Optimizing the building operation is critical for improving a facility's thermal, energy, and economic performance while maintaining comfort. In this context, an energy audit is usually suggested, but it seldom is used as a diagnostic tool due to the complexity and the associated cost. The current investigation aims to use a multi-phase energy audit approach to diagnose the building's operation deficiency and proposes pragmatic retrofitting strategies. Several levels of effort were applied, including a walk-through audit, spot and short-term measurements, generation and calibration of building simulation model, energy and economic analysis. Various energy management opportunities (EMOs), such as adjusting the thermostat setpoint, modifying the operation schedule of the air conditioning system, replacing the conventional lights with more energy-efficient lights, and increasing the airtightness, were identified. These EMOs were further analyzed using a calibrated energy model using DesignBuilder software. The results indicated that the energy consumption and the energy cost could be reduced by more than 56% and 54%, respectively, while the comfort is maintained. The return on investment for these EMOs ranged between 0.2 and 9.1 years, with 1.8 years for the combined EMOs case. The outcome from this diagnostic energy audit was confirmed in the post-energy audit phase when one of the EMOs was implemented, and its impact was monitored, which indicated an actual energy saving of 34%. This study suggests that a diagnostic energy audit should be frequently practiced. The study also shows that whole-building simulation tools can be reliably used for evaluating expensive retrofitting strategies.
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