I've been trying to learn how to do basic calculations on what size ducts are suppose to be on an existing unit. I'm a service tech and never really learned about the duct sizing and sizing of a unit. I need to know these things. It's so beyond frustrating to me because I feel like I'm so lost. Every single video I've ever watched it almost seems like the people teaching are teaching in a way as though the students already knows most of it instead of teaching a 5 year old this stuff. I wish there was like an extensive three or four hour video starting from the very very basics. When I go on a service call and a customer complains that their room is always warm, I want to know if the unit is sized right and if they have the proper air flow going into their room. I'm at the point now where I'm about to just give up because I feel like there's so many missing pieces.
Please explain Mr. Janowiak, what exactly is Effective length? Is it the amount of air we are losing or the amount of air coming out of the blower motor?
EL or more correctly put effective length is part of the TEL calculation and that is how we solve for the longest circulation path that is part of calculating your friction rate.
Hey Ed, what are the consequences of falling outside of the Acca wedge friction rate chart? That is .06-.1. This happens often when I try to size a duct system for a low pressure ducted mini split. Or with a conventional unit when my duct system is too long due to a tight, large custom home. Thanks!
Bruce Randall if the friction rate is low, you’ll have inadequate fan performance. If on the other side of the wedge you’ll have excessive velocity. Take a peak www.hvacrschool.com/the-friction-rate-chart-and-what-it-means/
@@edwardjanowiak Thanks for the reply. This is something I’ve tried understand for a while. Brian in that link says it helps keep the duct at a reasonable size. I can see that. But what is so magical about .06 - .18. Your tel/asp is what it is. Shouldn’t bigger ducts still deliver the correct amount of air? Or maybe Is the calculation of fitting length dependent on the friction rate staying between .06-.18?
@@brucerandall198 One of the phrases I've heard used to describe it is rate of return. You start to get into a situation with the lower friction where the duct work is physically too large. And the issues with that can be cost, whether it fits and one of the worst ones is that air moving at a velocity low enough to increase the temperature drop and or lower your supply temperature to the point where it causes the surface of our duct insulation to go below dew point. On the higher end with friction rates that end up being greater than .1 we end up with velocities that break “the rules” and we end up moving our duct slide to get our velocity within the limits so it's kind of a waste of time during the design process. If I calculate a friction rate of .14 and every time I line up my duct slide friction rate to my required CFM and I end up with velocities that are 1 1/2 times my limit it's an exercise in futility to continue to use that friction rate. The practitioner would be better off spending their time making sure that their available static pressure is somewhere between .2 and .3 (or do your own math and find a good Compromise on ASP) so when we use our duct slide we come up with realistic sizes versus velocity. I don't know if you did this on purpose, but I think you gave me an idea of the subject of another video.
Thanks Ed. I'll use this for our company training
I've been trying to learn how to do basic calculations on what size ducts are suppose to be on an existing unit.
I'm a service tech and never really learned about the duct sizing and sizing of a unit. I need to know these things.
It's so beyond frustrating to me because I feel like I'm so lost. Every single video I've ever watched it almost seems like the people teaching are teaching in a way as though the students already knows most of it instead of teaching a 5 year old this stuff.
I wish there was like an extensive three or four hour video starting from the very very basics.
When I go on a service call and a customer complains that their room is always warm, I want to know if the unit is sized right and if they have the proper air flow going into their room.
I'm at the point now where I'm about to just give up because I feel like there's so many missing pieces.
Please explain Mr. Janowiak, what exactly is Effective length? Is it the amount of air we are losing or the amount of air coming out of the blower motor?
EL or more correctly put effective length is part of the TEL calculation and that is how we solve for the longest circulation path that is part of calculating your friction rate.
Where do you get equivalent lengths for standard fittings? Obviously Menards isn’t giving out data sheets with their generic duct pieces 🤔
Hey Ed, what are the consequences of falling outside of the Acca wedge friction rate chart? That is .06-.1. This happens often when I try to size a duct system for a low pressure ducted mini split. Or with a conventional unit when my duct system is too long due to a tight, large custom home. Thanks!
Bruce Randall if the friction rate is low, you’ll have inadequate fan performance. If on the other side of the wedge you’ll have excessive velocity. Take a peak www.hvacrschool.com/the-friction-rate-chart-and-what-it-means/
@@edwardjanowiak Thanks for the reply. This is something I’ve tried understand for a while. Brian in that link says it helps keep the duct at a reasonable size. I can see that. But what is so magical about .06 - .18. Your tel/asp is what it is. Shouldn’t bigger ducts still deliver the correct amount of air? Or maybe Is the calculation of fitting length dependent on the friction rate staying between .06-.18?
@@brucerandall198 One of the phrases I've heard used to describe it is rate of return. You start to get into a situation with the lower friction where the duct work is physically too large. And the issues with that can be cost, whether it fits and one of the worst ones is that air moving at a velocity low enough to increase the temperature drop and or lower your supply temperature to the point where it causes the surface of our duct insulation to go below dew point.
On the higher end with friction rates that end up being greater than .1 we end up with velocities that break “the rules” and we end up moving our duct slide to get our velocity within the limits so it's kind of a waste of time during the design process. If I calculate a friction rate of .14 and every time I line up my duct slide friction rate to my required CFM and I end up with velocities that are 1 1/2 times my limit it's an exercise in futility to continue to use that friction rate. The practitioner would be better off spending their time making sure that their available static pressure is somewhere between .2 and .3 (or do your own math and find a good Compromise on ASP) so when we use our duct slide we come up with realistic sizes versus velocity. I don't know if you did this on purpose, but I think you gave me an idea of the subject of another video.
Please realize I’m doing about a 4 hour explanation in 7 minutes
@@Skinamer you can find me at ACCA.org and / or search my name + hvac school for more of me speaking on HVAC related topics.