1.Introduction
The technology of thermal insulation glazing films are maturely developed in recent years. The thermal insulation mechanisms of commercial glazing films are diversified. For the reason that the construction of glazing films is relatively simple and do not need scaffoldings, it is especially suitable for insulation upgrade of the fenestration of an existing building case. A previous research has showed that the glazing films are capable of reducing indoor solar radiation heat gains regardless of the films’durability. However, the performance degradation of films, especially for the optical performance, is the primary concern factor for application decision by architects, building investors, or film production companies in perspective of building energy conservation. The scope of the warranty of commercially available glazing film given by the production industry only includes its physical degradations, such as discoloring, losing adhesive capability, or appearing alveoli. There are no existing standards or regulations on how to adequately conduct a degradation experiment for the optical degradation of glazing films. The objective of this study is to propose a draft standard of the test method on the degradation of optical properties of adhesive films for building glass by literature reviews and pilot accelerated degradation experiments. The proposed test method provides a standardized optical performance accelerated degradation method for the application of identifying the commercial films’ performance degradation curve.
2.Methodology
As there are no existing international standards or regulations of the optical performance degradation test method. Most of these standards are focused on the weather durability testing, which is not sufficiently coincide with the aim of this study. Therefore, an extensive literature reviews were conducted regarding the artificial weathering methods of a variety related materials as fundamental references for formulating the standards of the testing method on the degradation of optical properties of adhesive films for building glass. In view of it lacks definitions on how much degradation exposure time is needed for optical performance degradation test; we planned and conducted a preliminary artificial degradation study. Two major types of the commercially available glazing films were tested using the accelerated weathering/degradation equipment for 1800 hours to understand their sensitivity between the exposure intensity and exposure time. This pilot study is conducted in the national building material testing laboratory.
3.Major findings
（1）Literature reviews of international standards on the testing method for material degradation is conducted. It is found that no existing standards are exclusively for glazing film’s optical degradation, most of them are for weathering test. The German standard, DIN BS EN15752-1, and the Japanese standard, JIS A5759, are the standards exclusively for building glazing films but still is focused on the weathering test.
（2）In this study, both solar reflective and absorptive type films were tested using accelerated degradation machine for study the effect of their optical properties degradation against exposure time due by UV light exposure. After 1800 hours testing, we observed that there is circa 11.0% and 9.7% decrease in the solar heat gain coefficient (SHGC). In contrast, there is no evident degradation in the reflectivity and transmissivity of the visible light as well as the reflectivity of the solar radiation.
（3）By referencing to the existing international and domestic standards, the degradation method, specification of the testing equipment, and the standardize degradation procedure were established.
（4）A standard for the testing method on the degradation of optical properties of adhesive films for building glass was drafted. The content includes using UVA-340 ultraviolet light as the lighting exposure source to a three steps’ degradation procedure utilizing accelerated degradation machine.
（5）A conversion method of the equivalent exposure time between the natural and artificial degradation was proposed in this study.
4.Recommendations
Base on this research an immediately feasible recommendation is reached: The major results of this project is drafting a standard draft of the testing method on the degradation of optical properties of adhesive films for building glass based on the findings of the degradation experiment. To promote the utilization and application of glazing films on existing buildings as a means of green building renovation, it is suggested to deliver this draft standard to the Bureau of Standards, Metrology and Inspection, Ministry of the Economic Affairs, for further consideration of formulating a formal CNS standard.