ICF and the ongoing Thermal Mass Discussion
Last Post 17 Feb 2012 05:03 AM by jmagill. 138 Replies.
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TexasICFUser is Offline
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27 Jan 2012 07:30 AM
Hello Lbear you said:

"I think an overlooked issue is that the EXTREME high temperatures we experience, it requires the engineers to up size the units to make to sure they can handle 115F temps. So while my A/C units are "over sized" when you look at the temps in the 90F's but they are not "over sized" when you look at the temps in the 115F+ range. If you calculated the tonnage based on 90F-100F, then the system would be overworked when it hit 115F - 120F. "

Granted humidity is a much bigger problem here in Texas but if your A/C is running properly it will pull it out if it's present.  It's going to be present more often if you build a very tight house.   I would think the 115 high with low humidity would be less painful than 100 with 60%+ humidity.   At any rate, we had 30 or so consecutive days here that were 100+ this past summer the problem is not the "high" but the "low".  It was not unusual to have an 80-85 degree low - I seem to recall a few 90 degree lows when we hit 108 or so a few times.

I'm not an A/C guy but I would think one should size your system more on it's own environment e.g. what happens to the building if left alone with no power at all.   In other words, does it really matter what the high is if the building never see it or reacts to it.   What if your building was entirely10 feet underground would you size your A/C to handle 115F outside worst case scenario?    Perhaps you would size it to maybe 80F worst case scenario.   

As you know, with ICF the bigger the swing the better.  If it was 100 all day and 60 all night and your left your home tuned off (zero power).  I would bet your wall temp would stay very close to 80.    Some of this 80 would be lost to the earth and you'd find the home quite comfortable.   It takes a while for an ICF home to "realize" that the temperature has gone up or down.   If the mass is insulated it will be even slower.  

Of course there's not magic to it the walls, slab, mass etc. are just assymtotically (sp?) going to the average daily temperature and being pulled down a bit by the earth capturing some of the heat.   Regards.

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27 Jan 2012 09:58 AM
It doesn't take much of a dehumidifier or AC duty-cycle to deal with the latent loads from humidity sources inside the house- the MUCH bigger load in humid areas like southeastern TX where the out door dew point can hang in the 70s F for weeks and even top 80F multiple times per summer is the latent loads of the ventilation air. TexasICF's example of 100F/60% RH correlates with a dew point (the measure of the absolute humidity) of ~83F at sea level, which it truly downright gag-me miserable outdoors, and represents a huge latent load from ventilation air. By contrast 115F/30% RH has a dew point of 75F- still a substantial latent load and quite steamy (but you can at least breathe that stuff sitting in the shade sipping a tall cool one.)

In Lbear's part of AZ the latent loads from ventilation air are much lower than TX, if still substantial at times, and if high ventilation rates are desired it's still worth considering ERV rather than HRV for the active ventilation, especially if going with high-mass construction and a high SEER continuously variable speed compressor which will dehumidify less. High mass high-R houses have a reduced peak load as well as a much reduced average load, provided you do the site engineering, orientation, and envelope tweaking to reduce unwanted summertime solar gain. In a high mass house with continuosly variable speed compressors a pre-cooling strategy can also be effective, allowing you to undersize the mechanicals and still be comfortable during the afternoon peaks, which doesn't work quite as well with stick built (unless you add a lot of mass elsewhere, fully inside the thermal envelope.)

The effects of direct solar gain often trumps outdoor air-temps in terms of what defines the peak sensible AC load the clear air of AZ. High solar reflectance/moderate emissivity exterior finishes can make a real difference, even after the site-factors, roof angles, and glazing have all been optimized.

Although having mass in the walls is useful, direct heat gain through the walls (even an R10 wall) is a relatively small fraction of the total solar gain. Glazing and roof/attic gains are far bigger factors. But having a lot of thermal mass at least SOMEWHERE in the house is good for both comfort and energy efficiency.
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27 Jan 2012 11:13 AM
TexasICF: If it was 100 all day and 60 all night and your left your home tuned off (zero power). I would bet your wall temp would stay very close to 80. Some of this 80 would be lost to the earth and you'd find the home quite comfortable. It takes a while for an ICF home to "realize" that the temperature has gone up or down. If the mass is insulated it will be even slower.

ARghhh! For the 19th time, put your Nudura wall in a ORNL hot box and stop guessing about ICF mass effect. Alternatively, honor the rules about unsubstantiated insulation claims and restrict you comments to Nudura's published claims. Many things happen in a household during a day: doors open; sunlight streams; meals cooked; laundry washed, heat that would build up in an ICF house because the concrete is behind 2.5 inches of foam. Meanwhile here is the difference in dynamic mass benefit between ICF walls and exterior foam: http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/figures/figure5.pdf

The Cliff notes for Phoenix: an R10 house with concrete exposed to the interior is an effective R28. The R17 ICF house is an effective R27. And, if you kvetch about measly R17 blocks, TexasICF, my next post will be the ORNL graf showing that the less foam in an ICF wall, the BETTER its DBMS coefficient.

Dana, while winter temp swings in the upper midwest are extreme, they don't count in dynamic benefit because the average is well below comfort levels and the heat is going only one way (out). Interior mass and icf are pretty close in MN (i.e. mass effects are equally modest.)
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27 Jan 2012 11:21 AM
To clarify, less foam equals a higher mass effect multiplier in Phoenix.
BrucePolycreteUser is Offline
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27 Jan 2012 11:29 AM
What's the installed cost of the R17 Intmass wall vs that of the R17 ICF wall, and what are the expected energy coast savings ($'s) in that 1,540 sqft one story rancher each year?
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27 Jan 2012 01:32 PM
I have no knowledge of construction costs in Phoenix. I did a R10 intmass wall in Pa for about $7/sf as semiDIY. (Hired a moonlighting mason; acted as his helper.) The wild card in most markets is how competitive ICF is. I'm guessing that cmu in AZ is very competitive.

Potential savings is even less knowable. Glazing? Orientation? Attic R value? HVAC efficiency? Walls figure well down on the list. What's more, the difference between R17 and R27, to correct ICF in Phoenix for published mass effect numbers, won't add up to big bucks, Surely, it is a far cry from TexasICF's inference that ICF houses in Phoenix don't need airconditioning.
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27 Jan 2012 01:42 PM
In PA (except the cities of Pittsburgh & Philly) the installers cost for a 6" Polycrete wall is about $9.50/sqft. He will charge the GC $12 - $12.50.That's R23.25.
LbearUser is Offline
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27 Jan 2012 03:49 PM
Posted By toddm on 27 Jan 2012 11:21 AM
To clarify, less foam equals a higher mass effect multiplier in Phoenix.

How about Northern AZ-Prescott? It doesn't get AS HOT but we still see 30-35 degree temperature swings from peak day temps to early morning temps. Here is the graph:


Average Temp Graph - Chino Valley, AZ



Would I still see a higher mass effect multiplier in the Prescott area?
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27 Jan 2012 04:17 PM
Your area would be right up there, but I'd be guessing. If you have a site that would accommodate passive solar you'd be golden (unobstructed southerly view with no one looking back.)

Dmaceld gave you the link to UCLA's design tools. Climate Consultant has a chart that tells you how many hours a year high mass or passive solar/high mass would keep you comfortable without hvac. HEED allows you to rough out your design with windows, doors and house orientation in place and model its performance. It pretty easy to use, has ICF options if I remember right, and plugs you right into DOE2 without "interpretation" by TexasICF or me.

Bruce Polycrete, Climate Consultant liked high R ICF for Pa a whole lot better than my plan but who is rational about houses, eh? Given the window walls in my Frank Lloyd Wright tribute. passive solar and interior mass make sense even all that glass does not.

Two more economies in the hybrid ICF approach to high mass: No mesh necessary for stucco. Cost me $4.50/sf. Parging interior walls cost less than dry wall, again as semiDIY, but Bill Warthen did such a marvelous finishing job that we textured everything: parged walls, drywall and ceilings. Around here anyway, skilled trades aren't hard to find and they love an opportunity to show their stuff.
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27 Jan 2012 07:19 PM
Posted By toddm on 27 Jan 2012 04:17 PM
Your area would be right up there, but I'd be guessing. If you have a site that would accommodate passive solar you'd be golden (unobstructed southerly view with no one looking back.)

Dmaceld gave you the link to UCLA's design tools. Climate Consultant has a chart that tells you how many hours a year high mass or passive solar/high mass would keep you comfortable without hvac. HEED allows you to rough out your design with windows, doors and house orientation in place and model its performance. It pretty easy to use, has ICF options if I remember right, and plugs you right into DOE2 without "interpretation" by TexasICF or me.

Bruce Polycrete, Climate Consultant liked high R ICF for Pa a whole lot better than my plan but who is rational about houses, eh? Given the window walls in my Frank Lloyd Wright tribute. passive solar and interior mass make sense even all that glass does not.


The home will be positioned to face due south, with the majority of the windows on the south side of the home. I hope to utilize as much passive solar gain as possible in this home. During winter solstice the sun would be positioned just above the mountain range from east to west. Here is the view facing south but it was taken during summer solstice:



So I hope with the ICF, good windows, and passive solar design to keep my heating costs low.

Do you have any pics of your Frank Lloyd Wright tribute home?
 
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27 Jan 2012 09:03 PM





 
That's a beautiful view, Lbear and the climate there is nice.  I can see why you'd want to live there.

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27 Jan 2012 09:59 PM
Posted By Lbear on 27 Jan 2012 07:19 PM

The home will be positioned to face due south, with the majority of the windows on the south side of the home. I hope to utilize as much passive solar gain as possible in this home. During winter solstice the sun would be positioned just above the mountain range from east to west.

So I hope with the ICF, good windows, and passive solar design to keep my heating costs low.

Here's a link to a neat calculator to plot sun position throughout the year http://solardat.uoregon.edu/SunChartProgram.html.

I used it when I was designing my house to calculate how long of an overhang I needed to block direct sun in the summer and maximise sun entry during the winter through the SW facing windows in my house. It worked out. Right now we have fairly direct sunlight coming in during the afternoon. In the middle of the summer there is no direct sun coming in. The info from the plot not only played into the overhang design but also helped me determine window height above the floor and the height of the windows. I'm actually rather proud and quite pleased with what I was able to accomplish.


Even a retired engineer can build a house successfully w/ GBT help!
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28 Jan 2012 02:24 AM
Posted By dmaceld on 27 Jan 2012 09:59 PM

Here's a link to a neat calculator to plot sun position throughout the year http://solardat.uoregon.edu/SunChartProgram.html.

I used it when I was designing my house to calculate how long of an overhang I needed to block direct sun in the summer and maximise sun entry during the winter through the SW facing windows in my house. It worked out. Right now we have fairly direct sunlight coming in during the afternoon. In the middle of the summer there is no direct sun coming in. The info from the plot not only played into the overhang design but also helped me determine window height above the floor and the height of the windows. I'm actually rather proud and quite pleased with what I was able to accomplish.



THANKS! I will give it a shot!

Should the west side have fewer windows because of the summer sun setting in the west?
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29 Jan 2012 08:23 AM
I haven't updated this recently: http://www.flickr.com/photos/58061641@N06/

With passive solar, you'd definitely want mass exposed to the interior. An ICF wall would be little use in a late-aft overheating episode because the interior foam would delay its buffering effect.

Generally, you don't want windows facing west because there is no way to shade them. In my case, trees do the job quite well.
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29 Jan 2012 04:20 PM
Posted By toddm on 29 Jan 2012 08:23 AM
I haven't updated this recently: http://www.flickr.com/photos/58061641@N06/

With passive solar, you'd definitely want mass exposed to the interior. An ICF wall would be little use in a late-aft overheating episode because the interior foam would delay its buffering effect.

Generally, you don't want windows facing west because there is no way to shade them. In my case, trees do the job quite well.

Very nice home!

What made you decide to go with ICF ?
toddmUser is Offline
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30 Jan 2012 08:28 AM
The slab is sitting on ICF stem walls but the house itself is autoclaved aerated concrete, or AAC. Quite common in Europe. Less so here. They are solid blocks of regular Portland manufactured in a way that the block weighs about a fifth of what regular concrete weighs. The blocks are self insulating: R1.25/inch of wall. The wall has reinforced concrete cores every 4' and bond beams at floor heights.

Hybrid ICFs are also self-insulating, typically by incorporating styrofoam in the concrete mix. The blocks are drystacked and filled with concrete, typically in a honeycomb pattern. R values are well below conventional ICF but I hope you realize by now that interior mass and modest insulation work better in your part of the world. Google Apex and Rastra. Apex is based in AZ if I remember correctly. So is E-crete, an AAC manufacturer. The trouble with hybrid is that shipping costs get prohibitive pretty quickly.

Drystack is not as simple as it seems but these blocks are an architect's wet dream. If you can draw it you can build it, particularly with AAC.
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03 Feb 2012 03:58 PM

Todd, 

Very nice home!   

I do like the DBMS ORNL stuff -- but it is the lack of definition around effective R-value or R-value equivalent that's made it appear that ICF vendors are misleading potential buyers as they market R-value.   Consider from the report:
  

R-value Equivalent for Massive Systems is obtained by comparison of the thermal performance of the massive wall and light-weight wood-frame walls, and they should be understood only as the R-value needed by a house with wood-frame walls to obtain the same space heating and cooling loads as an identical house containing massive walls. There is not a physical meaning of the term “R-value Equivalent for Massive Systems.”

 

That is a little difficult to follow but let's go with it.   ORNL shows that in Phoenix the Dynamic Benefit of Massive Systems (DBMS) is significantly better for an R-17 wall with the mass on the inside than for an R-17 ICF wall with mass in the middle (between the foam).   And they show:   DBMS = R-value equivalent/Actual R.   Therefore, based on the chart we have:

 

R-value equivalent for R-17 ICF wall is about 25.

R-value equivalent for R-17 Internal mass wall is about 40.


To your point about DBMS in Phoenix it doesn't get any better anywhere else for DBMS. 
 

But I don't think it's all that clear --- for example --- how does AAC fit into that?   From ORNL:


Masonry or concrete walls having a mass greater than or equal to 30 lb./ft 2 (146 kg/m2) and solid wood walls having a mass greater than or equal to 20 lb./ft 2(98 kg/m2) are defined by the Model Energy Code [1] as massive walls. They have heat capacities equal to or exceeding 6 Btu/ft2   0F [266 J/(m2k)]. The same classification is used in this work.


Solid wood walls weighing 20 lb/sqft have specific heats great enough to give them an exceptable heat capacity to classify them as "mass".  By the same token, some AAC is just under this baseline of
6 Btu/ftF heat capacity and some thicker AAC is over it a bit.  Basically, AAC is mass system with a low heat capacity. Incidentally, ASHRAE defines a wall to be "mass" if it's heat capacity exceeds 7 Btu/ft2 F.  This difference would exclude some walls from being classified as mass. 


How does ICF fit?  Your typical 6" core ICF wall has a heat capacity of around 13 Btu/ft2 F. Thus ICF is a very high in heat capacity or about twice the ORNL baseline value.   What impact does this have on the report results.  I don't know but more heat capacity is good for DBMS.   ((Actually, I don't know this for sure as it applies to laboratory DBMS but I do know that if heat capacity is extremely high then it will take a long time for a building to "know" that it got cold outside and in fact despite diurnal swing it will also take a long time for the building to "know" that it "got colder" outside. ))  


What about R-value?

AAC actual R-value is about 8-10 (from what I gathered in search) and ICFs actual R-value is about 22.


If we look at Phoenix and utilize the DBMS for R-10 you still have an a strong effective R-value of about 25 which is actually still quite impressive.

So how does this translate back to the effective R-value chart for R-17 mass walls?   This value would be off the chart but based on the y=mx+b line they provided it's about 30 (it's off the chart as are almost all ICF brands on the market today). 
 
http://www.ornl.gov/sci/roofs+walls...html#whole 

I dug around quite a bit and found some other ORNL reports that did not attempt the dynamic part and seemed to say the opposite.

Since they have used least squares or similar to derive a straight line I don't think this is out of line.


I don't know for sure about this one way or the other but using this chart for AAC and ICF comparison is a little like using a screwdriver as a hammer.   It works but only to a point.  Regards. 

 

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06 Feb 2012 07:20 PM
No need to guess about AAC, Texasicf. AAC manufacturers built a representative wall in an ORNL hotbox, plugged the data into Doe2 and published effective R value numbers that the FTC accepts as legitimate claims.. Feel free to google. If memory serves, Phoenix was an effective R24. I used Washington DC to plug an effective R17 into RESCHECK and get my building permit. (Today, you'd need 10inch AAC walls to meet code in pa.)

No point in "translating" thermal mass either. If nudura, your brand, were to make effective R value claims the company must jump through the FTC hoops first. It doesn't and it hasn't, one guesses, because as ray Gladstone wrote earlier in this thread, why hand ammunition to your rivals by affirming that interior foam limit ICF's ability to buffer temp swings over 24hour periods?

Good news. TexasIcf. We are not as dumb as you think.
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07 Feb 2012 07:24 PM
Posted By toddm on 06 Feb 2012 07:20 PM
No need to guess about AAC, Texasicf. AAC manufacturers built a representative wall in an ORNL hotbox, plugged the data into Doe2 and published effective R value numbers that the FTC accepts as legitimate claims.. Feel free to google. If memory serves, Phoenix was an effective R24. I used Washington DC to plug an effective R17 into RESCHECK and get my building permit. (Today, you'd need 10inch AAC walls to meet code in pa.)

No point in "translating" thermal mass either. If nudura, your brand, were to make effective R value claims the company must jump through the FTC hoops first. It doesn't and it hasn't, one guesses, because as ray Gladstone wrote earlier in this thread, why hand ammunition to your rivals by affirming that interior foam limit ICF's ability to buffer temp swings over 24hour periods?

Good news. TexasIcf. We are not as dumb as you think.


Not as smart as you think either if you think hot boxes are the answer.
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08 Feb 2012 08:46 AM
An ad you didn't see during the super bowl: ford expedition! 50mpg!* (downhill, in neutral) So,FBBP, what's your view of the EPA?
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