Glass–film-combination: Opto-physical properties and energy saving potential of a novel greenhouse glazing system

A combination of anti-reflection coated glass and ethylene tetrafluoroethylene film is introduced as a novel glazing system for greenhouses and similar buildings. It combines the advantages of the individual materials (durability/low weight; favourable condensation behaviour/self-cleaning) and of single and double layer systems (light transmission/insulation). By inflating/deflating the glass–film interspace, the additional insulation can be switched on and off. Since no standard method for this purpose is available, a hot box-system was developed to measure heat transfer coefficients (U-values) of different models of the glass–film-combination (GFC) and other commonly used greenhouse glazing materials at different surface inclinations; with or without condensation. Surface inclination did not greatly influence heat transfer. Condensation increased the U-values more pronounced for single layer-systems than for the GFC. Influences of wind velocity on heat transfer decreased with the degree of insulation. Overall, when mounted with adhesive tape, the energy efficiency of the GFC was 38% higher compared to customary float glass. The energy saving potential of plastic profile mounted GFC versions was 50% and 64% for the double and triple layer system (ETFE-film on both sides of the glass pane), respectively. PAR transmission of the GFC was similar to single pane float glass, its UV transmittance markedly higher.

► Development and test of a glass–film-combination as a novel, energy saving glazing system.
► Additional insulation can be “switched” on/and off according to requirements.
► Development and test of a hot box system for measuring U-values under practice-like conditions.
► Energy saving up to 67% (reference: float glass); reduced influence of condensation and wind speed.