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A calibrated energy model should play a central role in building out a decarbonization plan because it provides insights on:
The steps to follow include:
Key outputs from the energy modeling workflow should include data driven charts showing energy end use breakdown and costs, carbon footprint of each utility, building carbon emissions vs. LL97 targets and fines, and who "owns" the carbon footprint (i.e. tenants, building operations). It is important to note that not all energy models are created equal. For a deep energy retrofit project, the accuracy of the energy model should align with ANSI/ASHRAE/IES Standard 90.1. Code or LEED energy models that were developed for the building in the past are not appropriate for this effort. You can learn more about building energy modeling here. Below is a selection of the energy modeling software packages used to support the case study findings presented in this Playbook, and throughout the industry.
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Build and Calibrate the Initial Energy ModelAn energy model is developed in multiple phases. In the first phase, the energy modeler must build an initial model that captures the geometry, material attributes, occupancy types, MEP systems and basic information about the building’s operations. The energy modeler should also include surrounding buildings that may impact sun exposure on the different facades of the building under study. This initial model will produce a rough estimate of how the building performs every hour during the year. Then in the next phase, the energy modeler must hone the model’s accuracy by “calibrating” the initial model to measured utility data and detailed building operations information. Code or LEED energy models that may have been created for the building during its initial design and construction should not be used in deep energy retrofit study efforts because they do not reflect the actual performance of the building under study.
IN PRACTICE - CASE STUDY EXAMPLES
LESSONS LEARNED & KEY CONSIDERATIONS
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Create the Baseline Energy ModelThe baseline model represents the current systems and operations of the building, adjusted for “typical” weather conditions and other criteria. Energy savings for all proposed ECMs will be calculated relative to the baseline model performance.
IN PRACTICE - CASE STUDY EXAMPLES
LESSONS LEARNED AND KEY CONSIDERATIONS
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Analyze Individual ECMsIn this task, the energy modeler will run all ECMs in the energy model and extract associated energy, carbon and cost savings for each. For this task, the energy modeler will need the baseline energy model and the finalized list of ECMs that will be evaluated.
IN PRACTICE - CASE STUDY EXAMPLES
LESSONS LEARNED & KEY CONSIDERATIONS
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Group, Sequence, and Package ECMsAs the Energy and Carbon Modeling phase is progressing, a preliminary financial analysis of individual ECMs will also take place in parallel. Preliminary results from the financial analysis will help inform this phase of modeling. Individual ECMs should not necessarily be discarded based solely on their associated capital cost; expensive ECMs can be grouped together with related financially viable measures to optimize savings and make a more comprehensive business case that maximizes CO2 reduction while still addressing investment return hurdles. Once ECMs have been grouped, an implementation duration and timeline should be established for each. This will depend on factors like short term project budgets, tenant lease turnover, operational budgets, and maintenance schedules. The ECMs should then be sequenced according to their implementation timeline so that energy savings for each ECM can be captured accordingly. Finally, several ECM packages should be assembled for owner evaluation. Each package will include a different combination of ECMs to be implemented with varying degrees of cost and carbon impact. This variety will provide the owner with options to choose from when striving to balance the project objectives and constraints.
IN PRACTICE - CASE STUDY EXAMPLES
LESSONS LEARNED & KEY CONSIDERATIONS
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Generate a Decarbonization RoadmapOnce the finalized ECMs have been grouped, sequenced, and packaged, the energy model can be run to obtain final results. These results will be used in the detailed financial analysis and will represent a time-dependent decarbonization roadmap for the building. The final results will include energy savings, energy cost, and CO2 reduction for each package under study, and should be post-processed according to the anticipated implementation timeline to reflect the gradual and overlapping impacts of each measure over a 20- or 30-year time horizon. CO2 reduction over a longer time horizon should include a changing electric grid carbon coefficient to account for grid decarbonization. Figure - ESB 2.0 Case Study - Electrical Carbon Coefficient Projections
IN PRACTICE - CASE STUDY EXAMPLES
LESSONS LEARNED & KEY CONSIDERATIONS
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