Citation: Zakri, W.; Mellouli, S.; Fageehi, Y. Performance Assessment of Three Latent Heat Storage Designs for a Solar Hot Water Tank. Sustainability 2023, 15, 640. https://doi.org/10.3390/su15010640 Academic Editor: Sergio Nardini Received: 16 November 2022 Revised: 7 December 2022 Accepted: 21 December 2022 Published: 30 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Performance Assessment of Three Latent Heat Storage Designs for a Solar Hot Water Tank Waleed Zakri , Sofiene Mellouli * and Yahya Fageehi Mechanical Engineering Department, College of Engineering, Jazan University, Jazan 45142, Saudi Arabia * Correspondence: sofiene.mellouli81@gmail.com Abstract: Solar hot water tanks (SHWT) based on a latent heat storage system are gaining momentum for their integration into solar heater water collectors. They can efficiently store daytime solar thermal energy and shift on-peak period loads to off-peak periods. However, their performance is generally limited by the tank configuration, the design of the thermal storage system, and the selection of the appropriate phase change material (PCM). This work presents a numerical investigation of three SHWT-PCM storage designs. A mathematical model was developed to predict the effectiveness of the geometric design and operating conditions in the SHWT-PCM system. Moreover, a sensitivity analysis was performed on the PCM type and PCM thermo-physical properties. The obtained numerical results demonstrated that the energy efficiency of the SHWT-PCM system was significantly impacted by the PCM thermo-physical properties (melting temperature, thermal conductivity, and enthalpy). In addition, it was found that using encapsulated PCM tubes with an external PCM jacket in the SHWT can result in a thermal efficiency of 70%. Keywords: solar hot water tank; thermal energy storage; PCM; water tank configuration 1. Introduction The present energy scenario is easily analyzed by the rapid depletion of fissile fuels as well as greenhouse gas emissions, which is alarming for alternative energy solutions. One of the solutions considered is the proper use of renewable energy sources. Electrical energy consumption in buildings, especially for air conditioning and water heating loads, uses about two-thirds of the total energy demands [1]. Therefore, it is essential to limit energy consumption in buildings. Shifting a portion of the electricity consumption from the on-peak period’s electricity demand to the off-peak period could have significant economic, environmental, and social impacts. Among renewable energies, solar energy has the highest potential [2]. This energy source presents storage challenges, as thermal storage can take the form of sensible or latent heat. Storing solar thermal energy during surplus periods and reusing this heat over other nightly periods of the shortfall would improve the performance of this system as well as enhance the operation of the solar water heaters. Integrating thermal energy storage via latent heat thermal energy is a promising technology to transfer on-peak load periods to off-peak load periods. Thermal energy storage systems can be easily integrated with building a wall, solar water collectors, and domestic hot water tanks. The production of domestic hot water is a major concern, particularly the impact of the energy efficiency, size, and volume of the storage tanks [3]. The integration of phase change materials (PCMs) makes it possible to provide solutions using latent heat instead of sensible heat to store thermal energy. Thus, this work mainly concerns the detailed study of heat transfer within water heaters with various designs, with a numerical [4] and experimental [5] approach. By integrating a solar water heater into a latent heat storage system, the most important and common designs are (i) employing PCM capsules in the water tank that conventional solar collectors power, (ii) employing the use of a conventional solar collector with the addition of a separate PCM unit, and (iii) adopting integrated solar Sustainability 2023, 15, 640. https://doi.org/10.3390/su15010640 https://www.mdpi.com/journal/sustainability