Mash temp is higher than temp leaving heat exchanger?

[jbuffone]

I've now brewed 2 batches using the BCS controller to manage the temp of the wort leaving my heat exchanger. It is generating spot on temps, within 1 degree when using the PID around a set point like 150! I am having one issue, the temp in the mash itself is running about 2.5 degrees higher than that leaving the exchanger. Has anyone else had this experience? I would have expected, if anything, the temp in the mash would be lower than that leaving the exchanger. The exchanger is a 5 gallon pot with 25' copper coil within that the wort runs through. The exchanger has a heating element in it that is being controlled by the BCS PID. The temp probe is located right outside the exchanger as the wort leaves and goes back into the mash.

What could cause the mash temp to be higher than the temp leaving the heat exchanger? One theory I have is that my mash tun is extremely well insulated (R-22) and all lines have R-5 insulation, the cover of the tun is clamped on tight...could the pressure building up within the tun along with its thermal mass be generating incremental heat beyond that leaving the exchanger? Does anyone have any ideas for me. I'm fairly certain the temp gauges are all calibrated.

I've been using the temp in the mash, not that leaving the exchanger as the data of record. Would you all suggest that is the right read?

Thanks for any insight or suggestions you all may have.

John

[ECC]

Hey John. My guess is that the temperature probes are mislabeled? I would double check the wiring. Remember that everything starts with zero not one, Temp0, Temp1, etc.. Something else could possibly be going on, but I'll default to Occam's razor first

If you had the Mash Temp associated (controlled) with the element output, its not unheard of for the Heat Exchanger temperature to be 2.5deg warmer. Although with your insulation I would expect them to converge eventually.

Which Temp Probe is the element associated with?

[ECC]

What kind of Mash Tun do you have? Is the lid really air tight?

[jbuffone]

The temp probes are definitely not reversed as I only have 1 probe connected to the BCS, that is the one at the heat exchanger out. The other probe is a analog probe within my mash tun. I calibrated the analog probe to the one connected to the BCS.
The mash tun is a 25 gallon stainless pot from northerbrewer. The lid is very tight as its a 3/4 plywood lid, the bottom layer has aluminum and its on with two clamps.

[WolfPlott]

I would say that the thermometer may not be completely linear. If you calibrated the thermometer to the thermister, then the two could be identical at one temp, and off at a higher temp. Thats the only thing I can think of, if the wiring is correct.

If the heat exchanger is the only source of heat, then there is no other energy source to add heat to the mash. Its not possible for the mash to be a higher temp that the one you measured at the heater... that I know of...

[mpilchuk]

The temp probes are definitely not reversed as I only have 1 probe connected to the BCS, that is the one at the heat exchanger out. The other probe is a analog probe within my mash tun. I calibrated the analog probe to the one connected to the BCS.
The mash tun is a 25 gallon stainless pot from northerbrewer. The lid is very tight as its a 3/4 plywood lid, the bottom layer has aluminum and its on with two clamps.

Just for the fun of it, Throw another temp probe on the BCS and stick it in the mash and see what happens. You don't have to have the temp probe associated with anything it will just tell you the temp.

Of course as I type this, I realize that getting a temperature reading from a mashtun is not an exact science. I put one of the temp probes from the BCS in a Stainless Steel thermowell and I can move it around the mash. The temps change as I move it (of course letting it stabilize before moving it).

Getting solid temperature readings are the same as getting a Gravity reading on a Hydrometer. They are not exact as all temp probes and Hydros aren't the same. Also you can have a device that is accurate in one temp range and not accurate in another range more so with analogue than with digital IMHO.

I put all my trust in the BCS probes and even if they are high or low, I adjust my temp settings when I find that it affects the outcome of the beer.

[jbuffone]

I ran a test comparing the analog temp gauge in the mash tun and the digital temp probe from the BCS, monitoring the difference every 10 degrees in water. (the probes were right next to each other) At 100 degrees they started to deviate a 1/2 degree, 1 degree at 110, 2.5 degrees between 120 and 142, 3 degrees from 148, etc. So as you suggested while the probes were calibrated at one temp they were not as the temp rose.

Thanks for the help with this.

[mpilchuk]

Good. Glad you tested it. I have really started to not trust all kinds of measuring devices( but not my trusty Refractometer, that I always trust). This brewing is a great lab experiment. We learn as we go and hopefully we remember what we learned. I do not always remember what I have learned and sometimes it takes two or three tries.

Last brew I did with the BCS, I came up with two RULES for myself to follow.

1. Increase the water to grain ratio EVERY time.

I have already learned this once before. The wort has to be pumped through a heat exchanger. The grain absorbs water and some liquid evaporates as I mash. You can't exchange heat if your pump can't pump the wort through the heat exchanger.

2. If there is a problem with the heat control in my system, fix the problem within the system.

After the available liquid dropped off from above, I used some propane heat to get the temp back up. Then I went over. Then added cold water to my heat exchange heat water which cooled it off too much so it went low.

That's two more things to remember for myself. I am a better brewer than my last batch now and I will be until I forget the above.

Maybe I should make some posters to hang in my brew area to remind me.