HLT Heating Dynamics

[Quaffer]

This may be old hat for you who have your electric breweries up and running, but I am trying to catch up. I would have found this information useful.

I was curious what the dynamics of heating water in the HLT is like, and I need to find out what happens to the volume of water below the heater element during boil. The latter because I am planning to mount the BK heater several inches above the bottom so to minimize interference with the trube cone forming during whirl pool. If the water below sits undisturbed during the boil I will need to change plans for the BK.

First the location of the components. With 6 gallons of water in the HLT I have 8.25" of water above the recess in the bottom of the keggle. As I drain water, first the float switch trips and drops out the heater contactor at 5.5" water. At 5" the 5500W heater element surfaces, then the PT100 temperature probe at 3" of water. The PT100 is mounted in a sight tube 'T' from Brewhardware.com.

I filled the HLT with 6 gallons of 50°F water. I turn on the PID in manual mode with 100% power. I have a remote temperature probe suspended at the surface of the water.

The surface water starts heating up immediately, but the PT100 is locked at 50°F for 6-8 minutes. At 15 minutes the PT100 reads 60°F and the surface probe is at 180°F. That is a temperature difference of 120°F in only 5.25" of water. Talk about extreme stratification!

The surface temperature keeps rising but at 20 minutes it comes to a stop at 208°F. At this point the PT100 starts increasing in temperature more quickly. The water is not boiling but it is very agitated. I think this stirs up the cold water at the bottom.

At 40 minutes, give or take, the surface and the PT100 comes up to 211°F and I have a boil. At my elevation water boils at about 211.5°. I can maintain a vigorous boil with 60-70% power on the PID. The PT100 fluctuates around 211°F.

So, one conclusion is I will need to recirculate HLT for heating strike water. I only have one pump so during mash (MLT recirculating) I will need to stir the HLT. It is not so critical because I will accept temperatures between 160-175°F for sparge.

The other conclusion is that it will be fine to mount the BK heater several inches above the bottom, because the boil will agitate the water below the heater.

I hope this information is useful to someone. If you have a different experience please let me know.

 

[audger]

The surface water starts heating up immediately, but the PT100 is locked at 50°F for 6-8 minutes. At 15 minutes the PT100 reads 60°F and the surface probe is at 180°F. That is a temperature difference of 120°F in only 5.25" of water. Talk about extreme stratification!

how far in does this PT100 probe stick into the tank? it sounds like the water around the probe is getting stagnant and not registering temp changes.

The other conclusion is that it will be fine to mount the BK heater several inches above the bottom, because the boil will agitate the water below the heater.

this is what i would imagine happen

 

[BrewMoreBeers]

Interesting... I would love to read how this shakes out as I am planning my first kettle HLT as we speak.

 

[onthekeg]

I generally stir the water every now and then to maintain an even temp throughout as the water is heating up.

 

[Quaffer]

how far in does this PT100 probe stick into the tank? it sounds like the water around the probe is getting stagnant and not registering temp changes.

I is a 4" probe, it sticks in a good 2" into the tank.

this is what i would imagine happen

Yes, me too, but I needed good evidence before I put the hole saw to the shiny pot. In theory it could have boiled only the water above the heater.

 

[audger]

hmm, as long as the probe extends inside beyond the wall of the tank, i would think it would be more accurate then it seems to be.

just FYI, too, you can buy the same probe for 1/2 that price from grainger
http://www.grainger.com/Grainger/DWYER-Temperature-Sensor-6CTY4

that is what i use, they also sell a 6" one for another $1.

 

[conpewter]

with my E-HLT I have to either stir or recirculate the water to get a consistent temp. The E-BK has no issues since the activity of the boil stirs the wort easily.

 

[bruin_ale]

I saw the exact same with my HLT. For the BK, the probe is at about the same height as the element and there's not much volume below it - plus as you find, a good rolling boil really mixes things pretty well.

Anyways, I tried the aquarium pump thing (using an aquarium bubbler tube at the bottom of the HLT to cause better mixing) and I tried using my march pump to circulate while heating. Neither worked to my satisfaction. I was getting about a 20 degree differential using the pump, a little better with an aquarium pump and the March - and about a 30 degree differential with just the aquarium pump.

So, I bought an AC motor - used some spare 3/8" copper I had around for a shaft and soldered some brass stock to the end as a prop. I built a wood jig to hold it in place on top of my keggle HLT. Now, when my temp probe says 165 - I measure it slightly higher at the top but not much - and if I fill the mash tun the water coming out is 165 - so I'm hitting my mash temps exactly.

 

[kal]

with my E-HLT I have to either stir or recirculate the water to get a consistent temp. The E-BK has no issues since the activity of the boil stirs the wort easily.

That's exactly what I do. I recirc out the bottom and back into the top of the HLT to avoid stratification/temperature differentials.

The water input at the top is pointed such that when the water enters, it circulates around the kettle:

In the boil kettle the boil is so vigorous that it is self-stirring. No issues.

Kal

 

[Quaffer]

I saw the exact same with my HLT. For the BK, the probe is at about the same height as the element and there's not much volume below it - plus as you find, a good rolling boil really mixes things pretty well.

Anyways, I tried the aquarium pump thing (using an aquarium bubbler tube at the bottom of the HLT to cause better mixing) and I tried using my march pump to circulate while heating. Neither worked to my satisfaction. I was getting about a 20 degree differential using the pump, a little better with an aquarium pump and the March - and about a 30 degree differential with just the aquarium pump.

So, I bought an AC motor - used some spare 3/8" copper I had around for a shaft and soldered some brass stock to the end as a prop. I built a wood jig to hold it in place on top of my keggle HLT. Now, when my temp probe says 165 - I measure it slightly higher at the top but not much - and if I fill the mash tun the water coming out is 165 - so I'm hitting my mash temps exactly.

Really! I did not realize recirculating was so inefficient. I was planning on having the pump suck from the HLT dip tube, push the water through the RIMS tube where it will get additional 750W boost, then dumping it at the top of the HLT.

I may have to build a stirring motor too. Thanks for sharing.

 

[Quaffer]

That's exactly what I do. I recirc out the bottom and back into the top of the HLT to avoid stratification/temperature differentials.

The water input at the top is pointed such that when the water enters, it circulates around the kettle:

In the boil kettle the boil is so vigorous that it is self-stirring. No issues.

Kal

Kal, thanks for your great post. The recirculation you do is what I had in mind. I am relieved it works good for you, maybe it will for me too.

 

[HHP]

I guess the lesson here is to not underestimate the power of convection...

Good Eats fans will remember the episode where he demonstrates this when talking about thawing food. Cold running water will melt things much faster than just a pot of hot water. The reason is convection.

 

[Quaffer]

hmm, as long as the probe extends inside beyond the wall of the tank, i would think it would be more accurate then it seems to be.

just FYI, too, you can buy the same probe for 1/2 that price from grainger
http://www.grainger.com/Grainger/DWYER-Temperature-Sensor-6CTY4

that is what i use, they also sell a 6" one for another $1.

Doh! I mean thanks!

 

[bruin_ale]

give recirculating a try.. the pump recirc definitely helps, I found it wasn't quite good enough for me - there was still a noticeable stratification. It may be the shape of the keggle or where my element vs. where my temp probe are located (temp probe is below the element slightly. The stir did the trick, but it's a bit of a PITA. One place the stir motor is nice is when I'm using my HERMS. If you only have 1 pump, you can't use that to recirc the HLT and the Mash at the same time - so it's nice to be able to stir the HLT to get good heat exchange while still pumping the mash through the HERMs coil.

BTW - I'm not disagreeing with Kal, I'm sure his setup works perfectly. That's why I say it might be something specific to my setup.

 

[kal]

Bruin_ale: Put your feedback temp probe in the plumbing, that's usually the best way. That's what everyone here seems to say to do so that's where I have mine and it works great.

For example, here's my HLT set to 149F and reading 149F (right PID), and my mash is at 149F (left PID):

Both probes have been calibrated.

I set my HLT to the mash temp I want and the HERMS coil in the HLT keeps my mash at exactly the same temp. I also recirc my HLT water pump at 100% so it's recirc'ing and stirring pretty fast. The march pump with 1/2" front inlet I use helps with better recirc too from what I understand (easier priming too).

Kal

 

[BrewMoreBeers]

Kal... Just to clarify, your temp probes are in the HLT out to recirculate and the mash out from herms coil? Is that correct?

 

[kal]

Kal... Just to clarify, your temp probes are in the HLT out to recirculate and the mash out from herms coil? Is that correct?

No. Both my HLT and MLT temp probes are attached to the outputs of the kettles like this:

A wide shot while I'm mashing:

(Ignore the fact that both pumps have their valves completely closed... they should be completely open during mashing... my mistake - the picture's was not taken during a real brew session...)

I used to have the MLT temp probe at the output of the HERMS coil on the HLT as you mention, but that temp always read the same as my HLT temp so it was completely redundant. The two numbers were always the same, all the time (when the wort pump was running of course). So I moved the MLT temp probe it to the output of the MLT.

This way I can see how fast (or slowly) my HLT grain temp follows behind the MLT water temp as I do step mashes or go to mashout. For example, when it's time to mashout, I turn the HLT temp up to (say) 168F and the HLT temp slowly rises to that value. The MLT also slowly rises but is a few minutes behind.

Kal

 

[bruin_ale]

Bruin_ale: Put your feedback temp probe in the plumbing, that's usually the best way. That's what everyone here seems to say to do so that's where I have mine and it works great.

Good point.. I think I looked at your setup to figure out how to solve my problem and that was one solution. Since I only have one pump, I can't use it to circulate the mash and the HLT at the same time - so I think the stir motor was the other solution. If I put the probe at the output of my HLT, but I don't recirculate the HLT - I'll have the same issue.

BTW, with the stir my HLT temp also matches my HERMs output temp. But I have a BCS so I have 4 temp probes - BK, HERMs out, Mash (a 12" probe sticking through the top of my cooler into the bed of the Mash), and HLT.

I could probably get rid of HERMs out, but not sure where I'd put a 4th one except perhaps to log ambient for fun.

 

[kal]

Good point.. I think I looked at your setup to figure out how to solve my problem and that was one solution. Since I only have one pump, I can't use it to circulate the mash and the HLT at the same time - so I think the stir motor was the other solution. If I put the probe at the output of my HLT, but I don't recirculate the HLT - I'll have the same issue.

Actually I imagine it'll be worse: Putting a temp probe in plumbing only makes sense if you recirc. If you don't recirc that temp probe will read really low. Sorry, I should have made that clearer. Instead of:

Put your feedback temp probe in the plumbing, that's usually the best way.

I should have said:

Put your feedback temp probe in the plumbing and recirc, that's usually the best way.

Kal