Hot Tip

It can take anywhere from a few days to a few weeks to generate meaningful energy modeling results. Schedule the due dates for modeling results so that they can inform your design process.

For items outside the owner’s control—like lighting layout, fans and pumps—the parameters for the design and baseline models must be identical.

All known plug loads must be included in the model. The baseline and design-case models assume identical plug loads. If your project is deliberately attempting to reduce plug loads, demonstrate this by following the exceptional calculation method (ECM), as described in ASHRAE 90.1-2004. Incorporate these results in the model to determine energy savings.

Provide as much project and design detail to the modeler as possible. A checklist is typically developed by the energy modeler, listing all construction details of walls, roof, slabs, windows, mechanical systems, equipment efficiencies, occupancy load, and schedule of operations. Any additional relevant information or design changes should be brought to the modeler’s attention as soon as possible. The more realistic the energy model is, the more accurate the energy use figure, leading to better help with your design.

The design-case is modeled using the schematic design, orientation, and proposed window-to-wall ratio—the model will return design-case annual energy costs. Earn points by demonstrating percentage reductions in annual energy costs from the design to the baseline case. EAp2 is achieved if the design case is 14% lower than the baseline in new construction (or 7% less in existing building renovations).

The baseline model is the designed building with mechanical systems specified in ASHRAE 90.1-2004, Appendix G, for the specific building type, with a window-to-wall ratio at a maximum of 40%, and minimally code-compliant specifications for the envelope, lighting, and mechanical components. It can be developed as soon as preliminary drawings are completed. The baseline is compared to the design case to provide a percentage of reduction in annual energy use.

Projects using district energy systems have special requirements. For EAp2, the proposed building must achieve the 14% energy savings without counting the effects of the district generation system. To earn points in EAc1 you can take advantage of the district system’s efficiency, but you have to run the energy model again to claim those benefits.

Model development should be carried out following the PRM from ASHRAE 90.1-2004, Appendix G, and the LEED 2009 Design and Construction Reference Guide, Table in EAc1. In case of a conflict between ASHRAE and LEED guidelines, follow LEED.

If your project is using BIM software, the model can be plugged into the energy analysis software to provide quick, real-time results and support better decisions.

Simple, comparative energy analyses of conceptual design forms are useful ways to utilize an energy model at this stage. Sample scenarios include varying the area of east-facing windows and looking at 35% versus 55% glazing. Each scenario can be ranked by absolute energy use to make informed decisions during the design stage.