Power Engineering Dictionary
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RACEWAY - Any support system, open or closed, for carrying electric wires.


RADIANT HEATING - Heating system in which warm or hot surfaces are used to radiate heat into the space to be conditioned.

RADIATION - Transfer of heat by electromagnetic waves.


RAM AIR - Air forced through the condenser due to the rapid movement of steam from the turbine exit.

RANKINE SCALE - Name given the absolute (Fahrenheit) scale. Zero (0) R on this scale is -460F.

RANKINE TEMPERATURE - Degrees Fahrenheit plus 491.60.

RAPTURE MEMBRANE - A metal membrane (pressure relief device) designed to rapture at a predetermined pressure.



RAW MAKEUP WATER - Untreated water fed to a system to replace that lost.

RAW WATER - With water treatment it means untreated feedwater or water in its natural state, prior to any treatment.


REAGENT - A substance, chemical, or solution used in laboratory to detect, measure, or react with other substances, chemicals or solutions.

RE-CARBONATION - A process using carbon dioxide gas to stabilize and thereby prevent precipitation of calcium carbonate from cold process lime or lime-soda softened water.

RECEIVER - An auxiliary storage receptacle for fluids.

RECEIVER DEHYDRATOR - Small tank which serves as liquid refrigerants reservoir and which also contains a desiccant so remove moisture. Used on most automobile air conditioning installations.

RECEIVER HEATING ELEMENT - Electrical resistance mounted in or around liquid receiver. It is used to maintain head pressures when ambient temperature is low.

RECEIVER-DRIER - Cylinder (container) in a refrigerating system for storing liquid refrigerant and which also holds a quantity of desiccant.

RECIPROCAL - A format defined by 1 divided by the complex number.

RECIPROCATING COMPRESSOR - Compressor which uses a piston and cylinder mechanism to provide pumping action.

RECORDING THERMOMETER - Temperature measuring instrument which has a pen marking a moving chart.

RECTIFIER - A device used to convert AC current into DC current.

RECUPERATOR - Equipment for transferring heat from gaseous products of combustion to incoming air or fuel. The incoming material passes through pipes surrounded by a chamber through which the outgoing gases pass.

RED WATER - Water that has a red, cloudy appearance caused by suspended red iron oxide.

REDOX POTENTIAL - A process designed to determine if a corrosion process will occur.

REDUCING ELBOW - A fitting that makes an angle between two joints of pipe and that decreases in diameter from one end to the other.

REDUCING FLANGE - A flange fitting used to join pipes of different diameters.

REDUCING NIPPLE - A pipe fitting that is threaded on both ends and decreases in diameter from one end to the other.

REDUCING TEE - A "T"shaped pipe fitting with openings of two different sizes. The relationship:

REDUCTION - Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound.

REED VALVE - Thin, flat, tempered steel plate fastened at one end.

REFRIGERANT - The fluid used for heat transfer in a refrigerating system, which absorbs heat at a low temperature and a low pressure of the fluid and rejects heat at a higher temperature and a higher pressure of the fluid, usually involving changes of state of the fluid.

REFRIGERANT - The working fluid used in refrigerators.

REFRIGERANT CHARGE - Quantity of refrigerant in a system.

REFRIGERANT CONTROL - Device which meters flow of refrigerant between two areas of a refrigerating system. It also maintains pressure difference between high-pressure and low-pressure side of the mechanical refrigerating system while unit is running.

REFRIGERATING CAPACITY - The ability of a system to remove heat as compared with the cooling effect produced by melting of ice.

REFRIGERATING EFFECT - The amount of heat transferred by one kg of refrigerant as it circulates in the refrigeration system.

REFRIGERATION - Controlled transfer of heat from a lower temperature to a higher temperature region.

REFRIGERATION OIL - Specially prepared oil used in refrigerator mechanism which circulates, to some extent, with refrigerant.

REFRIGERATOR - A device to transfer heat from a low temperature to a high temperature medium.

REGENERATE - The solution used to restore the activity of an ion exchanger. Acids are employed to restore a cat ion exchanger to its hydrogen form; brine solutions may be used to convert the cat ion exchange to the sodium form. The anion exchanger may be rejuvenated by treatment with an alkaline solution.

REGENERATION - Restoration of the activity of an ion exchanger by replacing the ions adsorbed from the treated solution by ions that were adsorbed initially on the resin.

REGENERATIVE CYCLE - Is a gas turbine cycle employing a heat exchanger to recover some of the heat before discharging the gases from the gas turbine to the atmosphere, to recover some of the from

REGENERATIVE GAS TURBINE - Referring to a gas turbine employing heat exchanger between the compressor and the combustor for the purpose of recovering heat.


Register: A grille equipped with an integral damper or control valve.

REJUVENATION - (see regeneration)


RELATIVE HUMIDITY - The amount of moisture the air holds relative to the maximum moisture the air can hold at the same temperature.

Relative Humidity (RH): The ratio of water vapor in the air as compared to the maximum amount of water vapor that may be contained.

RELATIVE HUMIDITY -The ratio, expressed as a percentage, of the amount of water vapor present in a given volume of air at a given temperature to the amount required to saturate the air at that temperature.

RELAY - An electromechanical switch that opens or closes contacts in response to some controlled action. Relay contacts can be normally open (NO) and/ or normally closed (NC). Relays may be electric, pneumatic, or a combination of both.

RELAY, THERMAL - A switching relay in which a small heater warms a bimetal element which bends to provide the switching force.

RELIEF VALVE - Safety device on a sealed system. It opens to release fluids before dangerous pressure is reached. Also called pressure relief valve.

REMOTE SYSTEM - Refrigerating system in which condensing unit is away from space to be cooled.

Remote Temperature Set Point: Ability to set a temperature control point for a space from outside the space. Often used in public areas.

RESET - A process of automatically adjusting the control point of a given controller to compensate for changes in outdoor temperature. The hot deck control point is normally reset upward as the outdoor temperature drops. The cold deck control point is normally reset downward as the outdoor temperature increases.

RESET RATIO - The ratio of change in outdoor temperature to the change in control point temperature. For example, a 2:1 reset ratio means that the control point will increase 1 degree for every 2 degrees change in outdoor temperature.

RESIDUAL - Means small amount of, like oxygen, sulfite, acid., etc..

RESISTANCE - The opposition which limits the amount of current that can be produced by an applied voltage in an electrical circuit, measured in ohms.

RESISTANCE, THERMAL - The reciprocal of thermal conductance.

RESISTIVE LOADS - Electrical loads whose power factor is one. Usually contain heating elements.

RESONANT VIBRATION - Everything has a natural frequency. This frequency is effected by two properties: Mass and Stiffness. This "natural frequency" is the cause of many vibration problems in HVAC equipment. If you strike an object (say a tuning fork or a bell) it will continue to vibrate at its natural frequency until damping extinguishes the vibration.

RESTRICTOR - A device for producing a deliberate pressure drop or resistance in a line by reducing the cross-sectional flow area.

Return Air: Air returned from conditioned or refrigerated space.

RETURN-STEAM CONDENSATE - That steam produced by a boiler which returns to the boiler after it has condensed.

REVERSE CYCLE DEFROST - Method of heating evaporator for defrosting. Valves move hot gas from compressor into evaporator.

REVERSE CYCLE REFRIGERATION - A refrigeration system which uses reject heat to produce warmth.

REVERSE DEIONIZATION - The use of an anion-exchange unit and a cation-exchange unit-in that order-to remove all ions from solution.

REVERSE OSMOSIS - A process that reverses (by the application of pressure) the flow of water in the natural process of osmosis so that it passes from the more concentrated to the more dilute solution.

REVERSIBLE PROCESS - A process by which a fluid is made to undergo a change of state and by traversing the path in exactly the reverse of the original path is returned to its original state, and all associated systems are similarly returned to their original state.

REVERSING VALVE - Device used to reverse direction of the refrigerant flow depending upon whether heating or cooling is desired.


RINSE - The operation which follows regeneration; a flushing out of excess regenerate solution.

ROTARY COMPRESSOR - Mechanism which pumps fluid by using rotating motion.

RUNNING CURRENT - The current that flows through a load after inrush current. Usually called "full load current".

RUNNING TIME - Amount of time a condensing unit is run per hour or per 24 hours.

RUST - A visible corrosion product consisting of hydrated oxides of iron. Applied only to ferrous alloys.

RYZNAR STABILITY INDEX - An index based on calcium carbonate pH of saturation vs. actual pH to determine scaling or corrosion tendencies of a water (R.I. = 2 pHs).

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