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Flexible duct 2
- Thread starter coffmarm
- Start date
That does sound rather large. Probably 20" is the max normally available. I've spec'd/seen some 42" diam. fabric ducts like DuctSox, but that's probably not what you had in mind.
Could you not employ some smaller parallel paths to accomplish this task?
Could you not employ some smaller parallel paths to accomplish this task?
- Thread starter
- #3
No, it's an existing duct arrangement used in four different places so it would be a big deal to modify them all - even if I could get the funding approved. The existing 42" flex ducts are almost 30 years old and I can't find any record of who the original suppier was. I found that sells flex duct up to 60" diameter, but their's can't take the 5" WC pressure.
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- #4
ChrisConley
Mechanical
ABC Manufacturer's of Canada makes custom fabric and PVC lined duct for the mining industry.
I know they will consider specialty runs.
I know they will consider specialty runs.
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- #5
EmeraldCoastHVACR
Mechanical
Can't help you on this, but I attached an engineering study by ASHRAE professors on the performance of flex vs metal duct.
Very informative
Very informative
- Thread starter
- #6
Contractors and I always have discussions about length of flex duct and the manner in which it is installed. I detail its use carefully both on drawings and specifications and contractors pooh-pooh the reasons for the details but do it after they have to remove and replace a couple of pieces.
I have seen the bad results of sloppy flex installations in too many balance reports.
I knew about the high pressure loss, but the paper indicates that my calculations are off by about 10%. All the more reason to limit the use of flex duct.
Excellent paper.
I have seen the bad results of sloppy flex installations in too many balance reports.
I knew about the high pressure loss, but the paper indicates that my calculations are off by about 10%. All the more reason to limit the use of flex duct.
Excellent paper.
ChrisConley
Mechanical
I'm glad they could help, they're a good bunch down there. I worked on the expansion to their plant a few years back.
EmeraldCoastHVACR
Mechanical
To summarize that paper:
The only time flex came close to galv steel was fully extended and there was considerable loses when at 94% efficiency, which is extremely rare (i've never seen it) in the field.
Expect to see flex duct losses approaching 50% compared to galv metal; in addition, expect to see losses using ductboard with liners more than 33% compared to metal(ASHRAE design manual).
From a techs point of view, my experience shows that ductboard & flex systems lower seer ratings 2 to 3 points with all the deteriorating effect that low-airflow systems give(too numerous to mention here).
The only time flex came close to galv steel was fully extended and there was considerable loses when at 94% efficiency, which is extremely rare (i've never seen it) in the field.
Expect to see flex duct losses approaching 50% compared to galv metal; in addition, expect to see losses using ductboard with liners more than 33% compared to metal(ASHRAE design manual).
From a techs point of view, my experience shows that ductboard & flex systems lower seer ratings 2 to 3 points with all the deteriorating effect that low-airflow systems give(too numerous to mention here).
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