I disagree that it would cool down instantly, the efficient R-value of the walls and roof would prevent that, just as a thermos retains the heat of liquids for an entire day

It would not cool down instantly- insulation would hold it in, at least for a while, as no insulator is perfect except a perfect vaccum.

The way thermal mass works is by storing heat that is not circulating in the room air– it is held in dense things like masonry. Then, as the air cools, the heat moves out of the masonry into the room air– heat moves from hot to cold till the temperature equalizes.

A friend has an old house with either little or no insulation in the walls. When it's real cold the oil burner runs till the temp hits 70 degrees. Then it shuts off for 10-15 seconds– till the temp hits 69 degrees– then it goes back on. There's not much insulation or thermal mass in her house.

But my original question has not been answered. Can anyone tell me what a 10' x 10' SIP wall would cost vs a 10' x10' ICF wall for the same R value?

Of course a real house won't cool down instantly, if you read that paragraph again you will notice I said a house with absolutely no thermal mass. In real life, it is physically impossible to build such a house. If you even put up these efficient walls you mentioned, the inside of the walls will have thermal mass. Is there air inside your house? Your house has thermal mass. Are you inside your house? Your house has thermal mass. Everything has thermal mass.

If you were able to build a house with very minimal thermal mass using some sort of vaccum machine to suck out all the air and AeroGel walls to provide maximum R value with minimal masss, you would find no matter what the R value of the walls, the house would cool very quickly. It is simple thermodynamics.

In a real house it won't cool instantly, but the less thermal mass you have, the quicker it will be.

A thermos is the perfect example. It has R-Value(the thermos) and thermal mass(the heated liquid). Now, lets take two identical thermoses. Fill one all the way to the brim and put the lid on it, and just pour a small amount in the other one, just a sip or two, and put the lid on. Leave them alone for 8 hours and come back. You will find the one filled to the brim is still piping hot and the one with just a sip or two is almost cold. Why is this? The liquids were the same temperature when they went in. The R-Values are the same. It is because the thermos with more liquid has more thermal mass, so as the heat leaks from the thermos insulation, there is less of a drop in temperature per unit volume, even though there will be equal amounts of BTU's lost when the thermoses were the same temperature.

what R-value do you want to compare?

Actually you are wrong about why the liquid in the thermos with a few sips in it get cool. The near empty thermos would still have a large space filled with air, air that is much cooler than the hot liquid. The air would absorb heat from the liquid till the temperature of the liquid and air equalized.

The liquid filled thermos stays hotter longer because there is little room temperature air to pull heat from it. Now if you could remove the air from the near empty thermos before filling it, it's liquid would stay as hot as in the full thermos.

I have my own coffee analogy. I buy coffee in a paper cup. It's too hot to drink when I first get it. If I wait a minute, it's a good drinking temperature. After another minute, it's too cool. If I pour it into a ceramic mug when I first get it, it cools enough to drink it right away, as the cool ceramic mug pulls heat out of the coffee. Several minutes later, it's still a good drinking temperature, because the mug has thermal mass, (and I suppose more insulation), than the paper cup. The mug stores heat and gives it back to the coffee as it cools.

Let's say an R-value of 25.

$7.92 per sq. foot installed solid 10' x 10' x 6" steel SIP wall is an R- 25.5

Doesn't thermal mass take more energy to heat/cool (as in charging a battery) than a insulated envelope in the first place?

I see thermal mass as a plus if you can incorporate things like passive solar (free heat to charge up the thermal mass).

slenzen;

good point

Have you ever heard that a frig or freezer is much more efficient when nearly full? That is due to thermal mass. Once the mass is brought to temperature it is more efficient. Mass costs more and takes longer to get to temperature but maintains it better, cheaper.

You are right about the coffee mug, but you are confused about the thermos. Considering the specific heat per volume of air is 0.001297 and the specific heat of water (major component of coffee) is 4.186, your idea that the air is what is cooling down the coffee is incorrect. If there was 10 times as much air as there was coffee, for every degree the coffee cooled down by being in contact with the air, the air would heat up (1/10)(4.186/0.001297)=322.7 degrees. That is going to be some hot air! It would work exactly the same in a vacuum as it does with the air in it. You could also preheat the air using a hair dryer until the air was the same temperature.

slezen, You are right, it is like charging a battery, but once the battery is charged you can run off of it for a while. I am not saying to use thermal mass and no insulation, I am saying using them both together.

In the spring and fall, thermal mass will dampen the swings in temperature like a spring in your car dampens the impact when you hit a pothole. Every spring and fall, I can turn off your heat/ac and my house stays about the same temperature, 68-74. If I had more thermal mass, it wouldn't even swing that much. This is how PAHS works.

In the winter, it is a little harder to understand how it will benifit you. For example, let's say you have a heater that is set to kick on at 68 and off at 72. On a cold night that heater cycles on for 15 minutes, and then off for 10 minutes. 10 minutes is the time it takes for your house to cool off by 4 degrees.

The most inefficient part of the heating cycle is when the heater is first kicking on and heating up, as it is using fuel and you aren't getting much heat(2 minutes). Then it runs at full blast for a while (10 minutes). Then it keeps running the fan until the furnace cools back off (3 minutes).

Now, lets take the same house and double the thermal mass. Now the house will take 20 minutes to cool 4 degrees. The heater cycles on, heats up (2 minutes), runs at full blast for twice as long because it has twice as much stuff to heat up(20 minutes) and cools off(3 minutes).

Notice that the heater is running at full blast for the same amount of time every hour in both scenerios, however you only have to heat up and cool down the furnace half as much, saving you a good amount of energy.

I didn't say anything about a coffe mug?

I apologize, I must have been looking at the wrong reply when I wrote your name in there.

"You are right about the coffee mug, but you are confused about the thermos. Considering the specific heat per volume of air is 0.001297 and the specific heat of water (major component of coffee) is 4.186, your idea that the air is what is cooling down the coffee is incorrect." -- Besides the air, there is also the lining of the thermos, either glass or stainless steel. The hot liquid you pour into a thermos will lose heat to the inner wall as well was the air. And a few sips of coffee in a large thermos will cool quite a bit trying to heat the inner wall and the air in the thermos. What is in the thermos can't effect how well the vacuum insulates- either there's a thermal bridge or there is a vacuum. I have heard that to make a thermos keep things hot longer you should pour hot water into it to heat the inside, then dump the water and add the coffee, that way the coffee does not have to warm the inside of the thermos. I'd heard that freezers work best when packed, but that refrigerators work best when air can circulate around items. I don't know if they meant energy-wise, or that food keeps better when the air circulates.

Doesn't thermal mass take more energy to heat/cool (as in charging a battery) than a insulated envelope in the first place? I see thermal mass as a plus if you can incorporate things like passive solar (free heat to charge up the thermal mass). ------------ But once charged it keeps the temperature constant so the heat can stay off for longer periods. My worry would be that a weekend home with high thermal mass would get cold during the week while the thermostat is set to 45 degrees and be hard to warm up on friday night. Any home I'd be planning would be very well insulated and tight. The question would be "am I better off spending money on more insulation or adding thermal mass?"

Thermal mass between 2 layers of insulation (ICF) is basically thermally neutral (no benefit or problem), especially in the winter.

Thermal mass on the interior of a continuously conditioned space is beneficial, especially if passive heating is used.

The same thermal mass delays the response time in both directions (warm up and cool down) in setback situations.

In your situation, insulation is the best investment.

Bruce

You are right about the weekend home, it is the same scenerio as an automatic thermostat. For a "weekend" home you should be mainly focused on insuation. However for your primary residence, I would say a mix of both. You can get to a cerian point where adding more wall and attic insulation becomes meaningless, especially considering how much losses there will be in the windows. In a situation like that, in a home that will be heated/cooled all week, thermal mass can really start to shine.

And commercial buildings are another thing all together, right? That is this forum's heading. Maybe the instigator of this thread would want to clarify whether his inquiry is related to an anticipated commercial project, with a description of the project, eg: size, usage, location, etc, or whether he was , indeed, asking his questions in connection with a residential project.

My answer to his basic questions:

1. Which insulates best? 6 1/2" (5 1/2" EPS with nominal 1/2" OSB skins) vs 5" EPS ICF Forms encasing 6" to 8" of concrete. "about the same"

2. Which costs less? "The SIP wall will likely be roughly 50% to 60% of the cost of the ICF wall when completed." (Assuming that both are built by
experienced, competent, professionals. An owner/ builder may be able to narrow that margin a bit, but maybe with a "bit more of a challenge" with
the ICF approach)

Now my 1/2 cents worth: (As a distributor and project consultant for both systems)
1. Best reasons to use ICFs in residential projects: (A better choice in many commercial projects)
a. Definitely stronger in hurricanes, tornados, flooding, and, to some degree, fires (though some will debate the value of a scorched concrete shell)
b. You want a concrete house, and you can afford it!

2. SIPs, besides providing a super insulated building envelope, (with all of the caveats regarding proper installation, different types of foam and skins, etc.
etc) have proven to be very strong in earthquakes, as well as tornados and hurricanes. Having said that a SIP wall will not stop a 100 + MPH wind driven
missile (2 x 4, tree, etc) as an ICF wall likely will.

In closing, Just a philosophical question/comment: I wonder how many of the "pros", who participate in these forums, could do without some of the petty bickering, sarcastic comments, etc., that seem to emanate from a limited number of regular participants? It seems to me that visitors to the site (our potential clients) might take us a bit more seriously if everyone maintained a business like decorum in their posts.

The Sipper;

Your comments are mis-information

    ... steel SIPs will stop 2x4 projectiles and are impact tested- with Florida Product approval, structures have been engineered up to 180 mph.
Steel SIP schools are used as hurricane shelters in Lee County (Ft. Meyers)
Steel SIPs are also utilized in the manufacture of safe rooms.

Are ALL of my comments "mis-information", or just the one pertaining to "steel sips and missles" (aka "projectiles").................in Florida?