Towards FV temp control...

[The-Engineer-That-Brews]

Just to prove I've been listening to the sage advice (@foxy and others) about the importance of fermentation temps, I'm making steady progress on a design based on a heat exchanger coil plumbed in to the FV. For various reasons this had more change of approval by the management than a FermFridge

So at the weekend I finished the coil itself, made from 10m of 1/4" tubing. In fact the flow resistance of this stuff is pretty high, so to avoid overworking the pump I'm using two 5m runs in parallel (also, two small pipes have more surface area than one larger one).

The cross-pieces at the bottom are to keep it central in the FV by the way.

Next step is to hook the coil up to the pump and the Peltier heater/cooler. It's a 60W device (12V, 5A) so for a 30 litre brew I think that should correspond to a heating/cooling rate of 2ºC per minute hour. I think that should be adequate, but if not then I do have a second device to add in parallel.

 

[The-Engineer-That-Brews]

Hmmm - OK, just done a little further research on Peltier devices. Apparently they have a pretty low efficiency in the 'cooling' mode, down around the 5% mark; so my '2ºC per hour' estimate is looking more like 0.1ºC per hour when cooling.
Still, so long as the tank is reasonably well lagged the only heat energy it has to cope with should be the exothermic heat of the yeast metabolism, so I shall just have to see how that works out :-)
Certainly won't be 'cold crashing' with this rig tho...

 

[The-Engineer-That-Brews]

Now considering whether for the cooling side, it might be more effective to use a solenoid valve to mix mains water into the circuit when/if needed.
I'm not sure what minimum fermenting temps people use, but suspect warmer than my mains water at around 8-12ºC.

 

[DarrenSL]

I like your ideas and ambition but heating and cooling 30 ltrs of wort needs quite a lot of energy. Maybe you could DIY a glycol chiller/heater? That would be a perfect solution to temperature control and also allow you to ferment at lager temperatures and cold crash.

 

[The-Engineer-That-Brews]

heating and cooling 30 ltrs of wort needs quite a lot of energy

Yes: 4.183 kJ per litre, per °C to be precise. That’s how I arrive at the figure of 2°C per hour with a 60 Watt heater, or a far less impressive 0.1°C per hour with a 5% efficient 60W cooler.

Maybe you could DIY a glycol chiller/heater?

That sounds interesting; I’ll have a look, thanks!
Erm... no. Nice but not the kind of thing you can DIY. And waaaay too £££ to consider buying.

For now, however, I’m just aiming at sufficient temperature control to brew a ‘Best Bitter’ using WLP013... lager, cold crashing etc can wait for V2.0

 

[The-Engineer-That-Brews]

OK - just done some testing.

On test, a single 40x40mm Peltier module gave a cooling power of about 4 Watts (11% efficiency).
That's better than I'd expected and means that with two devices I could cool a 21 litre fermentation at about 0.3 ºC/hr.

I reckon that's workable for managing the temperature of an ale fermentation in the 20-17 degree range, which is my objective at the moment; but I do have to agree with @DarrenSL that it's never going to cut it for lagering. However I now have an alternate plan, which involves an old portable air conditioning unit I found in the spare room... MWahahaha...

Results
1 litre of water, single Peltier device 40x40mm
run time: 2,500 sec
initial temp: 21.0 ºC (ambient)
final temp: 18.6 ºC
power supplied: 24W (3A x 12V)

Analysis
The 1kg of water was cooled by 2.4 ºC.
The specific heat of water is about 4,200 kJ/kgºK.
So the useful work done was about 10.1 Joules, equating to a cooling power of about 4 Watts.
Comparing to the input power, the system efficiency was about 11%

Conclusion
System efficiency was better than expected but would reduce as the temperature difference increased.
Using two devices to cool a 21 litre fermentation should give a cooling rate of around 0.3 ºC per hour

 

[The-Engineer-That-Brews]

Right then: looks like this bad boy has a refrigeration unit in it...

 

[LED_ZEP]

I started making a heater/cooler using peltier chips. Unfortunately my lack of metallurgy knowledge meant I used stainless steal sheets as heatsinks to spread the heat like a heating pad, only to find out that SS is a poor conductor of heat. I'm waiting to get some aluminium replacements.

 

[The-Engineer-That-Brews]

I started making a heater/cooler using peltier chips.

Nice to hear I'm not the only one ... how many chips are you using? The 'hot' sides get pretty toasty...

 

[Rodcx500z]

Right then: looks like this bad boy has a refrigeration unit in it...

View attachment 33255View attachment 33256View attachment 33257

I am loving this thread, cant wait to see what you come with

 

[The-Engineer-That-Brews]

OKaaay, so apparently 12,000 BTU is about 12,660 kJ; so the cooling capacity should be about 3.5kW

 

[LED_ZEP]

Nice to hear I'm not the only one ... how many chips are you using? The 'hot' sides get pretty toasty...

I'm using four 60w 12v in two parallel pairs in series to heat an area 400mm x 600mm. using 10amp 120w switching power supply so only running them at half power. I know they're not efficient but I'm only looking to keep 6 dj's at about 22c so only need about 4c above ambient through winter. The Dj's will be boxed in with the heatsink forming the floor of the box and a thermostat to control.

 

[The-Engineer-That-Brews]

using 10amp 120w switching power supply so only running them at half power

Interestingly, although the specs say "12V @ 5A", when I stuck mine on the meter at 12V it only takes 3A (i.e. 36W) ... I think the 5A only applies if you crank em up to 16V

Also the efficiency also inevitably falls off as the temperature difference across the device increases unfortunately

 

[LED_ZEP]

I'll be running the well within spec then. should give them a longer life.

 

[The-Engineer-That-Brews]

And perhaps you can use the waste heat output to keep the greenhouse happy...?

 

[LED_ZEP]

My thoughts were that once the temp gets up to 22c because of the thermal mass in 6 dj's and the insulated box around them it wouldn't actually be on that much to worry about any inefficiency.

 

[The-Engineer-That-Brews]

My apologies as I'm sure you already know this, but while they are cooling, the OTHER side of those Peltier modules get extremely hot.... In total, while cooling, there is about 9 times as much net heat coming out of them as cold, if you see what I mean?

 

[The-Engineer-That-Brews]

Helpful of them to include a schematic wiring diagram... I see there is even a reverser valve on the refrigerant circuit, so this baby can heat as well as cool. Neat!

 

[LED_ZEP]

My apologies as I'm sure you already know this, but while they are cooling, the OTHER side of those Peltier modules get extremely hot.... In total, while cooling, there is about 9 times as much net heat coming out of them as cold, if you see what I mean?

I'll be using them to heat so not an issue but I did think that I could reverse the polarity in summer and use to cool if the room gets above 25c.
I may have look at ebay for an air con unit like the one you have there.

 

[The-Engineer-That-Brews]

I may have look at ebay for an air con unit like the on you have there.

It's basically one of these - mine was from Homebase back in the day, but doubtless this will be extremely similar on the inside. I'll keep you posted on how my conversion is progressing, but it could be as simple as just rerouting the inlet and outlet air flow