F. Giovannetti1* and K. H.C. Fischer2

1 Institut fur Solarenergieforschung Hameln (ISFH), Am Ohrberg 1, 31860 Emmerthal, Germany
2 Karl Fischer Glasgrobhandlung, Gottlieb Daimler-Str. 46-48, 71711 Murr, Germany
* Corresponding Author, giovannetti@isfh. de

Abstract

The paper presents experimental results of suitability tests for the use of microstructured films as suspended layers with light-redirecting properties in multiple glazing systems. Our investigations focus on the optical and the mechanical properties of the films as well as on the durability of the insulating glass units. UV-stabilized composite films are identified as best performing product and are thus chosen for prototyping a prismatic film designed for seasonal shading. Simulations based on measured material data confirm the potential of the system under development, which combines improved insulation, passive use of solar energy and overheating protection. For a triple glazing with 2 low-e coatings we calculate a thermal transmittance (U-value) between 0.6 and 0.8 W/m2K, depending on the gas-fill and the gap width, and an incident angle dependent solar heat gain coefficient (SHGC) variable from 0.58 to less then 0.10.

Keywords: glazing, solar energy gain, overheating control, microstructures

1. Introduction

Static or movable prismatic systems have been in use for a long time in architecture as sun-shading or daylight redirecting devices [1, 2]. Due to the high costs related to the elaborate manufacturing and integration, their use is limited to demonstration or prestigious buildings so far.

As their optical functionality is independent of the prism dimension, the replacement of expensive panes by microstructured films is a promising approach to reduce the overall cost of this type of products, which could help to develop a larger market. Appropriate technologies and materials to manufacture large area microstructured films for architectural applications have been intensively investigated in the last years [3, 4]. Further work is now required with regards to assembly, characterization and long term monitoring of the whole glazing system.

The purpose of the project presented in this paper is the development of a cost efficient and energy saving multiple glazing for the use in glass facades or transparently insulated walls, which integrates a prismatic film as seasonal shading device [5].

The insertion and suspension of a film, which has already successfully been implemented with low-emissivity coated films, is here investigated with structured film as an alternative solution to lamination. This results in a triple unit with two air or gas gaps without having the weight and the thickness of a triple insulating glass (Fig.1).