How is my RIMS defying the laws of physics??

[EvilBrewer]

Been using my RIMS for a few months now with good results...still learning some of the nuances associated with using the PID. But overall great, very happy.

The last few beers have not attenuated as much as I would have expected based on past experiences with the same yeast and mash temperatures. So, this past weekend, I decided to double check the temperature of the mash itself as compared to what the PID was displaying for the wort circulating through the RIMS. I suspected the mash temp might be higher than the PID was displaying--and hence higher FG's. Also want to say that I've calibrated my RIMS temp sensor using a lab thermometer so I'm fairly confident that it's accurate.

Here's the weird thing...
Upon measure the temperature of the mash using my lab thermometer, I found that the mash itself was consistently about 5 degrees *higher* than what my PID was displaying (for the recirculating wort). I measured the temperature of the wort as it returned to the MLT from the RIMS (using the lab thermometer) and it measured almost precisely the same as what the PID was displaying so, the RIMS is performing its function correctly--that being: it is maintaining the recirculating wort at the temperature I've set. So, how is it that my mash is measuring higher?? I tried stirring the mash really well to distribute the temps and eliminate any potential hot spots, etc...but same results; the mash would eventually level out about 5 degrees higher than whatever the PID was displaying. I don't have any other heat sources for the MLT.

 

[jjohannes]

But does your PID display the setpoint or the actual measured value? If it is the former it seems you have a steady-state error typical of a P controller. So perhaps the I and D terms need tweaking?

EDIT: After reading your post again and reading a little about RIMS it realise I'm probably in over my head... But I'm also curious: where in the system do you measure the temperature and could it have a bearing on the results? And have you tried adding an offset in your controller to get rid of the temperature difference?

 

[EvilBrewer]

But does your PID display the setpoint or the actual measured value? If it is the former it seems you have a steady-state error typical of a P controller. So perhaps the I and D terms need tweaking?

EDIT: After reading your post again and reading a little about RIMS it realise I'm probably in over my head... But I'm also curious: where in the system do you measure the temperature and could it have a bearing on the results? And have you tried adding an offset in your controller to get rid of the temperature difference?

I measure the temperature of the wort on its way out of the RIMS tube; pretty standard. There are 2 temperature displays: the configured temp and actual temp. The PID actually is offset, from when I calibrated the thermometer...only about 1.5 degrees I think. But what puzzles me is that I've validated the RIMS's temperature by using a lab thermometer on the wort as it returns to the MLT.

I'm either doing something wrong in my temperature measurements, or the temperature of the grain bed is somehow rising above where the RIMS maintains the wort. I'm hoping for the former, as the latter would shatter my understanding of the universe

Maybe I'm missing something obvious?

 

[GilaMinumBeer]

I'm just spitballin here but, could it be due to thermal convection? The heat rising in the liquid column offsetting by 5 degrees prior to surface evaporation?

 

[EvilBrewer]

I'm just spitballin here but, could it be due to thermal convection? The heat rising in the liquid column offsetting by 5 degrees prior to surface evaporation?

That's over my head (as far as whether it's plausible)...but it sounds like you're saying that there is some kind of cumulative effect; that the heat is accumulating to the extent that the temperature actually rises. I considered that but again...over my head.

 

[chocotaco]

How are you measuring the temperature leaving the RIMS tube? Are you using the same thermometer to measure the mash temperature?

What if there is a stream of hot liquid from passing over the element, surrounded by a "tube" of cooler liquid, and the temperature hasn't mixed well enough when it hits your thermometer? The thermometer's probe could be in a cool zone, but the temperature of the wort once it's mixed is higher than measured.

Maybe if you insert some kind of turbulence generating blockage between your heating element and your thermometer?

 

[HDIr0n]

Show us a pic of how your RIMS is setup.

 

[judsonp]

I'm only somewhat familiar with how RIMS works (but more familiar with thermodynamics). Stupid questions:

Do you see the same problem if the whole system is filled with just water?

What's the input temperature to the heater? If the heater is turning on at all, then the input temperature must be below the set point. The output temperature is the same as the set point, apparently. But the temperature you're measuring in the MLT is above the set point. So apparently the input temperature is well below the MLT temperature, which means you definitely have a cold spot of some kind.

 

[EvilBrewer]

Show us a pic of how your RIMS is setup.

You would ask that wouldn't you?

Here's a pic of the exact same RIMS tube that I use...with the same port configuration. Element on one end; temperature sensor on the other. In/Out ports on the body of the tube. I have it sitting horizontally when in use.

https://lh5.googleusercontent.com/-...MAGE_CC9AF6F6-B4DD-48CA-837F-9731DA3FD4B3.JPG

 

[EvilBrewer]

I'm only somewhat familiar with how RIMS works (but more familiar with thermodynamics). Stupid questions:

Do you see the same problem if the whole system is filled with just water?

What's the input temperature to the heater? If the heater is turning on at all, then the input temperature must be below the set point. The output temperature is the same as the set point, apparently. But the temperature you're measuring in the MLT is above the set point. So apparently the input temperature is well below the MLT temperature, which means you definitely have a cold spot of some kind.

I haven't tried it with just water but I see your point (I think)...you suspect the grain is causing different temperature zones. Still doesn't explain the *higher* temp though, right? Minor clarification: yes, I have run the RIMS with just water; that's how I heat the strike water...I just haven't measured to see if this same phenomenon exists when it's only water.

I have not measured the input temperature to the heater but yes, it makes sense that it would be lower than the configured set point--and the PID uses the heater to adjust as it flows through the tube.

 

[brewingmeister]

Try switching the temp probe with the out port and see if the problem persists.

 

[jjohannes]

Do the two displays (actual vs set) show the same temp? And couldn't the problem be solved by simply entering a negative offset?

 

[rshortt]

Maybe your strike temp was too high. In that case the body of your mash would be hotter than the wort coming out the RIMS tube.

 

[GotPushrods]

Is your RTD probe long enough to stick out near the exit port? Or is it back aways in a cooler eddy at the end of the tube?

 

[EvilBrewer]

Is your RTD probe long enough to stick out near the exit port? Or is it back aways in a cooler eddy at the end of the tube?

That's possible...but I'm pretty sure my probe is long enough. Wait, what are we talking about here? Ha...but yeah, it extends into where the "current" of wort would flow while recirculating through the tube. And remember, I checked the temperature of the wort as it re-entered the MLT (having just passed through the RIMS tube) and it matched that which was displaying on the PID.

I think I'm gonna try running it with just water to see if it still occurs.

 

[jjohannes]

How did it turn out? Were you able to solve the problem or find an explanation?

 

[DragonHartBrewing]

Hey Evil,
Just checking do have your temperature probes inserted in a thermowell? I have found that if you don't use some type of silicone heat sink compound that you will stand the risk of not getting a accurate reading due to the air space in between the well & probe will work as a form of insulation resulting in a bad reading.
Cheers, Steve

 

[EvilBrewer]

Revisiting this issue after an 8 month hiatus. Ran it with just water last night and I'm seeing the same phenomenon. The PID is measuring 155F, and indeed that is what my laboratory thermometer is measuring from water returning to the MLT (post RIMS tube and PID therm probe). But immerse that same lab thermometer deeper into the MLT and the temp increases by 7-8 degrees F.

I even stopped the recirculation, stirred the water around in the MLT a bit and then measured just in case of some sort of crazy temperature stratification. But no...it still measured higher than the PID. I don't remember the difference...maybe 5 degrees higher than PID, but that could just be cooling during the stirring.

So...WTF. Any ideas?


Sent from my iPhone using Home Brew

 

[MoanaDrifter]

What temp is the water that you add to your MLT? ie, are you heating it up to temp on the stove and then using the RIMS to maintain it, or are you adding room temp water and then bringing it up to temp with the RIMS?

If you're adding preheated water, maybe you're overshooting, and the water actually cools as it passes through the RIMS tube. Do you see the heater cycling while you're running?

 

[EvilBrewer]

What temp is the water that you add to your MLT? ie, are you heating it up to temp on the stove and then using the RIMS to maintain it, or are you adding room temp water and then bringing it up to temp with the RIMS?



If you're adding preheated water, maybe you're overshooting, and the water actually cools as it passes through the RIMS tube. Do you see the heater cycling while you're running?

Nope, I'm not preheating the water. I heated the water from whatever temp it was, coming out of the hose...so, about 70 F last night.

Is the heater cycling? The temp on the PID stays at 155 once that temp is reached. So I'd say it's not cycling the heater any more than normal.


Sent from my iPhone using Home Brew

 

[TNugent]

When you are using the lab thermometer to measure the temp of the water returning are you just putting it into the stream of water? If so, how about taking a measuring cup, say 2 cups, fill that with the returning water and put your probe in there. Just curious if that would show the same as your PID or if it would also show the increase. not sure why it would matter but it was a thought, something about the flow of water over the probe and the possibility of air being mixed in and throwing off the temp your getting from the moving liquid....

 

[TallDan]

Pics would help. Is your MLT a pot or cooler? Is it close enough to your HLT to be getting indirect heat from it? Sitting on a metal brew stand? On the stove above a warm pilot light? Do you have a hot girlfriend/wife/boyfriend/husband that stands right by it while you're brewing? Solar Flares? Inductance from overhead power lines? Were you anywhere near the Three Mile Island incident?

 

[EvilBrewer]

When you are using the lab thermometer to measure the temp of the water returning are you just putting it into the stream of water? If so, how about taking a measuring cup, say 2 cups, fill that with the returning water and put your probe in there. Just curious if that would show the same as your PID or if it would also show the increase. not sure why it would matter but it was a thought, something about the flow of water over the probe and the possibility of air being mixed in and throwing off the temp your getting from the moving liquid....

That's worth a try. I kind of did that last night but the results were inconclusive. I drew water from the out port of the MLT into an insulated coffee travel mug and measured the temp--which, if the lab therm inside the MLT is correct, would also have measured high. But I let it sit too long before I could get a measurement; and then I was thinking that the cup itself was definitely cooler than the water and so there had to have been a heat exchange. But I'll try your suggestion.



Sent from my iPhone using Home Brew

 

[EvilBrewer]

Pics would help. Is your MLT a pot or cooler? Is it close enough to your HLT to be getting indirect heat from it? Sitting on a metal brew stand? On the stove above a warm pilot light? Do you have a hot girlfriend/wife/boyfriend/husband that stands right by it while you're brewing? Solar Flares? Inductance from overhead power lines? Were you anywhere near the Three Mile Island incident?

Ha, I can answer some of these questions...the others could get me killed.

MLT is a keggle with duct insulation wrapped around it. I use a blichmann top tier system to give you a vague idea of the setup. Last night, I was not using any burners, so I think the indirect heat most likely does not apply.


Sent from my iPhone using Home Brew

 

[GoodDogShelby]

How fast are you recirc'ing? I can see you loosing heat in the tubing & fittings. Try slowing your flow down a bit.

I consistently run my PID set point about 2.5 deg higher than target to get the mash to the target. Your situation seems to be just the opposite.

 

[microbusbrewery]

How fast are you recirc'ing? I can see you loosing heat in the tubing & fittings. Try slowing your flow down a bit.

I consistently run my PID set point about 2.5 deg higher than target to get the mash to the target. Your situation seems to be just the opposite.

Along these lines, it's difficult to accurately measure the temperature of moving liquid, especially if the flow rate is fairly high. The slower the flow, the more accurate the temp reading. So if your running it with your ball valve all the way open, try throttling it back and see if the gap closes.

I've noticed this during the startup phase on my HERMS system. I have an element in my HLT and another in my standalone HEX. During startup I'll recirc from HLT through the HEX and back to HLT. If the ball valve is all the way open, the HEX probe always reads a lower temp than the HLT probe. And just in case anyone is thinking it's because the HLT element is heating faster than the HEX element, it's not. I've turned off the HLT element and still see the same behavior when the ball valve is full throttle.

 

[EvilBrewer]

Along these lines, it's difficult to accurately measure the temperature of moving liquid, especially if the flow rate is fairly high. The slower the flow, the more accurate the temp reading. So if your running it with your ball valve all the way open, try throttling it back and see if the gap closes.

I've noticed this during the startup phase on my HERMS system. I have an element in my HLT and another in my standalone HEX. During startup I'll recirc from HLT through the HEX and back to HLT. If the ball valve is all the way open, the HEX probe always reads a lower temp than the HLT probe. And just in case anyone is thinking it's because the HLT element is heating faster than the HEX element, it's not. I've turned off the HLT element and still see the same behavior when the ball valve is full throttle.

That's interesting; I had not considered that the temp measurement accuracy is somewhat dependent on flow rate. If that is the case, it would certainly explain my issue.

I recirc fairly slowly already--mainly so I don't end up with a dense cone of malt in the MLT at the end if the mash (wort returns tangentially, causing whirlpool effect)...such a dense cone it seems would lower efficiency.

I'll slow it down a bit more and see if it decreases the discrepancy. I'm also going to switch the position of the temp probe and exit valve on the RIMS TUBE.









Sent from my iPhone using Home Brew

 

[rlmiller10]

A few thoughts.

When you are checking the RIMS discharge temp could you tell if the heating element was on? If you are getting a several degree cycle you might have just measured when at the beginning of the cycle, before the temp had risen close to the off set point.

Is there a space the RIMS input water is cooling before it gets to the tun? i.e. the input temp is getting cooled and thus keeping the RIMS on longer. That would still require some measurement problems at the RIMS discharge as well.

Is there a small black hole in your tun that is distorting classical physics as we know it?