Practical
limitations
Although an accurate, intelligent calculation
of the required air volume for a breeze conditioning system has been
made, there are practical limitations in most buildings that may seriously
affect the final results. By giving these limitations proper consideration
in the planning stage, the system can usually be modified to compensate
for them. Some of the more common limitations are listed here.
Partitions
within the building
It is obvious that interior partitions
restrict and interrupt the flow of air through a structure. The
effect of these partitions on the system must be analyzed and solutions
found.
Plan View Effect of partitions on designed air flow
pattern
Large cross-sectional
area
In buildings with very high ceilings. the cross-sectional
area factor may become unrealistic in calculating the required air
volume. In most instances, inexpensive baffles can be installed
across the building width to reduce the effective cross-section
to an area 10' or 12' above floor level.
Another limitation of the very high ceiling or roof is the difficulty
of maintaining the air velocity near floor level. The baffle method
just described is usually the best way to reconcentrate the air
flow along the floor level where it will be effective in providing
personnel comfort. In large buildings, baffles may be required at
l00-foot intervals to keep air flow near the floor level.
Section View Problem of large building cross section
Machinery,
raw materials and finished goods that obstruct air circulation
These obstacles, like interior partitions, must
be considered and methods worked out to overcome the problems they
create to the proper circulation of air through the structure.
Unfavorable
location of heat-producing machinery
Frequently, the location of heat-producing machinery will seriously
interfere with the
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preferred pattern of air circulation. This situation can destroy the
effectiveness of the system. An alternative plan to overcome the problem
is essential.
Section View Problem of unfavorably located heat
source
"Short
circuits"
Operations within the area frequently require wall
openings or loading doors that will drastically interfere with the
desired airflow pattern. In some cases, individuals may open windows
that should remain closed to maintain effective air circulation.
A remedy for each of these problems is required.
Restricted
intake openings
For maximum efficiency and economy, a good layout
will avoid the restricted intake opening. The type of exhaust equipment
normally utilized is most economical and efficient if static pressure
in the system is 1/8" or less. To obtain this condition, air
velocity through intake openings should not exceed 1,000 feet per
minute, A lower figure is usually desirable.
Common
sense considerations
Location
of exhaust fans
It is usually wise to locate the exhaust fans near
the area where heat-producing machinery is found. This has the very
practical advantage of exhausting this superheated air near its
source and preventing a heat build-up in other areas.
Prevailing
wind direction
If side wall locations are to be utilized for air
intake or exhaust, it is desirable to consider the prevailing wind
direction during the summer season. If the ventilation system can
be oriented to take advantage of prevailing winds, the efficiency
of the system may be increased considerably, Systems that incorporate
roof exhausters are usually not affected by a prevailing wind.
Economy
of the "long dimension"
Where air velocity is the critical factor
in a breeze conditioning system, use of the "long dimension" of
the building or room is highly desirable. By moving air through
the long dimension, the cross-sectional area is reduced and less
air volume is required to obtain the needed air velocity.
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