Looking for some feedback/recommendations. I'm planning on installing a York YZF heat pump (single stage affinity) along with a york air ecm air handler with about 12 - 15 kw of electric back up. The cottage is 1700 sq ft with 9 1/2 ft walls, plus a 4 foot crawlspace. It's 6" concrete walls with R25 Logix. I did a load calc (load calc.net) and come up with about 16k cooling and 35k heating load(ahhh the joys of a -30 manitoba winter). I know I'll never get enough heat out of the heat pump unless I grossly oversize it, which I don't want to do. I was originally going to install a 2 ton heat pump with a 3 ton air handler, but I'm thinking of upsizing the pump to a 2 1/2 ton. I'm planning on dumping about 200 cfm of air into my attached garage, which isn't included in the load calc, incase anyone is wondering why the 3 ton air handler. Ok, lets hear it! Thanks, Greg

loadcalc.net doesn't have wall options that are anywhere near relevant for estimating the peak losses in an ICF wall, so your heat load numbers are probably at LEAST 10% high, if not 30% high, depending on how well the other components like windows/doors/attic could be entered. That 35K is probably more like 25-30K (25-30MBH), but you don't specify at what outside design temp that is. I suspect your design temp is something like -25C or colder.

The COP efficiency of the YZF series even at -8C/17F in the 2.5 range, and between -20C & -15C (probably your binned hourly average in January) it's COP is probably about 1.5, and at -25C it's probably 1 (or even less.)

The capacity tables of different air handler/compressor combinations here:

http://www.upgnet.com/PdfFileRedirect/632151-YTG-F-0714.PDF

The capacity at -20C will be at least 25-30% lower than it is at -8C/+17F.

Where in Manitoba are you located (so we can find the nearest weather station, to estimate the 99% outside design temps)? It's a pretty big province with climates that range from cold to VERY VERY cold.

You may be better off with a pair of Mitsubishi MSZ-FH15NA ductless units, which deliver about 13-15,000 BTU/hr @ -25C with a COP of about 1.8 at that temp, using electric baseboards or similar for temperature balance/backup in the rooms doored-off from the spaces with the ductless heads. At -10C your COP will still be 3-ish. If you raise the setpoint of the ductless 3 degrees higher than the doored off rooms the ductless will still be carrying a large chunk of the load for those rooms (more, if you leave the doors open.) See: http://www.mitsubishipro.com/media/946493/fh_product_guide.pdf

Thanks for your input. It's located about 1 hr north east of Winnipeg (LacduBonnet area). Design temp is -23F (-30C). I've definitely settled on a ducted central system. I originally was going to get a Bryant extreme evolution (Carrier Greenspeed), but I have a tough time dropping an extra 3k for it. The pay back isn't there over a 20 yr span. Weather charts show our average highs of -10C and lows of -20C, with probably an average of 5 - 10 nights a year of -30C. I would guess throughout a winter, I'm probably going to have about 1 full month where the heat pump will be off and I'll be on strictly electric. Additionally, I'm installing a wood stove, so when we're at the cottage that will be the main source of heat.

Eyeballing it on the scrolled out temperature graph on Weatherspark's datasets for Lac du Bonnet, your binned hourly mean temp is about -15C/+5F, so capacity issues aside, the York would be delivering piss-poor efficiency performance in your location.

A pair of dedicated modulating mini-duct cassette units like the SUZ-KA18NA.TH would be able to muster 10,500 BTU each (21,000 BTU/hr total) @ -15C outside/+20C indoors with a COP of about 3, if the capacity & total power consumption numbers on page 26 are any guide.   It's possible to split the output of a mini-duct cassette to as many as 4 rooms (though 2-3 are more typical.)  That would be more capacity than a 3-ton York at that temp, and 2x the efficiency. Having 2 units would also make zoning issues easier.

Fully centralized systems are prone to system efficiency hits that don't show up in the extended temp capacity sheets. To come close to hitting the numbers both the ducts and house need to be PERFECTLY air sealed, the duct system needs to be perfectly balanced, and the total duct runs need to be short.  Any duct leakage or return/supply imbalances result in air-handler driven air infiltration, since it creates pressure differences between rooms, with the "great outdoors" becoming an unintended part of the pressure equalization path. That translates in to a higher heat load whenever the air handler is running, a heat load that doesn't show up in the Manual-J. 

Mini-splits don't have that issue, since the air handler's supply and return are fully inside the same room.  With a pair of tiny air handlers (like the SUZ-KAxx series mini-duct cassettes) located centrally to a few rooms there is still potential for power-driven infiltration, but since the duct runs are all VERY short & direct, that potential is less, and only a few rooms would be affected at one time.

The installed cost of a pair of -KA18s (3 tons, nominal) may be comparable  or slightly more than 3 tons of York, but the amount of heat you'd get out of it per kwh would be substantially more.  If your design heat load at -23C is ~30,000 BTU/hr, they should be able to pretty much cover the average load even in January- you could just leave them on, supplementing with resistance heating in rooms that aren't keeping up.  Internet pricing on them runs USD$2700-3000 each so the raw hardware costs (including mounting, refrigerant lines and ductwork) would come in under $6500, total installed system cost for the pair could be in the $10K range, less with a bit of DIY sweat-equity. (A pair of ductless FH15s would cost even less, and have enough capacity to cover your whole load at -23C.) But it would use about half the amount of electricity of the solution you're considering.

At your mid-winter temperature averages a Greenspeed or Extreme Evolution wouldn't be reasonable options either, despite the very substantial installed price. The 3 ton Greenspeed may have slightly more capacity at -15C, but not the efficiency, when the duct losses & air infiltration of fully centralized systems are factored in.  Play around with the different pairing options, viewing the graph under the "Heating Capacities" tab.

If you aren't always there, then I'd consider a house design that can safely freeze with little preparation. When wood heat is involved, I'd consider a wood boiler plus water (edit: plus antifreeze) storage such that wood can be burned quickly and then supply consistent heat for many hours.

Have you come up with a garage door that creates an airtight seal?

Thanks for the feedback guys. I appreciate your input.

With an outdoor wood boiler I'd worry about freeze-up during cold snaps during absences or power outages in a location as cool as Lac du Bonnet.

This is sort of off-topic, but looking for a super quick answer; other than: "it depends". More like a generic answer, if possible.

If this dude builds him an ICF house that is air-tight and therefore needs an air exchanger, doesn't the cost of the air exchanger steal all the cost-benefit from having an air-tight, high R-value home?

James, in most of Canada, and I would imagine in many parts of the US, it is mandatory to have an HRV (or ERV or similar), to introduce fresh air. Whether it's stick built, ICF or ??? The biggest reason for us is the tighter the building, the higher the humidity will be and the more air exchange that should be required. There is a fine line between exchanging enough air to keep a healthy house with reasonably low RH, and costing you a small fortune to heat in a -30F winter. Obviously, the warmer the climate, the less heating cost becomes a factor.

doesn't the cost of the air exchanger steal all the cost-benefit from having an air-tight, high R-value home

No. You have to have air exchanged and you can either have the house just leaky enough, or you can control it and capture the energy in the outgoing air.

RH may or may not be an issue. But even when it's not, you need ERV/HRV ventilation for CO2 and pollutants.

Is it a big deal to over size with these new variable output units from mitsubishi?

http://www.mitsubishielectric.ca/en/hvac/city_multi/s_series_features_highlights.html

Posted By fallguy on 27 Sep 2014 08:48 PM
Is it a big deal to over size with these new variable output units from mitsubishi?

http://www.mitsubishielectric.ca/en/hvac/city_multi/s_series_features_highlights.html

Yes.

If the heads/cassettes are oversized by more than 50% for the room/zone loads efficiency suffers.

If the compressor unit is more than 50% oversized for the whole-building load, efficiency suffers.

These things don't have infinite turn-down ratios, and with either the heads or compressor cycling on/off most of the time rather than modulating, it won't be operating as efficiently as it could.