Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual page 46

Coefficient of Heat Transmission (Over-all)-U-:
The amount of heat (Btu) transmitted from air to
air in one hour per square foot of the wall, floor,
roof, or ceiling for a difference in temperature of
one degree Fahrenheit between the air on the
inside and outside of the wall, floor, roof, or
ceiling.
Column Radiator: A type of direct radiator. This
radiator has not been sold by manufacturers
since 1926.
Comfort Line: The effective temperature at
which the largest percentage of adults feel com-
fortable.
Comfort Zone (Average): The range of effective
temperatures over which the majority of adults
feel comfortable.
Concealed Radiator: See Convector.
Condensate: Water formed by cooling steam.
The capacity of traps, pumps, etc., is some-
times expressed in Ibs. of condensate they will
handle per hour. One pound of condensate per
hour is equal to approximately 4 sq. ft. of steam
heating surface (240 Btu per hour per sq. ft.).
Conductance (Thermal)-C-: The amount of heat
(Btu) transmitted from surface to surface, in one
hour through one square foot of a material or
construction for the thickness or type under con-
sideration for a difference in temperature of one
degree Fahrenheit between the two surfaces.
Conduction (Thermal): The transmission of heat
through and by means of matter.
Conductivity (Thermal)-k-: The amount of heat
(Btu) transmitted in one hour through one
square foot of a homogenous material one inch
thick for a difference in temperature of one
degree Fahrenheit between the two surfaces of
the material.
Conductor (Thermal): A material capable of read-
ily transmitting heat by means of conduction.
Convection: The transmission of heat by the cir-
culation (either natural or forced) of a liquid or a
gas such as air. If natural, it is caused by the
difference in weight of hotter and colder fluid.
Convector: A concealed radiator. An enclosed
heating unit located either within, adjacent to, or
exterior to the room or space to be heated, but
transferring heat to the room or space mainly by
the process of convection. A shielded heating
unit is also termed a convector. If the heating
unit is located exterior to the room or space to
be heated, the heat is transferred through one
or more ducts or pipes.
Convertor: A piece of equipment for heating
water with steam without mixing the two. It may
be used for supplying hot water for domestic
purposes or for a hot water heating system.
Cooling Leg: A length of uninsulated pipe
through which the condensate flows to a trap
and which has sufficient cooling surface to per-
mit the condensate to dissipate enough heat to
prevent flashing when the trap opens. A thermo-
static trap may require a cooling leg to permit
the condensate to drop enough in temperature
to permit the trap to open.
Degree-Day: (Standard) A unit which is the differ-
ence between 65° F. and the daily average tem-
perature when it is below 65°F. The "degree
day" on any given day is equal to the number of
degrees F. that the average temperature for that
day is below 65° F.
Dew-Point Temperature: The air temperature
corresponding to saturation (100 percent rela-
tive humidity) for a given moisture content. It is
the lowest temperature at which air can retain
water vapor.
Direct-lndirect Heating Unit: A heating unit
located in the room or space to be heated which
is fully or partially closed. The enclosed portion
is used to heat air which enters from outside the
room.
Direct Radiator: Same as radiator.
Domestic Hot Water: Hot water used for purpos-
es other than house heating such as laundering,
dishwashing, bathing, etc.
Down-Feed One-Pipe Riser (Steam): A pipe
which carries steam downward to the heating
units and into which heating units drain
condensation.
Down-Feed System (Steam): A steam heating
system in which the supply mains are above the
level of the heating units which they serve.
Dry-Bulb Temperature: The temperature of the
air as determined by an ordinary thermometer.
Dry Return (Steam): A return pipe in a steam
heating system which carries both condensation
and air.
Dry Saturated Steam: Saturated steam contain-
ing no water in suspension.
Equivalent Direct Radiation (E.D.R.): See
Square Foot of Heating Surface.
Extended Heating Surface: Heating surface
consisting of ribs, fins, or extended surfaces
which receive heat by conduction from the
prime surface.
Extended Surface Heating Unit: A heating unit
having a relatively large amount of extended sur-
face which may be integral with the core contain-
ing the heating medium or assembled over a
core, making good thermal contact by pressure,
or by being soldered to the core or by both pres-
sure and soldering. An extended surface heating
unit is usually placed within an enclosure and
functions as a convector.
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