Home Education Glossary of Terms
Glossary of Technical Terms - R

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Radiant Heating: A heating system in which only the heat radiated from panels is effective

Radiation: Transfer of heat by heat rays

Radiator: A heating unit exposed to view within the room or space to be heated

Radiator Valve: A valve installed on a terminal unit to manually control the flow of water through the unit

Range: Pressure or temperature of a control

Rankine scale: Absolute Fahrenheit scale

Reactance: Opposition to alternating current by either inductance or capacitance or both

Reciprocating: Action in which the motion is back and forth in a straight line

Recirculated Air: Return air passed through the conditioner before being again supplied to the conditioned space

Rectifier Electric: An electric: An electrical device for converting ac into dc.

Reducing Fitting: A pipe fitting designed to change form one pipe size to another

Reed Valve: Thin flat tempered steel plate fastened at one end.

Refractory: A material that can withstand high temperature

Refrigerant: Substance used in refrigerating mechanism to absorb heat in evaporator coil and to release its heat in a condenser

Refrigerant Charge: Quantity of refrigerant in a system is capable of transferring

Refrigeration Effect: The amount of heat in Btu/h the system is capable of transferring

Refrigeration: The process of transferring heat from one place to another

Refrigeration oil: Specially prepared oil used in refrigerator mechanism it circulates with refrigerant

Register: Combination grille and damper assembly covering on an air opening or end of an air duct

Relative Humidity: A ratio of weight of moisture that air actually contains at a certain temperature as compared to the amount that it could contain if it were saturated

Relay: Electrical mechanism which uses small current in control circuit to operate a valve switch in operating circuit

Relief Opening: The opening in a draft hood to permit ready escape to the atmosphere of flue products

Relief Valve: Safety device designed to open before dangerous pressure is reached

Repulsion-Start Induction Motor: Type of motor which has an electrical winding on the rotor for starting-purposes

Resistance: The opposition to current flow by a physical conductor

Resonance: The pipe organ effect produced by a gas furnace when the frequency of the burner flame combustion and the pressure wave distance in the burner pouch are in exact synchronization

Return Air: Air returned from conditioned or refrigerated space

Return Piping: That portion of the piping system that carries water from the terminal units back to the boiler

Reverse Acting Control: A switch controlled by temperature and designed to open on temperature drop and close on temperature rise

Reverse Cycle Defrost: Method of heating evaporator for defrosting purposes by using valves to move hot gas from compressor into evaporator

Reverse Return: A two pipe system in which the return connections from the terminal units into the return main are made in the reverse order from that in which the supply connections are made

Reversing Valve: The control used to regulate the flow of refrigerant in a heat pump

Rheostat: An adjustable or variable resistor

Rich Mixture: A mixture of gas and air containing too much fuel or too little air to complete combustion of the gas

Rollout: A condition where flame rolls out of a combustion chamber when the burner is turned on.

Rotary Compressor: Mechanism which pumps fluid by using rotating motion

Rotor: Rotating part of a mechanism

Running Winding: Electrical winding of motor which has current flowing through it during normal operation of motor

Run-Out: This term generally applies to the horizontal portion of branch circuits

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