Vav diffuser controls

A method of controlling an HVAC system, the HVAC system comprising an air handling unit to produce a supply airflow, the air handling unit being connected via a ducting system to a plurality of VAV diffuser units, each VAV diffuser unit influencing air temperature in a corresponding zone by delivering supply air to the zone, wherein

• the air handling unit comprises at least one supply air fan or motorised supply air damper;
• and
• each diffuser unit comprises a diffuser, a motorised variable damper to alter a diffuser airflow rate of a diffuser airflow delivered by the corresponding diffuser unit into the corresponding zone, and a diffuser pressure sensor for determining a pressure of the diffuser airflow;
• wherein
• the HVAC system further comprises a plurality of zone temperature sensors;
• the HVAC system further comprising at least one control unit connected to the supply air fan or motorised supply air damper, each diffuser unit motorised variable damper, each zone temperature sensor and each diffuser pressure sensor;
• the method comprising determining a target thermal capacity for a selected diffuser unit with reference to a target diffuser airflow rate and a target diffuser temperature differential and controlling the motorised variable damper of the selected diffuser unit with reference to the determined target thermal capacity for the selected diffuser unit.