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Old 09-12-2011, 05:19 PM   #1
bigljd
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Default Direct 'fire' MLT using electric hot plate?

I'm still brewing with propane out in my brew shed, but have visions of converting to electric and have been researching all the different ways to set up a system. I have really only seen 2 options for temp controlling a mash in a MLT, either a PID controlled RIMS or HERMs system.
I was wondering if anyone has tried using an electric hot plate under an MLT to 'direct fire' heat into a kettle or keg. To keep temps consistant throughout the MLT, you'd have a false botton and use a pump to recirculate, and the power to the hot plate could be controlled by a PID with a thermocouple in the MLT to turn the hot plate on or off as needed to maintain temps.

Here is a random example of a hot plate:
http://www.amazon.com/Waring-SB30-13...ref=pd_sim_k_4

One issue I could think of is the weight of a full MLT could crush the hot plate. If it were mounted into a brewstand where the bulk of the weight was supported by the stand, not the hot plate it seems like it would work.
It would only need to maintain MLT temps or maybe raise them slowly if you wanted to step mash.
Is this crazy - would it work?


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Old 09-12-2011, 06:30 PM   #2
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the only reason i would go the 'heat the mash from the bottom" route would be if i were not using a pump and couldnt pump the wort thru a HERMS or RIMS. since you have a pump, why not go that route?

FYI an imersion-style heating element is around 95% efficient at turning electricity into heat. a hot plate would be between 25% and 75% (possibly slightly higher, depending on how well the implimentation). the difference between wasting 5% and 50% of the electricity is pretty apparent.


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Old 09-12-2011, 07:04 PM   #3
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the only reason i would go the 'heat the mash from the bottom" route would be if i were not using a pump and couldnt pump the wort thru a HERMS or RIMS. since you have a pump, why not go that route?

FYI an imersion-style heating element is around 95% efficient at turning electricity into heat. a hot plate would be between 25% and 75% (possibly slightly higher, depending on how well the implimentation). the difference between wasting 5% and 50% of the electricity is pretty apparent.
I guess my reason for exploring this method is that it seems easier to build. I'd just need a small shelf under the MLT to support the hot plate - the shelf could be adjusted upwards so that the hot plate would contact the bottom of the MLT. The hot plate would then be plugged directly into the control panel. No HLT copper coils to install or RIMs tubes to build, wire up and keep clean.
True, it probably wouldn't be as efficient, but since it would only be maintaining mash temps I don't think a lot of energy would be required or lost.
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Old 09-12-2011, 08:49 PM   #4
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I don't see why it couldn't work. Your approach with using a good false bottom and recirculating is just the same as doing a direct fired RIMS system. The only difference is you'd use an element underneath the kettle instead of a flame.

I'm not a fan of RIMS tubes due to how dirty they get and the cleaning involved.

I like your idea - give it a shot!
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Old 09-13-2011, 07:54 PM   #5
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i suppose if you are only using it to maintain temperature/replace heat lost (and not trying to raise from mash to mashout) it would be simpler. i find myself using my HERMS heater for lots more though. and cleaning is a non issue- i just hook up the "out" of my immersion chiller into the HERMS coil and let it flush clean hot water thru (and collect it in the HLT for cleaning the rest of the system later). i also use it to boost the power of the propane burner while initially heating the water, so it gets sterilized before each use.

ive never been a fan of using the HLT as a HERMS, either. that much themal mass is just too unweildy for fine temperature control.
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Old 09-14-2011, 01:09 AM   #6
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I don't see why it couldn't work. Your approach with using a good false bottom and recirculating is just the same as doing a direct fired RIMS system. The only difference is you'd use an element underneath the kettle instead of a flame.

I'm not a fan of RIMS tubes due to how dirty they get and the cleaning involved.

I like your idea - give it a shot!
Thanks - I don't have access to the electric in my shed right now, and don't have space in my house to brew there, so these are just ideas bumping around in my head for now. I'm stuck with propane until we move hopefully in the not too distant future.

Quote:
Originally Posted by audger View Post
i suppose if you are only using it to maintain temperature/replace heat lost (and not trying to raise from mash to mashout) it would be simpler. i find myself using my HERMS heater for lots more though. and cleaning is a non issue- i just hook up the "out" of my immersion chiller into the HERMS coil and let it flush clean hot water thru (and collect it in the HLT for cleaning the rest of the system later). i also use it to boost the power of the propane burner while initially heating the water, so it gets sterilized before each use.

ive never been a fan of using the HLT as a HERMS, either. that much themal mass is just too unweildy for fine temperature control.
How is your HERMS setup? I think I've only seen people use HERMS in an HLT - what are the alternatives?
Most of my brews are single infusion/fly sparges with no mash out, so I am really only interested in maintaining mash temps, or on a rare occasion maybe doing a protein rest and then raising the temp up to the sach rest. I'd think a 1300 watt hot plate would be able to raise the temps ~ 20 degrees reasonable well if I needed to.
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Old 09-14-2011, 02:43 PM   #7
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i use a 1 gallon stainless steel container that i installed a 1/2" legnth of copper coil and a 2kw heating element into, with a total cost of <$20. with a power ratio of 2kw/gallon, you can raise or lower the temperature pretty fast. if you had a 5 or 10 gallon HTL as the heat exchanger, it would take that much longer to adjust the hot-side temperature of the HEX (or you would need 10,000 to 20,000 watts of heating power in it to get the temperature to move as quickly as this).

http://img.photobucket.com/albums/v2...r/fa759760.jpg
http://img.photobucket.com/albums/v2...r/4032eac7.jpg
http://img.photobucket.com/albums/v2...r/b9f4e1f7.jpg

temp probe that controls the heater is located directly in the exit stream of the HEX
http://img.photobucket.com/albums/v2...r/7bbb3bd2.jpg

at a flow rate of 1.5gal/min, and with a thermal mass of 6 gallons of water, plus the gallon in the HEX, plus the mass of the 1/2 keg mash tun i use; this HEX will heat the water by an average of 5.1 degrees in a single pass (difference between input and output temps); it will heat that total thermal mass by ~1 degree per minute (94.6 degree change in 92 minutes); and uses 3.2kWh to do so. (so it costs me 6 cents per gallon, per 100 degree change, or 60 cents to heat 10 gallons from 70* to 170*)

that means that if you want 170 degree sparge water, your HLT can be anywhere between 165 and 170, and when you run it thru the HEX, it will come out exactly at 170 (if your HLT is your HEX, then this wouldnt work). it will also hold mash temperatures +/- 1 degree while mashing, but that has a lot to do with how well the mash tun is insulated.
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Old 09-15-2011, 03:02 AM   #8
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I like your design for a HERMS - it's a good idea I think. It's definitely is more flexible and efficient than using the HLT for your HERMs.
I will say though, that even though you are only heating 1 gal of water in your container, I think you'd still be expending more energy to heat that 1 gal than the energy I would lose to inefficiency by 'direct firing' with a hot plate. I only mention this because you were talking about efficiency in an earlier post. Unless you are using that 1 gal as part of your sparge water, the stored energy in that 1 gal is wasted. Granted it's not enough to be bothered worrying about though.
The most efficient method would be putting an element in the MLT, but I know that is not a good idea usually because of potential scorching.
It would be a bit more work to build than slapping a hot plate on a shelf under the MLT, IMHO.
Thanks for sharing the pics though - if I go the HERMs route I'd seriously consider copying your setup.


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