not sure if this is the correct forum (mods please move if appropriate)

I have a 2300sqft main floor and 2300sq ft basement all ICF to to roof.  The windows are all basically facing east and west and are all triple pane double argon double low e  r8 casement or fixed windows. roof insulation will be approx r 60.  The walls basement and main floor are 9' high and the basement is 6 feet in the ground with no walkout.  I also have a 1100 sq ft garage 12'ft high attached to the house 2X8 construction filled with fiberglass batts.  Located near saskatoon, saskatchewan, canada

I am trying to determine whether the heating system seems reasonable. I am being quoted a slant fin electric boiler with a radiator coil to provide forced air heat to the main floor.  The garage and slab in the basement are radiant heat.  Also the garage and basement have 2"xps under the foam.  I am being sized a heating system of 45KW for the electric system which seems really high to me (this does not include domestic hot water).  My other option is propane in which case they are quoting a 60000BTU 95% furnace plus a viessmann vitoden 100 series boiler for the slab heat and domestic hot water.

Prices for either system are very close to the same.   electric consumption will cost me more but I was leaning that way, however, if I exceed 50kva peak usage then each additional kva is charged at 10.87 per kva and I am afraid that with the electric system if it is sized properly I will be exceeding the 50 kva with my other loads by a fair amount in which case I would need to go to propane, however, if the contractor has oversized my elelctric by a large amount, then I may only very rarely exceed the 50kva demand charge limit.  I have asked them and they say ask an electrician, which is a waste because I know 50 kva is 50 kw in resistance based appliances, it is more a questions of how often am I likely to be using the full draw on the electric boiler given my construction and climate.

Just in case people are wondering power in my area is 9.7 cents/KWh and propane is currently 46 cents/litre or $1.74/us gallon.  I know the propane is cheaper but with electric I get rid of annual cleaning of burners, etc, no risk of carbon monoxide and do not need to have a tank sitting around. 

Thoughts.

Shouldn't they do a heat loss analysis on your home?

It would appear there is quite a bit at stake here, both in terms of energy and cost.

45kw is about 153.5KBTU/hr, which seems about 2-3x overkill for most homes that size at Saskatoon's -32C/-26F outside design temp, let alone for an ICF house with high performance triple-panes. Even 60K may be overkill for the propane furnace (even before adding in the Vitodens) given your U-factors, but not super-overkill. It depends on how warm you intend to keep the garage, the R-value and tightness of the garage door, but the heat load for just the house is probably at or under 10kw (32KBTU/hr) at design condition. Have you (or anyone else) done a heat load calculation (ACCA Manual-J) or similar?

You'd probably do fine with half that amount of electric boiler plus a mini-split. The mini-split would probably average a COP of about 2.0 seasonally and would heat the whole place at a COP of 3+ in the shoulder seasons, cutting your total power use in half (but not your peak.) The Mitsubishi H2i series still deliver ~70% of their rated output at an outside temp of -25C (but at a sub-2 COP at that low temp) and you'd probably be able to heat the place fine with it most winter days. Cutting your average power use in half (or more) takes the sting out of an peak charges you might rack up, but if you started out with a 20-25kw boiler as the Hail-Mary backup for a 2 or 3-ton ductless solution you'd have a much lower operating cost, and have some margin on the 50kva limit:

At a COP of 1 (all electric boiler) and 9.7 cent electricity you're getting (3412/0.97=) ~35,000 BTU/$.

With a ductless averaging a COP of 2 it's twice that, or 70,000 BTU/$.

With $1.75/gallon propane in a 95% burner you're getting ( (0.95 x 92,000)/1.74= ) ~ 50,000 BTU/$

Even though your design temps are on the cool side, the mean hourly temp for the month of January is typically around -8C, a temp at which a decent ductless is still running a COP >2, but when it's truly cold and using more of the electric boiler it kills the average. At 0C it should be running COP of 3+.

It appears to be an ideal situation for a Daikin Altherma unit. The unit can do both radiant and fan coil heat and has electric resistance boost for those colder than rated winter days.

In Saskatoon, you should consider solar and the Daikin unit integrates well with solar.

It also is designed to operate in what they call "bi-valent" mode which means in conjunction with some other kind of boiler.

i only plan on keeping the garage at 5 degrees C or there abouts in the winter.  As far as a calculation when I asked they said they did a calc but when I asked how it could be so high the guy just started to tell me that for the basement a rough figure is 20btu/ft garage 30 btu/ft and main floor 25-30 btu/ft.  I dont feel confident, but at the same time I dont want to find out I am under sized.  Is there a good site that I can go to and do my own manual J or other?

I have found most HVAC designers do not understand ICF. Ask him to check his numbers again using U value and I believe he will come back to you with new results

http://www.hvaccalc.com/

$50 for 60 days, last I checked.

Chris is probably right. ICF, done right, greatly reduces HVAC loads.

What are you going to do when the power goes out?

generator, only difference between electric and propane is I need a bigger genset.  You cant run furnace, boiler pumps etc without power anyway.  Not a problem as I live on a farm

amazing I told them to do a proper calc not just rule of thumb and within 10 minutes they came back with an electric boiler size of 15kw.  I have no confidence now.  I didnt think they could do a calc that fast, and for it to change from 45 to 15 makes me really wonder.  I guess I will have to figure out a way to do it myself (kind of like everything else anymore if you want it done right).

Posted By jojo12 on 07 Nov 2012 08:19 PM
i only plan on keeping the garage at 5 degrees C or there abouts in the winter.  As far as a calculation when I asked they said they did a calc but when I asked how it could be so high the guy just started to tell me that for the basement a rough figure is 20btu/ft garage 30 btu/ft and main floor 25-30 btu/ft.  I dont feel confident, but at the same time I dont want to find out I am under sized.  Is there a good site that I can go to and do my own manual J or other?

Rule of thumb estimates like that are a total crock, guaranteed to oversize even in code-min timber framed structures. 

Heat load is about the area & U-factors of the exterior + air leakage.

Your wall U-factor is only slightly above HALF that of min 2x6 construction by a factor of nearly 2 even without factoring in the mass effects and the rise in low-temp R value for the exterior EPS.

Your window U-factors are also roughly half  to 2/3 that of a code-min window.

A 2x8 studwall with rock wool or high-density fiberglass batts has a U-factor about 2/3 that of typical 2x6 construction.

Even if the BTU/ft rules of thumb suggest were somehow correct (and not insanely oversized, which they are), your total heat load would be only about 2/3 that of a "typical" house.

But in fact, those rules of thumb typically  oversize by 70-100% (2x oversizing), even for typical construction. So if the rule of thumb sizing adds up to 100KBTU/hr, the real heat load is usually in the 50K-60K range.  

And your real heat load would then be at most about bout 2/3 of that, or 33-40K range. 

The last thing you want is a 100KBTU heating plant for a 33K load, especially when you look at what that does to your peak volt-amp figures when cold-starting a massive radiant slab with an electric boiler.  The efficiency on the electric boiler is the same in either case, but the 100K boiler is capable of pulling 3x the V-A peak of a 33K boiler.

But down sizing using the same crappy rules of thumb would be a mistake.  Do a real manual-J using real U-factors/construction-type, and plug in a relatively low ventilation rate.  Take pains to air seal the place carefully as you build it and you won't have an issue even if you sized the heating plant to EXACTLY what the Manual-J says.  Your peak loads are delayed and somewhat lower due to the mass effects, and there is inherent bias in the calculation tools to the high side.

FWIW: There are many old-school heating contractors in my neighbor hood (design temp = -15C) who use 25BTU/foot rule of thumb for 2x6 construction, 35BTU/ft for 2x4 construction, and it's no wonder that many if not most heating systems  here are 3-4x oversized for the actual heat load, easily verified by simple fuel-use per heating degree-day arithmetic.  That's not an efficiency disaster if it's a condensing hot air furnace (it's still stupid), but when you're potentially banging against the limits of the power transformer the way you would be, oversizing by 3x is a real issue to be avoided. (What, you needed to be good down to -150C just in case a large comet hits and the resulting dust blacks out the sky for 3-4 years?)

Posted By jojo12 on 08 Nov 2012 01:33 PM

I guess I will have to figure out a way to do it myself (kind of like everything else anymore if you want it done right).

Your best bet is to find an HVAC contractor who uses WrightSoft heating/cooling program. It handles ICF. It was right on the money for my house. If he's a good honest contractor he'll charge you separately for the calculations. If you don't want to use him for the install you can take the calcs to another contractor and have them bid using the calcs.

To do your own calculations you have some options, albeit not as accurate as Wrightsoft (it costs 1000s of $$ for a contractor to buy it) but will give you a good estimate to judge the contractor's numbers by. As mentioned above, HVAC Calc is well worth the money. It's easy to use and has good output. I used it. I also used another program that is good, even though it is no charge, is HEED. You'll find it here: HEED Download Page There is a link there to weather data, which when followed will get you to a data file for most cities in North America.

You could do a Daikin Altherma with a propane boiler running in bivalent mode. When you needed the extra heat, the boiler would fire. This would get you radiant heat and heat for your fan coil at good efficiency for most of the year. An added bonus would be that you could substantially downsize the generator because the propane boiler could carry the heating load during power out situations. You would also have cooling in the summer.

I am trying to do my own calculation using hot2000 as the software.  I am not sure in the software how to incorporate the garage, but if I am using the software correctly it is showing a electric size of 18kw which is based on peak demand plus 10% plus .5kw.  Not sure how accurate that is but it is sure difficult to be confident when the heating contractor gives a initial estimate of 45kw then a supposed calculated value of 15kw then I calculate and without garage I get 18kw so I am really dumbfounded now.

18kw==61,000BTU/hr, which is a credible number for a house that size & construction @ -32C, but so is 15kw (~51,000 BTU/hr). The tool might be hitting 15% to the high side on the peak loads if it's not factoring in mass-effect. Hot2000 is a reasonable tool delivering results in the range of other simulation/estimation tools the few times I've played around with it, but I don't recall if it factors-in thermal mass the way DOE2/BeOpt does. IIRC DOE2 has reasonable dataset coverage for Canada. BeOpt is a freebie down based on DOE2 (the basic tool you have to pay for but not BeOpt), targeted for optimizing cost/performance of the building components.

http://beopt.nrel.gov/

Taking a rough WAG of 15% peak reduction due to the high-mass walls, that 18kw comes in pretty close to 15kw which would be right in there with that other calculated value, but it takes more than 10 minutes to do any REAL calculation, so I agree, confidence is low that their methods carry any more validity than the 15% reduction WAG I just took. It could be about right, but I wouldn't bet my dog's life on it.

Well I went through the software as best that I can without knowing some info such as hrv recovery rates, etc.  and I entered the garage as a separate building (so no common walls included), I also ran  the numbers based on a 25% over sizing factor just for safety and the software comes up with a 30-32KW requirement.  So i have told them to send me the report from their software so that I can see the results, because I am pretty sure they have not modeled the house at all.  I have not told them my estimate yet, but we will see what their response it.

If your really want to go all electric.  Google the Daikin Altherma.  Its an air to water heat pump designed for radiant heating and domestic hot water and it can cool as well.

I have a couple of houses running on pure electric while the HO decides on heatpump or boiler. I use a 120gal commercial water heater which can be built with up to 48kw and I adapt it with a solid state relay and a Tekmar outdoor reset control. This gives a variable water temps based on outdoor temp which saves quite a bit of money. If you need a temporary solution or a backup system, this would work. I've never been a fan of propane when there is a non combustion product available because the running costs can be similar, at least in Ontario and the Maritimes. I don't know the propane costs in Saskatoon.

If going with a HP, the tank can then be used as a buffer and/or for solar

Posted By MarkS on 12 Nov 2012 10:22 PM
If your really want to go all electric.  Google the Daikin Altherma.  Its an air to water heat pump designed for radiant heating and domestic hot water and it can cool as well.

While the Altherma would improve the overall seasonal COP and work efficiently at the average wintertime, it won't handle anything like a the anticipated load @ -20C,  and nowhere near 30kw @ -32C (the 99% outside design temperature here), a temperature at which probably won't run at all, and if it does it'll be at lower efficiency than an electric boiler.  With an Altherma you'd still need the full sized electric boiler as backup.

But 30kw @ -32C still seems quite large for a house that size unless there is a lot of window area and very high ventilation rates.  There's no real science to support ASHRAE specified ventilation rates, and as long as you're judicious about open flames/cooking/smoking indoors, simply running the HRV under dehumidistat control to keep the interior moisture below 35%RH @ 20C the indoor air quality would still be excellent in most homes, despite being below ASHRAE spec. 

Building with a minimum of VOC-emitting construction materials helps, and if you use a lot of formaldehyde emitting materials even high ventilation rates help very little- it doesn't get better until it fully outgases.