Experimental Study on Photothermal Properties of Colored ETFE Foil

To meet the requirements of architectural design, colored ETFE foils have been developed and applied to modern large public buildings. However, as a new material, research on the properties of colored ETFE foils is relatively limited, especially the typical photothermal properties of ETFE foils. Starting from practical engineering applications, nine kinds of colored ETFE foils and one kind of colorless transparent ETFE foil, which were used in the Chengdu Agricultural Expo Park as representative samples, were selected for experimental testing of their light transmittance and thermal properties. Firstly, a UV visible near-infrared spectrophotometer was used to measure the transmittance and reflectance of the test foil in the solar radiation band. By comparing the trend and fluctuation of the solar radiation curves between colored ETFE foils and colorless transparent ETFE foil, the changes in the light transmittance and thermal radiation property of colored ETFE foils and colorless transparent ETFE foil in the solar radiation band were analyze. The visible light transmittance and solar radiation coefficient of the test foil were calculated and obtained. The thermal conductivity property of the test foil was measured using laser scattering method, and the thermal conductivity coefficient and thermal resistance of the test foil at room temperature were calculated. The changes in photothermal property parameters of ETFE foils with different colors are summarized and compared them with colorless transparent ETFE foil. The results show that: 1) in the ultraviolet region, both the transmittance and reflectance of colored ETFE foils are at a low level (not exceeding 30% in total), and colored ETFE foils have strong absorption capacity for ultraviolet rays. In practical use, attention should be paid to the aging problem of colored ETFE foils. 2) The visible light transmittance and solar radiation transmission coefficient of colored ETFE foil are lower than those of colorless transparent ETFE foil, and the thermal conductivity is slightly lower than that of colorless transparent ETFE foil. The solar radiation absorption coefficient and thermal resistance of the colored ETFE foil at the same thickness are both higher than those of colorless transparent ETFE foil. 3) The main factor affecting the visible light transmittance and solar radiation coefficient of colored ETFE foils is the depth of the foil color. The lighter the foil color, the greater the visible light transmittance, the greater the solar radiation transmission coefficient, and the smaller the absorption coefficient. As the color of the foil deepens, the absorption ability of the foil to sunlight gradually increases, and the transmission and reflection coefficients are relatively low. 4) The main factor affecting the thermal resistance of colored ETFE foils is the foil thickness. Under the same thickness, the thermal resistance of colored ETFE foils is 7%-14% higher than that of colorless transparent ETFE foil. The research results indicate that using colored ETFE foil as a building enclosure structure can increase the reflection and absorption of solar radiation by the enclosure structure, and to some extent block heat conduction, reducing the problem of excessive indoor lighting and summer overheating.