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HIDDEN

Energy & Carbon Modeling

Inputs for this task include the well-organized compilation of information and data collected during the Discovery Phase. Refer to the “Learn the Building” section for specific information of what should be collected.

Define and Understand the Purpose of the Energy Model

The purpose of energy modeling in this context is to provide high-accuracy estimates of potential energy, cost and carbon savings for energy conservation measures (ECMs) under consideration. The energy model should incorporate site weather data for a typical year as well as detailed information about building geometry, building construction, systems, operations, and occupancy. The energy model will use this information to simulate the building’s energy consumption for every hour of the year.  

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. 

The goal at this phase of the project is not to create an exact replica of the building—doing so would require modeling effort and investment in building metering that does not yield improvements in model accuracy that will improve decision making. Instead, energy models routinely include simplifications that maintain fidelity to metered data and an appropriate level of detail to form a basis of comparison for ECMs under consideration.

Create the Initial Energy Model   

The initial energy model should reflect the basic components of the building including geometry, HVAC systems, occupancy, and basic building operations. The initial model will generate an energy profile for the building that can be compared to measured utility data for calibration purposes.

Calibrate the Initial Model to Measured Data 

Calibrating the initial energy model is an iterative process intended to align the simulated building performance with measured utility data. Calibration should occur across all utilities and should apply to demand in addition to consumption. At the end of the calibration effort, simulated energy performance for the building’s existing condition should be consistent with measured building performance within +/- 10. Exceptions to this rule may be allowed for situations such as a chance in building use, or the impact of COVID. 

The output of this task will be a calibrated energy model that accurately reflects the building existing conditions within a reasonable margin of error. This calibrated model is the foundation of the Baseline Energy model discussed in the next section.

Inputs for this task include: 

• The calibrated energy model 
• TMY weather data 
• List of planned upgrades, tenant lease turnover schedules 

Make Necessary Adjustments to the Baseline Model - To create a baseline energy model, the calibrated energy model consumption should be adjusted to account for the following: 

• Weather - Typical weather data for the site can be modeled using TMY3 data files, which capture and compare typical performance and eliminate any extreme weather event effects that may have occurred in the baseline year. TMY3 files are produced by the National Renewable Energy Laboratory and can be freely accessed and downloaded from the EnergyPlus website. 
• Occupancy (Lease Turnover or COVID) - The baseline energy model should be adjusted to account for any fluctuations in building occupancy that are expected to occur over the study period. For example, tenant lease turnover schedules should be collected during the Discovery Phase and accounted for in the baseline model. Similarly, any disruptions to building occupancy, such as those experienced during the COVID 19 global pandemic, should be captured in the baseline model. In order to understand the full magnitude of ECM impacts, it is important to separate energy reductions resulting from ECMs versus those resulting from lower occupancy levels. 
• Planned Upgrades – The baseline model should be adjusted to account for any planned projects that will impact the building’s energy consumption. By capturing these savings in the baseline model, the project team will avoid projecting ECM savings that are no longer available because they have already been captured by planned projects.  

The baseline model represents “business as usual” building energy consumption and associated energy cost. It is the reference point used to determine the energy savings of potential ECMs and track progress towards reaching project objectives. 

Generate Detailed End-Use Breakdowns – Once the baseline energy model is complete, the project team can begin to gain additional insight into how the building uses energy. A particularly useful output of the model is a detailed end-use breakdown like the one shown below:

The energy modeler will be able to analyze this end use breakdown and identify systems that appear to be high energy consumers. Hypotheses should be vetted by the engineer and facilities team based on their understanding of the building.

Document Assumptions and Review Initial Results with the Team - After the initial baseline model has been built, the energy modeler should review his/her/their assumptions and the resulting load breakdowns with the project team. The modeler should then solicit feedback from the engineers and building operators who have greater insight into the current building operation and systems design. Feedback should be incorporated into the next iteration of baseline model. The feedback loop between the energy modeler and the building team will be an iterative process that will continue throughout the duration of the project as more information is collected from the building. 

Overlay Carbon Emissions - Once the baseline energy consumption results are refined, the associated operational carbon emissions can be calculated by multiplying the annual energy consumption by a fuel-specific carbon coefficient. Carbon coefficients represent the greenhouse gas emissions intensity of different energy sources and are used to determine a building’s total greenhouse gas emissions in tons of CO2equivalent. This analysis will identify the primary contributors to greenhouse gas emissions in terms of fuel type, system, and ownership (end-user that is driving the demand). 

Refine the Preliminary List of ECMs - At this point, the energy modeler and engineer should work together to refine the preliminary list ECMs that was developed in the “Build the BAU Base Case” task. The additional information gleaned from the detailed end use breakdown should be used to validate the initial list of measures and to identify new areas of focus that were not identified in early phases of the project. 

Deliverables from the baseline energy model work include the following: 

• Baseline energy model is a reference for potential energy, carbon and cost savings   
• Building energy consumption and detailed end use breakdowns 
• Documented baseline system assumptions  
• Finalized List of ECMs for study in the energy model

For this task, the energy modeler will need the baseline energy model and the finalized list of ECMs that will be evaluated.  

Develop a Modeling Strategy for Each Energy Conservation Measure (ECM) – Before the modeler begins modeling each ECM, he/she/they should develop a modeling strategy for each measure including performance characteristics and any important assumptions. Documenting model inputs and modeling strategy for each ECM will make it easier to troubleshoot if there are any surprising results. 

Run ECMs in the Model and Analyze Results -Once all ECMs are explicitly defined and the modeling strategy has been finalized, the modeler will run each ECM to create a proposed energy model. The proposed energy model is what is compared to the baseline energy model to estimate energy, carbon and cost savings. The energy modeler will extract savings for each ECM from the proposed model, which will enable the team to study the individual impact of each ECM and vet the results. Energy savings for individual ECMs should be compared to industry experience to gauge their validity. When surprising results arise, the team must explore why and either justify the inputs or modify them according to additional information.    

Refine and Troubleshoot as Needed - Assumptions may need to be revised after this initial review of the results, especially if there are unexpected results.  

Compare Mutually Exclusive ECMs - In some cases, the team may develop mutually exclusive ECMs. These competing ECMS must be compared to determine which is the most energy efficient and by what margin. The energy model can be used to run multiple ECM options and compare estimated energy savings between them. The project team should decide which mutually exclusive ECMs should be advanced into the future rounds of analysis before packaging ECM in the next phase of modeling. 

Assess Maximum Theoretical Potential for Energy Savings -The final energy consumption of the proposed model will factor in all the energy savings associated with the ECMs. This resulting value is the theoretical minimum energy consumption for the building, assuming all technically viable ECMs are implemented. At this point it is helpful to determine the percent reduction from the baseline and evaluate how this theoretical minimum stacks up to the project objectives. Important questions to answer include:   

• Does the theoretical minimum energy consumption meet or exceed the project’s energy and carbon goals, and if so by how much?    
• Which ECMs contribute most significantly to the energy and carbon reductions and are they likely to be financially feasible?   
• Are most of the energy savings attributable to a few select ECMs or are energy savings spread evenly amongst many small measures?   

The analysis of the energy modeling results can be facilitated by the creation of ECM waterfall charts which show the baseline energy consumption / carbon emissions and the progressive impact of each ECM on these values. The final energy consumption and carbon emission of the proposed model will establish the theoretical minimum.   

Outputs and deliverables of this work include: 

• Initial energy, carbon and cost savings for individual ECMs. Based on this initial review and analysis, the team will identify further data collection required to refine the modeling assumptions and improve the accuracy of the outputs.  
• Actionable information regarding which mutually exclusive ECMs are most impactful and should be advanced to the next phase of modeling. 
• The maximum theoretical energy savings and carbon reduction for the building. This will give the project team an indication of how many ECMs may need to be implemented to meet the project objectives.  
• Initial energy cost savings for each measure, which can be used to inform preliminary financial analyses.

For this task the project team will need the following inputs: 

• Energy, carbon & cost savings from the proposed energy model 
• Preliminary ECM capital costs estimates -Preliminary results from the financial analysis will provide approximate NPV values for each ECM based on the projected energy cost savings and capital costs. These results will be used to identify those ECMs that are economically viable on their own, those that are worth pursuing due to large carbon impact, and those that should be discarded at this point due to technical infeasibility, cost, or low carbon impact. Those ECMs that are economically viable on their own may be grouped together with related, and costly, but effective, ECMs to help build a stronger business case.

The inputs for this task include: 

• The finalized ECM Packages 
• Carbon coefficients for the Future Grid 

Run Final ECM Packages in the Model and Analyze Results -The modeler should update the proposed model based on the final list of ECM packages and intended implementation sequence. Energy results should be provided for each ECM, even if there are several ECMs that are intended to be grouped together, as this provides granular data for the financial analysis to be conducted down the line. This is important because each ECM may have distinct capital costs, maintenance costs, and incentive implications which may impact the financial viability of the measure.     

For the purposes of reducing the modeling time, it may be assumed that a given ECM’s savings are recognized at once, even if it is anticipated that the ECM and associated savings will be realized over a period of several years. These savings can be split proportionally according to the intended timeline in a post-processing exercise without a major impact to the results, so long as the sequence of the ECMs is correct.    

Calculate Savings from the Baseline - The final run of the proposed energy model will produce energy, carbon and cost information that should be compared to the baseline energy model to determine anticipated savings. During this exercise, project teams should consider the following:  

• The energy model provides energy costs for each run, but it may be beneficial to conduct advanced tariff analysis that evaluates the anticipated annual hourly energy consumption for each package. Given the energy consumption results from the model, and the implementation timeline, a composite file of hourly data can be created to accurately reflect the percentage of each ECM that has been implemented each year. This will result in an energy consumption profile that reflects the expected annual peak and associated demand charges. More accurate utility costs can be calculated using this information. At a minimum, a utility cost escalator should be applied to the initial calculated energy cost savings to capture the impact of changing rates over time.  

• The anticipated CO2 emissions reductions associated with each ECM can be calculated by overlaying today’s carbon coefficients onto the energy savings results. For a greater level of accuracy, the carbon coefficients from LL97 can be overlaid on the annual energy consumption for the years where this data is available (2024-2029). Beyond 2029, project teams should consider different electrical grid decarbonization projections and overlay evolving carbon coefficients on the yearly energy consumption. For example, New York’s Climate Leadership and Community Protection Act (CLCPA) targets 70% renewable energy by 2030. Assuming the grid meets the goals and schedule of the CLPCA, the carbon coefficient for electricity for the year 2030 will be much lower than it is today.   

The final energy modeling results should include energy savings, energy cost savings, and CO2  reduction for each ECM package studied.