Vacuum insulation in cold chain equipment: A review

In 2017, 11.41 million refrigerators and 1.85 million freezers were sold in USA alone; each unit consuming approximately 500 kWh/year with an average life expectancy of 12 years. Traditionally, fridges and freezers have been insulated with polyurethane foam (thermal conductivity >0.020 W/m.K). There is a significant scope of reducing the heat gain by the cooled interior space from external environment by employing better insulation materials such as vacuum insulation panels (VIPs) than polyurethane foam. VIPs can achieve a thermal conductivity of <0.002 W/m.K. This paper presents an overview of heat transfer theory for VIPs and historical research into VIPs suitable for fridges, freezers and reefer trucks. A refrigerator with 56% of its external surface area covered with VIPs is reported to reduce the energy consumption by 21% compared to that consumed when using polyurethane foam. This means a potential energy saving of 1260 kWh_p over the lifetime of a refrigerator and 5 billion kWh_p if 25% of all fridges were VIP insulated. A proportionate reduction in the concomitant carbon emissions is predicted.