ASHRAE-Standard-55 - Page 069

Extracted Content

L3.2.2 Time-Integrated Analyses, (Long-Term over Typical Day, Season, or Year)

a. Measures

1. Trend logging of physical measurements over time

2. Temperature and humidity in the occupied zone. Globe temperature (temperature measured within a globe exposed to radiation exchange with surrounding surfaces) closely approximates operative temperature to in most indoor situations. For greater accuracy, globe temperature measurements may be combined with shielded air temperature measurements to calculate mean radiant temperature, which, when averaged with the shielded air temperature, provides operative temperature.

3. Measuring indoor air movement over time is very difficult and rarely done. In many indoor situations, the indoor air speed conforms to the still-air conditions of the PMV comfort zone (0.2 m/s [40 fpm]), in which case air speed measurement is not necessary.

4. The number of hours in which local discomfort may be expected is estimated using the local thermal discomfort limits in Section 5. Local discomfort exceedance hours are added to hours in which the comfort zone requirements are exceeded (exceedance occurs when |PMV| > 0.5). b. Criteria Metrics

5. The prescribed metric is the exceedance hour (semantically equivalent to discomfort hour) predicted during occupied hours within any time interval. See the definition in Section 3 and formulas in Section 7.4.2.2.1. Units are in hours. No limits are prescribed.

6. In addition, it is possible to account for the severity of exceedance at any time, using a metric analogous to the familiar degree-day. Weighted exceedance hours (equivalent to degree-of-discomfort hours) are the number of occupied hours within a defined time period in which the environmental conditions in an occupied zone are outside of the comfort zone boundary, weighted by the extent of exceedance beyond the boundary. Units are thermal sensation scale units times hours. The formula for the PMV comfort zone uses terms defined in Section 7.4.2.2.1:

WEH =  [ Hdisc (|PMV| – 0.5)]

Units are thermal sensation scale units times hours. This is a useful metric but is not required in Standard 55. No limits are recommended. 3. Temperature-weighted exceedance hours: It may be useful to convert PMV comfort zone WEHs to a temperature-times-hours scale using the conversion 0.3 (thermal sensation scale units)/°C (0.15 [thermal sensation scale units]/°F). The unit for temperature-weighted exceedance hours is temperature times hours. This is a useful metric but is not required in Standard 55. No limits are recommended. 4. The WEH for the adaptive model also uses a temperature-times-hours scale:

WEH =  [ H>upper ( Top - Tupper ) + H<lower ( Tlower - Top )]

This is a useful metric but is not required in Standard 55. No limits are recommended. 5. Expected number of episodes of discomfort, rate-of-change exceedances, and local discomfort exceedances within a time period of interest.

These are useful metrics but not required in Standard 55. No limits are recommended.

ANSI/ASHRAE Standard 55-2023 67