If the outside temp remains below the inside temp for a length of time great enough to create a steady state heat flow situation, the concrete offers no thermal mass advantage. Concrete has a negligible R value. It's basic thermodynamics - many people on this board could benefit from the class. I love ICF, it's a great technology, but on this one area, you can't argue against the numbers from the cold climate studies.

If the outside temp remains below the inside temp for a length of time great enough to create a steady state heat flow situation, the concrete offers no thermal mass advantage. Concrete has a negligible R value

I think the key phrase here is "for a length of time great enough to create a steady heat flow situation". What is the definition of "a length of time"?...1 Hour...4 hours...12 hours....24 hours...3 days...1 week???

How would this compare to Conventional stick build or SIP using the same criteria???

Is "R" value really the fundamental absolute factor by which to judge excactly how 6" of concrete proforms sandwiched between 2 2" thick pices of EPS in contact with the footing (Basement) below the frost line???

Here in northern WI, it hasn't been above 10 degrees F for well over a week now.   Two nights ago it was 29 below zero.  Last night was a balmy 18 below.  I have no test data to confirm, but I feel reasonably certain that an ICF wall would be at a steady state by now.

How would it compare to conventional or SIP build?  Well.... the insulating members of each building construction type will continue to provide resistance to thermal transfer.  Be it the styrofoam on the inside/outside of an ICF wall, the styrofoam on the inside of a SIP, or the glass/cellulose/etc in the studwall of a conventional build.   In pure heat transfer terms - concrete has no insulating value....  In this condition, all pure R value is provided by the styrofoam in the ICF assembly.  The concrete is acting as a one-way heat transfer conduit, there is no storage of heat, just transfer.

Now, let's talk air sealing.  I love ICF and SIP BOTH for the airtightness they bring to the envelope.  HUGE benefit.  Air sealing and thermal mass benefit are two totally separate concepts.  ICF and SIP both derive a huge portion of their benefit over conventional due to the airtightness they bring.  R is important, but airtightness is just as important.  When you bring the 2 together, then you are talking about the way a house should be built.

I love ICF.  I'm 90% certain my new home will be a 100% ICF shell.  However, I go into the design/build with the knowledge that in the dead of winter, my walls are an R25ish, virtually airtight system.   Actually, I'll probably build with the TF System forms with 4" thick EPS on the inside and outside.  I'll have an R-39, airtight wall structure.   Anyways,  in my climate, there is no thermal mass benefit during the vast, vast majority of the heating season.  Anyone who believes otherwise needs to do more study and take Thermodynamics 101. 

If you can show me how the temp of the footing (probably around 55 degrees) has any affect on a first story concrete core, I'd love to see it.  Remember - heat always moves to cold, not the other way around.

The key phrase in this discussion is "steady state". In most climates, most of the time, you will see a fluctuation in outdoor temperature every day. The concrete is not an insulator, but it is a shock absorber, or a "choke point." If the temp outdoors goes from, say, 0F to 30F during a 24 hour period, the average temp against the outside wall will be something on the order of 15F. That means the heating system inside the house needs to be designed for an effective outdoor temp of 15, not 0. The total heat loss over the 24 hour period will be close to the same as for a non concrete wall, but the instantaneous load will be less. So yes, the concrete does provide a thermal benefit.

If thermal mass is defined, or thought of, in the context that the concrete moves heat into and out the interior of the house during a 24 hour period, then no, there is no thermal mass benefit if the outdoor temp remains below the indoor temp for more than a day or two. That's because there will be a continuous, but variable, outflow of heat. But the variability will be much greater at the outdoor surface than on the indoor surface.

According to the HEED program (Home Energy Efficient Design) from UCLA, there is a 12 hour lag in the heat transfer through 6" of concrete. That means in summer here in SW Idaho by the time the solar heat is making its way through to the inner wall surface, the outer wall surface is cool from the night air and the heat is going back out.

Richntiff

For the most part I tend to agree with you; however if concrete cannot store heat than how can it store cold? (maybe retain would be a better term) Is not any solid mass (earth, sand, rock, metal, concrete) by it's nature a solid matter storage resevior, releasing it's energy gradually? Do ICF's really proforn better in warm vs. cold climates?

Please allow me to "Breathe some life" into this concrete core. What if (just like the human body) one were to equip this concrete core with some veins and arteries ( say 3/4" PP tubing); circulating them below the roof tile (passive solar heat) and returning back underneath the foundation (Basement Floor) using the earth as a storage resovoir. If - as you pointed out - your footing temp would be +/- 55 F; one could deduct that the center of the building underneath your basement floor would be even higher than that. Would this not create a rather constent core temperature (even say 50 F - worst case); using "Free energy" (earth and sun) throughout not only all exterior walls but the roof as well? Fluid flow would remain relativly constant and require (just as our Heart) a relatively small pump to maintain circulation.

Just curious...what is the "R" factor of your clothing that you wear in those "Balmy" WI temperatures (I envoy you not - according to those standards; its t-shirt weather @ +14 F here in St. Louis). Glad to be leaving for the World of Concrete in Vegas this comming week!

Just some (frozen) food for thought!

H. Brandl has researched and implemented a similar design in Europe.  He runs refrigerant-filled high-density-polyethylene (HDPE) piping through the pilings and foundations of hi-rise buildings.  Below is an exerpt from one of his papers.

"PRINCIPLES OF GEOTHERMAL UTILISATION OF
FOUNDATIONS (ENERGY FOUNDATIONS)
Energy foundations may comprise base slabs, piles, barrettes,
slurry trench systems (single elements or continuous
diaphragm walls) and concrete or grouted stone columns
(‘energy columns’). Combinations with near-surface earth
collectors or retaining structures are also possible. Energy
foundations can be used for heating and/or cooling buildings
of all sizes, as well as for road pavements, bridge decks etc.
Concrete has a good thermal conductivity and thermal
storage capacity, which makes it an ideal medium as an
energy absorber (heat exchanger). To use these properties
for energy foundations, high-density polyethylene plastic
pipes of 20 or 25 mm diameter, with 2.0 or 2.3 mm wall
thickness respectively, have to be installed within the concrete.
They are placed to form several individual closed coils
or loops, which circulate a heat carrier fluid (heat transfer
medium) of either water, water with antifreeze (mainly
glycol), or a saline solution."

"The key phrase in this discussion is "steady state". In most climates, most of the time, you will see a fluctuation in outdoor temperature every day. "

I could not agree with you more. That is why climate specific design is monstrously important.

"The concrete is not an insulator, but it is a shock absorber, or a "choke point.""

Yes, if the outside temp cycles above the indoor temp. If it stays below the indoor temp, the heat flow is still from inside to out, and this buffering effect is NONEXISTENT. Believe me, I wish it wasn't, but it is. You can't argue with physics and engineering. The rate of transfer is impacted - but by delta T and materials that possess significant R value, not my little magical concrete men who parcel out heat loss at differing rates.

" If the temp outdoors goes from, say, 0F to 30F during a 24 hour period, the average temp against the outside wall will be something on the order of 15F. That means the heating system inside the house needs to be designed for an effective outdoor temp of 15, not 0. The total heat loss over the 24 hour period will be close to the same as for a non concrete wall, but the instantaneous load will be less. So yes, the concrete does provide a thermal benefit. "

Correct me if I'm wrong, but don't all regions of the country have a design temperature based on historic climatic conditions? And how is this different for an ICF vs. a stick or SIP structure??? Instantaneous load? sorry - I don't buy that argument, unless you can provide sound scientific data to back it up. It just doesn't add up. Instaneous load is handled, again, by the high R value materials.

I should temper my comments - all this R value talk is obviously not taking into account the other huge benefit of ICF construction - air sealing. In my climate, I take the air sealing value of ICF (and SIP) to be a bigger benefit, or as big of a benefit, as the R value of the wall assembly.

The HEED data you cite - direct solar gain on an uninsulated concrete wall is wholly different than the discussion I think we are having here.

Donnerwetter - your idea is an intruiging one, I like it! Now I have more research to do... Pump issues, head losses, power consumption - but a cool idea!!!

The issue with heat and cold is that you have to think of it on a molecular level. On that level, cold can be associated with lower molecular 'vibration'. Heat, with higher 'vibration'. It is the principal of entropy - things tend toward lower energy, vibration. Cold wins. That's just the way it is!

Today it's HOT here - it's practically above zero!! And, it's snowing... R value of my clothing? Not high enough! I'm considering going on a high calorie diet to become 'super-insulated' :-)

It was stated above in a post that heat moves to cold which I agree. :-D If the concrete footings are in contact with +/-50F earth wouldn't that heat move up into the ICF wall. Granted the concrete core won't be 50F but it will be heated by the earth which is a constant 50F. I wish I would have planted a temperature sensor in my concrete wall. I bet someone has. My ICF house is in central MN so we experience very very cold temps and is now heated by only an electri plenum heater. This year has had a lot of very cold dips some down into the -20s. Last week we almost set a record for consecutive days below zero. I have no measuring equipment for the concrete core (6") on my ICF but I have electric usage and temperature graph via my utility provider. When we hit a cold snap and the temp never gets above -10F for two to three days and temps dip to -25F at night my electric usage goes up by only 6% and I don't see that increase until we are through the second day (and that increas is real short). That's a drop in temperature from 10F to -25F (35 degree drop). That proves to me that thermal mass is working. Any other non-thermal mass structure would see the need for increased heat in proportian to the drop in temperature. I don't need any more proof than that graph of my electric usage to know that there is a thermal mass in effect in my walls.
As for the steady state of the concrete core... my understanding of insulation testing is that the steady state is when both sides of the object being tested are at the same temp. From there they begin tesing the thremal resistance. I can guarantee that the concrete in my walls never reaches a steady state. How could it??? Inside temp at 70F, outdoor temp at cold to very very cold, footing sitting in earth at +/-50F. If that concrete core is even 1 degree warmer than the outdoor temp, my Delta T is reduced compared to what it would be in another structure without that thermal mass. I agree that in cold climates the thermal mass benefit is reduced as compared to a desert where temps go above and below the indoor temp in a 24 hour period. There were other reasons we built with ICF and I even had the upper levels bid with 8.25" SIPS at one point. All insulation in my new home is either ICF (all exterior walls) or closed cell polyurethane spray foam for the ceilings. Anyone checking out this site is on the right path to building an energy efficient home and that is what counts, no matter what method they use. :-D

mlevendo

Thermal mass does have a quantifiable effect when temperatures are changing as in the scenario you describe.

In a steady state, there is no measurable effect. This has been shown by several studies including the one I posted above by the CMHC.

Steady state might be a rare thing in reality, though.

Rgb

Are you, perchance, forgetting about specific heat? Think about it. It is what creates "inertia" for heat transfer. I'll discuss this more later, if need be. R value is only one of the physical properties that comes into play in heat transfer.

Yes. The design temp is that at which a correctly sized heating system will keep the home interior at the desired temp by running 100% of the time. Historically, only something like .5% of temperature readings will be below the design temp for heating. Because an ICF wall provides inertia that modulates the transfer of heat as compared to a conventional wood frame wall, or a SIP wall, the heating system will seldom, if ever, be called upon to provide the quantity/minute of heat that would be transferred through a frame wall at the design temp.

What I call instantaneous is more accurately called very short term, minutes as opposed to hours.

An analogy is a bathtub with water. Suppose you restrict the water level to 1" and open the drain fully for 1 minute out of every 5 and you open the faucet full open. Now, don't let the tub drain completely. You open the drain and immediately turn the faucet on full force which almost keeps up with the outflow. At the end of the minute you close the drain, and 30 seconds later you turn off the water in order to stay within the 1" level. Now compare that to what you can do if you can have 10" of water in the tub. You open the drain, same as before, but it takes much longer for the tub to empty, and before it's empty you close the drain. In the meantime turn on the faucet half open. Because you can let it run until the level is 10" it will run longer, but at a lower flow rate. The same quantity of water enters and leaves the tub in both scenarios, but the supply in the second case is smaller. In this analogy the water goes in one direction all the time. It never goes back into the faucet! The tub provides storage that allows the incoming and outgoing flow rates to be different, but the volume over time is the same. That is exactly what happens with heat going through an ICF wall because of the ability of concrete to store and release heat. Of course the heat leaving the wall isn't on and off like this simple analogy, but the underlying concept is the same.

The HEED data I refer to is the program output for my ICF house, not a bare concrete wall. If you really want to see the results I'll reinstall the HEED program and get the graphical output to post here. Looking at one graph I do have, for August, the time lag may be more like 9 hours, not 12.

With regard to specific heat - you are right, it can be considered a form of inertia. The 'inertia' of a concrete mass that is exhibiting heat transfer consistently in one direction is absolutely negligible, regardless of the outside temp moving up or down. As long as it stays below the indoor temp, heat is transferring in one direction. There is no inertia, there is no buffering, there is no magic here. I'm done.

R value is only one of the physical properties that comes into play in heat transfer.

demaceld; I agree 100%. It is my humble opinion the the "M" Factor" is the fundamental absolute factor by which to judge ("M" Factor = the amount of "MONEY"; expressed in Kw or in $ - either U.S. or Canadian spent each month to maintain confortable interior conditions).

I sure hope that this heated discussion could be put to good use for all readers in the northern regions and maybe assist in providing that "superinsulation" - along with that high calorie diet -:).

Speaking of "heat" - and the retention thereof; I propose a rather simple experiment:

a.) using 3 same sized styrofoam coolers with lid, fill each full with concrete, water, and Foam (eps, xps or PU) respectfully.
b.) place a temp probe in the center of each cooler
c.) place all 3 coolers in a cold enviorment (Wisconson would work quite nice)
d.) monitor core temperature and record (hourly)

It might be very possible that the "magic" of concrete might be brought to light!

I am with richntiff. Once the ambient temperature drops below your thermostat setting and stays there, thermal mass is a no longer a factor in energy use except for HVAC sizing. Here is a report based on an Oak Ridge study for AAC that demonstrates the effect of climate on high-mass houses. http://safecrete.com/aac/products/techmanual/pdf/thermal.pdf AAC is an air entrained lightweight concrete with an r value of about 1 per inch. The study adjusts R-value=8.31 for an 8-inch AAC wall for the wall's thermal mass benefit in various U.S. cities.
The result was an effective R value of 21 in Phoenix, where hot days and cool nights match up nicely with AAC's eight hour thermal lag. It dropped to an effective 14 in Washington, where similar swings are common in spring and fall at least. In Minneapolis, the effective R value was 12 because of the relatively short time that the mean daily temperature is 70ish.
Unless... Even at the north pole, you can articifially induce thermal lag with a wood stove or a big bank of south facing windows. But you'd want the mass exposed to the house's interior, which rules out ICF.

opsss...Forgot the control cooler. The fourth cooler to contain just the temperature probe in the center...

But you'd want the mass exposed to the house's interior, which rules out ICF

Respectfully disagree. A "lopsided ICF consisting of 2" plus EPS (depending on region) - 6" concrete - =/- 1" EPS adheard to MGO2 board (the interior EPS to act as a condensation/vapor barrier would require, in my humble opinion; an entirely new set of calculations.

In addition; as the study by H. Brandl (along with many others points out):

Concrete has a good thermal conductivity and thermal
storage capacity, which makes it an ideal medium as an
energy absorber (heat exchanger). To use these properties
for energy foundations, high-density polyethylene plastic
pipes of 20 or 25 mm diameter, with 2.0 or 2.3 mm wall
thickness respectively, have to be installed within the concrete.
They are placed to form several individual closed coils
or loops, which circulate a heat carrier fluid (heat transfer
medium) of either water, water with antifreeze (mainly
glycol), or a saline solution."

This gentleman, is possible with all ICF systems and may well be possible with other exterior walling systens (both new and existing) as well.

And yes - Such an ICF combination does exist

toddm,
Don't rule out icf for the north pole just yet!
I've come across integraspec and they offer an ecf (exposed concrete face) option mainly used for elevator shaft but could very well be advantageous for residential use in specific climates as stated.

I'll let you go first on lopsided ICF, Donnerwetter, because I am sure you look better in your skivvies than I do in mine. In inducing thermal lag, we are making two bets: First, that a heat source is capable of meeting daytime heat loss and banking enough heat to carry the building overnight; and second that the deposit and withdrawal can be done expeditiously on a 24-hour basis. If we can't overcome the interior insulation in an ICF home in that timeframe, our heat source will overheat the air instead.
Happily the radiant heat industry has accumulated much knowledge on this subject. Here is one bit of conventional wisdom that casts doubt on the lopsided approach. Yes, you can carpet a radiant floor if you use a rubber pad (r=0.3). Use a conventional pad (r=1.6/2.0) and you have problems.

The CMHC report states that the ICF wall has equal thicknesses of EPS on both sides. For a given temp on the warm side and a given temp on the cold side, the temp in the middle of a conducting material will be half way between the two temps. Has to be if the material is uniform all the way through. Now take the ICF wall in the report. The concrete has nearly the same temp on both its surfaces, which means the heat is moving through it with very little resistance. So since the concrete is in the middle of the EPS it's temperature ought to be about half way between the warm and cold temps, right? Take a close look at Figure 4 in the CMHC report. You'll see the warm side of the insulation stays right about 19C, and the concrete stays right at 9C. The coldest reading on the cold side of the EPS is -15C and least cold reading is about -3C. Half way from 19C to -15C is about 2C and from 19C to -3C is about 8C. Why isn't the concrete at 2C and 8C, respectively? Why is it always above the midpoint temp on this chart? Thermal mass, maybe?

There are two mechanisms working here.  The first is the thermal isolation provided by the EPS and the second is the thermal mass of the concrete.

The CMHC included on 2 graphs...one is "quasi steady state", where the core temp IS about midway between the inside and outside wall temp.  In the "significant fluctuation" graph, the core temperature was several degrees lower than in the quasi steady state graph, with a larger delta T to the exterior.  What we know is that the flucuating exterior wall temperatures was hardly seen (0.5°C) at the exterior surface of the concrete.  That is the insulation working.  The very small change at the outside of the concrete did not show on the inside concrete surface.  That is the thermal mass working.

What we don't know is the temperatures for the preceding few days.  Because of the excellent insulation properties AND the thermal mass, I believe that the concrete core temperatures follow the average daily outside temps by 2 or 3 days, i.e., the response time is days, not hours and it changes slowly because of both mechanisms. Per the CMHC report, the thermal isolation is the primary driver

This report (and others) tell me that where the average exterior temp is below the interior temp, the concrete (thermal mass) in the middle of an ICF is thermally neutral...it does not save or cost any energy.  Thermally, an ICF performs essentially as a SIP in these conditions. 

In other weather conditions, I think think the situation may be different, but lets do that on another thread.

Thermal mass is real and can be a benefit, especially if it is exposed to the interior of a continuously conditioned space and even more so if passive heating is used.  Conversely, it takes longer to respond in a vacation or night setback situation.

The issue is that putting thermal mass between two pieces of insulation largely defeats any thermal mass benefit. 

ICF provides tight construction (as long as the window/door/roof details are well done), provides excellent thermal resistance, provides structural integrity and durability along with good fire resistance.  It is the material of choice for my new home, but its "thermal mass" properties do not enter into the equation at all.  It is neither a benefit or problem.

Bruce

I think it could, but I think you are better off putting energy into the interior where you have both layers EPS working for you than putting it into the core where you have just one layer between your heat source and the outside.

Bruce