This made me think. I would kind of expect the energy consumption of a fridge to be related to the surface area of the cooled volume rather than the volume itself. It's not necessary to spend any energy cooling air that is already surrounded by equally cold air.
Assuming all fridges are cubes, doubling the volume of the fridge will increase the surface area by a factor of 2^{2/3} = 59%. This will also be true if the fridge has any rectangular dimensions and you double the volume by scaling it up evenly in all three dimensions.
Things are more complicated if you scale the dimensions of the fridge unevenly.
> Assuming all fridges are cubes, doubling the volume of the fridge will increase the surface area by a factor of 2^{2/3} = 59%.
You don’t have to assume any shape for this, as long as the shape remains the same, and that it is not fractal. You could have a spherical fridge and it would still be true.
> You don’t have to assume any shape for this, as long as the shape remains the same, and that it is not fractal. You could have a spherical fridge and it would still be true.
Why assume that the old fridge will be geometrically proportional to the new fridge? I think that's particularly unlikely to be true in the case of a person replacing their existing refrigerator.
> I would kind of expect the energy consumption of a fridge to be related to the surface area of the cooled volume rather than the volume itself.
I'd expect that for a fridge that's permanently closed, but what if you open it regularly? I'd expect a lot of the cold air inside (so volume) to mix with the room-temperature air once you open it..?
> Things are more complicated if you scale the dimensions of the fridge unevenly.
They are. Unless you reach the scale of the walk-in fridge, you don’t want a fridge to be deeper than an arm’s length, and even small fridges have that depth because they’re designed to fit a kitchen top, which also is scaled for an arm’s length.
Vertical scaling is a bit more flexible, but will stop at about 2 meters (until you reach sizes that you can drive a forklift in)
On the plus side, if you scale things evenly, wall thickness also goes up, so heat losses per m² of area will go down.
The energy consumption of a fridge depends on what it takes to cool the entire contents within a fridge, because heat from center of the food will travel to the surface when the surface cools down. Till the temperature of the entire food item matches the set temperature of the fridge, the fridge will be running. When you open the fridge, warm air enters the fridge, and the contents of the fridge gain heat.
Then there's variability depending on thermal conductivity and specific heat capacity of various foods. So what you're trying to calculate is heavily dependent on the actual contents, not just surface area.
Of course, fridges have cycling behavior similar to an AC that turns on as soon as temp dips below a set temp, but has a window of sorts. Making the above math even more complicated.
> The energy consumption of a fridge depends on what it takes to cool the entire contents within a fridge, because heat from center of the food will travel to the surface when the surface cools down.
This assumes that the dominant energy expenditure of the fridge is bringing new food down to fridge temperature.
But almost all of the contents of a fridge have been in there for a while and are already at fridge temperature. Most of what the fridge is doing is maintaining the internal temperature against the outside environmental temperature.
Biggest factor for many people is that the fridge is wedged in an alcove with insufficient gaps for air flow, so it drowns in it's own waste heat and efficiency plummets.
Oh, that's a good point! Indeed, from what I can see American fridges are indeed larger. Mine has a volume of ~250 liters (of which 180L are fridge and 70L are freezer).
Those sizes exist in the US, often called compact refrigerators or apartment refrigerators. (although these days most apartments have the full size American-style fridges too)
These are becoming more popular in Europe, my mother for instance bought it, which I can't comprehend since she lives just with her husband. On top of that she bought also chest freezer for effin 2 people household. Meanwhile my family of 4 has no issues to use ~210cm regular Whirpool fridge with bottom freezer.
I don't like the idea of American fridges, they waste lot of space on the separator middle wall, I think the best compromise who is not fine with regular fridge are now a bit wider fridges but with single vertical door.
My Chinese in-laws have vertical fridge which has 3 sections, top regular door fridge, middle drawer which goes directly outside (not sure whether it's chilled or frozen), no need to open anything and bottom freezer with door.
> My Chinese in-laws have vertical fridge which has 3 sections, top regular door fridge, middle drawer which goes directly outside (not sure whether it's chilled or frozen), no need to open anything and bottom freezer with door.
We have these in the US.
We also have some with a door-on-a-door for the fridge portion, so you can grab e.g. a can of soda or some mustard out of the inset door which only accesses a little storage on the door itself, without opening the entire fridge.
Neither is as common as other styles (the latter especially—that's kind of a gimmicky expensive-fridge feature) but they exist.
American refrigerators have the freezer on top and the refrigerator section on the bottom. There are other configurations available, but freezer on top is the default and most efficient. Otherwise there are freezer bottom, freezer bottom with a drawer, side-by-side (this is probably the one you're referring to, and they don't seem to be very popular anymore in my experience), french door with freezer bottom, as well as custom shapes (counter depth, narrow, built-in, etc.). But a cheap basic fridge is always freezer top.
> American refrigerators have the freezer on top and the refrigerator section on the bottom.
This was probably true up until the 90s. At that point side by sides became pretty popular with the left side being a freezer and the right side being a fridge, full height. See:
After these broke the trend of the top freezer, other styles became more popular. These days one of the most popular style is the "french door" where there are two side by side doors for the fridge compartment up top with a drawer below for the freezer.
Top freezer fridges these days are often seen as a very outdated and out of fashion style of fridge usually only relegated to the bottom tier models of fridges. If you go into most appliance stores you'll see row after row of french door, several side by sides, and then a couple of super basic top freezers.
Personally, IDGAF about "style" for a fridge when it comes to door arrangements. I like my side by side the most as then I have both fridge and freezer items as convenient heights instead of only really having a freezer at eye level and having to duck down to grab anything in the fridge.
My North American in-laws live in a household of two and have three stand-alone freezers. Plus a kitchen refridgerator that's so big that you could call it a walk-in fridge.
Western Europeans are rapidly gaining on Americans but it's funny to see how much in denial they are about it even though it's impossible to miss when leaving the house.
