Bypass Tank Integration for Quick Start-Up and Peak Load Support in Thermal Storage Heating Systems

Abstract

Supercooled phase change materials are highly promising for space heating applications due to their ability to release latent heat upon crystallisation initiation, even at ambient temperatures. This property enables more effective solar energy utilisation and significant reductions in carbon emissions for short- to medium-term thermal storage. However, the widely used sodium acetate trihydrate has a melting point of 56–58 °C, which often necessitates auxiliary heating in cold seasons or when sudden short-term demand arises during morning warm-up and evening peaks. To address this limitation, this study proposes a bypass tank configuration incorporating a coil-integrated latent heat storage unit filled with erythritol, enabling rapid high-temperature boosting (10–20 °C) during morning warm-up and evening peak periods for a short time. The erythritol tank is charged via PV-powered electric heaters and engaged only when sodium acetate trihydrate storage cannot maintain the required supply temperature and heating. A dynamic model of the coil-integrated tank was developed, experimentally validated, and further examined through CFD simulations to capture discharge behaviour under varying inlet temperatures and flow rates. Real weather data and building heating profiles were used to evaluate the system’s practical boosting capability. Results show that a 35 L erythritol tank can sustain outlet temperatures above 50 °C at moderate flow rates, deliver boosting durations of up to 22 min, and reliably support dual-peak operation within a single day. The findings highlight the effectiveness of erythritol as a high-temperature bypass storage medium for improving quick start-up performance, reducing reliance on auxiliary electric heaters, and enhancing operational flexibility in solar-assisted heating systems