Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual page 48

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 Reducing Valve: A device used to
decrease the pressure of a gas or liquid.
Prime Surface: A heating surface with the heat-
ing 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 trans-
fers 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 maxi-
mum 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 heat-
ing 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 tem-
perature 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
substance 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.
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 boil-
ing 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 pas-
sage of steam. See Thermostatic, Float, Bucket
Trap.
Superheated Steam: Steam heated above the
temperature corresponding to its pressure.
Supply Mains: The pipes through which the heat-
ing 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.
Thermostat: An instrument which responds to
changes in temperature and which directly or
indirectly controls the room temperature.
Thermostatic Trap: A steam trap which closes
when the steam reaches it and opens when the
temperature surrounding it drops. This occurs
when cold condensate or air reaches it. The tem-
perature sensitive element is usually a sealed
bellows or series of diaphragm chambers con-
taining a small quantity of volatile liquid.
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.
49