Dirty grid woes and the overshadowing of embodied carbon

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Hi all,

I’m in the process of wrapping up an early phase carbon study of a high performance mass timber/concrete hybrid high rise building. There has been a lot of emphasis on designing low carbon facade and structural systems on this project.

The preliminary results are fascinating. All the embodied carbon savings compared to a business-as-usual concrete high-rise get surpassed by the operational carbon savings in year 5 of operations.

These types of situations make it very challenging to keep low embodied carbon features in a building design with the cost premium that they come with. For example, the low carbon aluminum option in the window wall assembly is a $1.5/gsf premium. While this feature demonstrates almost a 25% carbon reduction on the total enclosure design, holistically, it’s a drop in the bucket across the life cycle of the building.

How have others approached this?

Thanks !
Scott

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Hi Scott, the way we look at it is where can we have the biggest levers?

In this case, with operational carbon being so intensive, it sounds like it might make more sense to focus on operational improvements rather than spending more on a lower carbon option for the façade.

The other thing we try to keep in mind is when the carbon is going to be emitted - in this case, since you’ll see operational carbon emissions outpace embodied carbon savings within 5 years, again, it sounds like operational carbon would be a good target to spend money to reduce. Especially since this building will continue to keep emitting for years and years to come. If it took 60 years to match the embodied carbon reductions, I’d focus more on the embodied side.

Only caveat - you might want to check your operational emissions against the cambium long range marginal emission data sets. Cambium | Energy Analysis | NREL

Combining that data set with an 8760 model from your energy modeler, you can get a rough idea of how the building will perform as the grid shifts to a cleaner grid. I don’t imagine this will have enough effect over the first few years, but it helps give a better long term picture.

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Hi @jschwartzhoff,

Thanks for the response! I wholeheartedly agree with focusing efforts on biggest impact.

It is a challenging tight rope to walk, as I know how important embodied carbon is, so it pains me to suggest focusing elsewhere.

My operational carbon emissions analysis starts with todays current grid emissions (914 lb/MWh) but implements a linear grid cleaning scenario of zero by 2050. There is no policy in place to enforce this, but it is the state’s goal.

It would be interesting to expand the analysis to look at operational emissions on an hourly time scale using Cambrium’s data set, but we aren’t quite there yet.

Thanks again,
Scott

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Glad to help. Your approach seems reasonable, and at worst, it’s overly generous to near term emissions given that there’s no policy to enforce the change which means the grid might be really dirty!

On the embodied vs operational carbon - any near term carbon emissions that we can avoid from the atmosphere helps, no matter where it originates. it’s great you’re looking at them both. Good luck with the reductions.

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Hi Scott, I wonder how the embodied carbon avoided impacts would look against a clean grid (mostly renewable) scenario and if it’s the proportion of total carbon, or the actual amount that is in question here. If the proportion was more like 50% over 60 years (like some diagrams show to illustrate time value) would the case be more clear? The benchmarking efforts for embodied carbon would help here to determine how the project is doing compared to similar projects’ CUI and evaluate it in isolation (which I think has value).

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Hi Lara,

It would be interesting to change the grid performance and recalculate for fun. That would be a simple test. What wouldn’t be so straightforward is what would this building look like in Seattle or California, since the design/climate/etc would be drastically different and influence things holistically.

I’d also like to see the updated CLF benchmarking report for comparison! This project, for structure + enclosures only is 288 kgCO2e/m2 (proposed) vs 340 kgCOe/m2 (BAU). Next steps are to evaluate interiors and MEP.

Scott

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There are a number of options but I’ll start with renewables. The analyses I’ve presented in the past using Cambium data show on-site renewables as one of the larger measures which can be implemented to reduce operational carbon emissions when you’re in a dirty grid. They quite simply have a larger impact in a dirtier grid region than one with more renewables—this is more evident at the hourly timescale.

And I’ll throw out that we don’t have a great methodology to compare the day 0 upfront embodied carbon vs the years of future emissions to trade that off against. You’d have to set up a discount rate but the calculation begins to morph into the absurd as with a theoretical carbon free grid you can’t justify any added materials which might result in lower operational emissions.

I’d stick with reducing the initial A1-5 as much as possible within budget and tackle B1, B6 and B7 separately. That sounds weird from the guy who preaches avoiding sub-optimization but here we’re talking about measuring everything and then tackling them—even though some are interlinked.

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Hi @JamyBacchus,

I’ve found similar, focusing on on-site renewables makes sense in dirty grid conditions, even with future grid cleaning scenarios considered. That said, with small footprint high-rise, you just don’t have the space to generate energy efficiently. I’m not fully convinced building-integrated PV is the answer either, since generation is curbed at 90 degree tilt. Though east/west 90 degree tilt PV could help cover energy use when the grid is more carbon intense… I’d want to compare the up front embodied carbon and use Cambrium data for this, but EPDs are few and far between.

Regarding day 0 vs future emissions - are you talking about Time Value of Carbon? The concept of carbon cut today (embodied) is more valuable than carbon cut over time (operational)? If so, do you have a method for calculating that compounding factor if you wanted to compare day 1 savings vs the same amount of savings spread out over 5-10 years?

Appreciate the thoughts !
Scott

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Hey! it’s exactly these sorts of comparisons that, years ago, we built our free tool EPIC to handle. Many of the paramaters dscribed here - a few different grid projections from Cambium (High Cost Renewable Energy, Mid-Case, and 95% Decarbonization by 2045), embodied carbon emissions from solar PV (from the peer-reviewed literature), solar energy production (straight from NREL!) - are included in the model

I 100% agree with your basic premise, Scott. The biggest whole life carbon hot spot is typically operational emissions. But once you electrify and increase efficiency (plus solar if it makes sense regionally), the next hot spot is embodied carbon in structure and envelope, after that its embodied carbon in interiors and MEP, then refrigerants, etc. etc. This isn’t to say that it’s a fool’s errand to address embodied carbon in structure/envelope, but that emissions reductions need to be target the biggest hot spots first (as you indicate) and then keep pushing on the next obstacle, and the one after that, so on and so forth.

In Chicago (where your profile says you’re located), I see the following patterns. Here, I’m assuming a combined structural and envelope carbon intensity of 288 kgCO2e/m2. I’m excluding interiors, MEP, and refrigerants from the scope of analysis (but it can be included as well!); assumption of a baseline EUI of 72 kBtu/sf/yr and 40% of energy from onsite fossil fuels; savings assessed in 2030.

  • Rapid grid decarbonization:
    • 2030 operational emissions savings from electrification: -48 kgCO2e/m2
    • 2030 operational emissions savings from 20% EUI reduction: -106 kgCO2e/m2
    • 2030 operational emissions savings from 1kW solar per 1000 sf: -157 kgCO2e/m2
    • Embodied carbon savings: -52 kgCO2e/m2
  • Slow grid decarbonization:
    • 2030 operational emissions savings from electrification: -44 kgCO2e/m2
    • 2030 operational emissions savings from 20% EUI reduction: -112 kgCO2e/m2
    • 2030 operational emissions savings from 1kW solar per 1000 sf: -167 kgCO2e/m2
    • Embodied carbon savings: -52 kgCO2e/m2

This confirms many of the points raised on this thread:

  • Solar is a great choice on dirty grids!
  • Efficiency is always classy :]
  • Electrification is important for all kinds of reasons (health, wellness, supporting the transition) but it gives a lower net carbon savings on a very dirty grid.
  • Generally, these conclusions are robust for a range of Illinois-specific grid decarbonization scenarios

But as soon I commit to these three measures (solar, electrification, and a lil bit of efficiency), ~90% of the remaining emissions before 2030 come from embodied carbon. This is why, as I see it, the answer to “is operational or embodied emissions more important” needs to be “yes and yes!” - taking a strategic aaproach on every project to ensure that we are first targeting the most impactful reductions, then chasing the hot spots as far as we can!

If you want to chat re: setting up this kind of analysis in EPIC, I’m happy to help! DMs are open.

A postscript re: BIPV - we did this at Boulder Commons and it was a big hit! One of the factors on the projects that really made it work was that there was a railroad easement behind the site to ensure that the panels were unshaded.

I also have a Python workflow for hourly emissions from now til 2050 using time series data from Cambium. Happy to share or talk methods!

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Hi Jack,

I appreciate the response and your optimism!

Unfortunately, our analysis isn’t quite showing the same results you suggest. We aren’t using Cambrium data (yet), but we are assuming a decarbonizing grid (to zero) between now and 2050 (despite there being any policy to support it in the state this project is in).

Any way you cut it, starting with 900+ lb co2 per 1 MWh generated is going to heavily influence the building’s carbon emissions, even with an aggressive grid cleaning scenario. It is just such a high starting amount… We actually found total lower operational emissions using gas fired equipment (using EPA’s gas emissions factor) for space heating and dhw for the first 20 years of operation. Fully electrifying on day 1 resulted in more carbon emissions for the first 20 years of operating. Would love to be wrong about this!

I think I would actually move refrigerant up on your list of hot spots. Considering VRF is on so many projects and can leak up to 10% of its R410A charge annually, can result in a substantial amount of ghg emissions. Check out MEP 2040’s refrigerant impact calculator if you haven’t yet: https://www.refrigerantimpact.org/.

What is your starting grid emissions factor for your example? Agreed that on-site solar during the first 20 years of operating would be huge, but small foot print high-rise doesn’t really support that strategy. Would love to have access to large scale community solar, but we aren’t there yet either. How is electrification giving you lower net carbon if the grid is very dirty? It would be the opposite.

Thanks,
Scott

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Ah cool! Here’s a graph of the Cambium data behind our analysis. This is mid-case, but you can toggle between the different scenarios in the NREL Scenario Viewer:

Screenshot 2023-10-05 at 9.25.59 PM
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You’re 100% right that on a kWh for kWh basis, the electrical grid is dirtier than natural gas burned on site, but there are a few other wrinkles when considering the emissions savings from electrification. We consider all these in our models–and do so as a result of our expert review process–but definitely always open to other approaches as well -

  • When we count emissions from natural gas combusted on site, we also factor in upstream methane leakage of 2.4% (on-site and in transmission). This is, in one sense, to align our emissions calculations for natural gas with those for materials (all upstream) and electricity (which, in Cambium, counts ‘precombustion’ emissions). It’s also probably a very conservative estimate - I’ve seen papers that cite gas leakage incurred by demand as high as ~5%. When a building electrifies, we are also no longer counting leakage incurred by demand for natural gas. So that’s part of what we see in our model.

  • The other thing we consider that makes a difference is that generating 1000 kBtu of heat from fossil sources can be done much more efficiently w/ all-electric equipment. Our models assume a COP of 2 which, again, is relatively conservative. So our assumption of electrification is that it carries a moderate efficiency boost as well (not many people out there electrifying with resistance heat, save for situations with a high-performance envelope and no need for cooling). So this will also affect our model results for electrification, but it’s a relatively minor effect. Here’s the cleanest explanation of this (which I’m sure you already know, but others might not) from the EnergyStar Source Energy Technical Reference:

Screenshot 2023-10-05 at 9.40.01 PM
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On the topic of refrigerants - you’re probably right, yeah. Some of the authors of the tool you mentioned help review the inclusion of refrigerant emissions in our models - results can be staggering : ( Your point re: VRF comes up on our projects often - the system is still the best solution in some situations, but we can’t (yet!) use R-32 as a replacement for R-410A in California. No perfect answer there …

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@jackrusk
I appreciate the follow up and all the data you’ve been sharing. I would love to sit down sometime and hash this out.

I understand you need to make some generalizations in your assumptions for your tool to work at a large scale, but that results in some limitations when you are looking at unique cases.

At our project scale, in this cold of a climate, it is incredibly difficult and very very costly to use heat pumps for centralized space heating and domestic hot water. An all electric option would perform fairly poor both from a carbon and cost perspective with the current technology and market limitations. You can see this in your table with the last column showing the comparison for electric resistance heat. Geo always comes up, but you can’t get enough load out of the ground for high-rise density with the site footprint available.

Love the added premium on upstream leakage for gas, I’m going to include this in our analysis. Do you know if the typical e-grid emissions numbers (from the EPA tool or NREL or Cambrium) include distribution losses?

Agreed re: VRF, it most often can be the best option due to its energy efficiency. That said, lack of low gwp refrigerant options in the US is a big issue for whole building carbon emissions.

Scott

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I’ve been following this with great interest. In my opinion, any carbon reduction right now is a good carbon reduction, so mass timber is a positive. Could we do more? Can we optimize carbon reductions for cost? Yes, but finding carbon reductions that align with clients goals so they actually are built is critical, and it’s very possible that Mass Timber resonates with this client in a way that electrification does not.

Here are a few minor points to add, things to consider re: electrification.

  • In 10-25 years, when low-carbon design is standard and very possibly required for existing buildings in this area, the transition away from fossil fuels will be expensive to upgrade service, rebuild mechanical rooms, and change system types. An all-electric building will hedge against that.
  • Over half of the electricity in the US is in areas where laws and commitments are for 100% (or 90%) renewable energy by 2050 or earlier. Driving up demand now likely means utilities are induced to build more renewables earlier. Chicago/ComEd are woefully behind from what I’ve read, but power is often traded across state lines, so adjacent greening should help. Cambium takes these effects into account I believe.
  • JLL is suggesting that low-carbon office space (not sure if this is an office or not) rents at a premium now. While they don’t define low-carbon, I would guess that fossil fuel free is part of it. https://www.us.jll.com/en/trends-and-insights/research/soaring-demand-for-low-carbon-offices-will-outstrip-supply.
  • Fossil fuels on site create local air pollution. A CFD analysis can show which people in nearby places will be breathing in the pollutants.

-Kjell

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Hi @Kjell_Anderson !

I appreciate you chiming in. I was curious to hear your thoughts :). And thank you for letting me bounce some envelope calcs off you behind the scenes.

I’m finally seeing some of our clients and developers see the value in reducing carbon, which is awesome. But just like with energy efficiency measures, they are looking for the best returns possible. Have you had any success using the social cost of carbon as an additional leverage item?

Would I love to see mass timber on every project (generally speaking), heck yes! But if it’s between mass timber and Passive House level operational performance in the Midwest due to limited funds, I’m pushing for the operational carbon reductions, based on these findings.

In this case, mass timber was a priority to this development’s mission, so there was no selling to do, but these results have me thinking hard about it for other projects.

Luckily PHIUS requires project to be all electric-ready, so space and capacity is being planned for so that this project can switch over in 15-20 years, which seems to be the best carbon case based on the results.

Thanks for sharing the JLL reference! Fascinating. And point taken on gas burning, while it likely isn’t affecting the building residents (this is multifamily), it is still impacting the community.

I think I’m most coming away from this thinking harder about biogenic carbon and where the line gets drawn. Should the design/development be penalized for what could happen to the timber 60 years from now?

Thanks,
Scott

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My opinion on biogenic carbon for mass timber structure – which is not backed up by standards at all – is that IF we haven’t figured out a carbon-conscious end of life for wood in 60 years (2083! 33 years after we are a ‘carbon neutral’ society) we have entirely failed in climate action and a bit of rotting wood is not the biggest worry we have.

For 10-year life cycle biogenic carbon materials we should consider the end of life as potentially being released back into the atmosphere. We could account for the carbon value of storage during this 10-year period, but this is another rabbit hole.

We’ve proposed a more transactional LCA where we focus on what we have agency over right now. It is imperfect but may help us make carbon smart decisions.

-Kjell

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@Kjell_Anderson Agreed wholeheartedly. Thanks for sharing those biogenic perspectives!

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One more thought: Do we generally agree that new buildings, in bulk, induce new electrical generation capacity? Do we agree that nearly all new generation capacity is renewable energy in the US (currently it’s mostly renewable energy + coal to gas conversions)? If so, one conclusion is that new buildings (and especially all-electric new buildings) contribute to the build-out of the cleaner grid.

It’s not a strong argument, though.

-Kjell

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Kjell,
I’m following your logic and I’d generally agree. I think gas being better in certain areas for the next 10-20 years is more of a devils advocate position. It isn’t anything I’d come out of the gate proposing.
Thanks,
Scott