cases. Because surveys require engaging the occupants and consuming some of their time, it is necessary to have a well-planned communications approach and to use a survey that is optimized for length and content. The timing and frequency of repetition must also be weighed.

ANSI/ASHRAE Standard 55-2023 59