Unless your building is occupied at night, its likely if you find that your plant is running during unoccupied periods, you may think something is not quite right with the BMS. This is not always the case. For heating applications, and during cold weather, the most likely cause will be a frost protection regime. The BMS reads internal and external temperatures and will commit the heating systems to provide protection to plant and frozen pipes and even the building fabric. Generally the frost set points can be adjusted easily.
Ventilation plant may run during the night if the system is set up to take advantage of ‘free cooling’. This is where the BMS will determine that during periods where the days are warm and the nights are cool, this cooler air can be used to cool the building for the next day of occupation.