Numerical Investigation and Seasonal Optimization of a Phase-Change-Material-Integrated Solar Water Heating System

Tavakolpour, Yahya; Oloomi, Seyed Amir Abbas; Zare, Mohammad Hasan; Agha Mirjalily, Seyed Ali; Mazidi, Mohsen

doi:10.22034/ijumes.2026.2108559.1419

Numerical Investigation and Seasonal Optimization of a Phase-Change-Material-Integrated Solar Water Heating System

Document Type : Original Article

Authors

Yahya Tavakolpour

Seyed Amir Abbas Oloomi

Mohammad Hasan Zare

Seyed Ali Agha Mirjalily

Mohsen Mazidi

Department of Mechanical Engineering, Ya.C, Islamic Azad University, Yazd, Iran

10.22034/ijumes.2026.2108559.1419

Abstract

Solar water heating is a mature, low-carbon technology for supplying domestic hot water, yet the intermittency of solar radiation creates a persistent mismatch between supply and demand, particularly in buildings with large, time-varying thermal loads. Integrating phase change materials (PCMs) for latent thermal storage can bridge this gap, but the combined influence of PCM type, material fraction, flow rate, and season on performance remains insufficiently characterized; this study therefore develops and optimizes a PCM-integrated flat-plate solar water-heating system for building applications. A three-dimensional computational fluid dynamics model was built in COMSOL Multiphysics, solving the coupled mass, momentum, and energy equations with the effective-specific-heat method for phase change and the P1 radiation model. Two commercial storage materials, RT35HC and paraffin wax, were compared with water at 3% and 6% material fractions and standard and doubled flow rates across the twelve months of the year, using seven indicators: energy requirement, energy-storage performance, harvested energy, PCM melt fraction, valve-opening time ratio, outlet temperature, and overall performance. The findings show that increasing the flow rate enhances convective heat transfer and PCM melting, although excessive flow shortens the residence time for heat transfer to the PCM; water, RT35HC, and paraffin wax display distinct seasonal patterns, with RT35HC performing strongly in the warm months. The conclusion shows that no single material–flow-rate combination is optimal year-round, so PCM selection and flow-rate control should be chosen jointly within a season-dependent operating strategy.

Graphical Abstract

Numerical Investigation and Seasonal Optimization of a Phase-Change-Material-Integrated Solar Water Heating System

Highlights

· A three-dimensional COMSOL Multiphysics CFD model evaluates a PCM-integrated flat-plate solar water-heating system for building applications.

· PCM type, material fraction (3% and 6%), flow rate, and twelve-month seasonal operation are varied together within a single numerical framework.

· Two commercial PCMs, RT35HC and paraffin wax, are compared with water across seven complementary performance indicators.

· Higher flow rate enhances convective heat transfer and PCM melting, but excessive flow shortens the residence time for heat transfer to the PCM.

· No single material–flow-rate combination is optimal year-round, so a season-dependent PCM and flow-rate selection strategy is recommended.

Keywords

COMSOL Multiphysics

phase change material

seasonal optimization

solar water heating

thermal energy storage

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