Dynamic Modelling and Part-Load Behavior of a Brayton Heat Pump

Abstract

Among the environmental-friendly technologies recently proposed in the literature, high-temperature heat pumps represent a promising solution to foster the complete penetration of renewables within the power grid. Such systems may be based on closed Brayton cycles and leverage many existing components. As they are meant to provide high-temperature heat while using renewable electricity, their potential field of application ranges from industrial heating to energy storage. Several variants are currently under development to assess the feasibility of such systems in providing flexibility to the electricity grid. To do so, they need to operate in part-load conditions and quickly react when the load must be adjusted. In this regard, this study investigates the transient capabilities of Brayton heat pump technology. To this extent, a detailed transient model of a novel prototype proposed in the literature is presented, accounting for controls, thermal inertia and volume dynamics related to heat exchangers and piping. Furthermore, the model is used to assess the transient performance of the system in response to sudden load variations, which is achieved by adapting the turbomachinery operating velocities. Results show that the system can safely operate in part-load conditions with regulation times compatible with industrial needs.