Energy Modeling: Early and Often

Thanks in part to green building programs and codes, whole-building energy simulation has become more common over the last two decades, but it’s not necessarily having a big impact on design decisions— let alone energy savings.

“Validating the final design is really important to validate LEED points and validate code compliance,” notes Maurya McClintock, Assoc. AIA, of McClintock Façades Consulting. As McClintock and others note, though, when modeling is only used late in design—after the massing, orientation, envelope and glazing design, and mechanical systems in a building are already specified, and hundreds of hours of work have already been put into those designs—the modeling might have little value beyond keeping score.

“It blows me away that that’s where we are,” says Marcus Sheffer, an energy consultant with 7group. As critics have pointed out, a “green” building modeled to save a certain amount of energy doesn’t necessarily end up doing that. Given accurate inputs, models are accurate at forecasting energy use, says Sheffer, but “models can’t accurately predict the future”: actual operating conditions will always differ from modeled conditions. This typically happens because equipment and controls are installed differently than modeled, or because weather patterns or occupancy are different than expected. The real value of modeling is not predicting energy use but making relative comparisons among design options, says Sheffer.