Grey-box models of chiller evaporator for practical integration in building automation systems

This paper presents the development and validation of grey-box models for estimating the chilled water temperature difference ΔT_chw across the chiller evaporator, with potential applications as virtual sensors in building automation systems (BAS) or integration into other mathematical models. The models are established for two scenarios, variable and constant chilled water flow rates under quasi-steady-state operation. These models require a small number of input variables and are characterized by strong adaptability. Three case studies of different chillers are used to validate the proposed virtual sensors with both static and dynamic windows methods, and help in the generalization of the proposed method. The models demonstrate high accuracy and robustness, achieving a root-mean-squared error of 0.19 °C in one case study. This study addresses the gap in the availability of simple yet reliable models that can be practically integrated into building automation systems for virtual sensing, virtual calibration, fault detection and diagnosis, and HVAC system control and optimization.