How to avoid over/under shoot with HERMS in HLT?

[kal]

Note: I asked this question in a different thread but it was unrelated to the original subject so a separate thread probably makes more sense....


I'm trying to figure out my HERMS/mash process.

I plan on putting a temp probe on the output of my HERMS coil coming out of the HLT and let the PID set the HLT water temp. During mash one pump will recirc the HLT water to avoid stratification, another will recirc the MLT wort.

But I'm confused about overshoot/undershoot of strike and sparge temps since the HLT is doing dual duty. Seems many people do the setup I'm describing including stevehaun so I'll use his setup as an example:

I use one pid in my system. The thermocouple is located between the heat exchanger (herms coil) and the return manifold at the top of the mash tun. I fill my mash tun with the mash water and the HLT with the sparge water. I set my PID to my desired temp and start pumping the mash water thru the herms coil. The HLT heats up to several degrees above the temp I dialed in for my Mash tun and gradually my mash water is heated to the desired temp.

The part I don't understand is how strike is done. So you fill both HLT and MLT with water, set the PID to, say, 156 and you mentioned that your mash water temp will then read about 154. Perfect. Both the MLT and HLT are nicely and warmed up.

But when you dump in all grain the temp of the MLT water is going to drop considerably due to the thermal mass. Do you just let it drop and let the system get back to 154? How long does that take? Or do you aim a bit high knowing that you're going to lose some when you dough-in?

This is the part that confuses me about having a HERMS coil in the HLT as really, the ideal setup is a HERMS coil some container OTHER than where you heat up your strike/sparge water. In other words, how do you get the right strike temp? If your HLT strike water's set much higher than your target to compensate for the grain cooling off the water when you dough-in, doing a constant re-circ of the wort through the same strike water in the HLT is going to then heat the wort too high even if you immediately after strike reduce your HLT water PID setting down to the desired time. Right?

Do you do this and let it overshoot and then settle down slowly? Or do you undershoot and let the system raise it slowly? One or the other's the only option right?

When my mash is completed, I set the temp to 168F. When I reach the desired mash out temp, my HLT water is about 175F

Ok, so after the ~60 miinute mash you raise your PID temp from ~156 to 168 to raise the wort temp. Once the wort's at 168 the HLT water's at 175. Got it. But isn't 175F too hot for sparging? I thought you weren't supposed to go over 170F for sparge water because of tannin extraction.

Kal

 

[Bobby_M]

Keep in mind, HERMS may be in my future but I'm speaking in theory at this point. You would want to get your HLT water up to a calulated strike temp based on your calibrated MLT heat loss and your grain bill with the assistance of software like BTP or Beersmith. That's probably in the neighborhood of 185F. Once you move that large volume of water from the HLT to the MLT, you'll need to top it off with fresh water anyway. That colder water will bring the HLT temp back down in the mid 100Fish or close. You can stop your recirculation pump temporarily until the HLT gets back up to your mash temp maintain temp, then let it rip.

When your mash hits 168 and your HLT (now sparge water) is at 175, start the sparge and drop your HLT controller down to 168. You'll lose a bit of heat as the water makes it through the tubing and into the MLT and you're adding such little water anyway that you're not going to go too far over 170F. If you find it happens, shoot for 166F for the mashout.

 

[bnscherm]

Personally, I use two PID controllers on my HERMS setup. One controls the pump based on the MLT temperature, and the second strictly controls the HLT temp.

For a five gallon batch I preheat about 10 gallons of water to my strike temperature (set on a timer over night), based upon my grain bill . Usually for me this is in the 172 degree range. I pump my strike water volume onto the grains in the MLT, and wait a few minutes for the temperature to equalize (after stirring). At the same time I set my HLT to 180 degrees, this gives me a heat buffer for later. Cooling induced by the tubing and pump usually results in my mash temperature being a little low. I then turn on the recirculation pump, and set my MLT controller to 154 degrees. Within a few minutes the mash will come up to temperature.

To Mash out I bump the Mash PID controller up to 170 degrees and after about ten minutes I get up to 170 degrees and the HLT has cooled back down to about 170 degrees. I wait ten more minutes, and begin sparging with the now 170 degree HLT water.

Hope this helps.

PS. I'm using a 1500W 110V element in the HLT.

 

[bnscherm]

One more thing. I don't have any type of stirring/circulation mechanism in the HLT with the heat exchanger. I think that this may be a benefit for my system. By doing this I can keep the HLT temperature higher and still not overshoot my mash temperature. A high flow rate through the heat exchanger allows the wort in the MLT to come up to temperature more evenly without temperature gradients, while at the same time cooling the water around the heat exchanger in the HLT to eliminate a temperature overshoot.

This makes the heat exchanger less effective (slower), but I think it may be a benefit in my system with only a 1500W heater.

 

[stevehaun]

Kal:
Let me describe my system with the caveat that every system is different and you will have to dial yours in.

My HLT is a keggle with a 25 foot 1/2" OD copper heat exchange coil. My mash tun is a 55 gallon HDPE barrel. My thermocouple is located between my heat exchange coil and the wort return manifold on top of my mash. I have two 4500 watt elements in my HLT. I do not stir or circulate the water in my HLT. I also do not measure or control the temp of the water in my HLT.
When I did 15 gallon batches I heated my strike water by pumping it thru the heat exchange coil. Now that I am doing 30 or 35 gallon batches, I heat all my water in my boil kettle to 150F and then transfer it to the MT and HLT. I set my PID to 7F above my desired mash temp. I begin pumping my strike water thru the heat exchange coil. I mash in when the strike water is 5F above my desired mash temp. I turn off the pump, add the grain, and stir. I then set my PID to 2F above my desired mash temp and then begin recirculating wort thru the heat exchange coil. I learned thru trial and error that these temps will usually give me dead on mash temps. When I first started, I tended to undershoot and let the HERMS correct the temps. It is easier to raise the temp than lower it. The time it takes for the HERMS to fix the temp is dependent primarily on the mash volume, wattage of your HLT, and wort flow. When I did 15 gallon batches, my temps rapidly corrected. Now that I am doing 30-35 gallon batches it takes considerably longer to correct the temp. However, to answer your question, I think it is better to undershoot and allow the HERMS to correct or dial in your desired mash temp.

Tannin extraction during sparging is a function of pH and grain bed temp. My sparge water is about 175F but I batch sparge and my grain bed never gets above 168F during the sparge. As Bobby_M said, if you are concerned about it, use a lower temp for your mash out. I don't think raising temps for mash out is all that critical anyhow.

 

[eccsynd]

But I'm confused about overshoot/undershoot of strike and sparge temps since the HLT is doing dual duty.

This is why I'm a big fan of a separate heat exchanger for recirculating systems. I think this site sums it up very well:

Design Logic

 

[kal]

Thanks for the discussions guys. Very enlightening. Goes to show there's a million different ways to skin a cat and none of them are incorrect!

One question: Is there something cheap/reusable that has a similar thermal mass as grain that I can use to do some trial tests once I get it all set up? I'd like to try a few different approaches and see what happens but don't want to go through 100 lbs of grain in the process.

Some additional questions:

You would want to get your HLT water up to a calulated strike temp based on your calibrated MLT heat loss and your grain bill with the assistance of software like BTP or Beersmith. That's probably in the neighborhood of 185F. Once you move that large volume of water from the HLT to the MLT, you'll need to top it off with fresh water anyway. That colder water will bring the HLT temp back down in the mid 100Fish or close.

That's not a bad idea. I was thinking of putting the strike water into MLT from the start and using HERMS to warm it up. (No extra water needed as the HLT will be full too). But your idea makes sense too.

Personally, I use two PID controllers on my HERMS setup. One controls the pump based on the MLT temperature, and the second strictly controls the HLT temp.

This is very interesting too.
Where do you have your MLT temp probe? It has to be right in the MLT right? (Nothing else would make sense to me since the wort isn't always recirculating since you're controlling the pump).

Since the wort's not moving when the pump's off you don't find you get hot/cold spots in the grain? (I could have sworn I read about that). I take it you have the PID set up so that the pump stays on/off a few minutes at a time to avoid cycling it too much? Or this may not even be required ... it may just do that naturally (?). (I'm gussing).

One more thing. I don't have any type of stirring/circulation mechanism in the HLT with the heat exchanger. I think that this may be a benefit for my system. By doing this I can keep the HLT temperature higher and still not overshoot my mash temperature.

Possibly. Yes. My plan was for one of the pumps to constantly recirc the HLT water to avoid uneven heat. Should help too with HERMS heat transfer as you mention. The other pump could then cycle on/off as needed to recirc the MLT sweet wort.

If I'm not mistaken, I think this is exactly what the B3 BrewSculptures do. (Someone correct me if I'm wrong).

It is easier to raise the temp than lower it. The time it takes for the HERMS to fix the temp is dependent primarily on the mash volume, wattage of your HLT, and wort flow. When I did 15 gallon batches, my temps rapidly corrected ... I think it is better to undershoot and allow the HERMS to correct or dial in your desired mash temp.

Bingo. This was my gut feeling too. Glad to have it affirmed. Thanks! My 20 gallon HLT will have a 5500W element which hopefully should be able to raise temps fairly fast. I'm only doing 10 (maybe 15) gallon batches too.

I'm trying for the simplest process possible, but maybe it's as simple as:

- Filling both the MLT and HLT
- Setting the HLT to something slightly below strike temp so that I undershoot on purpose
- Doing a continual recirc until both are heated up
- Set HLT to mash temp
- MLT pump off, Mash in, MLT pump on
- MLT temp should rise quickly (within 4-5 mins?) to correct mash temp
- Wait, drink a beer, etc.

I'll certainly be doing some tests to see how it works out, and what the rise times for my setup are.

This is why I'm a big fan of a separate heat exchanger for recirculating systems. I think this site sums it up very well:

Design Logic

Yes - agreed! It certainly simplifies things. Excellent design logic BTW. I've referred to it many times in the past but it's been a while. I need to go back and re-read everything again.

Thanks everyone!

Again, if anyone has ideas on something to use to simulate the thermal mass of grain I'm all ears. Maybe like a bucket of nails or something. Or marbles (I have a bags and bags of them - don't ask). Or I know! Lego or Duplo. The kids have boxes and boxes of them. I can just see the confused look on my 2 and 5 year old's faces: "Sorry kids, you can't play with your lego right now... Daddy's practicing making beer".

Kal

 

[bakins]

This discussion is one reason I went RIMS. (well, still under construction.) I looked at the separate HERMS "container" way as well - but RIMS was just easier for me. But that's for me...

 

[BrewBeemer]

Thanks for the discussions guys. Very enlightening. Goes to show there's a million different ways to skin a cat and none of them are incorrect!

One question: Is there something cheap/reusable that has a similar thermal mass as grain that I can use to do some trial tests once I get it all set up? I'd like to try a few different approaches and see what happens but don't want to go through 100 lbs of grain in the process.

Some additional questions:


That's not a bad idea. I was thinking of putting the strike water into MLT from the start and using HERMS to warm it up. (No extra water needed as the HLT will be full too). But your idea makes sense too.


This is very interesting too.
Where do you have your MLT temp probe? It has to be right in the MLT right? (Nothing else would make sense to me since the wort isn't always recirculating since you're controlling the pump).

Since the wort's not moving when the pump's off you don't find you get hot/cold spots in the grain? (I could have sworn I read about that). I take it you have the PID set up so that the pump stays on/off a few minutes at a time to avoid cycling it too much? Or this may not even be required ... it may just do that naturally (?). (I'm gussing).


Possibly. Yes. My plan was for one of the pumps to constantly recirc the HLT water to avoid uneven heat. Should help too with HERMS heat transfer as you mention. The other pump could then cycle on/off as needed to recirc the MLT sweet wort.

If I'm not mistaken, I think this is exactly what the B3 BrewSculptures do. (Someone correct me if I'm wrong).


Bingo. This was my gut feeling too. Glad to have it affirmed. Thanks! My 20 gallon HLT will have a 5500W element which hopefully should be able to raise temps fairly fast. I'm only doing 10 (maybe 15) gallon batches too.

I'm trying for the simplest process possible, but maybe it's as simple as:



I'll certainly be doing some tests to see how it works out, and what the rise times for my setup are.


Again, if anyone has ideas on something to use to simulate the thermal mass of grain I'm all ears.

Kal

Go to; http://www.rackers.org/calcs.shtml

All the charts are there you fill in the blanks, it will give you the needed strike water temps.

Thanks Adam, the BCS-460 arrived today. I see no need for a 36" x 36" x 8" deep can for the unit to get lost in on the brew rig.
I like those smaller waterproof plastic control panels, even with SSRD's there should be plenty of space to keep it safe and dry.
Thanks again.

 

[kal]

I just went through and re-read some of the thoughts/ideas here. Good stuff.

I've been doing heat exchanger (HERMS) tests with water for a few weeks now and just brewed my first AG batch a couple of days ago and it was a big grain bill too: 23lbs to make an AIPA.

I thought I'd post my findings.

To summarize my setup:

(From left to right: Brew Kettle, MLT, HLT)

The HLT with 50' HERMS coil, 5500W element, and water return at the top:

All are 20 gallon blichmann stainless pots. There is a 50 foot 1/2" stainless HERMS coil in the HLT along with a 5500W heating element controlled by a PID and temp sensor at the output (you can see the wire coming out of the 'T' junction at the bottom of the HLT). I recirc the HLT strike/sparge water full-tilt continuously with a pump.

I have nothing hooked up to the MLT in terms of temp control. I simply recirc the MLT wort through the HERMS coil in the HLT.
I do have a temp probe located at the HERMS coil output on the HLT (see the second wire higher up on the "T" output) that monitors the temp of temp of the returning mash fluid. It's not needed but it's nice to see and reminds me if I've forgotten to turn on the mash pump. The mash probe temp always matches the HLT probe temp when the pumps are running as it should since it's right at the output of the coil.

In my setup I found the easiest thing to do is to simply fill the MLT with the right amount of strike water, fill the HLT, and then set the HLT to the mash temp (let's say 152F). Turn on the pumps and let everything heat up and equalize. After ~30 mins or so everything's at 152F.

Once all the water's at 152F I turn off the mash pump and dough in. The mash temp drops due to the 72F grain of course. Once doughed in I turn the mash pump back on and after a few minutes my mash temp is back up to 152F everywhere in the grain bed. My analog Blichmann thermometer in the mash tun lets me know how the temp raise is progressing. The first time through I also used a known accurate meat probe to measure the temp in various spots in the grain bed. Everything was exactly at 152F after ~20 minutes. I just need to make sure to recirc the mash fast enough to avoid stratification (lesson learned).

This seems to work great for me and results is zero guesswork or having to know the offsets between tanks. I don't need to worry about overshooting. I just dial in the mash strike temp on the HLT PID, let the water in both vessels heat up to strik temp, dough in, then set the timer to 60-90 minutes (plus an extra 20 for ramp back up to strike temp) and walk away. The alarm/timer on my control panel lets me set a reminder when the next action is needed (mashout). At mashout I simply crank the HLT temp up to 170F and 15-20 minutes later the entire grain bed's at 170F ready for sparging.

Which remind me: I need to build a sparge arm of some sort. I fly sparged manually by hand last time. I'm thinking something (preferrably) stainless under (and fastened) to the MLT lid with an 1/2" NPT fitting out the top so that I can add a QD...

Kal

 

[bakins]

This seems to work great for me and results is zero guesswork or having to know the offsets between tanks. I don't need to worry about overshooting.

Very nice. I'm surprised the temps even out so well. Nice to know.

 

[kal]

I was surprised too. It think what helps is:

- I use thick silicone hoses (thicker than most, about x2 the wall thickness of those sold by B3).
- The distance between the HERMS output and the mash input is only one 4 foot hose.
- My HERMS output is always at the HLT temp probably helped becase (I recirc the HLT with a pump running full tilt and I use a 50' HERMS coil.

I also recirc my MLT pretty hard too. Though this would only help with ramp times and nothing else.

Kal

 

[Orangevango]

My new system will have a 5500 watt element in the HLT so I plan on this system:

• Fill HLT and heat water to strike temp (as calculated by beer smith)
• Dough in by pumping water over from HLT
• add a couple gallons of cool water to get temp UNDER the mash temp
• Set PID to mash temp and stir mash thoroughly while the HLT ramps up (1 or 2 minutes)
• begin recirculation of both MLT

The 5500 watt element should get that HLT temp up very very quickly.

So I'm not going to avoid undershoot, I'm going to use it to my advantage.

 

[The Pol]

Using the HLT as the STRIKE water heater, HERMS HEX and for SPARGE water is easy. Here is how it is done on my HERMS

1. HLT filled and heated to strike temp. +12F (this allows for heating of the MLT before mash in) Pump strike qty to the MLT.

2. I created a spreadsheet that you enter your HERMS strike/recirc temp. and water qty. parameters in. It will tell you how much water at a specified temp you must add to the HLT after you pump out the strike water, to bring it to recirc. temp. This is all done while the MLT is pre-heating. Not only this, but it will bring the HLT water qty up to exactly what I need to sparge with, so when I start the sparge, I can walk away as I run the HLT and MLT dry into the kettle to hit my pre-boil volume.

3. MLT and HLT temps. are both equalized and I mash in

4. Turn on pump.

5. Mash for 50 min.

6. Turn up HLT to 175F

7. Pump keeps running

8. Mashout complete

9. Sparge with water that is at 175F in the HLT

It is really efficient, it is really easy, and there are no temp issues in the HLT

 

[salzar]

One question: Is there something cheap/reusable that has a similar thermal mass as grain that I can use to do some trial tests once I get it all set up? I'd like to try a few different approaches and see what happens but don't want to go through 100 lbs of grain in the process.

Could just use a smaller mass of metal in place of the grain. Basically if both the grain and metal start at the same temperature, the mass of grain times its heat capacity equals the mass of metal times its heat capacity. M2=M1 * C1/C2

 

[salzar]

Well I was off about heat capacity, but the density is much higher for metals.

Grain is about 1.54 kJ/kg/C. Stainless Steel 316 is about 0.5 kJ/Kg/C. You would need about 3 times the weight of grain in steel to have the equivalent thermal mass.

 

[salzar]

Also one could use glass stones and steel balls to simulate heat transfer through the packed bed of the mash.

 

[bakins]

- I use thick silicone hoses (thicker than most, about x2 the wall thickness of those sold by B3).

Did you list the source somewhere?

 

[kal]

Did you list the source somewhere?

Off ebay.

It was "Sani-Tech Tubing STHT-C-500-5F New in Package". Sold by someone called Nora Stark after others mentioned her here back in the fall of 2008. I bought it in Nov 2008. She used to have a lot of it but searching now reveals nothing. I bought 50' for $31.99 plus shipping.

Kal