A
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| Absolute Pressure |
The total of the indicated gage pressure plus
the atmospheric pressure. Abbreviated "psia" for pounds per square inch absolute.
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| Absolute Temperature |
Temperature measured from absolute zero using an absolute temperature scale (e.g. Kelvin).
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| Absolute Zero |
Temperature at which all molecular motion ceases (-460 °F, -273.15 °C, and 0 K.)
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| ACH, Air Changes Per Hour |
The number of times that air in a house is completely replaced with outdoor air in one hour.
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| Aeration |
Act of combining substance with air.
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| AFUE - Annual Fuel Utilization Efficiency |
The ratio of annual output of useful energy or heat to the annual energy input
to the furnace.
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| AHU (Air Handling Unit) |
The inside part of the A/C system that contains the blower, cooling (evaporator) coil, and heater.
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| Air Change |
The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air
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| Air Coil |
Coil on some types of heat pumps used either as an evaporator or condenser.
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| Air conditioner |
Equipment that conditions air by cleaning, cooling, heating, humidifying, or
dehumidifying it. A term often applied to comfort cooling equipment.
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| Air conditioning |
A process that maintains comfort conditions in a defined area.
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| Air Cooler |
Mechanism designed to lower temperature of air passing through it.
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| Air Diffuser |
Air distribution outlet or grille designed to direct airflow into desired patterns.
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| 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.
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| Air Distribution |
The transportation of a specified air flow to or from the treated space or spaces, generally by means of ductwork.
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| Air Gap |
The space between magnetic poles or between rotating and stationary assemblies in a motor or generator.
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| Air Handler |
Fan/blower, filter and housing parts of a system.
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| Air Infiltration |
Leakage of air into rooms through cracks, windows doors and other openings.
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| Air Sensor |
A device that registers changes in air conditions such as pressure, velocity,
temperature, or moisture content.
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| Air Source Equipment |
Heat pumps or air conditioners that uses the outdoor air to transfer heat to and from the refrigerant in the unit.
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| 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.
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| Air Vent |
A fitting used to vent air manually or automatically from a system.
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| 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.
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| 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).
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| Anemometer |
An instrument used to measure air velocities.
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| 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.
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| ASHRAE |
A leading HVAC/R Association - American Society of Heating, Refrigerating and Air Conditioning Engineers - http://www.ashrae.org/
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| ASTM |
American Society for Testing and Materials.
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| Automatic Control |
Controls that react to a change in conditions to cause the condition to stabilize.
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| Automatic Expansion Valve |
A refrigerant control valve that maintains a constant pressure in an evaporator.
|
| 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.
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| Axial Fan |
A device that propels air in an axial direction.
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B
|
| Balance Point |
The lowest outdoor temperature at which the refrigeration cycle of a heat pump will supply the heating requirements without the aid of a supplementary heat source.
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| Balancing |
Process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems.
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| Barometer |
An instrument for measuring atmospheric pressure.
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| Blower |
An enclosed air-moving device which redirects the airflow by 90 degrees towards one or more exit points.
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| BTU (British Thermal Unit) |
Quantity of heat required to raise the temperature of one pound of water
one degree Fahrenheit.
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| Burner |
A device used to prepare and burn fuel.
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C
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| Carbon Dioxide |
A by-product of natural gas combustion that is not harmful.
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| Carbon Monoxide |
A colorless, odorless, highly poisonous gas produced when carbon burns without sufficient air nearby.
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| Centrifugal Fan |
A device that draws air in axially and discharges it radially.
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| CFC (Chlorofluorocarbon) |
A class of refrigerants. Generally refers to the Chlorofluorocarbon family
of refrigerants. Sometimes called Freon.
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| 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.
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| Charge |
Amount of refrigerant placed in a refrigerating unit.
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| Circuit Breaker |
A device that opens an electric circuit when an overload occurs.
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| Combustion |
A reaction called rapid oxidation or burning produced with the right combination
of a fuel, oxygen, and heat.
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| Comfort Zone |
The range of temperatures, humidities and air velocities at which the
greatest percentage of people feel comfortable.
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| 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.
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| Condensate |
The moisture collected on an evaporator coil.
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| Condensate Pump |
A small pump used to pump condensate to a higher level.
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| 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.
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| Condensing Temperature |
The temperature at which a vapor changes to a liquid.
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| 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.
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| Conduction |
The transfer of heat through a solid material.
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| Conformal Coating |
Material coating to protect fan from harsh environmental conditions.
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| Convection |
The movement of heat by fluid flow(e.g. air, water).
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| 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.
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D
|
| Damper |
A device that is located in ductwork to adjust air flow.
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| DB |
Dry Bulb Temperature
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| dB (Decibel) |
A decibel describes the relative loudness of a sound on a logarithmic scale.
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| Defrost Cycle |
The process of removing ice or frost buildup from the outdoor coil during the
heating season.
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| 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.
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| 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.
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| 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.
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| 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.
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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.
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| 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.
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| EPA (Environmental Protection Agency) |
Environmental Protection Agency - http://www.epa.gov/
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| Evaporation |
The condition that occurs when heat is absorbed by liquid and it changes to vapor.
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| 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).
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| Exfiltration |
Uncontrolled air leakage out of a building.
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| Exhaust |
The air flow leaving the treated space.
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F
|
| Fahrenheit Scale |
The temperature scale that places the boiling point of water at 212°F and the freezing point at 32°F.
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| Fan |
A device that produces a pressure difference in air to move it.
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| Fan Cycling |
The use of a pressure control to turn a condenser fan on and off to maintain a correct pressure within the system.
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| Fan Laws |
A family of mathematical relationships that allows the calculation
of new operating characteristics from known system conditions.
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| 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
|
| HCFC (Hydrochlorofluorocarbon) |
A class of refrigerants. Generally refers to Halogenated Chlorofluorocarbon
family of refrigerants.
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| 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.
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| 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.
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| 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.
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| Heat Pump |
Compression cycle system used to supply heat to a temperature controlled space.
Same system can also remove heat from the same space.
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| Heat Recovery Ventilator (HRV) |
This device bring fresh, outside air into a home 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.
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| HFC (Hydrofluorocarbon) |
A class of refrigerants. Generally refers to Hydrofluorocarbon family
of refrigerants
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| Humidifier |
A device that adds moisture to warm air being circulated or directed into a space.
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| Humidity Sensor |
A device designed to regulate humidity input by reacting to changes in the
moisture content of the air.
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| Humidity |
The amount of moisture in the air. Air conditioners remove moisture for
added comfort.
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| HVAC |
Heating, Ventilating and Air Conditioning
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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.
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| IAQ |
Indoor Air Quality
|
| IGBT |
Insulated Gate Bipolar Transistor.
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| Impedance |
The resistance or opposition to airflow in a system. Same as back pressure or static pressure.
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| Impeller |
The component of a fan assembly that is composed of a number of contoured blades.
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| Induction |
Process by which the primary air sets into motion an air volume,
called secondary air, in the room.
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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.
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L
|
| 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.
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| Linear Feet per Minute (LFM) |
A unit of measurement. The velocity of the air.
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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.
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| 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.
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P/Q
|
| PCB |
Printed Circuit Board.
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| 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.
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| Plenum |
An air flow passage.
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| 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).
|
| Refrigerant |
Substance used in refrigerating mechanism. It absorbs heat in evaporator by
change of state from a liquid to a gas, and releases its heat in a condenser as the substance
returns from the gaseous state back to a liquid state.
|
| 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.
|
| 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.
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| 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.
|
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.
|
| Wet-bulb Temperature |
When a wet wick is placed over a standard thermometer and air is
blown across the surface, the water evaporates and cools the thermometer below the dry-bulb temperature.
This cooler temperature (called the wet-bulb temperature) depends on how much moisture is in the air.
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