Brochure

133
Hoffman Specialty
®
Glossary of Terms
Glossary of Terms
Glossary of Terms
The definitions given in this section are only those
applying to heating and particularly as used in this
catalog. Some do not define the terms for all usages.
Absolute Humidity: The weight of water vapor in grains
actually contained in one cubic foot of the mixture of air
and moisture.
Absolute Pressure: The actual pressure above zero. It is
the atmospheric pressure added to the gauge pressure. It
is expressed as a unit pressure such as Ibs.per sq. in.
absolute.
Absolute Temperature: The temperature of a substance
measured above absolute zero. To express a temperature
as absolute temperature add 460° to the reading of a
Fahrenheit thermometer or 273° to the reading of a
Centigrade.
Absolute Zero: The temperature (-460°F. approx.) at
which all molecular motion of a substance ceases, and at
which the substance contains no heat.
Air: An elastic gas. It is a mechanical mixture of oxygen
and nitrogen and slight traces of other gases. It may also
contain moisture known as humidity. Dry air weighs
0.075 Ibs. per cu. ft.
One Btu will raise the temperature of 55 cu. ft. of air one
degree F.
Air expands or contracts approximately 1/490 of its
volume for each degree of rise or fall in temperature from
32° F.
Air Change: The number of times in an hour the air in a
room is changed either by mechanical means or by the
infiltration of outside air leaking into the room through
cracks around doors and windows, etc.
Air Cleaner: A device designed for the purpose of
removing air-borne impurities such as dust, fumes, and
smokes. (Air cleaners include air washers and air filters.)
Air Conditioning: The simultaneous control of the
temperature, humidity, air motion, and air distribution
within an enclosure. When human comfort and health are
involved, a reasonable air purity with regard to dust,
bacteria,and odors is also included. The primary
requirement of a good air conditioning system is a good
heating system.
Air Infiltration: The leakage of air into a house through
cracks and crevices, doors, windows, and other openings,
caused by wind pressure and/or temperature difference.
Air Valve: See Vent Valve.
Atmospheric Pressure: The weight of a column of air,
one square inch in cross section and extending from the
earth to the upper level of the blanket of air surrounding
the earth. This air exerts a pressure of 14.7 pounds per
square inch at sea level, where water will boil at 212°F.
High altitudes have lower atmospheric pressure with
correspondingly lower boiling point temperatures.
Boiler: A closed vessel in which steam is generated or in
which water is heated by fire.
Boiler Feed Pump: A pump that is governed by a control
that monitors the actual boiler water level; and only adds
water to the boiler when the boiler needs it. The pump
controller is mounted on the boiler.
Boiler Feed Unit: A pre-packaged system consisting of a
tank, pump, and makeup water line that returns condensate
to the boiler
Boiler Heating Surface: The area of the heat transmitting
surfaces in contact with the water (or steam) in the boiler on
one side and the fire or hot gases on the other.
Boiler Horsepower: The equivalent evaporation of 34.5 Ibs.
of water per hour at 212° F. to steam at 212° F. This is equal
to a heat output of 33,475 Btu per hour, which is equal to
approximately 140 sq. ft. of steam radiation (EDR) .
British Thermal Unit (BTU): The quantity of heat required
to raise the temperature of 1 Ib. of water 1°F. This is
somewhat approximate but sufficiently accurate for any
work discussed in this catalog.
BSPT: British Standard Pipe Thread
Bucket Trap (Inverted): A float trap with an open float. The
float or bucket is open at the bottom. When the air or steam
in the bucket has been replaced by condensate the bucket
loses its buoyancy and when it sinks it opens a valve to
permit condensate to be pushed into the return.
Bucket Trap (Open): The bucket (float) is open at the top.
Water surrounding the bucket keeps it floating and the pin
is pressed against its seat. Condensate from the system
drains into the bucket. When enough has drained into it so
that the bucket loses its buoyancy it sinks and pulls the pin
off its seat and steam pressure forces the condensate out of
the trap.
Calorie (Small): The quantity of heat required to raise
1 gram of water 1°C (approx.).
Calorie (Large): The quantity of heat required to raise
1 kilogram of water 1°C (approx.).
Cavitation: Term used to describe when condensate
flashes into steam as it passes through a negative pressure
in the eye of a centrifugal pump impeller. Steam pockets
may form in the impeller eye and then implode as they
enter a positive pressure in the impeller passage.
Centigrade: A thermometer scale at which the freezing
point of water is 0° and its boiling is 100°.
Central Fan System: A mechanical indirect system of
heating, ventilating, or air conditioning consisting of a
central plant where the air is heated and/or conditioned
and then circulated by fans or blowers through a system of
distributing ducts.
Chimney Effect: The tendency in a duct or other vertical air
passage for air to rise when heated due to its decrease in
density.