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Is Appendix G becoming irrelevant?

asked 2019-01-11 10:00:21 -0500

Jim Dirkes's avatar

updated 2019-02-23 11:11:27 -0500

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?)

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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's avatar mdahlhausen  ( 2019-01-11 11:53:48 -0500 )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's avatar Jim Dirkes  ( 2019-01-13 17:36:55 -0500 )edit

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

Jim Dirkes's avatar Jim Dirkes  ( 2019-01-13 17:37:32 -0500 )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's avatar bbrannon4  ( 2019-01-13 21:49:01 -0500 )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's avatar Jim Dirkes  ( 2019-01-14 08:19:58 -0500 )edit

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answered 2019-01-14 12:02:02 -0500

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).

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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's avatar Jim Dirkes  ( 2019-01-14 13:27:40 -0500 )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's avatar Jim Dirkes  ( 2019-01-14 13:30:11 -0500 )edit

Jim, I disagree with the use of "MUST" for your #2 above. Maybe in practice, projects typically comply with the envelope in 5.5 in order to achieve the desired savings, but you don't have to if you can achieve the energy savings through a different part of the building. For example, the energy use of large buildings with a relatively small surface area to volume ratio typically isn't affected by the envelope construction since it is internal load dominated. In this case, you don't need to and probably shouldn't comply with 5.5 since money would be better spent on other systems.

anchapin's avatar anchapin  ( 2019-04-04 06:42:28 -0500 )edit

...and Joe Deringer, with whom I'm collaborating on a presentation and who teaches the 90.1 course for ASHRAE, agrees with YOU. I think I'm beginning to distinguish now between "prescriptive" and "mandatory". Can't say that the language is very clear in the Standard, but I'm happy to be proven wrong (in this case).

Jim Dirkes's avatar Jim Dirkes  ( 2019-04-04 07:00:32 -0500 )edit

There are two paths for code compliance, following the mandatory and prescriptive requirements of Sections 5-10 (Prescriptive Compliance) or follow Section 11 which requires the design meet Sections 5.4, 6.4, 7.4, 8.4, 9.4, and 10.4 (mandatory requirements only) and can use trade-offs for other items.

App G is an alternative to Section 11 that can be used to quantify performance beyond the 90.1 standard. App G also requires the design to meet the mandatory requirements only and can trade-off other items. Note that exterior lighting power is mandatory in 9.4 but interior isn't (part of 9.5).

anchapin's avatar anchapin  ( 2019-04-04 07:51:50 -0500 )edit

answered 2019-04-02 15:44:53 -0500

Not to hi-jack the thread, but we are undertaking a study currently comparing 90.1-2016 Appendix G results within the new LEEDv4.1 rating system and projects we have completed under 90.1-2010 Appendix G for LEEDv4. The results are not pretty.

A project which achieved 16 points in v4 is achieving 3 points in v4.1. That's with energy & carbon. This an office project, climate 4A, really great envelope, well designed shading, 50% lighting reductions, and decoupled DOAS + Air-source VRF. While the study is on-going and we are going to look at more project types & climates; I'm not real sure how I can 'sell' this to teams that 'hey, this is a great building, and you get no LEED points.' More projects will be going LEED prescriptive; which is fine, but isn't an energy model. And 'just add renewables' isnt a solution to every job.

Has anyone else done this study on their projects yet?

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ASHRAE 90.1-2016 is a lot more stringent than ASHRAE 90.1-2010. Do you have onsite generation? And are your "50% lighting reductions" versus 90.1-2010 or 90.1-2016?

mdahlhausen's avatar mdahlhausen  ( 2019-04-03 00:48:53 -0500 )edit

The building has a 90.1-2010 reduction of 27% (yes, it is not 50%, have 2 projects we're testing and fouled this detail between the two. Other project is still to be compared, but has a 60% reduction. ) Mia culpa on the flub.

Looking at 90.1-2016, this building has a 11% reduction. Verses a 90.1-2016 Appendix G LPD it has a 40% reduction. These are both pretty good reductions while maintaining lighting levels.

No on-site renewable on project. Owner did not want on-site and did not carry any budget. Still achieved a 47% reduction in v4.

dradair's avatar dradair  ( 2019-04-03 08:37:48 -0500 )edit

As the EUI goes down, plug load becomes a larger percentage of the energy use which is fixed between baseline and proposed. That makes it harder to get a greater % reduction without generating onsite energy. So an 11% reduction seems appropriate.

Also consider that some building codes are moving to net-zero as code in 5-10 years for commercial buildings, and LEED should be leading edge. 11% reduction versus 90.1-2016 isn't really innovative green design anymore, so the 3 LEED energy points seems appropriate. LEED Platinum should be NZE, and LEED Gold should be close to NZE. Get some PV.

mdahlhausen's avatar mdahlhausen  ( 2019-04-03 10:24:40 -0500 )edit

May have been a bit unclear - the 11% is only for lighting, it is 11% below 90.1-2016. The building is showing a 5% PCI / PCI_t reduction. For a building that achieves 47% below 90.1-2010 Appendix G that is a huge swing. If this is the intent, then this is more like "LEEDv5". Not some minor incremental update. I'd also be interested to know how/if USGBC did some studies to look at the impact with the percent-to-points table.

The building has an EUI of 42 kBTU/SF; 1/3 of that is plug/misc loads that is held constant. It's realistic for the building use. NZE? No. But good design? Yes.

dradair's avatar dradair  ( 2019-04-03 11:39:35 -0500 )edit

Also, 'get some PV' is fairly tart & doesn’t match reality on many projects. Project owners will & have balked at this on real projects. Whether its cost, or location (dense urban), or other. I’ve had had that happen, multiple projects. LEEDv4.1 also cut off-site credit significantly.

So, we do load reductions and HVAC studies to inform design. But certification is dismissed. Projects will quit pursing LEED if it does not match the realities of the AEC industry.

Thus, emphasizing Jim’s point of Appendix G may lose its relevancy as a ‘high performance’ standard if not careful.

dradair's avatar dradair  ( 2019-04-03 11:46:15 -0500 )edit

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Asked: 2019-01-11 10:00:21 -0500

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Last updated: Apr 02 '19