Performance Modeling of Building Energy Usage: Real Data for REAL Savings
The Bonneville Power Administration (BPA) has been using a free add-in to common workplace software and two easily available data inputs to verify savings from energy efficiency projects. Regressionbased energy modeling is a technique that uses observed energy use and measured temperature to model behavior of an existing building. These empirical models reflect actual building operations and observed response to temperatures, unlike theoretical energy models (such as eQuest or EnergyPlus) that assume design conditions and ideal operation. Readily obtainable data—energy consumption (such as daily usage from advanced meters or monthly billing data) and recorded outdoor temperature from a nearby airport—are used with a free Excelbased tool called ECAM+ to construct models of baseline and postretrofit energy use. These empirical models describe real-world building energy response to outside air temperature, and can be normalized to typical local temperatures to determine the energy savings from major retrofit projects. They can also help spot operational issues during the project performance period. This modeling technique is especially useful for hard-to-measure, interactive projects such as controls or retrocommissioning, but can be applied to any project with savings expected to be greater than a few percent of whole-building energy use.
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