Frequency thermal characteristic and parametric study of multi-functional building envelope for coolth recovery and thermal insulation: Modelling and experimental validation

The exhaust air insulation (EAI) wall provides a new solution to utilize the low-grade coolth energy of exhaust air in conditioned rooms for preventing the heat gain through the building envelope. Such a multi-functional building envelope takes advantage of the exfiltration process of the cool indoor exhaust air to block the inward conductive heat flux within building envelope in cooling season, and then cooling load is effectively decreased. Previous studies demonstrate the excellent thermal insulation performance of the EAI wall. However, current studies still lack a highly efficient compactional method for simulating the dynamic thermal performance of this wall. Moreover, thermal characteristics of the wall still have not been investigated in frequency domain, which would offer significant design guidance. To address these critical challenges, a frequency-domain finite-difference (FDFD) model of the EAI wall was developed in this study to analyze its transient heat transfer with high computational efficiency and no stability problem. An experimental platform was established to conduct the experimental analysis of the EAI wall and verify the proposed FDFD model. Moreover, the validated FDFD model was used to numerically evaluate the thermal characteristic of EAI wall in frequency-domain. The influences of some design parameters on the decrement factor and phase delay of the wall were also considered in numerical investigation. The result demonstrates that the frequencies of outdoor thermal disturbances exhibit a remarkable impact on the thermal characteristic of EAI wall. The decrement factor of the EAI wall can decrease to near zero for all the frequencies of outdoor thermal disturbances, when airflow velocity reaches to 0.005 m/ s or thickness of porous medium increases to 50 mm. This means that the EAI wall could effectively moderate the impact of outdoor thermal disturbances towards the indoor thermal environment under most scenarios of outdoor thermal disturbances. The outcomes of this study can provide a high-efficiency transient heat transfer model and some important design guidelines for this wall. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The exhaust air insulation (EAI) wall utilizes low-grade coolth energy to reduce cooling load effectively. A frequency-domain finite-difference (FDFD) model was developed to provide a high-efficiency transient heat transfer model and important design guidelines for the wall.