RIMS and HERMS temperature sensor position

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RIMS and HERMS temperature sensor position

Post by PeeBee » Mon Mar 26, 2018 7:59 pm

(EDIT: I'll continually update this post if any relevant new information comes in. Update details in the footnotes. Last updated 2 April 13:10).

Deciding where to put a temperature sensor in a HERMS ("Heat Exchanged Recirculating Mash System") can be perplexing, especially if the sensor is feeding back to a "PID" controller that automatically manages the heating element in the HLT ("Hot Liquor Tank"). And therein lies the source of disagreements. HERMS uses the heat exchanger to manage the heat in the mash liquid, and therefore the mashtun: But HERMS does not control the flow of heating liquid through the heat exchanger (as is the case in many other process control examples), instead it controls the temperature of the water in the HLT. This difference opens up different ways of thinking compared to many examples published about heat exchanger process control. RIMS heats the mash (process) liquid directly so avoids these arguments (but generates a few of its own).

Let's start with a somewhat stylised diagram of a HERMS setup.
HERMS.jpg
RIMS ("Recirculating Infusion Mash System") is much the same but the element ("E") is actually in the recirculating mash so there is no HLT holding the heat-exchange coil of recirculating mash. The element is going to be electric in RIMS but a gas burner could be used to heat the HLT for HERMS (more likely it is electric too - I've never seen a gas version but they exist).
RIMS.jpg
The diagrams illustrate the four likely locations for placing a controlling temperature probe: A, B, C and D. The pump ("P") recirculates the mash. Ideally all four locations read the same temperature, and they will for all minor changes to temperature; the actual location of the temperature probe becomes important when big hikes in mash temperature are being made, either when initially heating to the mash temperature or stepping the mash temperature up for stepped mashes or "mash out" at the end.

The advance that has come with both systems (HERMS and RIMS) is the "recirculating" bit. The mash liquid is separated from the grain (by a false bottom or the like), heated, and then returned to the grain. Previously insulation was the prime choice for keeping the mash temperature steady, or else heat was applied directly (there are also methods of manually separating portions of mash and heating it, such as in "decoction" mashing). The problem with directly heating the mash is the high proportion of solids in a mash which limits heat transfers to slow conduction, not faster convection (with associated currents), which will create pockets of cooler or hotter mash unless stirred well, and the solids can burn to the heating surfaces. Constant recirculation also stands in for convection currents, keeping the temperature throughout the mash more consistent.

"A" is one logical location for the temperature probe controlling heating of the mash i.e. in the tank with the heat source (the HLT). But is it the best? The most likely controller being used is of the "PID" type, because they are very good, but unless they have been very carefully tuned they can also be horribly slow at converging the set (desired) temperature with the actual temperature. And placing the probe at "A" has the effect of exaggerating this slow convergence. Tuning could accept a small temperature overshoot to speed up convergence, but most users are not going to be developing the necessary knowledge to fiddle about with these controllers in such detail. As a location for the controlling temperature probe in HERMS "A" may require a complete shift of thinking to select. No wonder the sensor location for HERMS causes such division of opinions.

"B" is a logical location for the temperature probe in RIMS because there will be no location "A". Location "B" (and "C" and "D") is actually in the recirculating mash stream. Many documented examples of heat-exchanger processes will show the location of temperature sensors at "B".

"C" as a location seems to be ideal because it's in the mashtun (MT) with the mash. But even with recirculation, temperature through the thick stodgy mash can't be guaranteed uniform so isn't a good candidate for a sensor controlling mash temperature.

"D" would seem a reasonable location, but there would be considerable lag between heating and seeing the result at "D". Meanwhile there would be undesirable over-heating of the recirculated mash unless very careful tuning was undertaken (far more so than if "A" was used - somewhat defeating any point of not using "A"). "D" is a good location for monitoring because it will help confirm when the system has achieved equilibrium (i.e. heating has done its work to reach the desired temperature and the system is now just maintaining it): Without such monitoring the system can be the source of uncertainty.

So, what of "B", the same location as would be logical for RIMS (the HLT and HERMS coil sort of replaces the RIMS tube). Can this be a better location than "A" for HERMS? When temperature changes are small the sensors at "A" and "B" will most likely be reading the same temperature. But for big jumps the heat exchanger may start lagging behind the speed at which the HLT is being heated. Meanwhile if the sensor is at "B" the controller could be allowing the HLT to over-heat (the controller is being told the temperature is too low): But that will also mean the heat-exchanger will not be lagging behind the desired temperature by quite so much (because more heat is being provided to the heat-exchanger). And as long as the mash is sucking enough heat out of the HLT for the over-heating to stay within "reasonable" limits, the over-heating should get less and less as the desired temperature is converged on.

So "B" is ideal? Minimal tuning yet much of "A's" slow convergence is countered. This does depend on the dynamics of the brewing setup design but this can be ignored for most brewery designs. Some may not want to risk "B" and will stick with the "safe" sensor location of "A" (over-heating the HTL is very unlikely). Even if a brewing setup is found to be incompatible with this "B" approach, a far coarser and cheaper controller (than a PID controller) could be used on the HLT to limit its potential over-heating. The amount of lag between the HERMS coil and the HLT will depend on the flow rate of mash fluid through the coil (and the efficiency of the coil - note "rate" must take in the possibility of a stuck mash) so using location "B" releases the convergence of actual MT temperature and desired MT temperature from those factors too.

But there is a snag (for HERMS). If any sensor location other than "A" is used to control the temperature of the MT, the HLT cannot be heated using the same PID controller unless the recirculation system is operating. This might not be an issue for many, and it will not be a problem to work-around for the handy folk who would like the challenge. But the limitation may prove unsurmountable for some, in which case using location "A" is the only option. Another snag when not using "A" (for HERMS) is if recirculation is interrupted (e.g. stuck mash): The controller may continue to instruct the HLT to keep heating (until it is boiling unless some sort of fail safe is worked in).

So to gain the potential benefits of using location "B" for HERMS (i.e. possibly faster temperature ramps) you must accept the HLT is out-of-bounds for ad-hoc little heating jobs when the recirculation isn't running. But would the HLT ever be required when the recirculation isn't running? The handy might develop a scheme to switch between locations, or work in a second controller for independently running the HLT, but such complexity is outside the scope of this article. But this division of options should keep arguments raging for some time to come. Or avoid this divisive option and plump for RIMS, but be warned the choice of RIMS over HERMS is just a source of even more arguments!

Footnotes:
27 March 17:00: Describe "A" as the "logical" position instead of "generally accepted". Because it seems rather more people than I expected are using "alternative" positions.
28 March 12:40: Add RIMS diagram and minor text edits to accommodate it.
28 March 16:45: Highlight a problem trying to use any location for the HERMS temperature probe other than "A".
30 March 10:55: Changes to narration about location "B" as a site and interim conclusions.
1 April 20:25: Adjust tone to sound a little more "neutral" about using location "B" over "A".
2 April 11:20: Adjustments because "other control processes" were represented with heating and process liquids the wrong way around.
2 April 13:10: Add note about boiling HLT hazard using location "B".
Last edited by PeeBee on Mon Apr 02, 2018 1:10 pm, edited 13 times in total.

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Re: RIMS and HERMS temperature sensor position

Post by Haydnexport » Mon Mar 26, 2018 8:27 pm

I'm pretty sure in virtually every build picture i have seen , the sensor location is always 'b'

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Re: RIMS and HERMS temperature sensor position

Post by Jim » Mon Mar 26, 2018 8:37 pm

I've not used anything recirculating myself, but I suppose multiple temperature probes together with good modelling software would be ideal. It would take some optimising though.
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Re: RIMS and HERMS temperature sensor position

Post by Eric » Mon Mar 26, 2018 11:15 pm

My system has three and uses a bit of Boolean algebra.
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Re: RIMS and HERMS temperature sensor position

Post by PeeBee » Tue Mar 27, 2018 12:09 am

Haydnexport wrote:
Mon Mar 26, 2018 8:27 pm
I'm pretty sure in virtually every build picture i have seen , the sensor location is always 'b'
You're "pretty sure"; does that mean you not so sure? Can you provide some links please?

From what I gleaned I can be pretty sure most builds on display show all sorts of things: But not where they put the flippin' temperature sensors! Even the well known "Electric Brewery" is a bit vague, but it certainly isn't located at "B".

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Re: RIMS and HERMS temperature sensor position

Post by Haydnexport » Tue Mar 27, 2018 12:34 am

pretty sure as in every herms rig i can remember seeing has had the temp on the return to the mt, why would it be anywhere else? And no i don't have any links , my brain doesn't save them I'm afraid.

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Re: RIMS and HERMS temperature sensor position

Post by Jim » Tue Mar 27, 2018 8:43 am

Eric wrote:
Mon Mar 26, 2018 11:15 pm
My system has three and uses a bit of Boolean algebra.
Your new set-up I take it. :)

What are you using as a controller?
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Re: RIMS and HERMS temperature sensor position

Post by PeeBee » Tue Mar 27, 2018 10:01 am

Haydnexport wrote:
Tue Mar 27, 2018 12:34 am
pretty sure as in every herms rig i can remember seeing has had the temp on the return to the mt, why would it be anywhere else? And no i don't have any links , my brain doesn't save them I'm afraid.
Thank you.

Anyone else provide documented "alternative" locations to "A"? My original post is backed by pure logic. This might put off people providing alternatives because they might worry that I will rip into the explanations (I've already been doing that elsewhere and have got over it!). But I'm assuming to put together a definitive guide to how temperature is controlled in HERMS (and RIMS) so my understanding "alternative" arrangements and how prevalant they are is important. I was pretty sure the well known "Electric Brewery" would provide backing arguments for my conclusions, but it seems that is using unexplained, logic defying, control too.

The result is to help anyone, not me.

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Re: RIMS and HERMS temperature sensor position

Post by Eric » Tue Mar 27, 2018 12:44 pm

Jim wrote:
Tue Mar 27, 2018 8:43 am
Eric wrote:
Mon Mar 26, 2018 11:15 pm
My system has three and uses a bit of Boolean algebra.
Your new set-up I take it. :)

What are you using as a controller?
That's me Jim. Three thermowells, three thermistors and three linked digital temperature control modules. Set those and off it goes until I care to alter the settings. It's not as good or easy as it sounds and makes you realise how easy it is to chase your tale in that Utopian dream.

The real world returns when you put a glass thermometer where no temperature probe exists.
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Re: RIMS and HERMS temperature sensor position

Post by jaroporter » Tue Mar 27, 2018 5:39 pm

4 thoughts as a simple rims user..

controlling A at a temperature calibrated for system inefficiencies seems to me the logical option for maintaining (note not arriving at) a mash temperature. this would also requite a thermometer at B though to monitor and calibrate.

controlling B should be fine with a well calibrated PID controller and quicker when ramping. this is the critical temperature in a fully recirculating system

most i've seen are at B though A also seems to be common enough.

this has all already been covered over n over. end of the day ye can debate it til the sun goes down but trial n practise is all that counts. and people's preferences just might be influenced by singularities in their personal equipment

i do like the drawing though!

not sure if you've looked at the electric brewery build manual? they're pretty clear about where and why they place their herms probe. spoiler alert.. controlled at A, monitored at D..
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Re: RIMS and HERMS temperature sensor position

Post by PeeBee » Tue Mar 27, 2018 8:06 pm

jaroporter wrote:
Tue Mar 27, 2018 5:39 pm
4 thoughts as a simple rims user..

controlling A at a temperature calibrated for system inefficiencies seems to me the logical option for maintaining (note not arriving at) a mash temperature. this would also requite a thermometer at B though to monitor and calibrate.

controlling B should be fine with a well calibrated PID controller and quicker when ramping. this is the critical temperature in a fully recirculating system

most i've seen are at B though A also seems to be common enough. ...
Thanks "jaroporter". Your thoughts are always welcome!

I should "lay my cards on the table". Position "A" is more obviously for controlling the MT heat source for me: Because I don't actually have a HERMS coil in the HLT. The HLT just supplies heated water to the jacket of a counter-flow heat-exchanger with the MT liquid recirculating through its core. Effectively exactly the same as a coil in the HLT but allows the coil to be second purposed as a wort cooler. It's also less easy to be deceived into thinking the temperature of the HLT isn't so vitally important when used in HERMS for controlling the temperature in the MT.
jaroporter wrote:
Tue Mar 27, 2018 5:39 pm
...
this has all already been covered over n over. end of the day ye can debate it til the sun goes down but trial n practise is all that counts. and people's preferences just might be influenced by singularities in their personal equipment

i do like the drawing though!

not sure if you've looked at the electric brewery build manual? they're pretty clear about where and why they place their herms probe. spoiler alert.. controlled at A, monitored at D..
I know. I thought I'd do it as a logical presentation (rather than airing personal prejudices) so people starting out can be clearer about it. You do still get questions from HERMS/RIMS beginners about where to put the sensors despite it having been gone over again and again.

And I'm being swayed away from "A" towards "B" but it's not a big deal with my brewery to try it as it already has sensors at both "A" and "B". I'm keen to have monitoring at "D" too so I can have the warm fuzzy feeling that all is well, but my post was written from the point of view of only having one sensor, and that for the controller not for comforting the anxiety-ridden.

No I haven't got the "Electric Brewery" manual. But my brewery design started out as an "Electric Brewery" clone; it just branched out when it became obvious that the "US" electrical design was completely out-of-sorts with UK practices. Thank you for confirming how the "Electric Brewery" goes about sensor positioning. Revisiting it I was beginning to worry that they used "D" as the site for controlling the MT temperature.

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Re: RIMS and HERMS temperature sensor position

Post by jaroporter » Tue Mar 27, 2018 9:13 pm

it's not a physical manual, it's all on the website. i read it when researching for mine (although rims was always going to be more suited for me)
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Re: RIMS and HERMS temperature sensor position

Post by PeeBee » Wed Mar 28, 2018 5:07 pm

Having convinced even myself that there might be better locations than "A" to fit a temperature probe controlling the MT temperature, I hit a snag! The snag isn't the end-of-the-road for alternative placements, but it might be for some. The first post has been updated to reflect this with the following words:
If any sensor location other than "A" is used to control the temperature of the MT, the HLT cannot be heated using the same PID controller unless the recirculation system is operating. This might not be an issue for some, and it will not be a problem to work-around for the handy folk who would like the challenge. But the limitation may prove unsurmountable for many, in which case using location "A" is the only option. Not for nothing is the "logical location" down as "A".

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Re: RIMS and HERMS temperature sensor position

Post by PeeBee » Thu Mar 29, 2018 12:18 am

EINBREW wrote:
Wed Mar 28, 2018 3:54 pm
... PeeBee, your coil is in the MT, around the inside edge, is it copper or SS?
Apologies for the delay responding, but to avoid the damage done in the last thread your posts are hidden from me and vetted before I can respond to them. Keeps the others happy?

Anyway. Best if you have a piccy of the HERMS "coil" in my brewery so you get on the right track. Photo is a bit old but not a lot has changed:
2015-11-20_WEB.jpg
It's obviously copper and obviously not in the MT (or the HLT; that's it in shot, along with the wort recirculation pump). The "coil" is topped off with a RIMS tube and the temperature sensor tucked into the Tee above it would be "location B" (the brewery is a HERMS/RIMS hybrid). The MT (and kettle) is on the work surface above it all.

But I was trying to write this article from Mr Any Body's point of view, not Mr Arent I A Cleverdick's perspective.

I do not imagine you are too happy with my latest conclusions that "location A" is the only practical location for the HERMS temperature sensor, but this time I am determined to find a solution to having the sensor at location "B". And it won't be one of Cleverdick's solutions.

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Re: RIMS and HERMS temperature sensor position

Post by Jocky » Thu Mar 29, 2018 7:23 am

Eric wrote:
Tue Mar 27, 2018 12:44 pm
Jim wrote:
Tue Mar 27, 2018 8:43 am
Eric wrote:
Mon Mar 26, 2018 11:15 pm
My system has three and uses a bit of Boolean algebra.
Your new set-up I take it. :)

What are you using as a controller?
That's me Jim. Three thermowells, three thermistors and three linked digital temperature control modules. Set those and off it goes until I care to alter the settings. It's not as good or easy as it sounds and makes you realise how easy it is to chase your tale in that Utopian dream.

The real world returns when you put a glass thermometer where no temperature probe exists.
That made me laugh. How many time have I thought

"THERE'S GOT TO BE A BETTER WAY!"

It turns out every time, no, just a different way with it's own compromises.

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