Friday, 22 July 2016

Getting the least out of your fridge

When we go to the local electrical store, especially to buy something, I'll often start asking questions about the design or manufacture of their products. This will usually result in blank faces or repetition of advertising dogma from the sales rep, and a kick from my better half, with a suggestion that I write to someone in the company rather than bothering the staff.

This happened when we recently went to get a new fridge. Our old fridge was thawing and on its last legs. Probably the compressor going. I suppose we could have got it fixed, but it wasn't a very good fridge to start with. They had replaced it for our old fridge, which had had problems with the ice maker, but the replacement never seemed very satisfactory. It was about ten years since we bought a fridge, and I was expecting a few quantum leaps in the technology, but the main evidence was for incremental improvements in insulation and compressor efficiency. Fridges are major domestic electricity users (10-20%), and the improved efficiency probably makes the new fridge worth it, at least in economic terms. The sales staff in the electrical shop were certainly enthusiastic to tell us this. Evidence from suggests three times less energy use between 2003 and 2013 models in Japan. And here's a graph showing electricity consumption of fridges in the US rising from their mass production in 1940s to a peak in the 1970s to a return to 1940s consumption around 2002, at a much larger size and for less money. (The flat part corresponds almost exactly to Bill Clinton's presidency, which may just be a coincidence.)

I had expected fridges to get a bit more intelligent. There has been some talk of smart grids, and now many houses are loaded with solar panels, which they were trying to sell in the very same shop. I expected the noble fridge, leader of the white goods, would be rising to this challenge by making more coolth when power is available, and using less power when it is not.

Blank faces.

Another question: why is the door for the fridge the same thickness as the door for the freezer? It's colder in the freezer, so wouldn't it make sense to have a thicker door with higher insulation?

More blank faces.

My answer to that question would be that it makes manufacturing easier, and fridges cheaper.

This article from Proud Green Home has some useful information on buying and using low energy fridges. It points out that smaller fridges use less energy, and that fridges full of food, or even bottles of water, will have less air to escape when the door opens and they will be much more efficient. This is in contrast to what the people in the electrical shops say: don't fill your fridge too full or the air will not be able to circulate and it won't cool your food properly. 

Why would they say such a thing?

Perhaps because they want you to spend more money on a bigger fridge!

Not only do smaller fridges use less power, they also contain less food. A significant proportion of bought food is thrown away uneaten, so unless you are able to guarantee none of your food is wasted, a bigger fridge probably just means you are going to throw away more food.

One technical development they seemed pleased with in the shop was a sensor inside the fridge looking at how cold things were. I don't understand how much of an improvement this is over a thermostat unless you are putting hot pans in there. As long as the insulation layer around the fridge is good, and heat is being pumped out, the temperature inside is going to be uniform soon after the door closes.  I will further investigate exactly what the control circuitry of the fridge is doing and what the green light on the door means.

The article also makes some interesting comparisons between different configurations. French doors would seem to be more efficient since you only need to open one door at a time, and therefore only lose half the cold air. However people often open both doors, and the doors may in fact be open longer as you are trying to remember which side of the fridge you left whatever you're looking for.

Also they show how more doors and more complicated configurations basically mean more heat loss. This will be no surprise to anyone who has been paying attention to my posts about thermal bridges. They point out that any fridge with ice and water going through the door will be less efficient than any fridge that doesn't do that. (Compare and contrast with the world's first passive house cat flap.) So if you're choosing for energy efficiency, they recommend getting one with a freezer at the top and no cat flap for water or ice.

Of course different countries have different shapes and sizes of fridge preference. Another question I had for the long-suffering sales rep was why their shop only had Japan-made fridges. A little searching on the web reveals that about the only universal in the global fridge market is that different markets favour products from different countries.