Controlling Air Leakage from Raised Access Floor Cavities

Transcription

1 Technical Bulletin #216 AIR LEAKAGE CONTROL Controlling Air Leakage from Raised Access Floor Cavities AIR LEAKAGE DEFINITION AND SIGNIFICANCE Air leakage is passage of pressurized air from an underfloor air supply cavity through elements other than the air diffusers. As test reports herein show, the volume of air that leaks between the panels in a bare raised floor will be reduced to exceptionally low levels by the application of overlapping carpet tiles or by the use of stringers lined with air-seal gaskets. The cavity can leak air also at the access floor perimeter where walls and columns extend from the floor slab; and through wall and slab penetrations created for ducts, conduits and pipes. By utilizing the sealing methods detailed in this bulletin, leakage in these areas can be reduced to levels that will not affect temperature control or air distribution performance. ELEMENTS OF AIR LEAKAGE CONTROL Floor Panel Integrity Floor panels need to be consistent in size and have straight edges to minimize panel seam leakage, and should therefore be the steel die-cut type. A system that relies upon heavy applications of carpet adhesive to fill large panel seams is not recommended, since this impedes panel removal and replacement. Quality of Installation The manufacturer s installation procedures must be followed to form the properly sized panel seams and thereby lessen leakage through the panel seams. Part 3 of Tate s Installation Manual: Installation of the Field, provides procedures for installing a floor that is square, level and sufficiently tight. And keep in mind that it is essential to hold other trade people working in the floor cavity responsible for maintaining the floor in its original condition during and after the installation. Sealing of Construction Seams and Penetrations Sealing of the perimeter where the access floor connects with walls and columns is crucial. The perimeter of a carpeted access floor can be sealed with snug-fitting perimeter panels, carpet extending completely to the wall, and wall base firmly pressed against the carpet. The perimeter of a floor without carpet can be caulked, gasketed or taped at the wall prior to installing wall base. All walls passing through the access floor must have drywall extending completely to the slab and be sealed at the slab line. All utility penetrations through walls and slabs for plumbing, electricity and voice/data cabling must be sealed. This sealing work should be performed by those who make the penetrations and inspected prior to installation of the access floor. Penetrations made after access floor installation must be sealed and inspected. For specifications and drawings on sealing of construction seams and penetrations, see pages Sealing of the Panel Seams The seams between floor panels in a PosiLock or stringer system will automatically be sealed against leakage if overlapping carpet tiles are applied. In the case of a floor that will not be carpeted, a stringer system with air-seal gaskets applied to the stringers will seal the panel seams. Page 1

2 LABORATORY TESTS Leakage through Panel Seams The data in Table 1 was derived from laboratory tests with access floor mockups constructed to simulate normal field conditions with typical sized seams between panels. Leakage occurring at the perimeters of the mockups was measured and subtracted from the panel seam numbers. Slight variations in leak rates are possible when compared to actual installations due to variations of installation tightness. TABLE 1: PANEL SEAM AIR LEAKAGE TESTS PosiLock -Cornerlock Understructure System (CFM/ Sq. Ft.) Bolted Stringer Understructure System with Stringer Gaskets (CFM/ Sq. Ft.) Static Pressure (in. w.g.) Bare Panels 18-Inch Glue-Down Carpet Tiles 1 PosiTile Carpet Tiles 2 Bare Panels Gravity-Held Bare Panels Cornerlock Test Number A A A B Notes: inch carpet tiles overlapped floor panels to cover the seams and were adhered with a light application of releasable adhesive. 2. PosiTile carpet tiles are 24-inch tiles applied without adhesive and do not overlap the panel seams, but precisely match the floor panels. 3. The combination bolted stringer & cornerlocked panel system was utilized. 4. Laboratory test reports are available through your distributor or by calling Tate's Technical Air Leakage through a Power, Voice & Data (PVD) Distribution Box Installed in a Panel A test was conducted to determine the volume of air that would pass through a high capacity PVD box installed in a 10.5 inch-square cutout in a ConCore panel. The test panel was covered with a 24-inch commercial carpet tile having a cutout matching the panel cutout. The PVD receptacle plate was fitted with two duplexes; the voice/data plate was fitted with three steel interface plates each of which was fitted with two RJ-45 connectors. With the PVD installed in the test panel, all other seams in the mockup were sealed so that leakage would be confined to the area of the cutout and PVD assembly. The results are as follows: Static Pressure Leakage (CFM) 0.05 in. w.g. : in. w.g. : 7.65 Laboratory test report is available through your distributor or by calling Tate's Technical Page 2

3 METHOD OF COMMISSIONING TEST The data derived in this test is used to calculate the maximum construction leakage and determines how much air is lost to leakage by the duct and air supply cavity. A good system will leak no more than 10-15% of the total volume of air forced into the cavity, while a marginal system may leak up to 20-25%. If leakage is beyond 25%, the cavity should be repaired to yield leakage of no more than 25%. The floor cavity should be tested in its completed condition after all perimeter seams and penetrations in the access floor, subfloor and walls have been sealed. If the floor is slated to have a carpet covering, it should be installed in the intended manner of application. All diffusers should be covered and sealed with self-adhesive protective sheets (or blank panels temporarily installed in their place). All panels and closures must be in place. Check all duct access doors for tight fit and closure. With the diffusers sealed, the system shall be brought to normal working pressure -- typically.05 to.10 inches w.g. in the plenum. The airflow of the supply fan system is measured by the air balance personnel and compared to maximum delivery volumes. The test volumes are recorded in the commissioning report. Any systems that demonstrate leakage/uncontrolled flow in excess of 25% design maximum should be corrected and retested. FLOOR CAVITY SEALING SPECIFICATIONS AND DRAWINGS To ensure that the cavity construction seams and penetrations are properly sealed (before, during and after access floor construction) the initial contract documents should include specifications and details clearly indicating sealing requirements and areas of responsibility. We offer the following construction specifications and associated drawing details for your reference (see pages 5-15 for drawings). See page 5 for a quick-reference diagram of common floor cavity sealing locations. SPECIFICATION Before the start of access floor construction, all slab-to-ceiling walls shall be sufficiently sealed at the floor slab-line as described below to maintain air tightness. All air duct, conduit, cabling and piping penetrations in the access floor cavity shall be sufficiently sealed as described below. The general contractor shall have the overall responsibility for meeting these requirements. Where applicable, the carpet installer shall comply with the carpet installation requirements described below (carpet installer requirements are in italics). Access floor seal at fascia/exposed edge: Precisely cut the fascia plate to meet the top edge of access floor, leaving no gaps. Apply metal tape over joint prior to application of carpet and angle trim. Secure fascia to access floor edge with angle trim. Perimeter seal at smooth walls and columns: Cut perimeter panels to fit within 1/16 inch or less of walls and columns. Carpet installer must ensure that carpet tiles fit snugly against all vertical surfaces. Finish all joints with wall base firmly pressed against carpet and access floor. For floors that will not be carpeted, follow specifications under Perimeter seal at nonsmooth walls and columns and Detail C. DRAWING DETAIL See Below See Below Detail A Detail B Page 3

4 Perimeter seal at non-smooth walls and columns: Where wavy/rugged surfaces prohibit perimeter panels from fitting uniformly close to the surface or where carpet will not be applied: Option 1: attach self-stick foam/rubber gasket to wall flush with surface of floor and press panels into gasket material. Option 2: install perimeter panels and fill joint with caulk/sealant prior to installation of carpet or wall base. Access floor seal at fire barrier below door threshold: Cut panels to fit within 1/16 inch of barrier. Options to seal joints: Option 1: cover joints between access floor panels and barrier by attaching threshold plate with gasket affixed to underside. Option 2: attach gasket to vertical surface of barrier flush with edge of floor and press panels into gasket material. Option 3: install panels and fill joint between floor panels and barrier with fire-rated caulk/sealant. Fire wall seal at access floor: Cut perimeter panels to fit within 1/16 inch of walls. Carpet installer must ensure that carpet tiles fit snugly against all vertical surfaces. Finish joint with wall base firmly pressed against carpet and access floor. For floors that will not be carpeted, follow specifications under Perimeter seal at non-smooth walls and columns and Detail C. Fire-wall seal at sub floor: Before the start of access floor construction, seal fire-wall along slab-line with fire-rated caulk/sealant that has rating equal to that of the wall assembly. Access floor seal at curb joint where floor covering is continuous from access floor to curb: Cut panels to fit within 1/16 inch (or less) of curb. If gap will be larger than 1/16 inch attach self-stick foam/rubber gasket to curb and press panels into gasket material. Overlap carpet or other tiles from access floor to curb. Access floor seal at curb joint where floor covering is not continuous from access floor to curb: Cut panels to fit within 1/16 inch (or less) of curb. If gap will be larger than 1/16 inch attach self-stick foam/rubber gasket to curb and press panels into gasket material. Bridge joint with transition strip or threshold. Cable cutout seal: Install manufacturer s trim for rectangular cable cutouts into panel cable openings and cut foam section to fit snugly into opening and support ledge. Fire wall seal at air duct, piping, conduit and cable penetrations: Cut openings into wall assemblies approximately equal to diameters of ducts, pipes or conduit / cable bundles passing through. Fill excess voids with firestop system materials to prevent passage of air. All excess voids must be sealed and inspected prior to installation of access floor whenever possible. Plenum divider seal at air duct, piping, conduit and cable penetrations: Cut openings into divider approximately equal to diameters of ducts, pipes or conduit / cable bundles passing through. Seal excess opening areas with duct or metal tape, caulk or sealant to prevent passage of air. All excess openings must be sealed and inspected prior to installation of access floor whenever possible. Access floor seal at piping penetrations: Cut openings into access floor approximately equal to diameters of pipes. Seal excess opening areas around piping passing through access floor surface with caulk or sealant to prevent passage of air. All excess openings must be sealed and inspected prior to installation of access floor whenever possible. Sub floor seal at piping penetrations: Fill excess voids or cavities around piping passing through sub floor with firestop system materials to prevent passage of air. All excess voids must be sealed and inspected prior to installation of access floor whenever possible. Detail C Detail D Detail E Detail E Detail F Detail G Detail H Details I, J, K Details I, J, K Detail L Detail L Page 4

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