CFM-88L 07/20/0923
Reading accuracy is improved by adjusting the register deflection blades to a four-way spreading pattern before starting the
measuring and balancing process. The deflection can then be readjusted for the desired deflection pattern after the final
balancing and readings are completed. Resetting deflection patterns after air balance usually has little effect on the air
delivery. Special top sizes may be ordered from our factory. The most popular size for sidewall outlets is 1' x 2' (13"x 25"
outside dimension).
11.7 14"x14"x14" SHORT TOP SET
This short top design is intended for use on return or exhaust air outlets. The use of this top size on deflection type supply
outlets such as multiblade diffusers or registers with the blades set for a spreading pattern is not recommended. The
14"x14"x14" top is too short to provide the attenuation of the jet velocities necessary to even-out the air flow over the flow
sensing grid and readings will not be reliable.
Reasonable accuracy can only be obtained on supply outlets when using the short top set if the outlet is at least 12" x 12"
with no air deflection, such as a perforated plate, bar grille, egg crate grille, or unfinished opening.
11.8 SYSTEM PROBLEMS
If the measured air delivery is less than expected, check the meter functions first, as described in Section 13.0 METER
ACCURACY FIELD TESTING. If the meter is functioning properly, check significant sources of error such as: duct leakage;
loose outlet connections; missing or loose end caps; belt slippage; backward fan rotation; closed or partially closed dampers
of any type; dirty filters or coils; foreign material caught in turning vanes or fan wheels or other locations where obstructions
can occur; square elbows without turning vanes; radical duct transitions; and any other situations where faulty system design
or installation errors can cause inadequate air delivery.
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