Development and Validation of a Generic Evaporator Model of Chillers

Chillers can consume up to half of a building’s total energy, and variables asscociated with a chiller evaporator are crucial for system operation, control, and design of chilled water loops. Although detailed physical models like computational fluid dynamics have been used to study evaporators, their complexity and high computational cost make them impractical for Heating, Ventilation, and Air Conditioning (HVAC) applications, particularly when operational data is limited in a building automation system. This paper presents a grey-box model for chiller evaporators under steady-state conditions by integrating both physical and data-driven approaches. Based on the analysis of evaporator energy balance and heat transfer on both the water and refrigerant sides, we derive a simplified equation with a minimal number of model inputs that are usually available in the building automation system. The proposed model aims to estimate the chilled water temperature difference across the chiller evaporator. We then validate the model with a dataset at 15-minute intervals from a real institutional building. Results indicate it achieved a high accuracy with a coefficient of variance of root mean square error of 3.9%. The proposed model can be used to study HVAC operation optimization, fault detection and diagnosis, ultimately contributing to improved energy efficiency and system reliability.