A | B | C | D | E | F | G | H | I | K | L | M | N | O | P | R | S | T | U | V | W | Z
For a glosary of HVAC Terms, please click here.
A
AC for alternating current, a type of electric current in which the polarity is constantly reversing causing the electron flow to reverse.
ACCA Air Conditioning Contractors of America
Acoustical Of or pertaining to sound.
AC or DC Abbreviation for equipment capable of operating on alternating or direct current.
A-Coil A heat exchanger consisting of two diagonal coils that are joined together in a manner that looks like the letter "A".
AFUE Annual Fuel Utilization Efficiency. A measure of a gas furnace's efficiency in converting fuel to energy - the higher the rating, the more efficient the unit.
AGA Abbreviation for American Gas Association, Inc.
Air Conditioner Any device that can change the temperature, humidity or general quality of the air.
Air cleaner (also Air Filtration System) Removes airborne allergens from your home.
Air Filtration System (also Air Cleaner) Removes airborne allergens from your home.
Air flow volume The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper air flow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.
Air handler An air moving and/or mixing unit. Residential air handlers include a blower, a coil, an expansion device, a heater rack and filter. Heaters for air handlers are sold as accessories. In some models heaters are factory installed.
ARI Air Conditioning & Refrigeration Institute
ASHRAE American Society of Heating, Refrigeration and Air Conditioning Engineers
B
BTU British thermal unit; the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit. The heat extracted from your home by an air conditioner is measured in BTUs.
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.
Burner (sealed combustion) A burner that obtains all air for combustion from outside the heated space.
C
CADR Clean Air Delivery Rate (CADR) provides the number of cubic feet of clean air a unit delivers each minute. Efficiency of the system times the air flow of the system.
Capacity The output or producing ability of cooling or heating systems. Cooling and heating capacities are referred to in British thermal units (BTUs) per hour.
Celsius The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol "C". To convert to Fahrenheit, multiply a Celsius temperature by 9, divide by 5 and add 32 (25 x 9 equals 225, divided by 5 equals 45, plus 32 equals 77 degrees Fahrenheit).
CFM Abbreviation for cubic feet per minute, a standard measurement of airflow. A typical system requires 400 cfm per ton of air conditioning.
Charge To add refrigerant to a system. This is refrigerant contained in a sealed system or in the sensing bulb to a thermostatic expansion valve.
CleanEffects™ (also Trane CleanEffects™) Trane Air filtration system that removes 99.98% of airborne allergens down to .1 microns from the filtered air, making it 100 times more effective that a standard 1” filter
Climatuff® Compressor The Trane Climatuff® Compressor was the world's first successful heat pump compressor. To this day it's the only compressor Trane uses in its residential systems. It's well known for its superior durability, its low noise levels, and high efficiency.
Comfort™ Coil (also Evaporator Coil or Indoor Coil) Part of an indoor air unit, it functions with the air conditioner or heat pump outdoors to cool and condition indoor air that flows over it by drawing out heat and moisture.
Compressor This is the heart of an air conditioning or heat pump system. It is part of the outdoor unit and pumps refrigerant in order to meet the cooling requirements of the system.
Condensate Vapor that liquefies due to the lowering of its temperature to the saturation point.
Condenser coil (or outdoor 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 the 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 A-coil built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed.
Crankcase heater This is the electric resistance heater installed on compressor crankcases to boil off liquid refrigerant that may have combined with compressor oil. Many newer cooling systems do not require crankcase heaters, however heat pumps do require crankcase heaters.
CSA Canadian Standards Association.
D
Damper Found in ductwork, this movable plate opens and closes to control airflow. Dampers can be used to balance airflow in a duct system. They are also used in zoning to regulate airflow to certain rooms.
DB (Decibels) A unit to measure sound.
DC Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.
Defrost To melt frost; as in from an air conditioner or heat pump coil.
Degree-day A degree-day is a computation that gauges the amount of heating or cooling needed for a building. A degree-day 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 This also referred to as a condensate pan. This is a pan used to catch and collect condensate (in residential systems vapor is liquefied on the indoor coil, collected in the drain pan and removed through a drain line).
Dry bulb temperature Heat intensity, measured by a dry bulb thermometer.
Dry bulb thermometer An instrument that measures air temperature independently of humidity.
Dual Compressors An outdoor unit featuring two compressors, one for everyday cooling and a second larger one for extreme temperature days. Provides superior durability designed for cost-saving efficiency and low sound levels.
Ductwork A pipe or conduit through which air is delivered. Ducts are typically made of metal, fiberboard or a flexible material. In a home comfort system, 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.
E
EER Energy Efficiency Ratio (steady state)
Electronic Air Cleaner (EAC) Electronically filters out magnetized airborne particles, from contaminants in indoor air sending them to a collector plate.
Energy Recovery Ventilator (also FreshEffects™ or TRANE FreshEffects™) Energy efficient system to exchange stale indoor air for an equal amount of fresher outdoor air.
ENERGY STAR® Trane high efficiency systems carry the ENERGY STAR label. The result of Trane's partnership with the U.S. Department of Energy, Environmental Protection Agency (EPA), ENERGY STAR products are more energy efficient and help reduce our whole earth's pollution problems. Choosing a Trane ENERGY STAR Comfort System assures homeowners of lower energy bills and improved indoor air quality for their home.
EPA Environmental Protection Agency
Expansion Valve A refrigerant-metering valve with a pressure or temperature controlled orifice.
Evaporator Coil (also Comfort™ Coil or Indoor Coil) Part of an indoor air unit, it functions with the air conditioner or heat pump outdoors to cool and condition indoor air that flows over it by drawing out heat and moisture.
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 (77 -32 equals 45, times 5 equals 225, divided by 9 equals 25 degrees Celsius).
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.
FreshEffects™ (also Energy Recovery Ventilator or TRANE FreshEffects™) Energy efficient system to exchange stale indoor air for an equal amount of fresher outdoor air.
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. The fuse is designed to break in order to save more expensive electrical components.
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.
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.
HEPA Filter Filter that traps airborne particles by forcing air through very dense mesh.
Hertz In alternating current (AC electricity), the number of cycles per second.
Horizontal Flow Often used in attics/crawl spaces, this furnace takes air from its side, heats it and sends warm air out the other side.
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.
Humidity, absolute Weight of water vapor per cubic foot of dry air, expressed as grains of moisture per cubic foot.
Humidity, relative 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.
HVAC Abbreviation for Heating, Ventilating and Air Conditioning
Hybrid Heat (also Hybrid System) Provides energy efficient comfort for moderate heating conditions. Can use either gas or electricity.
Hybrid System (also Hybrid Heat) Provides energy efficient comfort for moderate heating conditions. Can use either gas or electricity.
I
Ignition The lighting of a fuel to make it burn.
Indoor Coil (also Comfort™ Coil or Evaporator Coil) Part of an indoor air unit, it functions with the air conditioner or heat pump outdoors to cool and condition indoor air that flows over it by drawing out heat and moisture.
Indoor/Outdoor System (also Split System) The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler). Split systems must be matched for optimum efficiency.
K
Kilowatt (kW) 1,000 watts.
L
Latent Heat A type of heat, which when added to or taken from a substance, does not change the temperature of the substance. Instead, the heat energy enables the substance to change its state.
Load Calculation Assessed by a dealer, the calculation factors in a number of criteria in your home (square footage, number of windows, year-round weather concerns) and determines what size components you should include as part of your total comfort system.
M
Matched System System comprised of multiple Trane components designed and engineered to work seamlessly together to enhance overall performance, reliability and efficiency.
Media The material in a filter that traps and holds the impurities.
N
NATE North American Technician Excellence - certification acknowledging a dealer/technician as the one of the most knowledgeable and experienced at installing and servicing high performance, precision-engineered heating and cooling systems.
NEC National Energy Council / National Electric Code
NEMA National Electrical Manufacturing Association
O
OEM Original equipment manufacturer.
Operating Cost Cost of running your home comfort system, based on energy usage.
Orifice An opening or hole; an inlet or outlet.
Outdoor Coil (also Condenser Coil)In a heat pump, it takes in heat to warm your home. In an air conditioner, it dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid to cool your home.
P
Packaged System (or Packaged Unit) A single cabinet, typically installed outside, that houses both heating and cooling components
Package Unit (or Packaged System) A single cabinet, typically installed outside, that houses both heating and cooling components.
Payback Analysis Number of years required before your monthly energy savings offset the original HVAC investment.
PSI Pounds per square inch.
PSIA Pounds per square inch, absolute.
PSIG Pounds per square inch gauge.
PVC Polyvinyl chloride; a type of plastic.
R
Reciprocating Compressor A compressor whose piston or pistons move back and forth in the cylinders.
Reclaiming Returning used refrigerant to the manufacturer for disposal/reuse.
Refrigerant A chemical that produces a refrigerating effect while expanding and vaporizing. Most residential air conditioning systems contain R-22 refrigerant. R-22 is regulated under the Montreal Protocol and in the United States by the Environmental Protection Agency. R-22 is scheduled to be in production until the year 2020. It's used in approximately 95 percent of air conditioning equipment manufactured in the U.S. today.
Refrigerant Charge The required amount of refrigerant in a system.
Refrigerant Lines Two copper lines connecting the outdoor condenser to the indoor evaporator coil.
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.
SEET Seasonal Extreme Environmental Test—Trane facility that simulates series of rigorous tests to ensure the quality/reliability of outdoor units
Self-contained System A refrigerating system that can be moved without disconnecting any refrigerant lines; also know as a package unit.
Sensible Heat That 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.
Spine-Fin™ coil All-aluminum outdoor coil that features the patented Spine Fin™ design. It provides greater heat exchanging capabilities (meaning higher efficiencies) and is more resistant to corrosion than a traditional copper/aluminum coil.
Split System (also Indoor/Outdoor System) The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler). Split systems must be matched for optimum efficiency.
T
Thermostatic Expansion Valve A refrigerant metering device that maintains a constant evaporator temperature by monitoring suction vapor superheat; also called a thermal expansion valve.
Thermostat A thermostat consists of 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.
TRANE CleanEffects™ (also CleanEffects™) Trane Air filtration system that removes 99.98% of airborne allergens down to .1 microns from the filtered air, making it 100 times more effective that a standard 1” filter
TRANE FreshEffects™ (also Energy Recovery Ventilator or FreshEffects™) Energy efficient system to exchange stale indoor air for an equal amount of fresher outdoor air.
Two-stage compressor Compressor composed of a high and low stage to increase efficiency and comfort while reducing operation noise.
Two-stage heating / Two-stage cooling Two-stage heating and cooling 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.
U
U-Factor 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.
V
Vacuum A pressure below atmospheric pressure. A perfect vacuum is 30 inches Mercury (periodic symbol "Hg").
Variable-speed motor(s) The fan motor inside Trane's variable-speed air handlers is designed to vary its speed based on your home's heating and air conditioning requirements. Working in conjunction with your thermostat, it keeps the appropriate-temperature air (e.g. warm air on cold days) circulating throughout your home, reducing temperature variances in your home. It also provides greater air circulation and filtration, better temperature distribution, humidity control, higher efficiency, and quiet performance.
Volt The unit of measure used to describe a difference in electrical potential; abbreviated by the symbol "v".
Voltage The force that pushes electrical current along wires and cables.
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.
Z
Zoning 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.
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.
HVAC Terms
Definition of some common HVAC industry terms - absolute humidity, pressure, temperature and more
ABSOLUTE HUMIDITY - The weight of water vapor in a given amount of air. Grains per cubic foot
ABSOLUTE PRESSURE - Pressure measured with a base of zero.
ABSOLUTE TEMPERATURE - A temperature scale expressed in degrees F0 or C0 using absolute zero as a base. Referred to as the Rankin or Kelvin scale.
ABSOLUTE ZERO - The temperature at which molecular activity theoretically ceases. -456.69 F0 or -273.16
AIR CONDITIONING - The process of controlling the temperature, humidity, cleanliness and distribution of the air.
AIR, STANDARD CONDITIONS - Conditions at which BTU ratings for summer air conditioning equipment is rated. 95 F0 dry bulb, 75 F0wet bulb at the condenser inlet and 80 F0 dry bulb, 67 F0 wet bulb at the evaporator inlet.
AMBIENT - Refers to the temperature surrounding a body or unit under test.
ATMOSPHERIC PRESSURE - The weight of a 1 square inch column of the earth's atmosphere. At sea level this pressure is 14.696 pounds per square inch.
BIMETAL - Two metals with different rates of expansion fastened together. When heated or cooled they will warp and can be made to open or close a switch or valve.
BOILING POINT - The temperature at which the addition of any heat will begin a change of state from a liquid to a vapor.
BRITISH THERMAL UNIT (BTU) - The amount of heat necessary to change the temperature of 1 pound of pure water 1 degree Fahrenheit (oF).
CAPILLARY TUBE - A refrigerant control consisting of a small diameter tube which controls flow by restriction. They are carefully sized by inside diameter and length for each particular application.
CENTIGRADE - A temperature scale with the freezing point of water 00 and the boiling point 1000 at sea level.
CHECK VALVE - A valve designed to permit flow in one direction only.
COMPRESSION - The reduction of volume of a vapor or gas by mechanical means.
COMPRESSION RATIO - The ratio determined by dividing the discharge pressure, in PSI, by the suction pressure in PSI.
COMPRESSOR - A mechanical device used to compress gases. Three main types are: reciprocating, centrifugal and rotary.
CONDENSATION POINT - The temperature at which the removal of any heat will begin a change of state from a vapor to a liquid.
CONDENSING MEDIUM - The substance, usually air or water, to which the heat in a condenser is transferred.
CONDENSING UNIT - The portion of a refrigeration system where the compression and condensation of refrigerant is accomplished. Sometimes referred to as the 'high side'.
CONDUCTION - The transfer of heat from molecule to molecule within a substance.
CONTACTOR - An electromagnetic actuated relay. Usually used to refer to the relay which closes the circuit to a compressor.
CONVECTION - The transfer of heat by a moving fluid.
COOLING ANTICIPATOR - A resistance heater (usually not adjustable) in parallel with the cooling circuit. It is 'on' when the current is 'off", adding heat to shorten the off cycle.
COP - Ratio of work performed or accomplished as compared to the energy used.
CRANKCASE HEATER - Electric heating element that is used to heat the compressor crankcase to prevent migrating refrigerant from condensing and diluting the crankcase oil during the off-cycle.
CUBIC FEET PER MINUTE - A common means of assigning quantitative values to volumes of air in transit, usually abbreviated CFM.
CYCLE - The complete course of operation of a refrigerant back to a selected starting point in a system. Also used to describe alternating current through 360 space degrees.
DENSITY - Mass or weight per unit of volume. For example, standard air = .075 pounds per cubic foot.
DISCHARGE LINE - A tube used to convey the compressed refrigerant vapor from the compressor to the condenser inlet.
DISCHARGE PRESSURE - The pressure read at the compressor outlet. Also called head pressure or high side pressure.
DRY AIR - Air which contains no moisture vapor.
DRY BULB TEMPERATURE - Temperature read with an ordinary thermometer.
EFFECTIVE TEMPERATURE - An arbitrary concept which combines into a single value the effect of temperature, humidity, and air movement as sensed by the human body.
ENTHALPY - Total amount of heat in one pound of a substance calculated from accepted temperature base, expressed in BTU's per pound mass.
EQUIVALENT LENGTH - That length of straight tubing which has the same pressure drop as the fitting, valve or accessory (of the same nominal size) being considered.
EVAPORATIVE COOLING - The cooling effect of vaporization of a liquid in a moving air stream.
EVAPORATOR - A device in which a liquid refrigerant is vaporized. Some superheating usually takes place.
EVAPORATOR SUPERHEAT - The actual temperature of the refrigerant vapor at the evaporator exit as compared to the saturated vapor temperature indicated by the suction pressure.
EXTERNAL STATIC PRESSURE - The sum of the static and velocity pressures of a moving air system at the point of measurement.
FAHRENHEIT - A temperature scale with the freezing point of water 320 F and the boiling point 2120 F at sea level.
FEET PER MINUTE - A term assigned to a velocity of a moving air stream, usually express FPM.
FILTER-DRIER - A device that removes moisture, acid and foreign matter from the refrigerant.
FLASH GAS - Instantaneous evaporation of some liquid refrigerant at the metering device due to pressure drop which cools the remaining liquid refrigerant to desired evaporation temperature.
FREEZING POINT - The temperature at which the removal of any heat will begin a change of state from a liquid to a solid.
GAUGE PRESSURE - Pressure measured with atmospheric pressure as a base.
HEAT - A form of energy causing the agitation of molecules within a substance.
HEAT EXCHANGER - A device for the transfer of heat energy from the source to the conveying medium.
HEAT FLOW - Heat flows from a warmer to a cooler substance. The rate depends upon the temperature difference, the area exposed and the type of material.
HEAT OF COMPRESSION - The heat added to a vapor by the work done on it during compression.
HEAT OF THE LIQUID - The increase in total heat (Enthalpy) per pound of a saturated liquid as its temperature is increased above a chosen base temperature. (Usually - 400F for refrigerants). It is expressed in BTU's.
HEAT TRANSFER - The three methods of heat transfer are conduction, convection and radiation.
INCHES OF MERCURY - Atmospheric pressure is equal to 29.92 inches of mercury.
LATENT HEAT - Heat that produces a change of state without a change in temperature; i.e., ice to water at 32 F0 or water to steam at 212 F0 .
LATENT HEAT OF CONDENSATION - The amount of heat energy in BTU's that must be removed to change the state of one pound of a vapor to one pound of liquid at the same temperature.
LATENT HEAT OF FUSION - The amount of heat energy, in BTU's required to change the state of one pound of a liquid to one pound of solid at the same temperature.
LATENT HEAT OF MELTING - The amount of heat energy, in BTU'S, that must be removed to change the state of one pound of solid to one pound of vapor at the same temperature.
LATENT HEAT OF VAPORIZATION - The amount of heat energy in BTU's required to change the state of one pound of a liquid to one pound of vapor at the same temperature.
LIFT - To elevate a fluid from one level to a higher level.
LIQUID LINE - A tube used to convey the liquid refrigerant from the condenser outlet to the refrigerant control device of the evaporator.
MANOMETER - A tube filled with a liquid used to measure pressures.
MBH - One MBH is equivalent to 1,000 BTU's per hour.
MEAN TEMPERATURE DIFFERENCES - The mean of difference between the temperature of a fluid receiving and a fluid yielding heat.
MELTING POINT - The temperature at which the addition of any heat will begin a change of state from a solid to a liquid.
MERCURY MANOMETER - Used to measure vacuum in inches of mercury.
MICRON - A unit used to measure high vacuums. One micron equals 1/25,400 of one inch mercury.
MOLLIER CHART - A psychrometric chart. How-to convert between Mollier and Psyhrometric charts?
MUFFLER - Device installed in hot gas line to silence discharge surges.
OIL SEPARATOR - A device for separating out oil entrained in the discharge gas from the compressor and returning it to the crankcase.
PARTIAL PRESSURE - The pressure exerted by any individual gas in a mixture.
PITCH - The slope of a pipe line for the purpose of improving drainage.
PITOT TUBE - A device comprising a small diameter orifice projecting directly into an air stream measuring total pressure and surrounded by an annular section with small diameter entrances normal to the flow, measuring static pressure; both sections are usually connected to a manometer to indicate velocity pressure.
PRECHARGED LINES - Refrigerant line's which are filled with refrigerant and are sealed at both ends. The seals are broken when the lines are installed and the line charge becomes part of the total system charge.
PRESSURE DROP - The decrease in pressure due to friction of a fluid or vapor as it passes through a tube or duct or/and lift.
PRESSURE - TEMPERATURE RELATIONSHIP - The change effected in temperature when pressure is changed or vice versa. Only used at saturated conditions. An increase in pressure results in a temperature increase. A decrease in temperature results in a pressure decrease.
PUMPDOWN - Process of pumping refrigerant out of the evaporator and suction line at the end of the on- cycle by closing a solenoid valve in the liquid line and letting the compressor shut-off by the low pressure control.
PSYCHROMETER - A devices having both a dry and wet bulb thermometer. It is used to determine the relative humidity in a conditioned space. Most have an indexed scale to allow direct conversion from the temperature readings to the percentage of relative humidity.
PSYCHROMETRIC CHART - A chart on which can be found the properties of air under varying conditions of temperature, water vapor content, volume, etc.
QUICK CONNECT - Name given to the end connections on precharged lines which screw on to mated fittings of the outdoor and indoor sections. Tightening the quick connections ruptures the seals on the fittings and the line charge becomes part of the total system charge.
RADIATION - The transfer of heat without an intervening medium. It is absorbed on contact with a solid surface.
RECEIVER - A vessel for holding refrigerant liquefied by the condenser.
REFRIGERANT - A substance which produces a refrigerating effect while expanding or vaporizing.
REFRIGERANT CONTROL - A device used to meter the amount of refrigerant to an evaporator. It also serves as a dividing point between the high and low pressure sides of the system.
REFRIGERANT DISTRIBUTOR - A device which meters equal quantities of refrigerant to independent circuits in the evaporator coil.
REFRIGERANT MIGRATION - The movement of refrigerant through the system to the compressor crankcase during the off-cycle, caused by its attraction to oil.
REFRIGERANT OPERATING CHARGE - The total amount of refrigerant required by a a system for correct operation.
REFRIGERANT VELOCITY - The rate at which refrigerant is moving at a given point in a system, usually given in feet per minute (FPM).
REFRIGERATION - The transfer of heat from a place where it is not wanted to a place where its presence is not desirable.
REFRIGERATION EFFECT - The amount of heat a given quantity of refrigerant will absorb in changing from a liquid to a vapor at a given evaporating pressure.
RELATIVE HUMIDITY - The percentage of water vapor present in a given quantity air compared to the amount it can hold at its temperature.
RELAY - A device used to open and close an electrical circuit. The relay may may be actuated by a bimetal electrically heated strip, a rod wrapped with a fine resistance wire causing expansion when energized, a bellows actuated by expansion of a fluid or gas or an electromagnetic coil.
REVERSING VALVE - A device in a heat pump that is electrically controlled to reverse the flow of refrigerant as the system is switched from cooling to heating; also called a four-way valve.
RISER - A vertical tube or pipe which carries refrigerant in any form from a lower to a higher level.
SATURATED VAPOR - Vapor in contact with a liquid.
SATURATION - A condition of stable equilibrium of a vapor and a liquid.
SENSIBLE HEAT - Heat that can be measured or felt. Sensible heat always causes a temperature rise.
SIGHT GLASS - A glass installed in the liquid line permitting visual inspection of the liquid refrigerant for the purpose of detecting vapor in the liquid. They also generally have a device included to monitor moisture content of the refrigerant.
SLUGGING - A condition in which a quantity of liquid enters the compressor causing hammering and possible compressor damage.
SPECIFIC HEAT - The amount of heat necessary to change the temperature of one pound of a substance 10 F.
SPECIFIC VOLUME - The volume of a substance per unit of mass; i.e., standard air 13.33 cubic feet per pound. The reciprocal of density.
STANDARD AIR DENSITY - .075 pounds per cubic foot. Equivalent to dry air at 700 F and at sea level pressure.
STATE CONDITION - Substances can exist in three states - solid, liquid or vapor.
STATIC PRESSURE - The normal force per unit area at a small hole in the wall of a duct.
STATIC TAP - A means by which static pressures of a duct system may be read directly, usually consisting of a small diameter hole in the side of the duct connected to a manometer.
SUB COOLING - Cooling of a liquid, at a constant pressure, below the point at which it was condensed.
SUBLIMATION - A condition where a substance changes from a solid to a gas without becoming a liquid.
SUCTION LINE - A tube used to convey the refrigerant vapor from the evaporator outlet to the suction inlet of compressor.
SUCTION LINE ACCUMULATOR - A device located in the suction line that intercepts quantities of a liquid refrigerant and thereby prevents damage to the compressor.
SUPERHEAT - Heat added to a vapor after all liquid has been vaporized.
TEMPERATURE - A measurement of heat intensity.
THERMISTOR - Basically a semiconductor which has electrical resistance that varies inversely with temperature.
THERMOSTAT - A bimetal actuated switch to close and open a circuit to indicate or terminate operation of a heating or air conditioning system.
THERMOSTATIC EXPANSION VALVE - Refrigerant control which monitors the flow rate according to the superheat at the evaporator outlet.
THERMOSTAT SUBBASE - When installed with a thermostat it permits selection of function for heating, cooling, automatic changeover and blower cycling or continuous operation.
TON OF REFRIGERATION - The amount of heat necessary to completely melt one ton of 320F ice in 24 hours. 200 BTUs per minute, 12,000 BTUs per hour, 288,000 BTUs in 24 hours. This is based on the latent heat of fusion for ice which is 144 BTUs per pound.
TOTAL HEAT (Enthalpy) - Total heat energy in a substance. The sum of sensible and latent heat.
TOTAL PRESSURE - The sum of all partial pressures in a mixture of gases.
TRAP - A depression or dip in refrigerant piping in which oil will collect. A trap may be placed at the base of a suction or hot gas riser to improve oil return up the riser.
VACUUM - Any pressure below atmospheric pressure.
VAPOR BARRIER - The term applied to an impervious layer of material superimposed upon a layer of insulation. Vapor barriers are always applied on the warm side of the insulation layer.
VAPOR PRESSURE - The pressure exerted by vapor.
VELOCITY PRESSURE - In a moving fluid, the pressure capable of causing an equivalent velocity as applied to move the same fluid through an orifice such that all pressure energy expanded is converted into kinetic energy.
WATER MANOMETER - Used to measure pressure in inches of water.
WET BULB TEMPERATURE - Temperature read with a thermometer whose bulb is encased in a wetted wick.