Posted By sailawayrb on 22 Dec 2014 11:30 PM
...In reality, ICF effective R-value performance can be significantly higher or significantly lower than what a conventional R-value calculation of the ICF material would otherwise indicate depending on many variables (e.g., the indoor temperature HVAC set point, the outdoor temperature profile, the concrete thickness, the total insulation thickness, and the thickness ratio of interior/exterior insulation).

...a given ICF design may also provide decreased R-value performance for other outdoor temperature profiles.

Can you provide an example where the effective R value of an ICF wall (assume conventional 2.5" EPS on both sides of 6" concrete) is less than a comparable R value low mass wall?  Under what specific conditions, i.e. outdoor temperature, concrete core temperature, interior temperature, etc., would result in the ICF wall performing lower than the listed R value of its sub-components?

Yes Arkie, if you use the above link to our software and just enter 97537.3 (i.e., zip code + decimal point + 3) for the first value of the outdoor temp profile input parameter, the software will use our Rogue River, OR Fall outdoor temp profile which is:

0: 71F
2: 67F
4: 60F
6: 57F
8: 57F
10: 66F
12: 75F
14: 81F
16: 85F
18: 84F
20: 81F
22: 75F

This outdoor temp profile is for a typical mid-September Rogue River, OR day that was obtained using Weather Spark. The default values for all the other software input parameters are as shown on the software screen (e.g., 70F for the Indoor Temp HVAC Set Point, 2.5" for Exterior Insulation Thickness, etc). You will see that the software reports: R23.10 for Conventional R-value, R18.92 for Thermal Mass Effective R-value (i.e., what I stated previously and what you questioned previously), 1.645 BTU/D-SF for Total Conventional Heat Flow, and 2.009 BTU/D-SF for Total Thermal Mass Heat Flow. If you study the hour-by-hour Outdoor Temps, Thermal Mass Temps, Conventional Heat Flow Rates, and Thermal Mass Heat Flow Rates you can see why this is the case. In short, this is a case where the heat flow results in a total heat gain to the building and the total thermal mass heat gain is larger than the total conventional heat gain...1.645/2.009 x R23.1 = R18.92.

Actually, I think the hour-by-hour heat flow rate data provide more worthwhile information than the effective R-value. I say this because I don't consider the fact that the thermal mass is heating the building during a time when the outdoor temp is colder than the indoor temp set point to necessarily be a bad thing...seems more like a good thing to me... Perhaps there is a better way to reflect this in the effective R-value calculation than my current method?

When I originally built this software, I calculated the effective R-value for every 0.01 hour finite element and then averaged all 24,000 elements (i.e., averaged over 24 analysis period). This resulted in the effective R-value getting very large in some cases…like R500+. One reason this occurred is because some finite elements reflected when the indoor temp and the thermal mass temp values were nearly identical. This caused this finite element thermal mass heat flow rate to be zero, which then caused this finite element effective R-value calculation to have an infinity singularity, which then caused the averaged effective R-value to be very large…too large in my opinion to be real... And then there was also the dilemma of how to calculate the finite element effective R-value when the conventional heat flow rate and thermal mass heat flow rate were of the opposite sign (i.e., one is + heat gain and the other is - heat loss). So in the end, it seemed more appropriate to use the total heat flow method that I described previously. Clearly, exactly how one defines and calculates effective R-value, is an important consideration that significantly affects effective R-value and any associated conclusions with regard to this subject! I would certainly welcome and greatly appreciate any suggestions about this.

Of course it is real, if the thermal mass is at the indoor temperature there will be no heat flow, and the R value goes to infinity provided there is a temperature differential from the thermal mass to the outside. It just doesn't happen long enough to be very interesting as the thermal mass will start moving.

As far as explaining why the R value can drop I think a specific example could show it: When the outside temperature has been sitting low for an extended period the thermal mass in the center of the wall will be sitting at the midpoint between the inside and outside temperature, for example if it is zero outside and 70 inside the concrete will be sitting at 35. Now if it warms up outside above the 35, the thermal mass is still sitting at 35, so your heat loss still looks like 35 degrees though half your total insulation thickness, and until the thermal mass recovers to the midpoint the loss will appear higher than the outdoor temperature and insulation would otherwise provide. However, if the temperature outside is dropping the thermal mass will again lag, so your R value will be better than the steady state values would suggest.

Which goes to suggest that there is no free lunch, you still have to dynamically charge the thermal mass. The benefit is that those charging peaks are slow and less peaky, which can let you get away with much smaller heating and cooling equipment.

Sailor - how are you accounting for the different R-values of eps at different temperatures? The different R-value of the inside and outside eps based on temperatures?

Dave, I fully agree with you and great example too. The problem is that computers don't like dividing by zero. The total heat flow approach avoids the issue of having to limit or discard these singularities...and as you rightly stated, these singularities are real, even if brief and uninteresting, LOL! However, I am not convinced that the total heat flow approach is entirely the best/right way to calculate effective R-value either. There may in fact not be a "right" way and this may be why even using or discussing effective value may be hopelessly flawed.

FBBP, if you mean the fact that EPS R-value will vary between 4.3-5.0 between 25F-70F, I didn't account for it at all. However, both the interior and exterior EPS R-values can be entered as desired by the user so there is some capability to play that game if desired. It would an easy thing to add this refinement, but I don't think it would change the comparison between the conventional and thermal mass very much as this refinement would largely be the same for both.

Lbear, I updated the software to allow entering an indoor temp profile. I also updated the software instructions accordingly. I made the Rogue River portion of the indoor temp profile the same as that portion of the outdoor profile where it made sense to turn off the HVAC system and open the windows (or use ventilation)…which is during Rogue River Summer and Fall. As an example, for the Fall indoor temp this is:

0: 70F
2: 67F
4: 60F
6: 57F
8: 57F
10: 66F
12: 70F
14: 70F
16: 70F
18: 70F
20: 70F
22: 70F

This resulted in the Spring effective R-value staying the same R23.30, the Summer effective R-value increasing from R21.89 to R22.24, the Fall effective R-value increasing from R18.92 to R21.47, and the Winter effective R-value staying the same R23.36. This raised the average annual effective R-value from R21.87 to R22.59…still slightly less than the R23.1 conventional R-value. Frankly, I was expecting to see a more significant improvement in the effective R-value. There was in fact significant improvement in BOTH the total conventional heat flow and total thermal mass heat flow values, but since BOTH of these improved significantly, the effective R-value didn’t improve as much as I initially would have expected.

I am becoming more and more convinced that overall ICF improved performance results largely from reduced inherent infiltration rate and NOT from significantly improved effective R-value (i.e., NOT from thermal mass temp lag effect). Therefore, if true and given that we book keep R-value and infiltration rate separately when we do a heat gain/loss analysis, it likely makes little sense to use a higher R-value for ICF than the conventional R-value would indicate. However, it makes great sense to get the building infiltration rate value correct and I suspect that average infiltration rates are significantly less for ICF buildings than for other buildings...at least for most builders... I suppose this really isn't a big surprise, but the math and the physics appear to fully support this conclusion.

I must agree with Arkie -- there are a few "Problems" mentioned in this post -- for one -- in all of the reports I read and including my own empirical analysis the concrete core never varies by more than a few degree Centigrade from the set point in the building. Furthermore, most ICF dwellers and ICF experts don't bother moving their thermostat after they determine that it really doesn't matter much at all. Just keep it where you want it. That was something Richard Rue told me years ago and I had to see it for myself. Regards

Here is an interesting article & study on ICF walls and the concrete core temps:

ICF MAG - Temperature Wicking

Here is another article on thermal mass and ICF:

Thermal Mass for the Average Home

The ground temp wicking theory is interesting and this heat transfer transmission mechanism is not included in my ICF performance software. I can certainly see how ground temp wicking might improve ICF effective R-value when there isn’t much outdoor temp swing. For example, ground temp wicking could keep the thermal mass temp cooler than it might normally be in the Summer and warmer than it might be in the Winter. However, in normal ICF construction, the ground temp wicking effect would be insignificant compared to the dominant heat transfer effect resulting from the indoor/outdoor temp profiles. The thermal mass temp profile is largely governed by the difference between the indoor/outdoor temp profiles. Even the ground temp wicking theory ICF Magazine author states that the data presented are not conclusive and seems to indicate that the industry is still soul searching for a conclusive explanation that explains why they believe ICF performs better.

As I indicated previously, we have measured our ICF thermal mass temp profile in relationship to a constant indoor temp and our significant diurnal outdoor temp profile, and we have found BOTH the thermal mass absolute temp value and the temp time lag to be very consistent with the software. Really no surprise here as heat transfer theory has been well-understood for a long time... So the software provides an accurate forecast of the thermal mass temp profile that will result for a given indoor/outdoor temp profile. However, I would have to get very creative with the effective R-value calculation to show any significant improvement over the conventional R-value. Clearly the ICF companies are more creative than me in this regard, LOL!

The wicking article is flawed. Of course coupling the center of the wall to the ground increases thermal mass. But thermal mass is mostly a two way street - for part of the day it reduces the heating/cooling needed and at other times it adds to it. The author measured when the former was occurring and then concluded that wicking "contributes significantly to the energy efficiency of ICFs". Not to mention that depending on depth, the ground also creates a thermal bridge to the outside air - never a good thing.

For maximum use of thermal mass in Phoenix, use poured concrete walls with all of the insulation on the outside. Use the money saved over ICF to automate the interior ventilation needed.

Posted By South Texas ICF on 22 Dec 2014 11:36 PM
I've felt the walls during construction (roof and windows in) after a cold front of 25 degrees comes through and you can feel the walls radiating or putting heat out.

Concrete curing is an exothermic reaction and this is likely why it was "putting heat out" then. The only other possible explanation would be if the indoor/outdoor temp was previously hot such that this heated and "charged" the concrete before the cold front. In this case, the concrete would not put heat out for very long before getting cold and becoming "discharged" and the concrete would then subsequently remove heat from the building.

For fully cured concrete and the same thickness of the insulation on each side, if both the outdoor temp is a constant 25F and the indoor temp is a constant 70F for any length of time, the concrete will reach a constant temp of 47.5F (i.e., 25F plus 75F divided by 2). Of course, it is easy to prove that for constant temp profiles that the effective R-value is identically the same as the conventional R-value and this is not very interesting. We are more interested in understanding what happens to the effective R-value during more realistic dynamic temp profiles (i.e., not ICF company cherry picked, brief, singularities) and this is why I developed this ICF performance software. Although frankly, we are really much more interested in knowing the ICF hourly heat flow rate characteristics relative to our other building heat transfer mechanisms (e.g., HVAC system, solar heating, etc.) so we may better design a more fully integrated building.

Whenever a PROPER Manual J is done on an ICF home, it still results in an over sized HVAC load. The R-23 input that is done for the wall R-Values are not producing correctly sized equipment recommendations. I am not trying to use anecdotal evidence but there is something to be said when people living in ICF homes are experiencing better energy savings then the R-23 stated value.

When it comes to air tightness. Making a wood-frame wall air tight is no easy task. Stick frame building is naturally a leaky form of construction while an ICF/concrete wall building is naturally air tight. Finding contractors who will go around taping and sealing wood frame walls is difficult or impossible to find. The ones who are good at it charge an arm and a leg to do it.

The other factor which building scientists agree to is that nobody really knows how air tight a stick frame wall will be 10-20-30 years later after the house racks and twists and the house tapes and caulks dry up and pull away. One thing with wood is that it is always moving. It gets wet and dry, it expands and contracts, it can rot and be eaten by pests.

I highly doubt that these wood frame homes built today that get < 0.90 ACH @ 50Pa will remain as air tight 10+ years later.

Manual J worked great for buildings built in the 1950/60s. Whenever a PROPER Manual J is done for most new construction these days, it results in an oversized HVAC system. That is a well-known and industry accepted deficiency of the Manual J method. These days, you would have to do an INPROPER Manual J (or preferably use another method) to determine the PROPER size of an HVAC system for an energy efficient building. This is why ASHRAE has been highly motivated to improve building heat gain/loss analysis methods. The real issue is that the better methods are currently ahead of the available software tools and beyond the average usability level of the industry.

Yes, I am coming to the stark realization that all the hype about improved ICF performance really comes down to ICF just being R23ish which is higher than many current minimums and having greatly reduced infiltration rate than other construction methods. I can live with that and I won't be replacing my ICF homes anytime soon...

Posted By Lbear on 29 Dec 2014 01:11 PM
Whenever a PROPER Manual J is done on an ICF home, it still results in an over sized HVAC load. The R-23 input that is done for the wall R-Values are not producing correctly sized equipment recommendations.

I disagree, strongly. That is unless by oversized you mean 10% or less. My nephew HVAC contractor is proficient in using Wrightsoft for heating/cooling calculations, and in fact provides those calculation for other HVAC contractors in the area. Now how much Wrightsoft may vary from strict Manual J formulas I don't know, but I do know that for my house which I built in 2008, his numbers for the recommended system capacity were pretty much dead on, or maybe a bit oversized. Keep some factors well in mind when using Manual J numbers. Wrightsoft includes factors for ICF construction.

First, the calculation is based on steady state heat loss or gain at the design temperature for the location of the house. That right there tells you that the HVAC system will be oversized for about 90% of the time, which is why it needs to turn on and off. I believe we have all pretty well agreed that the thermal mass of concrete has much less influence when the outdoor temp is consistently above or below the indoor temp, although it will moderate the outdoor temperature swings.

Second, AFAIK Manual J calcs don't factor in the normal heat caused by occupancy, i.e., heat from bodies, from cooking, from light bulbs, etc., although I'm sure those values could be input if the designer wants to make a stab at guessing what they will be.

Third, HVAC equipment for homes seldom comes in a capacity rating exactly equal to the calculated load, so generally the next larger size will be selected.

In my case for my 2000 sq ft house for design temps of 9°F outdoor and 76°F indoors (yes that's quite warm but we tend to be cold blooded) the heat load was calculated at ~27k without ventilation load, and ~33k with ventilation load. The ventilation load accounts for infiltration as well as heat lost through the HRV. We installed a 36,000 Btuh Daikin heat pump. According to the Daikin engineering data manual at 9° its output drops to around 28k Btuh. At 0°F our house stays at 72 to 74° with the heat pump running steady. The heat from living activities compensates, I'm sure, for the ventilation load.

Lbear, recognize that any heating/cooling calculation is going to be in error to some degree, simply because there are so many variables that affect the heating/cooling load, such as heat from living activities, variability in outdoor temperatures, clouds masking solar heat, performance variation over time of any heating equipment, number of times doors are opened, amount of cooking, and so on. In my book a good Manual J calculation via a program like Wrightsoft is going to give you the best guess estimate of what real life is going to hand you. There is no such thing, and will never be any such thing, as absolute exactitude in heating/cooling calculations. I will say that of the programs I used to do HVAC calcs for myself, including HVAC Calc, HEED, and the program from American Concrete Association (or whatever their name is) the Wrightsoft numbers have been the closest to actual experience.

Yes Dmaceld, by oversized I mean anything greater than 0% or greater than reality. Even 10% is a huge error for a commercial building. Perhaps less critical for a typical residential home, but not insignificant. Otherwise, I pretty much agree with everything you wrote. Wrightsoft is better than most and I believe they now even have an ASHRAE RTS method module although I can't say how well it works.

Often times heat gain/loss analysis accuracy is more about how well the person doing the analysis works than about how well the software tool works. We have seen plenty of examples of badly done heat gain/loss analyses accomplished using otherwise good software. I am not sure what you mean by "experience"? I only trust an actual follow-up energy usage analysis for determining how well the heat gain/loss analysis agrees with reality...and we PE stamp all the analyses we accomplish. Of course by then, if the heat gain/loss analysis was not accurate, there isn't a whole lot you can really do about it other than learn from it...

Again, we are really much more interested in knowing the ICF hourly heat flow rate characteristics relative to our other building heat transfer mechanisms (e.g., HVAC system, solar heating, etc.) so we may better design a more fully integrated building.

What percentage of the heat loss from a typical residence is influenced by the r-values of the walls? My sense is that it is something on the order of 20%, maybe less. That means that the roof and ceiling insulation, the windows, floors and of course, infiltration all have much greater effects. Therefore, even a 50% "error" in calculating the walls results in a 10% error on the whole structure or less. That shouldn't really affect the entire load much.

Individual room calculations might be more affected, but then again, having too much window area, or poor windows on the north, for example, might be the biggest culprit in a heating error.

dmacled - is the actual living area 2000 square feet?

Sailawayrb, I agree 10% for a commercial building would be a serious miscalculation, except I would think that a small 10 person office building is going to more difficult to nail down closely than a 1000 person multi-story office building. The larger the building the more predictable will be the overall usage and variations caused by individuals will be of lesser influence. I can clearly understand the value of an hour by hour load profile for a large building, particularly when you are evaluating the loads of north vs south vs east vs west facing interiors, or when you are calculating in heat generating activities in one part of the building and you are designing a system to move heat from one portion of a building to another.

I think maybe in this forum it would be best to distinguish between residences and commercial buildings when discussing HVAC calculations. Commercial building calculations are going to be much more complex than residential.

In that regard what about DOE-II, I think it is, or whatever the current version is? Are you using it, have used it, or what? Or is that the basis for the software you are using? I'm just wondering. I looked at it a few years ago, and tried it out, but for my needs for my one house it was way overkill. Kind of like using a Mack truck to haul sand for a kid's sandbox! Have you used HEED? I used it to get an hour by hour temperature and load profile for my house. IIRC, at its core it is a Manual J program but the profiles were interesting to look at and consider.

By experience I mean observing the temperature of the house, the outdoor temps, and hearing the heat pump run, for the 5 years since building the house.

I note your reference, in an earlier post, to exothermic reaction of concrete. I believe I saw the effect of that in my garage. I can't be absolutely sure, but as I recall my garage, which is normally unheated, took less time to warm up during the first winter after building the house than it has the last couple of winters. The first winter it dropped to only about 55F in a time of steady outdoor temps under 10F when not heated. Since then it has dropped to below 50F for a similar outdoor temp profile.

Posted By FBBP on 29 Dec 2014 10:40 PM
dmacled - is the actual living area 2000 square feet?

Inside the walls is 2037 sq ft. Based on exterior dimensions it's 2243 sq ft., not including garage. I just looked to see what I had on the blueprints.

Posted By ICFHybrid on 29 Dec 2014 09:45 PM
What percentage of the heat loss from a typical residence is influenced by the r-values of the walls? My sense is that it is something on the order of 20%, maybe less. That means that the roof and ceiling insulation, the windows, floors and of course, infiltration all have much greater effects. Therefore, even a 50% "error" in calculating the walls results in a 10% error on the whole structure or less. That shouldn't really affect the entire load much.

Individual room calculations might be more affected, but then again, having too much window area, or poor windows on the north, for example, might be the biggest culprit in a heating error.

I'd have to look at my HVAC calculation spreadsheets but I think your 20% number is a bit low, but what you are saying is the case. Wrightsoft, and HVAC Calc, will give a room by room calculations that account for the orientation of the house and the windows in the room. Because of those factors is why I always say to have COMPETENT HVAC contractor or consultant perform the calculations. The room by room variations also impact duct sizing and runs.

As far as where the errors are most likely to occur, I would say in the door and window figures, and in filtration & ventilation. I believe the wall numbers are probably going to be the ones that are the most accurate in the end.