ICFs and Concrete

[GaryM]

I don't have any reference material on the shutters. Just remember seeing any playing with them when the wife and I were over there on vacation in the 80's. The ones I remember were kind of like a tambor door construction, but made of aluminum. They rolled into a box about 7" in height mounted above the window. there was a "tape" that was mounted on the inside. when you held the tape and moved it up, the panel slid down the tracks on the outside. This was on windows that were about 36" across and maybe 50" high. TRhe memory's a little fuzzy after 20 + years.

[Pat]

GaryM, Sounds like the ones they use in Florida but with different retract mechanism. Some of the aluminum ones are hollow and foam filled. Good stuff for discouraging "light duty" vandalism and not too motivated "smash and grab" or protecting glass from moderate wind blown debris but NOT suitable for tornado protection.

I haven't built our shutters yet. So far I have just the 8 carriage bolts with enourmous washers on their heads embedded in the 12 inch wall with an inch protruding. I hope to find some "industrial strength" piano hinges but failing that, I'll just use really HD regular style hinges, 4 sets per shutter on each side.

For the aesthetes among us, be advised that there are two easy ways to improve the aesthetics of the shutter instalation: 1. Extended traverse rods with over size drapes to cover the shutters when open or 2. Decorative and insulated cloth covers that "work" with the color csheme of the room and provide good window insulation when closed such as at night in the winter.

OK Gary, we'll accept your flimsy 20+ year fading memory excuse this time but be aware, that excuse has been overused as of late.

Keep us posted as your project progresses. My progress, if you can call it that, seems to be moving ahead at a rate approaching that of glaciers.

Pat

[Pat]

Gary, A couple questions... Did you use ICF for your stem wall or did you use conventional forms for it or what?

In consultation with my ICF source, I have decided to use ICF for my stem wall but will just thicken the slab under interior ICF walls. Makes insulation installation real easy.

I learned of yet another feature of ICF. With the concrete core of the ICF in contact with the ground or uninsulated footer, the concrete in your walls tends toward the temperature of the ground. In summer, the heat has to penetrate the outer EPS then heat up the cool concrete (mid 60's here but mid 50's in say, Wisconsin.) After warming the concrete then the heat has to penetrate the inner EPS. Similarly, in winter, the core is warmer than the outside temp and provides a little help.

I have ordered all of my PanelDeck and ICF. Deliveries should start arriving in a week or two.

Pat

[GaryM]

All the foundation wall, including the stem walls, are ICF construction. I had not heard the details you raise about the concrete acting as a "heat sink" of sorts, but it makes some sense. I wonder what the flow rate of heat through concrete is?

They were supposed to do the plumbing rough in on Thursday/Friday. May drive out this afternoon to see if it's so. If it's not it'll just make me upset. Why ruin a beautiful weekend!

Weather shows isolated thunderstorms for the four days starting Monday.

[Pat]

Gary, If the ICF stem sits on an uninsulated footing (at least uninsulated on the bottom) then that earth contact will tend to promote the effect I mentioned. The R-value of concrete is not very high. It is a decent conductor. R-value of concrete, tile, brick, and stone run around 1.0 +/- 20% with concrete close to about 1.0 in general (Wirsbo tables). Concrete has a fairly high specific heat also, not as high as water but still significant.

If you are "electrical" then think of the layers of EPS as resistors (R-value) and the thermal mass of the concrete as a capacitor that stores heat energy. Reference the sketch... An ICF wall lis a low pass filter. The applied voltage (outside temp), if higher than the concrete temp, forces heat through the R-value of the outside layer of EPS into the concrete core. If and when the core temp goes above the inside temp then heat is forced through the inside layer of EPS. As in the electrical analog, there is a phase shift and there are the equivalent of RC time constants.

As a thought experiment lets take the example of that time of year when the outside temp goes both above and below the inside temp. When it is hotter out than in, heat flows through R1 and begins to raise the temp of C1. If C1 is warmed above the inside temp then heat flows through the inside EPS into the house. It is likely that before much heat makes it to the inside that nightfall occurs and the outside temp falls below the core temp and heatflow is reversed. Heat flow continues from the core to the inside until the core temp is equal to the inside temp and then reverses direction as the core goes below the inside temp. There is a "phase lag" between the core temp and either the inside or outside temp.

The core exhibits a thermal flywheel effect, similar to a bare concrete wall but with significant differences, chief among which is the phase lag due to the high R value EPS. If you plot the outdoor temp and the core temp versus time you will find that the max temp ouside leads the max temp inside. The max temp in the core will be significantly later in the day than the max outside temp. The min temp will be similarly time (phase) shifted.

Being the curious sort, I will plant some thermal sensors in my ICF cores. It will only cost a couple bucks and will entertain me for a while. I will probably use a semi-conductor diode. Due to the still unrepealed laws of physics the forward voltage drop is a function of temp and a 10 cent 1N914 diode makes a decent temp probe for the temp range in question. I have designed electronic thermometers and temp controllers around them.

Pat

[GaryM]

I understand exactly what you are relating. I had just never considered the effect. It would be interesting as you mention to place temperature sensors at different heights in the wall, and perhaps in the backfill soil as well. Then work out a way to graph air temp, soil temp, concrete core temp and inside wall temp. See how the values changes and what the lagtime is. Might make a good project for some local college students.

[ScottAR]

If I'm understanding you correctly, I have noticed this effect in my house which has a brick veneer. The outside temp leads the inside temp by a few hours. For instance, the house is coolest in the mid-morning sun, followed with warming until about 8pm or so. The house doesn't really cool down much until midnight or later. I speculate the effect would be even more pronounced in ICF construction. Pronounced to the point where it would be desireable; cool during the day and warm at night.

I'm not an engineer but I stayed at a holiday inn once. [img]/forums/images/icons/grin.gif[/img]

[Pat]

Gary, Thre are some pretty inexpensive A to D (Analog to Digital) interfaces for a PC that work with some simple datalogging software that will capture, record, manipulate, and display data. I have an old single chanel Rustrak chart recorder I could multi-plex for multiple chanel recording. It is simplicity itself with a galvanometer meter movement and a hammer that physically strikes the meter's needle which makes a mark on the wax coated strip chart. Don't mention this to anyone as the Smithsonian or some such institution would probably want it for their antique instrument display.

Actually the DOE (U.S. Dept of Energy) through NREL (a Gov lab) and other institutions have done a lot of this sort of instrumentation. This sort of thing gets discussed in "Home Energy" magazine www.HomeEnergy.org This is sort of a "Consumer's Reports" magazine for home energy and IAQ (Indoor Air Quality) and other issues of similar interest. Well worth taking a look at it.

If you bury a thermosensor deep enough and you don't have geothermal activity, you will get a steady reading that is the time average of the surface temperature with a loooooong sampling window. The rate of change of the temp will reflect climate change. You won't see seasonal variations. As you move toward the surface the seasonal variations start being noticed but with a big phase lag.

I talked a couple days ago with a guy who used to install power poles all year. He has never seen the ground frozen a foot deep. The worst he saw after a prolonged bitter cold spell was about 6-8 inches. My deep earth temp (after 8 ft or so) is about 62.5 F. A real easy way to get our deep earth temp is to run a well for a bit and stick a thermometer in the water (at the well head not after going through a pressure tank and or a lot of pipe.)

I'm gambling that my insulated-on-the-outside-only basement walls won't sweat. They shouldn't with proper dehumidification during the A/C season. During the in between seasons where outside air is cool unough and you open the windows, I may get condensation if the wall temps are low enough. I have been thinking of delaying the final finishing in the basement until after I see what happens. If I have a problem, I can just put up a half inch of foam board with drywall over it.

You, of course, should never have much of a condensation problem with or ICF construction. Did you hear the hype about heating your house with a candle and coolinlg it with an icecube?

Pat

[Pat]

Scott, Right on target. The thermal mass creates a phase lag. ICF operate a little differently since they are insulated on both the inside and outside. The external insulation slows the heat flow from outside going into the wall and the inside insulation does the same for heat in the wall going into the house. The outside insulaltion reduces the amplitude of the temp fluctuations in the concrete core as well as delays the time when the core reaches its max temp. Then the inside insulaltion slows the flow of heat from the core into the house. This thermal system can be "tuned" for optimum effect, sort of...

There have been attempts to optimize the insulation versus thermal mass to derive max benefit from controling the captured heat. I built my mom a sunporch with a slab floor and a southern exposure window wall. In the winter in the early morning before sunrise the temp in the (unconditioned) sun room averages about 15-20 degrees higher than outside due to storing solar heat in the slab. My mom went out and bought a carpet for the sun porch. [img]/forums/images/icons/confused.gif[/img]

I told her it would cause the room to overheat in the middle of the day and be a lot colder at night and in the morning but... Oh well she wants the floor more comfortable.

The carpet will warm up quickly, converting sunlight to heat and overheat the room around noon and early afternoon. The carpet will insulalte the slab from the solar heat so there will be no storage to draw upon overnight so plants will freeze etc. (Never got below freezing so far with bare slab. The beneficial phase shift of the slab's storage will be lost. This ranks right up there with the in-floor hydronic heat that works really well until someone decides to put a nice wool oriental rug down and doesn't grasp why a nice warm rug would make the room so cold.

Thermal masses can be too large and not let the temp rise enough to be useful. Another not to well known concept which flies inthe face of the general belief that if a little bit is good then a whole lot more should be a whole lot better.

Gee Scott, I never stayed at the Holiday Inn much...

Pat

[GaryM]

Hey! More progress. SIP walls are going up on the lower level. Weather permitting, how many times have I said that in the last five months, they should be setting floor trusses Friday or Monday.

Attachment shows North and some of the West walls.