Most forced-air furnaces are designed for the
addition of a cooling coil. The coil is placed on the
output side of the furnace and uses a forced-air furnace
blower to circulate the air over the cooling coils. The
addition of a dehumidifier reduces moisture in the air.
The cooling unit, placed in any convenient location
outside the building, produces chilled water that is
circulated through the cooling coils near the air-
conditioned space. The air to be conditioned is then
blown over the cooling coils and is cooled by the chilled
water absorbing the heat from the air. The warmed water
is then returned to the unit.
You have probably seen fan-coil units in a school or
motel room. These units contain a fan, coil, falter,
condensate drain, and sometimes, an outside-air inlet. A
central unit furnishes air to the unit, and duct coils heat
or cool the air. The amount of air moving over the coils
and the temperature of the coils can be manually or
thermostatically controlled. A piping system provides
hot or cold water to each unit.
HEATING AND AIR-CONDITIONING
Figure 4-12 (a foldout at the end of this chapter)
shows a heating and air-conditioning layout for a
hospital. You can see that the air- conditioning plant
consists of four separate self- contained units, three of
which are located in the mechanical equipment room,
and one on the porch of the ward. Note the cooling
towers, that have not as yet been mentioned. In a
water-cooled air-conditioning system, cold water is run
over the coils of the condenser (rather than air being
blown over the coils). The purpose of the cooling tower
is to cool the water. Water is sprayed at the top of the
tower, and as it falls through the redwood louvers, it is
cooled by the air. Sometimes, large blowers force air
through the water, making the cooling tower more
efficient. You can read more about cold-water
air-conditioning systems in the UT2 TRAMAN.
In figure 4-12, you can see the line of air-
conditioning ducts running from each of the air-
conditioning units. Note that the section dimensions of
each length of specified size are noted on the drawing.
Notice, too, that these dimensions decrease as distance
away from the unit increases.
You should notice, also, that some spaces are heated
by radiators, rather than the air-conditioning system.
These spaces (all the toilets, for example) may contain
odors or gases that would make it inadvisable to connect
them with the air-conditioning duct system. On each of
the radiators, the heating capacity, in British thermal
units (BTUs), is inscribed. In each space not connected
to the air-conditioning system, you can see an exhaust
fan (for ventilation) shown. On each fan, the air capacity,
in cubic feet per minute (CFM), is noted.
In each air-conditioned room, you see a circle (or
more than one circle) on the duct. This indicates an
outlet for the conditioned air. In this case, the outlets are
diffusers, and the capacity of each diffuser, in CFM, is
inscribed. Note that this capacity varies directly with the
size of the space serviced by the outlet.
Steam lines from the boiler in the mechanical
equipment room to the air-conditioning units and
radiators appear as solid lines. Small diagonal lines on
these indicate that they are low-pressure steam lines.
Returns appear as dashed lines.
In the upper left corner, a detail shows the valve
arrangement on the steam and condensate return lines
to each of the air conditioners. Referring to the
mechanical symbols specified in MIL-STD-17B, the
detail indicates that in the steam line, the steam headed
for the unit passes agate valve, then a strainer, and then
an electrically operated modulating valve. This last
reduces the pressure to that for which the unit coils are
The steam condensate leaving the unit first passes a
gate valve, then a strainer, then a union, and then a steam
trap. This trap is a device that performs two functions:
(1) it provides a receptacle in which steam condenses
into water and (2) it contains an automatic valve system
that periodically releases this water into the rest of the
Beyond the steam trap, there is another union, next
comes a check valve, and finally a gate valve. A check
valve, as you know from the EA3 TRAMAN, is a
one-way valve. It permits passage in one direction and
prevents backup in the opposite direction.
CHECKING AND EDITING
Every drawing prepared in the drafting room must
be checked and edited. As a capable EA2, you maybe
delegated the job of doing so. When checking a
drawing, you are inspecting it to make sure that it
accurately conveys the information contained in the data
source. That source may be survey field notes, sketches,