Virtual Mass Flow Rate Sensor Using a Fixed-Plate Recuperator

The mass flow rate inside heating, ventilation, and air-conditioning units provides important information for fault detection and diagnosis (FDD) and for performance monitoring. Most commercial units are not equipped with physical flow rate sensors, and virtual sensors (VS) offer an alternative that provides improved FDD performance. This paper presents the virtual mass flow sensor for an air handling unit with a recuperator (a fixed-plate heat exchanger). The VS is based on the heat exchange process inside the recuperator. It estimates the mass flow of air only on the basis of temperature readings from the inlet and the outlet of the recuperator. Two different approaches to the design of the VS model are described here. The first approach uses a simplified physical description of the recuperator, and the second approach uses knowledge of the recuperator performance curve. Laboratory experiments have confirmed that the proposed VS can be utilized as a substitute for a physical mass flow rate sensor for monitoring and for fault detection.