Measurement of angle-dependent properties of different solar protection devices

Thomas Knauer, Tilmann Kuhn, Werner J. Platzer

Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, D-79110 Freiburg,

Fax: +49-(0)761/4588-9000, werner. platzer@ise. fraunhofer. de

Introduction

In the sixties of the last century solar calorimetric outdoor experiments have been performed on the combinations of solar shading devices and single and double glazed window units. From these experiments typical reduction factors for the effective total solar energy transmittance have been derived and published. In standards such as EN 832 or DIN 4108 part 6 tables with typical reduction factors of the main shading device types are given. However, for a more exact derivation of the total solar energy transmittance of a fagade including solar shading device, other means are needed.

Within IEA Task 27 we try to develop and check methodologies to characterize solar shading devices experimentally, and compare with different theoretical calculations. The experimental characterisation is based on a new generation of solar calorimetric testing devices developed within completed European and national projects. In this paper We want to compare experimental results using these devices with calculated results using some new and unvalidated standards for different combinations of solar protection devices and glazings.

State of the art

Solar calorimetric measurements are suitable for determining the total solar energy transmittance of a facade consisting of glazing plus solar protection devices. The methodology and measurement procedures have been developed in the European project ALTSET (Angular Light and Total Solar Energy Transmittance) [ 4] as well as the German project rEgES [ 6]. However, only few results have been published, for example in a comparison of the experimental results with a model based on raytracing and an adapted resistance network [ 5].

The European standardisation tried to improve methodologies to calculate the shading reduction factors in an approximate way using relatively simple algorithms, and finally issued a very rough calculation method in the standard EN 13363 part 1 [ 1] and a more detailed reference method has passed the formal vote recently (part 2 [ 2]). However, there are several restrictions and simplifications in both documents which do not allow to characterize solar shading devices using lamellae in a sufficient way.

Also the parallel activity of ISO, trying to develop a consistent standard for solar and thermal performance calculations of glazings, windows and shading devices does not solve this problem completely [ 3].

Similarly the European computer tool for glazings and shading devices WIS (Window Information System) has been developed further in a European network called WINDAT (www. windat. org). The modelling of solar shading in this tools is implementing the international standard ISO/FDIS 15099. All these algorithms based on standards are rather restricted in the scope as they can be applied only to special situations and describe only idealised systems (flat slats). Moreover, the modelling has not been validated by measurements. This gap should be closed with this paper.

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