Vapor Compression Refrigeration System for Cold Storage on Spacecrafts

NASA is looking for solutions for its long-term or distance food storage and transport applications. Achieving high thermal efficiencies and reliability while maintaining volumetric and mass efficiency has been the key challenge with these kinds of refrigeration/freezing systems in a microgravity environment. Previous state of the art refrigerator/freezer systems such as the ISS RFR, use thermoelectric thermal control with very low overall system COP of around 0.36 (in freezer mode).Alternatively, terrestrial cold food storage systems utilize much more efficient vapor compression thermal control systems, making the systems lighter and more compact. Currently, these systems do not have provisions to fulfill the load and reliability requirements of space applications and are also not designed for microgravity operation. An example would be Kelvinator KCCF220QW chest freezer. This freezer can maintain temperatures as low as 26͒C at COPs of around 2.2 to 2.4.Air Squared is proposing the development of a Zero-gravity Vapor Compression Refrigerator (ZVCR). The ZVCR is an oil-free, scroll driven, vapor compression food storage system that is thermally efficient, lightweight and reliable. Similar to conventional systems, the ZVCR will include four major components: compressor, condenser, expansion device and evaporator. But, instead of a heavy and oil lubricated working fluid compressor, it will use an advanced oil-free orbiting type scroll compressor and expander developed by Air Squared. Its oil-free design will remove system’s operational reliance on gravity while keeping the design compact & lightweight at higher efficiencies. For expansion work recovery, a scroll expander based on the same technology as the compressor will be used to further improve the system’s performance. Custom heat exchangers will be designed for efficient operation in microgravity while considering the size, weight and reliability requirements.