0.1 kWh per day fridge back to projects

An super efficient A++ class fridge takes about 180 kWh of electrical energy per year. According to a guy in Australia you can modify a chest fridge for use as a refridgerator and this would take about 0.1 kWh per day, or 36 kWh per year. This is about one fifth the energy consumption of this A++ fridge!!
The website: http://mtbest.net/chest_fridge.html

Curious to the truthfulness of this experiment I decided to build my own setup. The test setup has been made (10 april 2009) from an old chest type fridge(ten to fifteen years old). The fridge has a standard single phase induction motor (as have most refridgerators), see note*.

A small temperature controller is made that switches the compressor on at temperatures above 7 degrees Centigrade and off at temperatures lower than 7 degrees. Use is made of a small microcontroller to enable tweaking of the cooling process (e.g. automatic tuning PID control). A display shows the set temperature and the measured temperature and whether the compressor is running. Although the display has a backlit screen this is not connected to save power. When the compressor is off the power usage is around 1 Watt.

A test is done with a large fan blowing air at the refrigerator condensor plane, this resulted in a power usage of 12 watts on average or 0.288 kWh per day. Without the fan this was 14.5 Watts average or 0.348kWh per day. In both cases the room temperature was slightly above 20 degrees centigrade. Clearly, using a fan helps the efficiency of the fridge.

The results in a table:
Test setup Energy usage[kWh] Energy usage per day [kWh] Test time [hours] Average energy consumption [Watts]
With fan 0.06 0.288 5 12
Without fan 0.29 0.348 20 14.5

 

Alltogether, the fridge is energy efficient, but not as much as expected from the story described in the link above. Probably using a better fridge can improve this further, it is possible that the '0.1kWh guy' did use a very modern fridge, but nevertheless the fridge that he used was a larger one. My opinion is that 0.1kWh per day may be a bit optimistic for an old fridge, but it could be attainable with a modern efficient fridge and a lower environmental temperature. some more research to the fridge the '0.1kWh guy' showed that the fridge he used was in fact an A++ class freezer. So, for this thing to work you should first buy A++ class equipment.

With such a setup, you still have only a refridgerator but you probably want a freezer as well... A good A++ combi fridge uses about 0.5 kWh per day, compared to my test setup this would be much more efficient, since you now have a freezer as well. The chestfreezer the '0.1kWh guy' used, uses 0.47 kWh per day when used as freezer (found in the product specs). With a modified refridgerator of truly 0.1 kWh per day you will end up with 0.57 kWh per day, which is only slightly more than the combi fridge. Of course you can improve the freezer efficiency as well (by insulating), but I personally think that this will be a difficult task and resulting in an ugly and very large freezer.

Concluding: This modification is truly nice when you only need a refridgerator and it is only working well when you are modifying a modern energy efficient freezer to a refridgerator.

 

*Note: This induction motor uses one coil to keep the motor running, but uses an additional coil to start the motor in the right direction, that is why fridge motors have such a large inrush current. This high startup current is necessary to get the motor to run properly, otherwise it would not even start. I was planning to use a solar cell system to make a complete standalone cooler system, but the high inrush current needed could cause a problem here.


The fridge with the control panel in the front.


A close up of the control panel.


Inside the fridge on the left side the power supply is seen toghether
with the solid state relais. On the right side the compressor can be seen.
The power supply has been covered later on.