Friday, 18 July 2014

Is your freezer using more energy than it should?

Fridges and freezers are supposed to turn on and off controlled by a thermostat. Nearly 10 % of freezers don't (fridges are more reliable). On average these freezers use 330 kWh/year more than ones which are working normally - costing around £40/year. Is your freezer working? How can you tell and should you replace it if it isn't?

The last reports from the Household Electricity Study I have been working on since late 2012 are finally published [1]. This study analysed data collected from electrical appliances in 250 households - individual appliances were monitored in 2 minute intervals. To me, probably the biggest surprise in the whole study was the number of fridges and freezers that seem to be malfunctioning. Normally the energy profile shows clearly the compressor switching on and off controlled by the thermostat. The malfunctioning ones did not switch off, or only occasionally. Only a few households were monitored for a whole year but one of these had a fridge which malfunctioned during the period. At the beginning of January it was fine but during that month it grew gradually more erratic and by the beginning of February it was always on.
Energy profile for two chest freezers from 'Savings, Beliefs and Demographic Change' [1]
In fact mostly it was freezers that looked dodgy - about 9% of freezers, about 4% of fridge freezers and 2% of fridges. (These are only rough figures as our sample was fairly small - 12 our of 129 freezers had failed). Older appliances were much more likely to have gone wrong - about 20% of appliances over 15 years old had failed.

Not surprisingly, freezers that never turn off use more electricity. Four out of the top five energy consuming freezers were in the failed group, as shown in the chart below.
Each bar shows the annual electricity consumption of one freezer
from 'Savings, Beliefs and Demographic Change' [1]

So how would you know if your freezer has gone wrong? The easiest way is to listen for the sound of the compressor. If it is always on then you have a problem. If so what then?

I can only guess what was wrong because we were not able to inspect the appliances - we only had the energy profiles. My best theory is that the thermostat has failed in some way, in which case it is might be possible to replace it. If this is the case, then you should be able to tell by measuring the temperature. Normally a freezer should be about -18C but if the freezer is on all the time because of a failed thermostat then it is probably colder than that. If this is the problem then it explains why fewer fridges seemed to be dodgy - if your fridge is running too cold it will be much more noticable, especially if the food in it starts to freeze.

However, I could be wrong. If the temperature is too warm then it isn't working efficiently and never getting down to the desired temperature. This is serious as it affects how long you can keep food in it. If the problem is icing up that should be obvious. If there is a lot of ice around the door seals then these are leaking and need replacing. Alternatively it could be that the heat exchanger isn't working properly. It should be well ventilated and clean. This web page explains how to clean the heat exchanger. Sometimes there is a fan that blows air around the heat exchanger - if this isn't working then it can be replaced. If it is none of these then I am out of ideas and you need a repair man, or a new appliance.

[1] Household Electricity Survey (DECC) July 2014

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