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Condenser is big than air handler. Effect ???????

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fixmikelol

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Discussion starter · #1 ·
This is what I have... New Trane heat pump split system a year old. The air handlers are 5 ton but the condensing units have been replaced with 6 ton units. there are 6 of them like that. Why would some one do this ???? The complaint is that someone has to come out to defrost the units every other week. The air is humid as hell too.
I know this is not right but I have to explain this to the owner !!!!!!
 
#2 ·
Since a "Ton" is never a "Ton" (12,000 btu's )look @ the capacity of the "6" ton units @ design conditions, the check the capacity of the indoor coil and the ability of the fan--on the surface it may seem bad, but a little "verification" will eliminate and presumptive guesswork..........3 ton condensing units may only deliver 32 KBTU @ design, not 36KBTU
 
Discussion starter · #3 ·
Ok. The the trane btu's on a stand alone condenser is 74,000 with a match air handle is 77,000.
Max air flow is 2100@ 0.1 wc out of the air handler. 400cfm per ton in the south
 
#4 ·
fixmikelol said:
Ok. The the trane btu's on a stand alone condenser is 74,000 with a match air handle is 77,000.
Max air flow is 2100@ 0.1 wc out of the air handler. 400cfm per ton in the south
Click to expand...
Well, your static will be more than .1...not sure if you are looking @that chart correct---You need to look @ the OSA Design in your area, estimate your entering air WB and DB, go to the expanded ratings for the outdoor unit and see what the capacity is 74KBTU on a "6 ton" condenser does not seem correct, can you post model# of indoor and outdoor
 
#10 ·
I'm trying to think about how, if there is a 1 ton size mismatch, that the mismatch would cause the need for manually defrosting the outdoor units.

My initial though is that the defrost setting on the boards are all set too long. For instance, the jumper is on the 90 minute pins when it needs to be on the 30 or 60 minute pins. Where I am in the desert, 90 minutes works fine, but if you are in a more humid climate, then 30 or 60 might be better.

Another thought is that the defrost termination sensor on all of the units could have been put in a place that terminates defrost before all of the frost has been removed from the coils.

Model number might help as stated above.
 
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#11 ·
David Goodman said:
I'm trying to think about how, if there is a 1 ton size mismatch, that the mismatch would cause the need for manually defrosting the outdoor units.

My initial though is that the defrost setting on the boards are all set too long. For instance, the jumper is on the 90 minute pins when it needs to be on the 30 or 60 minute pins. Where I am in the desert, 90 minutes works fine, but if you are in a more humid climate, then 30 or 60 might be better.

Another thought is that the defrost termination sensor on all of the units could have been put in a place that terminates defrost before all of the frost has been removed from the coils.

Model number might help as stated above.
Click to expand...
very valid point, was assuming they were defrosting the indoor
 
Discussion starter · #14 ·
Ok. Found out some history on this.
The company that changed out the unit, was a change equipment only company, (you know the kind). The customer (previous owner) wanted bigger units. So, they put in 6 ton commercial heat pump condenser with a residential 5 ton air handler. Never did anything with the duct work. The supply trunk line is duct board, inside measurements is 10 X 23 with three 90* off the plenum before it starts it's run. I'd imagine the static pressure is high, (didn't get that far into it yet) the sub cooling is about 3 degrees, lol.
The existing air handler can not exceed 2000 cfm or it will sling water (per Trane) so that leaves me with about 333 cfm a ton of air.
I'm thinking new duct work. I just don't have room for 6 commercial air handlers. I size my ducts at .1 friction at 1200 fpm and 400 cfm a ton of air. See anyway to use the existing air handlers ????
 
#15 ·
fixmikelol said:
Ok. Found out some history on this.
The company that changed out the unit, was a change equipment only company, (you know the kind). The customer (previous owner) wanted bigger units. So, they put in 6 ton commercial heat pump condenser with a residential 5 ton air handler. Never did anything with the duct work. The supply trunk line is duct board, inside measurements is 10 X 23 with three 90* off the plenum before it starts it's run. I'd imagine the static pressure is high, (didn't get that far into it yet) the sub cooling is about 3 degrees, lol.
The existing air handler can not exceed 2000 cfm or it will sling water (per Trane) so that leaves me with about 333 cfm a ton of air.
I'm thinking new duct work. I just don't have room for 6 commercial air handlers. I size my ducts at .1 friction at 1200 fpm and 400 cfm a ton of air. See anyway to use the existing air handlers ????
Click to expand...
Rip it out and start over
 
#17 ·
I size heat pumps at 450cfm per ton.

however, regardless of the mismatch, with 3* subcooling, are you sure you're not undercharged
 
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#19 ·
I usually like 450 CFM heat pumps
3 degree subcooling sounds like you're low on charge...
If the indoor coils are icing up every week could be that they're just low on charge..
or the smaller metering device is acting as a restriction
but then your subcooling would be higher.
 
Discussion starter · #20 ·
Can you imagine what's going to happen when it does go into the heat mode with that little coil. LOL
Ok, who make's a 6 ton air handler that has a residential style case ?? No way I'm I going to get a TWE air handler in the space they have. I would like to (in this application) put in a dual circuit air handlers and stage them.
All the duct work has to be redone anyway.
I also would like to say thank you guy;s for all of your input.
 
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