The temperature of the environment generally below 5 degree Celsius during the winter. However average temperature setting of the refrigerator ( not freezer) is 0 to 10 degrees.Then let the air flow inside of the refrigerator . It is similar to keeping the vegetables milk etc outside of the window.
Concept is get the air from outside during the winter and control the inlet. Am I violating any law ?. As today we use the heater to warm the house and then cool the things using refrigerator.
It is very simple idea and easy to implement it. You may fine tune it using air filtering etc ...