I strongly doubt it will.
You'll probably have higher humidity.
Did we suggest your guy was incorrect when you told us the load calc came out to 1 ton more then you had.
Did he feel comfortable installing a 4 ton system even though your old unit is only 3 tons.
Ask him if he has a 3 ton coil instock, or if he can get one for Tuesday.
I bet he can.
Oh he would have no problem getting one from his distributor as they are standard stock, but I would have to tell him he's wrong based on your advice. And he would then need to tell the guy who did the Manual J that he is wrong. Oh and did I mention that the Manual J guy attends conferences and knows the difference between version 7 and version 8 and been doing these for decades.... The point is that if you are right, I'm screwed and if humidity becomes a problem I'll just replace the coil in a couple years.... Stupid?? yes it is. Of course, if he's right about the Manual J I'm screwed, although common sense says otherwise.
Do you want to know the irony of all this???
First contractor comes out asks if I'm happy and then quotes 3 ton xL16i with 3 ton coil. No offer of Manual J.
Second contractor is the one I've used for 30 years.. Same thing except this time when I mention I was happy but had been concerned about sizing when house was built 15 years ago, he offers to do Manual J. So results come back 36200 Total / 31050 Sensible and the guy sizing the unit is concerned and says if stay at 3 ton (33600/23600 with 3 ton coil) that we need more umph so coil is upsized, all based on standard practices they and others have done for years.... So essentially, if your're right I've been sort of screwed by Manual J.... Sometimes ignorance is bliss.
Unit goes in Tuesday, so this time next week we'll know and I'll post back if I'm not too depressed. It won't be to gloat either, just to post results so we can all learn from others experiences....
I hope all goes well, and maybe somehow humidity won't be a problem, hope for your case it won't be.
Actually, I would be happy to hear I'm wrong.
Originally Posted by wraujr
I hope you report back in a week, that your RH is less then 50%
I just don't believe its going to happen.
If Problem, Engineer makes Backup Plan
So for sake of discussion, let's say humidity gets worse because of 1st stage use during seasonal transition periods. Would it possible to run xL16i in 2nd stage only which would duplicate old 3 ton one-stage. Obviously I would have paid extra for features not used and could have bought xL15i, etc. But remember, this is just the "backup" plan... Thermostat is the Trane 803 and I am not trying to use unit/tstat to create IAQ humidity control.
For those familiar, would it require rewiring, dip switches on furnace, or are there options on the 803 tstat.
P.S. For info purposes how is SHR affected by CFM of blower???
Also, is SHR = 70% good, 75 OK, and 80 bad??? Just trying to get a feel for SHR....
70 good, 80 bad.
A lot of 2 stage are between 75 and 80 in first stage.
Low air flow removes more moisture.
High air flow removes less.
You can use plan c.
Have contractor come back and install 3 ton coil.
Humidty, Where I am at Know
Just as baseline info on my current situation:
Tsat at 76 and unit currently running (near end of cycle):
1st floor 75.2* 60%RH
2nd floor 79.0* 46%RH in bedroom (not near grill, different meter)
Never really paid attention to humidity except in heating with humidifier.
Unit runs maybe 10 miniutes and after it shuts off, 1st floor humidity goes back up.
House is single zone two story colonial hence temp delta....
What are the things to look for when "analyzing" humidity so I can get a baseline on current setup....
Last edited by wraujr; 08-30-2008 at 10:34 AM.
Reason: Bad Typing
Outdoor temps and humidity.
Indoor temps and humidity.
To Silver06: thanks for sharing your experience with humidity when you replaced your 1-stage 3tonOD/4tonID with 2-stage 3ton system and how your humidity went down. But, remember you changed TWO things: one was OD/ID pairing and you went to 2-stage xL16i, so we can't really say whether your humidity drop was from going to 2-stage, or going to matched 3-ton, or maybe combo of both.... My old 3ton ID/OD pair is a single-stage and is giving me 60%RH, so hopefully xL16i 2-stage will reduce my humidity and that that 3ton OD paired with 4 ton ID will not affect it too much (I admit that the contractor's need to increase 2nd-stage Sensible will negatively affect Latent in 1st stage). Thanks again.
Yes, two things did change. To clarify, I got the XL19i, closer to a 50/100 split. But if your current system is a properly matched ID/OD combination, there might be a number of things causing the problem. It may be an older evaporator coil with wider spacing between the fins. Might have too much airflow going across the coil. If its a flow-rater metering device, it may be the wrong size or something else, or a TEV metering device that may be going bad or even infiltration into the struction, perhaps a negative pressure condition in the house.
To back track, back in '91, we had to replace our original evaporator coil that was installed new in the house in '69. Then a year later, we had to change the condensing unit. So we had a 3 ton coil with a 3 ton condensing unit. The new evaporator coil had a TEV on it, because the original furnace was still being used with a belt drive blower, and because the blower was a little undersized, they installed the TEV to make sure it controlled superheat, and hopefully never slugged liquid back to the compressor. With that combination, we were able to maintain about 40-45 percent relative humidity in the summer.
Then in '98, we replaced our old natural draft furnace with a new condensing furnace. Along with that was all new supply and return ductwork. This made a great difference in airflow to all rooms and made for a quiet operating system. Everything was measured and calculated using Manual J and D.
But, the salesperson who came to size and bid the job said that he was going to install a 4 ton evaporator coil to get more airflow through the system (Mind you, this was a 80k btu input furnace with a 3 ton blower). I asked how this would affect humidity. Being that I didn't know much about how this would make a difference, he told me since it had more surface area, it would take out even MORE humidity. I took his word for it. Also, the coil hung over the edge of the furnace and looked ugly.
A week after they installed it (this was in August) the humidity still had not come down below 58 percent. The lowest we were ever able to get the humidity was 52-53 percent. Of course the indoor temperature had to be lowered, and it felt cool and clammy. Even after lowering the fan speed, it hardly made a dent in the humdity.
Then in '07, we replaced everything but the ductwork, and installed a 80k btu XV90, a 3 ton indoor evap ARI matched to the 3 ton XL19i. I know a person can upsize the indoor coil to get better efficiency ratings, but I told them I wanted maximum humidity removal.
After the installation, our humidity levels dropped to the 40-43 percent range, and we were able to turn up the thermostat by quite a bit.
So, even a properly sized single stage system can remove quite a bit of humidity, as long as other factors such as infiltration and negative pressure and indoor humidity sources are taken care of.
In a lot of arid climates, they will sometimes oversize the evaporator coil for better sensible capacity, but if it gets humid, you want good humidity removal.
The pros will probably complain about my post, and I don't blame them. I just didn't want to see another person have the same kind of problems I did. I know that each case is different and this may be one of those cases, but this is an investment, and I know that beenthere and the other pros know what they are saying.
Sorry for the long post.
Thanks for the post with the details. Nothing wrong in my mind as all you did was post "just the facts maam"....
In my case the current 3 ton system is all matched and original and installed by builder 15 years ago and my humidity (now that I'm paying attention) is around 60%, so I only know 40% in the winter.
I will post back as to what happens to my humidity levels. Thanks again.
I feel the need to point out a couple of capacities. 3 tons is not always 36,000 BTUH as one might think:
Originally Posted by wraujr
XL14i -- With most coils, rated 35,000-37,000 BTUH total, 27,000-29,000 sensible.
XL16i heatpump -- rated 34,000-35,000 BTUH total, 25,000-27,000 sensible.
If you strongly favor the R410a refrigerant, then so be it. This is one of the selling points of the 16i over the 19i which is available in R22 only. I believe there is an in-between model 15i with excellent capacity and efficiency ratings, which with a variable speed air handler and dehumidistat could outperform your current system. The money saved could potentially be invested in a separate dehumidifier system, which could perform for the cool humid season. I could forward the specs in detail on the 14i, 16i and 19i, but don't have them for the 15i. Good luck with your choice.
Best wishes -- Pstu
Aware of Trane options, my selection process:
Want R410, R22 is now $35/lb and rising, R410 is dropping.
19i is dual compressor and much more expensive
15i is single-stage, wanted 2-stage.
So 16i it is. with 3OD/3ID = 33600/23600 (2nd Stage)
with 3OD/4ID = 34400, 24200 (2nd Stage) and I'm happy with these #'s
The sticking point is humidity removal in 1st stage and unfortunately I don't have those numbers, I do plan on calling first thing tomorrow and point out questions about humidity/sensible/etc in 1st stage.
At this point is there any one that could supply 1st stage data on the xL16i 3 ton (4TTX6036B1) with 3 ton coil (4TXCB036) and also with 4 ton coil (4TXCB048)?? The 2nd stage data is above from contractor... Oh, coil sits on TUH2B080 furnace. Thanks.