Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

Is Appendix G becoming irrelevant?

asked 2019-01-11 10:00:21 -0600

Jim Dirkes gravatar image

Dear modeling colleagues, I'm looking down the road a bit and it looks like this: ASHRAE 90.1 is becoming more restrictive and detailed with every new version. It regulates an ever greater number of design aspects. Pretty soon, it seems there will be very little incentive to go beyond the ever-increasing mandatory minimums for the vast majority of projects. As the baseline becomes more restrictive, the room for improvement becomes less or at least the ROI is poor. Does this sound correct? Am I missing something?

On a related note, there appears to be no option for demonstrating compliance without meeting all the mandatory minimums for "U" value, SHGC, EER, etc. ie, a particular building, in its uniqueness, may comply or exceed compliance when using less than the mandatory minimums - but that seems not to be an option. If it was an option, one could creatively attempt to reduce construction cost while maintaining low energy cost. (Am I correct that "mandatory" always is mandatory?)

edit retag flag offensive close merge delete



As long as there are architects that want window to wall ratios greater than 40%, there will be a demand for Appendix G calculations. I think there is still a generous amount of freedom in HVAC system type, daylighting design, massing, and controls to still meet Appendix G while not meeting some mandatory minimums. And based on the way 90.1 is set up, there will always be HVAC equipment on the market that is more efficient than the mandatory minimum. Trading off HVAC efficiency for higher glazing ratios will be with us for some time.

mdahlhausen gravatar imagemdahlhausen ( 2019-01-11 11:53:48 -0600 )edit

That makes sense. It seems, though, that the vast majority of buildings DON"T use > 40% WWR and will most likely just apply the prescriptive requirements and call it "done". Creativity and thoughtful analysis are, if that's true, not encouraged. Another aspect is that making prescriptive requirements applicable to the incredibly broad range of user requirements, climates and technologies is essentially an impossible task. Attempting that impossible task seems to be what ASHRAE is doing since there is no alternative path to meeting the prescriptions.

Jim Dirkes gravatar imageJim Dirkes ( 2019-01-13 17:36:55 -0600 )edit

If, for example, I can demonstrate better-than-baseline while NOT meeting all the prescriptive requirements, why not?

Jim Dirkes gravatar imageJim Dirkes ( 2019-01-13 17:37:32 -0600 )edit

I can't tell if you might be confusing 'prescriptive' with 'mandatory' in that last comment. Prescriptive requirements don't need to be met under one of the performance paths.

I'd also slightly disagree with your premise, or maybe just reword it. To me 90.1 is becoming more strict (as in more energy efficient, which is it's purpose), but not more restrictive. In my experience I don't think this has made it harder to comply with each new edition. That was also a main purpose of the newest update which solidifies the baseline, and will just adjust the compliance percentage in the future.

bbrannon4 gravatar imagebbrannon4 ( 2019-01-13 21:49:01 -0600 )edit

I am equating "prescriptive" and "mandatory". I'll use "mandatory" going forward. Probably I can simplify my concern by saying that: - Too much "mandatory" presumes that the standards writers can anticipate everything in sufficient detail to define a minimum ( and no one can anticipate everything) - I'd much rather see the standard allow EITHER meet / beat the Baseline OR meet / beat the mandatory requirements

Jim Dirkes gravatar imageJim Dirkes ( 2019-01-14 08:19:58 -0600 )edit

1 Answer

Sort by » oldest newest most voted

answered 2019-01-14 12:02:02 -0600

luisclv gravatar image

Mandatory elements in sections ending in X.4 are always required, but other sections can be traded-off.

I think that you may be confused about the difference between the prescriptive path requirements, and mandatory requirements that have to be met if you follow the performance path for compliance. In ASHRAE 90.1-2016 § 5 (related to the envelope construction) the mandatory provisions (§5.4) do not specify mandatory U-values, but rather items related to the construction and testing of materials for the envelope. Table 5.5-X can always be a trade-off.

§ 6.4 related to the mandatory provisions for HVAC, it also does not specify mandatory EER values, but items related to minimum acceptable performance and the conditions systems should operate and be controlled. For example, if you read §6.2.2 you will find:

Projects using the Energy Cost Budget Method (see Section 11 of this standard) must comply with Section 6.4, the mandatory provisions of this section, as a portion of that compliance path.

Meaning that you cannot have, for example, a 12 SEER Air cooled AC sized to less than 65 kBTU/h. However, I have found that the minimum requirements are still pretty low compared to the equipment currently in the marker. This half ton split AC has a SEER of 17 and is fairly inexpensive.

Similar situations happen with §7 (Hot Water) and §8 (Electric power), where the mandatory requirements dictate control strategies and operation conditions.

§9 (lighting) and §10 (Misc equipment) do have hard ceilings for the power that these applications can use, but in my opinion this is the area where manufacturers are being pushed to improve technologies. In my experience, most architects would not push to have 1000 W of incandescent lighting instead of 100W of LED.

In summary, I think that there still opportunity to take a lot of trade-offs in your design, but the Code is becoming more stringent in aspects that are difficult to model accurately (like lighting control based on actual occupancy).

edit flag offensive delete link more


Trying to summarize: 1. We MUST comply with all of the x.4 sections. This covers: * Envelope constructions, min. full & part load SHW, HVAC and "OTHER" efficiencies, voltage drop & receptacle control, lighting controls and exterior lighting power. In addition: 2. the envelope MUST meet 5.5 or what appears to be a very onerous trade-off 5.6 method (Thanks for flagging me; I never saw the alternative method :previously) 3. Lighting power MUST be pretty close to LED levels

That feels like 90+% of the energy use is mandated as minimum requirements. Thus....

Jim Dirkes gravatar imageJim Dirkes ( 2019-01-14 13:27:40 -0600 )edit

... ti seems that creativity is squelched because we're trying to manage only 10% and there is precious little incentive to go through all the effort. Standard 209 is encouraging early design modeling, which I highly favor, but I doubt it will get much traction when the designer can just "plug and play" the mandatory minimums. I'm discouraged.

Jim Dirkes gravatar imageJim Dirkes ( 2019-01-14 13:30:11 -0600 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer


Question Tools

1 follower


Asked: 2019-01-11 10:00:21 -0600

Seen: 102 times

Last updated: Jan 14