HVAC Glossary of Terms
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Air Balance - HVAC term for distributing air
through a system to precisely match the required amount.
Air Diffuser - HVAC term for an air
distribution outlet, typically located in the ceiling, which mixes
conditioned air with room air.
Air Exchange Rate - In HVAC the rate at which
outside air replaces indoor air in a space. Expressed in one of two
ways: the number of changes of outside air per unit of time - air
changes per hour (ACH); or the rate at which a volume of outside air
enters per unit of time - cubic feet per minute (CFM).
Air Handling Unit (AHU) -In HVAC refers to
equipment that includes a blower or fan, heating and/or cooling
coils, and related equipment such as controls, condensate drain
pans, and air filters. Does not include ductwork, registers or
grilles, or boilers and chillers.
Air Proving Switch -
Confirms air flow through ductwork. Commonly used with electric duct
heaters as a safety control that will not allow the heater to come
on unless air flow through the heater is confirmed.
Ambient Air - The air external to a building or device.
ASHRE - American Society of Heating Refrigeration and Air
Blower - In HVAC the fan in
an air conditioner that distributes the filtered air from the return
duct over the coil/heat exchanger. This circulated air is
cooled/heated and then sent through the supply duct, past dampers,
and through supply diffusers to the living/working space.
British Thermal Unit (BTU) - The amount of heat required to
raise the temperature of one pound of water one degree Fahrenheit,
equal to 252 calories.
CFM Cubic feet per minute -
HVAC term for the amount of air, in cubic feet, that flows through a
given space in one minute. 1 CFM equals approximately 2 litres per
Combustion Air - Air that provides the
necessary oxygen for complete, clean combustion and maximum heating
Compressor - A device used to compress air or
gases for mechanical or electrical power production, and in air
conditioners, heat pumps, and refrigerators to pressurize the
refrigerant; enabling it to flow through the system and to change
refrigerant from a gas to a liquid thus allowing the condenser to
release the heat to the outside when the pressure is released.
Condenser - The device in an air conditioner
or heat pump in which the refrigerant condenses from a gas to a
liquid when it is depressurized or cooled.
Condensate - A fluid formed when a gas is
Condenser Coil - The device in an air
conditioner or heat pump through which the refrigerant is circulated
and releases heat to the surroundings when a fan blows outside air
over the coils. This will return the hot vapour that entered the
coil into a hot liquid upon exiting the coil.
Convection - Transfer of heat from one point
to another by means of gravity.
Cooling Capacity - The quantity of heat that
a cooling appliance is capable of removing from a room in one hour.
Direct Vent - Pulls outside
air for combustion and vents combustion gases directly outside.
Draft Hood - A device built into or installed
above a combustion appliance to assure the escape of combustion
by-products, to prevent back drafting of the appliance, or to
neutralize the effects of the stack action of the chimney or vent on
the operation of the appliance.
Electronic Air Cleaner - An
electronic device that filters out large particles and contaminants
in indoor air. It then electronically pulls out tiny particles that
have been magnetized, such as viruses and bacteria, drawing them to
a collector plate.
Emergency Heat - The back-up heat built into
a heat pump system that is started when the outdoor temperature has
is too low for the heat pump to be efficient.
Fire Damper - A damper
installed in a duct system that is normally open, upon the breakage
of a heat sensitive link the damper will close.
Forced Air System or Furnace - HVAC term for
a type of heating system which uses air blown by a fan through air
channels or ducts to rooms to transfer heat to the living or work
Heating Capacity (Also Specific
Heat) - The quantity of heat necessary to raise the temperature
of a specific mass of a substance by one degree.
Heating Load - The rate of heat flow required
to maintain a specific indoor temperature; usually measured in Btu
HVAC - HVAC is an acronym for heating,
ventilation, and air-conditioning system.
Ignition Point - The minimum
temperature at which combustion of a solid or fluid can occur.
Latent Heat - Heat that when
added to or removed from a substance causes a change of state but
not a change in temperature.
Liquid Line - The line that carries the high
temperature high pressure sub cooled liquid from the receiver line
to the metering device.
MERV Rating - The MERV
(Minimum Efficiency Reporting Value) rating of a filter describes
the size of the holes in the filter that allow air to pass through.
The higher the MERV rating, the smaller the holes in the filter, the
higher the efficiency.
Natural-Draft Furnace - A
furnace in which the natural flow of air from around the furnace
provides the air to support combustion. It also depends on the
pressure created by the heat in the flue gases to force them out
through the vent system.
Natural Ventilation - In HVAC the movement of
outdoor air into a space through intentionally provided openings,
such as windows and doors, or through non-powered ventilators such
as hoods with close to 0 resistance.
Preventative Maintenance -
Regular and systematic inspection, cleaning, and replacement of worn
parts, materials, and systems. Preventive maintenance helps to
prevent parts, material, and systems failure by ensuring that parts,
materials and systems are in good working order.
R-410A Refrigerant - A
chlorine-free refrigerant that meets the EPA's newest, most
stringent environmental guidelines.
Radiant Floor heating - A type of radiant
heating system where the building floor contains channels or tubes
through which hot fluids such as air or water are circulated. The
whole floor is evenly heated. Thus, the room heats from the bottom
up. Radiant floor heating eliminates the draft and dust problems
associated with forced air heating systems.
Refrigerant - The compound (working fluid)
used in air conditioners, heat pumps, and refrigerators to transfer
heat into or out of an interior space. This fluid boils at a very
low temperature enabling it to evaporate and absorb heat.
Refrigeration - The process of the absorption
of heat from one location and its transfer to another for rejection
Refrigeration Capacity - A measure of the
effective cooling capacity of a refrigerator, expressed in Btu per
hour or in tons, where one (1) ton of capacity is equal to the heat
required to melt 2,000 pounds of ice in 24 hours or 12,000 Btu per
Relative Humidity - A measure of the percent
of moisture actually in the air compared with what would be in it if
it were fully saturated at that temperature. When the air is fully
saturated, its relative humidity is 100 percent.
Return Air - Air that is returned to a
heating or cooling appliance from a heated or cooled space.
Rough-In - Stage in the HVAC installation
process when ductwork and any other HVAC items that go behind the
finished walls or above the finished ceiling are installed.
R-Value - A measure of the capacity of a
material to resist heat transfer. The R-Value is the reciprocal of
the conductivity of a material (U-Value). The larger the R-Value of
a material, the greater itís insulating properties.
Sensible Heat - Heat that
when added to of removed from a substance causes a change of
temperature and not a change of state.
SEER - Seasonal Energy Efficiency Ratio - A
measure of seasonal or annual efficiency of a central air
conditioner or air conditioning heat pump. It takes into account the
variations in temperature that can occur within a season and is the
average number of Btu of cooling delivered for every watt-hour of
electricity used by the heat pump over a cooling season.
SONE Rating - A Sone is an internationally
recognized unit of loudness. Sones are a linear measure like inches.
Doubling the Sone value is equivalent to doubling the loudness. To
get a sense of what one Sone represents, one Sone is equivalent to
the sound of a quiet refrigerator in a quiet kitchen
Split System Air Conditioner - HVAC term for
an air conditioning system that comes in two to five pieces: one
piece contains the compressor, condenser, and a fan; the others have
an evaporator and a fan. The condenser, installed outside the house,
connects to the furnace (central air) or several evaporators, one in
each room to be cooled, mounted inside the house. Each evaporator is
individually controlled, allowing different rooms or zones to be
cooled to varying degrees.
Static Pressure - In flowing air, the total
pressure minus velocity pressure. The portion of the pressure that
pushes equally in all directions.
Suction Line - The piping between the
evaporator outlet and the compressor inlet.
Supply Duct - HVAC term for the duct(s) of a
forced air heating/cooling system through which heated or cooled air
is supplied to rooms by the action of the fan of the central heating
or cooling unit.
Tankless Water Heater - A
water heater that heats water before it is directly distributed for
end use as required; a demand water heater.
Therm - A unit of heat containing 100,000
British thermal units (BTU).
Ton / Tonne (Air Conditioning) - A unit of
air cooling capacity; 12,000 Btu per hour.
Variable Air Volume System (VAV)
- Air handling system that conditions the air to constant
temperature and varies the outside airflow to ensure thermal
Vent - A component of a heating or
ventilation appliance used to conduct fresh air into, or waste air
or combustion gases out of, an appliance or interior space.
Ventilation - The process of moving air
(changing) into and out of an interior space either by natural or
mechanically induced (forced) means.
Ventilation Rate - The rate at which indoor
air enters and leaves a building. Expressed in one of two ways: the
number of changes of outdoor air per unit of time (air changes per
hour, or "ach") or the rate at which a volume of outdoor air enters
per unit of time (cubic feet per minute, or "cfm").
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