I sort of started this thread elsewhere, but very poorly.
I have a Bryant Evolution A/C system, ductwork in my attic. reasonably sized ducts (8" feeds of 12x30 mains). system is a year old, ductwork is older. For yuks last night I checked the static pressure at the stat with the fan on high, and read 1.37!!! Then I thought - end of season - dirty filter! So I went up to the attic. With the filter slid out most of the way (so it's still blocking the opening in the side of the ductwork, but NOT the airflow), my static dropped to 0.8. So I sighed relief. Then I changed the filter and put it back, and the SP went back up to 1.34???
It's a Spacegard (Aprilaire) 2200 Media filter.
Does this make sense to anyone? It doesn't to me. Should I get a different filter? Should I stop checking my static?
I had a 4" Carrier media filter installed with my Infinity system (same as Evolution) and the rated static pressure drop for the filter is only 0.15" on high stage air flow (350CFM/ton). Not familiar with your filter, but .54" static pressure drop seems really high, what is the manufacturer's rating? That much drop would cause problems on almost any system.
Specs are on the last page of the brochure below - for 1400CFM the difference should be 0.15.
So - did a better test - took OUT the filter and CLOSED the enclosure - and the SP was 1.2. So it's not the filter, i just got a bad read by 'faking' the closed enclosure by blocking it (mostly) with the filter frame.
I don't think I have too much A/C. My old system was a 4-ton york with an 1800RPM fan that laster 20 years, and it did it's job fine, and we could tell when it was wearing out. THis summer the evolution did fine - kept the house cool AND dry, so it wasn't cooling too fast.
So do I have a problem?
[Edited by jeffw_00 on 11-10-2006 at 09:02 PM]
Yes, you have a problem. Your duct is too small. Your static should not be anywhere near that high. You probably had the same problem with the old system.....it just had no way of telling you. Will it work? Yes. Will it work properly and not have premature failures and give you proper efficency? No. Your contractor should have identified this problem and resolved it when the system was installed. Time to call them back.
If all else fails....Try reading the directions!
Tell it like it is and let the chips fall where they may.
Any views or opinions stated here are strictly my own.
thanks plain spoken - but if you look at my other thread "did I buy the wrong furnace" - you'll see that I can't really go back to the original contractor. (sigh) However, unlike the furnace, I believe I probably don't have a seriously mis-sized A/C system. I think a 3-ton would have been a bit light, and maybe the 4-ton is a bit too much, but not so bad that it makes any sense to replace it. unlike the archaic duct system on the furnace, the duct system for the A/C was put in by a well-regarded contractor and uses modern big mains and 8" feeds, and the old York didn't have premature failure. So let me ask...
1) How accurate is the SP reading on the evolution stat? I know it infers SP from the current drawn by the fan.
2) Can I solve this by adding RETURN CAPACITY? THe filter is in the return. Perhaps I have insufficient returns? With the filter in and the enclosure open, the static dropped to around 1.0 - maybe I just need to add another 12" return? (the original system had 5 8" returns for the whole system, and they were noisy, so I added a 12" return in the hallway and things got better - maybe i just need more of those?)
what else can I do?
The static pressure reading that the evolution gives you also states the CFM. They check static at maximum capacity of the furnace installed. If you've got a furnace that is capable of 5 tons of air conditioning it will check the static at approximately 2000 CFM and the 2200 is only rated for 1400 CFM.
it's a 4-ton system, and the high speed fan is about 1400 CFM
something makes no sense, or maybe it does:
my new furnace, on high:
about 1300 CFM
feed capacity = ~400 sq in
return capacity = ~500 sq in
Static = 1.0
my new AC, on high
about 1400 CFM
feed capacity = ~550 sq in
return capac = ~350 sq in
Static = 1.37
maybe I just need, like, a 16" return somewhere for the A/C?
Since it bothers you you need someone to check the static pressure of each side of the blower and see where it's choked. Then it can be determined what corrections need to be made.
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well, it doesn't bother me if it doesn't bother you. The unit seems to work properly otherwise, and it is able to achieve the 350CFM/ton (1400CFM) which is spec'd. So, is the fan working too hard? if not, I'm good
you know - doing nothing but opening the panel for my spacegard filter drops the static from 1.37 to 1.05. I think this system is starved for return (not surprising, it has 200 sq. in. more feed than return). It's really easy for me to add another return - why shouldn't I?
Sorry jeff, its working too hard.
An additional return or 2 may be the solution.
The sp of both the supply and return should be checked to see if both need attention.
Hi BT - I agree that it would be good to get someone to measure everything, but even with "good" companies, for some reason it's really hard to get anyone to measure anything around here 8-[
And anyway, does it matter? I thought the measurement from the stat was pretty much a smoking gun - I mean, all I have to do is take the cover off the spacegard compartment in the return (leaving the filter in place), opening up maybe 20 sq in of additional return, and the static drops from 1.37 to 1.03. If the problem was in the feed would you expect such a drastic drop in SP from such a small change in return capacity?
The good news is that adding a return is pretty trivial. (Adding a feed isn't too hard either, but there seems something contradictory there - i already have enough feed for comfort, so additional ones would be 'dumping air'.)
Anyway - The estimator is coming by wednesday to check out the furnace installation, and (for some reason) is bringing his bryant rep. I've dropped him a note about the A/C static pressure and will engage him on it wednesday.