temp difference above/below heating element

[0verdrive]

I've been working to install an electric system in my brewery, and finally got to the testing stage yesterday afternoon! While calibrating my RTD thermometers, I noticed a drastic temperature difference between the temperature shown on the PID and dial thermometer on my HLT.

At first, I thought that one of the thermometers was calibrated incorrectly - but I noticed that when I put my hand on the side of the keggle, I could tell a distinct difference between the temperature below and above where the heating element is installed. The heating element and RTD are installed about 5" from the bottom, and the dial thermometer is about 4". At only (approximately) an inch apart, the temperature difference between the two was 20-30 degrees!

I know that hot fluids rise, so there isn't much to cause the water below the heating element to heat up - but I didn't think the temperature difference would be so drastic! Has anyone else had this problem?

I'm concerned, because the water comes out of the HLT from a dip tube from the bottom of the HLT. If I raise the HLT to the appropriate temperature, the initial (several) gallons will be considerably cooler than I intend. I guess I could remove the dip tube, so the water at the bottom of the HLT isn't used, but that seems pretty wasteful - is there any other way to deal with this? (I can't stir very well, since the system is gravity fed, and is near the ceiling, making it difficult to get a long spoon in)

Thanks for the help/feedback!

~Dean

 

[ohararp]

Dean, this is when recirculation becomes hugely important. I'd definitely considering adding a pump and putting a probe on the outlet.

 

[DustBow]

You can also get a cheap pump and just pump air to the bottom of the kettle. The air will rise to the and "stir" the water to equalize the temps

 

[bigljd]

You can also get a cheap pump and just pump air to the bottom of the kettle. The air will rise to the and "stir" the water to equalize the temps

+1. I use a el cheapo aquarium air pump and pump air thru some of the blue silicone air hose from Petsmart. To keep the end of the air hose on the bottom of the HLT I loosely tied it around a heavy stainless steel washer. The washer sinks it to the bottom of the HLT, and keeps it from drifting around too much.

 

[waltherjt]

I've been working to install an electric system in my brewery, and finally got to the testing stage yesterday afternoon! While calibrating my RTD thermometers, I noticed a drastic temperature difference between the temperature shown on the PID and dial thermometer on my HLT.

At first, I thought that one of the thermometers was calibrated incorrectly - but I noticed that when I put my hand on the side of the keggle, I could tell a distinct difference between the temperature below and above where the heating element is installed. The heating element and RTD are installed about 5" from the bottom, and the dial thermometer is about 4". At only (approximately) an inch apart, the temperature difference between the two was 20-30 degrees!

I know that hot fluids rise, so there isn't much to cause the water below the heating element to heat up - but I didn't think the temperature difference would be so drastic! Has anyone else had this problem?

I'm concerned, because the water comes out of the HLT from a dip tube from the bottom of the HLT. If I raise the HLT to the appropriate temperature, the initial (several) gallons will be considerably cooler than I intend. I guess I could remove the dip tube, so the water at the bottom of the HLT isn't used, but that seems pretty wasteful - is there any other way to deal with this? (I can't stir very well, since the system is gravity fed, and is near the ceiling, making it difficult to get a long spoon in)

Thanks for the help/feedback!

~Dean

Dean, I feel your pain. I recirculate the HLT water constantly through a march pump to minimize this. Also, I calibrated my PID to the temp at the bottom of the tank.

 

[Yooper]

I have a motorized "stirrer" for my HLT. Either recirculation, stirring, or somehow agitating the water is necessary to avoid the temperature striation.

 

[0verdrive]

+1. I use a el cheapo aquarium air pump and pump air thru some of the blue silicone air hose from Petsmart. To keep the end of the air hose on the bottom of the HLT I loosely tied it around a heavy stainless steel washer. The washer sinks it to the bottom of the HLT, and keeps it from drifting around too much.

This obviously would be the cheaper option, and the easiest to implement. Which is good, since I'm starting to feel like this project will never end, and I'll never get to actually brew again.

That said, I'll probably try it to see how well it works. If it works well, I'll stick with it; otherwise, I'll probably get another pump.

Do you have any way of telling how well the pump works at removing the temperature differences? Does the water at the bottom of the HLT (which is presumably where your drain pulls from) match the temperature of the PID thermometer? Any idea whether I need a certain sized pump (that will pump a certain amount of air) to sufficiently mix the water?

 

[bigljd]

I've never gotten that scientific with testing my HLT, and honestly I don't think it matters that much. You just need to have some movement in the HLT to keep temps relatively consistent throughout, and I think even the cheapest air pump should do that. I've run probably 30 batches using the air pump and my beer turns out great, so that's good enough for me.