A smart freezer that buffers cold when electricity is cheap
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How much money will it save? This Sciendirect publication calculates a yearly saving of only €4. So it seems not worth it. But their model uses a temperature window of -16 to -27 Celsius and assumes a freezer that has a 4h safe food storage capacity in case of power blackout. However my freezer has a 17h safe food storage capacity and we can widen the temperature range to let's say -32 Celsius, so we might save €24 per year.
I used the Sonoff app (Ewelink) that stores 1 datapoint per hour. I configured the Ewelink app to turn on the compressor at -16 Celsius and turn off at -23 Celsius. The freezer was empty.
And it shows temperature cycles every 4 hours, with an empty freezer. Then I turned on super freeze and in about 7 hours it dropped to -38!
After 24 hours super freeze automatically turned off and temperature returned to -16 to -23 range. I want to repeat these measurements while the freezer is significantly filled.
So I added 26.5kgs of bricks.
Then the temperature cycles every 7-8 hours. Now I turned on the compressor permanently and want to see how low and how fast the temperature drop.
In about 10 hours it drops to -32 and but then it takes another 14 hours to drop only 5 degrees more to -37 Celsius. So I think the freezer becomes very inefficient below -32 Celsius. Then I turned off the compressor and it takes 10 hours to go from -32 to -16 Celsius. Now my freezer is 28% full (26.5kgs bricks) so I expect that a 50% full freezer can keep the temperature safe <16 degrees Celsius for 17 hours. That sound more than enough
I also want to redo these measurement in combination with power consumption. I want to know how inefficient my freezer is in super freeze mode.
Today I added the Sonof TH Elite smart temperature humidity controller to my freezer
Behind the top drawer is the original temperature sensor
Behind the middle drawer was an unused position for a temperature sensor.
And so I drilled a hole through the back of the freezer and mounted the DS1820 temperaure sensor.
The cable simply comes out of the back side, behind the heat radiator.
And the sonoff I screwed on the insulation material. It still doesnt control anything, it just measures the temperature.
In Sept 2022 I bought a second hand rusty EDY DV1564 freezer for 20 euro. Dimensions are 60*60*95cm. It was introduced in 2003, it has 95 liter volume, 8kg/24hr freezing capacity, 175 kWh/yr energyconsumption and can store food safe for 17 hours in case of power loss. It has 4 star rating which means temperature is -18 Celsius or lower and it has more than 4.5kg/24hr freezing capacity.
The front panel has a green power LED, a red high temperature warning LED and a yellow superfreeze LED. There is also a slightly hidden potentionmeter and superfreeze button. The superfreeze makes the temperature much less than -18 celsius for 24 hours to quickly freeze food.
Behind the upper drawer is a temperature sensor. Behind the middle drawer is also a positon for a temperature sensor but it is not used.
Behind the front panel is the control board. The left connector is for the temperature sensor, I measured 5k3 ohm so I think it is a 5 kilo ohm NTC thermistor. The board is powered with 230VAC from the brown (line) and blue (neutral) wire on the right connector. The output of the control circuit is the swicthed line (white) and it goes to the compressor.
On the compressor is a connection box. The right white cable is 230VAC power input. The left white cable goes to the front panel, where the blue and brown wire power the control circuit and the white wire is the switched line to the compressor. Behind the connection box, not visible, is a thermal overload protection and a starter circuit. A few online seraches later I made this wiring diagram (left).
The thermostat is AC powered and it switches the AC line to the compressor. Then I felt confident I could simply replace the thermostat with a Sonoff TH smart switch
Jasper Sikken
ToniTheAxe
icstation
Michael
Simon