As others have already said a decade and a half ago, high R insulation without much mass is easy. That’s not the problem.
The two main number sets that many consumers look at when comparing refrigerators the the external dimensions and the internal space. A unit that has thicker insulation would have less interior volume. When compared side by side in comparison shopping this is an issue. As the “energy guide” pricing is typically well below $100, size and capacity and features drive the market.
If energy efficiency was the primary consumer goal side-by-side and bottom-mount refrigerators would be gone and pull out drawer refrigerators would be the most common.
Aerogels have a have a remarkably high R-value for their thickness. They are also silly expensive. Not much has changed in the last 15 years, although electricity is more expensive and whitegoods in general are cheaper. Not enough to bridge the gap into a change in design tradeoffs I suspect.
Insulation has certainly come a long way in recent years. My oven, which is now three years old, is bigger inside than the one it replaced but fits into the same space. The outside of the old one used to be too hot to touch when it was in use but the new one barely gets warm. This with a typical differential of 160 degrees C.
My refrigerator installer told me that best way to improve refrigerator efficiency is to keep paper bags inside the refrigerator. These spaces trap the cool air and keep it from cascading out onto the kitchen floor.
Let’s say you add $200 to the cost of a fridge to make it super-insulated.
A. Is that going to pay off in terms of more than $200 savings in electricity? Even assuming that the fridge will last the lifetime of this thread.
B. Are people going to buy the fridge when there’s a $200 cheaper model right next to it? (This aspect drives a lot of product decisions.)
Many of the gains in fridge efficiency have been driven by those energy savings estimates pasted on the fronts of them. But there’s a limit to how far you can push things cheaply.
Not everyone buys the cheapest. There is a clear market for “quality” goods, even when said quality is more in the marketing than much else. Some people will pay the difference, just not everyone. Have a look Miele.
A fridge that will keep its contents cool twice as long in the face of a power outage would be a nice to have. I still vividly remember losing power for three days 18 months ago. Compensation cheque was nice, but losing the entire contents of the fridge wasn’t.
What really kills efficiency is the defrost cycle. Early monitor top refrigerators from the late 1920s and 1930s are nearly as efficient as refrigerators today because they had no automatic defrost, electricity was much more expensive then so good insulation was important, and the freezer is a much smaller proportion of the total volume. Today, very efficient defrost cycles and extra insulation in the freezer compartment are what have really made the big difference, because the refrigeration system itself hasn’t really changed much. It’s the early automatic defrost units from the 1950s through the 1970s when energy was through to be limitless that are the real electricity pigs.
Vacuum insulation panels have been used in (some) refrigerators for many years.
Vacuum insulation isn’t particularly good. When I was doing chemistry, our styrofoam calorimeters were better than our vacuum calorimeters.
The “vacuum-insulation panels” mentioned here aren’t vacuum flasks either. They are more like “vacuum styrofoam”. Except that they are made out of something stiffer than styrofoam, to support the vacuum pressure. And the main advantage is not that they are better insulators than closed-cell foam, the main advantage is that they are more robust than common closed-cell foam insulators.
True vacuum insulation, when coupled with polished metal interior surfaces, and minimal points of contact between the two sides, is extremely good. How good it actually is in practice, when you aim for all of those points but don’t quite hit any of them, can vary widely.
This is the issue. A “frost-free” fridge melts all the ice that builds up around the cooling coils on a regular basis. This probably uses as much heat as the cooling cycle, then it has to cool the coils all over again.
But the measure of how efficient a fridge is -how cold is it to the touch? Your fridge loses cold and your hot water tank loses heat by conduction through the walls. In order to do this, there must be a temperature differential. If the difference in temperature you feel is not that great, then that is not the major heat transfer factor. As mentioned, opening the door frequently is probably the worst loss, just as heating long, uninsulated pipes to feed a bathroom or kitchen is probably the bigger heat loss for hot water.
A typical house uses an average 900KWh a month for everything. But air conditioning could use 10KWh to 30KWh a day typically (3 to 9 hours running time) for some months.
The other, often overlooked, heat conduction path for a refrigerator vs. a thermos, is through the actual refrigerant lines to the heat exchanger in the back. Even when the compressor is off, that is a direct thermally conductive path between the inside and outside of the box.
The insulation is already excellent; if it wasn’t, you would notice severe condensation on the outside of the fridge under humid conditions. The only time I ever see that is on an admittedly inexpensive small fridge I keep outside on the back porch for beer.
It’s possible to get a super insulated fridge, you just have to make it yourself from a chest freezer. Chest freezers have 3x the amount of insulation and don’t lose cold from opening and closing so modifying one to be a fridge can cut the energy usage by 90%.