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OAFE-1500 Applications
 
PCI’s Outdoor Airflow Measurement System (Model OAFE-1500) has an operating velocity range of 100 to 10,000 fpm. However PCI recommends sizing the airflow measuring station so that the velocity at the point of measurement is at least 250 fpm. This can be accomplished using an integral inlet bell and/or blank off plate.
Figures 1 through 11 below show various installations of the Outdoor Airflow Measurement System in rooftop air handling units, outdoor air plenums, and ducted outdoor air intakes. For applications with dampers, the element orientation with respect to the duct width and height should be taken into consideration (elements should run perpendicular to the damper blades).
Rooftop Air Handling Unit with Rain Hood - Exterior Mounted Airflow Measuring Station
On a rooftop air handling unit with a rain hood, the airflow measuring station can be mounted on the exterior of the unit with the rain hood remounted on the intake side of the airflow measuring station. The airflow measuring station can be made with a 5” or 12” deep casing (see Figure 1) with mounting flanges matching the rain hood flanges. To accelerate the velocity and improve the velocity profile for better measurement accuracy, the airflow measuring station can also be constructed with an integral 4” radius inlet bell with an 8” or 12” deep casing (see Figure 2).
Figure 1   Figure 2
 
Rooftop Air Handling Unit with Rain Hood - Interior Mounted Airflow Measuring Station
On a rooftop air handling unit with a rain hood, the airflow measuring station can be mounted on the interior of the unit just upstream of the OA control damper. The airflow measuring station can be made with a 5” or 12” deep casing (see Figure 3) with mounting flanges matching the OA control damper flanges. To accelerate the velocity and improve the velocity profile for better measurement accuracy, the airflow measuring station can also be constructed with an integral 4” radius inlet bell with an 8” or 12” deep casing (see Figure 4). The OA control damper is remounted on the downstream side of the airflow measuring station.
Figure 3   Figure 4
 
Outdoor Air Plenum - Airflow Measuring Station Mounted Downstream of Louver
In an outdoor air plenum, the airflow measuring station can be mounted directly to the interior of the plenum just down-stream of the louver. To accelerate the velocity and improve the velocity profile for better measurement accuracy, the airflow measuring station is constructed with an integral 4” radius inlet bell with an 8” or 12” deep casing. On the air entering side a flat 1” flange is provided to accommodate mounting flat at the interior of the louver.
Figure 5
Outdoor Air Plenum - Airflow Measuring Station Mounted to OA Control Damper
In an outdoor air plenum, the airflow measuring station can also be mounted directly on the upstream side of the OA control damper. To accelerate the velocity and improve the velocity profile for better measurement accuracy, the airflow measuring station is constructed with an integral 4” radius inlet bell with an 8” or 12” deep casing and mounting flanges matching the OA control damper flanges.
Figure 6
Outdoor Air Plenum - Airflow Measuring Station Mounted to Minimum OA Control Damper
In an outdoor air plenum, where the OA control dampers are divided into minimum OA and economizer sections, the airflow measuring station can be mounted directly on the upstream side of the minimum OA control damper section for measurement of the minimum OA intake flow rate only. To accelerate the velocity and improve the velocity profile for better measurement accuracy, the airflow measuring station is constructed with an integral 4” radius inlet bell with an 8” or 12” deep casing and mounting flanges matching the OA control damper flanges.
Figure 7
Outdoor Air Plenum - Airflow Measuring Station Mounted Between Louver and OA Control Damper
In an outdoor air plenum, the airflow measuring station can be mounted directly to the interior of the plenum between the louver and OA control damper. The airflow measuring station can be made with a 5” or 12” deep casing (see Figure 8) with mounting flanges matching the louver flanges on the air entering side of the station and mounting flanges matching the damper flanges on the air exiting side. To accelerate the velocity and improve the velocity profile for better measurement accuracy, the airflow measuring station can also be constructed with an integral 4” radius inlet bell with an 8” or 12” deep casing (see Figure 9).
Figure 8   Figure 9
 
Ducted Outdoor Airflow Measuring Station
For applications with a ducted outdoor air intake to the air handling unit, a standard construction airflow measuring station is typically used. This airflow measuring station is 5” deep with 1.5” flanges (see Figure 10). The airflow measuring station may be installed in any duct configuration. However, the element orientation with respect to the duct width and height should be taken into consideration for ducted inlet applications with stations being mounted on the downstream side of an elbow (elements should run perpendicular to the axis of flow and across the velocity gradient). The accuracy of the installation is dependent on the flow conditions in the duct. The minimum installation requirements for the airflow measuring stations based upon a uniform velocity profile approaching the duct disturbance for flow rates less than 2,500 fpm are shown below (see Figure 11). These are not ideal locations. It is always best to locate the airflow measuring stations as far as possible from all duct disturbances, with upstream disturbances being the most critical consideration.
Figure 10
Figure 11
 
 
 
 
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