Application demonstration and performance of a cellulose triacetate polymer film based transparent insulation wall heating system

G. M. Wallner1, R. Hausner2, H. Hegedys3, H. Schobermayr4, R. W. Lang1’5 1>1nstitute of Materials Science and Testing of Plastics, University of Leoben, A 2) Arbeitsgemeinschaft ERNEUERBARE ENERGIE, Gleisdorf, A 3> Planungs — und Bauges. m.b. H. HEGEDYS-HAAS, Mitterlassnitzberg, A 4> Dr. Schobermayr Kunststofftechnik, Altenfelden, A 5> Polymer Competence Center Leoben GmbH, A

Abstract

For the application demonstration of Cellulose Triacetate (CTA) polymer film based transparent insulation (TI) structures a technically and ecologically optimized TI facade system was developed and used to equip a south-oriented wall of a solar house meeting passive house standard in Graz, Austria. The demonstration building was euipped with an appropriate data recording system for solar irradiation, temperature, heat flux and humidity. The practical experiences within the heating periods 2002/03 and 2003/04 are reported in this paper. For the optimized TI facade system a solar energy efficiency of about 43% and a U-value of 0.76 W/(m2K) were obtained. Although CTA absorbs a high amount of water no adverse condensation phenomena were observable visually. The reasoning for these findings is explained and related to construction details.

Introduction

At present mainly small-celled capillary and rectangular honeycomb transparent insulation (TI) structures based on PC are available on the market (e. g., www. okalux. de, www. polygal. com,www. les-twd. de). Due to the applied extrusion and cutting processes these small-celled commercially available TI structures contain bulk and surface imperfections which adversely affect solar transmittance. The production process is rather complex and not very flexible concerning the use of different materials or the optimization of the material. In previous years polymer film based TI materials were developed and introduced into the market (www. wacotech. de, www. advancedglazings. com). The processes to produce such structures, described in [1], are relatively simple and allow to process materials which are not easily melt processable (e. g., CA, CTA). However, the realized and commercially available absorber-perpendicular structures are rather large — celled with cell diameters of about 9 mm. In general, the large-celled film based structures have a rather low material fraction, which results in relatively poor infrared absorptance, which is a bottleneck for both, applications of TI materials in solar wall systems and in glazings with high emissivity surfaces.

To develop and optimize a small-celled, polymer film based absorber-perpendicular transparent insulation material especially for solar wall applications a research project was carried out at the former Institute of Polymer Technology (JOANNEUM RESEARCH) and at the Institute of Materials Science and Testing of Plastics at the University of Leoben (Austria) in close cooperation with the Fraunhofer Institute for Solar Energy Systems (Freiburg, Germany). Furthermore, an application demonstration project was carried on in cooperation with the Planungs — und Bauges. m.b. H. HEGEDYS-HAAS (Nestelbach, Austria) and the Arbeitsgemeinschaft ERNEUERBARE ENERGIE (Gleisdorf, Austria) focussing on the manufacture of the small-celled, polymer film based TI structures and their application at the facade of an ultra-low energy solar house. While the results of the

TI structure development and optimization are reported in several papers [e. g., 2, 3, 4], the purpose of this paper is to describe and discuss the results concerning the performance of the novel TI wall system including measurement results during the heating periods 2002/03 and 2003/04.

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