ANSI/ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy is an American National Standard published by ASHRAE that establishes the ranges of indoor environmental conditions to achieve acceptable thermal comfort for occupants of buildings.
[1] Predicted mean vote is an index that predicts the mean value of the thermal sensation votes (self-reported 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," "slight warm," "warm," and "hot.
If these requirements are met and the environmental conditions inside the building fall within the indicated ranges, then compliance is achieved.
Compliance is achieved if the conditions provide thermal neutrality, measured as falling between -0.5 and +0.5 on the PMV scale.
The methodology is based on the SET (Standard Effective Temperature) model, which provides a way to assign an effective temperature (at a standard metabolic rate, and clothing insulation values) to compare thermal sensations experienced at a range of thermal conditions.
To evaluate compliance, the ASHRAE Thermal Comfort Tool may be used, or a computer model validated against the code provided in Informative Appendix D of the standard.
[1] Radiant temperature asymmetry between ceiling and floor, and air and walls must be limited to reduce discomfort.
To reduce draft risk at temperatures below 22.5 °C (72.5 °F), air speed due to the HVAC system must be 0.15 m/s (30 ft/min) or below.
An accompanying table lists provisions for higher operative temperatures at air speeds above 0.3 m/s (59 ft/min) and up to 1.2 m/s (240 ft/min).
[10] Generally, the scale in thermal satisfaction surveys must end with options “very dissatisfied” and “very satisfied.” An open-ended response to document reasons for dissatisfaction should also be provided.
The Point-in-Time surveys, which shall be solicited and conducted during active occupancy hours, require gathering responses on a continuous or seven-point Likert scale from “very dissatisfied” to “very satisfied.” Thermal sensation questions should employ terms: “cold,” “cool,” “slightly cool,” “neutral,” “slightly warm,” “warm,” and “hot”.
For mechanically conditioned spaces, the PMV-based comfort zone has to be determined, which includes measuring and recording the metabolic activity and clothing insulation.
For occupant-controlled naturally conditioned space, the adaptive model shall be used to determine the thermal comfort boundaries.
The trending capabilities require data to be recorded at intervals of no more than 15 minutes, spanning a minimum of 30 days.
For a mechanically conditioned space at an instance in time, the PMV and SET model shall be used to establish the comfort zone, and the local thermal discomfort shall be evaluated against the limit posed this standard as well.
For occupant-controlled naturally conditioned spaces, the measured results shall be check with the comfort zone established by adaptive model.
This is the energy produced from a unit skin surface area of an average person seated at rest.
[1] Clothing insulation refers to the heat transfer of the entire body, which includes the uncovered parts, such as hands and heads.
The second method is to add or subtract individual garment clo value to achieve the clothing ensemble in question.
Section five of the ANSI/ASHRAE Standard 55 provides a table with clothing insulation of a variety of individual garments.
This table can be used together with the previous one, so that one can add or subtract the clothing ensemble from the clo value of each garment.
[1] The fourth method described in ANSI/ASHRAE Standard 55 can be used to determine the clothing insulation in mechanically conditioned spaces.
There is a figure in the section five of the standard which predicts the representative clothing insulation of the occupants as a function of the average outdoor air temperature at 06:00 am.
For the first, it is not correct to use the average clothing insulation value to determine the desired thermal conditions for all occupants.
These periodic revisions are based on a publicly reviewed addenda to the previous version available on ASHRAE's website.
[13] In 1992 the standard was updated with more extensive information on measurement protocols and an expanded definitions section.
The applicability of the cooling effect of air movement was expanded to apply to naturally conditioned spaces.