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Percent savings for a building optimized with an energy model

asked 2015-10-27 19:00:11 -0500

bjschmidly's avatar

updated 2015-10-28 08:58:53 -0500

What can a commercial building owner expect to save on his utility bills with a building (new construction) that was optimized with an energy model versus one that was built without one? I know the earlier you get an energy modeler on board the better = more savings, but is there a standard rule of thumb like 10-20% utility bills savings?

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answered 2015-10-28 09:54:57 -0500

updated 2015-10-28 10:06:24 -0500

DISCLAIMER: I'm assuming the owner cares about actual performance, not design performance...

I would tell the building owner that energy modeling alone will save him zero dollars. I would subsequently recommend he find a commissioning agent if he wants to save real $.

It really depends on the type of building, the energy modeling scope and who is creating the energy model. Most importantly, it depends on how the building is operated in the real world, outside of the simulation tool.

Unfortunately, I think an energy model has little impact on verified post-occupancy energy savings. While an energy model is a great tool for guiding the design team it does little to ensure that the design is properly executed and the building is operated efficiently. For example, I often find buildings touted to have "high performance" designs operating very poorly when retrocommissioning them because the systems are too complicated for the facility personal to operate properly.

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Very true. Just because a building is designed to perform well does not mean it will be operated as designed. Periodic (frequent? continuous?) commissioning is key.

__AmirRoth__'s avatar __AmirRoth__  ( 2015-10-28 10:52:14 -0500 )edit

Thanks, Lincoln. I guess I'm just trying to understand the business case for BEM. Is it regulatory/certification/group, i.e., AIA 2030, commitment that's driving it or is it a financial case? If it's the latter, what are the rules of thumbs for calculating ROI, NPV, etc., once you assume the building is/will be operated correctly.

bjschmidly's avatar bjschmidly  ( 2015-10-28 11:35:47 -0500 )edit

answered 2015-10-28 08:45:15 -0500

Great great question. I don't think there is a generally accepted answer, but maybe we can crowd-source one. My contribution will be to report on the data that we are seeing through the AIA 2030 Commitment (2014 progress report was just published, by the way, in case you want to dive deeper). First disclaimer: this is design performance. If firms do post-occupancy M&V, they are not reporting it. We will hopefully close that loop at some point in the near-ish future. Second disclaimer: projects that are not modeled are assigned performance levels that are typical of the prevailing energy-efficiency code for the building type.

That said, the benefit of modeling appears to be 20% at the low end. The reason I say low end is that this number includes a good number of projects that use modeling only for code-compliance or LEED points. We are not yet separating those projects cleanly from projects that use modeling to full effect, i.e., to inform design. We are also seeing a good number of modeled projects with energy savings of over 50%, including a fair number with savings of over 70%. Hard to imagine getting those kinds of savings without whole-building system-level analysis.

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Thank you, Amir. This is a very helpful response. Other than code-compliance and/or LEED points, and then there's the AIA 2030 Commitment, what's driving the up-tick in interest in BEM? Is it regulatory as is the case in California or is it post-occupancy M&V? If it's the latter, are you seeing this as a new revenue stream for architects or is LEED starting to mandate M&V to maintain certification?

bjschmidly's avatar bjschmidly  ( 2015-10-28 11:28:04 -0500 )edit

On the demand side, I think the drivers are the direct and indirect effects of regulation. Yes, some jurisdictions like California are directly mandating performance-path compliance. But more generally, more stringent codes are forcing folks to model in order to obtain beyond-code utility incentives. AIA 2030 Commitment is playing a role too. And maybe LEED has jumped up in adoption also. Don't know. On the supply side, there are simply more and easier to use tools out there, especially for the more advanced engines like EnergyPlus and ApacheSim.

__AmirRoth__'s avatar __AmirRoth__  ( 2015-10-28 12:06:25 -0500 )edit

Thanks, Amir. Greatly appreciate the follow-up answer...

bjschmidly's avatar bjschmidly  ( 2015-10-28 12:17:22 -0500 )edit

answered 2015-10-28 17:39:55 -0500

J's avatar

This depends completely on what you mean by 'optimized'. In my experience with mid-tier buildings in New Zealand the main impact of modeling the building is developers can actually get meaningful answers to questions like how much will I save if I change the glazing from X to Y or add in exhaust ventilation heat recovery. Again in my experience on the few projects I've worked on we hit 30%+ minimum savings over the initial business as usual plan. On the last project I did the results agreed with the model (which showed about 40% savings) too closely to be realistic. Had the interesting issue of explaining to the developer that the close agreement was just luck.

In New Zealand EECA (our local version of DOE) has started assisting with funding of the energy model but the real driver is making the accountants BELIEVE the results and then they are willing to invest in the building or increase the control system deadband etc. EECA targets 25% minimum as the cost-effective savings changes that need to be driven by the energy modeling to obtain their funding assistance.

Now if you meant optimizing the building to mean not changing equipment - changing controls / operations / settings than commissioning (perhaps informed with a model if it exists) would be the place to go. One of my associates claimed he just saved 50% - stupid building was running full tilt nearly 24/7! On one of the flash eco-buildings I was working on the commissioning agent found out the optimum start was not good and likely saved 5% in one winter evening.

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Here's an example to clarify 'optimization': A developer hires an architect to design a commercial office space for him in let's say Albuquerque, New Mexico. After finishing the design, the architect recommends a general contractor that goes out and builds it for the developer a year later with no energy modeling done. The utility bill on that building is 250,000kWh's a year x $.12/kWh = $30,000/year in energy charges. The peak demand is roughly 130kW's a month x $20/kW = $31,200 in demand charges. The total annual utility bill for this property is $61,200 a year.

bjschmidly's avatar bjschmidly  ( 2015-10-29 16:17:24 -0500 )edit

This is in comparison to an 'optimized' building through energy modeling with a goal of reducing the annual utility bill by 30%. Let's say the design and energy modeling team was successful in saving this amount and the new annual bill is $42,840/year. In addition, the extra cost to design and build this 'energy efficient' building was $200,000. Therefore, the annual savings are $18,360/year in utility bills divided into the $200,000 in extra costs for a 10.89 year simple packsack for the developer on a building with a 30-40 year useful life.

bjschmidly's avatar bjschmidly  ( 2015-10-29 16:26:27 -0500 )edit

This is what I had in mind when I referred to an 'optimized' building. I hope that makes sense. Thanks for your comments, too, by the way. They were great.

bjschmidly's avatar bjschmidly  ( 2015-10-29 16:27:09 -0500 )edit

Good. That a reasonable question and I can tell you that I'd be willing to promise 30% energy savings with less than 6 year simple payback in my market for optimizing a code-minimum building design. I'd target 40% in the model but would never promise more than 30%.

J's avatar J  ( 2015-10-29 18:50:10 -0500 )edit

Very good. Thank you. This is all very helpful/insightful.

bjschmidly's avatar bjschmidly  ( 2015-10-30 09:40:06 -0500 )edit

answered 2015-11-03 09:41:38 -0500

Archmage's avatar

I don't have any specific values for percent savings. But I think it useful to examine why doing modeling earlier is better. Building characteristics that have to do with form and fabric are harder to change as the design progresses and harder to change over the life of the building. Over time, controls, operation, and even HVAC systems will get changed, and although they are all very important to the utility bill they are also hard to model well. But things like design/geometry, windows, and insulation are more likely to remain fixed over the life of the building and fortunately have more robust modeling in BEM tools. I think the business case is stronger for form and fabric analyses, but the fraction of savings that can be attributed to those types of measures varies a lot across buildings.

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Asked: 2015-10-27 19:00:11 -0500

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Last updated: Nov 03 '15