A ventilation system controller based on pressure-drop and CO₂ models

In ventilation systems a considerable amount of energy is used for mass transport of conditioned air to provide the requested volume flows. Reducing volume flow while maintaining indoor air quality has leverage on energy efficiency and is commonly known as Demand Controlled Ventilation (DCV). Current implementations require Variable Air Volume (VAV) controllers to provide a defined volume flow to each room. The controllers measure the pressure difference and adjust the motor flap accordingly. This paper examines an approach that achieves DCV, but replaces the VAV-boxes with simple motor flaps. The missing pressure-drop measurements that allow calculating the volume flow are substituted by a model of the ventilation system. The authors develop a method for calculating the pressure drop in the ducts of a ventilation system that regards the topology and the components of the duct system. This model is coupled with a model for the CO₂ concentration in the rooms for all conditioned rooms in order to derive the required air volume flow. Using this model, a linear controller is developed that operates the ventilation system. It is shown that the presented approach operates the ventilation more efficiently, while maintaining comfort constraints and saving installation costs. The modeling effort of the current approach is expected to be reduced with the introduction of the Building Information Model (BIM) into building operation.