Shortridge Instruments AIRDATA ADM-880C, Руководство по эксплуатации

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ADM-880C 07/20/09 52
to the FlowHood base. This can result in an extremely uneven velocity distribution across the flow sensing grid when the flaps
are open. The air flow is more evenly distributed across the flow sensing grid when the flaps are closed.
Linear slot diffuser readings at less than 100 cfm per lineal foot of diffuser should be taken with the FlowHood flaps
closed . The AirData Multimeter will permit flaps closed, nonbackpressure compensated readings up to 500 cfm. In most
cases, the FlowHood backpressure effect on linear slot diffusers is not significant. Accurate readings can normally be
obtained with
flaps open readings on linear diffusers sized for more than 100 cfm per lineal foot.
The tendency of a sheet of air to cling to, or follow the side of the FlowHood top, can be reduced by using a top width
dimension that is as close as possible to the outlet width. Special transition tops can be constructed of corrugated cardboard
and duct tape. Custom dimension, cloth and frame top sizes may be ordered from our factory. A commonly used size is
5.25" x 47" with a 4.25" x 46" inside frame dimension.
12.6 SIDEWALL REGISTERS
The FlowHood may be used to measure air delivery of supply sidewall registers using the standard 30" length, 2'x2' top or
larger top sizes. It is best if the top dimensions closely match the outlet size to assure even air flow across the flow sensing
grid. Exact matching of hood size to the outlet size is not practical in most cases.
The standard 30" length top sizes may be used with equal accuracy on supply or return air outlets. However, small supply
outlets at high jet velocity, "punkah" diffusers or nozzle type outlets may cause an extreme concentration of air velocity on
portions of the flow sensing grid. The FlowHood readings will be inaccurate under such conditions.
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).
12.7 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.
12.8 SYSTEM PROBLEMS
If the measured air delivery is less than expected, check the meter functions first, as described in section 14.0 on 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.