Posted By sailawayrb on 25 Mar 2013 12:11 PM
This is another advantage I see with vertical ICF compared to horizontal ICF.

sorry but I missed that . How can it make a difference which way the foam is place over a mass?

Posted By FBBP on 25 Mar 2013 12:28 PM

Posted By sailawayrb on 25 Mar 2013 12:11 PM
This is another advantage I see with vertical ICF compared to horizontal ICF.

sorry but I missed that . How can it make a difference which way the foam is place over a mass?

I was going to say that the foam placement is not the issue...but thinking about it more now, that might be an advantage to vertical ICF too.  I will come back to this... 

My earlier comment was relative to how easy it would be to add PEX to a vertical ICF wall compared to horizontal ICF.  With a vertical ICF wall, one side of wall is fully open until you slide the vertical panels in just prior to the pour.  So I would think it would be much easier to install the PEX.

Back to the foam...  The new TFSystems product has 5" of foam on the exterior side and only 3/4" foam on interior side (with a zero option in the works)...or so it is reported.  As we all know, this is better than having 2.5" of foam on both sides from a thermal mass objective.

I have yet to use vertical ICF first-hand, so my comments here are purely speculative and I would enjoy hearing other opinions, but let's not hijack this thread!

I am not sure what you are calling "active thermal mass". if you are designing for passive solar, I would consider that 'passive' thermal mass. If you are simply calling the emitter 'active' thermal mass, then yes, I've worked on probably hundreds of warmboard jobs and our own shop is using it right now. Warmboard is definitely not a passive solar mass though, of course, and if you are designing to retain passive solar gain you need mass, either in wall or floor assemblies in most cases.

If you are doing passive solar design you can heat the mass, but you'll get better passive solar if you move the heat into low mass emitters and leave the floor ready to accept solar gain.

If we presume that most homes are NOT passive solar engineering exercises though, as is usually the case, in most homes the mass of the floor system is not integral to good performance. In fact it'sa hinderance more than a help to increase mass, unless the system is using very capable electronics in the hands of a knowledgeable designer. Speed of response can matter too... with warmboard, if you have the same very capable controls required to run a slab very well, you can use setback strategies if it makes sense for the shell you're living in, because the system is much more responsive.

Everything has its place. Low mass has significant benefits... high mass is great if you need heat storage out where the emitters are installed.

I am a little surprised at the cost of the full suspended concrete floor. ICFHybrid... I assume you're getting an extra good deal on that? If not, why are most homes not built with suspended slabs these days?

Posted By sailawayrb on 25 Mar 2013 10:10 AM
zone heat loss changes…which is typically very slowly as a result of outdoor temp changes. Once a high mass floor slab reaches the required surface temp, it tends to stay there

Need for rapid radiator temp changes occur when: 1) The sun pops out from behind the clouds and starts heating the room. 2) Return from vacation. 3) Grandma stops by and thinks 65F is 10F too cold. 4) Daily temperature cycles in some climates. 5) Any type of thermostat setback (think office building over the weekend). 6) Someone starts cooking in the kitchen.

High mass radiator = unresponsive radiator. I agree that in some cases (like the slab is going in anyway) it is the cheap option.

Posted By sailawayrb on 25 Mar 2013 12:38 PM

I was going to say that the foam placement is not the issue...but thinking about it more now, that might be an advantage to vertical ICF too.  I will come back to this... 

My earlier comment was relative to how easy it would be to add PEX to a vertical ICF wall compared to horizontal ICF.  With a vertical ICF wall, one side of wall is fully open until you slide the vertical panels in just prior to the pour.  So I would think it would be much easier to install the PEX.As we all know Back to the foam...  The new TFSystems product has 5" of foam on the exterior side and only 3/4" foam on interior side (with a zero option in the works)...or so it is reported.  As we all know, this is better than having 2.5" of foam on both sides from a thermal mass objective.

I have yet to use vertical ICF first-hand, so my comments here are purely speculative and I would enjoy hearing other opinions, but let's not hijack this thread!

sailawayrb -I not at all sure I can agree "As we all know". It might be better to have naked mass in a cooling dominated climate but not necessarily in a heating dominated climate. By and large you are talking of stacking a thermal floor on its end and calling it a wall. Therefore you have all the issues that Rob goes on about in the next post. There may be an upside to doing this if you have an excess of "free" heat (solar, wood burner or maybe even if you need to cool one area of a building and need somewhere useful to store the removed heat. If you are paying for the heat, I doubt it often makes sense to pump it into vertical storage that releases heat so quickly. What ever the source, you still need to contended with this emitter pumping heat into the room as fast as you pump it into the emitter. While I know that a number of the experts on GBT might disagree, I believe it is the ability of the captive core of the ICF that allows it to perform much better than conventional theory would expect it to in a heating enviroment. Mass can only reach its specific heat capacity if it is insulated. A chunk of concrete outside will very soon take on the temperature of the air. The atmosphere has the ability to give it or take from it unlimited numbers of btu's. Inside a house, naked mass will take from or give back to the air the equivalent amount of btu's that each s.h. per degree dictates. And with a highly conductive mass as concrete it does it very quickly. When you capture the mass between layers of insulation, it response very different.



As for TF Systems I have some concerns but like you say, maybe start a new thread over in ICFs and we can get feed back from those that have used it.

Rob, by “active thermal mass” I mean a high mass floor assembly (or perhaps a low mass assembly…) that has been augmented so that in addition to being able to add heat when required (i.e., when called upon to act as a radiator), it can also REMOVE, store and distribute excess heat acquired from passive solar heating when required. In other words, it’s ability to buffer building temps is NOT limited by its mass and heat capacity.

Yes, a “passive thermal mass” is typically adequate when about 50% or less of the heat load is harvested by passive solar heating. And Yes, when you start using an “active thermal mass”, you are no longer purely passive solar. However, when you start pushing toward harvesting 100% of the heat load from passive solar, an “active thermal mass” ensures that you will not have building overheating issues and also allows you to better distribute (albeit actively…) the harvested passive solar heat. So my question was whether you have ever used Warmboard (or another low mass floor assembly) to remove, store and distribute heat acquired from passive solar heating? Clearly, Warmboard would be worthless as a “passive thermal mass”, but I wonder how well it would perform as an “active thermal mass”.

Jon, I would agree that high mass radiators are not appropriate for a short-term, significant temp setback. We know that temp setback can significantly reduce heating costs if the setback time and the setback delta temp are significantly large. I would also agree that there may be times that being able to significantly and rapidly change the temp could be desired too. So YES, this could be a convenience/efficiency advantage that a low mass radiator would have over a high mass radiator. However, for the integrated designs that we do, wherein we harvest the majority of the heat load from free passive solar, this convenience/efficiency advantage becomes less worthwhile...unless Rob has some good data to convince me otherwise.

FBBP, maybe I wasn’t clear. The new TFSystems product has nearly all the foam on the exterior wall. I believe that is goodness relative to achieving a buffered indoor temp. I say this because TFSystems is doing Pensmore (72,000 SF home…) and they are putting PEX in the walls to augment cooling/heating. I would like to hear your concerns. We are going to TFSystems to get “trained” in a couple weeks, so I will share what I learn too…via a separate new or old ICF thread on this subject so as to no longer hijack this thread…

I assume you're getting an extra good deal on that?

I bid it out to the normal culprits. What I got back was $10, $12 and "I screwed up the last two I did so I don't want to do it unless I get $19.". Of course, he didn't really admit having problems with the last two, we just found out by the by...He SWAG'ed the materials and planned to pay a consultant to do it.....

The guy who got the job uses it all the time so I suspect his dealer price on the form is as low as it gets. It was actually LESS than $10/ft2. It was part of a bigger job, but we had it broken out as a line item that could be accepted or not, so it is probably a reasonable representation of extra cost if you are already pouring concrete on your job.

If not, why are most homes not built with suspended slabs these days?

Good question. I think the number one issue is fear of the unknown, both on the part of the contractor and the homeowner. We ran it to a fourth contractor who declined to bid, citing the high cost of renting bracing for 28 days..... If you recall, ours was braced with 2X6 frames that were later recycled for other structure.

I suspect that number 2 issue is poor understanding of how to span the distance and there is always the person who doesn't want a "pillar" in the basement. We kept our panels and slab thin by using bearing walls in the basement.

And, I have seen several people who don't want to incur any engineering costs which might happen if you try to fit the suspended slab to just any old design.

I have not yet seen any radiant solution that "redistributes" passive solar gain better than the air of the room would, which heats up much faster than anything other than the top layer of concrete in a floor. use a fan if you want to redistribute gain. If you want to store it, you need mass, period. but you know that, of course. the best I've done/seen so far is an ultra low watt pump constantly circulating unheated water in an uncovered slab where there was a solar gain/masonry heater main room. and I would still regard that as a borderline waste of time.. we did it because it was already piped.

anything that would be good at redistribution would be bad for storage and vice versa, short of some super duper phase change material.... mass makes it good for storage but delays the ability of the heat to transfer to the transport pipes in any radiant app I've seen. the only way I can squint and say otherwise is in a thin pour... say 2"... of regular concrete with a stain finish (not many people willing to do that)... so you have some mass but the pipe is close to the surface and no interfering insulation layers. I guess if you can get pipe in the top of thicker pour, that works too. haven't seen anyone who can chair pipe to 3" up and not crack/saw it later though. Maybe ICFHybrid knows someone

We have dual purposed hydronic radiant floor high mass slabs that are also exposed to harvest/buffer passive solar to distribute and store heat via tank storage. I posted the storage tanks that we favor somewhere on the forum not too long ago.

We have also experimented with sodium acetate (the stuffed used in ski hand warmers), but this was for long-term storage of excess hydroelectric power where the change-of-state exothermic chemical reaction from liquid state to solid state was subsequently used to provide building heat gain (i.e., essentially multiple chemical "heat batteries" triggered as called for). It is relatively easy to use electrical power to reach the temp required to convert sodium acetate in a solid state back to a liquid state for storage, but this would not be so easy using passive solar without getting into focused energy techniques. We posted about this several years ago on the Microcogen forum.

Yes, I've done that with storage tanks too. I also think it's a waste of time. but sometimes clients won't listen. getting the pipes up into the danger zone is a key detail.... passive solar heated slabs don't have even temp gradients from the surface down and the pipes don't see that much of the heat unless they are very high up. a detail I can't imagine working well with control cuts of any kind.... I suppose if you don't cross them with pipes, it could be made "safe". but again... why bother. just pour a little more concrete. or use a fan.

A chunk of concrete outside will very soon take on the temperature of the air.

I suppose for some definition of "soon". But exterior thermal mass (like a block wall) is effective in smoothing out daily swings in temperature and does save energy when the day/night temperatures vary above and below comfortable. And exterior mass doesn't require you to live with variations in interior temperature to achieve a savings (ie, you can get savings without sacrificing comfort!).

Would exterior mass work better covered with some amount of insulation so that it didn't heat up/cool down quite as quickly? That's a good question.

haven't seen anyone who can chair pipe to 3" up and not crack/saw it later though. Maybe ICFHybrid knows someone

Just to be perfectly clear about how it works; you chair the rebar and then tie PEX to the bar....

We were building water storage tanks from foam in basements back in the 80's as solar had just died with the first "energy crisis". I like the solar mass of concrete in warm sunny climates like, say, New Mexico and Arizona. Up north here you better have lots of panels and lot of solar storage in the form of water.

Primitive controls and emitters will more likely leave people uncomfortable. Warmboard's main advantage is the integration of structural flooring with a decent--usually low temperature--emitter dependent on floor coverings and heat loads for the room served.

Posted By NRT.Rob on 25 Mar 2013 04:59 PM
Yes, I've done that with storage tanks too. I also think it's a waste of time. but sometimes clients won't listen. getting the pipes up into the danger zone is a key detail.... passive solar heated slabs don't have even temp gradients from the surface down and the pipes don't see that much of the heat unless they are very high up. a detail I can't imagine working well with control cuts of any kind.... I suppose if you don't cross them with pipes, it could be made "safe". but again... why bother. just pour a little more concrete. or use a fan.

Rob - if the application actually made sense, control joints are not that hard to do. Say you want a 6" slab to break into 20' x 20' sections all you do is place thin material (say 3/16 x 3.5" wood or h.d. poly like cutting board material) in that grid pattern on the prepped base. The 3.5" is standing up ;-) There are different ways to hold them in place. Then you build your bar mat and attach your pex and it should be sitting in the top 2" of the slab. If you want pretty, you tool a radiussed grove right over the concealed break and it should crack as nice as can be.

Now Rob, you have got to feel a whole lot smarter, eh?

control joints/cuts are standard on almost every residential slab I've ever seen. since they are supposed to be more than 1/3rd slab depth, it's kind of an issue if you need to get your pipe up to the top 2" of the slab to absorb passive solar gain in any decent capacity. you'd have to run your pipes paralell and away from the cuts and define your cross points and drop the pipes at those points and make sure you have tight spacing to avoid heat striping AND hope the installer actually follows your details and that the control cut happens where it is supposed AND that nothing moved from the diagram/install to the concrete pour AND.... it probably still won't work that great. not better than a fan blowing the air into the rest of the home at low speeds (or using natural convection). and not better than thicker concrete in the area of direct radiation.

conduct down-through plastic-into water- transport away-reconduct out through plastic-into concrete can never beat simply: "conduct down - conduct back up as temperatures allow". Or "remove heat immediately before you even have a large temperature overshoot".

so again. why bother?

conduct down-through plastic-into water- transport away

Once it has gone back down and into the water, you can belay the story because it represents BTUs that the heating plant does NOT have to put into the system.

Have you ever done the control joints from the bottom up by embedding strips like FBBP just described? Doesn't take any more time than having the cutter work over the green slab.

Actually, the heated air ALSO moves comfortably into the house through the door without the aid of a fan. AND, the slab is appreciably thicker in this area to allow this process to go on longer before saturation. Modeling said just about 7" thick was where the benefit ran out and I was going to make it 8", but got into trouble somewhere else and had to let it be at a good 6" plus.

Oh, I didn't get what he was saying. Cuts from the bottom, that's interesting. thanks for the clarification. there are still greatly enhanced puncture risks with pipes that far up in a monolithic slab, but that does answer a lot of the issues, agreed. thanks for the nudge. Sorry to FBBP for misunderstanding that... read too fast.

as for the storage path though, you can't stop at "in the water". If all it does is heat up the water you stop transfer as soon as the temp rises, and you're basically wasting your time completely even thinking about this. It has to conduct back out to make it worthwhile to put it in the fluid in the first place, otherwise all you have done is add the thermal storage capacity of your fluid to your system. that's something, if you add super big tanks, but only in that case, and those tanks would have to be huge to be worthwhile because you're talking extremely low temperature changes which would result in negligible BTU storage... and it still has be conducted back out later, at a usable temperature. the entire point of redistribution is to bring the storage capacity of the rest of your mass into play and to keep the temp of your primary solar receiver as low as possible.


far better is, as you go on to say, to just use more concrete in the room that gets solar gain. or let the air do the work of moving heat. open doors aren't usually enough in most floorplans, but the fan assistance required is pretty low level too. If you have an ERV doing its job you probably already have the "fan" part covered.

I sure won't guarantee that a solar slab will work but I'll guarantee that it will crack where I want it to ;-)) Crack_inducer.pdf

Windows and living space make for a lousy solar collector. They are (typically) at the wrong angle, they lose heat at night, the living space gets too hot, they are hard to disconnect in the off season, ... Not sure where the attraction to "passive solar" is coming from.

Sure, orient the windows you are going to have anyway for solar gain. Beyond that, if you want to do solar, use PV or an active system (hydronic panels, water tank, etc).