ENTHALPY-MODEL SELECTION AND PRACTICAL IDENTIFIABILITY OF A MACROENCAPSULATED RT52 RADIANT FLOOR UNDER UNCERTAIN BRANCH FLOW
DOI:
https://doi.org/10.5281/zenodo.23321197Abstract
A hierarchy of reduced-order models was developed to determine what can—and cannot—be inferred about phase-change behavior from temperature measurements in a solar-driven radiant floor containing macroencapsulated RT52. The hydraulic topology treats the common-line mass flow upstream of a parallel split; the nominal equal split therefore gives a balanced flow in the PCM branch, while a flow-split sensitivity range was retained. Three model levels were compared: a sensible-only counterfactual (M1), a local-thermal-equilibrium enthalpy model with fixed RT52 properties (M2), and a finite PCM–concrete coupling model with a separate PCM state and a latent-participation factor (M3). During the charging-dominant interval, M2 reduced the joint residual sum of squares relative to M1 and was favored by the corrected Akaike Information Criterion AICc under the nominal split. The AICc preference remained positive across the sensitivity range. However, M3 did not justify its additional parameters: the fitted PCM–concrete conductance approached the local-equilibrium limit, the characteristic equilibration time was small compared with the sampling interval, and the finite-coupling formulation was penalized by AICc. Full-cycle stress tests further showed that the inferred latent-participation factor could shift significantly when physically plausible nuisance-parameter bounds were imposed. The charging record therefore supports an enthalpy representation, but PCM mass, finite PCM–concrete conductance, and exact latent participation are not uniquely identifiable from the available data. Model preference and parameter identifiability must be reported separately in PCM thermal-storage experiments.Keywords
phase change material, enthalpy method, AICc, practical identifiability, RT52, reduced-order model, radiant floor, parameter estimationReferences
Mazo, J., Delgado, M., Marin, J. M., & Zalba, B. (2012). Modeling a radiant floor system with Phase Change Material (PCM) integrated into a building simulation tool: Analysis of a case study of a floor heating system coupled to a heat pump. Energy and Buildings, 47, 458–466. https://doi.org/10.1016/j.enbuild.2011.12.022
Rebelo, F., Figueiredo, A., & Vicente, R. (2026). Almeida RMSF, Ferreira VM. Thermal performance of radiant floor systems incorporating phase change materials: effects of latent heat and phase change temperature range. Results in Engineering. 2026;32:112750. https://doi.org/10.1016/j.rineng.2026.112750. https://doi.org/10.1016/j.rineng.2026.112750
Lin, K., Zhang, Y., Xu, X., Di, H., Yang, R., & Qin, P. (2004). Modeling and simulation of under-floor electric heating system with shapestabilized PCM plates. Building and Environment, 39, 1427–1434. https://doi.org/10.1016/j.buildenv.2004.04.005
Kuznik, F., Johannes, K., Franquet, E., Zalewski, L., Gibout, S., Tittelein, P., Dumas, J. P., David, D., Bédécarrats, J. P., & Lassue, S. (2016). Impact of the enthalpy function on the simulation of a building with phase change material wall. Energy and Buildings, 126, 220–229. https://doi.org/10.1016/j.enbuild.2016.05.046
Iten, M., Liu, S., & Shukla, A. (2018). Experimental validation of an air-PCM storage unit comparing the effective heat capacity and enthalpy methods through CFD simulations. Energy, 155, 495–503. https://doi.org/10.1016/j.energy.2018.04.128
Khattari, Y. (2020). El Rhafiki T, Choab N, Kousksou T, Alaphilippe M, Zeraouli Y. Apparent heat capacity method to investigate heat transfer in a composite phase change material. Journal of Energy Storage. 2020;28:101239. https://doi. org/10.1016/j.est.2020.101239.
Serikawa, M., Satoh, M., Mae, M., Nozue, Y., & Hayashi, Y. (2022). Numerical models of heat storage with respect to phase change materials considering hysteresis. Journal of Energy Storage. 2022;55:105758. https://doi.org/10.1016/j. est.2022.105758. https://doi.org/10.1016/j
Feng, F., Fu, Y., Yang, Z., & O’Neill, Z. (2022). Enhancement of phase change material hysteresis model: A case study of modeling building envelope in EnergyPlus. Energy and Buildings. 2022;276:112511. https://doi.org/10.1016/j. enbuild.2022.112511. https://doi.org/10.1016/j
Buonomano, A., & Guarino, F. (2020). The impact of thermophysical properties and hysteresis effects on the energy performance simulation of PCM wallboards: Experimental studies, modelling, and validation. Renewable and Sustainable Energy Reviews. 2020;126:109807. https://doi.org/10.1016/j.rser.2020.109807. https://doi.org/10.1016/j.rser.2020.109807
Dolado, P., Mazo, J., Lázaro, A., Marín, J. M., & Zalba, B. (2012). Experimental validation of a theoretical model: Uncertainty propagation analysis to a PCM-air thermal energy storage unit. Energy and Buildings, 45, 124–131. https://doi.org/10.1016/j
Courtois, E., Glouannec, P., Magueresse, A., & Loulou, T. (2022). Estimating thermal properties of phase change material from heat flux measurements. International Journal of Thermal Sciences. 2022;172:107307. https://doi.org/10.1016/j. ijthermalsci.2021.107307. https://doi.org/10.1016/j
Dolado, P., Lázaro, A., Marín, J. M., & Zalba, B. (2011). Characterization of melting and solidification in a real scale PCM-air heat exchanger: Numerical model and experimental validation. Energy Conversion and Management, 52, 1890–1907.
Chen, W., Liu, Y., Liang, X., Luo, F., Liao, T., Wang, S., Gao, X., Zhang, Z., & Fang, Y. (2023). Experimental and numerical investigations on radiant floor heating system integrated with macro-encapsulated phase change material. Energy. 2023;282:128375.
Jin, X., Yang, J., Li, M., Huang, G., & Lai, A. C. K. (2022). Experimental and numerical study on the thermal energy storage performance of a novel phase-change material for radiant floor heating systems. Building and Environment. 2022;223:109491.
Rebelo, F., Figueiredo, A., & Vicente, R. (2026). Almeida RMSF, Ferreira VM. Experimental analysis of a radiant floor system incorporating phase change materials: Thermal performance and energy efficiency. Journal of Energy Storage. 108 10/2026 2024;102:114084. https://doi.org/10.1016/j.est.2024.114084. https://doi.org/10.1016/j.est.2024.114084
Rebelo, F., Brett, M., Figueiredo, A., Vicente, R., & Simões, N. (2026). Almeida RMSF, Ferreira VM. Experimental evaluation of a radiant floor system incorporating macroencapsulated phase change materials for improved heating and cooling performance. Energy. 2026;360:141692. https://doi.org/10.1016/j.energy.2026.141692. https://doi.org/10.1016/j.energy.2026.141692
Cheng, W., Xie, B., Zhang, R., Xu, Z., & Xia, Y. (2015). Effect of thermal conductivities of shape stabilized PCM on under-floor heating system. Applied Energy, 144, 10–18. https://doi.org/10.1016/j.apenergy.2015.01.055
Sharshir, S. W., Joseph, A., Elsharkawy, M., Hamada, M. A., Kandeal, A. W., Elkadeem, M. R., et al. (2023). Thermal energy storage using phase change materials in building applications: A review of the recent development. Energy and Buildings. 2023;285:112908. https://doi.org/10.1016/j.enbuild.2023.112908. https://doi.org/10.1016/j.enbuild.2023.112908
Zhou, D., Zhao, C. Y., & Tian, Y. (2012). Review on thermal energy storage with phase change materials (PCMs) in building applications. Applied Energy, 92, 593–605. https://doi.org/10.1016/j.apenergy.2011.08.025
Karaağaç, M. O. (2025). Experimental investigation of a novel PCM-enhanced underfloor heating system for energyefficient sustainable buildings. Applied Thermal Engineering. 2025;275:126891. https://doi.org/10.1016/j. applthermaleng.2025.126891. https://doi.org/10.1016/j
Qiao, X., Kong, X., & Fan, M. (2022). Phase change material applied in solar heating for buildings: A review. Journal of Energy Storage. 2022;55:105826. https://doi.org/10.1016/j.est.2022.105826. https://doi.org/10.1016/j.est.2022.105826
Prakash, J., Roan, D., Tauqir, W., Nazir, H., & Ali, M. (2019). Mada Kannan A. Off-grid solar thermal water heating system using phase-change materials: design, integration and real environment investigation. Applied Energy, 240, 73–83.
Singh, B., Rai, R. S., Yadav, P., Srivastava, S., & Yadav, C. (2025). Application of phase change materials in solar water heating systems—A comprehensive review. Solar Energy Materials and Solar Cells. 2025;293:113888. https://doi.org/10.1016/j. solmat.2025.113888. https://doi.org/10.1016/j
Khamraev, S., Kamolov, B., Tadjiboyev, S., Axmedova, B., Burieva, N., Ochilov, M., Samatova, S., & Sharopov, U. (2026). Experimental and theoretical analysis of thermo-hydraulic performance of a solar-collector-based hydronic floor heating system under climatic conditions of Uzbekistan. Energy. 2026;348:140399. https://doi.org/10.1016/j.energy.2026.140399. https://doi.org/10.1016/j.energy.2026.140399
Rathore, P. K. S., & Shukla, S. K. (2019). Potential of macroencapsulated PCM for thermal energy storage in buildings: A comprehensive review. Construction and Building Materials, 225, 723–744. https://doi.org/10.1016/j.conbuildmat.2019.07.221
Akaike, H. (1974). A new look at the statistical model identification. IEEE Transactions on Automatic Control. 1974;19(6):716–.
https://doi.org/10.1109/TAC.1974.1100705.
Sugiura, N. (1978). Further analysts of the data by Akaike’s information criterion and the finite corrections. Communications in Statistics - Theory and Methods, 7(1), 13–26. https://doi.org/10.1080/03610927808827599
Burnham, K. P., & Anderson, D. R. (2002). Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach. 2nd ed. New York: Springer; 2002. Springer; 2002.
Ljung, G. M., & Box, G. E. P. (1978). On a measure of lack of fit in time series models. Biometrika, 65(2), 297–303.
Voller, V. R., Cross, M., & Markatos, N. C. (1987). An enthalpy method for convection/diffusion phase change. International Journal for Numerical Methods in Engineering, 24(1), 271–284. https://doi.org/10.1002/nme.1620240119
Khelladi, M., Hemis, M., & Panigrahi, S. S. (2026). Indirect effects of solar energy on phase change material-based thermal energy storage unit. International Communications in Heat and Mass Transfer. 2026;172:110333. https://doi.org/10.1016/j. icheatmasstransfer.2025.110333. https://doi.org/10.1016/j
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