Green Star New Zealand: Removing GWP-stored for bio-based products

Green Star NZ has launched a new embodied carbon methodology – Green Star NZ – Embodied Carbon. This guideline acknowledges the importance of reducing both upfront carbon and whole-of-life embodied carbon emissions – from raw materials extraction right through to demolition and disposal. 

In this article, we highlight a new indicator – GWP-stored (GWP-s or GWPS) required to be removed for bio-based products in upfront carbon reporting. We plan to provide automated upfront carbon reporting for Green Star NZ which will be available in eTool at some point in the future. Meanwhile, we have proposed a method to help you calculate and report GWP-stored using our powerful All Impact Details spreadsheet generated from eTool.

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What is GWP-stored?

According to the Green star NZ Embodied Carbon Methodology (referenced by EN 15804:2012+A2:2019),

GWP-biogenic (GWP-b or GWPB) is Net of:

  • Carbon emissions from degradation of biomass via incineration, landfill, composting, or an accounting
    adjustment (reported as a positive number), and
  • Carbon removals through formation of biomass during photosynthesis (a negative number).

GWP-stored (GWP-s or GWPS) is:

  • GWP avoided by removals of CO2 into biomass from all sources except native forests. GWP-stored should be a negative number, as it is a removal of CO2 from the atmosphere.

Depending on the standard followed, GWP-total and GWP-biogenic may either include or exclude GWP-stored for products that contain stored biogenic carbon.

eTool – LCI Source V.17, V.18 and latest V.19 are aligning with EN15804 2019 A2 and reports GWP Biogenic separately, please refer to Separate Reporting for Biogenic Carbon. However, the GWP-Stored cannot be separated out from the LCI Source. GWP Biogenic is the Net GWP-B and there is no breakdown of emissions and removals.

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A method for calculating and reporting GWP-stored

At the moment, the best suggestion is to follow the calculation methodology from the NZGBC guidance as below:

You would need to calculate the GWP-stored manually for now. However, this manual calculation can be done easily using the All Impact Details. Below is a step-by-step calculation method:

Step 1: Download the ‘All Impact Details’ spreadsheet from your Design.

Step 2: Open the spreadsheet. In the ‘Environmental Pivot Table’ sheet, select the relevant fields such as GWP,  GWP F, GWP B and GWP L, Material Mass, Master Template Name, Module, and Element Process Name in the Pivot Table fields.

Step 3: Sort the elements/materials which have stored biogenic carbon in the “Element Process Name” fields before calculating the GWP-S 

Note that only modules A1-A3 should be selected for the material impact calculation. The waste impact during construction (module A5) is already included as the software automatically applies the construction waste factors when calculating the impact in modules A1-A3. There may still be a relatively small material impact of any products lost or damaged in transport that comes under model A4. However, its GWP-B and GWP-S would be considered insignificant as only a small amount of material quantity may be lost or damaged in transport and some of the impact would be emitted at the end of material life.

Step 4: In the ‘Environmental Pivot Table’ sheet, create additional fields including GWP S and GWP-total for Upfront Carbon.

After creating additional fields including GWP S and GWP-total for Upfront Carbon, you will be able to select these fields to add to report

In this example, GWP-S was calculated by multiplying Material Mass (A1-A3 only) with the formula provided in NZGBC guidance.

  • GWP S = MaterialMass*(1-0.1)*(0.5)*(-44/12)
  • GWP-total (Upfront Carbon) = GWP F + GWP L + (GWP B-GWP S), OR
  • GWP-total (Upfront Carbon) = GWP-total (as reported) – GWP S.

Please note that you would have to assume a % water content and biogenic carbon content based on the material if you don’t have this information. In EPDs following EN 15804+A2, there will be a statement of “Biogenic carbon content in product”. To convert this to GWP-stored, multiply by -44/12 to convert stored elemental carbon to equivalent carbon dioxide, according to NZGBC guidance.

As GWP-stored is a new indicator required for upfront carbon reporting, we are working on the most accurate way to capture the GWP-S and producing the Upfront Carbon Reporting for Green Star NZ. Watch this space!

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