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Performance based design annual energy cost

Sifu

Sifu

SAWHORSE
Joined
Sep 3, 2011
Messages
3,318
I am a little confused. The 2018 IECC (OK, the IECC always has me more than "a little confused") required a building to be equal to or less than the annual energy cost of the ref. design. The 2021 IECC requires it to be equal to or less than 80% of the ref. design. Unless I read that wrong, the 2021 requires a significant reduction in energy costs...but the "preamble" in the commentary to IECC section 407 says the building must be equal to or less than the ref. design. Given that the "preamble" is not code, it makes me wonder if I am misunderstanding this.

From the preamble:
The general procedure is to show that the annual energy cost for the proposed building is less than the annual energy cost of the standard reference design. The designer calculates the annual energy costs for two buildings: the proposed building and the standard reference design.
From the code: (407.2)
2. An annual energy cost that is less than or equal to 80 percent of the annual energy cost of the standard reference design.

To confuse me a little more, the original version of the 2021 IECC that I have listed it at 85%. The 80% is listed in the premium access "updated" code.

Am I misunderstanding this? I received a report today that shows the "anticipated annual energy cost savings for the proposed building is 10.4% less than the baseline building". I read this as it being 89.6% of the ref. design unless I am reading this wrong as well.
 
Oh wait, now I see. 2018 401.2 seems to be a scoping provision and says to follow one of three paths, the third is the performance option...I guess, because it includes 407 in the list of sections that must be followed, and it has a technical requirement in #3 for 85% of the design. So in the '18 I take the 85% code requirement from 401.2 #3, which tells me to comply with several sections, one of which is 407. 407.2 has another list of sections that must be complied with, which is similar but doesn't include itself, 401.2 or 408, and then 407.3 tells me the design only has to be less than or equal to the ref. design, not 85%. So you have to choose 401.2 #3 which is the performance method, but not called the performance method in 401.2, to get to 407 which is called the performance method throughout the code and is titled "Total Building Performance", but apparently not quite all of the performance method because by itself it only requires the building be less than or equal to the ref. design and is only part of the path, but 407.3 disagrees with the technical requirement in the scoping provision of 401.2 #3. We can't get to the 85% requirement from 407, because 401.2 isn't listed, but it's OK because we apparently can never get to 407 without 401.2 where the 85% requirement is.

So I guess the '18 had an 85% requirement, the first edition of the '21 had an 85% requirement, and the later edition of the '21 moved it 5% to 80%. I guess someone realized what a mess the '18 was and "fixed" it, except for the first edition which they apparently missed the major change of the 5% drop.

NOW I understand the IECC. Only a 5% reduction......I think.

Sorry, more of a rant than an answer to my own question I guess.
 
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