Height for temperature sensor in HLT?

Hi All,

What height is the temperature sensor mounted relative to the total boil height? Is there much temperature variance in height or does the vigorous convections in the boil sort that?

I'm tempted to mount at the same level as the elements (thinking 2* 3kW or 3 * 2.0kW - I've a 32A supply in the garage ready for a welder) so that I know that this is the hottest bit and maybe a second up high to monitor?

Most of the analogue dials seem to be mounted just above the height of the drain.

Thanks!

I would say close to the tap is good as it tells the temp of whats coming out 1st, also give it a good stir to see if the temp changes.

DocTrucker said:

Hi All,

What height is the temperature sensor mounted relative to the total boil height? Is there much temperature variance in height or does the vigorous convections in the boil sort that? ...

Click to expand...

I've got mine 30-50mm above the element. But I made the mistake of fitting one above the element (Kettle), and one 90degrees to it (HLT). The kettle sensor appears to react much faster. But you soon get to know that and at the end of the day it doesn't make any difference to the final outcome.

As you said, vigorous convections, and they sort themselves into organised cyclic currents. I've read the best place is just above the element so as to get fast response (for PID control). But I think being consistent is more important. Because convection currents are at work there's not much point worrying about temperature variance with height.

Er .... I must be missing something!

Pure water boils at 100 degrees celsius at atmospheric pressure and wort will boil at slightly above that temperature.

As far as I know ALL brews recommend a "rolling boil" which is easily seen ...

... and for pure water it will still occur at 100 degrees celsius at atmospheric pressure.

The amount of heat being put into the liquid (be it water or wort) will increase the rate of boil but it will not increase the temperature of the liquid.

However, to check the temperature of the wort when the heating has been turned off and it has been cooled down I recommend that the probe is located just above the outlet pipe. :thumb:

Dutto said:

Er .... I must be missing something!

Pure water boils at 100 degrees celsius ...

Click to expand...

You have. The title says HLT so I presume the temperature being checked is anything but a boil.

(I've just come from a cat fight in another thread so I make no excuses for being grumpy :nah:).

peebee said:

You have. The title says HLT so I presume the temperature being checked is anything but a boil.

(I've just come from a cat fight in another thread so I make no excuses for being grumpy :nah:).

Click to expand...

Er ... the original Post asked ...

"What height is the temperature sensor mounted relative to the total boil height?"​

... so my answer is correct assuming that the person posting this question (like 99.999% of us) has a boiling column of less than about 10 metres high!

Had I been incorrect in my assumption, the last paragraph regarding the level of the probe AFTER cooling is again correct.

In synopsis, as I was answering the original Post and even added a proviso should I be wrong, why get grumpy with me?

Dutto said:

Er ... the original Post asked ...

Click to expand...

Okay, we've proved the OP is at variance with the thread title. So if "DocTrucker" wants a clearer answer without the squabbling a bit more clarification to the question is in order.

Meanwhile I filched this from www.geol.umd.edu (via Google) which might (or might not) help.

Thanks for the input.

My original question refers to a Hot Liquor Tank and it may double up as a copper but not 100% settled on that yet. So, I'll need about 73C for the strike water and I'm guessing a little more for sparge. I'll read up on the specific values but will be building it to be boil capable. I'm assuming significant convection would still be present around 70C, but not as much as a rolling boil.

Yes, generally speaking a higher total heating wattage doesn't mean a higher temperature. I'm taking this as high as I can to save time. Have a recent preference for multiple little 2kW units so I can still finis a brew if one or two elements are lost.

More heat capacity would only raise ultimate temperature if your heat loss was high and your heat input low and input approached loss.

DocTrucker said:

Thanks for the input.

My original question refers to a Hot Liquor Tank and it may double up as a copper but not 100% settled on that yet. So, I'll need about 73C for the strike water and I'm guessing a little more for sparge. I'll read up on the specific values but will be building it to be boil capable. I'm assuming significant convection would still be present around 70C, but not as much as a rolling boil.

Yes, generally speaking a higher total heating wattage doesn't mean a higher temperature. I'm taking this as high as I can to save time. Have a recent preference for multiple little 2kW units so I can still finis a brew if one or two elements are lost.

More heat capacity would only raise ultimate temperature if your heat loss was high and your heat input low and input approached loss.

Click to expand...

Right. Well I'd still mount just above the element (others are going to disagree) but keep it low else you limit the minimum fill size you can work with.

What that little diagram doesn't illustrate is, viewed from above, those cyclic "cells" may be two in number, or four, six ... And if you have multiple elements that's going to muddy the picture further. Who knows how to predict it? Or even if there's any need to (I doubt it). One thing is sure; they'll form as long as the water isn't ice, so forget that 70C assumption.

As for 73C: My HLT is limited to 76C. It's fine for sparge water, but for strike heat I'd recommend the ability to get couple more degrees (78C). My HLT doesn't normally heat the mash water, The RIMS heater does that (hybrid design) but I'm having to depend solely on the HLT while figuring out the current defect in the RIMS heater: Meanwhile 76C is proving to be a limitation.

So to summerise people's comments:

Above and reasonably close to the heater is best for the response of the heater controller. If you were unfortunate enought to locate in a colder spot there would be a significant time delay in the effect the heater turning on and the sensor detecting a raise.

If side exit; above the outlet would give best indication of the temp of the water you are about to use.

Keep the sensors as low as practical to increase the volume size range of brews you can work with.

Regardless of sensor location a good stir would be advisable before trusting readings.

Due to what has already been said and calibration issues consistency in your brewing is king as far as repeatability is concerned.

peebee; when you say you're limited to 78 do you mean that is a design limit or that is the maximum yours reaches with the heaters on 100%? If the latter is your tank insulated, what size is it, and what heating capacity does it have?

peebee said:

What that little diagram doesn't illustrate is, viewed from above, those cyclic "cells" may be two in number, or four, six ... And if you have multiple elements that's going to muddy the picture further. Who knows how to predict it? Or even if there's any need to (I doubt it). One thing is sure; they'll form as long as the water isn't ice, so forget that 70C assumption.

Click to expand...

Perhaps badly phrased on my part but I'd say we are agreeing with each other. My assumption was that at 70 degrees there would be significant convection currents (just less so than the obvious currents in a rolling boil) that would act to mix the temperature, reducing the varience in temperature throughout the tank, and hense the relative importance of sensor location.

DocTrucker said:

... when you say you're limited to 78 do you mean that is a design limit or that is the maximum yours reaches with the heaters on 100%? If the latter is your tank insulated, what size is it, and what heating capacity does it have? ...

Click to expand...

76C is a design limit. The PID controller is configured to limit the range. So it could be fixed (to 78C) in a jiffy. If I could be bothered. Effort gets focused on getting the RIMS heater back working.

The tank isn't insulated. It is 70L stainless and has a 6KW element. The element is 6KW but is actually 3x2KW element components wired in series (or was it parallel :wha: ) - it could be wired for 3 phase.

Want to check it out? http://www.thehomebrewforum.co.uk/showthread.php?t=63149.

Thanks for the link. I'll have a look at that.

I've found some boil time graphs that should give me an idea of how much heat is being lost from the a plain SS pot with no insulation. I'm guessing the insulation is a nice to have if it's cheap but since £1 of electricity covers running a 6kW element flat out for 1hr23 then a home brewer is unlikely to see payback in money alone for many brews! Time maybe another issue, but as the boil time plots that I've seen don't have much of a curve to them then I'm assuming the time saving is unlikely to be great either.