Dynamic simulation and experimental validation of a solar air system with rock-bed storage for space heating and domestic hot water production

This study presents an innovative solar heating system for cold climates, based on a concentrating air solar collector coupled with a rock–bed thermal storage unit. The system supplies both space heating and domestic hot water in residential buildings. The system novelty lies in its capability to perform interseasonal thermal storage thanks to a rock-bed storage, enabling the transfer of surplus solar energy while dynamically switching between storage charging and DHW production modes according to seasonal demands. This operational flexibility was achieved through control algorithms implemented in MATLAB. A numerical model developed in TRNSYS was validated against experimental data from a test facility at Wroclaw University of Technology. Annual simulations performed on a three-story residential building in Krakow, Poland, demonstrated that the system achieves a 75% solar fraction for space heating (6600 kWh of 8858 kWh annual demand) and 66% for domestic hot water production. Winter performance shows solar fractions ranging from 54% to 72% during peak demand months, while in mid-season months the solar contribution achieved 83–100% coverage. The rock-bed storage maintains temperatures above 50 °C throughout the year, reaching 250 °C in summer. A hierarchical control system optimizes seasonal operation through coordinated management of storage charging, space heating distribution, and DHW production. To assess the complete performance of the system, auxiliary electrical consumption was detailed evaluated considering requirements for circulation fans and pumps, accounting to 705 kWh/year. Results demonstrated that concentrating solar air collectors with rock-bed storage represent a viable solution for substantial fossil fuel displacement in cold climate residential applications, while maintaining an acceptable level of parasitic electrical consumption.