Chiller Info Needed

[segallis]

I am building a chiller for my 17 Gal conical fermentor. It seems that most DIY builds involve chilling a thermal glycol/water reservoir to something well below target fermentation temperature, and then cycling flow of the coolant through the fermentor when needed. I would think a better approach is to cycle the cooling fluid continually, and chill the water/glycol source as needed to maintain the fermentation target temp (thereby, keeping the reservoir temp close to the target fermentation temp).

I base this on several factors. One being that the latter method will operate with much a lower temperature differential across the entire system. The advantages would be:

* Less thermal loss and better overall efficiency​

* Less temperature variation inside the fermentor due to:​

* Coolant is closer in temperature to the wort temp​

* Flow is continuous, not sporadic​

* Less temperature gradients within the wort (since the wort isn't moving, large temp differentials and low duty cycle would cause more gradients since the coil is super cool but for less time)​

* Total heat transfer for a continuous duty cycle requires less mass in the cooling source (Q ∝ P*t)​

* Air transfer in the fridge is more efficient when running continuously, compared to trying to maintain a super-cooled reservoir, where you need faster chilling of the reservoir.​

I am expecting the cooling coils in the fermentor to have at least 10X to 100X better thermal conductivity than the heat absorbed by the conical through the insulated jacket, so I would expect little variation between the wort temp vs the continuously circulated coolant temp.

I have also seen posts that suggest a 5000 BTU A/C is better suited to the task than a mini-fridge - which has me baffled considering that the A/C unit has the capacity to chill a half BBL fermentor more than 40 degrees F in one hour (excessive in my opinion - I can tolerate about 1/10 that rate) !!!???

If anyone has experimented or has data to clarify any of this, I would appreciate the info.

I plan to run a few experiments next week trying to quantify the heat absorption through the fermentor jacket, the cooling rate of a mini-fridge on a reservoir, and the ability of continuous circulation to maintain a set temp within the fermentor.

 

[Bobby_M]

5000 btu is a bit overpowered for a single fermenter, but a mini fridge is underpowered at only 300-500 btu. If you try the mini fridge, don't think that you're going to put a tank inside and rely on that air gap heat transfer. The coil has to be submerged.

 

[Ale-75-IT]

I plan to run a few experiments next week trying to quantify the heat absorption through the fermentor jacket, the cooling rate of a mini-fridge on a reservoir, and the ability of continuous circulation to maintain a set temp within the fermentor.

I don't exactly know if I understand what you're trying to achieve. Some months ago I tried to use a mini fridge (40W on power outlet) as main source to cool down a water/glycol reservoir to keep cool one or more cornelius kegs inside an insulated structrure. The goal was to mantain them to 5 C° in summer (outer temperature of about 25 C°).
I ended up with another approach, using an ice-cream machine (90w) to cool down some glycol (inside ice-cream maker chest) and recirculate it via some very long thin plastic tubing outside a cornelius keg. It barely works (but haven't tried in a hot summer yet).
I'm not an engineer so I'am not able to calculate and predict the system behaviour. I ended with a trial and error approach.
What I've understood so far is that keg/tubing insulation is critical: you have to keep cold inside whatever it takes! Another bottleneck for me was the efficiency of heat (cold) transfer between the ice-cream machine evaporator and the glycol. If you submerge in glycol an air exchanger (from a window unit) I expect plenty of surface to transfer heat, but if you exchange heat/cold in a little vessel.... It gave me lot of troubles because glycol kept freezing (so I had to place a temperature probe inside the vessel to stop compressor at certain temperatures).
The final thought goes to controlling the whole process. I had to create a custom control unit (using an ESP32 and some coding). This was funny but not easy, for me at least.

Apologizing for my poor high school english, I hope to have given you some suggestions.

Bye,
Ale

 

[segallis]

5000 btu is a bit overpowered for a single fermenter, but a mini fridge is underpowered at only 300-500 btu. If you try the mini fridge, don't think that you're going to put a tank inside and rely on that air gap heat transfer. The coil has to be submerged.

So I did some experimenting with a dorm fridge. My fridge was able to put out ~340 BTU/hr with the evaporator coild submerged in 2 gallons of water. My 1/2 bbl Chronical fermentor, with the neoprene jacket installed, was absorbing as much as 160 BTUs of heat when the temperature differential was about 30F, about 50 to 100 BTU when the temp differential was in the 7 to 10 degree range.

With the fridge running full time, the fermentor temp dropped by 15 degrees F in 12 hours. Obviously 100% duty cycle ofn the fridge is not practical and would destroy the fridge, which is designed to run at about 30% duty cyle.

I then cycled the fridge with a 50/50 duty cycle (30 mins on/30 mins off), which is a reasonable max duty cycle. The fridge was able to hold the fermentor at 20 degrees F below ambient temperature (with the 50/50 duty cycle). This would correspond to a fridge source supply and fermentor heat absorption equillibrium of about 130 to 150 BTU/hour.

So I conclude that I could potentially get away with the dorm fridge and FTSS coil for fermentations down to about 55F in the winter and 65F in the summer for my Florida garage. But I opted to go with my previous solution where I build a thermal box around the fermentor connected to the fridge. The 1/2 bbl fermentor isn't that big and the box is actaully smaller than my previosu box that held two 7 gal fermonsters.

For my current brew, the fridge has averaged only a 10% duty cycle. The box method can easily get the wort temp 30F below ambient (I haven't tried to measure the lower limit yet). And no ftss coils or neoprene jacket to clean. Plus the wort temperature perfectly tracks the fridge ambient temp.

Hope this data is useful to someone out there.

-G