ABSOLUTE HUMIDITY - The weight of water vapor in a given amount of air.
ABSOLUTE PRESSURE - Pressure measured with the base of zero.
ABSOLUTE TEMPERATURE - A temperature scale expressed in degrees oF or oC 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 oF or -273.16oC.
AIR CONDITIONING - The process of controlling the temperature, humidity, cleanliness and distribution of the air.AIR, Standard Conditions - Conditions at which capacity ratings for air conditioning equipment is rated.
AMBIENT - Refers to the temperature surrounding a body or unit under test.
ATMOSPHERIC PRESSURE - The weight of a 1 unit column of the earth's atmosphere.
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 0 oC and the boiling point 100 oC 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 (Pa), by the suction pressure in PSI (Pa).
COMPRESSOR - A mechanical device used to compress gases. Three main types - 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.
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.
DENSITY - Mass or weight per unit of volume.
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.
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 32 oF and the boiling point 212 oF 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 - 40 oF for refrigerants).
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 at32 oF or water to steam at 212 oF.
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 liquid 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.