Guideline 3 - Insulation Systems / Vacuum insulating panels (VIP)
Vacuum insulating panels (VIP)
Insulation made of man-made materials
Vacuum insulating panels (VIP) are also considered current state-of-art insulation materials VIP is a nearly gas-tight enclosure surrounding a rigid core, from which the air has been evacuated. Fumed silica is used as the core material and several metallized polymer laminate layers are used as the envelope.
VIP is produced as panels and they cannot be adjusted at the construction site as the vacuum between the components in the panel then will be lost.
The review by Jelle (2011) gives values for thermal conductivity as low as 0.003 – 0.004 W/(m K) in just-from-manufactured condition and up to 0.008 W/(m K) after 25 years of exploitation. The reduction of thermal properties with the time is typical for VIP, as moisture and air slowly replaces the vacuum inside the VIP. Based on the type of foil used, thermal conductivity after 100 years can be in the range of 0.006 – 0.016 W/(m K). The decrease in thermal properties is the main disadvantage of all VIP. In the case VIP is damaged by some sharp objects the thermal conductivity can reach up to 0.020 W/(m K).
The main advantage of VIP is 5 - 10 times lower thermal conductivity compared with traditional insulation materials, with means that the same energy efficiency class can be achieved using much thinner layer of insulation material. This has great advantages in the case of internal insulation in historic buildings where loss of living area is reduced. Therefore even taking into account the relatively high cost of VIP, in the case of high value real estate, application of VIP is economic profitable.
Johansson et al. (2014) found that adding VIP to internal surface of historic brick walls lead to higher relative humidity in wooden beam ends and drying capacity on the side of VIP is substantially reduced. Relative humidity in the wall increases substantially when exposed to wind driven rain. Laboratory experiments show that brick and mortar were more capillary active compared to modelling results.