2,400+ Definitions
HVAC GLOSSARY
Every HVAC term, acronym, and industry phrase — defined in plain English.
Non Condensable Gas
Non-condensable gases are atmospheric gases like nitrogen and oxygen that…
Non-Condensable Gases
Gases such as air or nitrogen that do not condense…
Normalized Leakage
A dimensionless metric that relates measured envelope leakage area to…
Normally Closed Valve
A control valve configured so that it is fully closed…
Normally Open Valve
A control valve configured so that it is fully open…
NPLV
NPLV, or Non-Standard Part Load Value, is a single-number metric…
O M Manual
An O M (Operations and Maintenance) Manual is a comprehensive…
Occupancy Sensor
An occupancy sensor automatically detects human presence in a room…
Occupancy Sensor Override
A BAS function that temporarily switches a zone from unoccupied…
Occupied Mode
Occupied Mode is an operational state where HVAC systems actively…
Occupied Setpoint
The temperature or other controlled variable target that a zone…
Occupied Space Refrigerant Limit
The occupied space refrigerant limit is the maximum allowable charge…
Occupied Zone
The occupied zone is the region within a conditioned space…
Odor Control
Odor control refers to the removal or neutralization of unwanted…
ODP (ozone depletion potential)
A relative index expressing how much a refrigerant degrades stratospheric…
ODP Motor
ODP (Open Drip-Proof) Motor features an open design with ventilation…
Off Gassing
Off gassing is the release of volatile organic compounds (VOCs)…
Off Grid Inverter
An off grid inverter converts DC power from solar panels…
Off Grid System
An off-grid solar system operates independently without connection to the…
Offset
In proportional control, the steady-state difference between the setpoint and…
Ohm
An ohm (Ω) is the unit of electrical resistance that…
Oil Analysis
Oil analysis tests compressor lubricant samples to detect metal particles,…
Oil Charging
Oil charging is the process of adding or replacing lubricating…
Oil Furnace
An oil furnace is a heating appliance that combusts fuel…
Oil Management
Oil management encompasses all practices and equipment designed to maintain…
Oil Miscibility
Oil miscibility refers to the ability of refrigerant oils to…
Oil Nozzle
A precision atomizing device at the tip of an oil…
Oil Return
Oil return is the process of returning circulated refrigerant oil…
Oil Separator
An oil separator is a device that removes suspended oil…
Oil Trap
An oil trap is a piping configuration that captures and…
Oil Viscosity
Oil viscosity is the measure of an oil’s resistance to…
On Demand Recirculation
On-demand recirculation systems pump hot water through supply lines only…
On Demand Water Heater
An on-demand water heater heats water only when needed, providing…
OPC UA
An open, platform-independent industrial communication standard that provides secure, reliable…
Open Circuit Voltage
Open circuit voltage (OCV) is the maximum voltage a photovoltaic…
Open Loop Control
A control configuration in which the controller calculates and applies…
Open Source HVAC
Open Source HVAC refers to heating and cooling systems, controls,…
Open System
An open system allows both energy and mass to cross…
Open-Loop Geothermal System
A geothermal configuration that pumps actual groundwater from a well…
OpenADR
OpenADR (Open Automated Demand Response) is an open-source standardized communication…
OpenHAB
OpenHAB is an open-source home automation software platform that integrates…
OpenStudio
OpenStudio is a free, open-source suite of tools developed by…
Operating Point
The operating point is the specific location on a fan…
Operating Room HVAC
Operating room HVAC systems maintain ultra-clean conditions preventing surgical site…
Operation Maintenance Manual
An Operation Maintenance Manual is a comprehensive document prepared by…
Operative Temperature
Operative temperature is the uniform temperature of an imaginary black…
Optimal Start
Optimal Start is an automated control strategy that calculates when…
Optimal Stop
Optimal Stop is a control algorithm that deactivates heating or…