2,400+ Definitions

HVAC GLOSSARY

Every HVAC term, acronym, and industry phrase — defined in plain English.

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Ultraviolet Germicidal Irradiation
The application of UV-C wavelength light within HVAC ducts or…
UMC
Definition The Uniform Mechanical Code (UMC) is a model building…
Undercut Door
An undercut door is a door that has been intentionally…
Underfloor Air Distribution
Underfloor Air Distribution (UFAD) is an air delivery strategy in…
Undisturbed Ground Temperature
The natural, stable temperature of the earth at a given…
Unidirectional Airflow
Unidirectional airflow describes air movement in a single, consistent direction…
Uniform Energy Factor
Uniform Energy Factor (UEF) is the current standardized efficiency metric…
Unit Cooler
A packaged evaporator assembly with integral fan or fans and…
Unit Heater
A unit heater is a self-contained heating device that combines…
Unitary Controller
A factory-configured or limited-programmability DDC controller designed for a specific…
Unitary System
A unitary system is a self-contained HVAC assembly in which…
Universal Certification
Universal Certification, also called Type IV certification, authorizes technicians to…
Unoccupied Mode
Unoccupied Mode is a reduced-operation setting where HVAC systems operate…
Unoccupied Setpoint
A relaxed temperature target applied by a BAS during periods…
Upper Room UVGI
Upper room UVGI (ultraviolet germicidal irradiation) is a disinfection technique…
Utility API
A utility API is an application programming interface that allows…
Utility DSM
Utility DSM refers to demand-side management programs operated by electric…
Utility Grid
The utility grid is the complete electrical distribution network operated…
Utility Interconnection Agreement
A utility interconnection agreement is a legally binding contract between…
Utility Rate Schedule
A utility rate schedule is the official document filed with…
Utility Rebate Program
A Utility Rebate Program offers financial incentives provided by electric,…
Utility Scale Solar
Utility-scale solar refers to large photovoltaic power plants ranging from…
UV Air Purifier
A UV air purifier uses ultraviolet light radiation to inactivate…
UV Drain Treatment
UV drain treatment uses ultraviolet light technology installed in condensate…
UV Dye
UV dye (ultraviolet fluorescent dye) is a tracer chemical injected…
UV Germicidal Irradiation
UV germicidal irradiation (UVGI) is a disinfection technology using ultraviolet…
UVC Lamp Life
UVC lamp life refers to the operational duration of ultraviolet…
UVGI Efficacy
UVGI efficacy measures the effectiveness of ultraviolet germicidal irradiation systems…
UVGI Safety
UVGI safety encompasses protective measures and exposure limits established to…
Vacuum Procedure
The vacuum procedure removes air, moisture, and other non-condensables from…
Vacuum Pull Down
Vacuum pull down is a test that measures how quickly…
Vacuum Pump
A mechanical pump used to evacuate a refrigerant circuit to…
Vacuum Pump Oil Condition
The state of the oil in a vacuum pump, which…
Valve Actuator
A valve actuator is a device that opens, closes, or…
Valve Authority
Valve authority is a dimensionless ratio that measures a control…
Valve Sizing
Valve sizing is the process of selecting a control valve…
Vane Anemometer
A vane anemometer measures air velocity using multiple propeller-like blades…
Vapor Barrier
A vapor barrier is a material with a permeance rating…
Vapor Charging
Introducing refrigerant into a system in the gaseous phase, typically…
Vapor Compression Cycle
The vapor compression cycle is the thermodynamic process used by…
Vapor Compression Refrigeration
Vapor compression refrigeration is the dominant cooling technology that uses…
Vapor Injection
Vapor injection is an advanced refrigeration technique that injects high-pressure…
Vapor Pressure
Vapor pressure is the pressure exerted by a vapor in…
Vapor Pressure Deficit
The difference between the saturation vapor pressure and the actual…
Vapor Retarder
A vapor retarder is a material with permeance ratings between…
Vapor Retarder Class
A classification (Class I, II, or III) based on measured…
Variable Air Volume
Variable Air Volume (VAV) is an HVAC system design that…
Variable Capacity System
A Variable Capacity System is an HVAC system designed to…