DIRECTIONAL SELECTIVE TRANSMISSION WITH CYLINDRICAL LENSES

Directional selective transmission (DST) is a new principle involving the absorption of solar radiation in winter and its reflection in summer. Its main application is in combination with transparent insulation (TI). The beam radiation is focused on a pattern of transmitting and reflecting strips by means of a field of cylindrical lenses. Radiation from lower sun positions (winter) is transmitted, whereas that from higher sun positions (summer) is reflected. Diffuse radiation is partly transmitted in winter and summer. Applied to transparent insulation, DST is a means to protect buildings from overheating in summer. DST systems have no movable parts, are passive and maintenance-free. They arc self-switching between the seasons with a quasi-step characteristic between transmission and reflection. The maximum beam radiation transmission of south oriented DST systems at Osnabruck (north Germany) on a winter day is up to 64% and less than 5.5% on a summer day; global radiation is transmitted with 50% (winter) and 25% (summer); on clear days with 53% and 17%, respectively. The relation improves in other climates with more beam radiation. In this paper the principle of DST is explained, a prototype is shown with construction details, and an energy evaluation is presented with both experimental and simulation data. There is a satisfactory coincidence of experimental and calculated results.