With dramatically increasing electricity costs, one of the most popular search terms on google is how to save on the electricity bill. A subset of those searches is whether you can save electricity by switching off the freezer at night.
The replies to that latter search term are quite interesting as they miss the real point of the question and are potentially misleading. The Carbon Trust response was that, no, you are not going to save electricity as the compressor has to work harder when the freezer is turned back on. Of course, the Carbon Trust is absolutely correct. However, one can safely assume that those posing the question were really wanting to know whether they could save money by turning the freezer off at night.
If we look at the real question, that is saving money, then the answer is a qualified yes. You will save money by turning the freezer off at certain times of the day if you are on a time-of-use tariff. (Turning off at night would be a strange strategy as electricity tariffs are least expensive at night).
Night electricity rates are approximately half daytime rates and between 02:00 and 04:00 rates are even lower (check your electricity supplier for actual costs). This is why I set my dishwasher, washing machine and the charger for my EV to start at 02:00. If you turn off your freezer, for example at 20:00 and have it come on again at 02:00 then you will definitely save money but not electricity.
Commercial cold stores will often operate their refrigeration plant at much lower temperatures at night to make use of the cheaper tariffs. To do this the store will run at around minus 28 C during the cheaper night tariff and allow the temperature to rise to around minus 20C during the day. This technique can be used at home. How long you can safely turn your freezer off will depend on the level of freezer insulation, home ambient temperature, how often the door is opened, whether the freezer is full or not, and what is the lowest temperature that you can set the freezer to. Care will need to be taken and the use of a thermometer is advised. Even better, use a data logging thermometer to ensure that temperatures do not rise above minus 18 whilst you are experimenting with on/off times.
Before embarking on changing the on/off times for the freezer, there are some obvious first steps that should be undertaken to reduce energy consumption. These are:
- Make sure the freezer is out of direct sunlight
- Keep the coils at the back free from dust and at least 100 mm away from any wall
- Ensure the freezer is regularly defrosted
- Ensure food placed in the freezer is cool
The environmental advantage of this strategy is that night-time electricity is much greener than daytime. The proportion of electricity generated by wind, hydro and nuclear is higher at night and these are sources with no or very little CO2 emissions.
This advice is given in good faith, but no responsibility is taken for any subsequent loss or damage as the operating conditions are beyond the control of the author. It is the users responsibility to maintain a safe temperature in the freezer.
The author, Bob Sutcliffe, is a Chartered Engineer, Certified Energy Manager, and a member of AEE. Bob has carried out energy audits for many SMEs and multinationals over 30 years of consulting both in the UK and Ireland. Bob can be contacted at firstname.lastname@example.org.