Cooling fermentor sensor on fermentor or in air?

[ericmark]

I have for the first time used refrigeration, stocks are low and ambient temperature high so used the MH1210A temperature controller to control cooling set to 0.1°C differential and 10 minute delay, also have a energy meter plugged in and sensor is pressed hard against fermentor under a sponge to insulate. Also have a thermometer measuring ambient air temperature in the garage and air temperature in the freezer compartment of the fridge/freezer being used to brew in.

Started low at 18.6°C I had hoped the freezer motor would not be required, both the thermometer and controller were showing same temperature 19.7°C when I went to bed.

Today the motor has run used 0.03 kWh and freezer air at 18.2°C and fermentor at 19.9°C just 1.5 hours latter freezer air still at 18.8°C but fermentor has risen to 20.1°C the motor has not cut in again yet but clearly will soon.

Returning in the evening the motor has run again however not for long as went from 0.03 kWh to 0.04 kWh and the air temperature in the freezer (19.5°C) has got closer to the fermentor temperature (20.1°C), as to if due to weather, fact that fermenting has reduced, or other factors I don't know. But fermentor temperature does seem to be holding steady, this is not what I expected to happen, I thought the fermentor temperature would drop after each motor run by a few degrees, but this is not the case, so there is no real reason for monitoring air rather than fermentor temperature.

Test what would happen with a 0.3°C drop in set temperature. The fermentor was flashing between 19.5 and 19.6°C the temperature controller was reset to 19.3°C the fridge/freezer started for a few seconds energy meter went to 0.10 kWh the ambient in garage was 19.5°C and fridge showed 18.2°C neither changed during the test. Test started at 11:50 but freezer did not start to run proper until 11:55 it ran until 12:01 at which point fermentor was at set temperature of 19.3°C and the air in freezer was showing 16.1°C very quickly the temperature of air started to raise again. So rise is as below:-
Time – Air – fermentor
12:01 – 16.1°C – 19.3°C
12:05 – 16.5°C – 19.3°C
12:07 – 16.5°C – 19.2/19.3°C flashing
12:10 – 16.9°C – 19.2/19.3°C flashing
12:12 – 17.1°C – 19.3°C steady
12:20 – 17.3°C – 19.3°C steady reset temperature back to 19.9°C test complete
12:40 – 17.8°C – 19.4°C
The test was to see what the likely result would be if the STC-1000 was used instead of the MH1210A with a 0.3ºC instead of a 0.1ºC differential. The result was not as expected and showed there was no problem using 0.3ºC differential in fact likely better as a 6 minute run of the compressor was quite short and since it has to go thought the check sequence first after switch on a longer run is good.

 

[Alan_H]

I keep my temp sensor on the fermentor but I usually read a 1-2°C difference between ITC 1000 [lower] and the tape thermometer [higher] and I trust the latter, meaning I adjust the ITC temp accordingly.

 

[DoctorMick]

I have my sensor in mid air and I've never bothered monitoring the difference between the air temp and the fermenter, always assumed it'd be bloody close and could have sworn someone on here posted something a while ago showing it was. That'll teach me for being lazy and believing everything I read on the internet I suppose! :lol:

I'll be taking a sample from the fv in a few days so I'll measure the temp as soon as it comes out and see what the difference is.

 

[ericmark]

Now I am really scratching my head, I measure 4 temperatures Garage where the fridge/freezer is placed in the fridge under the fermentor no heating or cooling control, in the freezer air, and the last one is monitoring the fermentor in the freezer and is set to run freezer should the temperature exceed 18.8ºC and bring it down to 18.5ºC.

What does not make sense is the Garage is still at 18.4ºC the fermentor is at 18.3ºC and dropping and the air in the freezer is at 17.3ºC and dropping the energy meter shows the freezer has not run for a whole day so can't work out why the temperature is dropping below the ambient temperature of the garage? The fridge temperature is also dropping now 17.5ºC which is really too low, but that fermentor is nearly finished and ready to bottle so not really worried about it. The temperature was measured at 9 AM this morning 28 June 2016.

Outside the temperature is also low showing 17.9ºC in the windowsill at back of the house, earlier this month we were reading 22ºC at back of house and as the sun hit the garage door that resulted in 24ºC in the garage. So we are having a cold spell. What I intend to do is later today I will remove the controllers and swap them around so I have two sockets on the STC-1000 since at this time don't really need temperature control so I can work on them.

But although I expect a temperature drop how the freezer air is cooler than both ambient air in garage and fermentor temperature when the freezer has not run for 24 hours I just can't explain.

As to controlling air rather than fermentor temperature after running for the second time using the freezer I realise the time the freezer would run would be much reduced. On the first run to get the temperature down from over 20ºC to set 18.5ºC it dropped below 6ºC in the freezer and the motor ran for 40 minutes, the fermentor did not over shoot so to my mind there is no reason to measure the air for the controller it must be the fermentor. Both cooling and heating the freezer air sits around 2ºC lower then the fermentor during the early stages where the fermentation is producing heat.

With the heating it is easy to over shoot the heater does need to be quite small, I have found 8W is ample. Since with heating the garage is colder than freezer air and freezer air is colder than fermentor there is always a difference between freezer air and fermentor. But with cooling the garage and the fermentor are warmer than the freezer air so as fermentation completes the difference between freezer air temp and fermentor temp should decrease, and this is the case. But they should not be colder than garage without the freezer running, this I can't explain.

Only thing which I can see could cause it is if the evaporator which is behind a panel had got very cold and once the power was removed so the fan stopped it was very slowly absorbing heat again, but this seems very unlikely.

 

[DoctorMick]

So I checked the temp of my sample today and it was 23 where as the fridge was set to 20. Surprised by the difference and definitely need to compensate for that with the next brew.

 

[Dutto]

As you can see from the photograph, I put the sensor against the FV and then cover it with a few layers of kitchen towelling that is held in place by the FV handle. As a result, the temperature being measured is that of the FV but the temperature of the fridge will eventually get through the kitchen towelling and have an input.

I also adjust the thermostat on the heater so that it will cut out if the temperature controller on the Inkbird asks it to be "On" when the temperature of the heater is already high.

On the fridge side, I have a five minute "compressor delay" set on the Inkbird to reduce the chances of any "hot/cold" cycling getting out of hand.

On the whole, it works to within 0.5 degrees of the set temperature.

Hope this helps. :thumb:

 

[Inkbird]

Hi,

If you need more accurate temperature,I recommend PID thermostat. Such as Inkbird ITC-100 series. Here're 2 links for your reference
http://www.amazon.co.uk/dp/B00ADHNSGI
http://www.amazon.co.uk/dp/B00HVA23CK

For an ON/OFF(such as Inkbird ITC-308), I think it's enough for a homebrewers,while I know that many professor use PID temperature controller.

You'll find with what you have it's not the temp probes fault for over any shoots. It's the latent lag times in action = effect between the heater, fluid and temp probe. Which is where the PID controller and SSR will be learn (auto tune function) and then be able to predict temp ramp ups/downs.

The on/off controller may overshoot by 1C or so where as a pid controller runs off an algorithm designed to maximise efficiency when doing industrial sized heating jobs, so if tuned in correctly will heat upto the target without overshooting.

 

[DoctorMick]

Just picked up a bungee cord and a sponge so I can attach the sensor to the fermenter for my next brew, hopefully that'll help keep the temperature correct but I'll make sure I keep a close eye on it.

 

[Inkbird]

I keep my temp sensor on the fermentor but I usually read a 1-2°C difference between ITC 1000 [lower] and the tape thermometer [higher] and I trust the latter, meaning I adjust the ITC temp accordingly.

Please kindly note that ITC-1000/STC-1000 are ON/OFF thermostat. This is how they works.For a homebrewers,it's enough.

If you need more accurate temperature,please choose PID temperature controller, such as our ITC-100 series thermostats.