Experimental and Numerical Investigations on a Combined Biomass-Solar Thermal System

This paper presents investigations on a market available combined biomass-solar thermal system for heating and domestic hot water preparation designed for small residential applications. The system consists of a storage integrated pellet burner and a solar thermal loop delivering heat to the same storage over a heat exchanger. The investigations were performed in a project with the final goal of the optimization of the control strategy with an emphasis on the interaction of two subsystems – biomass and solar thermal.The work carried out includes comprehensive laboratory measurements on system components, simulations based on the obtained experimental data and field tests on three installed systems. Measurements on the integrated pellet burner and the storage were performed under different steady-state and transient operating conditions and selected load profiles for both space heating and domestic hot water. The performance of the solar collectors was measured on an outdoor test rig according to the method with quasi-dynamic conditions described in EN12975:2006 chapter 6.3 [1].The simulation was carried out in TRNSYS using previously validated models for all major system components [2,3]. The experimental data from laboratory measurements were used to parameterize the simulation models using optimization based on an evolutionary algorithm (particle swarm optimization). The parameterized simulation models showed very good agreement with the experimental data. Hence, it was a reliable basis for the comparison with monitoring data and will provide a basis for future system optimization.The four installation sights for field tests were chosen to include different types of buildings, thus providing information on system performance and behavior under different operating conditions. A comparison between the simulated and the measured performance of the system will be presented and discussed. In a next phase of the project, this comparison will help to identify potentials for further optimizations of the overall system with a focus on the system controller.