Figure 4-6.One-pipe water-heating system.
Figure 4-7.Two-pipe water-heating system: A. direct return;
B. reverse return.
A two-pipe system is shown in figure 4-7. In this
system, the supply main carries hot water, and the
cooled water is returned through a separate return pipe.
For a more thorough discussion of hot-water
heating systems and equipment, you should read chapter
10 of Utilitiesman 2, NAVEDTRA 10662.
Unit heaters are either gas-fired units or they consist
of coils of tubing that circulate hot water or steam. A
built-in fan behind the unit or coils blows the heated air
throughout the area it is heating. When used, unit heaters
are usually suspended from ceilings or are mounted high
on walls in large, open areas of garages, shops, and
When you are in a cold room, your sensation of chill
is due more to the loss of your body heat to the
surrounding surfaces than to the temperature of the air.
To compensate for this condition, a radiant-heating (or
panel-heating) system warms the surrounding surfaces
so that you are more comfortable at a lower air
temperature. This type of heating system consists of
hot-air pipes, hot-water pipes, or electric coils that are
embedded in walls, floors, or ceilings.
Most ventilating systems take advantage of the
natural environment. The ventilating system is designed
to use the natural forces of wind and interior-exterior
temperature differences to cause circulation and
maintain a continuous freshening of the internal air. In
general, air is permitted to enter through openings at or
near floor level and allowed to escape through openings
high on the walls or in ceilings and roof.
In mechanical ventilation, air circulation is induced
by mechanical means-usually by fans-that may be
combined with supply and exhaust duct systems.
Providing complete comfort conditioning for a
building involves more than simply controlling
temperature. It also includes providing balanced
humidity; fresh and clean air that is free of odors, dirt,
dust, and lint particles; and controlled air motion. Air
conditioning is the process that provides and controls
all of those conditions.
The cooling and warming of the air is usually
referred to as winter and summer air conditioning.
Winter and summer air conditioning is done by
installing both cooling and heating equipment in the
air-conditioning system. Of course, single units for
heating and cooling may be used separately.
Heating equipment for winter air conditioning is
most often automatic. Heating coils, usually built into
the air-conditioning unit, give up heat from the water or
steam that passes through them from a heating unit. Heat
may also be generated within an air-conditioning unit
directly by a gas-heating unit or by an electric heater.
No matter what type of heat is used, the goal is to heat