dmaceld,

In a blank wall, the core temp might be closer to the average temp between inside and out.

In a normal wall with a few doors and windows and foam cut away to install electrical boxes and pipes, the core is better isolated from the outside than it is from the inside.

It seems reasonable to me that the core temp will be slightly closer to the indoor temp than the outdoor temp.

rgb

Bruce,

I think that idea can make a lot of sense if the energy source provides only a low temperature feed.

A solar collector could be designed to operate at a temperature lower than would be useful inside the house. If you can use a low temperature, the collector will become more efficient, and can be much simpler. Lower levels of radiation can be harvested, so to speak.

Whether it would be worth the effort would be a site-specific decision.

rgb

RGB, you should take the question to the radiant section next door. Suppose you did put a regular carpet pad on your radiant floor and now you can't get the room temperature above 65. There are two ways of fixing it, short of ripping up the rug and starting over. You can insulate the cold side better, or you can raise the water temperature. That's R2 carpet pad. Tucking hydronic behind R10 ICF foam with an equal amount of insulation on the cold side? Don't think so.

"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".

Ahh yes - the heat source! Let me introduce Mother earth (that portion directly below the footprint of the building - underneath the basement floor). As posted earlier on this thread; temps there would be at least 55 F (actually it is quite warmer). Depleting this "Bank" in my humble opinion; would require "Withdrawals" far exceeding the energy required to maintain a constant exterior wall core temperature of 55 F (worst case). Furthermore one should not ignore the "Deposits" made in the summertime; where one would prefer a "cool 55 F wall vs. a warm 55 F wall".

In respect to the "expeditious deposit and withdrawl" - remember that the fluid flow is constant, in order to maintain the steady wall core tepmerature.

"If we can't overcome the interior insulation in an ICF home in that timeframe, our heat source will overheat the air instead."

This would be correct IF THE HEAT SOURCE EXCEEDED THE INTERIOR TEMPERATURE. Please note; unlike conventional radiant heat, this system's porpose is to maintain a steady core temperature of the concrete (a temperature barrier) of say 55 F (minimum); thus narrowing the delta T to less than 20 F (again, worst case) no matter what the exterior ambient temperature (-20 or 120 F) is. The exterior ICF wall by itself (along with the roof) becomes the only relevent factor.

"I am sure you look better in your skivvies than I do in mine."

I wouldn't bet on that; even though sometimes I wish it were so :-).

In summeray I respectfully submit as follows:
1.) While Concrete has a poor "R" factor; it does have great thermal storage capacity with good thermal conductivity.
2.) Using near surface geothermal heat (or cool) energy; steady exterior wall temperatures (55+ F) can be achieved.
3.) Terra (earth) as well as Sol (sun) energy has an unlimited supply available in regard to heating and cooling of all buildings no matter what climate zone.

My posts are based on the performance of my ICF home in central Minnesota. I do not have any temperature probes in my concrete to give any temperature measurements but I do have my electric usage per day along with the temperature on a graph via my electric providers website. The house is not lived in at this time because interior work is being done on and off. The house is heated 100% by an electric plenum heater. The thermestat is kept at a constant temperature for the entire house. What the graphs show is that there is a 2 to 3 day delay in the demand for more heat when the outdoor temps fall for an extended period of time (2 or 3 days).
Temps during the day may be 10F and fall to -5 or -10 at night. If these temps continue for several days my electric usage is a straight lline. This to me would show that the thermal mass of the concrete is evening out the highs and lows. If the temperature falls by over 15 and remains there (highs of no more than -5F and lows of below -20F) for 2 to 3 days. My electric usage does not start to increase until well into the second day. The electric use increase is slight and by the time that the cold snap is over, my usage goes back down to what they were before the cold snap. This has to be the effect of thermal mass. I also believe that the delta T is reduced because the concrete core is warmer than the exterior temps which also reduces my electric usage. So from this experience I disagree with those that say there is no thermal mass benefit for an ICF wall in a cold climate such as Minnesota. Granted the thermal mass effect is not as beneficial as it would be in a location where the outdoor temps rise above and below the interior temp in a 24 hour period.

I have enjoyed reading this thread.  But I wonder....How does an ICF wall behave in the summertime when daytime outside air temperatures (OAT) are consistently 100 degrees F and nighttime OAT's are 80 degrees F? 

As the ICF concrete temperature climbs higher and higher isn't your air conditioning system (set at, say, 75 degrees F) fighting to overcome the apparent "thermal mass" effect well after the OATs decline?  Will I have a $1000 air conditioning bill?

Thanks.
Dan

Not an expert, I'm making plans to break ground on my ICF in the next two months, but your concern about the *cooling* is one of my main goals for ICF.

I agree with this thread that concrete thermal mass is a buffer, to "smooth" temperature swings (over a day or days).  However, it seems to me that the concrete->footers->ground is a source of FREE energy.

Even if sustained outside heat moves into the walls, it should "wick out" through the footers into the ground.  Thus, for ICF to the roof, the ground should help cool my whole house (don't know how thick the concrete realistically needs to be to cool all of the second story, though).  This "free cold" is a property of ICF, rather than SIPS, because of its contact through the footer into the ground.

Ditto for wicking heat out of the ground up the house when the outside sustained temperature is constantly below your desired inside temperature (the ground should be free heat).

Further, it seems you can store a lot of energy in the ground under your house ... if that smooths out the seasons over a whole year, that would be great.

This makes sense to me, but I don't have data.  However, this would be consistent with some of the anecdotal observations where it seems the concrete is doing something "more" than an R-value of nothing (e.g., you're implicitly tapping a geothermal buffer).

"I agree with this thread that concrete thermal mass is a buffer, to "smooth" temperature swings (over a day or days). However, it seems to me that the concrete->footers->ground is a source of FREE energy."

Do to the slow movement of heat/cooling through concrete you will not have enough surface contact with the earth to make more than a few degree of difference in interior temps.

Yes there may be some small benefit from the thermal mass in an ICF product with ICI( concrete in the middle) but it is not enough to off set the price difference as opposed to spending the same amount(Per sq ft of wall) for a SIP product and getting more insulation.

The are other reasons to go with ICF over SIPs but don't fool yourself that dollar for dollar an ICF and it's ecapsuated thermal mass will give you better heating and cooling cost savings.

But ... isn't the whole basement wall in contact with the 50F-55F ground the same as the first floor wall in contact with the (hot or cold) outdoors?

That should be equal surface area for each.

Further, even if it's just a "few degree[s] of difference in interior temps", that's my point:  It's a free few degrees (however much you get).

I understand it's a surface-area/mass problem, and I understand that only the footer has "efficient" transfer to the ground because everything else has insulation.

However, my assertion is that if the outside is an "infinite source of heat" (or cold), then the ground is an "infinite source of cold" (or heat), because the basement wall offsets the first floor wall (both have the same surface area and same insulation), so the transfer from the "outside" should be similar.

Further, the basement wall is in contact with *mass* (the earth), while the first floor is in contact with *air*.  May not matter, but if it did, it would benefit my theory.

If heat transfer through concrete were truly efficient, the basement wall would provide mass stability that extends beyond the first floor (e.g., to the second floor).  The discussion of embedding a PEX circulation system in the walls merely increases the efficiency of the transfer, but some of that transfer would happen anyway.

"Too much is as bad as too little" ... I agree to a point.  However, "too much" merely stretches the time required for equilibrium.  If you have 50' thick concrete walls, then your thirty days of 90+F weather isn't enough to overwhelm your house, but rather, internal house temperature would find a constant differential with the average annual outdoor temperature (e.g., the "too much" mass lets you time-shift energy across seasons).

Yes and it all boils down to dollars and cents. Are you saving enough using this technology to have it make a financial difference in a feasible time?.

Throwing money and more moving parts (pex in the concrete) may make that particluar system work better but you may have been better off choosing a simpler and more cost effective( in the short run and long run) system in the first place.

Let me put it another way.

I bet I could build the same house design as you. Tweek it for solar put the insulation on the exterior of the concrete instead of the inside and save 10 to 15 percent or more on your heating and cooling costs and have less moving parts to repair.

I could do the same thing but use the same dollars you spent of ICF walls replace them with SIPs, get more insulation for my money and save even more on my heating and cooling costs.

"However, my assertion is that if the outside is an "infinite source of heat" (or cold), then the ground is an "infinite source of cold" (or heat), because the basement wall offsets the first floor wall (both have the same surface area and same insulation), so the transfer from the "outside" should be similar."

Because this same surface will leaking heat through the heating season , it ends up to be a wash, not a gain.

If ICF construction taps a limitless source of free energy as Donnerwetter suggests, you'd think some enterprising sales exec would hire a laboratory to document it. Anyone see studies of his Terra effect?
Or should we be thinking of ICF heat loss in two stages: first from the conditioned space through the interior foam to the concrete core, and from there through the exterior foam into the atmosphere and, yes, down the wall through the footings into the earth.
As for Sol, there's a reason the dynamic benefit of mass occurs or fails to occur in 24-hour periods. Otherwise average is average no matter how you build. (The ICF wall that shrugs off a cold snap will also shrug off the warmup.)

Yes Toddm - These studies have been documented and were published in the 2005 VDI (society of German Engineers); Dipl. Ing. Edmond D. KRECKE; as well as by the IWR (Internationaler Wissenschaftlicher Rat - International Scientific Council of Energy Saving Construction Technologies) - Prof. Dr. Eduard KONOPKA (Technical University Stuttgart; Germany), Prof. Dr. Roman ULBRICH (Technical University Opole), and the Ministerio de Educacion Y Ciencia - Consejo Superior de Invertigacioner Cientificas Instituto de Automatica Industrial; Prof. Dr. Ing. Dommingo Guinea DIEZ in Madrid, Spain.

If anyone is interested, I do have English versions. Please PM me

I think you may be talking about apples and oranges here.

As I understand it, Donnerwetter's proposal is to use PEX tubing laced INSIDE the concrete core of ICF.  Heat is collected by tubing under the roof and stored under the basement slab.  Cooling is provided by tubing buried underground outside the building.  Heating/cooling water is piped through the walls to provide sort of a"virtual" insulation to minimize heat gain/loss from the interior.

Please let me know if my understanding is not correct.

The "heat sink" effect of having the concrete core of an ICF wall sitting on a footing below grade will probably be applicable for just a few feet above the footing.  This is no magic bullet.

Bruce

If your reference is this -- http://www.isomax-terrasol.eu/uploads/media/ISOMAX-TERRA-SOL-engl.pdf -- you're talking about active and passive solar harnessed for seasonal heat storage, ICF only peripherally and dynamic thermal mass not at all. Gotta admire their ambition, though, and their budgets. Note the photo where workmen are carriyng what appears to be a hundred yards of stainless steel pipe within pipe. Wonder what that baby costs.
By contrast, an adobe house in New Mexico, in an admittedly friendlier climate than Poland, can get the same result with mud.

"...I could do the same thing but use the same dollars you spent of ICF walls replace them with SIPs, get more insulation for my money and save even more on my heating and cooling costs...."

And still have a product that is impermeable to humidity, mold and moisture? With a 4 hour fire rating? :)