Brochure

137
Hoffman Specialty
®
Glossary of Terms
Glossary of Terms
Thermostat: An instrument which responds to changes in
temperature and which directly or indirectly controls the
room temperature.
Thermodisc Trap: A steam trap that operates by the
cycling of a free-floating disc. The disc cycles in reaction
to the inlet pressure of condensate and air against the
bottom of the disc and pressure from flash steam that is
trapped between the top of the disc and the trap cap
chamber. Inlet pressure forces the disc off its seat. Flash
steam, created from hot condensate reacting to the
lower downstream pressure, builds pressure of top of the
disc in the cap chamber and forces the disc down onto its
seating surfaces. Pressure in the cap chamber drops due
to cooling from natural heat losses. When the inlet
pressure becomes greater than the cap chamber
pressure, the cycle repeats.
Ton of Refrigeration: The heat which must be extracted
from one ton (2,000 Ibs.) of water at 32° F. to change it
into ice at 32°F. in 24 hours. It is equal to 288,000 Btu/24
hours, 12,000 Btu/hour, or 200 Btu/minute.
Total Heat: The latent heat of vaporization added to the
heat of the liquid with which it is in contact.
Total Pressure: The sum of the static and velocity
pressures. It is also used as the total static pressure over
an entire area, that is, the unit pressure multiplied by the
area on which it acts.
Trap: See Steam Trap, Thermostatic Trap, Float Trap,
Bucket Trap, Float and Thermostatic Trap and Themodisc
Trap.
Tube Bundle: A single tube (pipe) formed into a tight
array so as to present a large surface area in a small
space.
Two-Pipe System (Steam or Water): A heating system in
which one pipe is used for the supply main and another
for the return main. In a two-pipe hot water system each
heating unit receives a direct supply of the heating
medium.
Unit Heater: A heating unit consisting of a heat transfer
element, housing, fan with motor, and outlet deflectors or
diffusers. It is usually suspended from the ceiling and its
heat output is controlled by starting and stopping the fan
by a room thermostat. The circulation of the heating
medium (steam or hot water) is usually continuous. It is
used primarily for industrial heating.
Unit Pressure: Pressure per unit area as Ibs. per sq. in.
Up-Feed System (Hot Water or Steam): A heating
system in which the supply mains are below the level of
the heating units which they serve.
Vacuum Heating System (Steam): A one- or two-pipe
heating system equipped with the necessary accessory
apparatus to permit the pressure in the system to go
below atmospheric.
Vapor: Any substance in the gaseous state.
Vapor Heating System (Steam): A two-pipe heating
system which operates at or near atmospheric pressure
and returns the condensation to the boiler or receiver by
gravity.
Velocity Pressure: The pressure used to create the
velocity of flow in a pipe. It is expressed as a unit pressure.
Ventilation: Air circulated through a room for ventilating
purposes. It may be mechanically circulated with a blower
system or through circulation with an open window, etc.
Vent Valve (Steam): A device that permits air to be forced
out of a heating unit or pipe and closes against water and
steam.
Vent Valve (Water): A device that permits air to be forced
out of a heating unit or pipe and closes against water.
Warm Air Heating System: A warm air heating plant
consists of a heating unit (fuel-burning furnace) enclosed
in a casing, from which the heated air is distributed to the
various rooms of the building through ducts. If the motive
head producing flow depends on the difference in weight
between the heated air leaving the casing and the cooler
air entering the bottom of the casing, it is termed a gravity
system. A booster fan may, however, be used in
conjunction with a gravitydesigned system. If a fan is used
to produce circulation and the system is designed
especially for fan circulation, it is termed a fan furnace
system or a central fan furnace system. A fan furnace
system may include air washer, filters, etc.
Wet Bulb Temperature: The lowest temperature which a
water-wetted body will attain when exposed to an air
current.
Wet Return (Steam): That part of the return main of a
steam heating system which is completely filled with water
of condensation.
Wet Saturated Steam: Saturated steam containing some
water particles in suspension.
Glossary of Terms (cont’d)