Induction cooktop
heats a cooking vessel with induction heating, instead of infrared radiation from electrical wires or a gas flame as with a traditional cooking stove. For all models of induction cooktop, a cooking vessel must be made of a ferromagnetic metal such as cast iron or stainless steel or at least compounded with a steel inlay. Copper, glass and aluminum vessels can be placed on a ferromagnetic interface disk which enables these materials to be used.
In an induction cooker, a coil of copper wire is placed underneath the cooking pot. An alternating electric current flows through the coil, which produces an oscillating magnetic field. This field induces a magnetic flux with a resulting eddy current in the pot equivalent to theelectric current in the coil. The eddy current in the metal pot produces resistive heating which heats the food. While the current in the coil is large, it is produced by standard household power supplies. |
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This form of flameless cooking has certain advantages over conventional gas flame and electric cookers, as it provides rapid heating, improved thermal efficiency, and greater heat consistency, yet with precise control similar to gas. In situations in which a hotplate would typically be dangerous or illegal, an induction plate is ideal, as it creates no heat itself.
The high efficiency of power transfer into the cooking vessel makes heating food faster on an induction cooking surface than on other electric cooking surfaces. Because of the high efficiency, an induction element has heating performance comparable to a typical consumer-type gas element, even though the gas burner would have a much higher power input. Induction cookers are safer to use than conventional cookers because there are no open flames. The surface below the cooking vessel is no hotter than the vessel; only the pan generates heat. The control system shuts down the element if a pot is not present or not large enough. Induction cookers are easy to clean because the cooking surface is flat and smooth, even though it may have several heating zones. Since the cooking surface is not directly heated, spilled food does not burn on the surface. Since heat is being generated by an induced electric current, the unit can detect whether cookware is present (or whether its contents have boiled dry) by monitoring how much power is being absorbed. That allows functions such as keeping a pot at minimal boil or automatically turning an element off when cookware is removed. Because the cook top is shallow compared to a gas-fired or electrical coil cooking surface, wheelchair access can be improved; the user's legs can be below the counter height and the user's arms can reach over the top. |
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Limitations |
Cookware must be compatible with induction heating; glass and ceramics are unusable, as are solid copper or solid aluminum cookware for most models of cooker. Cookware must have a flat bottom since the magnetic field drops rapidly with distance from the surface. (Special and costly wok-shaped units are available for use with round-bottom woks.) Induction disks are metal plates—much like a skillet with no sides—that heat up non-ferrous pots by contact, but these sacrifice much of the power and efficiency of direct use of induction in a compatible cooking vessel. Further, cheap induction cookers regulate the transmitted power by simply powering the field on and off for specified times, like mostmicrowave ovens do. If a pot with a thin bottom is used, the contained liquid boils intermittently. This does not occur with cookware that has a thicker bottom or with better induction cookers.
Manufacturers advise consumers that the glass ceramic top can be damaged by impact, although cooking surfaces are required to meet minimal product safety standards for impact. Aluminum foil can melt onto the top and cause permanent damage or cracking of the top. Damage by impact also relates to sliding pans across the cooking surface, which users are advised against. As with other electric ceramic cooking surfaces there may be a maximum pan size allowed by the manufacturer.
A small amount of noise is generated by an internal cooling fan. Audible noise (a hum or buzz) may be produced by cookware exposed to high magnetic fields, especially at high power if the cookware has loose parts; better-grade cookware with welded-in cladding layers and solid riveting should not produce this type of noise. Some users may detect a whistle or whine sound from the cookware, or from the power electronic devices. Some cooking techniques available when cooking over a flame are not applicable. Persons with implanted cardiac pacemakers or other electronic medical implants are usually instructed to avoid sources of magnetic fields; the medical literature seems to suggest that proximity to induction cooking surfaces is safe, but they should always check first with their cardiologists.Radio receivers near the unit may pick up some electromagnetic interference.
An induction (or any electric) stove will not operate during a power outage. Older gas-stoves do not need electric power to operate; however, modern gas-stoves with electrical ignition require an external ignition source (e.g. matches) during power outages.
Manufacturers advise consumers that the glass ceramic top can be damaged by impact, although cooking surfaces are required to meet minimal product safety standards for impact. Aluminum foil can melt onto the top and cause permanent damage or cracking of the top. Damage by impact also relates to sliding pans across the cooking surface, which users are advised against. As with other electric ceramic cooking surfaces there may be a maximum pan size allowed by the manufacturer.
A small amount of noise is generated by an internal cooling fan. Audible noise (a hum or buzz) may be produced by cookware exposed to high magnetic fields, especially at high power if the cookware has loose parts; better-grade cookware with welded-in cladding layers and solid riveting should not produce this type of noise. Some users may detect a whistle or whine sound from the cookware, or from the power electronic devices. Some cooking techniques available when cooking over a flame are not applicable. Persons with implanted cardiac pacemakers or other electronic medical implants are usually instructed to avoid sources of magnetic fields; the medical literature seems to suggest that proximity to induction cooking surfaces is safe, but they should always check first with their cardiologists.Radio receivers near the unit may pick up some electromagnetic interference.
An induction (or any electric) stove will not operate during a power outage. Older gas-stoves do not need electric power to operate; however, modern gas-stoves with electrical ignition require an external ignition source (e.g. matches) during power outages.
Efficiency
An induction cooker is faster and more energy-efficient than a traditional electric cooking surface. It allows instant control of cooking power similar to gas burners. Other cooking methods that use flames or red-hot heating elements have a significantly higher loss to the ambience; induction heating directly heats the pot. Because the surface of the cook top is heated only by contact with the vessel, the possibility of burn injury is significantly less than with other principles of heating. The induction effect does not directly heat the air around the vessel, resulting in further energy efficiencies. Cooling air is blown through the electronics beneath the surface but emerges only a little warmer than ambient temperature.
According to the U.S. Department of Energy, the efficiency of energy transfer for an induction cooker is 84%, versus 74% for a smooth-top non-induction electrical unit, for an approximate 12% saving in energy for the same amount of heat transfer.
Energy efficiency is the ratio between energy delivered to the food and that consumed by the cooker, considered from the "customer side" of the energy meter. Cooking with gas has an energy efficiency of about 40% at the customer's meter and can be raised only by using very special pots, so the DOE efficiency value will be used.
According to the U.S. Department of Energy, the efficiency of energy transfer for an induction cooker is 84%, versus 74% for a smooth-top non-induction electrical unit, for an approximate 12% saving in energy for the same amount of heat transfer.
Energy efficiency is the ratio between energy delivered to the food and that consumed by the cooker, considered from the "customer side" of the energy meter. Cooking with gas has an energy efficiency of about 40% at the customer's meter and can be raised only by using very special pots, so the DOE efficiency value will be used.
Environmental impact
When comparing consumption of energies of different kinds, in this case natural gas and electricity, the method used by the US Environmental Protection Agency refers to source (also called primary) energies. They are the energies of the raw fuels that are consumed to produce the energies delivered on site. The conversion to source energies is done by multiplying site energies by appropriate source-site ratios. Unless there are good reasons to use custom source-site ratios (for example for non US residents or on-site solar), EPA states that "it is most equitable to employ national-level ratios". These ratios amount to 3.34 for electricity purchased from the grid, 1.0 for on-site solar, and 1.047 for natural gas. The natural gas figure is slightly greater than 1 and mainly accounts for distribution losses. The energy efficiencies for cooking given above (84% for induction and 40% for gas) are in terms of site energies at the customer's meters. The (US averaged) efficiencies recalculated relative to source fuels energies are hence 25% for induction cooking surfaces using grid electricity, 84% for induction cooking surfaces using on-Site Solar, and 38% for gas burners.
Source-site ratios are not formalized yet in Western Europe. A common consensus should arise on unified European ratios in view of the extension of the Energy Label to domestic water heaters. Unofficial figures for European source-site ratios are about 2.2 for electricity, 1.0 for on-site solar, and 1.02 for natural gas, thus giving overall (referred to source energy) efficiencies of 38% and 84% for induction cooking surfaces (depending on source electricity) and 39% for gas burners. These provisional figures need to be somehow adjusted due to the higher gas burner efficiency, allowed in Europe by a less stringent limit on carbon monoxide emission at the burner. European and US standards differ in test conditions. The US ANSI Z21.1 standard allows a lower concentration of carbon monoxide (0.08%), compared to the European standard EN 30-1-1 which allows 0.2%. The minimum gas burner efficiency required in the EU by EN 30-2-1 is 52%, higher than the average 40% efficiency measured in US by DOE. The difference is mainly due to the weaker CO emission limit in EU, that allows more efficient burners, but also due to different ways in which the efficiency measurements are performed. Whenever local electricity emits less than 435 grams of CO2 per kWh, the greenhouse effect of an induction cooker will be lower than that of a gas cooker. This again comes from the relative efficiencies (84% and 40%) of the two surfaces and from the standard 200 (±5) grams CO2/kWh emission factor for combustion of natural gas at its net (low) calorific value. Gas cooking efficiencies may be lower if waste heat generation is taken into account. Especially in restaurants, gas cooking can significantly increase the ambient temperature in localized areas. Not only may extra cooling be required but zoned venting may be needed to adequately condition hot areas without overcooling other areas. Costs must be considered on an individual situation due to numerous variables in temperature differences, facility layout or openness, and heat generation schedule. Induction cooking using grid electricity may surpass gas efficiencies when waste heat and air comfort are quantified. |
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Design
An induction cooker transfers electrical energy by induction from a coil of wire into a metal vessel that must be ferromagnetic. The coil is mounted under the cooking surface, and a large alternating current is passed through it. The current creates a dynamic magnetic field. When an electrically conductive pot is brought close to the cooking surface, the magnetic field induces eddy currents in the pot. The eddy currents flow through the electrical resistance of the pot to produce heat; the pot then in turn heats its contents by heat conduction.
Standard vs Induction Cooktops
In this video we compare a standard cooktop with a Induction Cooktops by testing the time it takes to boil water and then cool down again.