Thanks, for all the replys about my system replacement. They've helped me decide to stay with the 3 ton design and understand the Manual J calc.
I wanted to start a thread specifically on the pluses/minuses of tweaking system performance thru coil changes.
At this point, the contractor is tweaking the performance of the A/C by changing the coil from 3 ton to 4 ton. The Manual J has my house at just over 3 ton and contractor is not pushing upsizing whole system to 4 ton, but would like to "tweak" the performance of the 3 ton system. He is using Trane data (I think its a computer program) to analyze the combinations, so I would think these matches would be Trane approved. What he got:
3 ton xL16i / 3 ton coil - 33,600 Total and 23,600 Sensible
3 ton xL16i / 4 ton coil - 34,400 Total and 24,200 Sensible
Total up 800 BTUs
Sensible up 600 BTUs
SEER went from 15.5 to 16.0
Same 1200 CFM
Same physical size of "box" so it won't look funny
I am paying his cost for larger coil since not in orig. quote
(1) Is Latent simply Total - Sensible??, if so the Latent went from 10,000 to 10,200 which would mean slightly better humidity removal which seems like a plus.
(2) Did some googling and it seems that upsizing coils is an accepted practice done by other HVAC contractors although +0.5 ton seems more typical. I assume the tuning/matching of coils is mfgr approved as he's using software supplied by Trane and all components are supplied by Trane.
(3) Suction Pressure would be higher (I think). Would this or anything else affect the life of the compressor, etc.?? I would think that the charging levels for the system would be adjusted and that 10 years from now, a tech who's not aware of the 3ton/4ton match might not charge system proper.
This contractor is very professional, and is clearly working the numbers and not just using "rule of thumb" and he answers all my questions. I looking for others opinions/experience. Thanks in advance.