Building a HERMS Setup

Sat May 19, 2012 10:52 pm

I'm going HERMS, no need to go over the reasons, they are still valid and I'm in too deep to go back anyway ;-)

So far I've set up my 3 Keggles, I have a sweet false bottom mash tun with a thermowell and ball valve installed. In the HLT I have a 5/8" convoluted copper coil mounted via welded NPT fittings with quick disconnects on the outside, a thermowell, a brewmometer and a ball valve. The boil kettle has a ball valve, a brewmometer, and has been used successfully for about a year.

I'm going to use Ranco controllers to use temperature to control the propane burners and the pumps.

So, the first question is a basic one to building a HERMS system.

Q: How much overshoot will I see in my temperature when using a thermowell in the mash tun to control a pump that pushes the wort through the HLT coil?

The reason I ask is because I am going to do a dry run tomorrow. I will heat the HLT to ~180 manually and then monitor and adjust the temperature manually. I want to see what happens when I circulate water in the mash tun through the coil. My hypothesis is that I will way overshoot my temp because when the thermowell tells the pump to quit circulating wort (or in this case water), there will have been enough heat added to overshoot the mash by a number of degrees.

HERMS expert houghts?

~widget
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Re: Building a HERMS Setup

Sun May 20, 2012 6:06 am

While a 'wet' run will tell you everything is working, when it comes to the temperatures you are missing the huge amount of grain mass. The grains specific heat will take much more heat to bring it to temp, will hold that heat and will change temperaturemuch slower than water alone.

I think you'dbe best off just going for it once you know all the piece work and just go with smaller steps when increasing the mash temp. That will limitany over shoot you may have in your system due to measurement response lag.
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Re: Building a HERMS Setup

Sun May 20, 2012 9:36 am

I was thinking something similar, I didn't mention the thermal mass of the grain becuase I was pretty drunk when I wrote the original post and ran out of lucidity by the time it was written :-) The other thing I was thinking is about continuously stirring the mash while I step up/come up to temp to make the heat distribution as even as possible throughout the grain bed. More work, but seems like I would get less overshoot.

As I build this system I have a bunch of "what-ifs" that pop up and I was hoping to use the collective wisdom of the BN to help me work these through rather than having to learn everything the "hard way".

Thanks,

~widget
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Re: Building a HERMS Setup

Sun May 20, 2012 5:29 pm

Not to try to change your mind, but the same decision process lead me to doing a RIMS setup ILO Herms. With my false bottom dialed in now (no more stuck circulation issues) I hold temps very well. Set it and forget it.

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Re: Building a HERMS Setup

Sun May 20, 2012 9:24 pm

I can't go with RIMS, I have a track record - if it can be scorched, it will. :-)

That being said, I did a dry run on the mash side today with just water and no grain. I had checked everything separately, but wanted to see what data I could get in practice. My hypothesis was that I would wildly overshoot my temp and then watch it fall back into place. I figured I would have to set for a lower temp and then hone in from there. My experience was much different.

I think the key lesson of the day (which I really should have known) is that it’s all about temp differential.

First, I had a propane tank that was light, so I figured this test would be a good way to kill its remnants. I started recirculating far too early, when the HLT was at 155 degrees. That's about 25 degrees lower than at which I expect to run the system and I believe it proved to slow/shunt the effect of everything else I tested. Adding another variable to the equation was stupid, but I don’t think it had a non-translatable effect on the outcome of the test.

Second, I didn't expect the HLT water to drop in temp so significantly when I ran the mash tun liquid through the HERMS coil. The mash tun water temp was 63 degrees - I walked it up to 150 from there. In the first 5 minutes my HLT temp dropped 10 degrees, with a big flame under it. Note to self, when adding heat to one system, you are taking it away from another (dumbass). From there the temp steadily climbed (both in the mash tun and the HLT) and in the end I peaked out at 166 degrees in the HLT and hit my 150 in the mash tun.

Third, the massive temperature overshoot I expected never occurred. Once I hit 150 my pump shut off and I watched the temp closely. I was getting low on propane at this point and the flame was not as hot, but I still had 166 degrees of heat in the HLT. In about 8 minutes I lost heat in the mash tun and hit 149, the pump kicked on and brought it to 150 in about 3 minutes (while I watched the flame and temp die in the HLT). I have to imagine that the thermal mass of a bunch of grain would buffer any overshot of temp even further making this an extremely viable method to control mash temp. I also came to the conclusion that I need to insulate the mash tun. I currently mash in a Gott cooler and lose maybe a degree over the course of 90 minutes. If I expect to even be close to replicating my current recipes on the new system, I need to ensure I don’t have that kind of fluctuation in temperature.

All in all, it was a good system test. I’m glad I did this and am very happy with the results. I’m sure HERMS is going to be a great way to go for me. I’ll post more to this thread as the build out continues. Now I have to figure out how I am going to get a single tier stand for a bargain basement price.

~widget
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Re: Building a HERMS Setup

Tue May 22, 2012 8:06 am

I am gleaning much info from this thread. I have not decided witch way I want to go yet and I'm really interested in hearing your results when you start brewing with this system. BTW, I think the stirring at mashin is a good idea for the reasons that you mentioned as well as efficiency.
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Re: Building a HERMS Setup

Tue May 22, 2012 4:29 pm

I have an immersion HEx coil in the mash tun (same general principle, but the other way around), and what I find is that the temp where the probe is isn't the same as the temp where the probe isn't.

I understand that flow is increased around the walls of the mash tun. The reverse (plug flow) is what occurs in an open pipe, and may not be a factor here. But there are definitely channeling issues in a mash tun. The only way I can overcome this is with constant vourlauf and activating the heat exchanger when the probe detects low temp condition. Having said that, it works magnificently, and I can hold the mash at temp -1 all day.

I didn't go with the Herms system because I'd need a separate loop for vourlauf, and cleaning the inside of tubing gives me hives.

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Re: Building a HERMS Setup

Wed May 23, 2012 7:34 am

I wouldn't go with Rancos. They are just not designed for your intended purpose. They don't even have PID logic (which wouldn't help you here, either). Skimming the thread, if I understand properly - you are dead set on a HERMS setup. That's fine. I have one and I'm happy with it... I would suggest looking at the BrewTroller. They have logic built in to minimize overshooting. Basically, the farther away the mash is from it's intended target - the greater the differential will be between the HLT and the target. As the mash approaches - that differential shrinks. You can set a minimum differential to account for heat loss in the recirculation system.


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