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Home Brew Forums > Home Brewing Beer > Equipment/Sanitation > Using a PID to control a pump in a HERMS setup? A no-no?
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Old 12-31-2008, 08:22 PM   #1
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Default Using a PID to control a pump in a HERMS setup? A no-no?

I'm building a 100% electric setup with 3 Blichmann 20 gallon pots.

I will be using 5500W/240V ULWD electric heating elements in the HLT and the BK.

I'm planning on using a PID + 40A SSR/heatsink + RTD temp sensor to control both the BK and and HLT separately. Duplicate equipment for both to make it simpler (no cable switching needed). That part I understand. The boil kettle PID will be running in manual mode and in 'regular' mode(for lack of a better term) in the HLT.

Everything's going to be ordered from Auberins.com.

PID with SSR output:

Link: http://auberins.com/index.php?main_p...&products_id=3

Liquid tight RTD temp sensor, 4" probe, 1/4" NPT thread:

Link: http://auberins.com/index.php?main_p...products_id=85

40A SSR & Heatsink
SSR: http://auberins.com/index.php?main_p...products_id=30
Heatsink: http://auberins.com/index.php?main_p...products_id=77

There will be a HERMS coil in the HLT to recirc from the MLT to maintain mash temp and to allow for future step-mashes. I'm using an uninsulated Blichman 20 gallon pot for the mash so temp won't be maintained very well without HERMS and I don't want to cover up the nice pot with insulation.

I was going to put another RTD temp sensor in the MLT to cycle a pump on/off with a PID. This pump would recirc the sweet wort through 25' of copper coil in the HLT during mash. This would require a third PID. I was told however that I can't do this as a PID would try and cycle the pump on/off too much which isn't good for the pump. Makes sense, but this seems to be the way that the B3 BrewSculptures work. From the BrewSculptures user manual:

"If using the SMART or Digital SMART system, you will set the controller to 152°F and allow the recirculation to maintain the mash temperature for the entire duration of the mash. The pump will switch on and off automatically to recirculate the mash liquid through the coil in the hot liquor tank and back to the top of the mash tun. This will clarify the wort and will allow you to keep the temperature steady during the entire mash."

Sounds exactly like what I want to do. No? Or do I use some sort of LOVE-style controller with lag instead of a PID so that the pump doesn't get turned on/off fast? A LOVE controler just looks at the temp and either turns the output on or off instead of learning and cycling power (similar to duty cycle).

A LOVE controller:



Questions:

How do most single tier electric guys do HERMS? Do they have 3 PIDs (or 2 PID and a discrete on/off LOVE-style controller for HERMS)?

What am I missing here?

I've also never seen anyone with THREE controllers on their control panel. I understand that you can use one PID for the HLT and BK but then I assume you need a low voltage switch for the low voltage side of the SSR to choose which element the PID is controlling (I'm assuming that in manual mode a PID ignores the temp sensor).

I'm ready to place a large order at Auberins.com for the core electrical stuff but want to make sure my process is clear first.

Kal

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Old 12-31-2008, 10:40 PM   #2
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My understanding from reading a ton of threads and wanting to do the same thing is that you run the pump the entire time. The constant recirulation is one of the advantages, and you can control the temperature one of two pays.

The guy with the orange cooler setup Poi?, simply uses one controller to monitor the temperature of the HLT and calculates a 3 degree temp loss, so if he wants 152 in the mash, sets the HLT at 155. This insures you never go over temp, but would be slow to ramp up temps.

The other options are to monitor the temp in the mash, top, bottom, middle, output hose etc, and allow the HLT to get as hot as it needs to, however, you risk a serious temperature overshoot with this setup.

You can use a PID on the pump, if you went that route, but would need to set a dead zone to protect the pump.

If you went that route you would set the HLT to a desired temp and control the pump, but still be left with the decision of where to monitor the mash temp.

It seems to me, constant recirc, and controlling only the temp of the HLT is the best option.

Good luck with your setup.

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Old 01-01-2009, 12:09 AM   #3
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You could use the same PID on your HLT and mount another RTD in the output of your HERMS coil. Those RTD can be disconnected fairly easily or you could have a way to switch between two of them (just unplug) or just move the wire part between two "end" parts.

The PID will tell element heat the HLT to maintain your setpoint of the wort going out of the coil. You don't have to calculate any heat diffs or anything.

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Old 01-01-2009, 01:35 AM   #4
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Originally Posted by GuateBrewer View Post
My understanding from reading a ton of threads and wanting to do the same thing is that you run the pump the entire time. The constant recirulation is one of the advantages, and you can control the temperature one of two pays.

The guy with the orange cooler setup Poi?, simply uses one controller to monitor the temperature of the HLT and calculates a 3 degree temp loss, so if he wants 152 in the mash, sets the HLT at 155. This insures you never go over temp, but would be slow to ramp up temps.
Makes sense. Would work perfectly for single infusion mashes which I mostly intend to do (at least at the start).

Question: While my Blichmann pots have great temperature dials on them it would be nice to be able to have a digital readout showing the temp of the sweet wort in the MLT to see how closely it matches to the HLT at a quick glance since both displays could be side by side in the control panel.

A PID/RTD combo not controlling anything could be used but seems like a bit of a waste or is it? $44+32 for the two... I suppose it's not that bad. Do people monitor mash temp digitally using something different?

Quote:
The other options are to monitor the temp in the mash, top, bottom, middle, output hose etc, and allow the HLT to get as hot as it needs to, however, you risk a serious temperature overshoot with this setup.
My worry with this method is having the HLT water get way too hot for sparging.

I think I'm starting to see why RIMS is used.... you can get fast ramp times for step mashes without screwing up your HLT temp.

Quote:
It seems to me, constant recirc, and controlling only the temp of the HLT is the best option.
Probably right since I don't see myself doing much more than single infusion mashes and you can basically get HERMS for "free" (minus the 25' or so of copper coil in the HLT).

I'll have two pumps as well so one can be set to recirc the MLT sweet wort through the HERMS coil while the other can be used to recirc the HLT water to keep it at a constant temp all over.

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Good luck with your setup.
Thanks. You too!

Kal
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Old 01-01-2009, 01:49 AM   #5
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You could use the same PID on your HLT and mount another RTD in the output of your HERMS coil. Those RTD can be disconnected fairly easily or you could have a way to switch between two of them (just unplug) or just move the wire part between two "end" parts.

The PID will tell element heat the HLT to maintain your setpoint of the wort going out of the coil. You don't have to calculate any heat diffs or anything.
Ok, so PID is controlled by RTD at the HERMS coil output and is heating water in HLT. Got it.

I think the previous poster mentioned the possibility of temp overshoots but now I'm not sure how that could happen, but then I'm still learning.

An example:

Say you're doing step mashes and have been sitting at 122F (protein rest) for a while. You've got the sweet wort continually recirculating through the HERMS coil with the RTD temp sensor at the HERMS coil output. The HLT is at 122F, the MLT is at 122F. You then want to crank the temp up to 154F in the MLT for the starch conversion so you set the PID to 154F. The PID's now going to turn the HLT element on/off to try to get the output of the HERMS coil from 122 to 154F as fast as is possible all the while trying to avoid overshoot of the HERMS coil output temp by not overheating the HLT water (right?).

I mean, it could get the HERMS coil output to 154F faster it heated the HLT water to 200F but then as soon as 154F at the HERMS coil output was reached the HERMS coil would just keep pulling heat out of the HLT water and you'd overshoot in the MLT eventually with no way to get back down.

The whole point of PIDs is to avoid over/undershoot because they learn and look at ramp time and reduce/increase the output to compensate so that you LAND at the expected temp without really needing to understand exactly what's in the system, no?

So how can it possibly overshoot? I'm missing something.

Kal

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Old 01-01-2009, 03:24 AM   #6
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Yea, what you said is basically it. It shouldn't overshoot. And, as others have said, the actual HLT water will probably be only 3 degrees or so hotter than mash, so it's not too high for sparge. Just be sure you have plenty of copper to get good transfer rate.

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Old 01-01-2009, 03:38 AM   #7
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Yea, what you said is basically it. It shouldn't overshoot. And, as others have said, the actual HLT water will probably be only 3 degrees or so hotter than mash, so it's not too high for sparge.
Excellent. My logic makes sense then!

Quote:
Just be sure you have plenty of copper to get good transfer rate.
Good point. My HLT is 20 gallons. What's considered "plenty" of copper? 25' of 1/2" copper tubing?

Just had a thought: How about using a convoluted CFC? I'm going to be ordering one anyway (like the Northern Brewer ChillZilla seen here) for chilling at the end of the boil. I could recirc the HLT water through the outer water layer and the sweet wort from the MLT through the inner convoluted pipe. Should give me just about the best heat extraction possible and no need to buy an extra copper coil for the HLT.

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Old 01-01-2009, 03:23 PM   #8
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Just had a thought: How about using a convoluted CFC? I'm going to be ordering one anyway l

I tried the same with a plate chiller and it just didn't work out. I think the coil of copper in HLT works best for HERMS. If you get it to work, though, go for it.

Yes, 25' of 1/2 should be good. Make sure it doesn't actually contact the element. So you will have to suspend it somehow or make some legs for it.
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Old 01-02-2009, 04:17 AM   #9
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Quote:
Originally Posted by kal View Post
I'm building a 100% electric setup with 3 Blichmann 20 gallon pots.


I was going to put another RTD temp sensor in the MLT to cycle a pump on/off with a PID. This pump would recirc the sweet wort through 25' of copper coil in the HLT during mash. This would require a third PID. I was told however that I can't do this as a PID would try and cycle the pump on/off too much which isn't good for the pump. Makes sense, but this seems to be the way that the B3 BrewSculptures work. From the BrewSculptures user manual:

"If using the SMART or Digital SMART system, you will set the controller to 152°F and allow the recirculation to maintain the mash temperature for the entire duration of the mash. The pump will switch on and off automatically to recirculate the mash liquid through the coil in the hot liquor tank and back to the top of the mash tun. This will clarify the wort and will allow you to keep the temperature steady during the entire mash."

Sounds exactly like what I want to do. No? Or do I use some sort of LOVE-style controller with lag instead of a PID so that the pump doesn't get turned on/off fast? A LOVE controler just looks at the temp and either turns the output on or off instead of learning and cycling power (similar to duty cycle).



I'm ready to place a large order at Auberins.com for the core electrical stuff but want to make sure my process is clear first.

Kal

On many PID controllers you can set the cycle time. On the ones I am most familiar with (Barber Coleman 7EM) the max time is 90sec.


edit - I looked at the manual for your PID. The cycle time is adjustable from .5-125 seconds. I haven't automated anything but the HLT in my brewhaus yet, but I'm a electrician in a plastic factory & deal with this stuff on a regular basis...

I doubt that turning the pump on/off every 2 min. is going to do much damage.
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Old 01-02-2009, 04:34 AM   #10
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Control the temp of the HLT water for the HERMS heat exchange. The further your temp probe gets from the heating medium, the larger your lag time and threat of temp overshoot.

If you think that temp overshoot is a myth, there are a few HBTers here that have built similar rigs and can testify to its reality.

NEVER control a HERMS or RIMS by measuring temp in the MLT. You need to have absolute control over the temp of the wort coming out of the heat exchanger.

The reason many people put the thermowell in the HLT water is that depending on your heat transfer to the coil, your HLT water could heat up to a temp that exceeds what you will desire. By the time your circulting wort reaches the wet point, the HLT is too hot and the subsequent wort throught the coil will overshoot.

YOU CAN USE A HERMS LIKE THIS FOR STEP MASHING!!!!

#1. Strike to rest at 122F, DO NOT RECIRCULATE
During this rest (15-20 min) you heat your HLT to 155F to obtain 152F in the MLT when you begin your recirc.
#2. After the 122F rest, begin the ricirc with your HLT set at 155F to obtain say a 152F rest in the MLT.

You will have no chance of overshoot, and you will be able to do step mashes easily. I speak from experience.

Yes, it would be nice to heat the HLT to 200F or so to get a quicker step up in temp, but you cannot do that in a HERMS or RIMS. You never want to heat your wort in excess of your target temp.

A PID will still overshoot if you put your temp probe in the wrong location. If you are measuring the mash temp at the MLT... and it is say 3F too cold... the PID will command heat in the HLT to raise the temp. The PID is NOT looking at the resultant HLT temp though, so when you DO reach your target MLT temp your HLT will be 170F, why... becuase your PID isnt looking at it, it has no idea what it just commanded in the HLT. Where your heating element resides, is where your tempo probe must reside, so that the PID can see what it is commanding and the actual result.

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