Abstract
Polyurethane foam is the preferred insulator material in a wide range of appliances such as refrigerators and freezers. The recent phase out of CFC-11 has however decreased its insulation performance due to the need to adopt environmentally more benign blowing agents, such as HCFCs and hydrocarbons, all having higher gas thermal conductivity. This represents a serious drawback since specific regulations to reduce the energy consumption in refrigerators have been issued in recent years, and even more demanding reductions are under debate and expected to be applied worldwide by the turn of the century. In response to these requirements, Vacuum Insulated Panels (VIPs) technology has been studied and developed. Suitable components, filler, bag and a getter to maintain the necessary vacuum, have to be selected to ensure the high super-insulation properties which can be exhibited by VIPs. Among various core materials for VIPs, open cell foams present specific advantages in terms of performance, weight, processability and cost. In the present paper, the recent developments in the VIP technology are reviewed and discussed focusing the attention on the open cell polyurethane. The various gas sources deteriorating the vacuum during the panel life have been experimentally determined and evaluated by means of outgassing, permeation and gas analysis measurements on VIP components and finished devices. A suitable getter system able to cope with the gas load and to ensure vacuum performance and reliability is also described.
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