Brochure

135
Hoffman Specialty
®
Glossary of Terms
Selection Guides
Extended Surface Heating Unit: A heating unit having a
relatively large amount of extended surface which may be
integral with the core containing the heating medium or
assembled over a core, making good thermal contact by
pressure, or by being soldered to the core or by both
pressure and soldering. An extended surface heating unit
is usually placed within an enclosure and functions as a
convector.
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
discharged 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 Switch: A mechanical switch activated by a float on
the end of a rod. This device is used in controlling the
condensate pump, makeup valve, low water cutoff, etc.
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 heating 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 temperature. 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 liquid for water is
zero at 32° F. and increases 1 Btu approximately for every
degree rise in temperature.
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 boiler, furnace, or other
source of heat to the heating units from which the heat is
dissipated.
Heating Surface: The exterior surface of a heating 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.
Low Pressure Steam: As defined by ASME, low pressure
steam is 15 PSIG or less.
Low Water Cutoff: Float switch inside the boiler feed
receiver set to prevent pumps from operating at low
water level conditions.
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”).
NPSHR and NPSHA: Are short for Net Positive Suction
Head Required and Net Positive Suction Head Available.
NPSHR curves for centrifugal pumps are needed because
all centrifugal pumps operate at a lower pressure in the
impeller eye than the pressure existing at the pump
suction flange. The curve identifies the pressure over and
above fluid flash point or vaporization pressure, which is
needed at the pump impeller eye and takes into account
decreased pressures within the pump.
NPT: National Pipe Thread
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 heating
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.
Glossary of Terms (cont’d)