This forum has seen endless discussions about the thermal mass benefits of ICF homes. Lots of talk and virtually no data. This seems like an excellent time of year to find a really cold night to actually take a relative measurement of the thermal mass of a house, either ICF or other construction method.

Simply turn down the thermostat at bedtime from 70 F or whatever value it is normally set to, and see what the inside temperature drops to by morning, assuming that the thermostat is set low enough that the heat does not come on during the night. It is also necessary to record the outside temperature at the time the thermostat is turned down, as well as the outside temperature in the morning. Internal heat loads should be limited to the refrigerator, warm bodies, and minor electrical loads.

I have done this experiment for my house, and would be interested to see what others find for both ICF and other houses. Yesterday morning the low here was 4 F, while this morning it was -10 F, and I have the data as described above for both nights. Share you data and I will share mine.

It would be interesting to quantify thermal mass in a house with measurements (vs modeling). It would also be interesting to see more data on the negative effect of thermal mass on thermostat setback (less temp drop at night and more btu to bring the temp back up). I've seen claims from almost no effect to "I don't do thermostat setback at all in my high mass home" (ie, 100% elimination of a benefit that is substantial in many low mass homes).

On the other hand, less than 24 hour thermal mass related measurements and Winter only tests can be misleading to some.

OK, I'll play. I've included 3 shots of my Wi-Fi thermostat from yesterday noon, 6am, and 8:45am today (the sun is out and warming the place up). The building (our cottage/retirement home, in the future) is built with Silver Fox ICF  R27, and Fox bucks, It is a 1200 sq ft bungalow w/walkout basement. I put R15 under the basement floor and have approx. R60 in the ceiling, and the windows are triple glazed vinyl. Its been a year now since I began building and am now down to trim work, I am wanting to get a blower door test done this spring to see how good I sealed it up. I use a 40BTU propane forced air furnace for heat, I had a 1200L tank installed last June, it is also used for BBQ and a 14Kw gen, which exercises once a week, to date I have used 20% of the tank (started at 80 now at 60%), at $.63/L x 300L is approx. $190 for propane since July and keeping building heated at 58F when we are not there and 72 when we are. 




Here is a blog of the progression of my build  http://kasshabog.blogspot.ca/

Yes, more data would allow better model validation. Just keep in mind that we need ALL the corresponding indoor temp, concrete temp, and outdoor temp data. Also keep in mind that data is very specific and only applicable to the building and climate it was acquired. So without a good model, the data is useless for forecasting and quantifying ICF performance.

Stuie- Thank you for responding. Data for your house are interesting to me because the house is a very well insulated ICF-walled house that is roughly similar in size to my non-ICF house. You have a conditioned basement, while I have a conditioned crawl space. Your house is 1200 sq. ft per floor for two floors (main floor plus basement), while mine is 1600 sq. ft. for one floor with a 9 ft. ceilings, plus the 4 ft. high crawl space. Your house is better insulated than mine, which is R-60 ceiling, about R-27 main floor, but only R-19 crawl space, and only R-5 under the crawl space. I have either triple-pane or double-pane with interior storm windows, depending on how you define things. Do you have u-values for your windows. Mine are 0.31 and 0.29 for different orientations, but with the insulated cellular shades, the u-values are about 0.24.

It would be an easier comparison if you could heat your house to a constant beginning temperature (72 F or whatever) for the day, and then set back the thermostat after the sun is down or at bedtime. That way we can reduce questions about solar heating, which it looks like your house is very good at. I would guess that it might have been cloudy and/or raining for your data starting at noon, but there is still some chance of solar heating during the afternoon.

If we can ignore solar heating for your data, then you are showing a heat loss rate of 0.61 degF/hr at a temp differential of about 44 degF. I have one set of data here when the outside temp. averaged about 1 degF, and I took measurements from 10:46 pm to 7:28 am, and saw an interior temperature drop of 8.1 degF. This would be 0.94 degF/hr at an average differential of 61.9 degF. So my loss rate is higher, but the temp differential is also higher.

How can we estimate the effect of the temperature differntial? We could divide the loss rate by the temperature differential, to get 0.014 degF/(hr * degF) in your case, and 0.015 degF/(hr * degF) in my case. However, just as in defining degree days, we need to account for the fact that a house does not cool down at all if the inside temp is 70 F or 72 F and the outside temp is 65 F, or for modern houses even lower, due to internally generated heat. If we try to account for this effect and take 7 degF off the differential temperatures for both cases, then the cooling rates are 0.17 degF/(hr * degF) in both cases.

I think that I also have data where my heat loss rates are higher, but it looks like very crudely that we have similar heat loss rates. I will also try to take data with lower differential temperatures between interior and exterior measurements. If you can take night-time only data where interior temperatures are equilibrated before the setback time, that would be helpful.

jonr-

My interest in the cooling rates for houses at large differential temperatures is intended to take a direct approach at semi-quantifying the thermal mass effect. The stored heat energy available for heat loss is equal to mass * specific heat * absolute temperature. Therefore, it would seem to me that if we take two houses with similar thermal resistance (R-values and areas) and similar large temperature differentials, then if the thermal mass effect is significant, then the cool-down rate will be lower for the high thermal mass house. On the other hand, if the thermal mass is "hidden" behind too much insulation, then it may not be effective in limiting the cool-down rate.

Now this approach only provides some measure of the relative effective thermal mass. The saving of heating (or cooling) energy by moderating temperature swings requires different outdoor temperatures, but it is dependent on the thermal mass effect that is difficult to measure as the outdoor temperatures approach the indoor temperatures.

Do you agree?

sailawayrb -

I was not really asking for sufficient data for model verification, but rather, just some simple tests to see if there are any remarkable effects of thermal mass on cool-down rates for ICF houses, or if the thermal mass is too well insulated from the interior house temperatures to be effective.

BEopt provides pretty good estimates for annual energy use for my house, but I have not attempted to use it for cool-down rate calculations. If I can make sense out of modeling the cool-down rates, I will share it.

Perhaps you would be interested in modeling three "identical" houses that only differ in wall construction, concrete with exterior insulation, ICF, and wood frame. I have done some quick and dirty calculations with BEopt for Phoenix, and, if I remember correctly, the differences for annual energy use were not large. It is probably unfair to mention it, since I did not save the results.

Hi Lee,

I trust you read the other thread about our ICF performance program:

ICF Effective R-value

My goal with this program was to successfully quantify and study just the ICF thermal mass effect. Once you start including all the other building thermal effects, it is hard to separate and study the ICF thermal mass effect. It is certainly true that you need to include all the significant building thermal effects when you model the energy performance of a given building design. However, there is no shortage of modelling software that accomplishes this with some degree of success.

What I would be very interested in obtaining is actual indoor/concrete/outdoor temp profiles for ICF buildings located in diverse climate zones so I could better validate our ICF performance program.

BTW, I also firmly believe that having a valid model is far more important than comparing actual measured building performance numbers. There have already been several studies conducted where multiple, nearly identical buildings were constructed to just allow measuring the difference ICF contributed to the overall measured building performance. While the results may be interesting and get some folks overly excited and make claims they shouldn't; this data can NOT be extrapolated to any other building designs or any other building locations with any reasonable degree of validity. So only a valid program/model that allows us to accurately forecast the actual ICF effective R-value of the specific building design and specific location will enable us to improve our ability to better design energy efficient ICF buildings.