2,400+ Definitions
HVAC GLOSSARY
Every HVAC term, acronym, and industry phrase — defined in plain English.
100 Percent Renewable
100 Percent Renewable refers to electricity sourcing or generation exclusively…
222nm UV
222 nanometer UV is a specific far ultraviolet wavelength that…
254nm UV
254 nanometer UV is the traditional ultraviolet wavelength used in…
A1 Refrigerant
An A1 refrigerant is a classification defined by ASHRAE Standard…
A2L Refrigerant
A2L refrigerants are mildly flammable cooling fluids classified as having…
Above Ceiling Space
Above Ceiling Space refers to the plenum area between the…
Absolute Filter
An absolute filter is a high-efficiency air filter that removes…
Absolute Humidity
Absolute humidity measures the actual mass of water vapor present…
Absorption Chiller
An Absorption Chiller uses thermal energy rather than electricity to…
Absorption Refrigeration
Absorption refrigeration is a cooling technology that uses heat energy…
AC Coupled Storage
AC coupled storage systems connect batteries to the electrical grid…
AC Power
AC power, or alternating current power, is electrical energy delivered…
ACCA
ACCA (Air Conditioning Contractors of America) is the primary US…
ACCA Manual CS
ACCA Manual CS (Commercial Space Load Calculation) is a standardized…
ACCA Manual D
ACCA Manual D is the industry-standard methodology published by the…
ACCA Manual J
ACCA Manual J is an industry-standard procedure developed by the…
ACCA Manual N
ACCA Manual N provides the methodology for calculating residential heating…
ACCA Manual P
ACCA Manual P, formally titled “Residential Duct Systems,” is an…
ACCA Manual RS
ACCA Manual RS (Residential Sprinkler System) is a technical standard…
ACCA Manual S
ACCA Manual S is a standardized procedure published by the…
ACCA Manual T
ACCA Manual T establishes procedures for selecting proper ductwork sizing,…
Access Door Mechanical
An access door for mechanical systems is a hinged or…
Access Panel
An access panel is a removable cover providing entry to…
Accumulator
An accumulator is a pressure vessel installed in the suction…
ACH50
ACH50 measures the air changes per hour at 50 pascals…
Acid Burnout
Acid burnout occurs when acids formed inside the refrigeration system…
Activated Carbon Adsorption
Activated carbon adsorption is a filtration process where volatile organic…
Activated Carbon Filter
Activated carbon filters remove odors, gases, and chemicals through adsorption,…
Active Chilled Beam
An active chilled beam is an HVAC terminal unit that…
Active Design
Active design uses mechanical systems including HVAC equipment, controls, and…
Active Solar System
An active solar system uses electric pumps and controls to…
Actual COP
Actual COP is the real-world coefficient of performance measured or…
Actuator
An actuator is an electromechanical or pneumatic device that converts…
Adaptive Comfort Model
The Adaptive Comfort Model recognizes that occupants adjust their clothing,…
Adiabatic Cooler
An adiabatic cooler combines dry cooling with indirect evaporative pre-cooling,…
Adiabatic Process
An adiabatic process is a thermodynamic change in which no…
Advanced Metering Infrastructure
Advanced Metering Infrastructure (AMI) is a comprehensive system combining smart…
AFCI
AFCI stands for Arc Fault Circuit Interrupter, an advanced electrical…
Affinity Laws
The Affinity Laws are mathematical relationships governing how pump and…
AFUE
AFUE (Annual Fuel Utilization Efficiency) is the standard measure of…
Aggregated DER
Aggregated distributed energy resources combine multiple small-scale generation and storage…
Agrivoltaics
Agrivoltaics is the practice of simultaneously generating solar energy and…
AHRI
AHRI is the Air-Conditioning, Heating, and Refrigeration Institute, a nonprofit…
AHRI 210/240
Definition AHRI 210/240 is a certification standard developed by the…
AHRI 310/380
AHRI 310/380 is the industry standard published by the Air-Conditioning,…
AHRI 340/360
Definition AHRI 340/360 is a certification standard for commercial air…
AHRI 365
AHRI 365 is a performance rating standard published by the…
AHRI 550/590
Definition AHRI 550/590 is the certification standard for water-cooled chillers…