My Chest Fridge Conversion
You may recall I mentioned that we had an old fridge/freezer running in our garage as a second fridge. With three young kids in the house, we go through a lot of milk, juice, yoghurt and wine. Having a second fridge lets us buy larger quantities of these things once a week, instead of needing to go to the shops every day or two.
I measured the energy use of the old clunker with my MS5116 mains power meter, and was surprised to learn that it was using 2.5 kWh of electricity per day. Our total household energy consumption at the time was around 20 kWh per day, so this thing was responsible for 1/8th of that!
A lot of hard-core sustainability geeks around the internet (especially those living off-grid) have toyed with the idea of converting a chest freezer into a fridge. The theory is that it will use a lot less electricity because the horizontal lid doesn’t let the cold air fall out when it’s opened, and it has very thick insulation compared to a fridge. People are claiming some amazing power consumption figures, but would it really work that well?
I bought a 210L chest freezer for $90 second-hand, and ordered a FridgeMate MkII digital temperature controller online for $50.
A little bit of wiring is required to set up the digital temperature controller. It’s basically a temperature sensor that can switch a 240v power supply on or off. The simplest way to install it is to take a short electrical extension cord and cut it in half. You can then strip back the wires and connect them into the back of the FridgeMate according to the supplied wiring diagram. This gives you an extension cord with a temperature controller in the middle. One end of the power cord plugs into your powerpoint, and the freezer plugs into the other end.
The photo below shows how mine is wired up – it should help if you’re having trouble following the schematic wiring diagram. In the photo, the right-hand cord is the end with the male plug (i.e. that plugs into the power point) and the left-hand cord has the female plug (i.e. where the fridge plugs in). The cord in the middle with the red and white wires is the temperature sensor, which needs to sit somewhere inside your freezer but not touching the walls. For safety, the controller should be mounted in a project box so nothing can come in contact with the live wires on the back of it.
The FridgeMate can either cut the power when the temperature rises above the set point (if you’re using it to control a heating mat or belt), or it can cut the power when the temperature drops below the set point (if you’re using it to control a fridge or cooling coil). It has a lot of configurable parameters, and comes with an instruction book on how to modify them all, but the instructions list out the recommended settings for use with a fridge. This makes it very easy to program.
Once it’s all set up, the freezer can be plugged in and the power turned on. It didn’t take long for my little freezer to drop to my set point of 3 degrees C, at which point the FridgeMate cut the power. I then opened the lid for a while, and as the temperature rose the FridgeMate cut back in and cooled it down again. Perfect!
So, how much electricity does my chest fridge use?
Once it was loaded up and stabilised, I left the MS6115 on the chest fridge for 24 hours. When I came back, it was reading a cumulative usage of just 0.2 kWh! Given the limited 1-decimal-place reading, I’m calling that 0.2-0.3 kWh. Not bad at all – it’s around 1/10th of the old fridge (at 2.5 kWh/day).
And how is it in use?
I thought it was fine, but the true test of the usability of the chest fridge was what Megan thought. After a week or so of use, she’s quite happy with it. We’re keeping all the bottles of milk, juice and wine on the bottom of the fridge. Smaller bottles (beer, ginger beer, etc) go on the step, and items like yoghurt, butter, etc go in the basket. Megan actually finds it easier to lift and rearrange the bottles from above than to slide everything in and out on a normal fridge shelf. You have very easy access to everything in the fridge without having to move stuff around.
Someone asked me what the ambient temperature was when I did these power tests. I didn’t actually measure it at the time, but it would have been around 20 degrees C during the day in the spot where the fridge sits. It probably dropped to about 10-12 degrees C overnight, I’d guess.