I am thinking about using ICF in Phoenix area because the thermal mass will allow it to out perform standard stick built. However, I hear that ICF companies often claim a higher effective R-value than you actually get. How can I accurately determine the effective ICF R-value so I may accurately determine the cooling and heat load? I will be a owner builder and I want to understand everything well before doing anything dumb.

Posted By icfbound on 22 Dec 2014 07:48 PM
I am thinking about using ICF in Phoenix area because the thermal mass will allow it to out perform standard stick built. However, I hear that ICF companies often claim a higher effective R-value than you actually get. How can I accurately determine the effective ICF R-value so I may accurately determine the cooling and heat load? I will be a owner builder and I want to understand everything well before doing anything dumb.

The True R-Value of an ICF block like Nudura (2.5" EPS x 6" concrete x 2.5" EPS) is around R-23. Since there is no thermal bridging in ICF this is a true # of the wall R-Value.

Now here is where the location of the build plays a role into what they call the "dynamic benefit for mass systems" or DBMS:

ORNL DBMS Study

The studies show that climates like the desert southwest (Phoenix) and the south (Miami) worked best for ICF. The claim is that the R-23 ICF walls can perform as high as a R-30 through R-50 wall due to the thermal mass and air tightness that comes with ICF walls.

ORNL and ASHRAE Study - Manual J

One must also not overlook the other advantages of ICF vs wood frame:

• Fire protection rating of 2-4 hours
• No air infiltration through a solid ICF wall
• No wall cavities for rodents, bugs, mold or rot
• Better sound barrier to stop exterior noises - STC 51 Rating
• Termite and rodent resistant
  
• Greater strength - ability to withstand 150 mph winds and airborne debris
• Will stand the test of time (look at the 1,000+ year old man-made structures, they are masonry/concrete)
  

Hi icfbound.
We are building our ICF home in the Phoenix area right now, also Owner Builders. We are happy to share all kind of information and show you our home. Send me a private message with your email address and I'll send you our address.

ICFBound, you might want to try exercising our free DIYer ICF performance software:

Borst ICF Performance Software

I have pasted an excerpt from our software instructions that addresses this subject with regard to our experience:

“ICF typically consists of 2.5 inch thick EPS forms which are filled with 6 inch thick reinforced concrete which results in a thermal mass that is sandwiched between the exterior and interior insulated forms which are left in place after the concrete pour. ICF companies often claim exaggerated ICF “effective” R-value performance based on the thermal mass characteristics of ICF. 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).

So while a given ICF design may provide increased R-value performance over a low thermal mass wall for a given outdoor temperature profile and some period of time, a given ICF design may also provide decreased R-value performance for another outdoor temperature profile. Given that not many climates have a constant outdoor temperature profile; it can be very challenging to design ICF such that it actually provides equal or better performance than low thermal mass walls. However, ICF provides other benefits that often make it the right wall assembly choice for energy efficient buildings (e.g., increased fire resistance, increased structural life, increased structural strength, reduced inherent infiltration, reduced outdoor noise transmission, and thermal mass characteristics that can be successfully designed and better integrated with passive solar heated buildings).”

One can’t really discuss this subject without first defining “conventional R-value” and “thermal mass effective R-value”. Again, I will plagiarize by pasting some more excerpts from our software instructions:

“Conventional R-value (Degrees F-Hour-Square Feet/BTU) - This is the ICF total R-value when the individual R-values for all the materials used in the ICF are simply summed as is conventionally done. Please see our Heat Loss Analysis Calculator for more information about how this conventional R-value is determined. Changing the concrete thickness/R-value and the insulation thickness/R-value may significantly change this output parameter.”

“Total Conventional Heat Flow (BTU/Day-Square Feet) - This is the total heat flow between the building interior and the outdoor temperature that occurs during the 24 hour analysis period. This output parameter is determined by multiplying the inverse of the Conventional R-value output parameter by the difference between the Indoor Temp HVAC Set Point and Outdoor Temp Profile input parameters and by using finite element time/temperature numerical differentiation/integration analysis as is conventionally done. The total daily building heat gain/loss may be determined by multiplying this output parameter by the exposed ICF wall total square foot area. The average hourly building heat gain/loss rate may then be determined dividing this value by 24 hours. Changing the indoor temperature HVAC set point, the outdoor temperature profile, the concrete thickness/R-value and the insulation thickness/R-value may significantly change this output parameter.”

“Total Thermal Mass Heat Flow (BTU/Day-Square Feet) - This is the total heat flow between the building interior and the thermal mass that occurs during the 24 hour analysis period. This output parameter is determined by multiplying the inverse of the sum of the Interior Insulation R-value per Inch and Concrete R-value per Inch input parameters by the difference between the Indoor Temp HVAC Set Point input parameter and Thermal Mass Temp output parameter and by using finite element time/temperature numerical differentiation/integration analysis. The total daily building heat gain/loss may be determined by multiplying this output parameter by the exposed ICF wall total square foot area. The average hourly building heat gain/loss rate may then be determined dividing this value by 24 hours. Changing the indoor temperature HVAC set point, the outdoor temperature profile, the concrete thickness/R-value, the insulation thickness/R-value, and the thickness ratio of the interior/exterior insulation may significantly change this output parameter.”

“Thermal Mass Effective R-value (Degrees F-Hour-Square Feet/BTU) - This is the ICF effective R-value when the temperature profile of the concrete thermal mass material in the center of the ICF is considered. This effective R-value is determined by multiplying the Conventional R-value output parameter by the ratio of the Total Conventional Heat Flow and Total Thermal Mass Heat Flow output parameters. Changing the indoor temperature HVAC set point, the outdoor temperature profile, the concrete thickness/R-value, the insulation thickness/R-value, and the thickness ratio of the interior/exterior insulation may significantly change this output parameter.”

For a standard 2.5” EPS + 6” Concrete + 2.5” EPS ICF design that would have a conventional R-value of R23.10, in our southern OR diurnal climate (which is as good as it gets for maximizing ICF performance), our effective R-value during Spring, Summer, Fall and Winter would be R23.30, R21.89, R18.92 and R23.36, respectively. This only translates to an average effective R-value of R21.87 which is less than the conventional R-value of R23.10.

As you can see and learn by exercising our ICF performance software, it is certainly possible to achieve significantly higher effective R-value by changing the ICF design parameters to optimize the performance for a given outdoor temp profile. It is easy to achieve effective ICF R-values well in excess of twice the conventional ICF R-value, but only for the specific outdoor temperature profile that the ICF design parameters were optimized. I suspect that this is what some ICF companies advertise, but you will likely only be able to achieve it for some very brief moment in time and perhaps pay a performance penalty for much of the other time.

You will note, my rambling focuses purely on R-value and does NOT attempt to “factor in” infiltration rates of one assembly versus another. It is certainly true that ICF can be accomplished so as to have significantly less infiltration than a stick built building, however, that isn’t always guaranteed or always true either.

How can I accurately determine the effective ICF R-value so I may accurately determine the cooling and heat load?

Use R-23 and round your heating and cooling needs down if it comes out close to a choice. Make sure you add all the additional factors like air layers, wall coverings and siding. And, make sure you use more accurate air infiltration estimates instead the old rule-of-thumbs.

If you want to split the hair finer, use R-30 and don't round your equipment down. I wouldn't go beyond that without a much more sophisticated analysis of your home.

My ICF home is performing better than the projections.

Lbear is correct. The eps r value on nudura and fox is roughly R-22. The problem is it's misleading because the (R-value) should not be used for marketing. The newer software sure helps a lot. You can download the rescheck software from doe and play with it. Real world example your ice box aka refrigerator. It has a r value of maybe 6 but keeps ice frozen. It does this by air infiltration. Open the door and warmer air causes it to melt, same principle in a house. You can build a passive house out of wood, how ever it takes lots of tricks to get it done. Getting an Icf house that tight takes tricks also, but just not much on the walls itself. It's the openings and the roof part of the envelope to get it sealed up. I've built big Icf homes with 40's hers scores and wood frames with mid 50's hers but it takes the system to work together. Air sealing is very important on top of thermal mass. The thermal mass really shines when it gets cooler and or cold. When it's 50's outside and 75 inside you only have 25 degree split. Same thing goes at 100 outside and 75 inside. When its zero outside and 75 its a huge benefit. 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. To me it's a no brainier, but in the end ICF isn't fit for everyone's budget. We all wish it was. Concrete structures last, well a really long time. These wood frame homes are ok, but were starting to see a bunch of them starting to fall apart from the rush of 05-08. Mostly bad flashing details and no one paying attention to details. All about time is money and who is responsible for the weatherization of the home. Framer, stucco contractor, roofer or the builder who signed the permit.... Well you get the just of it.. Sorry to get off topic a bit.

Take a look at this previous discussion here on ICF home HVAC sizing:

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/4/aft/82806/afv/topic/Default.aspx

Within that link is a link to software specifically designed for ICF home HVAC sizing; although, it currently appears to be out of stock.

Work with a competent HVAC consultant and/or contractor who uses software such as Wrightsoft to do heating/cooling calculations. Wrightsoft includes design parameters for ICF. In my experience of one house the WS calculations have proven to be quite close to actual loads. Another thing I would STRONGLY suggest is you use a heating/cooling system with a wide performance range so it's output will match the actual real time load of the house. I have a Daikin heat pump system. It uses a variable speed compressor so heating and cooling output varies in line with the heating/cooling load. Such a system can compensate quite well if you happen to oversize the system, or if the heat pump capacity requirement varies significantly between heating and cooling.

NOTE: Heating and cooling calculations absolutely is the one area of house construction you DO NOT want to tackle if you are not experienced in doing so. There is too much at risk, with comfort needs trumping money savings by a long way. There is nothing wrong with using programs as mentioned above to get a feel for the system size requirements, and to provide a confidence factor in the contractor recommendations, but if you don't do such calculations on a regular basis let the HVAC consultant or contractor do it. Give real consideration to a split process, i.e., use a consultant to design the system, and have a contractor install per design.

Also, there is a lot more to proper system design than just picking a heat pump or furnace/AC unit with a capacity large enough for the whole house. A good designer will calculate heat/cool loads on a room by room basis and size the ducting accordingly. The north side of the house has different loads than the south side, and the east is different from the west, especially when you start factoring in windows. And pay attention to windows, doors, and infiltrations. On a per unit of area basis those three have much greater impacts than does wall configuration.

As the ORNL DBMS study shows, it is the dynamic outdoor temp profile that determines the dynamic thermal mass temp (i.e., the temp of the ICF concrete core) for ICF. It is the real time difference between the building interior temp and the thermal mass temp (i.e., NOT the outdoor temp) that then determines the interior building heat transfer rate and hence the real time effective R-value for ICF. So one can’t say that ICF has a single effective R-value and that this value is always greater than what the conventional static R-value calculation would indicate. Dmaceld is correct that you need a HVAC system that can efficiently deal with variable loads, but that is pretty much always the case and not ICF dependent.

As a point of illustration, think about what happens when the outdoor temp does not change for a couple of days. In this case the effective R-value would become identically the same as the conventional R-value, 23.10. There are also times when the thermal mass temp is such that it is adding or removing either less heat or perhaps even moving heat in the direction contrary to what is desired and this causes the effective R-value to be lower than the conventional R-value at this time. There are also times when the thermal mass temp is such that it is adding or removing more heat as is desired and this causes the effective R-value to be higher than the conventional R-value at this time...and these are the times and the effective R-values that the ICF companies advertise and that we would prefer occurred most of the time...but one might want to run their actual numbers...

If you are using software that doesn’t require you to enter your dynamic seasonal outdoor hourly temp profiles into the software, the software is likely just using some average effective R-value based on your zip code that hopefully has some basis of validity. Unless you actually measure your hourly indoor, outdoor and thermal mass temps (or perform an existing building energy usage study), you don't really know your actual real time or average effective R-value. Most folks like to know what their building assembly R-value will be before they construct the building and size the HVAC system.

Posted By sailawayrb on 22 Dec 2014 11:30 PM

“Conventional R-value (Degrees F-Hour-Square Feet/BTU) - This is the ICF total R-value when the individual R-values for all the materials used in the ICF are simply summed as is conventionally done. Please see our Heat Loss Analysis Calculator for more information about how this conventional R-value is determined. Changing the concrete thickness/R-value and the insulation thickness/R-value may significantly change this output parameter.”

“Total Conventional Heat Flow (BTU/Day-Square Feet) - This is the total heat flow between the building interior and the outdoor temperature that occurs during the 24 hour analysis period. This output parameter is determined by multiplying the inverse of the Conventional R-value output parameter by the difference between the Indoor Temp HVAC Set Point and Outdoor Temp Profile input parameters and by using finite element time/temperature numerical differentiation/integration analysis as is conventionally done. The total daily building heat gain/loss may be determined by multiplying this output parameter by the exposed ICF wall total square foot area. The average hourly building heat gain/loss rate may then be determined dividing this value by 24 hours. Changing the indoor temperature HVAC set point, the outdoor temperature profile, the concrete thickness/R-value and the insulation thickness/R-value may significantly change this output parameter.”

“Total Thermal Mass Heat Flow (BTU/Day-Square Feet) - This is the total heat flow between the building interior and the thermal mass that occurs during the 24 hour analysis period. This output parameter is determined by multiplying the inverse of the sum of the Interior Insulation R-value per Inch and Concrete R-value per Inch input parameters by the difference between the Indoor Temp HVAC Set Point input parameter and Thermal Mass Temp output parameter and by using finite element time/temperature numerical differentiation/integration analysis. The total daily building heat gain/loss may be determined by multiplying this output parameter by the exposed ICF wall total square foot area. The average hourly building heat gain/loss rate may then be determined dividing this value by 24 hours. Changing the indoor temperature HVAC set point, the outdoor temperature profile, the concrete thickness/R-value, the insulation thickness/R-value, and the thickness ratio of the interior/exterior insulation may significantly change this output parameter.”

“Thermal Mass Effective R-value (Degrees F-Hour-Square Feet/BTU) - This is the ICF effective R-value when the temperature profile of the concrete thermal mass material in the center of the ICF is considered. This effective R-value is determined by multiplying the Conventional R-value output parameter by the ratio of the Total Conventional Heat Flow and Total Thermal Mass Heat Flow output parameters. Changing the indoor temperature HVAC set point, the outdoor temperature profile, the concrete thickness/R-value, the insulation thickness/R-value, and the thickness ratio of the interior/exterior insulation may significantly change this output parameter.”

For a standard 2.5” EPS + 6” Concrete + 2.5” EPS ICF design that would have a conventional R-value of R23.10, in our southern OR diurnal climate (which is as good as it gets for maximizing ICF performance), our effective R-value during Spring, Summer, Fall and Winter would be R23.30, R21.89, R18.92 and R23.36, respectively. This only translates to an average effective R-value of R21.87 which is less than the conventional R-value of R23.10.

Maybe I'm missing it, but I don't see anywhere in this discussion where the thermal lag of the concrete mass is considered in the calculation of effective R value.

The effective R values you calculated above don't really seem to jive with reality.  None of the numbers show any significant benefit over the base R value at any time of the year.  For a typical R23 ICF wall in the Summer, it has an effective R value of only R21.89?  And in the Fall it has an effective R value of only R18.92?  Really?   Those numbers don't pass my sanity check.

Sorry, I didn't discuss the details of the thermal mass (concrete) time lag. I only discussed the thermal mass (concrete) temp. It is of course this thermal mass time lag effect that governs how high mass assemblies such as ICF perform. The software uses the concrete mass (as determined from the entered concrete density and thickness) and the entered concrete specific heat capacity to determine the thermal mass heat absorption capability (i.e., the fundamental physics that cause the thermal mass time lag effect) and hence the resulting real time thermal mass temp that determines the real time effective R-value as previously described. This calculator exercises the fundamental heat transfer equations that govern this ICF thermodynamic system at a 0.01 hour (i.e., a 0.6 minute or 36 second) sampling rate over a period of four, twenty four hour days using finite element time/temperature numerical differentiation/integration analysis. Running the analysis over a four day period ensures that any error associated with the initial assumed thermal mass (i.e., concrete) temperature estimate becomes insignificant by allowing the daily thermal mass temperature profile to stabilize with the daily repeating indoor/outdoor temp profiles. The software output parameters are based on the fourth day of analysis data.

True, however, the other two seasonal effective R-values are above the conventional R-value! That was really my point...what you might expect based on ICF company claims is NOT reality. And unless you actually measure your hourly indoor, outdoor and thermal mass temps (or perform an existing building energy usage study), you don't really know your actual real time or average effective R-value.

Maybe I am oversimplifying it but the ICF basically moderates the vast diurnal exterior temperature swings. So if it is 95F in the daytime and then it drops to 55F at nighttime. The ICF mass wall will be slower to react to the temperature changes. A similar principle applies to passive solar techniques and exposed mass concrete floors. Therefore the interior temperatures of the home are moderated/slowed and don't react as quickly to the changing exterior temperatures.

The one "drawback" is if you let the interior temperature drop down to low (winter) or too high (summer), it will take longer to bring the interior temps to whatever you view is comfortable (65F-75F). One will have to run the heat or A/C at a longer interval to bring the home back to "comfortable" range. This is where occupant habits and preferences come into play.

If the homeowners are "active" and participate in things like operating window shades & opening windows at night/closing them in the AM, this is another factor where ICF will bring you more bang for the buck in terms of energy savings. It's not "necessary" to do so in an ICF/mass home but it will work better than the "set it and forget it" inactive occupant/homeowner.

I know some people who are too lazy to open the shades in winter to let in free heat from the sun.

Yes, all of what you describe Lbear is certainly true...especially the lazy part! This is one of the problems in determining the real time and average effective R-value, namely that the effective R-value will vary significantly if the indoor temp HVAC set point is changed. However, if you don't use the same indoor set point for BOTH the conventional and effective R-value determination, you are comparing R-value apples and oranges as the conventional R-value is largery unaffected by the indoor temp HVAC set point.

Posted By sailawayrb on 23 Dec 2014 12:54 PM
Yes, all of what you describe Lbear is certainly true...especially the lazy part! This is one of the problems in determining the real time and average effective R-value, namely that the effective R-value will vary significantly if the indoor temp HVAC set point is changed. However, if you don't use the same indoor set point for BOTH the conventional and effective R-value determination, you are comparing R-value apples and oranges as the conventional R-value is largery unaffected by the indoor temp HVAC set point.

Yes, I believe this is WHY it is been difficult to get a final resolution on the great "ICF debate" and how DBMS plays into the effective R-Value.

Scientific studies require a constant/control to have accurate and uncorrupted findings (I am not a scientist but I did stay at a Holiday Inn Express).

The problem with ICF is the constant is not always constant because of homeowner habits. I believe ICF works best and has the best energy results when the occupants of the home are interactive and do things to help work with the ICF mass wall. This would include allowing for a wider temperature swing inside of the home from AM to PM. Opening and closing of windows and operating of window shades. The biggest being allowing for wider temp swings in the home from morning to night. The "set it and forget it" homeowner mentality will not see the highest ROI for ICF in terms of energy usage.

My interior comfort range is from 67F - 78F for winter and summer. As long as the interior temps hover in the range, I can get by without heat and A/C. That's a good 11 degree range and it doesn't work for some people.
 

Yes, accurately testing a completed ICF building is indeed a very challenging endeavor for the reasons you indicated. However, doing a computer analysis where you can keep the required parameters constant (e.g., like indoor temp) to allow an apples/apples comparison is a relatively straight forward and trivial endeavor...assuming that you believe in the heat transfer physics and you don't make some dumb mistake with the software coding... There are always people who don't understand and don't believe in scientific/engineering methods that you will never convince. That's okay because good scientists/engineers are not in a faith based business where the ratio of believers to non-believers has any real significance. Good scientists/engineers merely present what they believe are valid data and defend the data until a credible case is made proving the data is not valid. So I stand by the previously presented data and the associated conclusions...at least until someone points out a dumb mistake that I made in the software code when implementing the 100+ year proven/accepted heat transfer equations...LOL!

BTW, I live in an ICF home (and I have lived in ICF homes since 1972 when I was a middle school student in Munich, Germany where my dad was an architect for 6 years)...so I love ICF construction too and have a strong bias for ICF construction! However, the truth must always be sought out and should never be feared... We have measured the hourly concrete temp and BOTH this absolute temp value and the temp time lag is consistent with our software.

Posted By sailawayrb on 23 Dec 2014 03:48 PM
Yes, accurately testing a completed ICF building is indeed a very challenging endeavor for the reasons you indicated. However, doing a computer analysis where you can keep the required parameters constant (e.g., like indoor temp) to allow an apples/apples comparison is a relatively straight forward and trivial endeavor...assuming that you believe in the heat transfer physics and you don't make some dumb mistake with the software coding...

Is it possible to create an algorithm that would take into account the thermal lag and occupant participation?

Well yes, the thermal mass (concrete) time lag is already addressed and properly accounted for as I previously explained to Arkie when he specifically asked about this.

Accounting for occupant participation (i.e., the "owner habits" you described) would be possible. The occupant participation would essentially require adding the capability to enter an indoor temp profile (i.e., like the outdoor temp profile). If an indoor temp profile was exercised, we could see what effect this has on the BOTH the conventional and thermal mass heat flow. However, we would somehow first need to correlate how the occupant participation affects the indoor door temp profile... I could certainly add the capability to enter an indoor temp profile if you would like to explore this more.

Thank you everyone. This is a lot info to read and learn from, but this is what I asked for :-) This is a great forum with lots of knowledgeable and helpful people.

Posted By Rafi on 22 Dec 2014 11:08 PM
Hi icfbound.
We are building our ICF home in the Phoenix area right now, also Owner Builders. We are happy to share all kind of information and show you our home. Send me a private message with your email address and I'll send you our address.

Thank you for this offer Rafi. As soon as I figure out how to PM you, I will do that.

icfbound: it should be easy to pm me: Just click on the little envelope you see at each "poster". Then a new window will open and the rest should be easy. When I do it, I get this error message: "Object reference not set to an instance of an object". I've googled the problem and it seems to relate with my program. Not sure how to fix it, but at least others can send me private messages. MERRY CHRISTMAS TO EVERYBODY IN THE FORUM!