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Electric heating is a process in which electrical energy is converted directly to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electricity device that converts an electric current into heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy. Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators.
Alternatively, a heat pump can achieve around 150% – 600% efficiency for heating, or COP 1.5 - 6.0 Coefficient of performance, because it uses electric power only for transferring existing thermal energy. The heat pump uses an electric motor to drive a reversed refrigeration cycle, that draws heat energy from an external source such as the ground or outside air (or the interior of a refrigerator) and directs that heat into the space to be warmed (in case of a fridge, the kitchen). This makes much better use of electric energy than direct electric heating, but requires much more expensive equipment, plus plumbing. Some heating systems can be operated in reverse for air conditioning so that the interior space is cooled and even hotter air or water is discharged outside or into the ground.
Radiant heaters operate silently and present the greatest potential danger of ignition of nearby furnishings due to the focused intensity of their output and lack of overheat protection. In the United Kingdom, these appliances are sometimes called electric fires, because they were originally used to replace open fires.
The active medium of the heater depicted in this section is a coil of nichrome resistance wire inside a fused silica tube, open to the atmosphere at the ends, although models exist where the fused silica is sealed at the ends and the resistance alloy is not nichrome.
Water can also be used as a heat-storage medium.
Heat pumps may obtain low-grade heat from the outdoor air in mild climates. In areas with average winter temperatures well below freezing, ground source heat pumps are more efficient than air source heat pumps because they can extract residual solar heat stored in the ground at warmer temperatures than is available from cold air. According to the US EPA, geothermal heat pumps can reduce energy consumption up to 44% compared with air source heat pumps and up to 72% compared with electric resistance heating. The high purchase price of a heat pump vs resistance heaters may be offset when air conditioning is also needed.
For domestic hot water supply, or industrial process hot water, permanently installed heating elements in an insulated hot water tank may be used, controlled by a thermostat to regulate temperature. Household units may be rated only a few kilowatts. Industrial water heaters may reach 2000 kilowatts. Where off-peak electric power rates are available, hot water may be stored to use when required.
Minerals present in the water supply may precipitate out of solution and form a hard scale on the heating element surface, or may fall to the bottom of the tank and clog water flow. Maintenance of water heating equipment may require periodic removal of accumulated scale and sediment. Where water supplies are known to be highly mineralized, scale production can be reduced by using low-watt-density heating elements.
Variations between countries generating electrical power affect concerns about efficiency and the environment. In 2015 France generated only 6% of its electricity from fossil fuels, while Australia sourced over 86% of its electricity from fossil fuels.Hannah Ritchie and Max Roser (2020) - "Fossil Fuels". Published online at OurWorldInData.org. Retrieved from: '
target="_blank" rel="nofollow">[1]; retrieved 2020-05-23 The cleanliness and efficiency of electricity are dependent on the source.
In Sweden the use of direct electric heating has been restricted since the 1980s for this reason, and there are plans to phase it out entirely – see Oil phase-out in Sweden – while Denmark has banned the installation of direct electric space heating in new buildings for similar reasons. The Green Electricity Illusion, AECB, published 2005-11-11, accessed 26 May 2007 In the case of new buildings, low-energy building techniques can be used which can virtually eliminate the need for heating, such as those built to the Passivhaus standard.
In Quebec, however, electric heating is still the most popular form of home heating. According to a 2003 Statistics Canada survey, 68% of households in the province use electricity for space heating. More than 90% of all power consumed in Quebec is generated by hydroelectric dams, which have low greenhouse gases emissions compared to fossil-fuel power stations. Low and stable rates are charged by Hydro-Québec, the provincially owned utility.Snider, Bradley. Home heating and the environment, in Canadian Social Trends, Spring 2006, pp. 15–19. Ottawa: Statistics Canada.
In recent years there has been a major trend for countries to generate low-carbon electricity from renewable sources, adding to nuclear power and hydro-electric power which are long-standing low-carbon sources. For example, the carbon footprint of UK electricity per kWh in 2019 was less than half that in 2010. However, because of high capital cost, the cost of electricity has not fallen and is typically 2-3 times that of burning fuel. Hence, direct electric heating may now give a similar carbon footprint to gas- or oil-fired heating, but the cost remains higher, though cheaper off-peak tariffs can reduce this effect.
To provide heat more efficiently, an electrically driven heat pump can raise the indoor temperature by extracting energy from the ground, the outside air, or waste streams such as exhaust air. This can cut the electricity consumption to as little as 35% of that used by resistive heating. Where the primary source of electrical energy is hydroelectric, nuclear, or wind, transferring electricity via the grid can be convenient, since the resource may be too distant for direct heating applications (with the notable exception of solar thermal energy).
The electrification of heat of space and water heating is increasingly proposed as a way forward to decarbonise the current energy system, particularly with heat pumps. In case of large-scale electrification, impacts on the electricity grid due to potential increase in peak electricity demand and exposure to extreme weather events needs to be considered.
For example: A lunch room in an office setting has limited hours of operation. During low-use periods a "monitor" level of heat () is provided by the central heating system. Peak use times between the hours of 11:00 and 14:00 are heated to "comfort levels" (). Significant savings can be realized in overall energy consumption, since infrared radiation losses through thermal radiation are not as large with a smaller temperature gradient both between this space and unheated outside air, as well as between the refrigerator and the (now cooler) lunch room.
Economically, electric heat can be compared to other sources of home heating by multiplying the local cost per kilowatt hour for electricity by the number of kilowatts the heater uses. E.g.: 1500-watt heater at 12 cents per kilowatt hour 1.5×12=18 cents per hour. When comparing to burning fuel it may be useful to convert kilowatt hours to : 1.5 kWh × 3412.142=5118 BTU.
Advantages of electric heating methods over other forms include precision control of temperature and distribution of heat energy, combustion not used to develop heat, and the ability to attain temperatures not readily achievable with chemical combustion. Electric heat can be accurately applied at the precise point needed in a process, at high concentration of power per unit area or volume. Electric heating devices can be built in any required size and can be located anywhere within a plant. Electric heating processes are generally clean, quiet, and do not emit much byproduct heat to the surroundings. Electrical heating equipment has a high speed of response, lending it to rapid-cycling mass-production equipment.
The limitations and disadvantages of electric heating in industry include the higher cost of electrical energy compared to direct use of fuel, and the capital cost of both the electric heating apparatus itself and the infrastructure required to deliver large quantities of electrical energy to the point of use. This may be somewhat offset by in-plant (on-site) efficiency gains in using less energy overall to achieve the same result.
Design of an industrial heating system starts with assessment of the temperature required, the amount of heat required, and the feasible modes of transferring heat energy. In addition to conduction, convection and radiation, electrical heating methods can use electric and magnetic fields to heat material.
Methods of electric heating include resistance heating, electric arc heating, induction heating, and dielectric heating. In some processes (for example, arc welding), electric current is directly applied to the workpiece. In other processes, heat is produced within the workpiece by induction or dielectric losses. As well, heat can be produced then transferred to the work by conduction, convection or radiation.
Industrial heating processes can be broadly categorized as low-temperature (to about ), medium-temperature (between ), and high-temperature (beyond ). Low-temperature processes include baking and drying, curing finishes, soldering, molding and shaping plastics. Medium temperature processes include melting plastics and some non-metals for casting or reshaping, as well as annealing, stress-relieving and heat-treating metals. High-temperature processes include steelmaking, brazing, welding, casting metals, cutting, smelting and the preparation of some chemicals.
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