2,400+ Definitions
HVAC GLOSSARY
Every HVAC term, acronym, and industry phrase — defined in plain English.
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…
Variable Flow
Variable flow hydronic systems adjust circulation pump speed and water…
Variable Frequency Drive
A Variable Frequency Drive (VFD) is an electronic controller that…
Variable Frequency Drive (VFD)
A Variable Frequency Drive (VFD) is an electronic controller that…
Variable Geometry Diffuser
An adjustable vane ring at the outlet of a centrifugal…
Variable Pitch Fan
A variable pitch fan (VPF) is an axial fan designed…
Variable Primary Flow
A chilled water plant design in which the chilled water…
Variable Refrigerant Flow
Variable Refrigerant Flow (VRF) is an advanced HVAC technology that…
Variable Setpoint
A variable setpoint is a target temperature that automatically adjusts…
Variable Speed Drive
A variable speed drive (VSD) is an electronic controller that…
Variable Speed Injection Mixing
A method of controlling supply water temperature in a radiant…
Variable Speed Motor
A variable speed motor (also called an ECM — Electronically…
Variable Torque Load
A variable torque load is a mechanical resistance that increases…
Variable-Base Degree Days
Heating or cooling degree days calculated using a base temperature…
VAV Box
A Variable Air Volume (VAV) box is an HVAC terminal…
Velocity Pressure
The pressure associated with the kinetic energy of moving air,…
Velometer
A direct-reading airflow instrument historically used to measure air velocity…
Ventilation
Ventilation is the controlled exchange of indoor and outdoor air,…
Ventilation Effectiveness
Ventilation effectiveness measures how efficiently a ventilation system removes contaminants…
Ventilation Rate Procedure
The Ventilation Rate Procedure is a prescriptive ASHRAE 62.1 method…
Verification Testing
Verification testing in HVAC refers to the systematic process of…
Vertical Loop Field
A geothermal ground heat exchanger configuration where boreholes are drilled…
Very High Pressure Category
The Very High Pressure Category includes systems operating at pressures…
VFD
A Variable Frequency Drive (VFD) is an electronic device used…
VFD Carrier Frequency
The switching frequency of the insulated gate bipolar transistors in…
Vibration Analysis Maintenance
Vibration analysis maintenance measures mechanical vibration in compressors, motors, and…
Vibration Analyzer
A vibration analyzer is a sophisticated diagnostic instrument that measures…
Vibration Isolation Pad
A vibration isolation pad is a resilient material placed under…
Vibration Isolator
A vibration isolator is a mechanical device engineered to reduce…
Vibration Meter
A vibration meter is a portable instrument that measures mechanical…