Use a Chest Freezer as a Fridge
Use A Chest Freezer As A Fridge
Find out how a chest freezer can be converted to operate as an energy efficient fridge
energy efficiency | electronics | carbonOne of the biggest power consumers in the home is the
fridge. Turned on constantly, opened frequently, filled with warm items needing to be cooled, and not generally very efficient, a fridge can often be responsible for a large chunk of the
electricity consumed in a home.
In this article we will look how a humble
chest freezer can be used as a fridge reducing electricity consumption by as much as
90%!
Chest Freezer
An example of a
chest freezer is pictured above. They are typically used in large homes for long term deep freeze food storage, or in shops and supermarkets to give consumers easy access to frozen goods. There are three key differences between a typical domestic fridge and a chest freezer:
1) Chest freezers have a
horizontal lid which you lift to access the contents. Warm air rises and cold air falls, therefore, when you open the vertical door of a fridge, a lot of cold air falls out and is replaced by air at ambient room temperature. This warmer air needs to be cooled down which of course increases electricity consumption. When the lid of a chest freezer is lifted, almost all of the cold air stays put exactly where we want it to be.
2) The
insulation on chest freezers is as much as
three times thicker than that built into a domestic fridge. This means that less electricity is required to maintain the temperature of the contents of a chest freezer.
3) The
thermostat of a chest freezer is set to around -25 degrees Celcius whereas that for a fridge is usually set to between 2 and 6 degrees Celcius.
Therefore, as points 1 and 2 above show us, a
chest fridge would be much more
energy efficient and result in less
carbon emissions than a typical domestic fridge. All that we need to do is find a way to modify, replace, or override the chest freezer thermostat so that it will maintain its contents at the desired 4 degrees Celcius rather than freezing them solid.
It is worth noting (and very surprising) that if you compare a fridge with a chest freezer of similar dimensions, the chest freezer with have a lower average power consumption despite having to keep its contents so much cooler.
Convert a Chest Freezer into a Chest Fridge
There are two ways to go about converting a chest freezer into a chest fridge. The first is to swap the fitted thermostatic temperature controller with one designed for fridges. This is very technical and well beyond the level of this article. The second option which we will discuss here is to use an external temperature controller. All that is required is a
thermostat, a temperature probe to be fitted inside the chest freezer, and a suitably rated
relay to switch the chest freezer power on and off as required.
There are many commercial
thermostats available on the market which can be used un-modified to control the chest freezer, but these can be expensive. In addition, you ideally want to have
hysteresis in the controller - i.e. it turns on chest freezer when its internal temperature goes over say 4 degrees, and turns it off again when it has fallen back down to 3 degrees. This greatly reduces the number of times the freezer compressor will be turned on/off per hour which
reduces electricity consumption and wear on the freezer.
For the simplest system see our article
Convert Thermostat to 12V Timer Switch in which we explain how to identify and replace the temperature measuring
thermistor. Instead of replacing the thermistor, it could be carefully removed, fitted to long leads, re-connected to the thermostat, and used to reliably measure the internal temperature of the chest freezer (which would be switched on/off by the latching
relay of the thermostat).
More Information and Useful Links
A fridge that takes only 0.1kWh a day - Detailed article by
Tom Chalko first published in Australia's
Renew magazine in 2005.
Freezer to Fridge Conversion - from the Otherpower.com discussion board.
Refrigeration Engineer - Some words of warning and things to consider.
Article Last Modified: 12:26, 30th May 2009Comment on this Article
If you have any comments on this article, please email them to
neil@reuk.co.uk.
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