Heat transfer modeling in vacuum insulation panels containing nanoporous silicas-A review

A vacuum insulation panel (VIP) is a very efficient thermal insulation system for buildings. A porous core material structure is evacuated and wrapped into a gas barrier envelope. Thanks to the low pressure, the total conductivity measured is as low as 5 mW/(m K) for best panels, six to ten times lower than conventional insulation materials. Thin insulation systems with very high thermal performance can thus be designed with VIPs. Heat transfer modeling in these panels is complex, resulting on four contributions of heat fluxes: radiative transfer, solid conduction, gaseous transfer, and envelope thermal bridge. These last years, several approaches have been investigated to estimate the contribution of each heat transfer mode. A complete first review on heat transfer modeling in vacuum insulation panels containing nanoporous silicas is conducted. Monolithic aerogel but also granular aerogels and nanoporous powders (pyrogenic and precipitated) are considered in this review. The parameters that play a key role in the total heat transfer are identified. A special emphasis is put to discuss the influence of pressure and humidity on the total conductivity. The results synthesis can be used to set up a design strategy to minimize the thermal conductivity and to understand the main aging mechanisms. (C) 2012 Elsevier B.V. All rights reserved.