How can I get an accurate calibration result?

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This is something you will need to work out by exploring various outputs and patterns. Calibration like this can be quite challenging. Based on the minimal information here, it appears that the model is too sensitive to outdoor conditions. Perhaps too much outdoor air or infiltration is cooling the zone in mild weather and adding to the load in summer? In order to help you here, we need to know more about the model, the climate location, etc. If the only metered data you have in overall electricity consumption for the building including plug loads, lights, etc., it will be very difficult to calibrate the model.