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Induction Cooktops


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Rats.  Now I'm considering the purchase, and it's gone up to $70.  Never mind, maybe later.

Nancy Smith, aka "Smithy"
HosteG Forumsnsmith@egstaff.org

"Every day should be filled with something delicious, because life is too short not to spoil yourself. " -- Ling (with permission)

"There comes a time in every project when you have to shoot the engineer and start production." -- author unknown

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  • 2 weeks later...

Has anyone heard about this high-frequency induction technology? It allows induction to be used with non-ferrous metals, including copper. Aparently it's been around since 2009, but I can't tell if it exists in any products.

 

The wikipedia article on induction mentions it, but says little except that the components are "relatively bulky."

 

Edited to add: this chowhound thread suggest a product exists in Japan. There's some info on it.

Edited by paulraphael (log)

Notes from the underbelly

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  • 11 months later...

Has anyone installed an induction range in the last two years that they would recommend.  I am looking at Bosch and Thermador and am looking to spend between $2000-2500, but the differences between the ranges are poorly explained.

Thanks

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They're the same company... there's probably not a lot of difference between the units you're looking at. I'm only using a portable unit but what I dislike about it is the fixed temperatures it offers aren't useful/accurate  - like 210F is well above boiling temperature (and it's not the altitude...). A consideration might be the size of the induction coils.

 

I love induction burners - I'd rather have gas but that's not an option for me. Worthwhile getting/migrating to induction-ready cookware.

Edited by NWsFirst (log)
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There is on the top end--i.e the Bosch benchmark has a different bridging mechanism, and the Thermador freedom(out of my price range) has a unique layout as well---and in the bundled deals offered for other appliances.

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I had an Electrolux induction range and really, really liked it. But then we sold our house and the range was sold with it. While it had two ovens, it sensibly had the larger oven above the smaller one as opposed to many other ranges I have seen where the smaller oven is above the larger one. Where I am now I had a Thermador cooktop installed and while I like it, I do believe preferred the Electrolux.

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Ever since induction appliances have come onto the US market, we've been contantly pummeled with the claim that they're far more energy efficient than the coil, smoothtop electric and gas alternatives.  It's been repeated so often and for so long that no one seems to seriously question the claim.

 

Well, except for the U.S. Department of Energy. 

http://energy.gov/sites/prod/files/20...

 

induction_efficiency.png

 

As it turns out, it's looking like a statistical dead heat between coil electric and induction (at roughly 72% efficiency).  And the makers of induction appliances aren't happy about the truth coming out.

 

There may be other reasons to choose induction over conventional electrics and gas, but energy efficiency appears not to be one of them.

 

So this claim of 90% efficiency should probably go the way of "Cast iron conducts heat evenly" and "Searing seals in juices."

Edited by boilsover (log)
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That's interesting reading. It should be noted that your excerpt is from a Notice of Proposed Rulemaking regarding the test methods, but as I read this it still looks as though the efficiencies of coil, smooth electric and induction are roughly equivalent using the hybrid-block method. The claims of higher efficiency for induction are from a 2009 study by a non-government group.

The other thing I took away from this is that the biggest efficiency bang for the buck is matching burner size to pot size. The efficiency was way down for a small pot on a big burner. No surprise, perhaps, except for the magnitude. This table is excerpted from Page 34 of the same document :

Screenshot_2015-07-13-17-31-35-1.jpg

Edited to add link and this followup information: the NOPR is for what's called a hybrid-block measurement method using a steel-and-aluminum block as opposed to measuring efficiency for boiling water. They show that the boiling-water method is less repeatable than the hybrid-block method. It's clear that certain commenters are not happy with the proposal or its implications.

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Nancy Smith, aka "Smithy"
HosteG Forumsnsmith@egstaff.org

"Every day should be filled with something delicious, because life is too short not to spoil yourself. " -- Ling (with permission)

"There comes a time in every project when you have to shoot the engineer and start production." -- author unknown

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Conventional Cooking Top Active Mode Test Procedure

 

The current active mode test procedure for conventional cooking tops involves heating an

aluminum test block on each surface unit of the cooking top. Two aluminum test blocks, of

different diameters, are specified for testing different size surface units. The small test block

(6.25 inches diameter) is used for electric surface units with diameters of 7 inches or less, and the

large test block (9 inches diameter) is used for electric surface units with diameters greater than 7

inches and all gas surface units. Once the initial test and ambient conditions are met, the surface

unit is turned to its maximum energy input setting. After the test block temperature increases by

144 degrees Fahrenheit (°F), the surface unit input rate is immediately reduced to 25 percent ± 5

percent of the maximum energy input rate for 15 ± 0.1 minutes. The efficiency of the surface

unit is calculated as the ratio of the energy transferred to the test block (based on its temperature

rise) to the energy consumed by the cooking top during the test. The cooking top cooking

efficiency is calculated as the average efficiency of the surface units on the cooking top. The

current active mode test procedure is compatible with gas cooking tops and electric cooking tops

with electric resistance heating elements (i.e., electric resistance heating under a smooth ceramic

surface and open coil electric resistance heating).

 

Test Block Construction

Induction cooking products are compatible with only ferromagnetic cooking vessels

because the high magnetic permeability of these vessels concentrates the induced current near

the surface of the metal, increasing resistance and thus heating. Aluminum is not a ferromagnetic

metal—its lower magnetic permeability allows the magnetic field to penetrate further into the

material so that the induced current flows with little resistance, and thus does not heat up when it

encounters an oscillating magnetic field. Therefore, the aluminum test blocks currently required

by Appendix I are not appropriate for testing induction cooking products.

 

As part of the January 2013 NOPR, DOE conducted testing to investigate potential

substitute test blocks for testing induction cooking products. DOE conducted tests using the same

basic test method specified in Appendix I, as described above, using carbon steel, carbon steel

hybrid, and stainless steel hybrid test blocks. 78 FR 6232, 6235 (Jan. 30, 2013). Table III.1

describes the construction of the current aluminum test blocks and the three substitute test

blocks.

Table III.1 Test Block Composition Descriptions

Test Block Classification

Test Block Composition

(Component and Material)

Aluminum One solid aluminum alloy 6061 block

Carbon Steel One solid carbon steel alloy 1018 block

Carbon Steel Hybrid Carbon steel alloy 1018 base + Aluminum alloy 6061 body

Stainless Steel Hybrid Stainless steel alloy 430 base + Aluminum alloy 6061 body

18

 

I was able to read the entire document without issue. The above (quoted for cdh) is a section from same sort of describing the test procedure they apparently used - despite an induction stovetop not being a 'conventional' one as yet. Changes were made to the 'test block' so it could be used on an induction cooktop.

 

However ... do I much care what the Dept. of Energy says? Ummm, not so much. First - I don't tend to 'cook' aluminum and ferrous iron blocks, etc. for dinner much these days. They are a bit heavy in the stomach. Second - I didn't buy my induction cooktops to save energy. I bought them because - a) they heat up much faster b) they heat more consistently c) they are safer overall.

 

(Sorry - copy/paste didn't retain the table formatting at the end of the above quote.)

 

Edited by Deryn (log)
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This isn't really new. Other agencies have also examined this. For example, the Electric Power Research Institute's (EPRI) study for the California Energy Commission. 

 

http://aceee.org/files/proceedings/2014/data/papers/9-702.pdf

 

And as Smithy referenced above:

 

 

These results demonstrate that induction cooking is not necessarily more efficient than conventional electric technology. [...] Yet the efficiency of conventional technology was shown to be highly dependent on the size of the cookware used. The full-power efficiency of conventional electric technology fell from 83% to 42% when testing the electric coil with the small cooking vessel. This demonstrates the impact of contact area on the efficiency of conductive heat transfer between the heating element and cooking vessel. When operated with small cookware, a greater portion of heat created by conventional technologies is radiated outward as losses. On the other hand, induction cooking was found to maintain high efficiency regardless of cookware size.

 

But cooking doesn't take place in a vacuum in a home. The extra heat generated by the gas or conventional electric stovetops may require additional home cooling, for example. (Of course the extra heat can be an energy savings in cold homes.)  

 

I also couldn't read past the first page of the DOE report referenced in the first post. So I don't know what type of induction cooktop they used for testing. The EPRI only used a couple of inexpensive countertop models - 1500 and 1800 Watts. Would the results have been different if they had used a full cooktop model?  

 

But as others have said, I didn't buy induction for energy efficiency. Although less heat in the kitchen certainly seems like energy efficiency to me. With a standard cooktop, I'd be turning on fans or A/C to cool the house down when the weather was at all warm. 

 

But there are so many other benefits to induction! 

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don't know what type of induction cooktop they used for testing. The EPRI only used a couple of inexpensive countertop models - 1500 and 1800 Watts. Would the results have been different if they had used a full cooktop model?  

 

* * *

 

But there are so many other benefits to induction! 

 

DoE doesn't identify what specific appliance models they used, but the tables make it plain that there were at least two with wattages in excess of 3000W--well beyond the capacity of the 110V/1800W hotplates.

 

Yes, of course induction has advantages, especially over electric coil and radiant.  But we can drop the fanfares and heraldic pronouncements over efficiency and focus on real differences.

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Some energy from an induction cook top is lost by radio wave radiation. Some energy is used up for the control and high frequency switching electronics, and many also have a fan to cool the electronics. 

 

The only 100% efficient electric heating is by a resistance immersion  heater.

 

dcarch

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