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Comparing operational carbon emissions to embodied carbon emissions.

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Patrick Donnelly
Associate Principal, Director of Sustainable Design
Integrus Architecture
LEEDuser Basic Member
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Here is a fundamental question regarding measuring operational carbon emissions that I'm sure many of you can clarify for me:  Let's say you are considering design options and you want to know the relative contribution of GWP of adding an additional inch of continuous insulation to the building envelope.  The GWP from embodied carbon will increase, but the GWP from operational carbon emissions will decrease.  I would think it is essential in this calculation to use source energy for the operational carbon emissions, as there really is no equivalent "site" energy for embodied carbon.  Have I got that right?

Thank you!

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Luke Leung
Principal
Skidmore, Owings & Merrill LLP
LEEDuser Basic Member
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Thu, 05/20/2021 - 18:01

Good to hear from others.   The metric should be "Whole Life Carbon" since the embodied carbon for more insulation, a smaller HVAC system, and less refrigerant should be accounted for, including the emboded carbon for maintenance, replacement, end of life etc. of a smaller HVAC system for the 60 years of study.   Operation energy/carbon likely lowered.

Thu, 05/20/2021 - 18:56

Luke – I agree, the holistic focus is appropriate, and carbon is a nice metric as it can span these disparate sources. We’ve been working and improving a holistic carbon tool (something for a future SDL show and tell) – more at this point for whole project benchmarking than comparing specific design cases, but was just talking about that this morning – and have found refrigerant leakage, while measurable, tending to be small compared to operational and embodied carbon impacts. But I realize this is based on assumptions, and currently using the default LEED refrigerant calculation loss assumptions as our basis. To answer Patrick’s question, I double-checked our methodology. We’ve been using EIA published factors for onsite combustion of fossil fuels, and for electricity, EGRID regional factors – unless the project has a different and more appropriate carbon factor. As I understand it, the lbs/kWh factors are inherently scaled to delivered (site) electricity, but your question made me realize their methodology description wasn’t entirely clear, so thought I’d ask this group to be sure. In fact, when I looked more closely at the EIA’s methodology, it said their factor for electrical generation was based on “gross generation: The total amount of electric energy produced by generating units and measured at the generating terminal in kilowatthours (kWh) or megawatthours (MWh).” So, not quite site energy, since its measured at the plant, but my understanding is that electrical delivery losses are small (~7%) compared to the thermal losses (factor around 3x what is delivered) that really drives the differential between site and source energy for electricity. So, maybe my carbon factors needed to be tweaked by 7% (or whatever appropriate factor) to represent the carbon per delivered site kWh, but these EIA factors already seem to have compensated for the majority of source to site losses since they are for generated energy. Did that make sense? Folk agree? Chris Flint Chatto AIA, LEED AP BD+C Principal ZGF ARCHITECTS LLP T 503.863.2324 E chris.chatto@zgf.com 1223 SW Washington Street, Suite 200 Portland, OR 97205 From: Luke Leung

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