Annual performance investigation of an earth-to-air heat exchanger filled with dual-PCMs: Numerical model development, thermodynamic performance and environmental analysis

Previous studies on phase change material (PCM)-filled earth-to-air heat exchangers (EAHEs) have primarily focused on their cooling performance. In this study, a numerical model was developed using the finite difference method, taking into account the effect of air condensation, and implemented in MATLAB. The model's accuracy was validated against both experimental and field measurement data. The validated program was then used to perform continuous three-year simulations for EAHE systems without PCM (Case 1) and with dual PCM filling (Case 2). The results indicate that the influence of initial conditions on the annual thermal performance becomes negligible by the third year. With integrated PCM, case 2 exhibits superior air cooling performance in summer compared with case 1 and a higher likelihood of condensation, with latent heat from air condensation accounting for 4.44–9.48% of the total heat transfer annually. Seasonal performance analysis shows that by adjusting the annual operating modes of both cases, the monthly energy savings, exergy, and seasonal energy efficiency ratio can be significantly improved, and the adjusted operating modes are economically feasible. Finally, under the adjusted ventilation paths and operating modes for summer, winter, and transitional seasons, case 2 achieves an annual single-pipe energy saving of 3603.18 kW h in Chongqing, with 25-year lifetime reductions of 72,838.28 kg, 674.52 kg, and 196.73 kg for CO2, SO2, and NOx, respectively. In summary, these findings deepen the understanding of the annual thermal performance of PCM-integrated EAHE systems and are expected to advance the practical application of this technology.