ASHRAE-Standard-55 - Page 021

Extracted Content

Table 5-12 Increases in Acceptable Operative Temperature Limits (  t 0) in Occupant-Controlled Naturally Conditioned Spaces (Figure 5-9) Resulting from Increasing Air Speed above 0.3 m/s (59 fpm)

Average Air Speed Va 0.6 m/s (118 fpm) 0.9 m/s (177 fpm) [1.2 m/s (236 fpm)]

1.2°C (2.2°F) 1.8°C (3.2°F) 2.2°C (4.0°F)

that applied to the subsequent day. For this option, the upper limit on the number of days in the sequence does not apply. (See Informative Appendix J for example calculation.) Mean daily outdoor air temperature tmda  out  for each of the sequential days in Section 5.4.2.1.1 shall be the simple arithmetic mean of all the outdoor dry-bulb temperature observations for the 24-hour day. The quantity of measurements shall be no less than two, and, in that case, shall be the minimum and maximum for the day. When using three or more measurements, the time periods shall be evenly spaced.

5.4.2.1.3 Observations in Section 5.4.2.1 shall be from the nearest approved meteorological station, public or private, or Typical Meteorological Year (TMY) weather file. Exception to 5.4.2.1.3: When weather data to calculate the prevailing mean outdoor air temperature

tpma  out  are not available, it is permitted to use as the prevailing mean the published meteorological

monthly means for each calendar month. It is permitted to interpolate between monthly means. 5.4.2.2 It shall be permitted to use the following equations, which correspond to the acceptable operative temperature to ranges in Figure 5-9:

Upper 80% acceptability limit (°C) = 0.31 tpma  out  + 21.3

Upper 80% acceptability limit (°F) = 0.31 tpma  out  + 60.5

Lower 80% acceptability limit (°C) = 0.31 tpma  out  + 14.3

Lower 80% acceptability limit (°F) = 0.31 tpma  out  + 47.9

5.4.2.3 The following effects are already accounted for in Figure 5-9 and the equations in Section 5.4.2.2 and, therefore, it is not required that they be separately evaluated: local thermal discomfort, clothing insulation Icl, metabolic rate, humidity, and air speed.

5.4.2.4 If t 0 > 25°C (77°F), then it shall be permitted to increase the upper acceptability temperature limits in Figure 5-9 and the equations in Section 5.4.2.2 by the corresponding  t 0 in Table 5-12.

6. DESIGN COMPLIANCE

6.1 Design. Building systems (i.e., combinations of mechanical systems, control systems, and thermal enclosures) shall be designed to maintain occupied spaces at thermal conditions that provide thermal comfort in accordance with one of the methods in this standard, considering all expected operating conditions (i.e., peak and partial load).

Design compliance shall consider all predictable representative occupants and expected indoor and outdoor environmental conditions, including but not limited to

a. Seasonal and typical outdoor environmental variations b. Seasonal clothing changes of the representative occupants c. Short-term average air temperature variability due to HVAC system design and operations including

thermostat deadband and cycling d. Indoor spatial variations in average air temperature, relative humidity, average air speed, and mean radi ant temperature, including the presence, or lack thereof, of direct solar radiation

6.1.1 Design Thermal Environmental Control Classification. For all projects demonstrating compliance through Section 5.3, design compliance shall indicate the Thermal Environmental Control Classification Level in accordance with Table 6-1 of each space type within the building.

Each control measure for environmental factors shall be readily accessible to occupants, when occupancy is expected and be either (a) or (b) as follows:

a. A user-adjustable thermostat with ability of the user to change set point by ±3°C (±5°F) b. Capable of changing the thermal environment of the space or individual occupant by the magnitude

specified in either Section 6.1.1(a) or (b) in 15 minutes or less from occupant control initiation while met and clo values are constant. For control measures that apply to a multioccupant space, the change must meet the requirements for all representative occupants.

ANSI/ASHRAE Standard 55-2023 19