HVAC GLOSSARY - R

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R-Value: A measure, in Btu / (ft2 F), of the resistance to transmission of heat by an insulating material. The higher the R-value of a material, the greater its insulating properties and the slower the heat flows through it. The specific value needed to insulate a home depends on climate, type of heating system and other factors.

Radiant: System that uses hot surfaces to radiate or convect heat into the environment without the use of fans or blowers.

Radiant Barrier: A device designed to reduce or stop the flow of radiant energy.

Radiation: The transfer of heat directly from one surface to another (without heating the intermediate air acting as a transfer mechanism).

Radioactive Decay: The disintegration of the nuclei of the atoms of radioactive (charged) elements with the concomitant release of alpha, beta, or gamma rays.

Radon (Rn) and Radon Decay Products: Radon is a radioactive gas formed and emitted by the decay of radium and uranium in rock. The radon decay products (also called radon daughters or progeny) can be breathed into the lung where they continue to release radiation as they further decay.

Re-Entrainment: Situation that occurs when the air being exhausted from a building is immediately brought back into the system through the air intake and other openings in the building envelope.

Receiver: Tank on the liquid side of a system that holds excess refrigerant in the system that needs to be there for proper operation.

Reclaiming: Processing or returning used refrigerant to the manufacturer or processor for disposal or reuse.

Recool: The sensible cooling of air that has been previously heated by HVAC systems serving the same building.

Refrigerant: Substance used in refrigerating mechanism. A substance that produces a refrigerating effect while expanding or vaporizing. Air conditioning systems use Refrigerant in the Evaporator Coil to cool air as it passes by. Refrigerants absorb heat in evaporator by change of state from a liquid to a gas and releases its heat in a condenser as the substance returns from the gaseous state back to a liquid state.

Refrigerant Charge: The amount of refrigerant contained within the air conditioning equipment and required for proper operation.

Refrigerant Lines: Two copper lines that connect the Condenser (Outdoor) Coil to the Evaporator (Indoor) Coil.

Registers: Combination grille and damper assembly covering an air opening or end of an air duct. Coverings for the ducts where they open to the conditioned space. (Same as Grilles).

Reheat: The heating of air that has been previously cooled either by mechanical refrigeration or economizer cooling systems.

Relative Humidity: (RH) Relative humidity is defined as the ratio of the water vapor pressure to the saturation vapor pressure (over water) at the temperature of the gas. RH = Pw/Pws * 100.

Relative Risk: The ratio of health impact incidence among exposed individuals to incidence among unexposed individuals.

RELs: Recommended Exposure Limits (recommendations made by the National Institute for Occupational Safety and Health (NIOSH).

Remediate: Fix

Reservoir: The environmental substrate, or source, of a particular organism. Reservoirs for indoor bio contaminants include stagnant water, moist surfaces, and dust collection sites.

Residential: The residential sector is defined as private household establishments which consume energy primarily for space heating, water heating, air conditioning, lighting, refrigeration, cooking, and clothes drying. The classification of an individual consumer¹s account, where the use is both residential and commercial, is based on principal use.

Resistance (Electrical): The ability of all conductors of electricity to resist the flow of current, turning some of it into heat. Resistance depends on the cross section of the conductor (the smaller the cross section, the greater the resistance), the material, the length of the flow path, and its temperature (the hotter the cross section, the greater its resistance).

Resistance (Thermal): The reciprocal of thermal conductance. (See R-Value).

Respirable Suspended Particulates: Particulates less than 10 μm in diameter that can enter the respiratory tract.

Retrofit: Broad term that applies to any change after the original purchase, such as adding equipment not a part of the original purchase. As applied to alternative fuel vehicles, it refers to conversion devices or kits for conventional fuel vehicles.

Return: The ductwork that carries air from the house to the air handler.

Return Air: Air drawn into a heating unit after having been circulated from the heater's output supply to a room. The air removed from an occupied space and returned to the air handler to be exhausted or recirculated.

RSES: A leading HVAC/R Association - Refrigeration Service Engineers Society - http://www.rses.org/