Energy modeling is not an event like the completion of a project's design documents, but like the design itself, it evolves as an important part of the process. The article below outlines the process of energy modeling from pre-design to post-occupancy and back to pre-design in a feedback loop of continual improvement.

Energy analysis should begin before the design even starts. The primary purpose of energy analysis is always to inform design decision-making. It is an instrument of evaluation that enables higher level discussions of systemic interactions that can enlighten the implications of various design strategies. Each energy modeling iteration is an opening to an informed design discussion by the entire team about the interactions between architectural and mechanical/electrical system design and their impact on both operating costs and construction costs. When used within an integrative design process, energy modeling has the potential to unlock hidden cost synergies that can lower both first cost and operating costs. The optimal energy modeling process varies a bit from project to project depending upon each unique situation but the possible phases are outlined below.

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Putting Performance in Context

‍‍An integrative process with a regenerative aim always grounds the project in its particular place so an evaluation of the site and local climate are key to informed design. Undertaking benchmarking to establish specific project performance goals enables the team to design toward a particular level of performance. The entire design team needs to be aligned around the performance goals and a set of principles as guides to action during the development of the design. These goals should be discussed and co-created in a charrette and following the meeting codified in the project's Owner's Performance Requirements (OPR).

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‍Identifying Nodal Intervention Points in Pre-Design

Energy modeling can begin very early in the design process, even before a formal "design" is on paper. These simple box models can be based on an initial version of the project (i.e. same area, number of floors, possible shape, etc.) and can be created very quickly. These models allow for the identification of the highest energy end uses (i.e. heating, cooling, lighting, etc.). This enables the team to establish priorities, begin to evaluate strategies, and get a performance snapshot relative to the project's goals.

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Finding the Form of Performance

Once the architectural team creates conceptual design sketches, energy models can be used to evaluate conceptual design options focused on the orientation, massing, overall form, window area, air flows, and self-shading to optimize the overall performance of the initial architectural design. These models can evaluate the interactive complexities of a wide variety of design strategies to determine which combination of strategies has the highest potential to deliver on the performance target.

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‍Making Your Building Less Demanding

As the project moves through schematic design and hones in on a particular design concept the next phase of modeling focuses on the reduction of the building's heating and cooling loads. The strategies now include an evaluation of both internal and external loads with an eye toward reducing the size of the HVAC equipment and eliminating certain HVAC system components. Bundles of interactive strategies are evaluated together to optimize the performance of the whole enabling the potential to reduce the first cost and the operating cost of the project.

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Finding Your Perfect Comfort Fit

Up until this point the modeling effort concentrates on the building's architectural design and internal loads in an effort to optimize those parameters before selecting and sizing the best choice for achieving the project's thermal comfort. Given the potential for the HVAC system size to affect the overall first cost of the system, it is important to conduct the evaluation in this particular order. Energy modeling is used as a part of a Life Cycle Costing study to evaluate the optimal system choice to meet the project's goals based on the load reduction from the previous phase. Once the particular HVAC system is selected it can then be optimized with further analysis regarding design details like equipment efficiency, heat recovery, outside air intake strategies like economizers or DOAS, displacement ventilation, and the elimination of perimeter treatments accounting for thermal comfort implications.

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‍Changing the Conversation

The old joke says that value engineering provides neither one. To ensure fully informed design decision-making, it is important to holistically evaluate potential design changes to determine not just the effect on first cost but also on operating costs to ensure the integrity of the design relative to its goals. Within a truly integrative design budget, line items cannot be isolated as there are potential cascading effects that can have a big affect on multiple building systems. Analysis at this phase ensures that value engineering adds real value and actually involves some engineering.

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‍Predicting Performance

The "final" model is often a compliance model that is used to predict savings (for LEED, tax credits, utility rebates, etc.) or to determine code compliance. Energy savings are determined by making relative comparisons to some sort of baseline. In some cases, it is the absolute predicted value that is critical such as when designing to a particular goal like an Energy Utilization Index or to achieve net positive status. In any case, the predication should be reflective of the range of possible actual energy use for the building type and climate and reality checked against databases of actual building energy performance (like CBECS data). It should go without saying that the more accurate the prediction the better.

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‍Do you design energy efficient buildings? How do you know?

The only way to know if you design energy efficient buildings is to gather the energy bills post-occupancy and compare the building energy use to the data from other similar existing buildings. Predictions are only as good as the assumptions behind them. It is important to create feedback loops by comparing the actual energy use to the predicted energy use and examining why they might be different. In this way you can use the energy models to create lessons learned on how to more accurately analyze and predict energy use for subsequent projects. Post-occupancy energy analysis can also be used to verify that the savings you predicted actually pan out in reality. The graph below is a monthly comparison of the predicted performance versus the actual performance of the building.

We strive to conduct a post-occupancy comparison on all of our energy models so we can share lessons learned and continue to develop our, and the design/construction team's, capability to design and construct green buildings with exemplary energy performance.