ASHRAE 55
ASHRAE Standard 55, officially titled "Thermal Environmental Conditions for Human Occupancy," is a widely recognized and applied standard developed and maintained by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). It specifies the combinations of indoor thermal environmental factors and personal factors that produce acceptable thermal comfort for a specified percentage of occupants within a space.
The primary goal of ASHRAE Standard 55 is to define thermal comfort and prescribe conditions that will be acceptable to a majority of the occupants. It addresses factors influencing thermal comfort such as:
- Air Temperature: The dry-bulb temperature of the air.
- Radiant Temperature: The weighted average of the temperatures of all surfaces surrounding an occupant, taking into account their respective areas and emissivities.
- Air Velocity: The speed of air moving around an occupant.
- Humidity: The moisture content of the air, typically expressed as relative humidity.
- Metabolic Rate: The rate at which a person generates heat, depending on their activity level.
- Clothing Insulation: The thermal resistance of clothing worn by an occupant.
The standard provides guidance and criteria for determining acceptable ranges for these parameters, taking into account the activity level and clothing of the occupants. It also addresses issues such as local thermal discomfort (draft, radiant asymmetry, floor surface temperature) and provides methods for assessing thermal comfort using tools like the Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD) indices.
ASHRAE Standard 55 is regularly updated to incorporate new research and best practices. It is used by building designers, engineers, and facility managers to create comfortable and healthy indoor environments in a variety of building types, including offices, schools, hospitals, and residential buildings. Compliance with ASHRAE 55 is often required by building codes and green building rating systems such as LEED.