Modeling the Proposed Design for Green Star

Life cycle assessment (LCA) is one of the most effective ways to evaluate how a building will impact the environment. According to EN 15978, the reduction in life cycle impacts of a building can be demonstrated through a comparative LCA. Nowadays, most of the “Green Building” rating schemes around the world have already integrated LCA into their credits and systems, acknowledging the value in understanding the whole-of-life impacts of the buildings which in turn can lead to better low carbon designs.

eTool is designed to meet the requirements of many international schemes and has been successfully utilised to improve the rating performance for many projects all over the world. In this article, we share some tricks and tips on how to effectively model a comparative LCA for building projects to meet Green Star requirements.

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What is a comparative LCA study?

Conducting a comparative LCA study for a building project following EN 15978 involves evaluating the environmental performance of different design options, encompassing various design strategies, materials, technologies, and construction methods. This approach empowers building stakeholders to make well-informed decisions, aiming to mitigate the environmental impact of construction projects and foster the adoption of sustainable building practices. For Green Star projects, a comparative LCA study is required where you will have to demonstrate the reduction of environmental impacts when the project building (Proposed Design) is compared to the reference building (Reference/BAU Design). Therefore, it is necessary to develop a Reference/BAU Design FIRST and get this design certified. After that, the Proposed Design can be modeled, incorporating improvement strategies to effectively illustrate the savings.

In eTool, it is necessary to model the Reference Design FIRST for Green Star projects. After that only can each improvement strategy be modeled in eTool to effectively demonstrate the savings leading up to the Proposed Design.

For more information about how to model Reference Design, please refer to this support post: Modelling Reference Design for Green Star.

Modeling Proposed Design

Before you start modeling your changes, you should scrutinise your design to identify ‘hot spot’ areas what require attention. Please refer to this support post for tips on how to do this.

It is important to have a well-organised list of improvement strategies before modelling them in the software. Any changes/updates of templates/elements in the improvements scenarios compared to the Reference design should be identified and recorded for your future references and third-party reviews. You can refer to this support post for modeling procedures.

Our Scenarios feature allows branching of design improvements for comparative LCA studies. Please refer to Modelling Design Scenarios – branching design improvement strategies for more information about using the “Scenarios” feature to model Proposed design.

In eTool, you can carry out a comparative LCA study in various stages of a building project. In doing so, you can create either different Structures to model design scenarios for each phase of the project (i.e. Concept Design, Preliminary Design, Detailed Design, Final Design, As Built phases) OR one Structure to model design scenarios and use Design Phase (Scenario Tree) feature to differentiate each phase of the project (see below). 

1/ Modelling Proposed design in different Structures for each phase

2/ Modelling Proposed design in one Structure and using Design Phase (Scenario Tree) feature to differentiate each phase

To select Design Phase, you can navigate to any Scenario in the Scenario Tree and click “Edit”. Under the “Design Phase” drop-off menu, you can now select a suitable phase and choose how you would like to implement this change. Don’t forget to click “Save”

There are two assessments for Green Star projects including Design Assessment (also referred as Design Review) and Certified Submission (also referred as As Built Submission) according to GBCA submission guidelines. Of which, the Design Assessment is aimed at projects early in the design development phase and is an optional assessment of progress to date. 

For Green Star projects, it is usually required to conduct two LCA assessments, one is for Design phase (e.g. Detailed design) and the other is for As Built phase. As such, you would have to model design scenarios for Design Assessment at the Design phase first. Then, if there are any design changes and/or updates for the Certified Submission, you would need to clone and update the model from Design phase to As Built phase. In this case, we recommend to model design scenarios in ONE Structure and use Design Phase (Scenario Tree) feature to differentiate each phase. Details are explained in the section below.

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Cloning & Updating Design Scenarios

There is no doubt that the design changes are unavoidable for any construction projects. For Green Star projects, LCA models usually need to be updated due to changes/updates in Materials and/or Operational Energy and Water. It is also important to note that certified designs are always locked from any further changes, therefore, you can not make direct updates. As such, the Cloning feature was developed to help you copy and update LCA models swiftly and seamlessly. There are several circumstances as below:

1/ Updating certified Reference/BAU design when Proposed Design has not yet been modelled and/or certified.

In this case, you can use the Scenarios feature to ‘clone’, update the design and resubmit for certification. This makes recording not only your design changes but also your improvement strategies later much easier. By using this way, we can also speed up the review process. The process is described below:

Step 1: Navigate to the “Add New” button in the Scenarios tab to Add New Scenario and click “Save”.

Step 2: Click the arrow button of the updated Reference/BAU scenario to Make Scenario Active by cloning the Reference/BAU and click “Save”.

Step 3: Make changes or update the design as required.

Step 4: Note that you will need to delete the current benchmark design in the Functions tab by selecting “None” as this new Reference/BAU is now the new benchmark. Don’t forget to click “Save”.

Step 5: Submit the new Reference/BAU design for certification before modelling Scenarios and Proposed design.

2/ Updating certified Reference/BAU design when Proposed Design have been modelled and/or certified (e.g. design changes/updates required, cloning LCA models of Design phase and updating them for As Built phase).

In this case, you would need to update both Reference and Proposed designs. There are two methods to update the LCA models. Whether the changes under consideration are minor or major, the responsibility of selecting the optimal approach ultimately lies with the study author. Either way, a step-by-step procedure is described below:

Method 1

Step 1: Clone the entire Scenario tree

Step 2: Update the new Reference design

We suggest that you rename the new Reference design to differentiate it with the previous one and avoid confusion.

Step 3: Submit the new Reference design for certification

For more information, please refer to this support post: Certify your design

Step 4: Update all Scenarios designs and Proposed design following the Reference design’s updates

It is important to note that when you clone the entire Scenario tree, the Scenario designs aren’t linked to each other. In other words, if you update the new Reference design, it won’t follow-through into the rest of the scenario design tree. This means that you’ll have to replicate all changes in every scenario design which has a higher chance for errors & rework.

You would also need to update the Benchmark Design for all Scenarios and Proposed designs. This is because when you clone the entire tree, the software does not automatically update the new Reference design as Benchmark Design for you.

Step 5: Submit the new Proposed design for certification

Method 2

Step1: Clone only Reference design

Step 2: Update the new Reference design

Step 3: Submit the new Reference design for certification

For more information, please refer to this support post: Certify your design

Step 4: Model Scenario designs and Proposed design from the new Reference design

For more information, please refer to this support post: Modelling Design Scenarios – branching design improvement strategies

Step 5: Submit the new Proposed design for certification

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Operational Energy and Water updates for LCA models in As Built phase

For GS projects, Operational Energy input is based on Green Star GHG calculator/Energy Modelling Report/NABERS reverse calculator while Operational Water input is based on Green Star Potable Water calculator. In the case that your Operational Energy and Water input has been changed for both Reference and Proposed designs in As Built phase, simply follow the above two methods to clone and update the LCA models accordingly.

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Material quantity updates for LCA models in As Built phase

We have recently received questions concerning the modelling approach for As Built phase, particularly in the case of material quantity updates. Should the material quantities be updated for both Reference and Proposed designs or only Proposed design? In this section, we share our current position on the modelling approach with regards to both previous and new GS guidelines.

For projects registered before December 2022 and following GS DAB and GS Interiors v1.1, v1.2, v1.3 guides

Based on our experience with GS projects, the GBCA may require your Proposed design to be compared with the Reference Design figures. So technically, any material changes at As Built phase (whether big or small) that are due to the design updates and not related to improvement strategies should be updated in Reference design before modelling improvement strategies for the Proposed design. This is because it might not be comparable and consistent when modelling and reporting improvement strategies with different quantities (i.e. quantities at Design stage compared to quantities at As Built stage). There is a potential of over or under reporting the benefits of improvement strategies when the quantities of two designs are different. Thus, material quantities should be updated for both Reference and Proposed designs at As Built stage.

For projects registered after December 2022 and following “Upfront Carbon emissions calculation guide”

We’ve recently reviewed the “Upfront Carbon emissions calculation guide” and identified several points that can lead to the confusion of how Reference design should be modelled. From our interpretation of the guide, the purpose of modelling Reference design based on Detailed/Technical design quantities is to capture improvement strategies from the Detailed design stage onwards. This might apply to some strategies such as the exposed concrete floor strategy. However, the size, scale, volume and function of the Reference and the Proposed designs needs to stay the same (i.e. same floor plan and area etc.).

According to the guide, the aim of the Reference design is to provide a point of comparison for reductions against, by developing a building that could have been built in place of the Proposed design provided no work was done to reduce its upfront carbon emissions. The Reference and Proposed designs need to have the same set of data sources and data hierarchy (i.e. drawings, schedules, etc.). The guide has also provided default specifications for Reference design of different building types. These points mean to us that the Reference design should be based on the same set of documents as the Proposed design and the material quantities of Reference design should be the same as Proposed design, except where there are improvement strategies to reduce embodied carbon emissions. For example, when modelling LCA studies for GS projects, we will have two separate scenario trees, one for Design phase and the other for As Built phase (refer to Modeling Design Scenarios section above). The tree for Design phase including the Reference and Proposed designs using the same set of Design phase documents (i.e. Detailed design drawings). The tree for As Built phase including the Reference and Proposed designs using the same set of As Built phase documents (i.e. As Built design drawings). Typically, the improvement strategies for the As Built phase will be the same as the Design phase. Only the material quantities are updated due to the difference between Design and As Built phases, which is not related to improvement strategies. If there are any quantity changes in As Built phase regarding improvement strategies from previous iteration (i.e. Design phase), we would need to explain why and what it is as well as model additional scenarios in the As Built scenario tree to show reductions in upfront carbon emissions.

In summary, at any point of conducting LCA studies regardless Design or As Built phases, we think that the Reference design should be based on the latest plans and BoQ, which enables a comparative and consistent improvement strategy modelling.

With that said, we recommend that it would be better to confirm with GBCA on which Reference and Proposed designs should be submitted for the As Built stage to meet GS requirements.


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Note on Modeling EPDs

When modeling EPDs in your study, please ensure that the LCI source used in the EPDs are consistent with the rest of your study to ensure alignment with EN 15978. For more information on the different types of data, please download and read this article: LCI Data.


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