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DEFINITIONS

refrigerant circuit in which a refrigerant is circulated for the ing parts, complete with motive power, in an enclosed unit of
purpose of extracting heat. said machinery.
REFRIGERATION CAPACITY RATING. Expressed as [BF] SHAFT. An enclosed space extending through one or
1 horsepower (0.75 kW), 1 ton or 12,000 Btu/h (3.5 kW), more stories of a building, connecting vertical openings in
shall all mean the same quantity. successive floors, or floors and the roof.
REFRIGERATION MACHINERY ROOM. See “Machin- [BF] SHAFT ENCLOSURE. The walls or construction
ery room.” forming the boundaries of a shaft.
REFRIGERATION SYSTEM, ABSORPTION. A heat- [A] SLEEPING UNIT. A room or space in which people
operated, closed-refrigeration cycle in which a secondary sleep, which can also include permanent provisions for liv-
fluid (the absorbent) absorbs a primary fluid (the refrigerant) ing, eating, and either sanitation or kitchen facilities but not
that has been vaporized in the evaporator. both. Such rooms and spaces that are also part of a dwelling
Direct system. A system in which the evaporator is in unit are not sleeping units.
direct contact with the material or space refrigerated, or is [BF] SMOKE DAMPER. A listed device installed in ducts
located in air-circulating passages communicating with and air transfer openings designed to resist the passage of
such spaces. smoke. The device is installed to operate automatically, con-
Indirect system. A system in which a brine coil cooled by trolled by a smoke detection system, and where required, is
the refrigerant is circulated to the material or space refrig- capable of being positioned from a fire command center.
erated, or is utilized to cool the air so circulated. Indirect [BF] SMOKE-DEVELOPED INDEX. A numerical value
systems are distinguished by the type or method of appli- assigned to a material tested in accordance with ASTM E84.
cation.
REFRIGERAT SYSTEM CLASSIFICATION. SOLAR THERMAL SYSTEM. A system that converts
solar radiation to thermal energy for use in heating or cooling.
Refrigeration systems are classified according to the degree
of probability that leaked refrigerant from a failed connec- SOLID FUEL (COOKING APPLICATIONS). Applicable
tion, seal or component will enter an occupied area. The dis- to commercial food service operations only, solid fuel is any
tinction is based on the basic design or location of the bulk material such as hardwood, mesquite, charcoal or bri-
components. quettes that is combusted to produce heat for cooking opera-
tions.
REFRIGERATION SYSTEM, MECHANICAL. A com-
bination of interconnected refrigeration-containing parts con- SOURCE CAPTURE SYSTEM. A mechanical exhaust
stituting one closed refrigerant circuit in which a refrigerant system designed and constructed to capture air contaminants
is circulated for the purpose of extracting heat and in which a at their source and to exhaust such contaminants to the out-
compressor is used for compressing the refrigerant vapor. door atmosphere.
REFRIGERATION SYSTEM, SELF-CONTAINED. A [FG] STATIONARY FUEL CELL POWER PLANT. A
complete factory-assembled and tested system that is shipped self-contained package or factory-matched packages that
in one or more sections and that does not have refrigerant- constitute an automatically operated assembly of integrated
containing parts that are joined in the field by other than com- systems for generating useful electrical energy and recover-
panion or block valves. able thermal energy that is permanently connected and fixed
in place.
[A] REGISTERED DESIGN PROFESSIONAL. An indi-
vidual who is registered or licensed to practice their respec- STEAM-HEATING BOILER. A boiler operated at pres-
tive design profession as defined by the statutory sures not exceeding 15 psi (103 kPa) for steam.
requirements of the professional registration laws of the state STOP VALVE. A shutoff valve for controlling the flow of
or jurisdiction in which the project is to be constructed. liquid or gases.
RETURN AIR. Air removed from an approved conditioned [BG] STORY. That portion of a building included between
space or location and recirculated or exhausted. the upper surface of a floor and the upper surface of the floor
RETURN AIR SYSTEM. An assembly of connected ducts, next above, except that the topmost story shall be that portion
plenums, fittings, registers and grilles through which air from of a building included between the upper surface of the top-
the space or spaces to be heated or cooled is conducted back most floor and the ceiling or roof above.
to the supply unit (see also “Supply air system”). STRENGTH, ULTIMATE. The highest stress level that the
[FG] ROOM HEATER VENTED. A free-standing heating component will tolerate without rupture.
unit burning solid or liquid fuel for direct heating of the space SUPPLY AIR. That air delivered to each or any space sup-
in and adjacent to that in which the unit is located. plied by the air distribution system or the total air delivered to
SAFETY VALVE. A valve that relieves pressure in a steam all spaces supplied by the air distribution system, which is
boiler by opening fully at the rated discharge pressure. The provided for ventilating, heating, cooling, humidification,
valve is of the spring-pop type. dehumidification and other similar purposes.
SELF-CONTAINED EQUIPMENT. Complete, factory- SUPPLY AIR SYSTEM. An assembly of connected ducts,
assembled and tested, heating, air-conditioning or refrigera- plenums, fittings, registers and grilles through which air,
tion equipment installed as a single unit, and having all work- heated or cooled, is conducted from the supply unit to the

18 2018 INTERNATIONAL MECHANICAL CODE 
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