Induction as a heat source for steam?

Joe V_2

Did a quick search but found nothing.

Went to a showroom to buy a glass surface range and ended up spending more than budgeted to  buy an induction range.  Never seen one before and  thought it was the best of all worlds when I saw it boil a pot of water in a fraction of time it usually takes.

The "eye" didn't get hot.  So, my question is, rather than lose heat up a chimney, why not an induction coil for a boiler's heat source?

Yes, I do have a little buyers remorse but what the heck?

David Nadle

Electricity costs

I'm guessing that the increased efficiency of induction heating does not make up for the higher cost of electricity vs. other fuels.

SWEI

Electric resistance heat

Is basically 100% efficient already.



Induction merely couples that energy more effectively to ferrous metal objects.  It's great for melting steel...

Joe V_2

and it

is cheaper than oil. plus it is a greener technolgy. it has to be efficient. you wouldnt even nedd a stack.

SWEI

It?

Not sure what you're talking about here.  Can you clarify?

JStar

Electricty

Electricity is 100% efficient, but damn expensive. My boiler would cost about $35 an hour to run.

BobC

Maybe not

In the Boston area electricity is about $0.15 / kwh, 1 kwh = 3,400btu so 100,000 btu's of electric heat would be $4.41 and it would be 100% efficient.



Oil in this area is about $3.60 per gallon (140,000 btu), at 85% efficiency that leaves us with 119,000 btu or $3.03 for 100,000 btu of heat.



So oil heat costs 68.7% what electric heat would in this market and natural gas is a lot cheaper.



Now if you were out in Nebraska where electricity costs a whole lot less you might be onto something.



All of this assumes I haven't done something stupid with the math - always a possibility.



Bob

David Nadle

Electric steam boilers

About half the electricity produced in the US is from coal, which is not very green, and another 1/4 is from natural gas. Even if NG plants burn with greater efficiency than your average boiler, electrical distribution losses probably wash out that benefit.

Inductive heating can never be more efficient than a resistive heating element immersed in the water. That is basically 100% efficient. They do make electric steam boilers for commercial applications, but if you had to heat a house with electricity it would be far more efficient to install electric baseboard than with electric steam generation. 

JStar

KW

You're right. I added an extra 1 by accident.

David Nadle

Too expensive

100,000 Btu/h is about 29.3 kW. Yes, it's $4.40 an hour but you would need about 120 A of 240 V service just for the heat. The thermal transfer to the water is 100% efficient but total system efficiency is not. Using baseboard you'd put the heat only where it was wanted and there's no waste heat of a boiler full of hot water.

And that's resistive. An induction heater is a moderately complex oscillator producing a high power, high frequency signal. A 30 kW model would probably cost 10 times that of a standard boiler.  

SWEI

Electricity

Whoa, guys!



I'm only comparing two different processes as regards their conversion of electricity to heat.

Joe V_2

But,

Most users with steam systems have electricity.   electricity produced by poluting coal will be offset by boilers that come off oil, and the environment benefits. So that makes steam greener.

It may not work everywhere, but in my neck of the woods, gas and electricity are competitive so if you wanted to green up, you can.   But the possibility of induction also opens up the the door to renewable energy like solar panels or wind turbines to create steam.  Granted, we would still need the cast iron mass to heat.  But it would be a cleaner, competitive and far more comfortable heat.

I know the technology to marry an inductive heat source to renewable energy may not yet exist in practical  form.  But it may one day.

As for cost...My neighbor is spending 50K to put in geothermal in an urban area so he can go off the grid in his near retirement.  Some folks will pay.

David Nadle

Hmm

Joe, I don't see where induction heating has any benefit in cost or efficiency over resistive for boiling water.

SWEI

coupling induction

To a renewable source Is perfectly viable today, it just doesn't make economic sense in most cases.  If and when it the economics change, induction heating will still have the same efficiency that resistance heating does in this application.

Joe V_2

I may be just dreaming

...But, when I saw a pot of water boil in about three minutes, compared to the ten  minutes it takes to boil the same amount on my current coil stove,  I couldn't help wonder if speed is a cost savings.

David Nadle

Immersion

Compare it to an immersion heater.

SWEI

not dreaming...

Just seeing a more efficient transfer of heat from the induction burner to a pan full of water.  Less heat flows into the cooktop and the surrounding air, so more can get into the water.



In a typical electric boiler, over 99% of the energy gets into the water because the heating elements are immersed in the water.  Induction would most likely end up less efficient for this application for two reasons:  First, there are losses in the inverter which drives the coils (I'd guess at least 2-3% here) and second, if the eddy current was induced in the boiler vessel, some portion of that heat will end up the boiler room instead of the water.  This happens with any boiler, but if the heat source is at the shell of the vessel rather than in the middle of the water, the losses would be greater.