Absolute Pressure
The total of the indicated gage pressure plus the atmospheric pressure. Abbreviated "psia" for pounds per square inch absolute.
ACH, Air Changes Per Hour
The number of times that air in a building is completely replaced with outdoor air in one hour.
Aeration
Act of combining substance with air.
AHU (Air Handling Unit)
The part of the A/C system that contains the blower, cooling (evaporator) coil, and heater.
Air Change
The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air
Air conditioner
Equipment that conditions air by cleaning, cooling, heating, humidifying, or dehumidifying it. A term often applied to comfort cooling equipment.
Air conditioning
A process that maintains comfort conditions in a defined area.
Air Cooler
Mechanism designed to lower temperature of air passing through it.
Air Diffuser
Air distribution outlet or grille designed to direct airflow into desired patterns.
Air Diffusion
Distribution of the air in a space, called the treated space, by means of devices, called air terminal devices, in a manner so as to meet certain specified conditions, such as air change rate, pressure, cleanliness, temperature, humidity, air velocity and noise level.
Air Distribution
The transportation of a specified air flow to or from the treated space or spaces, generally by means of ductwork.
Air Handler
Fan/blower, filter and housing parts of a system.
Air Infiltration
Leakage of air into rooms through cracks, windows doors and other openings.
Air Sensor
A device that registers changes in air conditions such as pressure, velocity, temperature, or moisture content.
Air Source Equipment
Heat pumps or air conditioners that uses the outdoor air to transfer heat to and from the refrigerant in the unit.
Air Terminal Device
A device located in an opening provided at the boundaries of the treated space to ensure a predetermined motion of air in this space.
Air Turnover Rate
The amount of air required to completely recirculate the air in a room or building one time would equal an “air turnover rate” of 1.0. This term is also called the “air change rate” in some cases.
Air Turnover Unit
Equipment typically located in the space to be conditioned that uses a high sidewall supply and low sidewall return concept to heat or cool the space. These units are typically made up of several sections stacked vertically and can include filters, heating sections, cooling coil sections, and air distribution sections as required by the application.
Air Vent
A fitting used to vent air manually or automatically from a system.
Air-Cooled Condenser
Heat of compression, plus the heat of absorption, is transferred from refrigerant within coil to surrounding air, either by convection or fan or blower.
Airflow
The volume of air moving through a blower or duct. Units of measure are cubic feet per minute (CFM), liters per second (LPS) or cubic meters per hour (m3h).
Anemometer
An instrument used to measure air velocities.
ANSI
American National Standards Institute is a nonprofit organization that publishes safety standards for the HVAC industry. These standards are used by other organizations and local code authorities to create test protocols that prove equipment can be operated safely when installed properly.
ARI (Air-Conditioning and Refrigeration Institute)
Air-Conditioning and Refrigeration Institute is a nonprofit, voluntary organization comprised of heating, air conditioning and refrigeration manufacturers. ARI publishes standards for testing and rating heat pumps and air conditioners to provide you with a standardized measure of comparison. So, ARI ensures a level of performance within the industry.
ASHRAE
A leading HVAC/R Association - American Society of Heating, Refrigerating and Air Conditioning Engineers - http://www.ashrae.org/
ASTM
American Society for Testing and Materials.
Atmospheric Pressure
The pressure exerted upon the earth's surface by the air because of the gravitational attraction of the earth. Standard atmosphere pressure at sea level is 14.7 pounds per square inch (psi). Measured with a barometer.
Automatic Control
Controls that react to a change in conditions to cause the condition to stabilize.
Automatic Expansion Valve
A refrigerant control valve that maintains a constant pressure in an evaporator.
Axial Fan
A device that propels air in an axial direction.
BacNet
BacNet is a communication protocol developed under the auspices of ASHRAE that allows open communications between pieces of HVAC equipment on a building. BacNet is not restricted to any particular manufacturer or line of equipment.
Balancing
Process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems.
Barometer
An instrument for measuring atmospheric pressure.
Blower
An enclosed air-moving device which redirects the airflow by 90 degrees towards one or more exit points.
BTU (British Thermal Unit)
Quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.
Burner
A device used to prepare and burn fuel.
Carbon Dioxide
A by-product of natural gas combustion that is not harmful.
Carbon Monoxide
A colorless, odorless, highly poisonous gas produced when carbon burns without sufficient air nearby.
Centrifugal Fan
A device that draws air in axially and discharges it radially.
CFC (Chlorofluorocarbon)
A class of refrigerants. Generally refers to the Chlorofluorocarbon family of refrigerants. Sometimes called Freon.
CFD
Computational Fluid Dynamics is a computer-based mathematical model of fluids in a space. In the HVAC industry CFD is used to simulate the direction, velocity, and temperature of air in a building.
CFM (Cubic Feet per Minute)
A standard measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system.
Charge
Amount of refrigerant placed in a refrigerating unit.
Chilled Beam
Chilled beams are a form of radiant cooling commonly used in europe. Chilled beams can be "passive" (no external source of air is provided) or "active" (some amount of air is provided from an external source...usually the ventilation air required for a space). Chilled beams are linear in nature normally measuring about 12" across and extending the length of a room. Chilled beams are installed in the ceiling.
Circuit Breaker
A device that opens an electric circuit when an overload occurs.
Combustion
A reaction called rapid oxidation or burning produced with the right combination of a fuel, oxygen, and heat.
Comfort Zone
The range of temperatures, humidities and air velocities at which the greatest percentage of people feel comfortable.
Compressor
Pump of a refrigerating mechanism which draws a low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high pressure or condensing side of the cycle.
Condensate
The moisture collected on an evaporator coil.
Condensate Pump
A small pump used to pump condensate to a higher level.
Condenser Coil
Part of the outdoor portion of a split-system air conditioner or heat pump. By converting refrigerant that is in a gas form back to a liquid, the coil transfers heat carried by the refrigerant to the outside air.
Condensing Temperature
The temperature at which a vapor changes to a liquid.
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.
Conduction
The transfer of heat through a solid material.
Convection
The movement of heat by fluid flow(e.g. air, water).
Damper
A device that is located in ductwork to adjust air flow.
dB (Decibel)
A decibel describes the relative loudness of a sound on a logarithmic scale.
DDC
Direct Digital Control is the method of activating, deactivating, and monitoring the control points in an HVAC system using computer-logic and microprocessors. This method of control includes the software that provides the instructions to the HVAC unit components and directs their action based upon the input from a variety of sensor types. DDC controls can be embedded in individual pieces of equipment, can be a total unit controller, or can be a remote computer that communicates unit operational commands via a network.
Dehumidification
The reduction of water vapor in air by cooling the air below the dew point; removal of water vapor from air by chemical means, refrigeration, etc.
Dew point
The exact temperature at which moisture begins to form.
Direct Gas-Fired Heater
The burner fires directly in the air stream being heated, rather than through a heat exchanger. 100% of available BTUs are delivered to the heated space because no flue or heat exchanger is required. This results in no wasted energy.
DOAS
DOAS stands for Dedicated Outdoor Air System. A DOAS piece of HVAC equipment is designed specifically to filter, temper, and control the amount of outside air that enters a building. DOAS equipment is typically used to provide the amount of ventilation air required by the building codes to satisfy the fresh air requirements for the building occupants. A DOAS unit is only a component of a much larger system. The remainder of the system is designed to satisfy the sensible cooling load of the building without concern for the outside air requirement.
DOE (Department of Energy)
The Department of Energy is a federal agency in charge of setting industry efficiency standards and monitoring the consumption of energy sources.
Duct
A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.
EER (Energy Efficiency Ratio)
A ratio calculated by dividing the cooling capacity in Btu's per hour (Btuh) by the power input in watts at any given set of rating conditions, expressed in Btuh per watt (Btuh/watt). EER & SEER can not be compared equally. EER changes with the inside and outside conditions, falling as the temperature difference between inside and outside gets larger.
Efficiency
A rating on comfort equipment is similar to the miles per gallon rating on your car.
Energy Recovery Ventilator (ERV)
This device preheats incoming outside air during the winter and pre-cools incoming air during the summer to reduce the impact of heating and or cooling the indoor air.
Evaporation
The condition that occurs when heat is absorbed by liquid and it changes to vapor.
Evaporator Coil
Part of a split-system air conditioner or heat pump located indoors. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmed refrigerant is then carried through a tube to the outdoor unit (condenser coil).
Exfiltration
Uncontrolled air leakage out of a building.
Exhaust
The air flow leaving the treated space.
Fahrenheit Scale
The temperature scale that places the boiling point of water at 212°F and the freezing point at 32°F.
Fan
A device that produces a pressure difference in air to move it.
Fan Cycling
The use of a pressure control to turn a condenser fan on and off to maintain a correct pressure within the system.
Fan Laws
A family of mathematical relationships that allows the calculation of new operating characteristics from known system conditions
Filter
A device for removing dust particles from air or unwanted elements from liquids.
Flow Coefficient
A dimensionless parameter relation air velocity to fan tip velocity. It's used to determine approximate fan width for centrifugal impellers.
HCFC (Hydrochlorofluorocarbon)
A class of refrigerants. Generally refers to Halogenated Chlorofluorocarbon family of refrigerants.
Heat Exchanger
This is a device that enables furnaces to transfer heat from combustion safely into breathable air. The primary heat exchanger transfers heat from combustion gases to the air blowing through the ductwork.
Heat Gain
The amount of heat gained, measured in BTU's, from a space to be conditioned, at the local summer outdoor design temperature and a specified indoor design condition.
Heat Loss
The amount of heat lost, measured in BTU's from a space to be conditioned, at the local winter outdoor design temperature and a specified indoor design condition.
Heat Recovery Ventilator (HRV)
This device bring fresh, outside air into a building while simultaneously exhausting stale indoor air outside. In the process of doing this, an HRV removes heat from the exhaust air and transfers it to the incoming air, pre-heating it.
HFC (Hydrofluorocarbon)
A class of refrigerants. Generally refers to Hydrofluorocarbon family of refrigerants
Humidifier
A device that adds moisture to warm air being circulated or directed into a space.
Humidity
The amount of moisture in the air. Air conditioners remove moisture for added comfort.
Humidity Sensor
A device designed to regulate humidity input by reacting to changes in the moisture content of the air.
HVAC
Heating, Ventilating and Air Conditioning
Latent Cooling Load
The net amount of moisture added to the inside air by plants, people, cooking, infiltration, and any other moisture source. The amount of moisture in the air can be calculated from a combination of dry-bulb and wet-bulb temperature measurements.
Latent Heat
Heat, that when added or removed, causes a change in state - but no change in temperature.
LEED
The Leadership in Energy and Environmental Design green building rating system is a nationally recognized benchmark for the design, construction, and operation of high performance buildings.
Linear Feet per Minute (LFM)
A unit of measurement. The velocity of the air.
LonTalk
LonTalk is a communication protocol developed by Echelon Corporation that allows various pieces of HVAC equipment in a building to share information and control signals. LonTalk is open to manufacturers who choose to pay Echelon Corporation a royalty for the use of the protocol.
Make-Up Air Equipment
Make-up air equipment is designed to draw sufficient outside air into a building to wholly, or partially, offset the amount of air that leaves the building via the exhaust system. Make-up air may, or may not, be tempered or filtered before being introduced into the building.
Manometer
An instrument that measures air pressure differences between locations. Tubes are usually attached to a manometer and run to the spaces where pressures are measured. Essentially a U-tube partly filled with a liquid, usually water, mercury or a light oil. The pressure exerted on the liquid is indicated by the liquid displaced. A manometer can be used as a differential pressure gage.
Motor
A device that converts electrical energy into mechanical energy. A motor can operate on direct current (DC) or alternating current (AC) voltage supply, not both.
Saturation Temperature
Also referred to as the boiling point or the condensing temperature. This is the temperature at which a refrigerant will change state from a liquid to a vapor or visa versa.
Sensible Cooling Load
e heat gain of the building due to conduction, solar radiation, infiltration, appliances, people, and pets. Burning a light bulb, for example, adds only sensible load to the building. This sensible load raises the dry-bulb temperature.
Sensible Heat
Heat, that when added or removed, causes a change in temperature but not in state.
Sound Attenuators
Components which are inserted into the air distribution system and designed to reduce airborne noise which is propagated along the ducts.
Specific Speed
A dimensionless parameter based on fan rotational speed, flow rating and pressure rating. It's a tool used to select the type of fan for a specific application. Each Different fan type achieves peak efficiency at a unique specific speed range.
Split System
Refrigeration or air conditioning installation, which places condensing unit outside or away from evaporator. These unit are connected together by a supply and return refrigerant lines.
Standard Cubic Feet Per Minute (SCFM)
The volumetric rate of airflow at standard air conditions.
Static Efficiency
A measure of an air mover's efficiency based on its air horsepower in terms of flow and static pressure vs. required shaft input power.
Static Pressure
The difference in air pressure between the suction side and pressure side of the blower. Unit of measure is inches of water column (in. wc) or Pascals (Pa).
Stator
The part of the motor that is fixed, typically found in the hub of the fan.
Subcooled Liquid
Liquid refrigerant which is cooled below its saturation temperature.
Superheated Vapor
Refrigerant vapor which is heated above its saturation temperature. If a refrigerant is superheated, there is no liquid present.
System Impedance
The resistance to air flow when moving air through an airflow system. Examples: air filters, air grilles and abrupt changes in flow direction.
System Operating Point
The point of operation of the air mover on its air performance curve. It is described by an airflow and static pressure point. The operating point is that point on the air mover performance curve where the system resistance curve crosses the air performance curve.