2,400+ Definitions
HVAC GLOSSARY
Every HVAC term, acronym, and industry phrase — defined in plain English.
Dip Tube
A dip tube is an internal pipe inside water heater…
Direct Circulation System
A direct circulation system pumps potable water directly through solar…
Direct Current
Direct current (DC) is a unidirectional flow of electrical charge…
Direct Digital Control
Direct Digital Control (DDC) is a computer-based system that automatically…
Direct Fired Chiller
A direct fired chiller is an absorption cooling system with…
Direct Liquid Cooling
Direct Liquid Cooling delivers coolant through tubes or channels connected…
Direct Vent
Direct vent systems draw combustion air directly from outdoors and…
Dirty Coil
A dirty coil accumulates dust, pollen, debris, and biological growth…
Discharge Line
The discharge line is the refrigerant piping that connects the…
Displacement Ventilation
Displacement ventilation is an air distribution strategy that introduces conditioned…
Display Case
A display case is a refrigerated cabinet with transparent glass…
Distributed Energy Resource
A distributed energy resource (DER) is a small-scale electric generation…
Distribution Effectiveness
Distribution effectiveness evaluates how uniformly conditioned air reaches all areas…
District Cooling
District cooling is a centralized system that produces and distributes…
District Heating
District Heating (DH) is a centralized system that generates thermal…
Diversity Factor
Diversity factor is the ratio of non coincident peak demand…
Diverter Valve
A Diverter Valve is a three-port hydronic component that directs…
Diverting Valve
A diverting valve is a three-way control valve that directs…
Division 23
Division 23 is the MasterFormat construction category that encompasses all…
DOAS
A Dedicated Outdoor Air System (DOAS) is an HVAC system…
DOE 2
DOE 2 is a pioneering whole-building energy simulation program developed…
DoE Appliance Standard
A DoE Appliance Standard is a minimum energy performance requirement…
DOE Appliance Standards
DOE Appliance Standards are federal energy efficiency requirements established by…
Door Sensor HVAC
A door sensor HVAC device monitors whether doors are open…
Double Effect Absorption
Double effect absorption is an advanced thermodynamic cycle that uses…
Draft Hood
A draft hood is a metal fitting installed at the…
Draft Inducer
A draft inducer is an electrically powered blower motor located…
Draft Inducer Motor
A draft inducer motor is a small fan motor that…
Draft Measurement
Draft measurement quantifies the pressure difference between a furnace or…
Drain Pan Treatment Tablet
A drain pan treatment tablet is a slow-release chemical pellet…
Drainback System
A drainback system is an active solar heating method where…
Dry Bulb Temperature
Dry bulb temperature is the actual air temperature measured by…
Dry Cooler
A dry cooler is an air-cooled heat exchanger that rejects…
Dual Axis Tracker
Dual axis trackers rotate photovoltaic panels along two axes, following…
Dual Duct System
A dual duct system is a type of central HVAC…
Dual Fuel System
A dual fuel system is an HVAC configuration that combines…
Duct Access Door
A duct access door is a hinged or removable panel…
Duct Blaster Test
A Duct Blaster Test is a diagnostic procedure that measures…
Duct Cleaning
Duct cleaning is the process of removing accumulated dust, debris,…
Duct Design
Duct design is the systematic process of planning and sizing…
Duct Elbow
A duct elbow is a fitting used to change the…
Duct Fabrication
Duct fabrication is the custom construction of metal or fiberglass…
Duct Friction
Duct friction refers to the resistance air encounters as it…
Duct Installation
Duct installation is the process of assembling and securing metal…
Duct Insulation
Duct insulation is thermal and acoustic material applied to ductwork…
Duct Leakage
Duct leakage occurs when conditioned air escapes from supply ducts…
Duct Leakage Tester
A duct leakage tester is a pressurized measurement system that…
Duct Liner
Duct liner is an insulation material applied directly to the…