Losing coldness due to opening door is really not very relevant. Most of the cold in a fridge is stored in the items you keep in the fridge, not in the air itse

Losing coldness due to opening door is really not very relevant. Most of the cold in a fridge is stored in the items you keep in the fridge, not in the air itself. A typical fridge holds maybe 1 kg of air inside it, and cooling 1 kg of air by 17 Kelvings is 17 kJ, which is probably a minute of compressor running. Opening a fridge and losing all cold air from it thus costs you probably something like a quarter of a cent.