## 1 Introduction
The energy exchanged by the sample between two steps is measured and, once the thermal equilibrium is reached, the next temperature step is applied. The sum of energy exchanged between each step enables the construction of the enthalpy curve of the PCM. Some authors use a fluxmetric method (FM) to characterize pure PCM [11, 12, 13, 14] or mortars containing encapsulated PCM [15,16]. For this method, the characterization is not performed with a calorimeter, as for DSC and STEP methods, but with a fluxmeter bench. The PCM is inserted inside a rectangular brick and two heat exchangers apply thermal loads to the sample. Fluxmeters measure the heat flux exchanged by the sample and a thermocouple is inserted inside the PCM to monitor the temperature. Compared with DSC and STEP methods, the FM method enables the characterization of larger samples, to directly monitor the PCM temperature and apply various thermal loads to the sample. This method also enables the numerical identification of the PCM properties by inverse methodology, and to model the thermal behavior of the sample for various thermal loads [11,12,17]. Many different kinds of PCM present a phase change temperature range and a latent heat suitable for DHW storage. However, other criteria including thermodynamic, kinetic, chemical and economic properties must be considered to select the most appropriate PCM for DHW storage [18, 19, 20]. Paraffins are the most commonly used PCM for DHW storage from solar production [21,22]. [PERSON] et al. [23] present a recent and detailed review on paraffin-based PCM, and [PERSON] et al. [24] provide a complete list of commercial paraffins. The specific heat of commercial paraffins is close to 2000 J kg\({}^{-1}\).k\({}^{-1}\)[22] and the latent heat is between 150 kJ\(\cdot\)kg\({}^{-1}\) and 230 kJ\(\cdot\)kg\({}^{-1}\)[24]. However, these good thermal performances are mitigated by a low density of around 800 kg\(\cdot\)m\({}^{-3}\)[24], which reduces the volumetric energy density. However, the main drawback of paraffins is their low thermal conductivity, usually close to 0.2 W\(\cdot\)m\({}^{-1}\cdot\)K\({}^{-1}\)[24]. Therefore, in order to reach the required power for DHW production, it is necessary to enhance thermal transfers between the PCM and the heat exchanger, by composite materials or fins [25; 26; 27]. In comparison with paraffin-based materials, fewer studies investigate the thermal performance of polymers as PCM for DHW storage. [PERSON] et al. [28] report promising potential for polyethylene-glycol 6000 (PEG6000), which appears to be economically competitive compared with conventional paraffin-based materials. As for paraffins, the specific heat of polymer PEG6000 is close to 2000 J\(\cdot\)kg\({}^{-1}\cdot\)k\({}^{-1}\)[29]. Most studies find a latent heat of around 180 kJ\(\cdot\)kg\({}^{-1}\)[29; 30; 31; 32], but higher values, close to 220 kJ\(\cdot\)kg\({}^{-1}\)[28; 33], or lower values, close to 150 kJ\(\cdot\)kg\({}^{-1}\)[34], might be observed in the literature for PEG6000. The thermal conductivity of PEG6000 appears to be slightly higher than paraffin-based materials with values of around 0.3-0.4 W\(\cdot\)m\({}^{-1}\cdot\)K\({}^{-1}\) depending on the studies [12; 29; 30; 35]. Concerning the phase change range of PEG6000, the melting temperature is suitable for DHW storage with a value close to 60 \({}^{\circ}\)C [28; 30; 31; 32; 33; 34; 35]. For the cooling process, polymers, such as PEG6000, are known to experience supercooling [36; 37; 38; 39], and it is natural to observe a different phase change temperature between heating/cooling processes. The degree of supercooling is influenced by the cooling rate [12; 39; 40; 41; 42], the size of the sample [43; 44; 45], and the roughness of the sample surface [46]. In the literature, various temperatures of crystallization may be found as experiments are carried out in different set-ups with different procedures: crystallization temperatures of 38 \({}^{\circ}\)C by [PERSON] et al. [35], 41.3 \({}^{\circ}\)C by [PERSON] et al.