What makes some refrigerators more energy efficient than others? I noticed that some 18-19 cu ft models use as little as 380 kWh annually, but there are others that use over 480kWh. The 380 kWh rating is for a 19 cu ft model and I saw a 9 cu ft model that uses a similar amount.

I am seeing many refrigerators that now come only with one control dial, is this to make them less expensive in manufacturing or does it help energy efficiency also? Seems like since the temperatures cannot be controlled independently would be a disadvantage, no?