HERMS folks: temp of HEX water compared to mash

[Walker]

Hey folks....

I'm about to pull the trigger and start accumulating gear for a HERMS rig, and I was just wondering: how much above the mash temp do you find the water in the heat exchanger? Or do things end up balancing out at the mash temp?

My exchanger would be a 25' IC in a 5 gallon stainless pot (wrapped in insulation).

 

[sjlammer]

I think you might want to ask a different question.

The most important question is. "What temperature should i set the HERMS reservoir"

I've found that if im trying to maintain the mash temperature, i need to set the Herms reservoir to the mash temp.

If i am trying to change the mash temp, i set the herms reservoir 3 degrees higher than the target temp.

 

[The Pol]

Heat Exchanger temp. on my system was 3F above the desired MLT temp.

Your system will have its own differential. Not hard to find though, should be able to nail it on the first mash

 

[Walker]

I don't think I am asking the wrong question... but now you have be doubting myself.

I'm going to put an in-line chamber at the output of the HEX coil to monitor the temp of the recirculating mash and use that temp to kick on and off the heating element in the HEX's hot water.

I was just curous as to what temp the water in the HEX would be while maintaining mash-temp ont he recirculating wort. I could see it needing to be a little hotter than the mash temp, and I was wondering if that was in fact true, and how much hotter it might be.

 

[Walker]

Heat Exchanger temp. on my system was 3F above the desired MLT temp.

Your system will have its own differential. Not hard to find though, should be able to nail it on the first mash

Thanks, Pol. That's what I was wondering. A small temp differential seems reasonable.

But, sounds like you guys use yoru PID to measure the HEX water suply directly. I was actually planning to build a very small chamber (like that kick ass "RIMS for dummies" thread), but use that JUST to house my thermocouple.

Am I doing this in a different way than the norm? I've got no problem marching to my own beat.

 

[The Pol]

I dont know what you are doing. You will have a coil in the HLT, pumping the wort through the coil. You are heating your HLT water with a RIMS type heater then???? If so, you are doing it a little differently, but totally reasonable

 

[Walker]

I dont know what you are doing. You will have a coil in the HLT, pumping the wort through the coil. You are heating your HLT water with a RIMS type heater then???? If so, you are doing it a little differently, but totally reasonable

Not quite. I think the only difference in the way I am picturing my system is where I put the temp sensor.

I will have a water-heater element heating the water in the HLT, and the coil will be submerged in there with the wort being pumped through it.

But, my temp sensor will be placed in a small flow-through chamber at the output of the coil, so that I am directly monitoring the temp of the recirculating wort.

This chamber is a short 1/2" stainless thing.

              +-------------------------+
wort-in ----> |                      ===|====== probe (to PID) 
(from coil)   +-----------------+    +--+
                                |    |
                                +----+
                                   |
                                   |
                                   V
                                wort-out
                              (back to MLT)

 

[The Pol]

OH, you have a thermocouple in the wort return line... okay. That is pretty common too. Do you have a mixing device for the water in the heat exchanger? That is pretty common, as you can get HIGH temp areas next to the element and cold areas outside of that.

Set your PID at your desired temp. I bet that will get it right.

 

[Walker]

OH, you have a thermocouple in the wort return line... okay. That is pretty common too. Do you have a mixing device for the water in the heat exchanger? That is pretty common, as you can get HIGH temp areas next to the element and cold areas outside of that.

Are you using a temp controller then, affixed to your temp. probe?

Yes, I'll have the heater element controlled by a PID connected to the probe.

I had not thought about a mixer for the water. F*ck.

 

[The Pol]

I edited my post, Id set the PID to my target temp.

 

[Hugh_Jass]

Yes, I'll have the heater element controlled by a PID connected to the probe.

I had not thought about a mixer for the water. F*ck.

a simple pond pump would mix the water adequately.

http://www.amazon.com/dp/B0017CVC3O/?tag=skimlinks_replacement-20

 

[Walker]

I edited my post, Id set the PID to my target temp.

Yeah, that part I was clear on. The original question was what temp the HLT water temp would end up being.

It was just a question asked out of pure curiousity, but now you having me thinking about the mixer crap.

I feel like a shoddy contractor, because I put forth a budget proposal to SWMBO and I'm going to go over.

 

[Walker]

a simple pond pump would mix the water adequately.

http://www.amazon.com/Submersible-Aquarium-Light-Water-Fountain/dp/B0017CVC3O

Yeah, but I plan to use that water as my sparge water after the first runnings are pumped to the kettle. I don't want to buy a second high-temp food safe pump.

 

[The Pol]

Well, it will be a few degrees warmer, maybe...

I understand the "budget" thing. These things can add up quick

 

[Hugh_Jass]

I don't run an automated HERMS, but I do recirc. the wort with a march pump with separate thermometers in both MLT and HLT. Usually, my HLT(where I keep my HEX coil) temp is usually 1 degree over MLT temp. It is different than your proposed set up though

edit: I use the HLT water as sparge water, too

Budgets are mere speculations

 

[Walker]

Well, it will be a few degrees warmer, maybe...

I understand the "budget" thing. These things can add up quick

Yeah... I know. SWMBO stared this mess, though. After seeing me brew with gravity a few times, she put forth the idea of buying a march pump before I fell off a ladder with 4 gallons of hot water.

Obviously I jumped at that proposal. You know.... for safety reasons.

Anyway, with a pump in my brewery, my mind started wandering and thinking about all the new options available to me.

Pump, check.
Copper coil, check.
Several large steel and aluminum pots, check.

HERMS started creeping into my thoughts, and I put out a budget of $150 to get the rest of the way there.

 

[Walker]

edit: I use the HLT water as sparge water, too

No concerns about that aquarium pump's materials? I have a small (non submersible) utility pump, but there's no way in hell I would drink anything that passed through it. Water gets murkey when it goes through that thing.

 

[Hugh_Jass]

You know, I have not used that pump in my recirc. and really never thought about chemical leeching. I just stir my HLT water every few minutes with my mash paddle. That was the easiest and cheapest solution for me.

 

[Walker]

You know, I have not used that pump in my recirc. and really never thought about chemical leeching. I just stir my HLT water every few minutes with my mash paddle. That was the easiest and cheapest solution for me.

Ah, Ok. YOu had me confused there for a second. I thought you were implying that you DO you one of those pumps, and then you said you didn't.

 

[CodeRage]

Walker, back to the question at hand.

I don't have any experience with HERMS but I do have experience in dealing with a PV located in less than optimal places. I think using the return line of the HERMS HEX for your temp control feedback is going to be an issue. For one the lag time is going to be huge which will cause one of two things
1. the HLT is going to keep heating, well over the desired mash temp. Once the MLT has reached the desired temp, there is still a large amount of heat energy stored in the HLT, and it is going to go right in to your MLT causing an overshoot.
2. The PID loop is sooo detuned that it is going to take a long time for your temps to rise.

Think of the HERMS as a big bass ackward CFC. A CFC can chill the wort very close to the coolant temp at .5-1gpm. A 3 gallon mash would take 3 to 6 minutes and add a few minutes to get the mass of the grain and HLT up you're looking at 5 to 10 minutes. This sound about right to you HERMS guys?

 

[Walker]

well..... ****.

I guess I've got some more thinking to do.

Do most HERMS folks put their probe directly in the HLT then?

 

[Walker]

Walker, back to the question at hand.

I don't have any experience with HERMS but I do have experience in dealing with a PV located in less than optimal places. I think using the return line of the HERMS HEX for your temp control feedback is going to be an issue. For one the lag time is going to be huge which will cause one of two things
1. the HLT is going to keep heating, well over the desired mash temp. Once the MLT has reached the desired temp, there is still a large amount of heat energy stored in the HLT, and it is going to go right in to your MLT causing an overshoot.
2. The PID loop is sooo detuned that it is going to take a long time for your temps to rise.

Think of the HERMS as a big bass ackward CFC. A CFC can chill the wort very close to the coolant temp at .5-1gpm. A 3 gallon mash would take 3 to 6 minutes and add a few minutes to get the mass of the grain and HLT up you're looking at 5 to 10 minutes. This sound about right to you HERMS guys?

Well... some more searching around here and I found a number of references to people using their probe at the output of the HERMS coil. No one mentioned having overshoot problems.

IN fact, one guy mentioned that he had to set the PID to a couple of degrees OVER his desired mash temp in order to maintain the mash where he wanted it.

 

[DrDirt]

OP. To answer your question: The temp difference between the HLT (and in turn, the heat exchange coil) will vary depending on a few factors.
1-What is the ambient air temperature?
2-What lengths and materials are you using for tubing?
3-Are your MLT and HLT covered to retain heat?
4-How high above the grain bed is your sparge arm?

I use thermal tubing and cover the HLT and MLT to retain heat. However, sometimes I have to use a substantial length of hose, from the output of the HEX to the sparge arm is up to about 4 feet of tubing. My last brew had a 12 degree difference between HLT and MLT temps (ambient temp was in the low 20's or teens). In the summer, using shorter hoses, I might only have a 1-3 degree drop.
You should be able to dial in your temp change during the first batch, and you'll tweak it from there. To minimize the differential make sure to use the shortest hose possible and insulate the vessels. In any case, if you're having to heat the HEX above 165 you could get some off flavors.

Hope this helps

 

[DrDirt]

...also. I'm not sure that you should be worrying too much about circulating the HEX water. I dont bother with that and haven't had a problem, here's my reasoning.
The heated water in the HLT (where the exchange coil is in my setup) should be moving about somewhat due to convection. Also, the wort is running through the entire coil and will move through and diferentials in exchange water temp, from to top to bottom of the HLT.
I vote that an additional circulation pump is not necessary for your setup, you can always add it later but dont let it stop you from going to HERMS.

 

[The Pol]

Well... some more searching around here and I found a number of references to people using their probe at the output of the HERMS coil. No one mentioned having overshoot problems.

IN fact, one guy mentioned that he had to set the PID to a couple of degrees OVER his desired mash temp in order to maintain the mash where he wanted it.

FWIW, I have seen people do this with PID control with great success. The water bath is a buffer between the element and the wort being heated. This is not the case in a RIMS. In a RIMS if you do not monitor close to the heat source, it can get away from you before the temp probe senses it. In a HERMS the heating meduim (water) will have a much slower temp rise.... much. (1-2F per minute) Your PID will be able to handle this fine IMHO

In a RIMS tube if the element is full on for 1-2 mins. you are probably boiling wort. In a HERMS you changed the temp. a couple degrees maybe and the PID will sense this during tuning and adjust.

Try it, dont fret just yet man. I have seen it done and some ppl swear by it. Do some water tests, autotune your PID, and I think you will be ok. If not, it is as simple as moving the temp probe.

 

[CodeRage]

FWIW, I have seen people do this with PID control with great success. The water bath is a buffer between the element and the wort being heated. This is not the case in a RIMS. In a RIMS if you do not monitor close to the heat source, it can get away from you before the temp probe senses it. In a HERMS the heating meduim (water) will have a much slower temp rise.... much. (1-2F per minute) Your PID will be able to handle this fine IMHO

In a RIMS tube if the element is full on for 1-2 mins. you are probably boiling wort. In a HERMS you changed the temp. a couple degrees maybe and the PID will sense this during tuning and adjust.

Try it, dont fret just yet man. I have seen it done and some ppl swear by it. Do some water tests, autotune your PID, and I think you will be ok. If not, it is as simple as moving the temp probe.

OKay, I see what you're saying. The Herms coil pretty much keeps up with the HLT temp any ways. Because of the large volume of water it takes a modest amount of time for the temperature to rise.

From a process controls perspective, I still don't think it is the best placement but it sounds like it would work. IF you're not crazy/demented enough to put 9kW of heat in the HLT

 

[The Pol]

OKay, I see what you're saying. The Herms coil pretty much keeps up with the HLT temp any ways. Because of the large volume of water it takes a modest amount of time for the temperature to rise.

From a process controls perspective, I still don't think it is the best placement but it sounds like it would work. IF you're not BORED enough to put 9kW of heat in the HLT

Fixed that for ya

 

[OLDBREW]

First off you have to figure out a good manifold design for ice chests, or use a full false bottom in the mash tun if using a cylinder type. This way when you recirculate the complete mash bed is keeping even temperatures through out. A bad manifold design will leave hot and cold spots in the grain bed (fluid dynamics).


If you look at the way a counter-flow chiller works, you can see the best efficiency comes when you have two opposing forces across the thermal wall, Like hot wort traveling one direction, cold water traveling the other creating a scrubbing effect on the thermal wall that allows better conductance, in turn allowing more heat transfer. Jamil's whirlpool giggy thing is another example with the immersion chiller.

The same goes on when you use a HEX coil in the HLT. The pump makes the wort flow through the tubing at a steady rate, so to make the transfer more efficient you need to stir the bath water in the opposite direction.

They sell mud(drywall compound) mixer paddles at the big box stores that can hook up to a drill for a stirrer. With a little engineering you can get a cheap outdoor Bar-B-Q rotisserie motor and mount that to some cutting board material(starboard)or wood. Then drill and pin the paddle to the motors flange. You sit the motor/board on top of the HLT with the paddle inside the coil. the motor stirs the water in one direction, then install the HEX coil so it flows in the other direction.

BTW More Beer sells convoluted copper now. This stuff is what is in the chilzilla counterflow chiller You get much greater heat transference with that type of HEX, then you do with smooth walled copper tubing

 

[Walker]

First off you have to figure out a good manifold design for ice chests, or use a full false bottom in the mash tun if using a cylinder type. This way when you recirculate the complete mash bed is keeping even temperatures through out. A bad manifold design will leave hot and cold spots in the grain bed (fluid dynamics).

My tun has a stainless false bottom in it.

They sell mud(drywall compound) mixer paddles at the big box stores that can hook up to a drill for a stirrer. With a little engineering you can get a cheap outdoor Bar-B-Q rotisserie motor and mount that to some cutting board material(starboard)or wood.

Ah! Thanks for the idea. I have a rotisserie motor for my grill already.

 

[Walker]

Try it, dont fret just yet man. I have seen it done and some ppl swear by it. Do some water tests, autotune your PID, and I think you will be ok. If not, it is as simple as moving the temp probe.

Well... yes, in the end, I would just have to move the probe, but given my budget and SWMBO's potential for wrath (she's full blooded Italian), I'd rather not buy $20 worth of stainless to make a monitoring chamber at the output of the coil if won't end up needing it.