Air grilles
Functioning Principals
Minimum Air Grille Sections To obtain acceptable noise levels at maximal blower speed minimum requirements for grille and ducts sections should be observed. The size of the transition box behind the supply air-grille is also important.
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Supply Air Grille Model / Section cm 2
Return Air Grille Model / Section cm 2
FCF Model 6,000 BTU 10,000 BTU 12,000 BTU 16,000 BTU 16,000 BTU
Duct Diameter
1 x 10 x 4’’ 1 x 12 x 4’’ 1 x 10 x 5’’ 1 x 12 x 6’’ 2 x 10 x 4’’
190 cm 2 235 cm 2 250 cm 2 390 cm 2 380 cm 2
1 x 11 x 8’’ 1 x 11 x 8’’ 1 x 14 x 7’’ 1 x 14 x 10’’
490 cm 2 490 cm 2 550 cm 2 800 cm 2
100 mm (4“) 100 mm (4”) 125 mm (5”) 125 mm (5”) 125 mm (5”)
Blower Outlets 90° turns with flexible ducts directly from blower outlets should be avoided at all costs as they introduce severe restrictions in the air-flow. All FCF blowers can be rotated through 45° steps to obtain a straight-line outlet from the blower. This facility should be used whenever possible. Return Grille Offset It should be avoided to place a return air grille directly opposite the finned coil surface of an air-handler, because this will allow propagation of direct blower-motor noise through the grille. The grille should be offsetted to chicane the return air to the coil inlet. Direct noise propagation will be reduced in a significant manner. Duct Type Webasto recommends insulated ducting for all installations, to reduce condensation. To avoid accidental crushing, flexible air-ducts should be of high quality with sufficiently strong steel spiral reinforcement. Spiral type ducts should be extended to their maximum length for the best interior smoothness. Large Vessel Requirements In general requirements for large vessels are even more stringent than the table above. These special requirements can be obtained from Webasto on request.
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