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Jun 08, 2022 View:

On demand versus steam heat

Can anyone help me out with this. I'm in a rural area and I'm going to be running on propane. I need to know which is more efficient for mashing. Running an on demand water heater at 10 gallons a minute heating 60 degree water to 160 (500 gallon mash) or heating with steam jacket on mash tun or direct steam in a hot water tank? Easiest install and smallest space is on demand. Is efficiency difference worth the cost difference?

Thanks

Rick


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I'm also rural and propane or 1p electricity is what I've got to work with as well. There is one more option I know of that you haven't listed. It's basically an element in a tube that you pump the fluid your trying to heat through, or you could use it as a closed loop system to heat glycol or similar and pump through a jacketed vessel. I believe they're called recirculating heaters, and I believe WattCo? was the company I spoke with about there's. there tech ran the #'s and said a 275w 220v version would get my 300g to boil in an hour. I posted on here 6-8 months ago(try searching recirculating heater) about them and received some opinions, mostly that it was a good idea, and that they're used commonly in Canada for beer making. That unit with a computer controller was around 7k$ A lot better than a steam boiler($), perhaps just a little slower? Ill be looking back into this in a few months for my mashing needs. Also it was not a big unit, pump and tube with an element in it on a stand with a little computer. I think it was Natrat who tossed out the idea of having it tied in with a tank on the roof using solar preheating and the element would just finish it off after that heat was exchanged. I really liked that idea. Cheaper than steam boiler, more versatile too. Could be used for temp control on fermenters too, or? Scrounge


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Just looked em back up. WattCo in-line heaters, check em out


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Scrounge - You will not get 300 gallons to boil in an hour if all you have is a single phase 240v/200a supply. At max you'll only have 48kw available, and that is not counting any of the numerous other large loads you'll likely be running simultaneously, for example, pumps, agitator motors, chiller, lighting, etc.

Let's say realistically, you can consume half that for heating, 24kw. That'll mean it'll take somewhere north of 4 hours to heat that 300 gallons of water from 68ish to boiling (realistically, probably closer to 5). This would require a 24,000 watt element, not a 275 watt element, a big 100 amps draw, which you will have serious challenges to find in a single 1p element, and probably just as challenging to wire. Even if you turned off everything, and the lights, unplugged your cell phone charger and the radio, you are still talking about 2 and a half hours.

You would need more than 100kw to bring 300 gallons to from 68 to a boil in 1 hour, which would necessitate heavy 480v 3 phase power, and some very expensive heating elements.

If you'll need to boil for a protracted period of time (cereal mash, aka corn), immersion elements will not work. You'll need to use a bain marie setup with a heat transfer oil, which will have lower efficiency, so you'd probably need at least 20% more power. Other factor here is your cost of electricity and propane, with large batch sizes, this means high input energy costs.

Rick - If all you need is 160, I suspect propane with a series of on-demand commercial water heaters is going to be the most realistic. You will need more than one daisy chained depending on how cold your input water is, and even more if you want faster heating (3 even). You'll need one hell of an insulated holding tank to prevent the already heated water from cooling down before the tank is full. Even with propane and on-demand it would probably still take more than an hour to fill up that 500g reservoir.

Direct immersion electric will be more efficient than steam jacket powered by electric, however you will probably be able to generate more BTUs with propane, and put more heat into the tank, even if the overall efficiency is lower. Like I said above, max realistic capacity on a 1p 200a 240v supply is going to be 48kw, with 24kw realistic, this is only 80,000-160,000 btu - pretty small, especially since it's pretty easy to find 199,000 btu commercial on demand propane water heaters. The Rinnai commercials with the commercial control unit can do upwards of 180 degrees output water temp with a ridiculous efficiency, and at a little over a thousand bucks a unit, they are dirt cheap. Well, dirt cheap, but you'll probably need 3 of them to hit 100-120 degree rise at anywhere near 10gpm. How big is your propane tank? You'll need to keep those guys on speed dial.

Like I said above, any kind of cereal mashing and boiling of grain is going to require steam jacket or electrically heated bain marie, otherwise you are going to turn that very expensive heating element into scrap metal, so this is always the biggest part of the decision.

Sweet spot for electric is really the sub 150 gallon range, once you get into the 300g territory, or even the 500g as mentioned above (or larger), the thing that made electric desirable initially (lower up-front cost, simplicity) completely reverse and it becomes significantly more expensive than the alternatives, especially if you factor in annual operating costs. Nat Gas generated Steam almost always wins in the end.


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Hey James. You are correct. I meant 275amp 220v. They make immersion elements up to 650 kw, but 3 phase im sure at that big Check em out Wattco Do the math for a boil time at 275amp 220v, I don't know how to do that, but the tech at Wattco did it and told me that size system would be real close. I have a 400amp commercial panel, so that's not a problem, even with running whatever else I need( pumps,etc ). It's not hard to wire appliances that big. I have a glass melting furnace in that size range, runs 24/7 last 8 yrs straight. Big wire, big breaker. Aluminum wire at that size to keep cost down. I'm not an electrical engineer, that's why I hire one if I need one, but the guys at Wattco crunched the #s and quoted me that. I don't know how to convert amps/volts/ to btu, but if you wouldn't mind running those #s again I'd love to see if he was close. I was/am really thinking of using one of these for mashing. Check out there web site. Sorry for the 275 watt typo up there hahahahgagag, that certainly wouldn't do it. Scrounge


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275 amps - Now you're cooking, yeah that's in the right ballpark for 300 gallons. I think a bit more than an hour, but I'd trust his calcs more than mine, he does this for a living.

If you are buying new, I'd suggest getting quotes from Watlow and Chromalox too. Otherwise, if you have some patience, you can probably find a suitable element in the surplus market for 1/10th the price of new. Many of these are ansi/iso flange mount, so be sure to account for any additional fabrication/welding costs to be able to mount the element to your tank.


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The system they quoted me is there element with an optional protective sheath depending on what your heating, mounted in a tube, with water in and water out. Simple turn key. Just need a pump, and u loop your water out of an insulated tank, thought the heater, back into tank, thermocoupler and little set point controller telling it what to do until it gets where u want it. No welding, just simple plumbing. Minimal floor space required. Sounds easy breezy! Hmmmmm. Scrounge


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Like a tube in tube heat exchanger, with a mega element in it.


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Thanks James,

The current plan was to have two inline on demand water heaters. We are getting pretty big ones and they are doing 10 gallons a minute, so basically an hour for fill up. So thank you for confirming what I thought was the best plan, but just wasn't sure.

Rick


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Just to be safe, check the curves of your on-demand heaters, many are spec'ed at 10gpm, but they can only do that with a lower temp rise, once additional temp rise is needed, they need to run slower, in some cases much slower.

I know plenty of homeowners that converted to on demand, and then ran into this trap the first time they tried to run the dishwasher and take a shower at the same time.