Passive solar component based on evacuated monolithic silica aerogel

Application of monolithic silica aerogel as transparent insulation material in a passive solar component for use in windows, solar walls, sunspaces is the objective of this study. This work concentrates on a specific construction which has been chosen both in order to protect the monolithic silica aerogel and to achieve efficient thermal insulation. The construction consists of a layer of evacuated monolithic silica aerogel between two layers of glass panes and a rim seal. Four prototypes have been made, each with a different design of the seal. Special attention has been given to the cold bridges at the edges since they may double the overall heat transfer coefficient compared with that of the centre value. The latest prototype measuring 1 m × 1 m contained evacuated aerogel with a density of 150 kg m−3 and a thickness of 18 mm. The measured centre and overall values of the heat transfer coefficient were 0.52 W m−2 K−1 and 0.57 W m−2 K−1. If the aerogel density and the thickness were 100 kg m−3 and 20 mm, the centre and overall heat transfer coefficients would be 0.37 W m−2 K−1 and 0.47 W m−2 K−1. Simulations have shown that, for a Danish location, windows with aerogel used in a single family house will annually save 878 MJ per m2 in comparison with ordinary double pane windows. For an unvented solar wall with aerogel, the net energy gain will be 80% higher than the savings obtained by adding 100 mm of conventional opaque insulation to the wall.