PHIUS Senior Scientist Graham Wright is back this week, this time following up on a comment made to his One Cereal Aisle, Many Cereals post from last week. Reader Sarah Larsen (thanks Sarah!) asked about embodied carbon issues. The answer, we thought, deserved its own post, and we hope, discussion.
First, here’s Sarah’s comment:
Graham, thank you for such a thorough and thoughtful post. As a licensed architect, and CPHC I am already inclined toward the PHIUS methods, but continue to be curious about the nerdy differences, how, and why they came to be. I am also incredibly happy with the relationships being developed between PHIUS and code/regulatory agencies; it is critical that energy-efficient building practices spread beyond the geeky few.
With that said where is the EMBODIED CARBON calculation in our standards?? I can’t stress enough how important it is that we take this into consideration. There are PHIUS certified buildings being developed touting their energy and sustainable credentials who are using products with CO2e paybacks that will almost certainly never be met. We have just 10 years to get this right – a 90 year ROI is not going to cut it! I am very much afraid that if we develop code requirements with blinders on to anything but energy *consumption* we will have the reverse impact that we are working toward – climate catastrophe – by packing our buildings full of foam rather than thoughtfully balancing carbon footprint throughout a life-cycle assessment (LCA).
LCA has some growing up to do, but tools such as Tally are already making better, more broad-thinking choices available to anyone who cares. It is critical that leaders such as PHIUS be talking about embodied carbon and the up-front resource demands of our built environment. I think we could adapt Michael Pollan’s advice on eating as the best way to consume other resources: Build efficiently; not too much; use mostly plants.-– yours in climate-conscious building – Sarah Larsen
Now, back to Graham:
We are aware of the issue but feel we are not yet to the point where we can outright standardize, that is, make hard and fast rules. The Norwegian Institute for Zero Emission Buildings came up with some different definitions depending on how many building life cycle phases are included.
We can move more aggressively to put up some resources and guidelines. There are a couple of books I have found that seem to be helpful for making design decisions:
Most of the thinking I have seen focuses on materials, but I am not convinced that is a broad enough view of it. Suppose one uses low embodied carbon materials but this requires a lot of expensive skilled labor. The money paid for that fans out into the general fossil-powered economy, which has a certain emissions intensity per dollar, so there are emissions associated with all that economic activity, so maybe you don’t come out ahead.
From that point of view, low-cost construction is low-emission construction, and everyone is trying to do that already. I remember back in 2013 or so, the IEA or the EIA put up an interactive data browser that let you see what they were thinking in terms of scenarios to limit warming to 2 degrees C. It was clear that they were not counting on much of a contribution from the building sector. It’s pretty clear that the reason for this is that the turnover of the building stock is too slow, there just isn’t enough time anymore.
As I recall in their 2 C scenario for the U.S., almost half the total savings came from decarbonizing the generation of electricity. The “electrify everything” movement has strengthened since, Architecture 2030 seems to be on board with that, recognizing that anything done in new construction standards doesn’t do anything about the existing buildings, which is most of the problem within that next-ten-years window — so the priority is to stop emissions from existing buildings by electrifying. This is part of the reason we modified the overall energy criterion for PHIUS+ 2018 — it allows for off-site renewables now and that is compatible with the “electrify everything” idea. Some people, like ILFI, go even further and just ban all combustion from building operations.
But back to the embodied emissions. Here is an idea I had about how that might be written into a rule. Let’s call it PHIUS+ Equity & Carbon 😀
It would address both equity and embodied energy/emissions with adjustment to the Source energy limit based on construction budget, on the idea I mentioned above, that embodied energies/emissions are roughly indicated by how much money is being spent, along with the emissions intensity of the national economy.
The adjustment would be based on the idea of limiting the total operating + embodied, so, operating + embodied < 714+221 = 935 kWh/sf for example.
SE * 70 yr + $CB * NatkWh / NatGDP < 10.2 kWh/sf.yr * 70 yr + $170/sf * NatkWh / NatGDP
SE = modeled net source energy for the project [kWh/sf.yr] — about 10.2 kWh/sf.yr
$CB = project construction budget [$/sf] — about $170 /sf, U.S.
NatkWh = National source energy use [kWh] — about 29 trillion kWh, U.S.
NatGDP = National gross domestic product [$] — about 19 trillion USD
This is mathematically equivalent to adding a penalty for high-budget construction and a credit for low-budget construction, which is in the equitable direction, on a world wide basis even. The emissions intensity of the Indonesian economy is actually higher than the U.S., I make it out to be 0.44 kgCO2e / USD, while the U.S. is 0.29 kgCO2e/USD. But they catch a break with the above scheme because their cost of construction is a lot lower, about $60/sf instead of $170 for the U.S., so multiply those two numbers together and the Indonesian building industry is putting out 0.44×60 = 26 kgCO2e/sf while the U.S. building industry puts out 0.29×170 = 49 kg/sf.
I switched to carbon accounting for a minute there, but I still prefer source energy accounting. It’s a pretty good proxy for emissions because 80% of the primary energy is coming from fossil fuel burning, but I like that source energy penalizes nuclear for being nonrenewable, whereas straight carbon accounting gives it almost a free pass.
Solving the above equation for Source Energy criterion:
SE < 10.2 kWh/sf + [($170/sf – $CB) / 70 yr] * NatkWh / NatGDP
This would also tend to do a favor for retrofit projects if they are able to save construction cost by reusing the structure — and that is the high-embodied-emission part, for concrete and steel buildings, from a materials point of view. The $170/sf could be generalized to a national average value as well, $NatCB. For residential projects, just substitute for the 10.2 as 3840 kWh/person * ResOcc / iCFA.
Probably only the operating-energy part of it tapers to zero in future. More emphasis can be put on initial-cost/embodied-energy savings by shortening the time frame. At 20 years instead of 70 they are about equal in the initial example. This would favor retrofits even more.