Damper Selection Guidelines
Discharge dampers and zone dampers should be sized for 100% of the air volume. Bypass dampers are also sized for 100% of the supply
air volume unless the Therma-Fusers are equipped with minimum flow stops when the bypass should be sized for an air volume equal to the
total turndown of the Therma-Fusers.
Select dampers at 1000 fpm face velocity or 1000 cfm per ft2 of face. If in doubt the damper should be oversized as slightly oversizing does
no harm and the additional cost of the next larger size damper is small. Undersizing will raise the pressure drop through the damper and could
result in lack of air for the last Therma-Fuser downstream or in an ineffective bypass.
AMCA Standard 500 provides only for testing of damper airflow and leakage and, as a result, most manufacturers of AMCA tested control
dampers do not publish sound data. Therefore, good judgment must be used when selecting and applying dampers to avoid excessive sound
transmitted through the duct or radiated into the space. The latter is of more concern if the damper is above an occupied space rather than in
an equipment room. Generally, dampers selected below 1000 fpm face velocity and applied at pressure drops of less than 1" wg will have
acceptable sound levels.
Extra caution should be taken when bypassing from a duct into a plenum. These installations are best either in or over a mechanical room.
Sound attentuation should be considered where dampers bypass into the ceiling plenum over an occupied space. This can be a commercially
available sound attenuator or 4 to 5 equivalent lengths of lined duct and an elbow for discharge away from the occupied space (usually up).
It is not necessary to be concerned that excessive leakage of a closed bypass damper will require an oversized system fan. VAV systems
rarely operate at design conditions which is the only situation where the bypass damper is closed. Furthermore, leakage from a damper is so
low that blade and jamb seals are not recommended. As an example, most dampers without seals leak 30 to 40 cfm per ft2 of face area at .5"
wg pressure differential which is only to 4% of the 1000 cfm per ft2 of face area that results from selection at 1000 fpm face velocity. However,
if blade and jamb seals are required, dampers should be selected no larger than 48 x 18 to stay within the torque available from the PIM.
Typical Performance Data for Multi Blade Control Dampers
Airflow Chart
VELOCITY IN FEET PER MINUTE (CFM/SQ. FT.)
Airflow with damper 90° (Full) open. [Test size: 24" x 24"]
This performance information is derived from testing in accordance with AMCA Standard 500; with test set up per figure 5.3 and
measurement apparatus set up per figure 6.5 of this AMCA standard.
Leakage Chart
LEAKAGE IN CFM PER SQUARE FOOT
Standard opposed blade without seals. Holding torque applied with 4 inch-pounds per square foot of damper area. [Test size 24" x 24"]
This performance information is derived from testing in accordance with AMCA Standard 500; with test set up per figure 5.5 and
measurement apparatus set up per figure 6.5 of this AMCA standard.
TWO YEAR WARRANTY
Acutherm warrants that its Pressure Independence Module, exclusive of any options and accessories (whether factory or field installed)
shall be free from defects in material or workmanship for a period of two (2) years from the date of shipment and agrees to repair or
replace, at its option, any parts that fail during said two (2) year period due to any such defects which would not have occurred had
reasonable care been taken, provided that such parts have been inspected by Acutherm and found effective and provided the units have
been given normal and proper usage and all parts and controls remain unaltered. Acutherm makes NO WARRANTY OF
MERCHANTABILITY OF PRODUCTS OR OF THEIR FITNESS FOR ANY PURPOSE OR ANY OTHER EXPRESS OR IMPLIED
WARRANTY WHICH EXTENDS BEYOND THE LIMITED WARRANTY ABOVE. ACUTHERM'S LIABILITY FOR ANY AND ALL
LOSSES AND DAMAGES RESULTING FROM DEFECTS SHALL IN NO EVENT EXCEED THE COST OF REPAIR OR
REPLACEMENT OF PARTS FOUND DEFECTIVE UPON EXAMINATION BY ACUTHERM. IN NO EVENT SHALL ACUTHERM BE
LIABLE FOR INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR DAMAGES FOR INJURY TO PERSONS OR
PROPERTY. Acutherm shall not be responsible for freight to or from its plant in connection with the inspection, repair or replacement of
parts under the terms of this limited warranty nor for cost of removal or installation. |
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Hayward, CA 94545
(510) 785-0510
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