Building a HERMS heat exchanger out of a SS thermos pot

Here's one a did a couple of years ago, you can build HE out of kettles and many other vessels however some people mus have shiny This is a 6 litre thermos pot from the usual German catering suppliers.Seems a little big but I have used it extensively and had no problem with latency, it gets up to temp very quickly.

I originally bought an asparagus steamer however changed my mind and bought theThermos pot and may use the steamer for a hopback later, or just veg. Here's most of the components.

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There's a few bits like 16mm silicon o-rings and PTFE tape missing frand I have some bits to buy, some heat resistant flex and a cable gland but apart from that its complete. The plumbing bits are :-

9m of 10mm copper tube bent around a 160mm drainage pipe
4 x 10mm capillary elbows
2 x 10mm to 3/8" BSP brass compression adaptors
2 x 3/8" to 1/2" BSP socket adaptors - stainless
2 x 1/2" hosetails - may change these but useful for pressure testing
1 x 3KW immersion heater from Backer
16mm silicon o-rings
PTFE tape
15A rated 1.5mm cored silicon heat resistant SIHF cable
6 - 9mm Cable gland

tools - except usual stuff
1 1/8" hole saw
51mm hole saw
16mm qmax cutter - all these I already had

Coil after soldering capillary fittings, trying it for size and marking it up for the holes.

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Marking up the hole ready for drilling with the 1 1/8" hole saw, want to get the hole right up against the top edge wiithout damaging it

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Continued.............

This is the hole ready for the smaller hole in the inner skin

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Making sure the 3/8" to 1/2" adaptor fits

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Making the inner 16mm hole with the Qmax

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Continued.......

Coil and fitting inserted, took a bit of wiggling to get it in, I put a thin 16mm silicon o-ring both sides of the inner skin and puts lots of PTFE on the 3/8" thread that goes through the inner skin, a bit fiddly being recessed.

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Underneath the pot, outer skin drilled to 51mm,

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the inner skin drilled with a 1/2" drill and the element inserted. The lead is off of a Tesco kettle and is just for testing, the final version will have a chunkier lead with ring solder terminals on the end to go on the element and I'll drill a hole to bolt the earth too. Will also add a cover. The lead comes through the side of the pot at the bottom though the insulation and will terminate directly on a Commando plug.

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cont......

Tightened up the element retaining nuts on the HX with a 19mm socket, the 51mm hole just gives enough room, wouldn't like to go much smaller. The copper washers go on the inside of the pot and the nut and plain washer underneath. it's water tight with hand hot water but need to test it with the element going so next step is wiring. Its a good idea to flush the copper pipe out with hot water as soon as you have finished soldering it to wash out the flux otherwise the flux keeps working and you get copper salts in the pipe that will taint your beer. I flushed this while testing whether the element leaks at the same time.

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I then put the 15A rated 1.5mm cored silicon heat resistant SIHF cable through a 15mm diameter hole in the side of the base of the pot and solder lugs onto them. The earth lug is bigger as I am going to bolt it to the base of the pot.

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Here's the element wired up and the earth bolted to the base of the pot. I then used a multimeter to make sure there was continuity between the earth and other part of the pot, there is some slicon sealer between the outer base and outer skin and I wanted to make sure this did not break earth continuity.

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continued......

I put a 6 - 9mm strain relief gland on the cable and squeezed it into the 15mm hole with a pair of pliers. that's it finished except for putting a commando plug on the end

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I did place a round blanking plate over the hole however I can't find the pic at the moment. Here's the finished article before I swapped the hose tails for quick release fittings

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And in situ in the brewery complete with its lid

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Cheers
Andy

Fantastic write up!

1st class

Thank you for an excellent write up of your HERMS project. 3+years on how has it worked out? If you were doing it again, is there anything you would change. I’m looking to build something very much along these lines and would welcome the opportunity to learn further from your experience.