From time to time, when a building owner knows that an energy model has been used in the design of a building, he or she may ask, “How much will my utility bills be?” This is certainly a legitimate concern for all building owners, as they may need to know how to set up billing arrangements for their tenants or be interested in negotiating long-term contracts with utility providers based on future use. Unfortunately, energy models are not good at predicting the actual energy use in buildings with a high level of accuracy, especially models constructed during the design phase of new construction projects.

Even the ASHRAE Standard 90.1 User’s Manual expresses concern that the results of energy models will be misconstrued. It states that the modeling guidelines presented in the standard are intended to provide a baseline for comparison of the estimated annual energy cost of the proposed building and the baseline building for the purposes of a rating. They are not intended to provide an accurate prediction of actual energy consumption or costs for the building as it is actually built. Although the energy analyst is expected to model energy use as closely as possible, there are many reasons why the actual building performance rating may differ from the predictions of the building performance rating method.

 

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