HVAC systems by Robertson HVAC - Heating, Ventilation, Air Conditioning

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 Conditioning Engineers.

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 second (l/s).

Combustion Air - Air that provides the necessary oxygen for complete, clean combustion and maximum heating value.

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 cooled.

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 space.

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 per hour.

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 or recuperation.

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 hour.

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 comfort.

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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