Posted By sailawayrb on 06 Jan 2015 09:34 AM
Interesting Craigtoo, you managed to find the one issue with the program that I mentioned previously:

“The only issue that I am currently aware of that causes the program any grief is if the total conventional heat flow and the total thermal mass heat flow end up being contrary total heat flows (i.e., one is heat gain and the other is heat loss). When this happens, the program would calculate a negative effective R-value, which of course would not have any rational meaning. So if this happens, the program just reports the effective R-value as “Unknown” and one would have to take a close look at the hour-by-hour report-out to better understand this. BTW, I recently added hour-by-hour effective R-value report-outs to help folks better understand what is happening real time. These hour-by-hour effective R-value report-outs are NOT used for anything other than this increased understanding. Thus far, I have not found an outdoor temp profile that has caused this issue to occur.”

Presumably, both the total conventional heat flow and the total thermal mass heat flow are small and of opposite signs causing the program not to know what “goodness” is for this condition (i.e., is reduced heat gain or reduced heat loss “goodness”) and therefore unable to determine the effective R-value?

The best advice I could provide at this moment would be to use the conventional R-value when this "Unknown" situation occurs. I would also suggest that you use Weather Spark to create an actual daily outdoor temp profile for your location that perhaps might not have this issue.

Thanks Sail...!

I had read your post which you've referenced above.

I downloaded genuine temp data for my area and it worked well.  Much more reasonable data.  It appears that if you input wide outdoor temperature swings where the average of that swing is close to your desired indoor temperature target the situation with contrary heat flows appears.  Which makes sense. 

The use of more reasonable (and legitimate) data from WeatherSpark gave more meaningful results. "You can't make chicken salad out of chicken &#$^"

Now, can we change the green color to more of a Clemson Orange? 

I am very happy to hear that worked for you Craigtoo! Yes, your understanding of how this issue occurs is both real and correct. If we don't know what "goodness" is with regard to the desired heat flow, we can't say if the ICF is behaving good or bad...

Hmmmm...Clemson Orange...you do know that I am a UT gal...

I see a possible problem of convincing the local building department that all of this data is valid. I've heard of some places not recognizing mini-splits as a valid heating system, for instance. I printed out all of my data from HVAC-Calc in case they argue about the efficacy of my envelope and HVAC system. Code requires that you have a heating system capable of maintaining 68 degrees F., and if you look at my set-up with an uneducated eye, it doesn't look possible. ICF and mini-splits are still rare around here, but luckily, our inspectors aren't very fussy.

Yes, most good inspectors will always verify that you used the required indoor/outdoor design temps and reasonable R-values, infiltration values, and areas. Inspectors may likely give you a harder time if you are not one the HVAC pros that they have developed a good working relationship.

We PE stamp all of our heat gain/loss analyses and we have never had any issues with inspectors accepting a more flexible and realistic HVAC engineering analysis. In short, we are not limited to only submitting analysis data from some well recognized HVAC software program (e.g., we have substantiated significantly derating the normally required heating/cooling capacity of a HVAC system on the basis that the building had additional/redundant heating/cooling capacity, allowing the reduced capacity HVAC system to operate more efficiently than it normally would). So I would fully expect that we will also be able to successfully substantiate derating the normally required heating/cooling capacity of a HVAC system on a similar higher ICF effective R-value basis.

Of course, we would never submit data nor perform a HVAC engineering analysis based on data that we could not substantiate was entirely valid and appropriate for the actual building design and location. So while we are licensed to properly engineer an integrated HVAC system, like inspectors, we are equally obligated and responsible for upholding the public welfare.