HVAC Terms

Air Conditioner Unit - HVAC Terms

There are several HVAC terms that your friendly Air Conditioning installer or repairman may use that may be unfamiliar to you. We hope that this list of HVAC terms and their definitions will help you to understand what he is trying to tell you. Air conditioning Arlington Tx (TNS Mechanical, LLC), technicians, of course, will try to explain things in layman’s terms. But, with a subject this specialized it is often difficult to communicate unless both people share a common vocabulary.

So, for those interested, here is a list of HVAC terms (Heating, Ventilation, and Air Conditioning). Some of the terms will be very familiar and some will not. A special thanks goes to Wikipedia for their help in providing definitions for this list.

HVACHVAC (Heating, Ventilation, and Air Conditioning) is a major sub-discipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency.

air changes per hour – The number of times per hour that the volume of a specific room or building is supplied or removed from that space by mechanical and natural ventilation. Abbreviated ACH.

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.

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. Abbreviated AH or AHU.

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. Abbreviated BTU or Btu.

Capacity – The rate at which the heating or cooling load
can be satisfied by a given equipment.

CFC – Chlorofluorocarbons are liquid refrigerants used in
air conditioners and heat pumps.

chiller – A device that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This cooled liquid flows through pipes in a building and passes through coils in air handlers, fan-coil units, or other systems, cooling and usually dehumidifying the air in the building. Chillers are of two types; air-cooled or water-cooled. Air-cooled chillers are usually outside and consist of condenser coils cooled by fan-driven air. Water-cooled chillers are usually inside a building, and heat from these chillers is carried by recirculating water to a heat sink such as an outdoor cooling tower.

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.

Compressor – a reciprocating or rotating device that
compresses a gas for reducing volume and increasing pressure of gases in order to condense those gases.

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 or an aqueous solution of ethylene glycol) to carry heat to a distant sink, such as ground (earth sink), a body of water, or air (as with cooling towers).

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. Abbreviated CAV.

controller – A device that controls the operation of part or all of a system. It may simply turn a device on and off, or it may more subtly modulate the set point of components. Most controllers are automatic but have user input such as temperature set points, e.g. a thermostat. Controls may be analog or digital.

damper – A plate or gate placed in a duct to control air flow by increasing friction in the duct.

deep lake water cooling – The heat is rejected to deep lake regions to cool homes and offices, reducing the energy costs.

Dehumidifier – A device that removes excess moisture from the air.

ΔT – (Also delta T) a reference to a temperature difference. It is used to describe the difference in temperature of a heating or cooling fluid as it enters and as it leaves a system.

duct – Specialized housing for the air flow.

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.

Energy Star® – A government supported branding used to signify more energy efficient products. The branding was developed by the US DOE and the US EPA.

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.

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. Abbreviated FCU.

flow – A transfer of fluid volume per unit time.

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. Abbreviated FAI.

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.

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.

HCFC – These are the hydro chlorofluorocarbons that are used as a refrigerant in air conditioners and heat pumps.

Heat Exchanger – The part of a furnace that takes heat from burning fuel and transfers it to the air which is used to heat your home. Also, a device, such as a condenser or evaporator, in which heat is added or removed in order to heat or cool your home.

heat load, heat loss, heat gain –  Terms for the amount of heating (heat loss) or cooling (heat gain) needed to maintain desired temperatures and humidities 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. Engineers use a heat load calculations to determine the HVAC needs of the space being cooled or heated.

Heat Pump – A heat pump is a heat transfer machine. It collects heat from one area (where it is not wanted) and deposits it in another (where it is desired). Therefore, it can act as either a heating device or a cooling device.

HFC – Hydroflorocarbon: This is used as a refrigerant in air conditioners and heat pumps.

HRV – Heat Recovery Venilator: 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 for adding moisture to warm air for your home.

Infiltration – This is unwanted “outside air” that enters your home through holes, gaps, and cracks.

intermediate fluid –  A liquid or gas used to transfer heat between two heat exchangers. An intermediate fluid is used when the hot and cold fluids are too bulky (such as air) or difficult to handle (such as halocarbon refrigerant) to directly transfer the heat.

Latent Heat – This is the energy that suspends moisture vapor in the air.

Load – The quantity of heat that must be added to or removed from the home to satisfy a specific level of service,i.e., to keep the space temperature at a specified thermostat setting.

louver – 1) Components made of multiple smaller blades, sometimes adjustable, placed in ducts or duct entries to control the volume of air flow. When used inside of ducts, their function is similar to that of a damper, but they can be manufactured to fit larger openings than a single-piece damper. 2) Blades in a rectangular frame placed in doors or walls to permit the movement of air.

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. Abbreviated MAU.

minimum outside air –  The lowest amount of fresh air flow that can be allowed into a recirculating system. This limit is sent to ensure that the interior air remains safe and comfortable to breathe.

Mold – a coating or discoloration caused by various fungi that develop in a damp atmosphere. Many molds are beneficial. For example, we use them to make penicillin, and antibiotics. But some molds can cause health problems.

NATE – North American Technician Excellence, the nonprofit organization that tests and certifies HVACR technicians.

outside air damper –  An automatic louver or damper that controls the fresh air flow into an air handler and modulates to the most energy efficient setting.

PMA – Planned Maintenance Agreement: An agreement or contract between a HVAC company and their customer which provides regular maintenance of the customer’s HVACR system.

packaged terminal air conditioner –  An air conditioner and heater combined into a single, electrically-powered unit, typically installed through a wall and often found in hotels. Abbreviated PTAC.

packaged unit or rooftop 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. Abbreviated RTU.

plenum space –  An enclosed space inside a building or other structure, used for airflow. Often refers to the space between a dropped ceiling and the structural ceiling or a raised floor and the hard floor. Distinct from ductwork as a plenum is part of the structure itself. Cable and piping within a plenum must be properly rated for its fire and smoke indices.

psychrometric – The study of the behavior of air-water vapor mixtures. Water vapor plays an important role in energy transfer and human comfort in HVAC design.

R-22 – (Freon) This is a refrigerant used in air conditioning systems which contains chlorine. The EPA has stated that R-22 cannot be manufactured after 2010.

R-410A – This is the refrigerant that replaces R-22. It does not contain chlorine and, by current standards does not appear to be hazardous to the environment.

Refrigerant – This is a fluid that absorbs heat at low temperatures and rejects heat at higher temperatures.

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

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 Side, Return, Return Air – The path the air takes to get to an air-handling unit or furnace so it can be cooled or heated. It is the “return” path.

SEER – The SEER (Seasonal Energy Efficiency Ratio) rating normally refers to electric air conditioning equipment.It is a measurement of the instantaneous energy efficiency of cooling equipment. EER, on the other hand is the steady-state rate of heat energy removal by the equipment.

smoke damper – A damper or adjustable louver designed to augment the ventilation of a space during a fire.

Split System – This is a two-component heating and cooling (heat pump) or cooling only (air conditioner) system. The condensing unit is installed outside the home and the air handling unit is installed inside the home.

Supply, Supply Side – The part of a cooling/heating system that “supplies” the conditioned air from the air-handling unit or furnace to your home.

system –  General term used to refer to the set or a subset of components that perform a specific HVAC function within a building.

terminal unit –  A small component that contains a heating coil, cooling coil, automatic damper, or some combination of the three. Used to control the temperature of a single room. Abbreviated TU.

thermal zone –  An individual space or group of neighboring indoor spaces that the HVAC designer expects will have similar thermal loads. Building codes may require zoning to save energy in commercial buildings. Zones are defined in the building to reduce the number of HVAC subsystems, and thus initial cost. For example, for perimeter offices, rather than one zone for each office, all offices facing west can be combined into one zone. Small residences typically have only one conditioned thermal zone, plus unconditioned spaces such as garages, attics, and crawlspaces, and basements.

Thermostat – A device that measures the temperature of the air in the home and turns on/off the heating or cooling equipment in order to make the air temperature remain within a pre-specified range.

Ton – A measurement term used by the air conditioning industry to characterize the cooling capacity of A/C equipment. (1 ton = 12,000 Btu/h).

underfloor air distribution – A method for providing ventilation and space conditioning by using the air plenum below a raised floor to distribute conditioned air through diffusers directly to the occupied zone. Abreviated UFAD.

variable air volume –  An HVAC system that has a stable supply-air temperature, and varies the air flow rate to meet the temperature requirements. Compared to constant air volume systems, these systems conserve energy through lower fan speeds during times of lower temperature control demand. Most new commercial buildings have VAV systems. VAVs may be bypass type or pressure dependent. Pressure dependent type VAVs save energy while both types help in maintaining temperature of the zone that it feeds. Abbreviated VAV.

Zoning, Zones, Zoned System – A single HVAC system that can meet the different heating and cooling needs of two or more different areas (zones) in the home or business. Each zone has its own temperature control (thermostat).

Why We Compiled This List of HVAC Terms

We hope that this glossary of HVAC Terms has helped you to understand some of the lingo that your Air conditioning service representative might use as you seek to buy or repair your air conditioning in Arlington Tx.

Hvac Terms