Design and Experimental Evaluation of a Controller for a Direct-Expansion Solar-Assisted Heat Pump with Propane

Given the growing demand for sustainable energy solutions, this study addresses the challenge of improving the efficiency and environmental performance of residential water heating systems. This work presents the design and implementation of a controller aimed at regulating the outlet water temperature of a direct-expansion solar-assisted heat pump operating with propane. A dynamic model was experimentally identified using the AutoRegressive with eXogenous input methodology and used to design a Proportional–Integral–Derivative controller via the direct synthesis method. To regulate the outlet water temperature, the controller acts on the water flow rate. The effectiveness of the controller was evaluated through computer simulations and experimental tests. Its robustness was assessed by considering parametric variations of ±15%, during which the system maintained stability and performance. The controller demonstrated good accuracy and performance, keeping the desired temperature stable even in the presence of disturbances, both in simulations and experimental evaluations.