HERMS Help: MLT overshoots target temp. during recirc. (a LOT!)

[CorgiBrew]

I've been running into a problem hitting mash temps with my new HERMS (electric, three-keggle, single tier). It goes like this:

1) I heat H2O in the HLT to the right strike temp (let's say, 163).

2) I pump enough hot H20 from the HLT into the MLT for the dough in.

3) I add grist to the MLT and replenish the HLT with cold H20, bringing the HLT down to mash temp, say 153. At this point, the HLT and the MLT are at the same temp.

4) My PID is set to maintain the HLT at 153, and I'm recirculating wort from the MLT through the Hex in the HLT.

5) all fine and good, but next thing I know, the PID is still showing 153 in the HLT, but mash temp in the MLT is climbing and climbing, finally stablizing somewhere around 160. Yipe!!!

Any thoughts on why this is happening? In my HLT, the temp sensor for the PID is at about the same level as the heating element (but offset so they aren't close), and the HEX sits right above the element. I've seen systems that stir the H20 in the HLT. Is that necessary? Maybe my HEX is picking up too much direct heat from the element? Also, even though I use a 4 inch sensor, it comes in through a tee that also is part of the sight glass, so it only sticks into the HLT about an inch. Could that be an issue?

 

[Budzu]

It really sounds like your problem has to do with temp difference as you observed. For recirculation in a herms, it is absolutely necessary to agitate or circulate the water in the HLT. What is happening is your element is heating, the hot water is rising up and heating the herms coil, going right past the temp probe before it can be read. The coldest water in the HLT is below the element, and around your probe.

I use a herms and I have a second pump simply recirculating the water in a whirlpool fashion. With this I get a perfect balance of HLT water and wort. Your other option that I know of is to mount a stirring device.

 

[Bobby_M]

Yup, sounds like you need to mount a motor in your HLT lid with a stirring rod down into the water.

 

[GilaMinumBeer]

Curious. Wouldn;t an easier solution be to dough in and start recirculating about 10 degrees a head of mash target temp? thus negating the need for more hardware and achieving the same result.

I mean, how long does it take for your system to ramp up 10 degrees?

 

[CorgiBrew]

Thanks Bobby. Hey, I notice that your weldless sightglass kit with thermometer's set up pretty much the same way as I have my sensor/sightgalss combo. Do you have any issues with the thermometer only sticking a little way into the keggle?

 

[CorgiBrew]

I use a herms and I have a second pump simply recirculating the water in a whirlpool fashion. With this I get a perfect balance of HLT water and wort.

Interesting. Could you provide some more details on your plumbing? In some ways, this sounds nicer than a motor-driven stirring thing.

 

[CorgiBrew]

Curious. Wouldn;t an easier solution be to dough in and start recirculating about 10 degrees a head of mash target temp? thus negating the need for more hardware and achieving the same result.

I mean, how long does it take for your system to ramp up 10 degrees?

Definitely an option (in fact, that's basically what I did with the one batch I've brewed with this system so far). But, having built the thing, I now have a pathological desire to get it to work right ...

 

[Budzu]

Interesting. Could you provide some more details on your plumbing? In some ways, this sounds nicer than a motor-driven stirring thing.

There is a diptube in the bottom, I am drawing off water from there, and putting it back in via the return which you see at the top of this pic. It is oriented slightly at an angle, to push the water directly against the coil, and to create a circulation. I placed my temp probe very close to my element. It is a 12" one from brewer's hardware. This pic is from my gallery, there are more if you want to see the outer plumbing.

 

[Bobby_M]

Thanks Bobby. Hey, I notice that your weldless sightglass kit with thermometer's set up pretty much the same way as I have my sensor/sightgalss combo. Do you have any issues with the thermometer only sticking a little way into the keggle?

Well, the thing with thermometers is reading them is a human manual process so it's not a big deal to give the liquid a stir to break up the natural stratification you get. With an automated setup like yours, the PID won't grab a spoon for ya.