Performance analysis and optimization of an integral collector storage (ICS) prototype with PCM

Standard solar systems for DHW production in residential buildings usually consist of a solar collector coupled with a water storage tank. Most of these systems also include auxiliary elements such as circulation pumps, sensors, controllers and safety equipment, giving a sort of complexity to the final installation. Furthermore, maintenance costs as well as space consumption represent some of the main drawbacks of this technology. For these reasons, even though conventional systems are currently well established on the market, "passive" solar systems are slowly gaining attention from both the practical and theoretical point of view, especially for their easy installation, smaller sizes and maintenance-free approach. Against this background, the topic of this thesis is an experimental and numerical study an new concept of integral collector storage (ICS) with heat pipes and phase change material (PCM) storage. An experimental analysis was carried out in Chambéry, France, studying the energy performances of a prototype that encloses in an aluminum casing a solar absorber, a thermosiphon heat pipes section and a storage cavity filled up with PCM. Solar radiation is transferred from the absorber to the PCM by means of the heat pipes, using methanol as heat transfer fluid. Thanks to a slight inclination, heat pipes act as thermal diode, limitating thermal losses during nightime. PCM storage cavity is made up by an honeycomb structure, improving heat transfer across it. A copper pipe wraps up the storage cavity allowing water flowing inside it and extracting stored heat for the user. A first experimental set was carried out under summer conditions, showing good results in terms of thermal stresses and global functioning. However, consinstent thermal losses occur over night, discharging the storage. After a thermographic analysis thermal bridges in the casing were spotted and structural improvements were performed to avoid undesired losses. A new experimental set was then performed in winter conditions, giving better results in terms of productivity and storage efficiency. Simultaneously with the experimental study, a numerical model was developed, able to simulate the physical behavior of the prototype. After having validated the model through experimental data, an annual simulation was performed, giving as result a solar fraction around 56%, comparable with traditional systems. Overall, the studied ICS represents a DHW source totally in line with other products on the market. However, numerous rooms for improvements are possible, especially regarding the absorber efficiency. Also, further optimization is definitely required by the heat exchanger between the storage cavity and the DHW coil. Possible future scenarios might include several ICSs grouped together in the same system, providing DHW with a real water withdrawal profile.