buckeyefarmer
Epic Contributor
So I need a good AC design guy..... 
Got my cheap anemometer ( I gotta look at it to spell it) today, and tried to get readings from all vents in ft/min. I then measured all vents, guessed at a K value to reduce the area blocked by metal (2 downstairs are wood vents), and got CFM numbers at each vent. Hard to get consistent numbers from the ceiling vents, numbers jumped a lot as I held it up. Avg button didn’t seem to avg.
downstairs is OK, but it's 3 ton, with 11 vents. Manual J said I needed around 500 CFM total, it's pumping out around 600 according to my measurements. The only room that needs more air is the last one, and one other room has more than it needs, so I think I can balance it. Downstairs is not a problem, the geo unit rarely if ever runs in high speed, stays in low.
Upstairs is off some. Manual J says I only need 361 CFM. Measurements says it's pumping out 616 CFM on a 2 ton unit, way more than it should. At 80 deg out and under, it works ok, except the 2 rooms over the garage stay warmer.
Original system was middle feed, had 2.5ton unit (I think). it split 2 ways into a 8x12, then drops to 8x8 on each end.
I changed to an end feed, so I increased to 8x16 on the feed end. But then i did another 8x16 to the rooms over the garage, which also reduce down to only 2 outlets, that is way oversized, but i was saved by having the unfinished room blocked off.
My numbers say the air is proportional split, 2 over garage flows 20%, the 8 original flow 80%.
I just think my manual J is off for the upstairs and the unit is undersized. With the rooms over the garage, it's more sf than downstairs, and the upstairs has the attic load. Supposively that was accounted for in the manual J, but the CFM required numbers are much lower. (361 vs 500).
If I use only one 8x16 off the AH, it will support more flow (fpm) for the 800 cfm coming off the AH, but since it's proportional, it works out ok.
The original attic install uses flex ducts to the registers, which is part of the problem. That reduces air flows. I put solid metal on the new ones I installed over the garage. I also put in dampers to adjust, the original does not have them.
It's only an issue when temps get above 90s. Winter is fine for heating.
since the rooms over the garage have a separate duct split from the AH, the fix is to remove the garage room from the geo system, and put those rooms on it's own dedicated system. I'm thinking a Mr cool with AH system will work. only need about 1 ton, and let the geo just handle the original load. The ductwork change in the attic looks good from my numbers. I'll run it again with the full 2 ton capacity, and see how it changes. Later today, it's 2 am. time to stop this fun.
I’ll add, since today only got to 84°, the upstairs is keeping up, it’s actually cold set at 73°.
Got my cheap anemometer ( I gotta look at it to spell it) today, and tried to get readings from all vents in ft/min. I then measured all vents, guessed at a K value to reduce the area blocked by metal (2 downstairs are wood vents), and got CFM numbers at each vent. Hard to get consistent numbers from the ceiling vents, numbers jumped a lot as I held it up. Avg button didn’t seem to avg.
downstairs is OK, but it's 3 ton, with 11 vents. Manual J said I needed around 500 CFM total, it's pumping out around 600 according to my measurements. The only room that needs more air is the last one, and one other room has more than it needs, so I think I can balance it. Downstairs is not a problem, the geo unit rarely if ever runs in high speed, stays in low.
Upstairs is off some. Manual J says I only need 361 CFM. Measurements says it's pumping out 616 CFM on a 2 ton unit, way more than it should. At 80 deg out and under, it works ok, except the 2 rooms over the garage stay warmer.
Original system was middle feed, had 2.5ton unit (I think). it split 2 ways into a 8x12, then drops to 8x8 on each end.
I changed to an end feed, so I increased to 8x16 on the feed end. But then i did another 8x16 to the rooms over the garage, which also reduce down to only 2 outlets, that is way oversized, but i was saved by having the unfinished room blocked off.
My numbers say the air is proportional split, 2 over garage flows 20%, the 8 original flow 80%.
I just think my manual J is off for the upstairs and the unit is undersized. With the rooms over the garage, it's more sf than downstairs, and the upstairs has the attic load. Supposively that was accounted for in the manual J, but the CFM required numbers are much lower. (361 vs 500).
If I use only one 8x16 off the AH, it will support more flow (fpm) for the 800 cfm coming off the AH, but since it's proportional, it works out ok.
The original attic install uses flex ducts to the registers, which is part of the problem. That reduces air flows. I put solid metal on the new ones I installed over the garage. I also put in dampers to adjust, the original does not have them.
It's only an issue when temps get above 90s. Winter is fine for heating.
since the rooms over the garage have a separate duct split from the AH, the fix is to remove the garage room from the geo system, and put those rooms on it's own dedicated system. I'm thinking a Mr cool with AH system will work. only need about 1 ton, and let the geo just handle the original load. The ductwork change in the attic looks good from my numbers. I'll run it again with the full 2 ton capacity, and see how it changes. Later today, it's 2 am. time to stop this fun.
I’ll add, since today only got to 84°, the upstairs is keeping up, it’s actually cold set at 73°.
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