COMcheck

[Sifu]

I have seen designers submit COMchecks with elements missing. For example, they leave off foundation perimeter and the program assumes there is no perimter to insulate and calculates it that way. Easy enough to figure out. I have one now where they include the perimeter, but do no insulate it at all. It isn't a small number at 1200' plus of perimeter. All other assemblies and data are striaght prescriptive so there are no trades. I would expect a poor result, yet the COMcheck exceeds code by 14%.

If that could be accurate then I can move on, but it doesn't seem like it should work out to a building that exceeds code by 14% so I am curious what some of the energy experts have to say. I have run my own test COMchecks/RESchecks before to test the system, and going straight prescriptive usually yields a passing score but I can't imagine it should work if the program understands there is 1200' of un-insulated slab.

 

[Yankee Chronicler]

I'm not an energy expert by any means, nor do I know the nuts-and-colts of the COMcheck algorithms. That said, I agree with you. My understanding is that COMcheck looks at satisfying (not exceeding) the minimum energy usage for a building, and alternative approaches (trade-offs) are measured against a prescriptive design as the baseline.

Knowing that, it certainly doesn't seem right that an otherwise straight prescriptive design that omits 1200 feet could even pass, let alone exceed the minimum by 14%.

You wrote that they left off the foundation perimeter so the program assumes there is no [foundation] perimeter to insulate. That's probably an accurate statement, but what happens if you include the 1200 feet of foundation and enter an insulation value of zero? That's the actual case, not a building with no foundation.

 

[Sifu]

I'm not an energy expert by any means, nor do I know the nuts-and-colts of the COMcheck algorithms. That said, I agree with you. My understanding is that COMcheck looks at satisfying (not exceeding) the minimum energy usage for a building, and alternative approaches (trade-offs) are measured against a prescriptive design as the baseline.

Knowing that, it certainly doesn't seem right that an otherwise straight prescriptive design that omits 1200 feet could even pass, let alone exceed the minimum by 14%.

You wrote that they left off the foundation perimeter so the program assumes there is no [foundation] perimeter to insulate. That's probably an accurate statement, but what happens if you include the 1200 feet of foundation and enter an insulation value of zero? That's the actual case, not a building with no foundation.

Maybe I didn't explain it well. The scenario is that they did include the 1200' with a value of zero. I only pointed out the other scenario because I have seen designers purposely leave it out to trick the system, but that isn't the case here. I don't get too wrapped up in the energy provisions. Show me the basics and I leave it alone. This one just doesn't pass the smell test.

 

[Yankee Chronicler]

You did explain it, I just read your post too quickly. My error -- apologies.

I don't have an answer. If everything is exactly to prescriptive values it should pass, but by closer to 1% than 14%. ( I think.)

 

[Sifu]

You did explain it, I just read your post too quickly. My error -- apologies.

I don't have an answer. If everything is exactly to prescriptive values it should pass, but by closer to 1% than 14%. ( I think.)

My thinking as well. I'll ask them to explain it. Hard to believe they want to have zero insulation at the slab, even if it works to min. code. Most every time I have seen an attempt to slip it by is because it was an existing condition, never on a new building.