Experimental Evaluation of Circulation Pump Control Impact on Performance and Energy Flexibility in Heat Pumps with Thermal Storage under Rule-Based and Model Predictive Control Strategies
Heat pumps, often integrated with thermal energy storage, are a promising technology for efficiently meeting building heating demands while providing energy flexibility. However, assessing their operational performance and the flexibility they provide is not straightforward, as it depends on multiple factors. Notably, circulation pump control, typically integrated within the heat pump and managed by the manufacturer, is often overlooked. Since it is generally not accessible for modification, it represents a significant constraint on heat pump operation and can substantially affect overall performance. Moreover, it limits thermal storage temperatures, reducing the system ability to exploit thermal inertia and provide energy flexibility. In this context, this study aims to experimentally assess the impact of circulation pump control on the performance and energy flexibility of a heat pump system coupled with a thermal energy storage system. The experimental setup consists of a hardware-in-the-loop configuration, in which a real water-to-water heat pump and a sensible thermal storage tank are integrated with a simulated building environment. Two different circulation pump control strategies are investigated. These strategies differ in the temperature difference imposed between the supply and return at the heat pump condenser. The impact of two high-level control strategies on system performance is evaluated: a rule-based control and a model predictive control, both tested in a laboratory setup. The predictive control is employed to activate energy flexibility, aiming to minimize electricity costs by exploiting the system thermal inertia. Results show that circulation pump control strongly influences system performance and achievable energy flexibility.