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Old 09-11-2009, 10:49 AM   #31
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Originally Posted by maztec View Post
However, BTUs on gas are hampered by a low efficiency - about 50%.

Now, assuming 50% efficiency on a gas burner (and that is high, they are usually rated at 30%)
Could you reveal your source for that data. This Oregon State University Fuel use Calculator says that the Heat Efficiency of Natural Gas is 78%.


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Old 09-11-2009, 11:10 AM   #32
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Now, Menu System (Swedish: :: MENU SYSTEM :: Induktionsherde - Induktionskochgeräte) does put out a standalone induction hob that puts out 6kW (6,000W) which is 20,472 BTUs. Using my calculations above, that hob should bring things to a boil in around 30 minutes.
If you look at the Menu System Single 6 kW unit and you need 440 volts to power it. Not a practical solution for Homebrewers.


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Old 09-11-2009, 02:12 PM   #33
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For research sake, Vollrath makes a 3 ply pot that screams on induction. A few imports like Update make a good single wall aluminum-clad bottom pot that work well and you should be able to find up to a 60 quart for less than $200.

The magnet test is for real. If you are interested in this technology, take a magnet with you when you shop for pots. If it sticks well it will work.
My mash tun is from Volrath - it's a great pot! Most of the pans I've bought to use to cook with are from Update and I love cooking with them.

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Could you reveal your source for that data. This Oregon State University Fuel use Calculator says that the Heat Efficiency of Natural Gas is 78%
I'm not sure what his source is, but the point he is making is that very little heat is lost. The pot is what heats up, not the element, so the only heat transfer is pot to contents. With Natural Gas, it goes flame to pot to contents. A lot of heat is lost to the air. If you are just heating air, like to heat a house, then you can get 78% efficiency. It is going to be much lower for cooking though.
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Old 09-11-2009, 02:52 PM   #34
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The efficiency of natural gas as a fuel is higher than its efficiency when used on a cooktop although its not quite as low as 30%. Much energy is wasted when using it to cook. You can tell by how hot your kitchen gets. Induction is 80-90%
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Old 09-14-2009, 08:16 AM   #35
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@Sawdustguy: The efficiency is lower than ambient heat (as others have explained). Natural gas cooking is generally rated between 30% and 40% efficiency - I went with the low end of the calculations on everything. When cooking with gas a fair amount of the heat is reflected down and away from the pot. When cooking with induction it is the pot that warms up and it only loses heat that is not absorbed [heat transfer flows in the most efficient direction - which is often whatever is coldest first]. As a result, direct heating of any type is more efficient than gas - except for ambient results, then gas is king. That said, I love using gas.

As for sources on that, there are several, most of which are tests done by induction hob producers (which is why I underguessed their typical estimate of 90% efficiency). However, wikipedia also has information on it. I do not have a direct link to an actual report by an independent agency to back me up - however, experience and physics match with the estimates I have seen.

As for 440v power on the Menu System 6kW unit, that is true, but the power unit can be converted -- I have been informed by an induction hob supplier here in the States (who does not provide Menu System themselves) that they have seen Menu System hobs used in U.S. kitchen, including standalone units, that have had a converter wired in by Menu System. The main thing here is to see if your residential power supply can actually put out 6kW of power, if it can't then the hob will draw too much power, pop a breaker, or just not work. 1 Watt = 1 Volt * 1 Amp. So x Amps = Watts/Volts = 6,000W/110V = 54A. The grid in the U.S. provides 220V/200A = 44,000W. I live in a older home with a 110V / 100A drop. That puts me well above the 54A need to reach 6kW. Therefore, instead, the trick is to get the unit converted - or, alternatively, buy an external conversion unit. This is doable using a step up transformer (to 440v it's two step up transformers, but it is doable). That said, it's doable.

----

@northernlad: You sir are a fountain of information. Thank you. So, it looks like I will probably have to go with the Menu System or another European model. One thought, perhaps I could find a unit with enough wattage, and then use a rack to suspend the pot - so it is just barely resting on the surface but the rack distributes all of the weight away from the hob. From what you said, it seems like there would be no problem with doing this? I could easily build a split C stand that holds onto the rim and handles of a large pot...

-----

Of course, the other option, would be to build a coil induction heater and then drop the pot into it. That would heat not just the bottom but the sidewalls, which would definitely move things to a boil. Albeit, it would be a bit ungainly - and I haven't played seriously with electricity like that in years; I wonder if my electrician cousin would give me a hand. I wonder what would happen if I put the heatsink under the pan as yet another heatsource, but put a fan across its bottom to keep the unit cool. Anyway, people have been making their own induction heaters: DIY Induction Heater - Hacked Gadgets - DIY Tech Blog I'm sure with a little bit of industriousness such a thing could be made for a pot . That is, assuming I can't find a decent hob at a good price.
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Old 09-14-2009, 12:29 PM   #36
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Originally Posted by maztec View Post
As for 440v power on the Menu System 6kW unit, that is true, but the power unit can be converted -- I have been informed by an induction hob supplier here in the States (who does not provide Menu System themselves) that they have seen Menu System hobs used in U.S. kitchen, including standalone units, that have had a converter wired in by Menu System. The main thing here is to see if your residential power supply can actually put out 6kW of power, if it can't then the hob will draw too much power, pop a breaker, or just not work. 1 Watt = 1 Volt * 1 Amp. So x Amps = Watts/Volts = 6,000W/110V = 54A. The grid in the U.S. provides 220V/200A = 44,000W. I live in a older home with a 110V / 100A drop. That puts me well above the 54A need to reach 6kW. Therefore, instead, the trick is to get the unit converted - or, alternatively, buy an external conversion unit. This is doable using a step up transformer (to 440v it's two step up transformers, but it is doable). That said, it's doable.
Actually you need to add 3 or 4 amps more if the unit could be run on 110 VAC. The pdf says that the device itself can be expected to dissapate between 300 to 400 watts of heat (you can see the large heatsink with fans in the picture in the pdf file). This has to accounted for also because the unit itself is not 100% efficient in delivering 6kW to the load. Another thing to consider is that the unit is speced at 3 x 400 to 440. I wonder if they mean 440vac 3 phase (common here in the US for industrial machinery). If that is true a simple transformer will not work. Getting this unit to work in someone's home is a stretch at best.
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Old 09-14-2009, 03:05 PM   #37
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Yeah, I think trying to convert a 440v unit to 220v woulld be more work than necessary and additional money. Getting a commercial unit wired 208/240v versus 115v is generally no charge but 440v is always an upcharge. So, you would be paying extra for the high voltage and then pay for a converter to lose the big pipe.
i would investigate a 208/240v 3500 watt commercial induction burner from Vollrath or Cooktek. Both make an excellent product and should be enough for full boils. The challange will always be whether the size of the cooking surface is the same the diameter as your pot. If your pot is bigger your efficiency goes down.
If you would like specific product notes and cut sheets for the burners let me know and I will send them from work.
And, yes a full boil is almost assuredly too heavy for the burner, but I will check weight limits.
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Old 09-14-2009, 03:19 PM   #38
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@northernlad: If you could send me those specs it would be great.

@Sawdustguy: I interpret their 6kW as 100% power; not max actual power. Am I wrong in this? That is the assumption I used in my earlier calculations that took efficiency into account. On a unit like that, if it was only 80% efficient, you would be losing about 1200W. However, I admit, I am not an electrician so could be wrong. And, they do mean 440vac 3 phase. As I said earlier, I have been informed [and had it confirmed today by Menu System] that they can change the power unit to work in a U.S. residential setting. Albeit, they won't be able to give me a price estimate for a few more days.

So, while it might be a stretch, what does it hurt to look into it? Am I going to be arrested by the U.S. Overlords of Power Decency for exploring my options?
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Old 09-14-2009, 03:38 PM   #39
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So, while it might be a stretch, what does it hurt to look into it? Am I going to be arrested by the U.S. Overlords of Power Decency for exploring my options?
It doesn't hurt at all. I just think there are more practical and less expensive solutions for heating a kettle. Simply mounting an 5500 watt electric heating element into a kettle is much less expensive and pretty efficient also.

If you read the pdf it does state that the unit itself does generate 300 to 400 watts of heat. That means to generate 6000 watts it uses a minimum of 6400 watts. There may be other losses also.
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Old 09-14-2009, 04:39 PM   #40
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The big daddy 69504 (about $2000): Vollrath | Food Service Catalog
The more realistic... 65920 (about $1000) Vollrath | Food Service Catalog

Or...MC3500(about$1400): CookTek® Induction Cooktops

I hope you had some idea of what these would cost before this post...


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