Commercial HVAC Industry Glossary of Terminology

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Air Filter

A device used to remove solid, particles from the air stream. Air filters are typically located on the return side of the fan and upstream of any cooling/heating coils, ASHRAE recommends a minimum MERV rating of 6 or higher.

ANSI/AHRI Standard 340/360

This is the standard for performance rating of unitary air conditioning and heat pump systems from 65,000 to 250,000 Btu/hr.


For cooling towers, the approach is the difference between the leaving cooling tower water temperature and the ambient air wet bulb temperature. For chillers, the approach is the difference between the leaving chilled water temperature and the evaporating temperature of the refrigerant.

ASHRAE Standard 55

Thermal Environmental Conditions for Human Occupancy Standard; ASHRAE 55 is intended to provide comfort and sustainability.

ASHRAE Standard 62.1

Ventilation for Acceptable Indoor Air Quality Standard; Compliance with ASHRAE 62.1 indicates that the building meets the minimum ventilation requirements set forth by ASHRAE Standard 62.1.

ASHRAE 90.1 Compliant

With respect to unitary cooling equipment, compliance with ASHRAE 90.1 indicates the equipment meets the minimum efficiency requirements set forth by ASHRAE Standard 90.1.

ASHRAE Comfort Zone

This is the range of indoor temperature and humidity conditions for summer and winter conditions that have been found to be acceptable by 80% of the surveyed occupants.

Barometric Relief Damper

This is a damper that allows excess air to exit the building to prevent over pressurization of the building.


Typically a centrifugal type fan inside of a housing, a blower is capable of delivering air flow at a higher pressure versus a fan.

Blower Proving Switch

A switch that provides confirmation that the blower is running.


This is the heart of the system, a machine that is used to compressor refrigerant gas. Compressor types include scroll, reciprocating, rotary, screw, and centrifugal.


Testing the installed HVAC system to ensure it complies with building requirements, codes, manufacturer’s specifications, and performance data. At the completion of the commissioning process the commissioning agent will issue a report documenting the results of the commissioning process.

Condenser Coil

A condenser coil is a heat transfer coil that condenses refrigerant and rejects heat from the system. The condenser coil is typically air or water cooled and is sized to reject the heat absorbed by the evaporator plus the heat of compression.

Condenser Fan Motor

A motor that is used to drive a fan/propeller to move air through an air cooled condenser.

Cooling Load

This is the total heat load that must be removed from the conditioned space per unit time.

Cooling Coil

A cooling coil is the heat transfer coil in which the refrigerant boils and heat transfer takes place. The cooling coil lowers the temperature of the air as it travels through the coil.

Cooling Degree Day

Used to estimate the energy required for air conditioning, a cooling degree day is approximately equal to the mean daily temperature less the base temperature.

Constant Air Volume (CAV)

A type of system that delivers a constant air flow quantity at a variable supply air temperature. Most residential systems are CAV systems.

Crankcase Heater

Helps prevent refrigerant migration to the compressor during the off cycle.


Typically used in zoning applications, a damper is a moveable plate installed in the ductwork used to direct or regulate air flow.


Direct digital control, control of HVAC processes and equipment via microprocessors.

Demand Control Ventilation

A ventilation strategy that introduces ventilation air based on CO2 levels in the occupied zone. The purpose of demand control ventilation is to provide the correct amount of ventilation air and to avoid costly over ventilation.

Discharge Air Heating Reset

A method of controlling coil leaving air temperature during heating based on the outdoor temperature.


Department of Energy; a federal agency that is responsible for setting HVAC minimum equipment efficiency standards.


Used to reduce the mechanical cooling load, an economizer allows the use of outside ventilation air for supply air when the enthalpy or temperature of the outdoor air is lower than required supply air during the cooling cycle.


Energy efficiency ratio; equal to Btu/hr ÷ Watts.

Energy Recover Wheel

May be referred to as heat wheel, used to recover sensible and latent energy from exhaust air.

Energy Star®

Applied to unitary equipment 20 tons or less, Energy Star® labeled equipment exceeds EPA guidelines for energy efficiency.

Exhaust Air

Removes air from inside the building to outside the building. Generally used for removing odors or for proper building pressurization.

External Static Pressure

Pressure that the fan must overcome due to losses after the fan or unit. Typical external static pressure loses include ducts, fittings, registers and diffusers. External Static Pressure does not include the pressure loss of the fan or unit.


A thermostat located on the evaporator coil that protects the coil from damaging ice build-up.

Full Load

The maximum load that a piece of equipment can handle.

High Efficiency

Term used to indicate that the equipment is more energy efficient than average.

High Pressure Switch

A switch that protects the compressor and system from abnormally high discharge pressure conditions.

Hot Gas Bypass

Used to control the capacity of the system at low loads, hot refrigerant gas is bypassed to the low side of the system to better match evaporator capacity to the load.


A device that introduces moisture into the air stream for humidification purposes.


A humidity sensor that is used to control heating and cooling equipment to maintain desired humidity levels.


International Energy Conservation Code; IECC is a code that establishes minimum design and construction requirements for energy efficiency.


Integrated Energy Efficiency Ratio; expresses cooling, weighted part load EER for commercial unitary air conditioning and heat pump equipment at different loads.


Integrated Part Load Value; the efficiency performance factor at part load cooling. This performance factor is weighted towards operating hours at part load.

Latent Load

Load due to moisture introduced into a building. Latent loads may come from ventilation air, people, equipment and infiltration. Latent loads are a concern for cooling and humidifying applications.


Leadership in Energy and Environmental Design; sponsored by the U.S. Green Building Council (USGBC), LEED is a certification program that guides the design, construction, operation and maintenance of buildings and homes.

Life Cycle Cost Analysis

Assesses the total cost of ownership. It includes material cost, installation cost, operating expenses, maintenance expenses and often replacement expenses. A life cycle cost analysis can be used to determine if a new or a high efficient system should be purchased.

Load Calculation

A detailed calculation of the heat loss/gain for the building that is used to size the heating and cooling equipment. Load calculations for commercial buildings are typically performed using software that takes into account historical weather data.

Low Pressure Switch

A switch that protects the compressor and system from abnormally low suction pressure conditions.

Make Up Air

Outside air introduced to the space to prevent negative building pressures and to provide ventilation air.


Minimum circuit ampacity; this is the minimum ampacity for the circuit supplying the equipment.

Mixed Air

Return air from the space and outside air mixed together.


Developed by ASHRAE as a rating system for filters, Minimum Efficiency Reporting Value rates filter performance on a scale of 1 to 16. The higher the MERV value the more efficient the filter is at trapping airborne particles.

Part Load

A load on a piece of equipment that is less than its maximum capacity. Most HVAC equipment operates the majority of time at part load.

Pay Back Analysis

This determines the period of time that is required for the investment to repay the initial investment. Includes factors such as: initial cost, maintenance cost and savings.

Programmable Thermostat

A thermostat that his capable of keeping different cooling and heating schedules, based on building usage, for efficiency and comfort purposes.


Heating air that has previously been conditioned. Often used to dehumidify air or to provide extra heating capacity.

Reheat Coil

Typically located downstream of the cooling coil in dehumidification applications, the reheat coil increases the temperature of the air after it passes through the coiling coil. This is a sensible heating operation.

Return Air

Air returned to an air handling unit from the conditioned space.

Roof Curb

Roof support structures for equipment to be placed on.


Seasonal Energy Efficiency Ratio; The SEER rating is the cooling output divided by the total electric energy input during a typical cooling season.

Sensible Load

The load required to keep the temperature in the space constant. Sensible loads can come from ventilation, infiltration, people and interior loads such as lights and electronics.

Smoke Detector

This is a device that detects smoke. Often installed in a space or in the return air path of an air handling unit.

Standard Efficiency

Term used to indicate that the equipment has average efficiency.

Supply Air

Air provided to condition a space.

Thermal Expansion Valve

A valve that meters the flow of refrigerant to the evaporator coil. The flow is metered based on superheat leaving the evaporator coil.


A temperature and humidity sensor that is used to control heating and cooling equipment to maintain desired temperature and humidity levels.

Total Static Pressure

Pressure that the fan must overcome due to pressure losses of the entire system. Typical pressure loses includes coils, filters, fan, ducts, fittings, registers and diffusers. External Static Pressure does not include the pressure loss of the fan or unit.

Variable Air Volume

A type of system that delivers a variable air flow quantity at a variable supply air temperature.


Mechanical equipment that has the ability to supply the space with ventilation air.


Volatile Organic Compound; emitted gases from solids or liquids. VOCs in a space is often reduced by supplying the space with ventilation air or by filtering the return air with a high performing filter.


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7 thoughts on “Commercial HVAC Industry Glossary of Terminology

  1. What parameters are there to determine whether a repair on a commercial HVAC (RTU M/n#RKKA-A048DK08E) is “major?”

  2. Looking to replace the grate on the top of my condenser. I has almost rusted completely.
    The center “circle/disc” measures 7″ diameter with four acorn nuts to fasten it. There are six other nuts on the perimeter on the grate to also fasten this piece to the top /horizontal side of the condenser. Cannot determine make or model.

  3. Is it necessary or recommended to install a trap / vibration loop on the hot gas and suction lines on a new scroll compressor replacement where a reciprocating compressor was originally installed if the loop does not exist.

    • Because scroll compressors do not have internally suspended components, it is recommended (but not always required) to incorporate a ‘shock loop’.
      Some systems (such as heat pumps) may have enough isolation and attenuation through the use of the reversing valve and associated tubing bends.

  4. We have discussed your question and have concluded we do not have enough information about your application to comment. I would suggest contacting your equipment OEM or a qualified contractor to advise you.

  5. Sir,

    I have a doubt regarding where to place a temperature & humidity sensor in a cold storage.
    And how many sensors that had to be placed in a large volume room
    Please provide me information about them

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