WHY IS ASHRAE CORRECT !
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Spiral Duct |
Rectangular Duct |
| Less Joints (estimated at 12 per 100 ft.) |
More joints (estimated at 40 per 100 ft)
Higher installation cost. |
| Less Metal - The lowest possible
friction loss for a given perimeter gives lower operating cost. |
More weight
Higher operating cost
with at least 72% more labor.
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| Ductwork sealing - Less joints mean lower sealing labor cost and less sealing material.
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More labor
More Material
No longitudinal seam assembly |
| Round duct will go thru trusses and places where
square duct will not fit.
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More job changes |
| Lower pressure drop |
As aspect ratio goes up - the static
pressure goes up increasing operating cost.
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| Aesthetically pleasing. |
Visually not appealing. |
| Lower air noise |
Audibly distracting to the user |
| Less potential for seam failure |
Lower bursting pressure, higher failure |
Less exterior insulation required |
More material
20 to 25% more labor |
| Less hanging straps |
Higher Material Costs
Higher Labor Costs |
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