Is anyone else data logging their fridge?

[Radian]

I've had a BT temperature sensor in our fridge for a while and forgot about it once the novelty wore off. I also log a power measurement for it and recently noticed it was becoming erratic. Yesterday, when I found my blueberries were frozen solid, I dug out the data for the preceding seven days temperature and got a nasty shock:

 

 

It was literally 'off the chart' at times. The electromechanical sensor is clearly not regulating the temperature at all well.

 

So yesterday, it dawned on me that I had everything in place to shift the temperature regulation into my own control - namely the battery powered BT sensor for input and the Tasmota MQTT power monitoring relay for switching. All I had to do is dial the fridge thermostat to max cooling (which it seems happy to do). The green trace shows when my new Node Red function flips the fridge on and off (with 0.5C hysteresis, orange trace added for raw temperature data in addition to daily and hourly averages that I had before). So that works. For now.

 

Of course the fridge light may be on or off depending on where in the cycle it is when you open the door, but that wasn't working anyway as  I failed to replace the faulty switch a while ago!

Seeing as how it was only the power logging that showed the light switch had stuck on back in March, and now that the huge temperature swings didn't quickly tip us off to the problem with the thermostat, I've been wondering if anyone else keeps an eye on their fridge?

[ProDave]

Ours did a strange thing.  I came down the other morning, went to get some bread out of the freezer and it was on the verge of thawing.  the freezer door was slightly ajar.  What surprised me was the compressor was not running.  I would have expected with the door ajar, the compressor would be running continuously to do it's best to keep it frozen, but it was not.

 

door now closed, all is working well, compressor coming on from time to time and all frozen.  I don't know how it works, but it is not a simple thermostat switching a compressor.

[MJNewton]

Have you got a combined fridge-freezer @ProDave? If so there’s a good chance it’ll only have a single thermostat and this will be located in the fridge hence it won’t ‘see’ the drop in freezer temperature. It assumes the door is (nearly) always closed and that the freezer temperature will follow that of the fridge (just with a -25C offset or whatever).

[SteamyTea]

Few years back I noticed my daily electricity usage had gone up. It was the fridge.

Seems it had degassed itself and was trying it's hardest to get down to temperature.

My current fridge used around 0.3 kWh a day.

I am not sure if that is good or bad.

[ProDave]

1 hour ago, MJNewton said:

Have you got a combined fridge-freezer @ProDave? If so there’s a good chance it’ll only have a single thermostat and this will be located in the fridge hence it won’t ‘see’ the drop in freezer temperature. It assumes the door is (nearly) always closed and that the freezer temperature will follow that of the fridge (just with a -25C offset or whatever).

It could be,  this is indeed a simple upright Fridge freezer.

 

The previous one in the old house, side by side had a thermostat to set the freezer temperature and then it cooled the fridge buy turning on or off a fan to blow cold freezer air into the fridge compartment to cool it.

[Pocster]

3 hours ago, Radian said:

my blueberries were frozen solid,

Painful 

[Pocster]

My fridge is equally strange especially in hot weather . All the chilled beer and wine seems to disappear.

[Radian]

3 hours ago, ProDave said:

I came down the other morning, went to get some bread out of the freezer and it was on the verge of thawing.  the freezer door was slightly ajar. 

Does happen. Another reason to log it, and I've also put in a pushover notification for when it goes over 8C which it did when we stored our shopping this morning. 

 

30 minutes ago, pocster said:

Painful 

I'll set 'em up, you knock 'em down.

[MikeSharp01]

7 hours ago, Radian said:

I'll set 'em up, you knock 'em down

Sounds even more painful.

[dpmiller]

Just be canny on the control- fridge compressors don't like short-cycling and the normal control strategy with a capillary stat is cut-in at setpoint, chill the coldplate to (say) -10c or so, rinse and repeat.

[Radian]

On 08/08/2022 at 06:59, dpmiller said:

Just be canny on the control- fridge compressors don't like short-cycling and the normal control strategy with a capillary stat is cut-in at setpoint, chill the coldplate to (say) -10c or so, rinse and repeat.

 

Thanks for the tip about short cycling. I think the thing is on its last legs so I'm just trying to squeeze a bit more life from it while we choose/get a replacement delivered. I think the refrigerant has diminished as it can't keep up with the recent hot weather. It will get down to set point during the night but once we start opening it during the day it struggles to recover. Yesterday, after lunch, it came on and stayed on for 6 hours yet the temperature kept creeping up. The thermal trip then went on the compressor! Now I understand why a few days before my intervention the temperature would mysteriously go off the top of the chart.

 

Now before I see it's in danger of tripping the cut out I can nurse it back by increasing the set point then gradually lowering it to something acceptable in the evening.

 

I was thinking of dragging it out to clean the radiator at the rear but I doubt that this entirely accounts for the inability to chill stuff in hot weather so it's new fridge time. But this made me wonder - MI's for integrated models don't seem to state that they need regular cleaning round the back while they always do for their free standing models! ( I know because I've downloaded the MI's for a number of models we're considering)

[Radian]

This week has been a nightmare for the ailing fridge saga. At first my workaround worked but then ran into the issue with the thermal trip on the compressor kicking in after several hours of getting nowhere with the cooling. Today it was even hotter, 26C in the kitchen late afternoon and at 16:00 the cutout cut out:

 

 

The brown trace is the motor power/10 so despite calling for 'coolth' (green trace) it just couldn't oblige, and tripped after only three hours. It then cooled for two hours and cut back in. Clearly my set point of 5.5C was just too ambitious given today's ambient.

 

So last ditch attempt to eek a couple more days while we get a replacement consists of (a) removing kick panels to maximise airflow:

 

and (b) pull air up the back of the cabinet, over the radiator fins with four PC fans:

 

 

(b) makes quite a racket but has dropped the temperature round the back by around 4C so is worth the 10W powering the fans if it gets us through the weekend. Similar temps forecasted for tomorrow so fingers and toes crossed.

[SteamyTea]

Was chatting a a fellow chef and he said his fridge kept cutting out.

I suggested that the pull it away from the wall a bit, and get a fan blowing air to the back.

" No good, it is next to the ovens"

 

 

[dpmiller]

does the current unit have a condenser fan and could it have failed? Undercounter integrated certainly do.

[recoveringbuilder]

What temperature should a fridge freezer be set at? Ours has the digital display and ability to set the desired temperatures for both but I haven’t a clue what these temperatures should be. Still trying to track down what uses the power when we’re both out all day, so the only things that are on then is the f/f the sewage treatment plant and the cctv. My neighbour who doesn’t live in her house had cctv installed at the same time as us by the same company and she has said that since it was installed she has seen a big rise in her usage, we plan to turn it off for a week when we’re at home to see what difference it makes 

[SteamyTea]

59 minutes ago, recoveringbuilder said:

What temperature should a fridge freezer be set at?

Fridge at 7°C and freezer at -23°C

Edited August 12, 2022 by SteamyTea

[Radian]

1 hour ago, dpmiller said:

does the current unit have a condenser fan and could it have failed? Undercounter integrated certainly do.

I don't think so, not without looking which would mean hauling it out of the cabinet. None of the spares sites list anything like that for these fridge-only tall units.

 

I think I'm getting a better understanding of the design though. Instead of being a last-ditch safety backstop, I suspect the thermal cutout on the compressor is set relatively low. Maybe 50C or lower. The reason I suspect this is I can see it coming in at a highly variable time ranging from 5hours of continuous operation to just an hour... depending on ambient. A few extra degrees ambient can reduce time to trip by hours.

 

When you look at the spec for fridges sold in temperate markets like the UK used to be, those rated 'N' max out at 32C ambient. They know the compressor run time will extend for higher ambient and the self heating will create positive feedback. Hence the control strategy is probably split over the thermostat and compressor cutout. This dual control may explain the wild swings I was seeing before my intervention.

 

Last night the kitchen reached its peak temperature and a 6C setpoint was simply not achievable. I can enhance my control to include a burst limit that reflects the need for the compressor to cool off, but it's dependent on monitoring ambient (or direct sensing on the compressor). Ambient is easier. Or I could just let it hit the thermal cutout but I suspect that will produce bigger overshoot. My strawberry's were very squishy this morning. 😟

 

[Radian]

46 minutes ago, SteamyTea said:

Fridge at 7°C and freezer at -23°C

7°C seems a little high to me. 8°C is supposed to be bacteria friendly so 4°C was the pre-energy crisis recommendation. Now the EU say 5°C

[SteamyTea]

1 hour ago, Radian said:

7°C seems a little high to me. 8°C is supposed to be bacteria friendly so 4°C was the pre-energy crisis recommendation. Now the EU say 5°C

Just going on what we have to keep ours at.

Cooking gets rid of the bacteria, usually.