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HVAC Terms and Definitions

The Heating, Ventilating & Air Conditioning, or HVAC, industry has it’s own technical language. In order to make it easier for you to understand the terms and acronyms we use, here are the most often used HVAC technical terms with their definitions. Feel free to ask us to help you understand any other technical words we use.

13 SEER: This is the new minimum efficiency standard (effective January 2006) for an air conditioner or heat pump. All new units must now meet this standard. Previously manufactured equipment may be used, sold, and installed. SEER is defined later.

ACCA: The Air Conditioning Contractors of America, a national trade association that represents heating, ventilation, air conditioning, and refrigeration contractors.

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

AFUE (Annual Fuel Utilization Efficiency): A measurement of the seasonal energy efficiency of gas heating equipment. It is the annual output energy of the equipment divided by its annual input energy, expressed in consistent units (i.e. Btu-out per Btu-in). Thus, the resultant value of AFUE is unitless. AFUE includes any input energy required by the pilot light but does not include any electrical energy or fans or pumps.

Ambient Temperature: The air temperature (usually the outdoor air temperature) surrounding the heating or cooling equipment.

Balancing or Air Balancing: Adjusting an air conditioning system so that the right amount of air is delivered to the right places in the building in order to achieve the desired heating or cooling effect at the most efficient rate.

Blower: An air handling device for moving air in a distribution system.

Boiling Point: The temperature at which the addition of any heat will begin a change of state from a liquid to a vapor.

BTU: Stands for British Thermal Unit — the amount of heat required to raise the temperature of one pound of water by one degree (Fahrenheit). Used to describe a device’s heating or cooling capacity. One BTU is approximately equal to the heat given off by a wooden kitchen match.

BTU/H: British Thermal Unit/per hour. One of the two (watts-hours is the other) standard units of measure ( IP System) for the amount of energy consumed by a process, the amount of energy transferred from one location to another, or the amount of embodied energy (such as the heat contents of fuels). Specifically, it is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. The term ‘kbty’ stands for “kiloBtu” or 1,000 Btu. The term of ‘Mbtu’ stands for “MegaBtu” or 1,000,000 Btu. One Btu/his equal to 0.293 watt-hours (Wh).

Capacity: The rate at which the heating or cooling load can be satisfied by a given equipment system designed to heat or cool and dehumidify a conditioned space or heat service hot water. Heating and cooling capacity is normally given on equipment nameplates in units of Btu/h. The air conditioning industry often uses units of “tons” to refer to equipment capacity. One ton of capacity equals 12,000 Btu/h.

Centrifugal Compressor: A type of compressor used in vapor compression refrigeration cycles where a rotating impeller is the device which compresses the refrigerant vapor. The vapor is drawn into the impeller axially, and is discharged radially after energy is added to the vapor within the impeller.

CFC: Chlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps, linked to the depletion of the ozone layer.

CFM: Stands for Cubic Feet per Minute. Commonly used to measure the rate of air flow in an air conditioning system. The higher the number, the more air is being forced through the system.

Compressor: A reciprocating or rotary pump for raising the pressure of air or another gas; this may be a single-stage or multistage unit. Reciprocating Compressor: a machine that compresses gases, composed of one or several cylinders; each cylinder contains a piston that is moved by a crankshaft through a connecting rod. Rotary Compressor: a machine having a rotating member that directly compresses fluid in an enclosed housing; the fluid pressure rises as the volume of the closed space decreases.

Condensation Point: The temperature at which the removal of any heat will begin a change of state from a vapor to a liquid.

Condenser: A device that transfers unwanted heat out of a refrigeration system to a medium that absorbs the heat and transfers it to a disposal point. There are three types of condensers: air-cooled condensers, water-cooled condensers, and evaporative condensers.

Condenser Coil: A series of tubes filled with refrigerant, normally located outside the building that removes heat from the hot, gaseous refrigerant so that it becomes liquid again.

Condensing Unit: Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control. It’s the outdoor section of a split system air conditioner or heat pump.

Cooling Capacity: A measure of the ability of a unit to remove heat from an enclosed space.

Cooling Load: Heat which flows into a space from outdoors and/or indoors.

COP: Coefficient of Performance: A measurement of the instantaneous efficiency of heating or cooling equipment. It represents the steady-state rate of energy output of the equipment divided by the steady-state rate of energy input to the equipment, expressed in consistent units(i.e. watts-out per watts-in or Btu/h-out per Btu-in). Thus, the resultant value of COP is unitless. Most vapor-compression heating and cooling equipment has COPs greater than unity. That means it delivers more heat energy than it consumes.

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, ACCA manuals, manufacturer requirements, and occupant needs. After commissioning, the technician will: provide documentation of testing, provide all equipment manuals, and ensure the system operates as specified.

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.

Damper: A valve or movable plate used in duct work that opens or closes to control airflow. Used in zoning to regulate the amount of warm or cool air entering certain rooms in a building.

Dehumidification: The reduction and removal of water vapor in air by cooling the air below the dew point.

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

Downflow Air Conditioner: A type of precision air conditioning system that discharges air downward, directly beneath a raised floor. Commonly found in computer rooms and modern office spaces.

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

EER: Stands for Energy Efficiency Ratio — a measurement of the efficiency with which a product uses energy to function. It is calculated by dividing a product’s BTU output by its wattage.

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 program that helps businesses and individuals protect the environment through superior energy efficiency. Products earn the Energy Star rating by meeting strict anti-pollution and energy-efficiency guidelines set by the Environmental Protection Agency and the Department of Energy. Products with the Energy Star rating will help you use less energy and save on utility bills.

EPA: The U.S. Environmental Protection Agency.

Filter: A device used to remove dust and other particles from air to provide healthier air quality and to protect the HVAC equipment. The higher the MERV rating, the better the filter. (see MERV)

Freon: (See R-22)

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

HCFC: Hydrochlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps. HCFCs were thought to contribute to the depletion of the earth’s ozone layer.

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 heat pump is a heat transfer machine, collecting heat from one area (where it is not wanted) and depositing it in another (where it is wanted). Therefore, it can act as a heating as well as a cooling device.

HFC: Hydroflorocarbon, used as a refrigerant in air conditioners and heat pumps. It has little or no effect on the ozone layer.

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 for adding moisture to warm air for your home.

HVAC: Heating, ventilating, and air conditioning

HVACR: Heating, ventilating, air conditioning and refrigeration

Infiltration: Air that enters your home through holes, gaps, and cracks, (e.g., plumbing or electrical holes, the heating and air conditioning system, doors, and windows).

IAQ: Indoor air quality

Kilowatt (kW): A measurement of the energy output of a device. Equal to 1,000 watts.

Kilowatt-Hour (kWh): A common unit of electrical consumption measured by the total energy created by one kilowatt in one hour.

Latent Heat : The energy that suspends moisture vapor in the air.

Load: The quantity of heat that must be added to or removed from the building (or the hot water tank) to satisfy specific levels of service – in other words, to keep the space temperature or hot water temperature at a specified thermostat setting ( see also the definitions of energy and thermostat).

Load Calculation: A mathematical determination of how much cooling and heating (BTUs) an HVAC system must deliver for occupant safety and comfort. It is based on a variety of factors: square footage, 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.

Matched System: An air conditioner or heat pump system composed of equipment that has been certified by ARI to work together to deliver the specified heating and cooling capacity at the stated efficiency rating.

MERV: Stands for Minimum Efficiency Reporting Value. A measurement of air filter’s ability to remove particles from 3 to 10 microns in size. The MERV scale ranges from 1 (least efficient) to 16 (most efficient).

Mold: A natural byproduct of the fungi family that thrives when organic substances and water combine under certain circumstances. Mold reproduces via spores that can remain dormant, yet viable, for years. Many molds are beneficial, however some molds can cause health problems.

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

Packaged System: A self-contained heating and/or air conditioning system which has all components located in one cabinet. It is placed on the ground, on the roof, or sometimes mounted through the walls of the building.

R-22: A refrigerant containing chlorine used in air conditioning systems. The EPA has mandated that R-22 cannot be manufactured after 2010 because it has been linked to the depletion of the ozone layer and global warming. Most commonly referred to by its trademarked name, Freon.

R-410A: The refrigerant that replaces R-22. It does not contain chlorine and is not hazardous to the environment.

Refrigerant: A fluid that absorbs heat at low temperatures and rejects heat at higher temperatures.

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.

Register: A combination grille and damper assembly covering an air opening or end of an air duct.

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, Return Air, Return Side: 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. The return side should be “balanced” with the supply side to ensure proper air flow and comfort.

(S)EER (Seasonal) Energy Efficiency Ratio: A measurement of the instantaneous energy efficiency of cooling equipment. It normally is used only for electric air conditioning equipment. EER is the steady-state rate of heat energy removal by the equipment in Btu/h divided by the steady-state rate of energy input to the equipment in watts. Thus, the resultant value for EER has units of Btu/Wh. The EER of a given system is always higher than the COP of that system by a factor equal to the number of Btu/h in a watt, or 3.413.

Sensible Heat: The temperature of the air. This type of heat is measured with a thermometer.

Setback Thermostat: A electronic thermostat with a built-in memory that can be programmed for different temperature settings at different times of the day.

Split System: A two-component heating and cooling (heat pump) or cooling only (air conditioner) system. The condensing unit is installed outside, the air handling unit is installed inside (preferably in conditioned space). Refrigerant lines and wiring connect them together.

Subcooler: This is a section of some condensers in which the temperature of the condensed refrigerant liquid is reduced. This improves the energy efficiency of the chiller.

Supercooled Liquid: Liquid refrigerant cooled below its saturation point.

Superheated Vapor: Refrigerant vapor heated beyond its saturation point.

Superheating: Creating a rise in temperature by adding heat energy to a refrigeration vapor.

Supply or Supply Side: The part of an HVAC system that takes (supplies) the conditioned air from the air-handling unit or furnace to your home. The supply side should be “balanced” with the return side to ensure proper air flow and comfort.

Thermostat: A control device that measures the temperature of the air in a home or the water in a hot water tank and activates the heating or cooling equipment to cause the air or water temperature to remain at a pre-specified value, normally called the set point temperature (see also the definitions of load and energy).

Ton (or Tonnage): Not 2,000 lbs by weight, but a unit of measure used to describe the cooling capacity of an air conditioning system. One ton of cooling is based on the amount of heat needed to melt one ton (2,000 lbs.) of ice in a 24 hour period (equal to 12,000 BTUh).

VRF (or VRV): VRF (Variable Refrigerant Flow) uses refrigerant as the cooling and heating medium, and allows one outdoor condensing unit to be connected to multiple indoor fan-coil units (FCUs), each individually controllable by its user, while modulating the amount of refrigerant being sent to each evaporator. By operating at varying speeds, VRF units work only at the needed rate allowing for substantial energy savings at partial-load conditions. Heat recovery VRF technology allows individual indoor units to heat or cool as required, while the compressor load benefits from the internal heat recovery

Zones, Zoned System, Zoning: A single HVAC system that can meet different heating and cooling needs in different areas (zones). Each zone of a home has its own thermostat with which it can regulate the temperature and humidity in its area. One “zoned air conditioner” could be set for a high temperature in one zone and for a lower temperature in the other zone. Zone systems have two or more zones.

I have confidence in Cooper Oates and would hire this company over any other HVAC company in the state.

Janet Rollins
Sacramento County Public Law Library

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Your team was very professional and detailed. The installers worked very hard and did an excellent job installing the units.

Joanne Kim
Rehabilitation Management Systems, Inc.

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I would like to thank you all for the successful completion of the HVAC redesign in the Bureau of Nursing.

Mark Elliott
Department of Consumer Affairs

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Awesome—You tell the bosses over there that your service tech is incredible—fast, knowledgeable…

Rhonda Higgins
DMG North, Inc.

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Dispatch is always available, whether I’m in the office, inspecting properties or out of town. COAC eases property…

Sharyn Verdon
Ramco Enterprises, Inc.

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I have confidence in Cooper Oates and would hire this company over any other HVAC company in the state.

Janet Rollins
Sacramento County Public Law Library

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What a nice change from what we have dealt with for years. This has made a piece of my job tons easier.

Teresa Heckley, ASO II
DHHS - Facility Management

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We want you to know that we are very pleased with the service you gave us, I especially want to thank you…

Tom Cabrera
Mailing Systems, Inc.

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I have confidence in Cooper Oates and would hire this company over any other HVAC company in the state.

Janet Rollins
Sacramento County Public Law Library

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I have confidence in Cooper Oates and would hire this company over any other HVAC company in the state.

Janet Rollins
Sacramento County Public Law Library

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