Beer fridge, sensor on FV or in free air?

[Bigcol49]

Personally I don't see it as a belief thing and I think there are many that genuinely want to understand what happens and what the differences are so they can make an informed choice.

Hi!
You are a committed "sensor in the air space" brewer, and to state that the experimenter "set it up wrong somehow" is more a statement based upon belief than on scientific conclusions.
As you say, both methods make beer. A brew fridge is an enclosed system, so I suppose it doesn't matter either way.

 

[Nial]

Well, rather than use an "off the shelf" solution for regulating FV temperature, I personally use a Raspberry Pi powered system.

Can I ask what system you use?

I already have 5 of them round the house, perhaps it's time for #6.

:-)

Nial

 

[BreadMurderer]

Can I ask what system you use?

I already have 5 of them round the house, perhaps it's time for #6.

:-)

Nial

I'd be interested too!

Geeky setup, possible wifi remote access for monitoring = cool (pun intended?). :)

 

[Twostage]

Hi!
You are a committed "sensor in the air space" brewer, and to state that the experimenter "set it up wrong somehow" is more a statement based upon belief than on scientific conclusions.
As you say, both methods make beer. A brew fridge is an enclosed system, so I suppose it doesn't matter either way.

I suppose I am a sensor in the air person, I didn't use to be though.

When I said they set it up wrong somehow I was observing that they didn't configure some of the experiments correctly and this is born out by analysing the results and is entirely scientific. They didn't use the same initial conditions for each experiment and the probe wasn't measuring what they thought it was. The only bit of belief is that I suggested the error was not insulating the probe, probably no way of knowing now.

I suppose the thing is that their thread has been referred to a few times as being definitive or at least a fair indication of what happens. I seem to be the only person who has spotted the fundamental errors which invalidate the conclusions.

You know, I can see myself doing what I've been resisting and posting on that thread :-)

 

[Robbo100]

@Nial and @BreadMurderer,

Check out my signature, there is a link to a how-to thread on this forum.

I have changed that code since that how-to was written (and I currently developing another one with a different display and a keypad for data entry). I would be more than happy to share my code and general plans.

the Raspberry Pi controller doubles as an HLT temp controller as well as a Ferm Fridge controller, and auto detects which it is connected to.

 

[Nial]

@Nial and @BreadMurderer,

Check out my signature, there is a link to a how-to thread on this forum.

Thanks Robbo, that's a fantastic writeup of your system!

I will investigate options.


Nial.

 

[Robbo100]

PM me if you are going to build something and I can help more (with code and simpler hardware).

 

[JapanBrew]

I would think you need to use both but at different times. Getting the wort to stabilize right after making and while the yeast is at its most active. My view you'd want the sensor in the air. Get the environment stable. Once it slows down, switch to the sensor on the FV. Just my thought. But then again depends on what your fermenting.

 

[MyQul]

Dont know much about this tbh. When I use my cool bag I just sit my thermometer on the top of my FV. But soon I will (hopefully) be getting a SS brewtech bucket with thermowell. So is there a third option? IN the FV using a thermowell?
Just putting that out there chaps, for those that know a lot more about this kind of thing than I do

 

[Robbo100]

If the question is simply "I have only one sensor, where am I best to put it" then as an engineer, I would say the following:

- A fermentation fridge is effectively a closed loop control system like any others (car steering, car suspension, aircraft controls, quad-copter drone control) and the more points of measurement you use, the better you can tune the system response.

- If you ONLY measure the air temperature, then you will get a very slow system response, but it will provide you with a good stable system when on condition. To explain this more clearly, imagine you have a wort temperature of 30 deg C (just out of the copper) and you want it to reach 19 deg C. If your control system measures air temperature, then your fridge will only ever get down to 19 deg, and will therefore asymptoticly reach the target value, very slowly (like the graph below). The system has no ability to force the fridge to a lower temperature (say 10 deg C) to speed up the cooling from 30 deg C to 19 deg C, because it doesn't ever know what temperature the wort actually is.

- If you ONLY measure the wort temperature, then you can have much faster system responses, but this can lead to problems of overshoots in the desired temperature, owing to the thermal inertial of the wort. Imagine the same scenario as above. The wort is at 30 deg C and you are measuring this temperature. The fridge will turn on and be permanently on until the wort reaches 19 deg C. This means that the air temperature of the fridge can get as low as it can (if you use a freezer, it could get really low) and you can get quite a fast system response. However, when the wort does measure 19 deg C, the chances are, that some of the fluid (e.g. at the surface) is actually quite a lot colder that the measured value, and the average temperature of the wort will undershoot the target value. This will turn on the heater and you will get a cyclic undershoot and overshoot characteristic. Depending on the system, this may damp out over time (as shown by the "slightly under damped" curve below), or may remain unstable for the duration of the fermentation (as shown by the "unstable" curve below). Of course, you won't see this happening, because you are only measuring one tiny point within the fluid, but it is happening.

So, it sounds from this, that the best solution would be to first measure the wort temperature until it is "on condition" and then swap to the air temperature for a stable environment. However, there are other things to consider. For example, if you are heating the system, then do you really want your greenhouse heater to be on fully and heating the air-temperature unconstrained? Could you get to an extreme temperature that might damage the inside of the fridge or cause hot-spots in the wort that are not ideal for the yeast (albeit there will be a good amount of convection within the FV so this is unlikely to be a problem under normal conditions).

All of this, is why I measure both air and wort temperature (I should really measure wort temperature in more than one place, but don't). I effectively use a control law that measures the difference between the target wort temperature and the actual wort temperature (which is called the "error signal") and then drives a target air temperature based upon a multiplication of this error signal (with the max difference in air temp being limited to stop freezing or heating damage). This gives a fast response for a desired change in temperature (e.g. crash-cool), but a slow and stable response during steady-state conditions. The best of both worlds!

I hope all this clears up the debate :lol:

 

[Bigcol49]

Hi!
I've had enough of this - we're going WAY too deep now.
Christ! We're only making beer!

 

[MyQul]

Hi!
I've had enough of this - we're going WAY too deep now.
Christ! We're only making beer!

What do you mean ONLY! Burn the witch! :lol:

 

[Robbo100]

I was just giving the correct answer to the question :-)

Only beer! Pffff.

 

[HisDudeness]

Hi!
I've had enough of this - we're going WAY too deep now.
Christ! We're only making beer!

My brain hurts, gonna skip the brewfridge and shove the FV in the airing cupboard......

 

[MyQul]

Joking aside, in a similar way to water treatment this seems to be one of those areas of brewing that you can go as far down the rabbit hole as your inclination takes you.

 

[dad_of_jon]

Joking aside, in a similar way to water treatment this seems to be one of those areas of brewing that you can go as far down the rabbit hole as your inclination takes you.

I'd agree, the big improvement is to have a brewfridge in the first place if you have temperature control issues just as not using untreated tap water improves your brews.

my sensor is a theromspike on top of the fv which i take a reading of in the morning and evening.

 

[JapanBrew]

Robbo, that's what I said.... In as few words as possible!! Haha. But really, that's right on the money.

 

[JapanBrew]

Bigcol, nice!!!! Haha

 

[MyQul]

I'd agree, the big improvement is to have a brewfridge in the first place if you have temperature control issues just as not using untreated tap water improves your brews.

my sensor is a theromspike on top of the fv which i take a reading of in the morning and evening.

I do the same with my (slightly cheaper deallink thermometer when I use my brew bag

 

[Spoon]

If the question is simply "I have only one sensor, where am I best to put it" then as an engineer, I would say the following:

pffffttttt, a real engineer would have done some maths, maybe used some Laplace transforms and arrived at an optimum solution.

He/she would then be overruled by the site operator though, who would just hit auto tune on the PID and wonder why it doesn't work.

I do like the idea of controlling based on the FV temp but controlling the FV-air deltaT rather than heat/cooling inputs. Are you doing that with a Rasbery Pi?