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Acronyms and industry terms are extremely common in the Heating, Ventilation and Air Conditioning industry. We hope that this Glossary of Terms, will help you to better understand some of the jargon that is commonly used. We know how important making an informed purchasing decision is. Understanding the industry terminology will ultimately help you to get the best performance from your home comfort system.
HVAC (heating, ventilation, and air conditioning)
The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency.
ACH or ac/hr (Air Changes per hour)
The hourly ventilation rate divided by the volume of a space. For perfectly mixed air or laminar flow spaces, this is equal to the number of times per hour that the volume the space is exchanged by mechanical and natural ventilation. Also called air change rate or air exchange rate.
A/C (Air Conditioner)
An appliance, system, or mechanism designed to dehumidify and extract heat from an area. Usually this term is reserved for smaller self-contained units such as a residential system.
AH or AHU (Air Handler or Air Handling Unit)
A central unit consisting of a blower, heating and cooling elements, filter racks or chamber, dampers, humidifier, and other central equipment in direct contact with the airflow. This does not include the ductwork through the building.
BTU/hour (British thermal unit)
Any of several units of energy (heat) in the HVAC industry, each slightly more than 1 kJ. One BTU is the energy required to raise one pound of water one-degree Fahrenheit, but the many different types of BTU are based on different interpretations of this “definition”. In the United States the power of HVAC systems (the rate of cooling and dehumidifying or heating) is sometimes expressed in BTU/hour instead of watts.
Coil
Equipment that performs heat transfer to air when mounted inside an air handling unit or ductwork. It is heated or cooled by electrical means or by circulating liquid or steam within it.
Condenser
A component in the basic refrigeration cycle that ejects or removes heat from the system. The condenser is the hot side of an air conditioner or heat pump. Condensers are heat exchangers and can transfer heat to air or to an intermediate fluid (such as water) to carry heat to a distant sink, such as ground (earth sink), a body of water, or air (as with cooling towers).
CAV (Constant Air Volume)
A system designed to provide a constant air flow. This term is applied to HVAC systems that have variable supply-air temperature but constant air flow rates. Most residential forced-air systems are small CAV systems with on/off control.
Damper
A plate or gate placed in a duct to control air flow by increasing friction in the duct.
Duct
Specialized housing for the air flow.
Dehumidifier
A dehumidifier is the equipment that extracts and removes humidity from the air. It works by cooling air to the point where water turns to liquid from vapor form and then the liquid is removed.
Diffuser
A diffuser is placed over ductwork, and it separates air with vanes going in differing directions. It evenly distributes air flow in the desired directions.
Economize
An HVAC component that uses outside air, under suitable climate conditions, to reduce required mechanical cooling. When the outside air’s enthalpy is less than the required supply air during a call for cooling, an economizer allows a building’s mechanical ventilation system to use up to the maximum amount of outside air.
Evaporator
A component in the basic refrigeration cycle that absorbs or adds heat to the system. Evaporators can be used to absorb heat from air or from a liquid. The evaporator is the cold side of an air conditioner or heat pump.
FCU (Fan Coil Unit)
A small terminal unit that is often composed of only a blower and a heating and/or cooling coil, as is often used in hotels, condominiums, or apartments.
Flow
A transfer of fluid volume per unit time.
FAI (Fresh Air Intake)
An opening through which outside air is drawn into the building. This may be to replace air in the building that has been exhausted by the ventilation system, or to provide fresh air for combustion of fuel.
Furnace
A component of an HVAC system that adds heat to air or an intermediate fluid by burning fuel (natural gas, oil, propane, butane, or other flammable substances) in a heat exchanger.
Gas Furnace Heat Exchanger
A gas furnace heat exchanger is responsible for the transfer of heat from inside the furnace into the air outside the furnace. The duct system then transfers this exchanged air to different rooms in the building or space.
Grille
A facing across a duct opening, often rectangular in shape, containing multiple parallel slots through which air may be delivered or withdrawn from a ventilated space. The grille directs the air flow in a particular direction and prevents the passage of large items.
Heating Coil
A heating coil is the part of the system that conducts heat. It allows electricity to act as fire.
Heat Exchanger
A heat exchanger is the part of the system that transfers heat from the hot parts of the machine or a system to the cold parts of the machine or system.
Heat gain/Heat load/Heat loss
Terms for the amount of cooling (heat gain) or heating (heat loss) needed to maintain desired temperatures and humidity’s in controlled air. Regardless of how well-insulated and sealed a building is, buildings gain heat from sunlight, conduction through the walls, and internal heat sources such as people and electrical equipment. Buildings lose heat through conduction during cold weather.
Heat Pump
A heat pump is a compressor that cycles hot or cold air. It is a device that is designed to move thermal energy in the opposite direction of heat flow by absorbing heat from a cold space which is released to a warmer space.
Heat Transfer
Heat transfer happens when heat moves from one area to another. It is an important and vital step in the process of cooling a space.
HSPF - (Heating Seasonal Performance Factor)
Heating Seasonal Performance Factor is the measurement of heat efficiency over the period of a heating season.
MAU (Makeup Air Unit)
An air handler that conditions 100% outside air. Typically used in industrial or commercial settings, or in "once-through" (blower sections that only blow air one-way into the building), "low flow" (air handling systems that blow air at a low flow rate), or "primary-secondary" (air handling systems that have an air handler or rooftop unit connected to an add-on makeup unit or hood) commercial HVAC systems.
Packaged Unit
An air-handling unit, defined as either "recirculating" or "once-through" design, made specifically for outdoor installation. They most often include, internally, their own heating and cooling devices. Very common in some regions, particularly in single-story commercial buildings. Also called a rooftop unit (RTU)
Radiant Floor
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 is heated from the bottom up. Radiant floor heating eliminates the draft and dust problems associated with forced air heating systems.
SEER (Seasonal Energy Efficiency Ratio)
The SEER (Seasonal Energy Efficiency Ratio) rating of a unit is the cooling output during a typical cooling-season divided by the total electric energy input during the same period. The higher the unit's SEER rating the more energy efficient it is.
Split System
A split system is the combination of an outdoor unit and an indoor unit. This is the most common type of system.
Thermostat
A thermostat is a control system that monitors and regulates a heating or cooling system. It can be used to set the desired temperature at which it keeps the environment either heated or cooled.
Two-Stage (cooling and heating)
A two-stage air conditioner is designed to operate on high and low settings during different weather conditions and seasons. The high setting is used during extreme weather, and the low setting is used during moderate weather. This type of air conditioner produces a balanced temperature and is in use for a longer period of time.
Zoning System
A zoning system sections a building or a space into zones which are controlled independently of each other. This is beneficial when different areas or rooms of a building have different temperatures as well as when the desired temperatures in different rooms are different. Temperature is controlled by different thermostats.