Virtual Power Consumption and Cooling Capacity Virtual Sensors for Rooftop Units

Implementation of advanced controls and diagnostic features in small commercial buildings typically requires realtime monitoring of the energy flows, such as the power consumption and cooling capacity of rooftop units. However, these measurements are expensive and therefore limit the application of these advanced features. In order to lower the measurement cost, virtual sensing technology for rooftop unit power consumption and cooling capacity are being developed. Power transmitters and thermocouples are installed on the rooftop units to train the virtual sensors. The idea is to recycle the power transmitters after training to save cost, and then the virtual sensors estimate hourly electrical consumption and cooling capacity using only low cost, non-invasive temperature measurements. In this paper, development and validation of the virtual sensors are presented. The virtual power consumption sensors are validated for 2 different rooftop units installed in the field, whereas the cooling capacity sensors are validated using 4 laboratory-tested rooftop units. The reliability of the sensors is also investigated by studying the uncertainty of the virtual sensor outputs under different operating conditions. A cost comparison between the virtual sensors and direct measurement methods is also conducted to evaluate the potential for widespread application of the virtual sensing technology.