Energy-saving potential estimation of retrofitting aged buildings considering external wall insulation degradation

This study presents the potential for improving energy performance by considering thermal performance degradation due to the aging of building envelopes. The U-value is a critical parameter for simulating a building's energy performance evaluation. However, because of the difficulty of in-situ measurements, many cases involve using standard or normative values for assessment. Nevertheless, considering the degradation of the external wall's insulation performance due to aging is crucial. We measured the thermal transmittance of external walls in 62 aged buildings constructed in various periods and quantitatively derived the degree of insulation performance degradation by comparing it with the legal standards at the time of construction. Moreover, to analyze the problems caused by neglecting the U-value deterioration in evaluating the energy-saving potential through retrofitting, a case study was conducted on 70 aged buildings where actual retrofit projects were implemented. We compared the cases by applying both legal thermal transmittance standards and corrected values based on actual measurements to the sites' pre-retrofit energy simulation models. The measurements showed that the aged buildings had an average insulation performance degradation of 49.69 % compared to the legal standards at the time of approval. Simply using the legal standard for the external wall's thermal transmittance underestimated the energy savings by 16.73 %. Furthermore, the study confirmed that correcting the U-value based on actual measurement data is essential for accurately evaluating the retrofit effect on aged buildings.