Continental Electronics 816R - Transmitter Cooling; Ventilation Methods

IV. TRANSMITTER COOLING
In many locations ventilating a building is preferred
over air conditioning. Air conditioning equipment
is mechanical and can break down, is initially
expensive, and is expensive to maintain and
operate. The 816R-6C transmitter can operate in a
room environment where temperatures can be as
low as -4° F to as high as 122° F. There are
several different ways to ventilate a room that will
be discussed in following paragraphs.
Exhaust Fans.
There are times when exhaust fans are the best
means of ventilating a transmitter space. If the
room is large and it is not possible to locate the
transmitter near an outside wall, exhaust fans may
be the only reasonable way to ventilate a room. It is
better in this situation to vent the transmitter
directly to the room or through a short duct to the
attic and use exhaust fans in the room or the attic.
It is important to arrange the transmitter exhaust so
that there is no chance of recirculation of exhaust
air back into the transmitter.
There are many good ways to make an installation
utilizing exhaust fans and one method will be
described here. If the room has a high ceiling
(more than 10 feet), install a drop ceiling about
eight feet from the floor. Vent the transmitter
exhaust directly into the space above the drop
ceiling. Let the transmitter take air from the room.
At the four comers of the drop ceiling install air
registers that will allow air from the room to escape
into the area above the drop ceiling. Install an
exhaust fan that will evacuate the area above the
drop ceiling. This method will not have the exhaust
fan competing with the transmitter fan and blower,
will prevent recirculation (providing exhaust fan
does not fail), and will provide ventilation for the
transmitter space. There are variations of this
scheme that will allow recirculation (controlled by
a thermostat) in the winter to heat the transmitter
space.
Although exhaust fans and blowers are the most
common method of ventilating transmitter spaces
they are not the best in some cases. The three
cautions listed below are some reasons for choosing
another method when there is a choice.
1. An exhaust fan allows unfiltered air into the
transminer by expelling air from the room or
building and pulling air into the room through
any and all openings in the room. The
transmitter space should be as clean and dust
free as possible. It is not likely that the
transmitter space can be air tight except for the
filtered air intake. The unfiltered openings will
allow dust and dirt into the transmitter space.
2. An exhaust fan results in dead air spaces since
it does not "stir" the air in a room which makes
"dead air spaces" possible. There is usually
only one intended air inlet to a transmitter
space and the air movement is from that inlet
directly to the exhaust fan.
3. In installations where the transmitter is ducted
to the outside and takes air from the room, the
exhaust fan is competing with the transmitter
cabinet fan and cavity blower for air through
the same room airinlet. In this situation, the
greater capacity of the exhaust fan will reduce
the transmitter cooling if the room air inlet is
not large in size. Where exhaust fans or
blowers are used, the room air intake must be
large enough so that the room in not under
negative pressure. Negative pressure at the
transmitter air inlet has the same detrimental
effect as back pressure of the same amount at
the transmitter air exhaust.
Positive Pressure
Positive pressure ventilation forces air into the
room and the air escapes through openings in the
room. The air may be forced into the room with
propeller type fans or with centrifugal blowers.
Propeller type fans move more air with smaller
motors than will centrifugal blowers. A 30 or 36
inch fan is quiet and can move more than 3000 cfm
of air into a room and use only a 1/4HP motor.
Some of the advantages of positive pressure
ventilation are:
1. All the air entering the room comes through
one opening which can be easily filtered. When
doors or windows are opened, air moves out
through the opening.
2. A fan blowing air into a room will "stir" the
room air reducing the risk of dead air space.