Definitions

A

Absolute Pressure

The total of the indicated gage pressure plus the atmospheric pressure. Abbreviated "psia" for pounds per square inch absolute.

Absolute Temperature

Temperature measured from absolute zero using an absolute temperature scale (e.g. Kelvin).

Absolute Zero

Temperature at which all molecular motion ceases (-460 °F, -273.15 °C, and 0 K.)

Aeration

Act of combining substance with air.

AFUE - Annual Fuel Utilization Efficiency

The ratio of annual output of useful energy or heat to the annual energy input to the furnace.

AHU (Air Handling Unit)

The inside 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 Coil

Coil on some types of heat pumps used either as an evaporator or condenser.

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 Gap

The space between magnetic poles or between rotating and stationary assemblies in a motor or generator.

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 Vent

A fitting used to vent air manually or automatically from a system.

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.

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.

Automatic Control

Controls that react to a change in conditions to cause the condition to stabilize.

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.

B

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.

C

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.

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.

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.

Condensate

The moisture collected on an evaporator coil.

Condensate Pump

A small pump used to pump condensate to a higher level.

Condensing Temperature

The temperature at which a vapor changes to a liquid.

Conduction

The transfer of heat through a solid material.

Conformal Coating

Material coating to protect fan from harsh environmental conditions.

Convection

The movement of heat by fluid flow(e.g. air, water).

COP (Coefficient Of Performance)

COP compares the heating capacity of a heat pump to the amount of electricity required to operate the heat pump in the heating mode.

D

Damper

A device that is located in ductwork to adjust air flow.

DB

Dry Bulb Temperature

dB (Decibel)

A decibel describes the relative loudness of a sound on a logarithmic scale.

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.

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.

E

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. Air source equipment is rated by SEER and geothermal equipment is rated by EER. 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.

EPA (Environmental Protection Agency)

Environmental Protection Agency - http://www.epa.gov/

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.

F

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.

G

Gage

An instrument for measuring pressure.

Geothermal Equipment

Heat pumps that uses the ground to transfer heat to and from the refrigerant in the unit. The unit circulates water through a heat exchanger in the to a closed loop buried in the ground or by pumping water from a well through the unit.

H

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 Pump

Compression cycle system used to supply heat to a temperature controlled space. Same system can also remove heat from the same space.

Humidifier

A device that adds moisture to warm air being circulated or directed into a space.

Humidity Sensor

A device designed to regulate humidity input by reacting to changes in the moisture content of the air.

Humidity

The amount of moisture in the air. Air conditioners remove moisture for added comfort.

HVAC

Heating, Ventilating and Air Conditioning

I

Inches of Water Gage or Column (IN WG or IN WC)

A unit of air pressure measurement equal to the pressure exerted by a column of water 1 inch high.

IAQ

Indoor Air Quality

IGBT

Insulated Gate Bipolar Transistor.

Impedance

The resistance or opposition to airflow in a system. Same as back pressure or static pressure.

Impeller

The component of a fan assembly that is composed of a number of contoured blades.

Induction

Process by which the primary air sets into motion an air volume, called secondary air, in the room.

K

KW

Kilowatt, equals 1000 Watts.

KWh

Kilowatt hour is the amount of kilowatts of electricity used in one hour of operation of any equipment.

L

Latent Heat

Heat, that when added or removed, causes a change in state - but no change in temperature.

Linear Feet per Minute (LFM)

A unit of measurement. The velocity of the air.

M/N/O

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.

P/Q

PCB

Printed Circuit Board.

Pascals (Pa)

A small unit of air pressure.

Pitot Tube

A sensing device used to measure total pressures in a fluid stream. It was invented by a French physicist, Henri Pitot, in the 1700's.

Plenum

An air flow passage.

Pressure Coefficient

A dimensionless parameter relating the static pressure potential of a fan to its tip velocity pressure equivalent. It's used to determine approximate fan diameter.

R

Radiation

The transfer of heat directly from one surface to another. (No intermediate air acting as a transfer mechanism required).

RH

Relative Humidity

RPM

Revolutions per minute, the measurement of fan blade speed.

Rotor

The rotating part of the motor which includes the propeller assembly.

S

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.

SEER (Seasonal Energy Efficiency Ratio)

The total cooling of a central unitary air conditioner or unitary heat pump in BTU's during its normal annual usage period for cooling divided by the total electric energy input in watt-hours during the same period.

Sensible Cooling Load

The heat gain of the home due to conduction, solar radiation, infiltration, appliances, people, and pets. Burning a light bulb, for example, adds only sensible load to the house. 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.

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.

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.

T

Thermometer

An instrument used to detect differences in the level of heat.

Thermostat

A device that senses temperature change and changes some dimension or condition within to control an operating device.

Ton

A unit of measure for cooling capacity. One ton = 12,000 BTUs per hour.

Total Efficiency

A measure of an air movers efficiency based on its air horsepower in terms of flow and total pressure vs. required shaft input power.

U - Z

Ventilator

Captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.

Venturi

The housing or frame of the fan.

W

Watt, the SI unit of power. In electricity it is Volts x Amps.

WB

Wet Bulb

WC (Water Column)

Common measure of air pressure used in HVAC systems.