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Author Topic: Just a thought- Induction hot water heater(?)  (Read 5715 times)
Stan
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« Reply #15 on: January 06, 2008, 11:46:53 AM »

Please educate me on induction stove tops. Microwave ovens heat water by disturbing the molecules with high frequency radiation. If you put the water in a metal container, the radiation doesn't reach the water. My concept of induction stove tops was low frequency radiation that disturbed the molecules in the metal container causing heat which transfered to the water. Is this not how they work?
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Sean
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« Reply #16 on: January 06, 2008, 12:01:23 PM »

Folks,

This whole discussion makes no sense to me.  There would be no reason to use inductive technology to make a water heater.

The reason induction is more efficient for cooktops has to do with heat loss to the environment.  With a stove, the food is inside a pan, and the heat source is outside the pan.  Conventional radiant technology tends to heat the environment around the pan, by which I mean not only the air but also the other parts of the cooktop itself, and this heat is "lost energy" as far as the cooking process is concerned.  By contrast, induction tends to heat only the pan, and thus more of the input energy is transferred to the food.  (Some energy is still lost as the pan itself radiates outward to the environment as well as inward to the food.)

(Another benefit of induction for cooking, versus radiant electric, is that it is more "controllable"  -- eliminating the thermal mass of the radiant elements means changes in the control knob are more instantaneously translated to the pan.  Probably not important when building a hot water heater.)

When it comes to a water heater, the mechanics are completely different.  The heating element is inside the tank, completely surrounded by the water it is heating.  Absolutely every watt that goes in to the element turns directly into heat, which is transferred directly to the water.  There is no opportunity for the heat to be lost to the environment at the element.  Of course, once you heat the water, heat migrates to the environment through the tank, which is why you want the best insulation, and as much of it, as you can get around the tank.  But that's true no matter how you heat the water in the first place.  (Incidentally, while any electric element is nearly 100% efficient, the same is not true for gas, where, inevitably, some of the energy is lost as hot exhaust goes up the flue.)

In fact, if you tried to build an "induction" water heater, you would be tempted to use a steel tank and heat that with induction.  Heating the tank, which is by definition on the outside of the water, would actually be less efficient than heating the water using an immersed element.  More of the heat will end up radiating outward from the tank into the environment, versus heating the water from inside.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com
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Jerry Liebler
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« Reply #17 on: January 06, 2008, 12:02:21 PM »

Stan,
    The induction of the cooktops involves magnetic coupling to and resistance of the pan bottom.  The cooktop is kind of like half of a transformer  with a primary winding and part of the core.  The pan completes the magnetic circuit and is quite lossy due to it's resistance so it gets hot.  Unlike a microwave there is no high frequency involved, in the induction cooktop it's all done at 60 Hz.
Regards
Jerry 4107 1120
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Sean
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« Reply #18 on: January 06, 2008, 12:08:25 PM »

Please educate me on induction stove tops. ...


Here are the basics:

http://theinductionsite.com/how-induction-works.shtml

-Sean
http://OurOdyssey.BlogSpot.com

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Stan
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« Reply #19 on: January 06, 2008, 12:30:54 PM »

I was aware that what I referred to as low frequency radiation was magnetic and Jerry says it is just 60 hz but the link from Sean says that it is high frequency, but doesn't say how high. Anyone know?
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« Reply #20 on: January 06, 2008, 01:42:59 PM »

You guys are way beyond how far I want to go with this but I really like the discussion.

One advantage of an induction water heater would be for folks who have all electric buses. If induction is more efficient, it would take less electricity to heat the water and thereby reduce overall capacity requirements.

FWIW,

TOM
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Jerry Liebler
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« Reply #21 on: January 06, 2008, 02:01:27 PM »

All,
    I should have been corrected.  The induction cooktops work NOT at 60 hz but also NOT at microwave frequencies of 2450 MHZ.  In fact they use frequencies in the range of 15,000 Hz to 50,000Hz usually refereed to as 'ultrasonic' frequencies.  At these frequencies most materials behave much more like the do at 60 hz than at microwave frequencies.
Regards
Jerry 4107 1120
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Stan
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« Reply #22 on: January 06, 2008, 02:17:06 PM »

Please excuse my cryptic posts. Lately I have been trying very hard to not post negative comments about the ideas of people who are trying very hard to re-invent the wheel. Since some of the ideas appear to lead into quantum physics there is a lot of room for controversy.
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Sean
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« Reply #23 on: January 06, 2008, 09:07:51 PM »

Sorry, I missed this question earlier:

another question for you tell me if I am close on this

1 gallon of propane = 1525 btu per min    tranlates to 26.81 kw per min to achive the same btu right or wrong
 

Umm, well, if you really just want a one-word answer, then: WrongWink

However, the more detailed explanation is that you are mixing up rates with quantities.

A gallon of "LP Gas" (what is mostly sold in the US as "Propane") holds around 91,000 BTU.  There is no "per minute" or "per hour" in that figure -- BTU's are a measure of energy, and that's how much energy is stored in a gallon of the stuff.

Appliances, on the other hand, are rated by how much energy they consume over time.  So heaters and stoves, for example, are rated in "BTU's per hour."  Many people, including those who write advertising copy, mistakenly write this number as simply "BTU's" -- but, rest assured, heaters and air conditioners can only be described by rates, such as "BTU per hour."

Electrical energy is generally described in the metric system, which uses different terminology.  In that system, a "Watt" (or KiloWatt) is a measure of Power.  Energy, by contrast, is power applied over a period of time.  So there is a translation between "BTU's Per Hour" and "KiloWatts", and there is also a translation between "BTUs" and "KiloWatt-Hours", but you can't translate between "BTUs" and "KiloWatts" -- they are different units.  It would be like asking how many gallons are in a mile.

For reference, 1,000 BTUs/Hr is roughly 0.3 KW (or 300 watts), and 1 KiloWatt-Hour is roughly 3,400 BTU's.

In your example, if your had a stove that was rated at 1,525 BTU's per minute (which is ridiculously high -- that would translate to a "BTU Rating" of over 90,000, where "BTU Rating" is marketing-speak for "BTUs per hour"), then that would, indeed, translate to roughly 26.8 KW (not KW per Minute).

Bear in mind, though, that the average residential gas burner has a "BTU Rating" of around 10,000 -- about a tenth of your example.  My own LP gas range has a pair of, I think, 6,000 BTU/Hr burners.  In "electric" terms, those would translate to 1,750 Watts each -- or about 15 amps at 120 volts.

The topic upon which you are touching, though, is quite germane.  There is absolutely nothing inherently more "efficient" about LP stoves than electric ones (in fact, quite the opposite is true), but, in an RV, getting enough electric power to the appliance can be a challenge.  Plugged in to shore power, you must consider that the average household electric range can use as much electric power as is available to the entire bus conversion (in fact, they use the same plug end).

The whole reason Induction is such an attractive technology in an RV is that it reduces the power consumption down to an amount that is reasonably managed on an RV power budget.  We use our induction stove anytime we have shore power available, or if our generator is running.  (Incidentally, a gallon of LP holds only about 91,000 BTU, whereas a gallon of diesel holds about 139,000 BTU.)

HTH.

-Sean

« Last Edit: January 06, 2008, 09:14:34 PM by Sean » Logged

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makemineatwostroke
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« Reply #24 on: January 07, 2008, 06:08:53 AM »

Thanks for the reply Sean a one word answer will work for me.but this something I would like to try, will it work probably not , and if I need engineering it's a phone call for me to Stewart and Stevenson they have hundreds. have a good day
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Hartley
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« Reply #25 on: January 07, 2008, 02:42:58 PM »

Sean,

Sure glad you jumped in here... The explanation that works.
You said what I was thinking... Smiley Smiley

It is all physics and physical properties of the heat source and container.

It's about what is doing the heating, Not the actual contents being heated
like a microwave does.

Recently an article of news said that using aluminum cookware may
contribute to alzhiemers. I have to make my wife throw out that old
aluminum pan along with the telfon coated stuff..
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DrivingMissLazy
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« Reply #26 on: January 07, 2008, 03:40:58 PM »

Sean, I wonder if a cast iron divot (is that the right word for those three legged things you set a hot pan on?) placed in a non ferrous container would heat up the contents of the container.

Richard
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« Reply #27 on: January 07, 2008, 05:34:10 PM »

Quote
I wonder if a cast iron divot (is that the right word for those three legged things you set a hot pan on?) placed in a non ferrous container would heat up the contents of the container

I'm not Sean, but our induction cooktop and also our portable induction burner require that the pot be set directly on the "burner".  If you set a steel spatula or even had an iron piece of jewelry on, it will not be affected by the magnetic induction burner. 

As for power usage, well, our portable unit plugs into a standard 120v outlet on a 15 or 20 amp circuit, but it does not have as much power as our built-in cooktop, which utilizes a 240v 30 amp and a 240v 20 amp circuit for a total of five induction burners.  The portable unit gets plenty hot for my use, but might not be hot enough for searing. 

Our induction cooktop does heat faster than any of our microwaves, but it is also drawing more amps while doing so.  I've never tried to experiment with a direct comparison that could read amp draw and such. 

The problem with water heaters is you have to either heat a larger body of water with less Btu's, or you need to heat less volume faster.  Tankless water heaters require much more fuel (electric or otherwise) because they are heating the water in a single pass, quite rapidly.  Personally, I think the best thing I've come across so far are the little Excell water heaters on Ebay, which are non-vented propane tankless units.  With the low gpm we run in our buses, these little units would do quite well. 

IMHO, Christy Hicks
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makemineatwostroke
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« Reply #28 on: January 07, 2008, 06:02:13 PM »

Christy,thanks for the info I found out today goofing off with a 1500w induction cook top that the pan has to be flat and works better if the pan is centered on the cook top and would not do anything on the edge also it looked to me that it cooks in a 8in circle.is this the way it works.Another thing I found out is the induction I bought does not like MSW inverter in a motor home I have but is ok with PSW inverter in my bus     thanks
« Last Edit: January 08, 2008, 04:57:03 AM by makemineatwostroke » Logged
Sojourner
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« Reply #29 on: January 07, 2008, 09:06:42 PM »

What Sean posted is common sense. It has been around for years….all TV screen light beam is induction heated to provide the results on screen to see video.

You can get an induction drum heater that will heat water tank as well at a price. Nearly 5 grand and use little more amount of energy than what Sean describes about immersed heating element.

No matter which type of method to heat water, it takes so much electrical energy to produce a given number of BTUs. There are many ways to heat water but only with better insulation and direct heating element into water that will be the best heat riser per KW (1000 watts) of electric power. This is 100% efficient along with proper sized wire gauge or larger from power source to heater unit.

Even better still that uses the least KW of electrical energy per given time is an instant demanding electric water heater which eliminates hot water storage tank to avoid heat loss while waiting to be used.

It is true that induction system will work but it is not practical just to heat plain old water. Why…because you need a tuned (out of tune won’t work well) high frequency AC at high current output power from inductor designs solid state converter supply. Plus it causes any electronic antennae or RF devices nearby to go haywire.

Here are some links that explain the system in detail and source of induction heater available for cash on hand:

Animated photo of induction: http://www.richieburnett.co.uk/indheat.html

http://www.ameritherm.com/aboutinduction.php

http://www.drumheating.com/

Oh well have fun in the mean time. Smiley Smiley

FWIW

Sojourn for Christ, Jerry
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