What is location?

You are all electric?

This is a replacement system? If so, what size are you replacing? What size is your heat strip?

Your quotes are from same dealer?

Any other supplemental heating source available?

Post back.

IMO

Thanks...new system replacing baseboard heating - propane is the only other alternative. Quotes are from the same dealer and they are highly recommended; thus the reason Trane was selected. The 20i is only 1k more however the cooling efficiency will be rarely used and its HSPF is 9.0 vs 9.2 for 16i.

Location Barrie Ont Canada - seasonal cottage... winter usage will be sporadic. Backup heat strip is 10KW and 5 Ton for 1,600 sq ft for heating was oversized to minimize strip usage.

Jim

I will say unequivocally that I do not like your strategy as far as oversizing to get the heating BTUs.

What size system are you replacing?

Has a load calc been performed?

How would you describe your winters, typical winter low, not extreme winter low?

Have you even given thought as to the size of your ductwork system to carry all these CFMs?

What is your electric rate?

You realize a10 KW heat strip would not temper the air on a defrost call and might be undersized for emergency heat?

I suspect a reputable dealer would not do this install without a signed waiver from the homeowner.

You want to pay attention though to AHRI Directory matches, BTU output at 45 degree and 17 degree fah plus of course the HSPF heating eff rating.

IMO

System is replacing baseboard heating that was never used in the winter (it could not provide sufficient heat). The heatloss/ducting was done by a professional (that's all they do) - ducting will be all new and size appropriately. Cost for electricity is .10kw & avg winter temp is 20F. The cottage is seasonal it will not be used during the deep freezes as we know there are design/heating limitations to this setup. The goal is to have efficient heating and some cooling most of the year.

Jim

Still don't care for the strategy.this is an accident in the making.

What is your heat loss load calc and at what inside/outside design temp?

You certainly don't need a 5 ton HP.

For info, the XL16i low stg is about 65-70% of high stage output. This HP utilizes a two stg step compressor; where the XL20i low stg is 50% of high stg and has two individual compressors. For your application,I would want a sgl stg HP like the XL15i or XR15 HP condenser, of course properly sized without the oversizing. I ass ume dehumidification is not an issue for your location/climate.

IMO

Sorry forgot one critical piece of info...crawl space is also heated so square footage is double. Heat load was calculated @ 74,241 and design info:

Outside db (�F) -15 84 Method F280
Inside db (�F) 72 75 Exposure category Exposed
Design TD (�F) 87 9 Construction category Tight
Daily range - M Number of stories 2.0
Inside humidity (%) 35 50
Moisture difference (gr/lb) 39 2

And yes dehumidification is not an huge issue. I understand the short run cycles may not properly dehumidfy however I am alright with that.

I was considering the XL16i because it had the highest HSPF...and then it was suggested go with the XL20i because of the internet thermostat connectivity.

Note the 15/16/and 20 are very similar in price. So the defining factor is efficiency, performance & reliability.

Thanks!

I would do the highest efficiency single stage in your case. I wouldn't oversize either. If you want to oversize then by no more than a half ton.

Great input - thank-you. So XL15i or XR15?

I am trying to understand your priorities and thought process. You want the most efficient unit to save money, but you don't seem to mind spending the extra money on an oversized unit. You are very concerned about having to use the back up resistance heating, but you say you won't occupy the cottage during deep freezes because the setup has been designed with limitations.

You have a reasonable electricity rate of 0.10Cdn per KwHr (mine is .18US$), so I would not be very worried about running the heat strips to supplement the heat. I think your strategy of getting a 5 ton unit is wrong. The most efficicent units are in the 3-4 ton sizes. I am also skeptical the contractor will install new duct work which will handle the air flow (2000CFM) for a 5 ton unit. If the duct work is insufficient you will have a system which will operate below the rated efficiency and noisy. Ideally you want a static air pressure in the range of 0.5-0.6. This becomes more difficult as the unit becomes larger.

My advice is to install a properly sized heat pump which is sized for the AC cooling load. You should add the required heat strips to provide enough heat for the cold days. Ideally the heat strips are staged.

You don't have to limit yourself to a single stage unit. The better products units are typically 2-stage. If you do get a 2-stage unit then get a good 2-stage thermostat.

Thanks - with the HP's COP 2 - 3x resistance the hope is to minimize resistance usage. So is the concern for an oversized HP that is will cycle on and off too much and thus not achieve MAX efficiency?

With the heatpump running, the supplemental resistance heat will 'add' heat. It won't take over. You will still have a decent COP in the 2-3 range if your supplement heat is not overbearing. Supplent heat can be staged which I recommend.

An oversized heatpump will cycle on and off in most weather except for the most extreme weather when it will run without cycling on and off and save a little on supplental heat. The problem with oversized is also if your ducts can't handle it you will have a lousy system.

Size correctly or slightly oversized and have supplemental heat strips that are staged.

Running non-stop is not bad. You will be surprised how well a heatpump that is sized correctly can maintain an indoor temperature even if its not oversized. When running non-stop that is more efficient and less wear and tear than starting and stoppin. I dwell on this because it seems like your concerned about the most extreme conditions which is why you want to oversize.

I would also focus on doing some insulating of your place. Adding more attic insulation is a great/cheap way to improve the heat-loss of your house. I would also put weather stripping on leaky windows/doors and seal any leaks around the foundation.

This will vastly improve comfort levels if heating with a heatpump.

don't know where you are
but why would you heat the crawlspace?

ditto the heatpump..sized correctly.
what is your location? it matters.
best of luck

Ontario, Canada

Posted by JimShorts (My Page) on Thu, Mar 29, 12 at 23:48
Thanks...new system replacing baseboard heating - propane is the only other alternative. Quotes are from the same dealer and they are highly recommended; thus the reason Trane was selected. The 20i is only 1k more however the cooling efficiency will be rarely used and its HSPF is 9.0 vs 9.2 for 16i.
Location Barrie Ont Canada - seasonal cottage... winter usage will be sporadic. Backup heat strip is 10KW and 5 Ton for 1,600 sq ft for heating was oversized to minimize strip usage.