Trane XL20i vs XL15i
This is a follow-up to my earlier post titled Trane XL19i sizing question. We have narrowed our heat pump decision to the new Trane XL20i (thanks for the estimate on the release date of this new model, Jimj). We are also considering the XL15i based on the tip from gary g and performance data that we downloaded from the ARI website.
To answer a question from gary g, the reason we are considering a 2-stage heat pump in Pittsburgh is because I truly have no idea what energy costs are going to be over the next 15 years, which is the expected life span we are hoping to get from the unit. I do think that heating with a heat pump will eventually become cheaper than heating with fossil fuels like propane and natural gas because McCain plans to subsidize electricity with nuclear power and Obama plans to subsidize electricity with renewables.
Right or wrong, we have decided to go with a 100% electric system and our goal is to set up the most efficient size unit and model for our combined heating and cooling needs over the entire year. I'm thinking this may mean compromising the cooling efficiency a little bit in favor of heating capacity, which will hopefully give us the lowest overall annual operating cost for our area.
We have also looked at geothermal, but we do not have enough room for a drilling rig to get into our back yard to install a system. So, we have decided to go with an air source heat pump and auxiliary electric heat strips in a variable speed air handler. My wife has been “Tranewashed” by one of her friends, so going with Trane will cause me less friction with the Mrs. Trane makes a decent unit and if something happens to it, I won’t have to hear her say I told you so.
Anyway, our heating requirement in Pittsburgh is much greater than our air conditioning needs. I think a 2.5 ton heat pump would be perfect for our cooling needs (we have a 1500 square foot brick home), but I’m thinking that size heat pump will require the auxiliary heat strips to support much of our heating needs during December, January, and February. I’m thinking that we might have the most efficient all-around system if we purchase a two-stage 5 ton XL20i heat pump. The COP would be above 1, even in the coldest weather, and I think the unit would not be short cycling during the air conditioning season because it could run on low stage at 50%. However, I realize this is just based on my simple math and it may not be that easy. I’m sure there is something I may be overlooking or a reason why this cannot be done.
We are going to contact the Trane rep that we have been dealing with over the phone and schedule an appointment with him to come to our house for sizing and pricing. We would like to know as much as possible prior to meeting with him though. We don’t want to waste his time or look stupid, if possible. His service so far on our current Goodman furnace has been excellent, and we will probably not even shop his price if his estimate is in the ballpark.
Yes, I do know about Goodman’s reputation, and the furnace was in the house when we bought it. We also have three carbon monoxide detectors that I installed after we replaced the heat exchanger. I hate that furnace. I plan to donate the carbon monoxide detectors to Goodwill after we get a Trane. I found out the hard way that some things are just worth researching and paying a little bit more for at the beginning to avoid problems down the road. So what do you think? Can we “oversize” our system with a 3, 4, or even 5 ton XL20i two stage heat pump, or should we just go with a single stage 2.5 ton XL15i?
Thanks again for all your advice. We really appreciate it.
Twilli says just because your all electric doesn't mean you can't get CO. Keep em they may save your life.
No Heat No Cool You need Action Fast
dam, mister i'm a trane dealer and i haven't even seen the xl20i yet. maybe you should wait till it comes out on a.r.i before you get your knickers in a twist over it. seriously just get a heat gain calculation from your trane dealer and he will let you know what size you need. too much cooling capacity is not a good option in most cases.
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not enough cooling capacity is just as bad!
Originally Posted by smittyii
2.5 tons of cooling for 1,500 sq ft sounds way too big.
I do think you're on to something with the two stage unit...
Originally Posted by larobj63
what is your basis for this comment?
i read the o.p. fast, but i dont remember seeing things such as, windows, insulation, ceiling heights, etc.
so how did you determine that it "sounds" to big?
If your house only requires 2.5 tons for cooling, you don't want a 5 ton 19i.
Originally Posted by SteelCitySteve
In first stage, its system capacity will still be more then 2.5 tons, because of the large coils.
A 2 stage 3 ton would work better.
Woops - my bad. I read it even faster, I guess! The lack of supporting data is bad enough - but 2.5 for 1500 sq ft isn't even remotely odd - I don't know what I read...
Originally Posted by Airmechanical
If you have a 2.5 ton system now, chances are that's all your duct system will handle. Probably not even that much So if you did want to grossly oversize, you'd have to double the duct system sizing just to get it to run reasonably efficiently. Then it could be rather drafty. A 5 ton unit moving that much air in 1500 sq ft could get rather drafty on a cold day when it is getting a 10° temp rise. Lots of 80° air blowing on your skin will feel COLD!!!! Cooling only running on 2.5 tons with a 5 ton duct system can give you some imbalance in the house.
Put in the right size. We had an energy expert give us a class. The guys asked about oversizing by 1/2 a ton on a heat pump. He said the gain in energy savings would be minimal at best.
Look at all the numbers on the heat pump. Why the recommendation on the new R410a 15i is it is one of the only Tranes that get some good heat output and HSPF numbers. Hopefully the 20i will too but haven't seen specs yet.
While I respect your knowledge I have a few questions:
I have an upstairs unit that will be replaced this fall. 1500 sq ft and load calc. is 4 tons. Are you saying this could be to drafty in the winter when heating (400 CFM less than a 5 ton but still alot of air to move)? I don't have sub zero conditions and will use either strips or gas when temp. drops below the design temp for heating via HP so you may be talking about the OP's situation of going to a sub zero switch over???
Originally Posted by BaldLoonie
Everyone who uses a 2 stage unit that the 1st stage AC is 50% would have imbalance problems?
For what it's worth I agree with the advice given by all to stay away from a 5 ton system when the load calls for 2.5 tons. I don't khow the efficiency of the system at sub zero conditions but any savings in fuel prices by oversizing the heat side seems to be off set by the lack of effeciency on the cooling side.
Have you done the load calc yet to determine how much cooling and heating you actually need? If not do that soonest and then get the extended data sheets (from your contractor) for the unit you are interest in. It will provide you with the rated output at various ambient temps. Most will go down to about 2*.
Using that data plot the heat loss from about 50* down to your design temp along with the unit output on a graph. Where the two lines intersect is the point where the heat pump can not carry the load without supplemental heat.
Then figure out how many hours (in one or two degree increments) you spend on average per winter lower than the point where the heat pump will not carry the load down to the design temp. Use that to determine the actual average dependency you will have on the strip heat in hours so that you can calculate what it is going to cost to provide the supplemental heat.