A calibrated energy model should play a central role in building out a decarbonization plan because it provides insights on:
- Current building energy and carbon profiles, and costs
- Potential energy, carbon and cost savings of energy conservation measures (ECMs)
- The impact of groups of ECMs, and the order in which they should be implemented over time.
The steps to follow include:
- An initial energy model is developed using commonly available building information such as architectural floorplans, MEP schedule sheets, and BMS sequences of operation.
- The initial model is then refined and “calibrated” to the building’s real utility data for each utility consumed, creating a baseline condition that ECM’s will be compared against.
- The baseline energy model is used as a test bed for individual ECMs to understand potential energy, carbon and cost impacts.
- Evaluate the financial performance of each ECM. These results will be used to identify strategies that are economically viable and should be considered further.
- Those ECMs that are economically viable on their own may be grouped together with other ECMs to help build a holistic business case for system optimization and maximum carbon reduction.
- During the evaluation process, the project team should take the evolving emission factors associated with utilities such as electricity and steam, as well as the impact of rising average and design day temperatures/humidity, into account.
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.
TABLE OF CONTENTS
Build and Calibrate the Initial Energy Model
An 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
Playbook Partner | Deliverables |
Empire State Building | |
PENN 1 | |
100 Avenue of Americas |
LESSONS LEARNED & KEY CONSIDERATIONS
- Determine energy model accuracy expectations early – Energy model accuracy can vary widely. For a deep energy retrofit study, the energy model should be highly accurate and align with ANSI/ASHRAE/IES Standard 90.1. Building management teams should set model accuracy expectations with the energy modeler at the onset of the project. This will help inform how assumptions are made and where the modeler should or should not simplify certain aspects of the model.
- Energy model calibration takes time but is worth the investment - Calibrating the initial energy model is a continuous and iterative process that can span multiple days or weeks depending on the complexity of the building. This time investment is well worth it because the quality of the energy modeling results is directly dependent on the quality of the calibration effort.
- Sync energy modeling assumptions with site observations - Even well-maintained buildings with stringent base-building and tenant standards have operational nuances and anomalies. Equipment may be shut off or sequences may be manually overwritten because the system wasn’t commissioned, wasn’t correctly integrated with the BMS, or was causing a localized issue that required a quick fix. This is especially true for older existing buildings that have had operations team turnover resulting in a loss of institutional knowledge over the years. For the energy model to accurately capture savings for ECMs, the calibrated model must reflect real-life operation. The project’s energy modeler should capture these nuances in the calibrated model whenever possible.
- Perfection is the enemy of "good enough" - The energy model will never perfectly simulate the performance of the building. There will also be a margin of error that comes from very specific nuances in building construction or operation that can’t be captured by a simulation-based software. The project team should set reasonable expectations for the level of modeling and calibration effort that aligns with AANSI/ASHRAE/IES Standard 90.1 but also conforms to the project schedule and status.
- Share model visualization with the project team – Energy modeling can be a complex topic that may seem inaccessible to non-technical audiences. To maintain good project team engagement during the energy modeling phase, the energy modeler should prepare and share data visualizations that can help tell the story of how the building uses energy. Graphs, rendering, and infographics are great examples of visual assets that can demystify the energy modeling process.
Create the Baseline Energy Model
The 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
Playbook Partner | Deliverables |
Empire State Building | |
PENN 1 | |
100 Avenue of Americas |
LESSONS LEARNED & KEY CONSIDERATIONS
- Document and review input assumptions – A robust energy model can be a reusable tool that can serve the building team for many years after the initial deep energy retrofit study. To ensure the information within the model is accurate and up to date, any inputs and assumptions should be documented and shared with the building management team. This will give the team the opportunity to correct any assumptions that do not align with the actual operation of the building and will create a log where inputs can be revised and updated as the building evolves.
Analyze Individual ECMs
In 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
Playbook Partner | Deliverables |
Empire State Building | |
PENN 1 | |
100 Avenue of the Americas |
LESSONS LEARNED & KEY CONSIDERATIONS
- Review and question surprising results- When reviewing preliminary energy savings it is important to make sure that the results make sense and question any surprising results. The energy modeling results are only as accurate as the modeling inputs. These assumptions must be vetted to ensure accurate savings. Data collection during this time will be useful to determine modeling assumptions. Assumptions can also be informed by the insights and advice from industry experts. Energy modeling is an iterative process and the model will continue to be refined as more information is collected.
- Identify high priority ECMs - Preliminary results may indicate that the majority of the energy savings available are attributable to a select number of ECMs. Implementing these select few ECMs may be all that is required to meet the project’s short-term objectives. The project team should focus on refining the inputs for these high impact ECMs to ensure accurate savings.
- Remember many small measures have a cumulative impact - To maximize savings and meet long-term project objectives like 80x50 it is likely that a wider array of ECMs will need to be considered for implementation. This holds true especially for buildings that have undergone recent renovations where the most impactful ECMs have already been executed. In this case it may be necessary to evaluate the cumulative impact of many small measures. Therefore, individual measures with minor carbon reduction impacts should not be dismissed too quickly.
Group, Sequence, and Package ECMs
As 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
Playbook Partner | Deliverables |
Empire State Building | |
PENN 1 | |
100 Avenue of the Americas |
LESSONS LEARNED & KEY CONSIDERATIONS
- Visualize the results - A helpful tool for analyzing ECMs results is a 2 x 2 matrix that shows the NPV vs. the CO2 reductions for each ECM.
- Consider non-energy benefits – Before eliminating measures because they have small carbon impacts, the project team should evaluate the non-energy benefits of the measure. If the non-energy benefits align with the owner’s overall sustainability strategy or make the building a more valuable asset, the building team may still wish to pursue the item. For example, a façade upgrade or replacement may not have a positive NVP but will make the building more competitive with newer buildings.
Generate a Decarbonization Roadmap
Once 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 phased 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
Playbook Partner | Deliverables |
Empire State Building | |
PENN 1 | |
100 Avenue of the Americas |
LESSONS LEARNED & KEY CONSIDERATIONS
- Total carbon emissions depend on the building and the grid - While building owners have control over how efficient their building is, they cannot control the long-term decarbonization of the electrical grid. Building owners can and should evaluate how they can optimize the energy performance of their building through the implementation of ECMs, but the total associated carbon emissions produced by the building will depend on both the magnitude of the energy consumed and how carbon-intensive the source of energy is. For this reason, it is beneficial to understand how different grid scenarios and emissions factors impact the ECM results. A cleaner grid in 2030 may be the difference between meeting or exceeding the LL97 emissions limit for that year.