ASHRAE-Standard-55 - Page 005

Extracted Content

method described in Section 5.4, “Determining Acceptable Thermal Conditions in Occupant-Controlled Naturally Conditioned Spaces (Adaptive Model).”

air speed: the rate of air movement at a point, without regard to direction.

air speed, average (Va): the average air speed surrounding a representative occupant. The average is with respect to location and time. The spatial average is for three heights as defined for average air temperature ta . For an occupant moving in a space, the sensors shall follow the movements of the occupant. The air speed is averaged over an interval not less than one and not greater than three minutes. Variations that occur over a period greater than three minutes shall be treated as multiple different air speeds.

climate data: hourly, site-specific values of representative meteorological data, such as temperature, wind, speed, solar radiation, and relative humidity. For cities or urban regions with several climate data entries, and for locations where climate data are not available, the designer shall select available weather or meteorological data that best represents the climate at the building site. (See ASHRAE Handbook—Fundamentals [ 1], Chapter 14 for data sources.)

clo: a unit used to express the thermal insulation provided by garments and clothing ensembles; 1 clo = 0.155 m [2] ·°C/W (0.88 ft [2] ·h·°F/Btu).

comfort zone: a zone whose boundaries enclose sets of environmental and personal conditions that provide thermal satisfaction according to the standard.

corrective power: the ability of a personal comfort system (PCS), expressed in degrees (°C [°F]), to correct thermal conditions toward the comfort zone, measured as the difference between two operative temperatures at which equal thermal sensation is achieved—one a temperature in the comfort zone with no PCS, and one with PCS in use, with all other environmental factors held constant. (See personal comfort system .)

direct-beam solar radiation: solar radiation from the direction of the sun, expressed in W/m [2] (Btuh/ft [2] ). Does not include reflected or diffuse solar radiation. Also known as “direct normal insolation” ( Idir ).

draft: the unwanted local cooling of the body caused by air movement.

environment, satisfactory thermal: a thermal environment that a substantial majority (more than 80%) of the occupants find thermally satisfactory.

environment, thermal: the thermal environmental conditions that affect a person’s heat loss.

exceedance hours: the number of occupied hours within a defined time period in which the environmental conditions in an occupied space are outside of the comfort zone.

garment: a single piece of clothing.

generally accepted engineering standard: see ASHRAE/IES Standard 90.1 [ 2] .

humidity: a general reference to the moisture content of the air. It is expressed in terms of several thermodynamic variables, including vapor pressure, dew-point temperature, wet-bulb temperature, humidity ratio, and relative humidity. It is spatially and temporally averaged in the same manner as air temperature. ( Informa- tive Note: Any one of these humidity variables must be used in conjunction with dry-bulb temperature in order to describe a specific air condition.)

insulation, clothing (Icl ): the resistance to sensible heat transfer provided by a clothing ensemble, expressed in units of clo. ( Informative Note: The definition of clothing insulation relates to heat transfer from the whole body and, thus, also includes the uncovered parts of the body, such as head and hands.)

insulation, garment (Iclu ): the increased resistance to sensible heat transfer obtained from adding an individual garment over the nude body, expressed in units of clo.

local thermal discomfort: the thermal discomfort caused by locally specific conditions such as a vertical air temperature gradient between the feet and the head, by radiant temperature asymmetry, by local convective cooling (draft), or by contact with a hot or cold floor.

metabolic rate (met): the rate of transformation of chemical energy into heat and mechanical work by metabolic activities of an individual, per unit of skin surface area (expressed in units of met) equal to 58.2 W/m [2]

(18.4 Btu/h·ft [2] ), which is the energy produced per unit skin surface area of an average person seated at rest.

occupant, representative: an individual or composite or average of several individuals that is representative of the population occupying a space for 15 minutes or more.

occupant-controlled naturally conditioned spaces: those spaces where the thermal conditions of the space are regulated primarily by occupant-controlled openings in the envelope.

ANSI/ASHRAE Standard 55-2023 3