29 AUG UPDATE: The Carbonator is now available. Visit sustainableengineering.co.nz/thecarbonator/ for a free download of the tool, to watch a recording of the webinar and download the slide deck.
It is a fact that a high-performance building almost always has higher embodied carbon emissions compared to a Code-minimum build of a similar type. Performing better invariably requires more materials. How does a designer optimise performance while minimising additional carbon emissions? Or compare alternate assemblies and components? The team at Sustainable Engineering Ltd wanted to find that sweet spot and that led us to develop an in-house tool that would do those calculations and guide good decisions.
We’re increasingly dealing with clients whose motivation for building better than Code is about reducing their overall impact on the planet. They want to do the right thing. This may be the most important motivating factor or it may sit alongside their desire for other Passive House benefits like comfort, or healthier living environments and low energy bills.
We wanted a simple LCA tool that compared embodied and operational carbon over the lifecycle of the building, so we built one. Using this tool, we’ve made incremental improvements and helped clients make good, informed design decisions. Our initial focus was on optimising insulation; now we’re also using our tool to help guide choices on different claddings, foundations types and refrigerants.
Over a large number of New Zealand projects, we’ve found that targeting Passive House performance is almost always better from the point of view of total carbon emissions over the life of the building compared to poorer performing choices. The exceptions prove the rule: occasionally very high embodied carbon insulations (think HCFC blown foams) installed at high R-values do not make sense when viewed from a carbon perspective, but those are very much outliers.
What The Carbonator is useful for
We’re pleased to see the massive interest in the public release of this tool but honestly I expect there are comparatively few people in Aotearoa that will end up using The Carbonator a lot, at least right now. They will all be confident users of PHPP who like mucking around in spreadsheets. Please note Sustainable Engineering has no plans to glam this tool up and release it commercially—we’re not software developers.
The Carbonator is not magic, the cute retro graphic notwithstanding. (Thanks, Pixabay).
To reiterate, The Carbonator is useful at the initial design stage, when you (and your client) need fast feedback on the total carbon implications of different material choices and quantities. It might take only 15 mins to model six variants, so long as all the elements are already defined. That’s super quick compared to other tools we use [see sidebar].
Once initial design decisions are locked in, clients can choose to invest in more detailed modelling. In the detailed design stage, we’ll switch to LCAQuick to produce detailed and reliable data about the project’s total carbon. This requires data from a quantity surveyor, real quantities that take into account wastage as well. This is the two stage process we followed when consulting on the Fletcher Living LowCO project, for example.
It’s horses for courses. You could in theory use LCAQuick at the initial design stage to investigate multiple scenarios for each product choice, but good luck finding a client that is happy to pay for all the time that would take—the QS as well as engineers/consultants. The Carbonator will provide (almost) instant results for some parameters and it’s pretty quick and simple to load new material data too.
How The Carbonator works
You open both the completed PHPP file and the Carbonator in Excel and fill in the options in The Carbonator. Assuming your construction elements are already pre-loaded from an earlier project, select the relevant elements from the drop-down menus and you’re pretty much done if you are using the defaults.
How the software pieces work together
Users can add novel construction elements and save them for future reference. You build the elements up by adding in all the constituent parts eg for a wall assembly. Your version of the tool will become more useful to your practice over time if you invest a small amount of time in populating it with data relevant to you.
It’s really fast and easy to get results when all the elements you are comparing are already loaded. And it produces a graph in the format that MBIE has suggested in their embodied carbon technical guidance, as you can see in the image above.
A real-life example could be the excellent question of whether your project should specify double or triple-glazing from a life cycle carbon perspective. With our relatively clean grid does the additional savings in operational energy offset the additional embodied carbon? To compare these you need to account for the additional embodied carbon to manufacture more glass and extra frame material to support three panes of glass—but the building will need less energy for heating and cooling so operational carbon will be less, for every year the building exists. Which option produces the least total carbon emissions? The Carbonator, estimates of quantities, EPD data and your PHPP model will answer that question.
Limitations
Of course there are limitations. The Carbonator only accounts for what you tell it to account for; for instance, you must remember to tell it there is concrete in your concrete slab! It also doesn’t account for wastage factors or the implications of transport from factory gate to site. Finally, Sustainable Engineering won’t be providing free support for users of this software. (You can book some consulting time with us if you genuinely want to get to grips with it and need some help to get started.)
What sits under the bonnet
Any carbon analysis rests on suppliers and manufacturers’ environmental product declarations, EPDs. Every single one of these is probably a PhD’s worth of original research. An EPD provides the impacts for a unit of the product (a ‘badness factor’) across the life cycle of the product. Thus an EPD in the carbon section might say, 1 m3 of H1.2 framing timber produces 180 kgCO2-eq in Stage A, none in Stage B, 300 kgCO2-eq in Stage C, -60 kgCO2-eq in Stage D and sequester 875 kgCO2-eq as biogenic carbon.
This graphic was produced by MBIE to illustrate the whole of life embodied carbon assessment. It was included in its Technical Methodology paper, released in 2022.
Because the EPD has done all of this difficult science and maths to develop these factors, they enable a simple calculation. Multiply the quantity used of a specific material by that material’s Badness Factor, to produce a number that quantifies its impact on the environment. Note that for these purposes we are only looking at the associated carbon emissions equivalents (the kgCO2-eq). It’s reasonably simple maths but it’s tiresome and The Carbonator automates it.
No, Badness Factor is not an official thing, I made it up and it’s stuck in our team’s conversations about carbon emissions. It cuts to the point. (And yes, a positive Badness Factor is a possibility, carbon storage is an example.)
How much you use x Badness Factor = this much impact on the planet
Do note that not all EPDs are created equal and that’s because context is everything. Aluminium has a lot less embodied carbon when it’s manufactured here using New Zealand’s comparatively clean electricity grid, compared to what’s manufactured in other countries where the grid is fired by coal. I welcomed the news that BRANZ and Masterspec are developing a national online resource of carbon data for construction materials and products. We want to use tools that draw from vetted reliable EPDs and this project will help with that. For now, our team pulls in EPDs from LCAQuick or manually adds ones we have reviewed.
Then The Carbonator uses the amounts of materials in the constructions and the different stages of emissions to calculate the carbon emitted from the embodied elements and the operational carbon from energy, water and replacement / maintenance to estimate the full life cycle carbon, as illustrated in this graph from MBIE. The green bars are energy and water, the carbon emissions associated with operating the building. While embodied carbon loads bookend the building’s life, it’s important to note the little spikes that regularly reoccur as components need replacing or repair (carpet, 15 years? Long run roofing, 28 years?). At end of life it’s assumed all components are recycled or sent to landfill.
MBIE Building for Climate Change Framework: Whole-of-Life Embodied Carbon Emissions Reduction Framework.
Understanding the process vs learning software
I learnt engineering by way of formulas and theories. I could generate results but had to show my workings and understand how I got there. Increasingly professionals of all types are relying on black box software that provides a result but zero insight into how that result was arrived at. One of the things I love about the PHPP spreadsheet is that using it teaches you building science. You can see what’s going on as you change inputs. The Carbonator is like that too, building it and using it taught our team how the calculations are done.
Most carbon calculation tools [see sidebar] are designed to be quick and easy to use and to reduce or eliminate the chance of user error. The methods used to produce results and the assumptions they make are typically not visible to the end user. Nothing in life is free: such a tool might be easy to use, but it won’t teach you the mechanics or help you identify when you need to vary the process. You’ll just end up trained to use the software, not in how the calculations work. We like and use LCAQuick for instance but the data is locked. You can’t add new information and you can’t see under the bonnet to learn from what it does.
The Carbonator uses an element-based approach, which will be familiar to users of the High-Performance Construction Details handbook. At the time I was working on that, we anticipated MBIE would only require consideration of stage A of the life cycle (from cradle to completion of construction). After consultation MBIE recommended considering the whole lifecycle, from stages A to D. That’s more complete but means we can’t just use the numbers on embodied carbon from the handbook, we have to add in the other life cycle stages. We can use The Carbonator to do that.We spent a lot of time revising The Carbonator to align with MBIE’s guidance about carbon calculations. You’ll recall our view that 90 years is the most suitable life span for a building … but that we fell in behind the short 50 year period MBIE decided on. The Carbonator produces a graph in the form MBIE wants to see, and which it advised would be required in the Building Code as part of the rollout of the Building For Climate Change programme. That was important work that I fear is being shelved right now thanks to a change in government priorities.
Other LCA tools
BRANZ LCAQuick
This is one of our favourites and our go-to during detail design, when the clients want (and will pay for) more precise answers about the CO2 impacts of the materials and design they have committed to. We still need to enter wastage and consider transport.
BRANZ CO₂NSTRUCT
This only has cradle to construction stages complete but it is good for assessing these early stages.
NZGBC HECC
This is only used as part of Homestar rating submissions. It’s easy to use and does look at all the stages but it’s locked down and not very flexible.
Actually
This is quick and integrated with the energy model. Only catch is, at time of writing, it hasn’t been released. (Full disclosure: Sustainable Engineering has been working on the energy model portion of the code.)
eTool and One Click LCA
These are popular commercial software programmes but we haven’t had any experience with them.