Got it. Thanks!

Posted By FBBP on 31 May 2015 11:17 PM
jimmyge - the standard ICF is more than enough. We are in Calgary Alberta and our 2 storey house performs at about R52. There are plenty of ICF houses built in Alberta with the same results. 11 to 12 inch ICF walls, foam under the slab and R50 in a well sealed, vented attic and you will have a home you can be proud of.

Also remember that you are in Minnesota, not New England or Arizona so other peoples experience with mini splits may not be your experience with mini splits. From the data available, mini splits have come a long way in the last few years but not sure they will handle your design temperature yet.

A couple of layers  to peel here...

No way does 2.5" + 2.5" ICF perform at R52 in a Calgary climate, measured by either peak or average load numbers. (Only when  measured by the dreams of ICF advertisers does it hit that performance! )  

But it'll cut the average energy use of the house by about 10% below the performance a 2x6 R20 wall (R14-ish whole-wall), in part due to the R22-ish whole-wall steady-state value of the ICF, in part due to the thermal mass effects.  At R20 whole-wall the windows will usually have a bigger effect on the peak & average load numbers in cold climates than any wall type.   IRC chapter 11 would allow an R15 (2" + 2" ) ICF due to the mass effect in a US climate zone 6 location (SE MN) due to the performance enhancement provided by the thermal mass, but it would have to be R20 if more than half the insulation is on the interior. The thermal mass effect is more than nothing in that climate, but it's not R44-equiavlent, not R52-equivalent, or anything like the crazy marketing numbers.  The best-case I can make for them in a cold climate would be about R28-ish equivalent, and that's only with a lot a caveats about site factors and the shape & orientation of the house, etc.   From a design point of view it's better to just simulate it with a tool like BeOpt or DOE2, with all of the local climate and site-factors factored in, than use a marketeer's fanciful "equivalent-R" number.

Then...

Both the Fujitsu xxRLS3s and Mitsubishi FHxxNA series  have fully specified output down to -25C/-13F or lower, and both will keep on putting out an unspecified amount of heat at even lower outdoor temps.  The Mitsubishi units will auto-stop at some low temp (the spec says -18F, but many have been observed running into the -20s) , but the Fujitsu units don't.  I know of a guy in Quebec heating with Fujitsu RLS2s (predecessor of the RLS3 series) who sailed through -34C/-29F temps last year without losing ground.

The coolest 99% outside design temps in  SE MN are in the -12F range, and it's fully possible to specify ductless solutions for that area.  The Fujitsu ducted mini-splits are fully characterized down to -5F, and would still be OK to use in SE MN, with a bit of padding on size.  Using the ducted versions might be a bit sketchy in International Falls or Winnepeg, but I'd still consider it in Calgary (with a 99% outside design temp of -17F.)  The ductless Fujitsus are fine in any of those locations.

Even if some mini-split can't quite keep up in some weather, a little resistance heat is easy to add and doesn't run enough to cost much to operate.

I agree, ductless minis have come a long way and will provide heat even frigid Zone 6 climates. Having experienced both central HVAC setup and mini splits, no doubt, minis are the way to go. I have yet to see a properly zoned HVAC system that works like they claim it should. There always ends up being cold and hot rooms because the system only knows two settings; ON or OFF. Minis allow for true adjustability and proper zoning. Plus they don't have the same temperature swings that HVAC systems typically experience. They now offer 30 SEER systems.

There is one more factor to consider when you are trying to figure out how ICF works so well with only five inches of foam. The conductive concrete column is set on a footing in the ground, so is constantly conducting ground heat upward. Our average soil temp is about 50. So at least part of the wall is 50 degrees inside. And of course it gets more and more close to ambient the further above ground you go. People I know that have these homes are incredibly happy with them. I am looking forward to the efficency.

Thanks for all the input, but I can't commit to mini splits. I need recirculation and filtration for air quality and humidity control in all parts of the home. I am not planning a mostly open floorplan, where mini splits would work well. So I would need four inside units. I am basically forced to have a second system for low temp periods in winter, so since no ducting with minis I would choose to tube the floor for RFH. With four or even three minis and a RFH system, I would spend more money then a standard ducted system with hi efficiency LP furnace and ac provided by air source heat pump, and HRV (about $12000 complete installed). Going with the latter equipment, I get blending of all the air with the fan on low, constant filtration, great fresh air distibution, proper dehumidification, with equipment that most anyone can service and maintain. I guess I have reached a point where I am less willing to experiment than I have in the past. I just want a simple reliable system. The house envelope is small and tight,so operating costs will be low with whatever system I put in.

"ICF ... conductive concrete column is set on a footing in the ground, so is constantly conducting ground heat upward"
The second law of thermodynamics:
"heat always flows spontaneously from hotter to colder bodies, and never the reverse"

So yes, in the heat of the summer concrete may be conducting 50o ground heat upward, but for a large part of the year it will be conducting heat downward into a vast heat sink. One good reason for a higher level of insulation on the interior side of the wall. You can also insulate under the footings with a high density foam.

Posted By Bob I on 07 Jun 2015 08:39 AM
 . . . You can also insulate under the footings with a high density foam.
 

At a higher cost, the footings can be insulated with FOAMGLAS which has a higher PSI. Although the correct type of EPS should be sufficient, some of my clients used FOAMGLAS by Pittsburgh Corning to insulate under footings.

So at least part of the wall is 50 degrees inside.

Never confuse undisturbed ground temp with a ground temp once you start adding or extracting heat from it. Ground coupling can work, but you need large, isolated contact areas.

Posted By jimmyge on 06 Jun 2015 10:54 PM
There is one more factor to consider when you are trying to figure out how ICF works so well with only five inches of foam. The conductive concrete column is set on a footing in the ground, so is constantly conducting ground heat upward. Our average soil temp is about 50. So at least part of the wall is 50 degrees inside. And of course it gets more and more close to ambient the further above ground you go. People I know that have these homes are incredibly happy with them. I am looking forward to the efficency.

Thanks for all the input, but I can't commit to mini splits. I need recirculation and filtration for air quality and humidity control in all parts of the home. I am not planning a mostly open floorplan, where mini splits would work well. So I would need four inside units. I am basically forced to have a second system for low temp periods in winter, so since no ducting with minis I would choose to tube the floor for RFH. With four or even three minis and a RFH system, I would spend more money then a standard ducted system with hi efficiency LP furnace and ac provided by air source heat pump, and HRV (about $12000 complete installed). Going with the latter equipment, I get blending of all the air with the fan on low, constant filtration, great fresh air distibution, proper dehumidification, with equipment that most anyone can service and maintain. I guess I have reached a point where I am less willing to experiment than I have in the past. I just want a simple reliable system. The house envelope is small and tight,so operating costs will be low with whatever system I put in.

Separate the heating & ventilation functions, each with their own ducts. You need ventilation even when there is essentially NO heating or cooling load to speak of, but the air volumes required are a tiny fraction of what you need for heating. A heat recovery ventilation system is the right solution for the ventilation fraction, and pumping low volumes of recirc/ventilation air through grossly oversized ducts for that function doesn't work as effectively.

Fujitsu's newest ducted mini-splits are remarkably better than those of just a few years ago (and better than their current competition on both low-temperature capacity & efficiency.)   The 1.5 ton -18RLFCD puts out something on the order of 15-18KBTU/hr @ -5F (if somebody has access to the extended temperature capacity tables on that unit I'd be much-obliged to know the actual numbers), and just one can handle the entire load of many ~1000-1500' reasonably tight code-min houses, and even bigger higher performance houses.  It's not quite as efficient as the wall-coil types, but it's as good or better than the wall coil types of five years ago were, and should* come in at an installed price WELL under $10, possibly under $7K if the heating duct design is simple enough.  This series are the only ducted heat pumps with low temp efficiency & capacity good enough to qualify under Efficiency Vermont's rebate program.

As with any HVAC equipment, having qualified local support (including distributor support) would be an important consideration.

And with any HVAC equipment, running realistic load numbers ahead of time is critical to getting something sized to where it is both comfortable and efficient.


*  "should" doesn't always mean "will", especially in low-competition markets.

pumping low volumes of recirc/ventilation air through grossly oversized ducts for that function doesn't work as effectively.

Bigger ducts are typically more energy efficient at any flow, but I agree. At some point (I haven't run the numbers), you aren't left with enough pressure to overcome the stack effect/wind effect/ push warm air down into a cooler basement. So flow to that area stops. Ideal is dedicated supply and return lines for HRV/ERV.