2,400+ Definitions
HVAC GLOSSARY
Every HVAC term, acronym, and industry phrase — defined in plain English.
Design Development
Design Development expands upon schematic designs by adding greater detail,…
Design Water Temperature
The supply and return water temperatures selected for a hydronic…
Desuperheater
A heat recovery device integral to some heat pumps that…
Dew Point
Dew point is the temperature at which air becomes saturated…
dew point (refrigerant)
The temperature at which the last drop of liquid evaporates…
Dew Point Control
An HVAC strategy that manages the temperature of surfaces or…
Dew Point Depression
The difference between the dry-bulb temperature and the dew point…
Dew Point Temperature
Dew point temperature is the temperature at which air becomes…
Dewpoint Hygrometer
An instrument that chills a mirror or sensing surface until…
Diaphragm Expansion Tank
A closed expansion tank with a flexible diaphragm separating a…
Differential Pressure Bypass Valve
A pressure-actuated valve installed across the supply and return mains…
Differential Pressure Reset
A control strategy that raises the chilled water or condenser…
Diffuser Neck Velocity
The average air velocity measured at the inlet connection, or…
Digital Differential Pressure Gauge
An electronic instrument that simultaneously senses two pressure inputs and…
Digital Manifold
A digital manifold is an electronic pressure and temperature measurement…
Digital Manifold Gauge
An electronic version of the traditional manifold gauge set that…
Digital Manometer
A digital manometer is an electronic pressure measurement device that…
Digital Refrigerant Scale
A digital refrigerant scale is a precision electronic weighing device…
Dilution Ventilation
Dilution ventilation, or general ventilation, introduces fresh outdoor air throughout…
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 Spark Ignition
A system in which a high-voltage spark electrode ignites the…
Direct Vent
Direct vent systems draw combustion air directly from outdoors and…
Direct-Expansion Evaporator
An evaporator in which refrigerant is metered by an expansion…
Dirty Coil
A dirty coil accumulates dust, pollen, debris, and biological growth…
Discharge Line
The discharge line is the refrigerant piping that connects the…
Discharge Line Temperature
The temperature of the refrigerant gas leaving the compressor outlet,…
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…
Distributor Nozzle
A precision orifice fitting at the outlet of an expansion…
District Cooling
District cooling is a centralized system that produces and distributes…
District Heating
District Heating (DH) is a centralized system that generates thermal…
Diverging Tee
A duct fitting that splits airflow from a single upstream…
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…