Trying to be fair!

Brad White_9

or even if I ever saw them! :) But in general if the evaporator is undersized or if the system itself is undersized, humidity control will be enhanced within reason. The system will run longer to meet sensible and will reduce humidity accordingly from that.

If the smaller evaporator was matched up to a larger condenser and the thing works at all, I can imagine you are getting very cold air off the coil, all the better for wringing out the recirculating sponge we call air.

My $0.02

Brad

Techman

Trying to be fair

Enough time has passed to get a responce from H.O. with a problem.This is in reference to the Lennox A.H. that was quoted at the 4T-5T size but the installed A.H. was sized at 3T-4T. With a 4T cond unit.Since everything else is identical,I now have a Q concerning the humidity levels within the structor from the two different sized A.H.'s.Would there be much difference in R.H. using the 3-4 coil as compared to using the 4-5 coil?

Techman

Identical

Hi Brad! This is a 4T load, and assuming EVERY thing is proper, the only difference is the evap coil size .The 3-4T coil would be set up for the 4T load, and/or the 4-5T coil would be set up for the 4T load.Would the humidity level's be that much different, to even worry about? Thank's!

Brad White_9

Not much

difference that I can see. If you are controlling to temperature (as are 95% of AC systems), humidity control is incidental -it is what it is, and will fluctuate while temperature is the controlled variable.

If you have an RH over-ride sequence, the system will choose the greater demand and meet that.

The coil range either way sounds like it will be just fine.

GW

Yes indeed, the laws of mechanics would tell me that the larger coil, with whatever metering device, would be a teensy bit warmer than the smaller coil with the same 4 ton metering device. Read on only if you want to go one step deeper into this subject.

I suppose there's a bit of controversy over this, and the manufacturers may not be always forthright, just my very humble opinion. They can get bigger SEER numbers with bigger evap coils. I have no idea what your background is, none whatsoever. Have you ever looked at the seer ratings from whatever manufacturer you're using? A 4 ton 14 SEER condenser (I hope you know what I mean... the 14 SEER "family") paired with a 4 ton evap (with TX, this is pretty much standard now unless you're talking cheap 13 SEER)most always will not get you a true 14 rating. You have to bump up to the next coil size (5 ton in this example), sometimes two sizes.

It's all a numbers game. Most hard core AC people discard the numbers game and match the two units. I have even heard of a guy that downsized the evap to run the sucker real cold (wicked dehumidification). But when there's rebate money on the line, we all typically play the numbers game, because God help the poor AC guy trying to explain to the HO that their new 14 SEER system doesn't meet 14 SEER rating for a rebate (like here in Mass).

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Constantin

...or

The HO and the installer have different ideas of what comfort is. Our installer assumed 70°F indoor, 96°F outdoor conditions (ASHRAE outdoor design around here for 1% is like 91°F and my wife and I never have the indoor temp below 74°F) when sizing the system. Luckily, I caught on before he was able to install the condensers (thanks EBERATT!) and we reduced the cooling capacity by 2 tons.

So, while our system is a ARI-listed configuration, each condenser is 1 ton smaller than the indoor AH. While such a config will increase sensible heat removal at the expense of latent heat removal, our infiltration is low enough for this to be OK. Considering that none of the outdoor units ever ran on stage 2 this summer, it's pretty safe to say that our system is still oversized.

EBEBRATT-Ed

It is a matter of the condenser/compressor reaching a balence point with the evaporator and its load. A smaller coiler will give you lower humidity but is that what you want?? And it comes with a price. You will burn more electricity with a smaller coil. The higher the suction pressure the compressor runs at the more efficient it will be and the less electricity it will use. The higher the suction pressure the more gas a compressor will pump. Probably not a huge deal in this job but the efficiency will suffer with a smaller evap coil.

Ed

EBEBRATT-Ed

Constantin-

I recall discussing your system(s) over at OTT some time ago and was wondering how you made out. As I recall you tonnage was prety low for the square footage you have although I'm sure you had an accurate heat gain to work from. Sounds like it worked out OK. Nice to have a few jobs with the right size equipment. Most of them are way oversized. Sounds like you picked the right stuff.


ED

EBEBRATT-Ed