Adventures in smallscale geek cooling (homeassistant, ESP32s and micropumps)

Pretty-much universally, all the beers I brew are ales so fermenting in the utility room provides decent-enough temperature control, sitting at 19-21 degrees year round except hot summers. I've swamp-cooled my fermenter before.

I've been playing with electronics for a while now, and don't have the space (or inclination) to get a separate fridge just to take a fermenter. I use a heat-belt, combined with automation and a smart plug to automate warming the beer, but there is no simple equivalent for cooling the fermenter.

So I set about playing with stuff to see what I could come up with, and here is what I came up with. Similar to many low-tech lagering/cooling approches, I don't need a separate fridge if I'm prepared to move cool blocks once or twice a day into a cold reservoir.

Simplified setup
Basically similar to low-tech lagering. Run a tube around the fermenter with both ends of the tube in a reservoir. Have a pump in the reservoir that pumps cold water around the fermenter when it's too warm. Lots of people use an inkbird, but thath's big and chunky, so I set about building my own

The reservoir
As mentioned, I don't have a lot of space and my fermenter is in the sky

But there is a small space next to the fermenter, where I can keep a small reservoir.
This 3L LocknLock tub fitted nicely next to the fermenter

I have a bunch of cool blocks. Some silicone tubing was bought from ebay.
The next thing was the pump. I didnt' need a big one, nor a powerful one. As long as water flows at a moderate speed, it'll cool the fermenter.
As it turns out, you can buy teeny tiny USB-powered pumps! The photo doesn't really show how small it is. It's 2.4W and only 6cm long. Plenty small enough to sit inside the tub. Apparently in shifts 2L of water a minute, which is plenty.

I wrapped the tubing around the fermenter 4 times, froze some tupperware tubs of water in the freezer, filled the fermenter with water and put the pump on. It dropped the temp by about 2 degrees in an hour. Plenty fast enough - no points for cooling too fast.
It turns out that 1L of ice does a lot of cooling


The controller
Obviously, having to turn the pump on/off manually is not going to work. So I needed some sensors and control software.

A tiny dallas DS18B20 temperature probe (which I'm pretty sure is what most things like inkbirds etc use anyway) costs about a dollar when got from AliExpress. Plus, it'll go into the fermenter thermowell. Bonus

I wired some dupont connectors to the end of the probe.
To control it, I got an ESP32 C3 microcontroller for about $1.50. Wifi included!


I then set about wiring it all up, in short wiring/soldering together:

1. The ESP32 microcontroller
2. 2x Dallas temperature probes (one for the fermenter theromwell, one for the cold reservoir)
3. A USB socket, so I can power the pump
4. Some protective diodes/resistors
5. A MOSFET to turn the pump on/off based on the output from the ESP32 (thanks to @The-Engineer-That-Brews for helping me out understanding the electronics, protection circuits and even sending me the MOSFET!)

I might get a wiring diagram set up, but here's a photo instead:

Red = 5V rail
Black = Neutral
Yellow = the 1-wire data protocol for connecting the two Dallas temperature probes
Blue = control signal to turn the MOSFET (white/black rectangle at the top of the blue wire) on/off
Bottom white plug = USB-C power
middle two cables: temperature probe connectors (dupont connectors)
Top USB cable is the power to the pump

Control software
I didn't want to write my own control software, because I already run homeassitant at home so can just use this for the control logic. So all I needed to do was install the ESPHome software onto the ESP32 chip, connect it to WiFi and home assistant, configure the ESPHome to have 2x temperature probes and 1x switch and away I went.

Then it was just a case of writing an automation in home assistant to go "when the temperature changes, if it's above the target temperature then turn the pump on, otherwise turn it off"

With a bit of finessing, it looks like this


The temperature will remain stable at the target temperature until the ice blocks melt and the reservoir heats up, so I have to swap out the blocks about twice a day. But the overall temperature swing is ~1-2 degrees if I lose the windo and it's actively fermenting and the yeast is being exothermic.

The last thing to do was to chuck the reservoir in a cool bag to keep it cooler and prevent condensation going everwhere


The final thing I need to do is onder and wire up a new temperature probe because they're not as waterproof as I had thought, and the one that I put in the ice bath stopped working shortly after I submerged it in water , which is why it reads as "unknown".

It's certainly not beefy enough to lager inside on a hot day. And If I use about 2-4 frozen 1L cubes of water it can get the temperature down to about 5 degrees before racking, but TBH I'm not that fussed as I just leave it a week and it clears up nicely without needing to chill hard. It takes the heat away during summer months, and was a fun project.

All-in-all, the kit cost me about ~£25 and hours of fun. And that £25 is less than an inkbird costs. And my controller is way tinier. And I made it

I have a vaguely similar setup. Have you considered an alarm or alert for the reservoir temp?

Yes. I had one of those set up initially the sent a notification to my phone (using home assistant notifications) if the reservoir went above 10°C.

Then I broke temperature sensor so am waiting on a new one being delivered

Agentgonzo said:

Yes. I had one of those set up initially the sent a notification to my phone (using home assistant notifications) if the reservoir went above 10°C.

Then I broke temperature sensor so am waiting on a new one being delivered

Click to expand...

I buy them 5 at a time. Some seem to work most of the time but not all and I just swap it out and bin it.

Good project. There is a lot of pleasure when it all comes together. Active fermentation is only a few days really which is when it needs cooling so swapping out ice blocks shouldn't be too onerous.

Twostage said:

Good project. There is a lot of pleasure when it all comes together. Active fermentation is only a few days really which is when it needs cooling so swapping out ice blocks shouldn't be too onerous.

Click to expand...

Indeed. I'm sure the novelty of swapping cool blocks will wear of eventually, but it's not too hard. I work from home so it's a good reason to get me out of my chair for a break.

Agentgonzo said:

The final thing I need to do is onder and wire up a new temperature probe because they're not as waterproof as I had thought, and the one that I put in the ice bath stopped working shortly after I submerged it in water , which is why it reads as "unknown".

Click to expand...

I used a nylon cable gland to fit a probe in my mash tun. Got one suitable for 6mm dia. cable. The rubber sleeve of the gland fits snug on the metal body of the probe and when the gland nut is fitted it's watertight. Just need to drill suitably sized hole in the reservoir (and seal that too).
Good to see a cat skinned differently!

Nice job there well done to you I was thinking of a small plug in cool box not sure if it would work

allotment_fox said:

Nice job there well done to you I was thinking of a small plug in cool box not sure if it would work

Click to expand...

Cool-boxes work nicely to maintain temperature (obviously).
Plug-in cool boxes (from what I've seen) use peltier elements to provide "top-up" cooling. Peltier elements are horrifically inefficient - about 5-15% (from memory) of the power you put in turns into actual cooling power. This makes them really quite expensive to run. I'd looked at those and just considered sticking a few peltier elements to either the cold reservoir, or directly to the outside of the fermenter, bypassing the cooling coils entirely. But they are so inefficient, that I didn't want to go down that route.

One thing to watch out for is that making bulk ice in the domestic freezer is hard duty, and I had massive frost build up.

Caramel Ox said:

One thing to watch out for is that making bulk ice in the domestic freezer is hard duty, and I had massive frost build up.

Click to expand...

Interesting. Do you know why?
I did it with sealable takeaway containers so there was no evaporation from the surface.
After I had a couple of those to make a base layer of cooling water, I switched to cool blocks. It's a frost free freezer and I haven't noticed any frost build up

Some interesting figures from this and previous brews.

• When brewing a High ABV beer (1.080 OG, belgian abbey beer with 2 sachets of yeast) the max temperature rise during active fermentation was about 1 degree every 2 hours - this was about 36-48 hours after yeast pitch, rising from 20° to 26°.
• Max cooling achieved by this setup during active fermentation was about 1° every 3 hours, which is plenty good enough. As long as I could keep enough ice-blocks in the cooling reservoir, it would maintain a stable temperature.
  During peak fermentation, I would change 2-3 cool blocks (probably a few hundred grams each) two or three times a day
• Obvs the colder you want to keep things, the harder it is to cool them. I'm brewing a pseudo-helles, and fermenting at 16°.

Agentgonzo said:

Cool-boxes work nicely to maintain temperature (obviously).
Plug-in cool boxes (from what I've seen) use peltier elements to provide "top-up" cooling. Peltier elements are horrifically inefficient - about 5-15% (from memory) of the power you put in turns into actual cooling power. This makes them really quite expensive to run. I'd looked at those and just considered sticking a few peltier elements to either the cold reservoir, or directly to the outside of the fermenter, bypassing the cooling coils entirely. But they are so inefficient, that I didn't want to go down that route.

Click to expand...

I had a play with peltiers and found they quite disappointing

Agentgonzo said:

Some interesting figures from this and previous brews.

Click to expand...

Mine are.... this needs to be a low cost solution, because in the Uk, you only really need it, if you are brewing in the last week of August and summer has arrived .
Else good stock control will solve the problem.

MashBag said:

Mine are.... this needs to be a low cost solution, because in the Uk, you only really need it, if you are brewing in the last week of August and summer has arrived .
Else good stock control will solve the problem.

Click to expand...

When fermenting inside, even in winter, the fermenter can reach up to 23-24º just by the heat generated by the yeast. This keeps it under control.
I could ferment in the garage, and use a heat-belt to keep the temperature up overnight etc, but that's more hassle than doing it all in the utility room.

Plus, just maintaining good stocks is less fun than playing around with electronics

Agentgonzo said:

Plus, just maintaining good stocks is less fun than playing around with electronics

Click to expand...

Spot on.

For completeness I brew outside and only carry a bottle on beer 'in'

I'd also considered doing an automated swamp cooler. Make a 'wet-jacket' from an old towel/tshirt etc and dip the end in a water tub to make sure that it wicks up water as it dries out. Then replace the whole cold-reservoir/tubing/pump with a USB-powered fan.
From my previous testing with a simple fan setup, it's plenty good enough to cool ales enough to stop them running away with heat. But I'm a bit concerned that prolonged use (especially not in summer) will end up with a lot of moisture buildup in the house - which we battle with in autumn/winter anyway.

Agentgonzo said:

Interesting. Do you know why?
I did it with sealable takeaway containers so there was no evaporation from the surface.
After I had a couple of those to make a base layer of cooling water, I switched to cool blocks. It's a frost free freezer and I haven't noticed any frost build up

Click to expand...

I think just because it was actively chilling constantly and the door was opened frequently letting more moist air in. Under normal usage a freezer stores already frozen food.

Really nice job there @Agentgonzo and I love what an innovative approach you’ve brought to the problem
In fact the controllers like Inkbird etc don’t use digital sensors like the Dallas probes, but analogue thermistors (which have a wider temperature range, but are less accurate).

@Agentgonzo

Brewpiless running on esp32 seems to do what you have achieved. Integrates with floating hydrometers and can adjust temperature related to gravity readings or run a profile. Also will relay to brewfather, brewspy and MQTT.
You can control pressure as well with automatic spunding.

But very good work by you though.

Perhaps a small heat exchanging type of camping fridge would provide an ongoing cool reservoir?