Size Matters - http://www.hvacmechanic.com/ Forums
Original message
| HotinFl
 |  "Size Matters"
, posted Tue 23 Sep 00:38  
Hey Everyone, a question about the size of my unit (Not certain that sounded right but, oh well) A bit of background.
I'm replacing our Trane, a split system 2 ton heat pump. It worked like a horse for 17 years but it's time is done. Of course we're replacing the condenser and air handler both. I've always felt the original unit was slightly underpowered as it ran far more than I'd have liked from day one. I'm debating between straight cool and heat pump as we get maybe 2 or 3 nights a year when the temps. dip into the 30's (Orlando). I'm inclined to think a straight cool with maybe a 10KW heat strip would suffice.
A modest little block house (1200 sq. feet under air), single story, no more windows than any other home I'd say. The house faces west, is not particularly well insulated and is exposed to direct sunlight from dawn till about 3:00 PM. I've noticed that my neighbors with the same floor plan as mine are typically having 3.5 ton systems installed as their old ones die out. Seems like a lot of AC but what do I know. I'd bet they are living in nicely cooled but slightly damp houses. Humidity is a great concern here in Cent. Fl.
Also considering the real value of SEER. Obviously it'll be 13 or better but it seems that most companies that rate a system as 14, do so with the exact same condenser as their 13, but with a half ton greater capacity air handler. Is that really of any worth? You do however pick up the Copeland scroll compressor (I wouldn't know a Copeland scroll compressor if it hit me in the head but it makes it sound like I know what I'm talking about, doesn't it?) at the 14 SEER and higher rating so maybe that makes it worth it.
I know that the variable speed air handler is the greatest thing since underwear, but why? I don't mind that 'cold blast of air' when the systyem kicks on. Hell, I'd never even noticed it before until someone told me it was a bad thing. That seems to be the primary selling point of the variable speed.
My wife and I will be in this home for many more years so I don't mind spending some bucks here but at some point it becomes a diminishing returns kinda thing. Certainly the budget is a concern as well.
Lastly (thanks for hanging in this long), we are going to have this done by professionals. I'm just looking for some objective opinions here and avoid being sold a bill of goods. I could swap the tranny in my wife's car in about a half hour, probably fix that annoying 'tiles coming off at liftoff' problem the space shuttle has always had, hell I've even replaced a couple of kidneys in my day but HVAC has me stumped and I ain't stupid enough to risk my investment by trying it myself. Thanks in advance. Mark.
|
|
Replies:
|
| HotinFl
| "Re(1):Size Matters" , posted Tue 23 Sep 18:20
|
| learner
| "Re(1):Size Matters" , posted Tue 23 Sep 11:07
Hi,
If I don't have a perfectly matched syste, I'd rather have a hard working little under sized system than short cycling over sized one(poor efficiency this way). Any way it gave you a good 17 years service. Let reputable pro do the load calculation and start from there.
|
| aircooled
| "Re(1):Size Matters" , posted Tue 23 Sep 08:44
Doesn't matter what your neighbor's have installed in there home.
I would ask for a load calculation to be done and then you will see what is needed for comfort. Might want to check out Carrier Comfort series Heat Pump and Variable drive air handler. Then along with cooling it will remove HUMIDITY better than a standard air handler. Note , that after Jan.2010 there will be NO MORE R-22 systems manufactured in the USA. So check out Puron (r-410A) systems.
"People will forget what you said people will forget what you did but people will never forget how you made them feel."
|
| Rpfingsten
| "Re(1):Size Matters" , posted Tue 23 Sep 01:46
HotinFl
Hello my friend from muggy Lousiana... let me tell you upfront that I am not an hvac contractor and have no credentials in that field, so take what I say for what it's worth. However I have spent the last 3 weeks or so doing extensive research on the subject of heat pumps as I am as we speak, having a 2 ton and a 5 ton system installed in my home. Because it's sooooo hot down here for sooooo long in the summer, I'm going with an 18 seer unit. Unlike you, during the winter we will see our share of winter days where the temp will be below 40 and into the upper 30's, so for this climate, a heat pump is a good idea. but you said you don't have but one or 2 days a year where you need heat. If that's the case then probably you could get by going with strip heat only and replacing your heat pump with a straight ac unit. I know one thing, a straight a/c unit will cost you less than a heat pump. However strip heat is not economical. I guess your decision will be based on how much during the winter you really need some form of heat.. as for the sizing of the unit, actually asked my contractor that today while he was working here at the house. He said as a "rule of thumb" he goes by 1 ton for every 400 sq. feet. My house is approx. 2700 sq. feet and can be zoned into two systems.. it works out just about right, the main part of the house is right at 2000 sq. ft ( that's the 5 ton's area ) and the remainder will be handled by the 2 ton unit. If your house is 1200 sq. feet I would think 3 ton would be sufficient. As for running a long time, it is my understanding that with these 2 stage motors they have now, that the units will actually run longer than the old units, but for part of that time are running at a slower speed, thus using less energy while maintaing a comfortable temp in your house. Good luck with it. Like I said, not my line of work, but just trying to pass along alittle info that I've picked up during the last week or two while researching my homes needs...
Roland
|
| | ampulman
| "Re(2):Size Matters" , posted Tue 23 Sep 06:20
ABSOLUTELY, do not have a new a/c installed without having a (documented) heat calculation performed.
You stated that your neighbors' units are bigger, but their homes are damp. You also stated that your unit runs longer than you would like.
This is why their homes are damp; yours is just fine. Their homes cool down fast, but because the unit 'short-cycles', there is not enough run time to properly dehumidify the house.
Meanwhile, your unit lasted 17 years (probably very few HPs do). I'll bet less starting and stopping had something to do with it.
Bigger is NOT better.
AM
|
|
|
|  |
|
