Performance comparison of two PCM candidates for new concept of compact thermal storage in solar DHW systems

Gilles Fraisse (1) , Maxime Thonon (1) , Laurent Zalewski (2) , Antoine Leconte (3) , Eric Francois (3) , Mickael Pailha (1) , David Cloet (1) , Robert Moracchioli (4) , Luc Traonvouez (5) , Erwin Franquet (6)

1 LOCIE - LabOratoire proCédés énergIe bâtimEnt
2 LGCgE - Laboratoire de Génie Civil et Géo-Environnement (LGCgE) - ULR 4515
3 INES - Institut National de L'Energie Solaire
4 DATE - Dynamique et Action Territoriales et Environnementales
5 INSULA, 44220 Coueron, France
6 Polytech'Lab - Laboratoire de Polytech Nice-Sophia

The latent heat of phase change allows to increase the energy density compared to sensible storage. In the building sector, it is possible to replace hot water tanks that are bulky due to their cylindrical shape, by smaller storage volume and parallelepiped geometry. The idea of the new concept is thus to propose a hybrid and modular storage component with a cavity containing the phase change material (PCM) delimited by two flat heat exchangers connected by slotted fins. The first step was to precisely characterize the behavior of the two selected PCMs during melting and solidification, without and with supercooling (respectively RT58 and PEG6000). The next step concerns the modeling of the storage cavity and then the optimization of the new full-size concept for solar domestic hot water systems. A prototype was experimentally tested for the two PCMs under real operating conditions with a reduced sequence of six days allowing the annual performance to be calculated. The experimental results confirm the known limit of PCM concerning its low thermal conductivity, which can penalize the power extracted from the storage during continuous withdrawals. The spacing of the fins thus plays a major role in heat transfer. The evaluation of the annual performances carried out on the prototype shows that the solar fraction is quite satisfactory, between 40 and 90% depending on the climate in France. The distribution of average temperatures observed within the PCM is directly correlated with the melting ranges. The RT58 is thus penalized compared to the PEG6000 because the start of the melting takes place at a much lower level (30°C against 52°C), which can lead to more frequent use of back-up. Regarding heat storage, the much lower density of the RT58 explains the difference in energy stored in the prototype (+34% for the PEG6000 between 20 and 80°C) knowing that the latent heat and the specific heat are of the same order of magnitude in both cases. Finally, the higher thermal conductivity of PEG6000 favors the heat rate exchanged during the storage charging and discharging phases.

Domaines: Autre

Gilles Fraisse, Maxime Thonon, Laurent Zalewski, Antoine Leconte, Eric Francois, et al.. Performance comparison of two PCM candidates for new concept of compact thermal storage in solar DHW systems. Journal of Energy Storage, 2024, 86 (Part A), pp.111198. ⟨10.1016/j.est.2024.111198⟩. ⟨cea-04512613⟩