ROC# 245471

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Absolute Humidity – The weight of water vapor per cubic foot of dry air, expressed as grains of moisture per cubic foot.

AC - Alternating Current; a type of electric current in which the polarity is constantly reversing causing the electron flow to reverse (as opposed to Direct Current, or DC).

ACCA - Air Conditioning Contractors of America.

Acoustical - Of or pertaining to sound.

AFUE - Annual Fuel Utilization Efficiency; a measure of a gas furnace's efficiency in converting fuel to energy.  Units with higher ratings are more efficient.

AGA - American Gas Association, Inc.

Air Conditioner - Any device that can change the temperature, humidity or general quality of the air.

Air Cleaner - Any device that removes undesirable particles from moving air.

Air Flow Volume - The amount of air the system circulates through your home, expressed in cubic feet per minute.  Proper airflow depends on clean filters, the ductwork, and the unit itself.

Air Handler – A unit that moves/mixes the air.

ARI - Air Conditioning & Refrigeration Institute.

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers.

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B

BTU - British Thermal Unit; the heat extracted from your home by an air conditioner is measured in BTUs, this is the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit.

BTUh - British Thermal Units per hour; 12,000 BTUh equals one ton of cooling.

Burner - A device that uses fuel to support combustion.

Burner Orifice - The opening through which gas flows to the air/gas mixing chamber of the burner.

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C

Capacity - The producing ability of a cooling or heating systems.

Celsius - The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol "C".  To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9, divide by 5 and add 32.

CFM - Cubic Feet per Minute; a standard measurement of airflow, a typical system requires 400 cfm per ton of air conditioning.

Charge - Adding refrigerant to a system.

Compressor - The heart of an air conditioning or heat pump system, it is part of the outdoor unit and pumps refrigerant to meet the cooling requirements of the system.

Condensation - Vapor that liquefies due to the lowering of its temperature to the saturation point.

Condenser Coil - In an air conditioner the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid.  In a heat pump system, the coil absorbs heat from outdoors.

Condenser Fan - The fan that circulates air over the air-cooled condenser.

Contactor - A switch that can repeatedly cycle, making and breaking an electrical circuit.  When sufficient current flows through the Acoil built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed.

CSA - Canadian Standards Association.

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D

DC - Direct Current; this type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.

Damper - Found in ductwork, this movable plate opens and closes to control airflow, they are used to balance airflow in a duct system, and are often used in zoning to regulate airflow to certain rooms.

Defrost - To melt frost.

Degreeday - A computation that gauges the amount of heating or cooling needed for a building. A degreeday is equal to 65 degrees Fahrenheit minus the mean outdoor temperature.

Dehumidifier - An air cooler that removes moisture from the air.

Diffuser - A grille over an air supply duct having vanes to distribute the discharging air in a specific pattern or direction.

DOE - Department of Energy.

Downflow Furnace - A furnace that intakes air at its top and discharges air at its bottom.

Drain Pan - Also referred to as a condensate pan, it is used to catch and collect condensate.

Dry Bulb Temperature - Heat intensity, measured by a dry bulb thermometer.

Dry Bulb Thermometer - An instrument that measures air temperature independently of humidity.

Ductwork - A pipe or conduit, through which air is delivered, typically made of metal, fiberboard or a flexible material.  The size and application of ductwork is critical to performance and is as important as the equipment.

DX - Direct Expansion; a system in which heat is transferred by the direct expansion of refrigerant.

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E

EER - Energy Efficiency Ratio.

EPA - Environmental Protection Agency.

Expansion Valve - A refrigerant metering valve with a pressure or temperature controlled orifice.

Evaporator Coil – Also called an Indoor Coil, it is the other half of an air conditioning system, located inside your home in the indoor unit, it is a tubing coil in which a volatile liquid evaporates and absorbs heat. This is where the refrigerant evaporates as it absorbs heat from the indoor air that passes over the coil.

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F

Fahrenheit - The temperature scale on which water freezes at 32 degrees and boils at 212 degrees; designated by the letter F. To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit number, multiply by 5 and divide by 9.

Fan - Any device that creates air currents.

Filter - Any device that removes impurities through a straining process.

Flue - Any vent or passageway that carries the products of combustion from a furnace.

Furnace - That part of the heating system in which the combustion of fossil fuel and transfer of heat occurs.

Fuse - A metal strip in an electrical circuit that melts and breaks the circuit when excessive current flows through it, which is designed to break in order to save more expensive electrical components.

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G

GAMA - Gas Appliance Manufacturers Association.

Gas Furnace Heat Exchanger - Located in the furnace, the heat exchanger transfers heat to the surrounding air, which is then pumped throughout your home.

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H

Heat Exchanger - An area, box or coil where heat flows from the warmer to the colder fluid or surface.

Heat Gain - Heat added to the conditioned space by infiltration, solar radiation, occupant respiration and lighting.

Heating Coil - Any coil that serves as a heat source.

Heat Loss - The rate of heat transfer from a heated space to the outdoors.

Heat Pump - A mechanical compression cycle refrigeration system that can be reversed to either heat or cool the controlled space.

Heat Transfer - The movement of heat energy from one point to another, the means for such movement are conduction, convection, and radiation.

Hertz - In alternating current (AC electricity), the number of cycles per second.

HSPF - Heating Seasonal Performance Factor; this rating is used in measuring the heating efficiency of a heat pump, the higher the number, the more efficient the heat pump system.

Humidifier - A machine that adds water vapor to the air to increase humidity.

Humidistat - A humidity sensing control that cycles the humidifier on and off.

Humidity - The presence of water vapor in the air.

HVAC - Heating, Ventilating and Air Conditioning.

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I

Ignition - The lighting of fuel to make it burn.

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K

Kilowatt (kW) - 1,000 watts.

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L

Latent Heat - A type of heat, which when added to or taken from a substance, does not change the temperature of the substance but instead, the heat energy enables the substance to change its state.

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M

Media - The material in a filter that traps and holds the impurities.

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N

NEC - National Energy Council or National Electric Code.

NEMA - National Electrical Manufacturing Association.

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O

OEM - Original Equipment Manufacturer.

Orifice - An opening or hole; an inlet or outlet.

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P

Package Unit - A heating and cooling system contained in one outdoor unit, typically installed beside, on the roof, or sometimes in the attic of a home.

PSI - Pounds per Square Inch.

PSIA - Pounds per Square Inch Absolute.

PSIG - Pounds per Square Inch Gauge.

PVC – Poly Vinyl Chloride; a type of plastic.

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R

Reciprocating Compressor - A compressor whose piston or pistons move back and forth in the cylinders.

Refrigerant - A chemical that produces a refrigerating effect while expanding and vaporizing.

Refrigerant Charge - The required amount of refrigerant in a system.

Relative Humidity - The amount of moisture in the air expressed as a percentage of the maximum amount that the air is capable of holding at a specific temperature.

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S

SEER - Seasonal Energy Efficiency Ratio; a measure of cooling efficiency for air conditioners and heat pumps, the higher the SEER, the more energy efficient the unit. The U.S. Government's minimum SEER rating is 10.

Self Contained System - A refrigerating system that can be moved without disconnecting any refrigerant lines, also know as a package unit.

Sensible Heat - Heat which when added to or taken away from a substance, causes a rise or fall in temperature.

Sensor - Any device that reacts to a change in the conditions being measured, permitting the condition to be controlled.

Setpoint - The temperature or pressure at which a controller is set with the expectation that this will be a nominal value depending on the range of the controller.

Split System - The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler), which must be matched for optimum efficiency.

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T

Thermostatic Expansion Valve - A refrigerant metering device that maintains a constant evaporator temperature by monitoring suction vapor superheat, sometimes called a thermal expansion valve.

Thermostat - A series of sensors and relays that monitor and control the functions of a heating and cooling system.

Ton - A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.

Twostage Cooling or Heating - Twostage cooling and heating is considered to be more efficient, because it operates at low speed most of the time.  However, on days when more heating or air conditioning is required, it switches to the next stage for maximum comfort.

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U

UFactor - The factor representing resistance to heat flow of various building materials.

UL - Underwriters Laboratories.

Upflow Furnace - A furnace in which air is drawn in through the sides or bottom and discharged out the top.

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V

Vacuum - A pressure below atmospheric pressure, a perfect vacuum is 30 inches Mercury.

Volt - The unit of measure used to describe the difference in electrical potential, often abbreviated by the symbol "v".

Voltage - The force that pushes electrical current along wires and cables.

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W

Watt - The unit of electrical power equal to the flow of one amp at a potential difference of one volt.

Wet Bulb Thermometer - A thermometer whose bulb is covered with a piece of water soaked cloth, the lowering of temperature that results from the evaporation of water around the bulb indicates the air's relative humidity.

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Z

Zoning System - A method of dividing a home into different comfort zones so each zone can be independently controlled depending on use and need; an air conditioning system capable of maintaining varying conditions for various rooms or zones.

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