Development of High Efficiency Core Materials for Vacuum Insulation Panels




Aini, Armin

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Vacuum insulation panel (VIP) is one of the recent innovations that can enhance the energy efficiency of buildings with slim construction. VIPs in pristine condition offer six to ten times higher thermal insulating capacity compared to traditional insulations. The high thermal performance of VIPs is achieved by applying a vacuum to an open porous core material which is encapsulated by a multilayer envelope, providing high resistance to air and water vapor entry. However, the core vacuum level decreases over time, mainly due to the penetration of air and water vapor through the envelope and into the pore structure of the core. The thermal performances of various VIPs are differently sensitive to the decrease in core vacuum level, depending mainly on the mean effective pore size of the VIP-Core. Glass fiber board is widely used as a macroporous VIP-Core due to its low density, high porosity, high mechanical stability, all of which provide high thermal performance at high vacuum. Compared to precipitated silica-VIP, glass fiber-VIP is more sensitive to the decrease in core vacuum level due to its larger mean effective pore sizes. The challenge for VIP-designers is to cost-effectively reduce the thermal performance degradation of glass fiber-VIPs during the service life. After developing an experimental setup for making VIPs and measuring their effective thermal conductivity, this study investigates the effect of two alterations on the thermal performance of a glass fiber board as the VIP-Core: 1) Hydraulic pressing of the VIP during evacuation; and 2) Addition of zeolite powder or diatomaceous earth powder to change the microstructure of glass fiber boards. The mean distance between fibers is reduced due to the pressing during evacuation. The mean effective pore size of the VIP-Core is reduced due to combined effects of pressing during evacuation and the addition of zeolite particles; and it is reduced further due to combined effects of pressing during evacuation and the addition of diatomaceous earth particles. Compared to the glass fiber board, the glass fiber-zeolite composite has on average 20% higher thermal performances at various vacuum levels. The glass fiber-diatomaceous earth composite has a comparable thermal performance with the precipitated silica, up to the vacuum level of P = 102Pa, in addition to have on average 30% higher thermal performance, at various vacuum levels, compared to the glass fiber board. This study concludes that the glass fiber- silica powder composite is a viable method for reducing the mean effective pore size of the VIP- Core.



vacuum insulation panel, high efficiency core materials, glass fiber board, glass fiber-powder composite