Replacing Old Systems
I want to replace (2) 20 year-old Trane XE 900, 3-ton, split systems. One split system for upstairs and one for downstairs. Current sytems are 20 years old, remain operational and did a decent job of cooling/heating.
Home is two-story, 3400 sq ft, 15% larger downstairs, with large and open stair-well. Climate is northern CA., Sacramento area, with mild winters and warm/hot dry summers.
Replacement systems, one for upstairs and one for downstairs, are Am Std, 3-ton, variable speed, R-410A, 15 SEER, enhanced high efficient TXV Coils 3-ton 12.5 EER, split systems, 95% AFUE downstairs and 80% AFUE upstairs. Totaline digital Thermostats. Both duck systems will be checked and repaired where required (C.E.C certificate requirement). Return duck is 15 inches upstairs and downstairs. Prefer to avoid replacing duck system, if possible.
Comments or suggestions are appreciated. Thank you.
Last edited by PSC; 04-12-2008 at 11:13 AM.
Reason: Changed incorrect SEER to EER for Coils
I'm guessing you meant 12.5 EER, not SEER. Since that kind of a match up would defeat the purpose of buying a 15 SEER condenser.
15" return round duct? Are you sure it isn't 16".
15" would be a little small for 3 tons.
80% upstairs, and 95% down, makes sense.
A/S equipment is ok.
Yes, you're correct 12.5 EER for coils. Thank you for correcting.
I'll check on the returns to be sure they're 15 inches and report here.
Return duck downstairs is 15 inches while upstairs is 16 inches. Might have something to do with tight area going from furnace to under house location for downstairs return but not sure. I suppose I could replace the downstairs return if one inch is material...is that your advice?
Depends how long it is, and the amount of bends and turns in it.
If your contractor knows how to test static pressure, he can determine if it should be replaced or not.
15" has a slightly high velocity for 1200 CFM of air. Is your return a little noisy.
In humid Florida,we'd be setting it for 350 a ton,so 1050 cfms.
The return is not noisy, like in loud, but you know it's on if you're nearby. Downstairs return is located in a open walk way area so "noise" is not really a problem.
Installer has an excellent reputation and has been in business nearly 45 years, I'm sure they're qualified to perform the test you suggest and I'll ask for it. The downstairs return run is about 32 feet with two 90 deg turns and one sweeping curve.
I think they run higher CFM's where he is, since they don't get the humidity like you do in FL.
No offense, but the correct term is duct, not duck.
LOL, no offense taken. I've been hunting ducks too many years and not concerned with ducts for just as many years!
Originally Posted by Random Guy
I was wrong regarding the sizing of the downstairs return. It's an oval shape with the "oval" length at 16" and the shorter length at 15". Upstairs return is 16" round. (thank you for the heads-up "beenthere")
Unlike my first bid that was provided by an installer/dealer, that frankly has a very good reputation, the second bid installer/dealer who also has an excellent reputation is completing a manual j/d calculation and spent a couple of hours at the house yesterday before submitting a bid. I will receive his bid in a couple of days and I was impressed with his efforts to provide an analysis rather than a “seat of the pants” recommendation like the first installer.
While I'm interested in having my replacement system sized correctly and installed properly, I'm also interested in having the best bang for the buck. Specifically, I'd like state of the art equipment but very durable and reliable equipment. I’ve tried to do my homework and have read a great deal about the debate between R-22 vs. R410A, two step compressors vs. single stage or even two compressors, variable speed fans, various filters available, SEER, EER, AFUE ratings and so forth. This forum is an outstanding resource of HVAC information for a guy like me.
Regarding the R-22 vs. R410A debate, clearly R-22 will become more expensive or disappear entirely over time but I'm not sure, at least in my case, it matters much. At my age, it’ll likely be someone else’s problem since the equipment will probably outlast me! It's doubtful but maybe a little risky that replacement R-22 becomes very expensive although, as I understand it, leaks of refrigerant are rare...is that true (for what it’s worth my 20 year-old Trane system never leaked and remains operable)?
Probably the smart move is purchasing equipment designed for R410A. Interestingly, Am Std best split unit still uses R-22 (18 SEER Allegiance) although I’d guess that will change to R410A soon.
Re SEER ratings, it appears higher is better although I don't think I'll see much utility bill savings in my area with a SEER rating much higher than 15.
Re AFUE, it appears higher % is better but again payback for equipment costs for higher AFUE in my area is questionable although I'll probably opt for 95% downstairs and 80% upstairs as stated earlier. Equipment cost differential between 95% and 80% AFUE is material (although I don't have the latest bid yet so I might be wrong about that).
I'm not an engineer but two compressors intuitively are better than one and two-step compressors appear to be more efficient than single stage ones although a bit more complicated piece of equipment. And, variable speed fan is superior to single speed ones. Since all are available to me which do you recommend?
Any other advice/recommendations you might have and post here, I'm very thankful to receive.
Last edited by PSC; 04-13-2008 at 11:51 AM.
Reason: Removed $ amount re difference between AFUE %
The 95% for downstairs since it will be doing some of the heating for the upstairs also.
The cost difference(you not allowed to post by the way), should not be hard to recover.
VS blower. If your in an areid are, you don't need it. If your in an are that has higher humidity in the summer, it will improve your over all comfort, by helping to keep the indoor RH lower. Some people are able to set their stat a little warmer because of the decreased humidity in the summer. And save a little more yet. 2 stage systems tend to help lower the humidity better during the mild days, then single stage systems.
Your cooling season length, temps and electric rates determine how high of a SEER you should get.
If your electric rate with all fee's is only 4 cents a KWH, you don't need high SEER.
Of course if its already over 10 cents a KWH, and you expect it to go up. Higher SEER is may count a lot a few years down the road.
Pursuant to the rules, I removed the $ comment re AFUE. Thank you for the reminder "beenthere" and thank you for your advice.
Do you think it matters much re R-22 vs R410A? The dual compressor Am Std model requires R-22 while the two stage is designed for R410A. Also, my existing system, of course, is R-22...if I move to R410A do you advise changing out the lines?
I give the customer their choice which refrigerant they would prefer. R22 will increase in price, but I can't tell you how much.
I'm not sure if Trane/AS, recomends changing the line set. But I prefer to change them.
Kind of eliminates risk of oil contaimination. JMO
Although I lean toward the higher SEER units in heat pumps. I don't recomend the highest SEER line.
The amount of savings between a 16, and a 19 SEER unit, is almost impossilbe to recover in the units life span. Unless your electric rate is already very high.(say 17 cents per KWH)
Currently the price of R22 is increasing.
Come 2010, the demand for it will drop. And every year after that demand will drop more.
So it may not continue to rise as some think, or it might..
If I was good at guessing comodities, I'd be rich, and retired.