Clarity on CFM calculations please

[elevatedvagabond]

I'm guessing that info would be located in Mfgr. Data... Or in Maual S calculations... Is that a correct assumption? All of that should be taken into consideration when equipment selection is made? I deal with mostly Trane split h.p's, so Comfortsite will come in handy if I am correct!

[elevatedvagabond]

In this case, the system did well all summer long... So, there are no complaints on performance. I am really just screwing around with the math

[elevatedvagabond]

Also, according to manual D... This would be @ approx. .24 friction rate with 1150 fpm velocity. So, to bring the velocity into check (900), the duct should have been sized @ 9x17 @ .24 f.r.
Once again, the system operates fine... A tad fast at the registers, but no complaints (it's a rental, and it just services a floor for my 4 year old) I'm really just trying to get into the nitty gritty.

[beenthere]

That BTU rating on the equipment is for a 95°OD Db, and a 80° ID DB with a 67° WB. At lower outdoor temps you will get a greater capacity.

[rundawg]

I'm guessing that info would be located in Mfgr. Data... Or in Maual S calculations... Is that a correct assumption? All of that should be taken into consideration when equipment selection is made? I deal with mostly Trane split h.p's, so Comfortsite will come in handy if I am correct!

Yes, the engineering/product data will give you the sensible and latent capabilities of matched pieces of equipment. Assuming the airflow is correct.

Using that info and matching it to heat load calculation done on the home, will give you the best results.

[elevatedvagabond]

Ahhhhh... It's clicking!!! I totally lost sight of the design temp. Stuff.... Sometimes you cannot see the forest through the trees!

[elevatedvagabond]

Thanks guys! I got it.

[elevatedvagabond]

I got to borrow my boss' Alnor Capture Hood. I measured each register independently. When I added them up I only tallied 680 cfm. If you remember from my earlier post, I was calculating 820 cfm via the heat rise method. I have yet to check the Fluke 922 against that calc. I am confused as to the possibility of lost cfm. I am not able to check the return cfm as it free drafts from the pedestal to a high 20x20 rafg. Is there an explanation of this? Or do I have a user error somewhere in my experiment?

[Elfshadow]

I got to borrow my boss' Alnor Capture Hood. I measured each register independently. When I added them up I only tallied 680 cfm. If you remember from my earlier post, I was calculating 820 cfm via the heat rise method. I have yet to check the Fluke 922 against that calc. I am confused as to the possibility of lost cfm. I am not able to check the return cfm as it free drafts from the pedestal to a high 20x20 rafg. Is there an explanation of this? Or do I have a user error somewhere in my experiment?

I'm no where near as educated as the others in this thread, but are your ducts sealed completely. My understanding is that you can a great deal of air flow if they are not.

[elevatedvagabond]

Don't you know, I totally overlooked that! I'm 99% sure that is the cause! Thanks man. The contractor here half a$$ed everything else, I'm sure duct sealant was not high on his list

[beenthere]

I'm no where near as educated as the others in this thread, but are your ducts sealed completely. My understanding is that you can a great deal of air flow if they are not.

Yep, easy to have X CFM through a furnace or air handler, But only get 70 to 80% of that air through the registers.