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Glossary
Air quality standards

What is ASHRAE 55?

Definition

ASHRAE 55, Thermal Environmental Conditions for Human Occupancy, defines the combinations of indoor environmental and personal factors that most occupants find thermally acceptable.

Where it is used

HVAC designers use it to set design conditions, commissioning agents and owners use it to judge existing buildings, and LEED and WELL reference it for thermal comfort credits. It is voluntary unless a code, lease or rating system adopts it.

Factors and the 2023 edition

Per ASHRAE, the standard weighs four environmental factors (air temperature, radiant heat, humidity and air speed) and two personal ones (activity and clothing). The 2023 edition consolidated its evaluation methods into two, standard and adaptive, added a method for discomfort from head to ankle temperature differences, covers a wider range of metabolic rates and replaced the compliance form with an example spreadsheet.

Comfort compliance as an operating number

Aqueduct measures air temperature and humidity per zone, not radiant temperature or air speed, so it tracks the operating side rather than a full 55 calculation. On a rooftop unit twin, comfort compliance and setpoint attainment are scored live, with a score of 90 or above counted as good, and a zone that misses comfort while running hard is flagged.

Questions

ASHRAE 55: common questions

ASHRAE 55 is the US standard for thermal comfort in occupied spaces. It explains how to predict whether most people will feel neither too warm nor too cool, using measured conditions plus clothing and activity, and how to survey occupants in existing buildings. It sits beside ASHRAE 62.1 for ventilation.

The adaptive model applies to naturally conditioned spaces where occupants open windows. Acceptable indoor temperature shifts with recent outdoor temperature instead of staying at a fixed band, reflecting that people in such buildings adapt their clothing and expectations to the season.

No. Acceptable temperature depends on humidity, air speed, radiant conditions, clothing and activity, so a winter office and a summer gym land in different ranges. Setpoints are a design choice within those ranges, which is why tracking how often zones hold them matters in operation.

By logging zone temperature and humidity continuously and checking how often they stay inside the agreed band. Aqueduct scores comfort compliance per rooftop unit and flags zones that miss it, which pairs with HVAC energy optimization so savings never come at the cost of comfort.

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