Numerical Investigation of the Thermal Performance of a PCM-Filled Glazing Cavity in a Trombe Wall System

Abstract

Trombe walls are widely used passive solar heating systems for cold winter climates, but suffer from large diurnal temperature swings and limited heat delivery after sunset. This study numerically investigates replacing the air in the double-glazing gap of a Trombe wall with a phase change material (PCM). A two-dimensional transient CFD model of a 4 m × 3 m room with a Trombe wall was developed in ANSYS Fluent using the enthalpy porosity method and the realizable k–ε turbulence model. Grid independence was confirmed with a 36,000-cell mesh, and the air-filled reference case was validated against published Trombe wall data within 9%. Hourly ambient temperature and solar heat flux records for a recent cold, clear winter day in Yazd, Iran, were imposed as boundary conditions. The PCM-filled cavity was cooler than the air-filled case shortly after sunrise, by about 1–1.6 °C, as the PCM resumed absorbing heat after releasing its reserve overnight. The two configurations converged around midday, after which the PCM-filled cavity became progressively warmer, reaching a margin of 4–6 °C in the early evening, and easing somewhat overnight while remaining the warmer of the two. The PCM-filled cavity also drove higher buoyancy induced velocities. The PCM layer’s nominal storage capacity was about 9.4 MJ per meter of wall length, over four orders of magnitude more than air, 89% as latent heat. Mean room temperature rose by 1.1 °C; the standard deviation and peak-to-peak swing increased accordingly, and time within the 20–26 °C comfort band fell from 59.8% to 47.0%, reflecting heat concentrated in the evening rather than spread evenly. Overall, the PCM-filled cavity increases heat availability specifically after sunset, when heating demand is greatest, rather than producing a general improvement in steady state thermal comfort, and does so without additional energy input.