The Sheet Metal Shop .Com

Duct Construction and Uses - Question???

CadMan - Sep 01, 2004 - 07:44 PM
Post subject: Question???

Can anybody tell me how to figure using equal friction method and static regain method? Which do more people use?

Bud - Sep 05, 2004 - 12:46 AM
Post subject:

There is a book " How To Design Heating - Cooling Comfort Systems. In this book is a chapter called Air and How To Move It...it goes over both of these, equal friction and static regain method.

It is not hard to understand once you understand what the different types of presures there are in a system. It is harder to explain but I will try and get something up 'Static Regain In a nut shell"

I'm not sure which is more used.

How are the duct design programs figuring this out. I would think many use the equal friction method or the simplicity of design load and reducing the size of the ductwork to maintain the static pressure for the remainder of the trunk to size only for the the CFM needed for the necessary run ..sometimes known as a reduced plenum.

I'm up for more discussion on this as well.

Bud

Bud - Sep 05, 2004 - 02:05 PM
Post subject:

Bud wrote:

There is a book " How To Design Heating - Cooling Comfort Systems. In this book is a chapter called Air and How To Move It...it goes over both of these, equal friction and static regain method.

It is not hard to understand once you understand what the different types of presures there are in a system. It is harder to explain but I will try and get something up 'Static Regain In a nut shell"

I'm not sure which is more used.

How are the duct design programs figuring this out. I would think many use the equal friction method or the simplicity of design load and reducing the size of the ductwork to maintain the static pressure for the remainder of the trunk to size only for the the CFM needed for the necessary run ..sometimes known as a reduced plenum.

I'm up for more discussion on this as well.

Bud

Thanks for sending my thought process Smile

in another direction for a bit and after reading the material again it seems apparant that the design needed would determine the most type used. This all depends on the job..the book pretty much states..

Static regain is the conversion of velocity pressure to static pressure. It is primarily used for balancing a string of registers all installed on a single main when there isn’t enough room between the register and the main to do any adjusting of the duct size…

I would still be interested in more discussion on air flow and on the use of this if anyone is interested...

Thanks again

dwahlman - Sep 16, 2004 - 05:28 PM
Post subject:

ASHRAE also has a continueing education course, I believe titled "Air System Designs" you may wish to go through. I have gone through two of their courses and have found them to be very professional and informative also.

cliffwilson - Oct 18, 2005 - 02:30 AM
Post subject:

EQUAL FRICTION SIZES ALL DUCT SECTIONS WITH THE SAME FRICTION LOSS. THIS MEANS THE SYSTEM STATIC LOSS IS THE DUCT LENGTH TIMES THE FRICTION RATE PER FOOT.
STATIC REGAIN SIZES DUCT SECTIONS TO MAINTAIN ACONSTANT STATIC PRESSURE AT ALL
OUTLETS.YOU CHANGE THE DUCT SIZE SO THAT THE CHANGE IN VELOCITY PRESSURE IS EQUAL
TO THE FRICTION LOSS IN THE PREVIOUS DUCT SECTION.