Dual PID control on fridge/freezer

[GeoffN]

After a fair bit of messing around and lots of research because I had not done enough research I have a fermenting and beer fridge in one. Three wife doors not like my hobby very much and more than one fridge would not be possible. Cooking being one of my other hobbies was being cramped by having to share space with cold beer.

A couple of months ago I bought two cheap PID controllers with type K thermocouples thinking that I could easily connect up the free fridge I was given so that I could use the freezer part as a beer fridge and the bridge part as a fermenting chamber. When looking around the net for some ideas how to do it I found that running a compressor control by a PID is a bad idea as it is not a resistive load. The general consensus seemed to be that it will kill the compressor super fast.

This is not entirely true. A PID controller can be used for fridge control it only has to be programmed to work as a STC. Simply P=0, oH=1 and the controller must be set for cooling control. Setting P=0 stops PID control and the controller operates as an on of switch. Setting oH=1 is setting a two degree hysteresis so that the compressor will switch off at a lower temperature than it will switch on.

OK so I got that working with one controller on the freezer and watched what the temperature was doing in the fridge. At 4°C in the freezer, the fridge was only 19°C. I decided that would not give me adequate control of my fermenting temperature. I needed separate control on the fridge so that I can think about doing a lager if I wanted to our working at the low end or high end of a yeasts range a little more easily.

I set up the second controller connected to a fan in the fridge so that cooling will occur independently of the freezer running. The alarm is set one degree lower than the control temperature and switched the internal light on in the fridge to heat if the temperature drops too low.

I don't have any pictures but here is a drawing of what I did. I hour it helps someone who is thinking of doing something similar.

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[elcarter]

This fridge have 2 compressors one for the freezer and the other for the fridge compartment?

If not I think I may see some issues.

Your diagram however is much better than I have done in the past.

 

[GeoffN]

Elcarter only one compressor in freezer. That is why the freezer is the beer fridge and will have to be colder than the fridge.

One problem that is needing a fix (easy to do) is that the internal light does not generate enough heat to warm the fridge part when the freezer part is cooling 20 tallies down. The fan that circulates the cold air round the freezer also pushes cold air into the fridge cooling it down too much. The 15w bulb does not generate enough heat. I'll set up a 100w one tomorrow and see how it copes.

I have a separate fan for controlling the fridge part when the freezer is at temp. So I'll not cause the freezer to get colder when cooling the fridge. The freezer is essentially been run as a heat sink to transfer heat from the warmer fridge into.

If you have anything else I've not thought about please chime in.

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[elcarter]

Just a few un-educated thoughts

A heater belt might be a more efficient and cost effective solution to a light bulb. More direct and heats by contact and air.

When I read that just a fan and a light bulb was enough to help maintain the freezer I had my doubts.

I would have a hazardous guess your probably going to freeze some of your beer when crash chilling your fermenter or lagering your beer @ 4 deg despite a fan.

I had a similar idea of using my fridge for a ferment / hop storage but the reality of it was the freezer was only good for storage for some glad wrap and other non temp essential brew gear.

It got far too cold then warm to quickly to possibly entertain the idea of controlling it.

You might have it though just my 2c

 

[dent]

Sounds like a pretty good start on getting it done.

I don't agree about putting the controllers in parallel like that - you could end up with the situation if you put a warm thing in the fridge side, the freezer side would start freezing whatever you got stored in there. I would have the second controller on fan and bulb only, since if the freezer starts to warm up as a result, the freezer PID will kick in anyhow.

I wouldn't bother with a bigger wattage light bulb as the socket will not be rated for it. Perhaps wire in a brew belt/heat pad/resistor with heatsink instead, so the surface temperature of the heater isn't excessive.

Also I would also set the startup timer on the heating/bulb to be something like 20 minutes so you're not wasting power one end fighting the other.

 

[GeoffN]

Thanks elcarter and dent

I guess I was not very clear. The freezer is controlled at 4°C (beer storage) and is the source for the cold air to cool the fridge to maintain fermenting temperatures. I live on the sunshine coast and need cooling far more than heating. This is controlled by one controller only. The fridge has an inbuilt fan that circulated air around the freezer for cooling to happen. The cooling portion is completely hidden behind some panels in the back of the fridge. This fan also pushes cold air into the fridge part.

The second controller drives an extra fan that pulls cold air from the freezer into the fridge completely independently from the inbuilt fan to give cooling for the fridge. Because the inbuilt fan also pushes cold air into the fridge I can't rely on ambient to keep the temperature at a reasonable range I'll have to add heat to the system. The second controller is set up to switch on the internal light. As you mentioned the Max bulb is 35w and that is not going to be enough. I have a spare bulb holder that I can install all I need is a higher wattage bulb. I'll investigate the heating wire option as that will be better.

I loaded up the freezer (4°C set point) with 40 tallies when I was done late afternoon yesterday about three hours later the fridge was at 12°C and the freezer was at 7 and still running. The beer was not cold yet, I'd put the TC under a bottle to try measure beer temperature not cooling space. I'll need more heating when I load up the freezer.

I should relabel the freezer to fridge and fridge to ferment chamber.

I had not thought about cold crashing or true lagering as that is something for the future. It should be possible to get the ferment chamber very close to the temperature of the fridge (freezer). One more thing to test.

I'm going to full my fermenter today with water and watch how quickly the temperature gets down to below 20°C. Water out the tap is about 27 so it will do just fine for an initial trial.

I'm still a kit and bits bloke so I'm not often going to be dealing with hot wort that needs cooling. I may be on the slippery slope but I'm digging my heels in as my wonderful wife correctly pointed out that I have to many hobbies already and making better than store bought beer is entirely possible with kits. Especially now with better temperature control.




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[QldKev]

It sounds like you are in for some expensive power bills to me. With a fridge producing coldness and a heat source fighting it to keep the area warm. I would look at trying to control the fan than moves the cooling air from the freezer into the fridge.

 

[Glot]

The only sense I can make out of this set up is that you are using one of the older two door fridge/ freezers that did not have an evaporator in the fridge section. Instead, they had a thermostatically controlled flap that allowed cold air to fall from the freezer into the fridge. If this is the case, instead of heating the fridge, why not rig up some way to electrically control the flow of cold air into the fridge. Maybe a cowling, a small fan and some spring loaded butterfly flaps or possibly small solenoid on some vanes. Perhaps the exhaust grill from a 100mm exhaust fan.

 

[GeoffN]

Qldkev. The heating does not turn on unless the freezer cooling is running for a long time. Under normal conditions I don't think it will be running the heating. The heating only heats the fermentation chamber. There is an offset of two degrees between the heating and cooling to stop any fighting going on. The heating is there to prevent the temp dropping low enough to stop fermentation.

Glot. Your correct on the type of fridge. I could go with the solenoid, but that is greater expense and complexity. I ran a controller on the freezer compartment for a while to see what is the lowest temp the fermentation chamber would get to. It only got below 18°C when I had loaded up the freezer compartment and it ran for about 3 hours non stop. The second fan is shrouded but cold air does flow through while the compressor is running.

I do realise that this may not be a good solution, it is a cheap solution. I do appreciate all the comments. Please keep them coming.

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[dent]

The second controller drives an extra fan that pulls cold air from the freezer into the fridge completely independently from the inbuilt fan to give cooling for the fridge.

Is the evaporator located in the freezer section? I figured you were using the second controller to run the built-in internal fridge fan, not an additional one. So when the fan isn't running, the evaporator chills the freezer section only (more or less).

I guess your fridge could be layed out differently to ones I've seen though.

I set up the second controller connected to a fan in the fridge so that cooling will occur independently of the freezer running.

Where did you put this one?

 

[elcarter]

Mine was the old style with a thermostatic flapper door valve.

Had to piss it off to get the 60L fermenter in there.

The plus side it no longer restricts the cooling from freezer to fridge and it's far more efficient also reduces the crash chilling time.

If you could some how get variable control over a flapper valve, including a complete seal with your temp controller you might be on a winner.

I'm now thinking a fan in my freezer might increase it's efficiency so I thank you for the idea.

 

[GeoffN]

Here are some pictures of the setup. Please excuse the quality.

The first is the stripped out freezer compartment. There is a cover over the evaporator and on the bottom of the freezer section. Airflow is through the two vents above the fan housing, over the evaporator and then under the floor to another vent at the front of the freezer section. I thought I would have to run this fan to make the fear work as the evaporator is not exposed. There is a cover on the back and on the for that have been removed in this picture. I was cleaning it all out

The second is the cover and fan that I installed to suck cold air out of the freezer. Air from the fermentation chamber blows back into the freezer through a vent connected to the floor of the freezer.

This is a picture of the controller currently cable tied outside the fridge. The top controller runs like an STC box and switches the whole fridge on and off. The bottom controller controls the fan on the above photo and also switches the internal light on.

Busy optimising TC placement so that the FV temp is closely reflected not just the fermentation chamber temperature. Took some ideas from AHB.

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[GeoffN]

TC is under the FV and reading the same temperature as the stick on thermometer on the side of the FV. I'm happy with that.

The next thing I need to get an idea of is how efficient the system is. I put the FV in at 30°C this morning messed around with the whole setup this arvo about 3 and the two was 24°C. Now it is 17°C, this is not fast chilling. How do other people do? 23l of water has taken almost 12 hours to go from 30°C to 17°C. What is normal?

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[Glot]

As suspected. Single evap frost free two door.
Your idea might actually work with some tweaking. You might even be able to do away with the heating in warmer conditions. Just find a comfortable setting for the cold air supply into the fridge. You will prob have a fairly wide temp variation but a lot better than nothing.

 

[Glot]

As suspected. Single evap frost free two door.
Your idea might actually work with some tweaking. You might even be able to do away with the heating in warmer conditions. Just find a comfortable setting for the cold air supply into the fridge. You will prob have a fairly wide temp variation but a lot better than nothing. Have fun experimenting with it.

 

[dent]

Sounds like inadequate air flow to me. My guess is the freezer section is staying too cold, so the compressor isn't going flat out like it should.

If the fan was working adequately, the freezer section would always be warmed up by what is happening in the fridge side, so the compressor would never stop until the fridge side was at the correct temperature.

 

[GeoffN]

Thanks dent, I think you are correct the air flow is inadequate. I'll play with that a bit over the coming days. I don't want to spend any more on it if I can get it to works with only some adjustment that will be first prize.

It is down at temp this morning. I'll watch over the next few days to see how well it controls. If it looks good I'll put a brew on so that I can do a real test, better beer.

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[GeoffN]

Update on this.

Fridge started tripping RCD. Took me more than a week to figure out it was the automatic defrost heating element that was causing the problem. Ripped it out and no more problems.

It is all good now. Compressor switches on less often than I thought it would and control seems very good. I've disconnected the light for heating as it is not needed, full fermenter is not affected by cooling off beer. Freezer part sits at 4°C so I have cold beer all the time.

I have the temp probe under the fermenter on a towel. The measurement seems very good to me. This rig is not as flash as many presented here but for $27 all up I am very happy that I have a fridge that stores almost 40 bottle of beer and can hold a fermenter. I'll also be able to put in two crates full for conditioning if I want to. One fridge does everything I wanted.

Going to do a Thomas Coopers pilsner. Have the fermenter cooling 18l of water to 14°C at the moment and will finish off tomorrow and pitch yeast when it is all back down to temp after adding kit and kilo.

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[GeoffN]

Another update.

Played with the controller for the fermentation part. This does not control the compressor so PID control is not going to break anything. Now have the fermenter sitting at a constant 14°C. Ducking air out of the cold part to cool the fermenter works for me.

I will not be able to cold crash effectively with this setup nor lager at 1°C for weeks. I am one up on no temperature control for fermentation and wife getting annoyed with beer bottles filling the fridge.

Fermentation is proceeding nicely and I have cold beer. I am a happy camper.

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[GeoffN]

Been runing with this setup for 3 months now. It is working well. I have eliminated the heating as I don't need it. Though when I refill the freezer section with warm beer the fermentation section does drop a degree or two below set point. The rest of the time it is controlling very well. Compressor fires up 2 to 3 times per day while fermenting.

I've been using it for brewing beer, Cider and Saurekraut and I always have cold beer available.

I may need heating in winter and if I do then I'll get it configured again. The joys of living in sunny Queensland not worrying too much about heating only cooling.