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Glossary of HVAC Terms

A

Absolute Temperature

A temperature scale expressed in degrees °F or °C using absolute zero as a base. Referred to as the Rankin or Kelvin scale.

Absolute Zero

The temperature at which molecular activity theoretically ceases. -456.69 °F or -273.16 °C.

Air conditioner

A mechanical device used to control temperature and air movement in a confined space.

Air Cooled System

A type of air conditioning system that uses air as a condensing medium and R-22 or R-410A as a refrigerant. In most air cooled systems, the condenser is located outside and the refrigerant is piped to it from the indoor unit. In air conditioning, the heat from the indoor space is transferred to the outside air. In a heat pump, the heat is drawn from the outdoor air and is used to heat the indoor air.

Air Filtration System

A device that removes allergens, pollutants and other undesirable particles from air that is heated or cooled.

Air Handling Unit

Equipment with a heating element and/or cooling coil and other components in a cabinet or casing.

Allergen

A substance that causes an allergic reaction. It includes dust, pollen, pet hair and dander, dust mites, mildew, lint, fungus, most tobacco smoke, cooking grease and bacteria.

B

Balancing or Air Balancing

Adjusting an air conditioning system so that the right amount of air is delivered to the right places in your home in order to achieve the right heating or cooling effect.

Bimetal

Two metals with different rates of expansion fastened together. When heated or cooled they will warp and can be made to open or close a switch or valve.

Bioaerosols

Microscopic living organisms suspended in the air that grow and multiply in warm, humid places.

BTU

British Thermal Unit. In scientific terms, it represents the amount of energy required to raise one pound of water one degree Fahrenheit. One BTU is the equivalent of the heat given off by a single wooden kitchen match. For your home, it represents the measure of heat given off when fuel is burned for heating, or the measure of heat extracted from your home for cooling.

C

Carbon Monoxide

An odourless, colourless, tasteless, poisonous and flammable gas that is produced when carbon burns with insufficient air.

Capacity or Load

A refrigeration rating system usually measured in Btu/h or kW/h.

Capillary Tube

A refrigerant control consisting of a small diameter tube which controls flow by restriction. They are carefully sized by inside diameter and length for each particular application.

CFM

Stands for Cubic Feet per Minute. This measurement indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being moved through the ductwork by the system.

Charge

The amount of refrigerant in a system.

Check Valve

A valve designed to permit flow in one direction only.

Coil

A heating or cooling element made of pipe or tubing, usually with plates or fins.

Commissioning

The final step in installing a heating or air conditioning system. Every component is checked and tested for compliance with codes, manuals, manufacturer requirements, and occupant needs. After commissioning, the technician will provide documentation of testing, provide all equipment manuals, and show the homeowner how to operate the system.

Compression

The reduction of volume of a vapor or gas by mechanical means.

Compression Ratio

The ratio determined by dividing the discharge pressure, in PSI (Pa), by the suction pressure in PSI (Pa).

Compressor

A mechanical device used to compress gases. Three main types – reciprocating, centrifugal and rotary.

Condenser (Heat Exchanger)

The outside unit of a heating or air conditioning system. Here the refrigerant condenses from a gas to a liquid and hot or cold air from the building is released to the outside.

Condensation Point

The temperature at which the removal of any heat will begin a change of state from a vapour to a liquid.

Condensing Medium

The substance, usually air or water, to which the heat in a condenser is transferred.

Condensing Unit

The portion of a refrigeration system where the compression and condensation of refrigerant is accomplished.

Conduction

The transfer of heat from molecule to molecule within a substance.

Contactor

An electromagnetic actuated relay. Usually used to refer to the relay which closes the circuit to a compressor.

Convection

The transfer of heat by a moving fluid.

Cooling Anticipator

A resistance heater (usually not adjustable) in parallel with the cooling circuit. It is ‘on’ when the current is ‘off”, adding heat to shorten the off cycle.

COP

Coefficient of performance. Ratio of work performed or accomplished as compared to the energy used. The higher the COP the more efficient a system is.

Cycle

The complete course of operation of a refrigerant back to a selected starting point in a system.

Cycling

Refers to the process of an HVAC system turning on and off. Some systems require less cycling than others, leading to higher energy efficiency and less wear on the system.

D

Damper

Found in ductwork, this movable plate opens and closes to control airflow. Dampers are used effectively in zoning to regulate airflow to certain rooms.

Dehumidifier

A device that removes excess moisture from the air.

Density

Mass or weight per unit of volume.

Discharge Line

A tube used to convey the compressed refrigerant vapour from the compressor to the condenser inlet.

Discharge Pressure

The pressure read at the compressor outlet. Also called head pressure or high side pressure.

Dry Air

Air which contains zero moisture vapour.

Dry Bulb Temperature (DBT)

Temperature read with an ordinary thermometer.

Duct

Conduits used to carry air. They can be round or rectangular, sheet metal or fibreglass or vinyl tubes. In air conditioning systems they carry air from the home to the air conditioning system or furnace and back to the home.

Dual Fuel System

A heating solution that combines a furnace and a heat pump to provide an economical way to heat a home. A heat pump is activated for moderate heating needs and a furnace is switched on when higher levels of heat are needed. This system helps maximise the energy efficiency of each unit.

E

EER (Energy Efficiency Ratio)

A ratio to determine the energy efficiency of an air conditioner. The higher the EER rating, the more efficient the unit. EER ratings are generally lower than SEER ratings because SEER ratings are seasonally adjusted while EER ratings are calculated against a fixed ambient temperature.

Effective Temperature

An arbitrary concept which combines into a single value the effect of temperature, humidity, and air movement as sensed by the human body.

External Static Pressure (ESP)

The measure of static pressure losses from ductwork, fittings, dampers, grilles, and any other devices located in the airstream. ESP listed in the equipment specification charts is the amount of external static loss that the unit lower can overcome at a specific CFM.

ENERGY STAR®

A government supported branding used to identify energy efficient products.

ERV

Energy Recovery Ventilator; a machine that draws fresh air into the home and exhausts stale air from the home. It uses a process to preheat or pre-cool (depending on the season) to reduce energy costs associated with conditioning the air.

Evaporative Cooling

The cooling effect of vapourisation of a liquid in a moving air stream.

Evaporator

A device in which a liquid refrigerant is vapourised. Some superheating usually takes place.

Evaporator Superheat

The actual temperature of the refrigerant vapour at the evaporator exit as compared to the saturated vapour temperature indicated by the suction pressure.

External Static Pressure

The sum of the static and velocity pressures of a moving air system at the point of measurement.

F

Fancoil

See Air Handling Unit

Fresh Air Intake

An opening through which outdoor air is drawn into a system.

Furnace

A self-contained heating unit that is designed to deliver heated air to a home.

H

Heat pump”

An air-conditioning system that can reverse the direction of refrigerant flow to provide either cooling or heating to the indoor space.

HEPA Filter

A High Efficiency Particulate Absorbing filter. A HEPA filter removes particles from the air by trapping them as air flows through.

HSPF (Heating Season Performance Factor)

A rating of the seasonal efficiency of a heat pump unit when operating in the heating mode.

HVAC

The classic acronym for Heating, Ventilation and Air Conditioning. Today, an HVAC system also includes air cleaning and moisture control.

Heat Exchanger

1. The part of a furnace that transfers heat from burning fuel to the air used to heat your home. Also, from a boiler to water for hydronic heating.
2. A device, such as a condenser or evaporator, in which heat is added or removed in order to heat or cool your home.

Heat Pump

A single refrigeration system designed to provide both heating and cooling. Compare to a furnace and an air conditioner, separate units that only heat or cool.

HRV

Heat Recovery Ventilator, a machine that brings fresh air into a home through a process that preheats the air so it has less impact on your utility bill.

Humidifier

A device that adds moisture to warm air for your home.

Humidity

A measure of the amount of moisture in the air.

Hybrid Comfort System

A home comfort system that combines a heat pump with a gas furnace (also available in packaged systems). For areas with colder temperatures, combining electric heating (heat pump) with gas heating (furnace) lets you choose from two fuel sources in order to respond to fluctuations in utility costs.

K

kW

The kW is a unit of energy. 1 kW = 3600 kJ = 3412 Btu.

L

Load Calculation

A mathematical determination of how much cooling and heating (BTUs or kWs) an HVAC system must deliver for occupant safety and comfort. It is based on a variety of factors: square meterage, building orientation, number of occupants, size and placement of rooms, number and size of windows and doors, amount of insulation, number of floors, and climate.

Latent Heat

The energy that suspends moisture vapour in the air.

Liquid Line

A tube used to convey the liquid refrigerant from the condenser outlet to the refrigerant control device of the evaporator.

M

Micron

A unit of measure equal to one millionth of a meter, or one thousandth of a millimetre.

Microprocessor

An electrical component consisting of integrated circuits, which may accept, store, control, and output information

Modulating Heating

Fully modulating heating provides greater fuel efficiency and ideal comfort control by constantly adjusting to changing temperatures in your home.

Mould

A natural byproduct of the fungi family that thrives when organic substances and water combine under certain circumstances. Mould reproduces via spores that can remain dormant, yet viable, for years. Many moulds are beneficial. For example, they are the “blue” in blue cheese, and we use them to make wine, penicillin, and antibiotics. However, some moulds can cause health problems.

O

Off-grid or Off-the-grid

An off-grid electricity-generating system operates independently from the utility grid, providing all of the electricity needed in the home. Stand-alone systems are much more expensive than grid-tied systems. However, for homes located in remote areas without utility service, or where installing power lines would be extremely costly, a stand-alone system is a good option.

Outdoor Unit

A component of an air-conditioning system which contains compressor, propeller fan, circuit board, and heat exchange coil. It pumps refrigerant to/from the indoor unit.

P

Particles

Any substances measuring less than 100 microns in diameter. The EPA has found that small particles (less than 2.5 microns) are responsible for the health effects of greatest concern.

Pitot Tube

A device comprising a small diameter orifice projecting directly into an air stream measuring total pressure and surrounded by an annular section with small diameter entrances normal to the flow, measuring static pressure; both sections are usually connected to a manometer to indicate velocity pressure.

Pumpdown

Process of pumping refrigerant out of the evaporator and suction line at the end of the on-cycle by closing a solenoid valve in the liquid line and letting the compressor shut-off by the low pressure control.

Psychrometer

A device having both a dry and wet bulb thermometer. It is used to determine the relative humidity in a conditioned space. Most have an indexed scale to allow direct conversion from the temperature readings to the percentage of relative humidity.

Psychrometric Chart

A chart on which can be found the properties of air under varying conditions of temperature, water vapour content, volume, etc.

R

R-22

An HCFC (hydrochlorofluorocarbon) refrigerant, often referred to by a brand name such as Freon®, used primarily in residential air conditioning systems. It is being phased out for its higher global warming potential (GWP) and ozone depleting properties.

R-410A

A non-ozone depleting refrigerant that has replaced R-22 as the preferred refrigerant of choice in the U.S., Japan, Europe & Australasia. R-410A performs at a higher pressure than R-22 and requires the use of different equipment than with R-22.

Refrigerant

A gas/liquid substance used to provide cooling by direct absorption of heat.

Refrigerant Lines

Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.

Refrigerant Charge (or, “charging the refrigerant”)

The procedure an HVAC technician performs to ensure that the system has enough of the right kind refrigerant for peak operating performance.

Refrigerant Operating Charge

The total amount of refrigerant required by a system for correct operation.

Relative Humidity (RH)

The percent of moisture actually in the air compared to the maximum amount of moisture the air can hold at that temperature.

Return Air

The air drawn into the heating unit after having been circulated through a room.

Reversing Valve

A device in a heat pump that is electrically controlled to reverse the flow of refrigerant as the system is switched from cooling to heating; also called a four-way valve.

Room Air Conditioner (Window Unit)

Standalone air conditioning unit that cools only where needed, usually installed in a window space. Generally less efficient than central air conditioning, but less expensive to operate.

S

Scroll Compressor

A specially designed compressor that works in a circular motion, as opposed to up-and-down piston action.

Slugging

A condition in which a quantity of liquid enters the compressor causing hammering and possible compressor damage.

Smart Home

A smart home features an advanced system that offers remote or automatic control of the systems around your home, including but not limited to, your HVAC system, lighting or security system.

SEER (Seasonal Energy Efficiency Ratio)

A rating of the seasonal efficiency of air-conditioning or heating units in cooling mode.

Split System

The most common type of residential system, it consists of two main components – a compressor and condensing unit installed outdoors, and an air-handler installed indoors.

Split-Ductless System

A system comprised of a remote outdoor condensing unit connected by refrigerant pipes to a matching, non-ducted indoor air handler and a remote controller. Special cases for introducing ventilated air may call for limited ducting to air handler from outside.

Split-Ducted System

A system comprised of a remote outdoor condensing unit connected by refrigerant pipes to a matching, ducted indoor air handler with minimal field installed ductwork and a wired remote controller.

Split-zoning System

A system comprised of a remote outdoor condensing unit connected by refrigerant pipes to a matching, indoor air handler that conditions single or multiple room space that is conditioned to a set temperature and is independent from other rooms within the same structure.

Static Pressure

The normal force per unit area at a small hole in the wall of a duct.

Sub Cooling

Cooling of a liquid, at a constant pressure, below the point at which it was condensed.

Sublimation

A condition where a substance changes from a solid to a gas without becoming a liquid.

Suction Line

A tube used to convey the refrigerant vapour from the evaporator outlet to the suction inlet of the compressor.

Suction Line Accumulator

A device located in the suction line that intercepts quantities of a liquid refrigerant and thereby prevents damage to the compressor.

Superheat

Heat added to a vapour after all liquid has been vapourised.

T

Thermistor

A semiconductor which has electrical resistance that varies inversely with temperature.

Thermostat

A temperature-control device, typically found on a wall inside the home. It consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system.

Ton

A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.

Tonnage

A unit of measure used to describe the cooling capacity of an air conditioning system. One ton of cooling is the amount of heat needed to melt a one ton block of ice in a 24 hour period.

V

Variable Speed Motor

The fan motor inside higher efficiency indoor and outdoor units is designed to change its speed based on your home’s heating and air conditioning requirements. Working in conjunction with your thermostat, it keeps the appropriate-temperature air (e.g., warm air on cold days) circulating throughout your home, reducing temperature variances. The variable-speed motor also increases dehumidification and is quiet because it runs at a lower speed most of the time. Plus, the consistent air circulation eliminates noisy startups and shutdowns.

Velocity Pressure

In a moving fluid, the pressure capable of causing an equivalent velocity as applied to move the same fluid through an orifice such that all pressure energy expended is converted into kinetic energy.

W

Water Manometer

Used to measure pressure in inches of water.

Wet Bulb Temperature (WBT)

Temperature read with a thermometer whose bulb is encased in a wetted wick.

Z

Zoning

A method of providing independent heating or cooling to different areas or rooms within a building or home, typically controlled by separate controls or by opening or closing the vents and ducts in each zone.

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