Fahrenheit:
A thermometer scale at which the
freezing point of water is 32° and its boiling
point is 212° above zero.
Flash (Steam):
The rapid passing into steam of
water at a high temperature when the pressure
it is under is reduced so that its temperature is
above that of its boiling point for the reduced
pressure. For example: If hot condensate is dis-
charged by a trap into a low pressure return or
into the atmosphere, a certain percentage of the
water will be immediately transformed into
steam. It is also called re-evaporation .
Float & Thermostatic Trap:
A float trap with a
thermostatic element for permitting the escape
of air into the return line.
Float Trap:
A steam trap which is operated by a
float. When enough condensate has drained (by
gravity) into the trap body the float is lifted. In
turn, the pin lifts off its seat. This permits the
condensate to flow into the return until the float
has been sufficiently lowered, to close the port.
Temperature does not affect the operation of a
float trap.
Furnace:
That part of a boiler or warm air heat-
ing plant in which combustion takes place.
Complete heating unit of a warm air heating
system.
Gauge Pressure:
The pressure above that of the
atmosphere. It is the pressure indicated on an
ordinary pressure gauge. It is expressed as a
unit pressure such as Ibs. per sq. in. gauge.
Head:
Unit pressure usually expressed in ft. of
water or mil-inches of water.
Heat:
That form of energy into which all other
forms may be changed. Heat always flows from a
body of higher temperature to a body of lower tem-
perature. See also: Latent Heat, Sensible Heat,
Specific Heat, Total Heat, Heat of the Liquid.
Heat of the Liquid:
The heat (Btu) contained in a
liquid due to its temperature. The heat of the liq-
uid for water is zero at 32° F. and increases 1
Btu approximately for every degree rise in tem-
perature.
Heat Unit:
In the foot-pound-second system, the
British Thermal Unit (Btu) in the centimeter-gram-
second system, the calorie (cal.).
Heating Medium:
A substance such as water,
steam, or air used to convey heat from the boil-
er, furnace, or other source of heat to the heat-
ing units from which the heat is dissipated.
Heating Surface:
The exterior surface of a heat-
ing unit. See also Extended Heating Surface.
Heating Unit:
Radiators, convectors, base
boards, finned tubing, coils embedded in floor,
wall, or ceiling, or any device which transmits
the heat from the heating system to the room
and its occupants.
Horsepower:
A unit to indicate the time rate of
doing work equal to 550 ft.-lb. per second, or
33,000 ft.-lb. per minute. One horsepower
equals 2545 Btu per hour or 746 watts.
Hot Water Heating System:
A heating system in
which water is used as the medium by which
heat is carried through pipes from the boiler to
the heating units.
Humidistat:
An instrument which controls the
relative humidity of the air in a room.
Humidity:
The water vapor mixed with air.
Insulation (Thermal):
A material having a high
resistance to heat flow.
Latent Heat of Evaporation:
The heat (Btu per
pound) necessary to change 1 pound of liquid
into vapor without raising its temperature. In
round numbers this is equal to 960 Btu per
pound of water.
Latent Heat of Fusion:
The heat necessary to
melt one pound of a solid without raising the
temperature of the resulting liquid. The latent
heat of fusion of water (melting 1 pound of ice)
is 144 Btu.
Mechanical Equivalent of Heat:
The mechanical
energy equivalent to 1 Btu which is equal to 778
ft.-lb.
Mil-lnch:
One one-thousandth of an inch (0.001”).
One-Pipe Supply Riser (Steam):
A pipe which
carries steam to a heating unit and which also
carries the condensation from the heating unit.
In an up feed riser steam travels upwards and
the condensate downward while in a down feed
both steam and condensate travel down.
One-Pipe System (Hot Water):
A hot water heat-
ing system in which one pipe serves both as a
supply main and as a return main. The heating
units have separate supply and return pipes but
both are connected to the same maln.
One-Pipe System (Steam):
A steam heating sys-
tem consisting of a main circuit in which the
steam and condensate flow in the same pipe.
There is one connection to each heating unit
which serves as both the supply and the return.
Overhead System:
Any steam or hot water sys-
tem in which the supply main is above the heat-
ing units. With a steam system the return must
be below the heating units; with a water system,
the return may be above the heating units.
Panel Heating:
A method of heating involving
the installation of the heating units (pipe coils)
in the walls, floor or ceiling of the room.
Panel Radiator:
A heating unit placed on, or
flush with, a flat wall surface and intended to
function as a radiator. Do not confuse with panel
heating system.
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