2,400+ Definitions

HVAC GLOSSARY

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

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Daylighting
Daylighting is the strategic use of natural sunlight through windows,…
DC Bus Voltage
The rectified and filtered direct current voltage present on the…
DC Coupled Storage
DC coupled storage systems connect batteries directly to solar panels…
DC Inverter
A specific inverter technology in which the compressor motor is…
DC Link Choke
An inductor placed in series with the DC bus inside…
DC Power
DC power, or direct current power, is electrical energy that…
Dead-End Duct
A duct section that terminates without an outlet, trapping stagnant…
Deadband
A range of values around a setpoint within which no…
Decay Test
A vacuum hold test performed after reaching target micron level,…
Decommissioning
Decommissioning in HVAC refers to the formal, systematic process of…
Decrement Factor
The ratio of the amplitude of the temperature fluctuation on…
Dedicated Outdoor Air System
A Dedicated Outdoor Air System (DOAS) is an HVAC configuration…
Deep Energy Retrofit
A Deep Energy Retrofit (DER) is a comprehensive building renovation…
Deep Vacuum
Deep vacuum is an HVAC refrigeration procedure that removes moisture…
Definite Purpose Contactor
A contactor designed and rated for a specific application such…
Defrost Board
A defrost board is an electronic control module installed in…
Defrost Control
Defrost control is a system integrated into heat pumps that…
Defrost Drain Pan Heater
An electric or hot gas heating element installed beneath the…
Defrost Heater
A defrost heater is an electrical resistance heating element installed…
Defrost Termination Switch
A defrost termination switch (DTS) is a temperature-sensing device, typically…
Defrost Termination Thermostat
A sensor that detects when outdoor coil temperature rises to…
Defrost Timer
A defrost timer is an electromechanical or electronic control device…
Degree of Saturation
The ratio of the actual humidity ratio of moist air…
Dehumidifier
A dehumidifier removes excess moisture from indoor air, reducing relative…
Delayed Ignition
A condition in which ignition of the gas-air mixture in…
Deliquescence
The property of certain hygroscopic salts to absorb moisture from…
Delta T
Delta T (ΔT) is the temperature difference between supply and…
Delta T Cooling
Delta T (ΔT) cooling measures the temperature difference between return…
Delta-T
The temperature difference between the supply and return water in…
Demand Charge
A demand charge is a fee assessed by utilities based…
Demand Control Ventilation
A ventilation strategy that automatically adjusts outdoor air supply rates…
Demand Controlled Ventilation
Demand Controlled Ventilation (DCV) automatically adjusts outdoor air intake based…
Demand Defrost Control
A defrost initiation strategy that monitors actual frost accumulation indicators…
Demand Factor
Demand factor is the ratio of actual simultaneous demand to…
Demand Flexibility
Demand Flexibility refers to the capability of HVAC systems and…
Demand Limiting
Demand Limiting is an HVAC control strategy that automatically reduces…
Demand Response
Demand response programs allow HVAC systems and building operators to…
Demand Side Management
Demand Side Management (DSM) encompasses utility programs and strategies that…
Demand-Controlled Ventilation
An automated ventilation strategy that modulates outdoor air intake based…
Density Correction Factor
A multiplier applied to fan and duct performance data to…
Depth of Discharge
Depth of Discharge (DoD) is the percentage of a battery’s…
Derivative Control
Derivative control responds to the rate of change of temperature…
Derivative Kick
An unwanted spike in PID controller output caused by a…
Desiccant Cooling
Desiccant cooling is a dehumidification process that uses moisture-absorbing materials…
Desiccant Dehumidification
A process that removes moisture from air by adsorbing or…
Desiccant Wheel
A desiccant wheel is a rotating cylindrical device packed with…
Design Conditions
Design conditions are standardized outdoor temperature, humidity, and weather parameters…
Design Day
A design day is a synthetic 24-hour weather profile representing…