ASHRAE-Standard-55 - Page 006

Extracted Content

occupant-controlled openings: openings such as windows or vents that are directly controlled by the occupants of a space. Such openings may be manually controlled or controlled through the use of electrical or mechanical actuators under direct occupant control. occupied zone: the region normally occupied by people within a space. In the absence of known occupant locations, the occupied zone is to be between the floor and 1.8 m (6 ft) above the floor and more than 1.0 m (3.3 ft) from outside walls/windows or fixed heating, ventilating, or air-conditioning equipment, and 0.3 m (1 ft) from internal walls. personal comfort system (PCS): a device, under the control of the occupant, to heat and/or cool individual occupants directly, or heat and/or cool the immediate thermal environment of an individual occupant, without affecting the thermal environment of other occupants. personal environment: the thermal environment immediately surrounding an occupant. predicted mean vote (PMV): an index that predicts the mean value of the thermal sensation votes (selfreported perceptions) of a large group of persons on a sensation scale expressed from –3 to +3 corresponding to the categories “cold,” “cool,” “slightly cool,” “neutral,” “slightly warm,” “warm,” and “hot.” predicted percentage of dissatisfied (PPD): an index that establishes a quantitative prediction of the percentage of thermally dissatisfied people determined from PMV. radiant temperature asymmetry: the difference between the plane radiant temperature tpr in opposite directions. The vertical radiant temperature asymmetry is with plane radiant temperatures in the upward and downward directions. The horizontal radiant temperature asymmetry is the maximum radiant temperature asymmetry for all horizontal directions. The radiant temperature asymmetry is determined at waist level, 0.6 m (24 in.) for a seated occupant and 1.1 m (43 in.) for a standing occupant. (See ASHRAE Handbook—Fundamentals [ 1], Chapter 9 for a more complete description of plane radiant temperature and radiant asymmetry.) readily accessible: capable of being reached quickly for operation without requiring those for whom ready access is required to climb over or remove obstacles or to resort to portable ladders, chairs, or other climbing aids. sensation, thermal: a conscious subjective expression of an occupant’s thermal perception of the environment, commonly expressed using the categories “cold,” “cool,” “slightly cool,” “neutral,” “slightly warm,” “warm,” and “hot.” shade openness factor: percentage of the area of a shade or blind material that is unobstructed. For woven shades, shade openness factor is the weave openness. solar transmittance, total (Tsol): total solar radiation transmittance through a fenestration unit, including glazing unit and internal blinds or shades. See Normative Appendix C for acceptable calculation methods. temperature, air: the temperature of the air at a point. temperature, air average (ta): the average air temperature surrounding a representative occupant. The average is with respect to location and time. The spatial average is the numerical average of the air temperature at the ankle level, the waist level, and the head level. These levels are 0.1, 0.6, and 1.1 m (4, 24, and 43 in.) for seated occupants; 0.1, 1.1, and 1.7 m (4, 43, and 67 in.) for standing occupants, and the mean height of the body for horizontal occupants. Time averaging is over a period not less than three and not more than 15 minutes. temperature, dew-point (tdp ): the air temperature at which the water vapor in air at a given barometric pressure will condense into a liquid. temperature, floor (tf): the surface temperature of the floor where it is in contact with the representative occupants’ feet. temperature, long-wave mean radiant (trlw ): radiant temperature from long-wave radiation from interior surfaces expressed as a spatial average of the temperature of surfaces surrounding the occupant, weighted by their view factors with respect to the occupant. (See ASHRAE Handbook—Fundamentals [ 1], Chapter 9.) temperature, mean daily outdoor air (tmda  out  ): any arithmetic mean for a 24-hour period permitted in Section 5.4 of the standard. Mean daily outdoor air temperature is used to calculate prevailing mean outdoor air temperature tpma  out  . temperature, mean radiant (tr ): the temperature of a uniform, black enclosure that exchanges the same amount of heat by radiation with the occupant as the actual surroundings. It is a single value for the entire body and accounts for both long-wave mean radiant temperature trlw and short-wave mean radiant temperature trsw . temperature, operative (to ): the uniform temperature of an imaginary black enclosure, and the air within it, in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual non

trlw

tmda  out 

tpma  out 

tr

and accounts for both long-wave mean radiant temperature trlw

trsw .

4 ANSI/ASHRAE Standard 55-2023