Brochure

136
Hoffman Specialty
®
Glossary of Terms
Selection Guides
One-Pipe System (Steam): A steam heating system
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 system in
which the supply main is above the heating 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.
Pilot Valve: A valve that uses a small valve to control a
large valve.
Pressure: Force per unit area such as Ib. per sq. inch.
Unless otherwise qualified, it refers to unit static gauge
pressure. See Static, Velocity, Total, Gauge and Absolute
Pressures.
Pressure Powered Pump: Motorless pump that uses
steam or air pressure to move condensate back to the
boiler room.
Pressure Reducing Valve: A device used to decrease the
pressure of a gas or liquid.
Prime Surface: A heating surface with the heating
medium on one side and air (or extended surface) on the
other.
Radiant Heating: A heating system in which the heating
is by radiation only. Sometimes used in a Panel Heating
System.
Radiation: The transmission of heat in a straight line
through space.
Radiator: A heating unit located in the room to be heated
and exposed to view. A radiator transfers heat by radiation
to objects “it can see” and by conduction to the
surrounding air which in turn is circulated by natural
convection.
Recessed Radiator: A heating unit recessed in
a wall but not enclosed.
Reducing Valve: See Pressure Reducing Valve.
Re-Evaporation: See Flash.
Refrigeration, Ton of: See Ton of Refrigeration.
Relative Humidity: The amount of moisture in a given
quantity of air compared with the maximum amount of
moisture the same quantity of air could hold at the same
temperature. It is expressed as a percentage.
Return Mains: The pipes which return the heating
medium from the heating units to the source of heat
supply.
Reverse-Return System (Hot Water): A two-pipe hot
water heating system in which the water from several
heating units is returned along paths so that all radiator
circuits of the system are of equal length
Sensible Heat: Heat which increases the temperature of
objects as opposed to latent heat.
Specific Heat: In the foot-pound-second system, the
amount of heat (Btu) required to raise one pound of a
substance one degree Fahrenheit. In the centimeter-gram-
second system, the amount of heat (cal.) required to raise
one gram of a sub
stance one degree C. The specific heat of
water is 1.
Split System: A system in which the heating is
accomplished by radiators or convectors and ventilation
by separate apparatus.
Sparge Tube: Slotted tube inserted in the condensate
return tank or boiler feed tank that injects steam to
preheat the condensate. Normally uses waste steam to
improve efficiency of the system.
Square Foot of Heating Surface: Equivalent direct
radiation (EDR). By definition, that amount of heating
surface which will give off 240 Btu per hour when filled
with a heating medium at 215°F. and surrounded by air at
70° F. The equivalent square foot of heating surface may
have no direct relation to the actual surface area.
Static Pressure: The pressure at which a pipe will burst. It
is used to overcome the frictional resistance to flow
through the pipe. It is expressed as a unit pressure and
may be in absolute or gauge pressure. It is frequently
expressed in feet of water column or in the case of pipe
friction in mil-inches of water column
per ft. of pipe.
Steam: Water in the vapor phase. The vapor formed when
water has been heated to its boiling point, corresponding
to the pressure it is under. See also Dry Saturated Steam,
Wet Saturated Steam, Superheated Steam.
Steam Heating System: A heating system in which the
heating units give up their heat to the room by condensing
the steam furnished to them by a boiler or other source.
Steam Trap: A device for allowing the passage of
condensate and air but preventing the passage of steam.
See Thermostatic, Float and Thermostatic, Bucket Trap,
Thermodisc Traps.
Storage Capacity: The volume of condensate that the
condensate receiver is capable of holding.
Superheated Steam: Steam heated above the
temperature corresponding to its pressure.
Supply Mains: The pipes through which the heating
medium flows from the boiler or source of supply to the
run-outs and risers leading to the heating units.
Tank Regulator: See Temperature Regulator.
Temperature Regulator: A device for controlling the
admission of steam to a hot water or liquid heating device
in correct quantities so that the temperature of the liquid
will remain constant.
Glossary of Terms (cont’d)