Solidification performance of an inline PCM tube bank for air-based residential HVAC thermal energy storage

Abstract

This study investigates the solidification performance of an inline cylindrical phase change material (PCM) tube bank integrated downstream of a residential mini-split air-conditioning unit for peak-load mitigation. Unlike prior air–PCM systems evaluated under passive or loosely constrained ventilation conditions, the proposed configuration operates under HVAC-constrained airflow and inlet temperature conditions representative of residential supply-duct operation. A dynamic building load analysis sized the system to offset a 1.14 kW peak cooling load over a 4-h period, corresponding to 92 L of PCM and 3.95 kWh of storage capacity. Transient solidification was modeled using a two-dimensional enthalpy–porosity formulation with adiabatic outer boundaries and negligible tube-wall resistance, while airflow was resolved using the SST k–ω turbulence model. Parametric analyses examined airflow rates of 118–307 L/s and inlet temperatures of 6–9 °C. Increasing airflow reduced solidification time from 12 h to 3 h, while total stored energy (latent plus sensible) decreased by up to 33.5%. Lower inlet temperatures accelerated charging by up to 47%. During charging, outlet air temperature evolved gradually toward the inlet condition, reflecting diminishing thermal driving potential as solidification progressed. The results quantify charging-time and energy-storage tradeoffs under realistic HVAC boundary conditions and provide design-relevant guidance for integrating inline PCM-based TES into residential air-conditioning systems.