Transparent internal wall insulation

For reasons of monument protection, interior insulation is often the only option of energy-efficient renovation of the exterior walls. In order not to cover and hide walls with interesting historic surface structures or paint layers, a transparent internal wall insulation based on insulating glazing has been developred and tested. Due to the uneven inner surface of the outer wall and the supporting structure of the glazing, always an air gap exists between the outer wall and the glazing. This cavity has to be airtight towards the warm and moist indoor air in order to avoid accumulation of moisture because the diffusion-tight glazing inhibits re-drying of this enclosure towards indoors. But air exchange with the room air can always happen via leaks. This can lead to mould or moisture damage of the original surfaces. A test setup with transparent internal wall insulation with double glazing was installed in the historic building of the Alte Schäfflerei (Old Cooperage) in order to observe the real behavior of the system. To avoid mould growth conditions in the cavity, an electric heating cable was installed to control the relative humidity of the cavity air. Via a control unit the heating cable warms the cavity air when a certain limit is esceeded so as to lower relative humidity. The main reason for installing transparent internal wall insulation is to reduce the heat flux of the wall in order to save energy. Therefore surface temperatures, relative humidity of the cavity, airtightness, heat flux and energy consumption of the heating cable were measured. The measured data shows that the controlling of the relative humidity in the cavity is necessary and the overall energy balance of the system shows that efficient retrofit is possible in this innovative way.