ASHRAE 1353-TRP Stability and Accuracy of VAV Box Control at Low Flows
Ran Liu and Adam Regnier
Iowa Energy Center Energy Resource Station
Variable air volume (VAV) systems with direct digital controllers (DDC) have been widely adopted in HVAC systems of commercial, industrial, and large residential buildings, because they provide better energy efficiency and occupant comfort. Normally, a VAV terminal unit defines a minimum airflow rate to satisfy the space ventilation requirement and/or the proper operation of a terminal heating coil, if so equipped. However, if the embedded airflow sensor becomes inaccurate, and the designed minimum airflow rate is less than the minimum controllable airflow rate, then a series of problems could happen, such as a lack of ventilation, uneven control of airflow, reduced damper and operator life, and energy waste. This study aims at identifying the strong factors and the relationship between the strong factors and the performance of the airflow sensor (e.g. flow probe provided with the VAV box), controller (e.g. differential pressure transducer included in a VAV box controller, and the data acquisition and control algorithms included in the controller), and terminal unit system (e.g. flow probe plus transducer/data acquisition plus control algorithm) through systematically designed laboratory and field tests.