Vacuum Insulation Panels: a promising solution for domestic refrigerators
Thanks to their low thermal conductivity, Vacuum Insulation Panels (VIPs) make it possible to greatly reduce the energy consumption of domestic refrigerators. However, their adoption comes up against problems of cost and lifespan.
In a review article1 recently published in the International Journal of Refrigeration, researchers from the Brunel University in UK point out that the global electricity consumption of domestic refrigerators is approximately 6% of the total electricity consumed and represents on average 14% of household electricity consumption.
Approximately 50% of the cooling load stems from the heat transmitted through the refrigerator walls. Typically, refrigerators are insulated with materials such as foams whose thermal conductivity is higher than 20 mWm-1K−1. Alternatively, using Vacuum Insulation Panels (VIPs), whose thermal conductivity is lower than 7 mWm-1K−1, can significantly reduce their energy consumption whilst maximising the usable inner volume.
Based on a comprehensive review of the studies published on this subject, the authors report reductions in energy consumption varying from 20 to 30% when the walls are insulated with VIPs instead of traditional polyurethane (PU) foam, depending on the thermal conductivity of the VIPs used. Furthermore, a 32% inner volume gain was observed when fumed silica VIPs were used in a domestic refrigerator’s side walls. The authors also report a payback period of 9.7 years for fridges and 4.5 years for freezers using VIPs with a thermal conductivity of 4 mWm-1K−1.
However, VIPs encounter obstacles to provide insulation of choice in refrigerators. The first one is due in particular to the uncertainties related to the lifetime of the VIPs. For example, for a VIP with chopped glass fibre strands as core, the service life (the time in which the thermal resistivity of VIP stays higher than 87 mKW−1) was estimated to be five years, significantly less than the lifespan of the refrigerator itself.
The current high cost of VIPs, which can be five times per unit area higher than conventional foam insulation, is another issue. The core accounts for the majority of the total VIP cost. Fumed silica, glass fibres and foams have been widely used as VIP cores.
Computer modelling of the complex heat transfer phenomenon is a priority to develop newer core composites and envelopes leading to more satisfactory cost-effectiveness VIPs with sufficiently long lifetimes.
(1) Verma S., Singh H., Vacuum insulation panels for refrigerators, International Journal of Refrigeration, April 2020.