Fabric Air Distribution Duct Installation Instructions
1. For optimum duct life, it is important that the metal discharge from the air handler/fan be constructed so as to minimize static pressure losses and eliminate System Effect. This can be accomplished with turning vanes in short radius metal elbows (1 1/2:1 CL radius); symmetrical rectangular-to-round metal transitions; long tapered metal reductions and/or metal discharge extensions (2 1/2 equivalent duct diameters) upstream of the fabric air distribution duct system.
2. Install Cable. The ducts are typically suspended from aircraft type cable anchored to the building, structural members or field fabricated brackets.
A. Align the cable with the fan, both vertically and horizontally.
B. Install a turnbuckle in the cable and tighten sufficiently to make the cable taunt. Be careful not to over tighten the cable. Five cable clamps are included with every turnbuckle.
3. Install Duct. Hang the duct on the aircraft type cable(s).
A. Depending upon the specific material, the duct can be furnished with grommets spaced every 6' along the top hem and hung with S-hooks placed through the grommets and over the cable(s). Close off the ends of the S-hooks with pliers so that the duct can not come off the cable(s) during inflation.
B. Fabric ducts can be furnished with optional metal or plastic snap hooks sewn to the duct and spaced every 6'. The duct is hung by attaching the snap hooks to the cable(s). Installation is much quicker and the duct can be easily removed for cleaning... etc.
C. Fabric ducts can be furnished with hems on the top and bottom of the duct. This option makes it possible to rotate the duct 180° for summer (down blow) and winter (up blow) operation.
D. Fabric ducts can also be furnished with hems at 3:00 and 9:00 o'clock (two point suspension) and other multiple point suspensions. The former option minimizes/eliminates duct droop when the air handler is not operating.
E. For optimum product life, it is important that the fabric duct runs straight without any kinks or bends.
4. Attach the duct to the air handler/fan. Slip the open end of the duct over the metal disharge transition or extension and secure with the stainless steel banding strap (worm gear band).
5. Turn on the air handler/fan. This is a test run to check the duct and its alignment to the air flow.
6. Flutter. Test run the system to locate any flutter in the duct. If there is flutter with the fan continuing to run, loosen the banding strap and draw up the excess duct by pulling it tighter onto the orifice at those locations where flutter is evident. It is also possible to remove flutter from the duct by pulling the duct from the closed end and "tying it off." The stretched duct should be secured with a light cable, chain or rope. Stretching the duct also minimizes "duct pop" when the system is being inflated.
7. Fine-Tune Alignment. It may be necessary to make adjustments to the alignment of the cable and duct to the air flow. Alignment is critical along the first 20-30' of the duct. Excessive air turbulence from the air handler/fan can damage the duct if it is not properly aligned. If the duct bounces severely or the duct wall flaps, the system is poorly aligned to the air flow.
A. To align the duct, move the far end of the cable either left, right, up or down. If the duct wall is flapping along the bottom, a simple adjustment of the first 20-30' of the cable could solve the problem. Install a vertical hanger (drop) 20-30' down the duct to raise the cable and align the duct with the air flow. Center the vertical hanger between the grommets and/or snap hooks.
B. If there is excessive cable sag over the length of the duct, additional vertical hangers (drops) should be installed. The hanger can be a light chain, jack chain, wire or cable. Location of each vertical hanger should be determined during the test run. Center the vertical hangers/drops between the grommets and/or snap hooks. Do not attach vertical hangers/drops to a grommet and/or snap hook. Do not install vertical hangers before the duct has been hung.
8. Some installations may result in the duct bearing against a building column or some other obstruction which cannot be removed. Such obstructions should not reduce the area of the ducts by more than 10% and it should be recognized that this is a compromise situation, which could shorten duct life due to wear or abrasion at the point of the obstruction.
IMPORTANT - Whenever bends are made in the run of duct or obstructions are encountered as described above, it is important for the installer to test the system for flutter at the fan orifice. Adjustments should be made as described above to remove the flutter before putting the system into service.