Some have a derate percentage to use above X amount of static.
Originally Posted by everythingair
If a current system with a PSC blower is moving 800 CFM at a .75" static. Then increasing CFM to 1000 would raise the static to roughly 1.17"
They end up using about the same amount of electric in that type of an install, and making the system loud.
VS blowers don't have CFM ratings at that high of a static.
This is what I was referring to when I mentioned the psc motor blower performance chart. If the psc motor that is installed in a particular blower is not rated to perform above a certain SP, then it is better to use a larger HP motor. This is essentially what equipment manufacturers do with high static blower furnaces. I believe the most that I have seen for SP for VS motors is .8 SP. A system that is that close to the edge can have issues with just a dirty filter.
Originally Posted by beenthere
My static for my VS is at 1.1....so i am having duct work done. I've never noticed any huffing though nor any "oil-canning" (ducts making loud noice from bowing in and out due to the pressure). My duct guy said the VS motors can run at 1.5 SP (of course I don't believe him). He is really good with sheet metal....but does not appear to possess the knowledge of the Pro's on this site.
Sorry if I'm asking dumb questions, but is the static pressure test something that can be done fairly easily by the contractor while he's here the first time, or is that something that needs special equipment and time to set up? Also I've got the flexible duct work installed, is that going to make a difference in terms of the SP?
The test equip. needed is very resonable,problem is many aren't trained to do so.
Flex designed correctly wouldn't be an issue.Flex would be larger ducts ,for the same static ,then meatl.
I sure wish more people understood this and stopped making flex out to be some sort of air killer.
Originally Posted by dash
Government is a disease...
...masquerading as its own cure
Ecclesiastes 10:2 NIV