Electric heating
Electric heating is a process in which
Alternatively, a
Space heating
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Space heating is used to warm the interiors of buildings. Space heaters are useful in places where air-handling is difficult, such as in laboratories. Several methods of electric space heating are used.
Infrared radiant heaters
Electric
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
Convection heaters
Natural convection
In a convection heater, the heating element heats the air in contact with it by thermal conduction. Hot air is less dense than cool air, so it rises due to buoyancy, allowing more cool air to flow in to take its place. This sets up a convection current of hot air that rises from the heater, heats up the surrounding space, cools and then repeats the cycle. These heaters are sometimes filled with oil or thermal fluid. They are ideally suited for heating a closed space. They operate silently and have a lower risk of ignition hazard if they make unintended contact with furnishings compared to radiant electric heaters.
Forced convection
A fan heater, also called a forced convection heater, is a kind of convection heater that includes an
Storage heating
A storage heating system takes advantage of cheaper electricity prices, sold during low demand periods such as overnight. In the United Kingdom, this is branded as Economy 7. The storage heater stores heat in clay bricks, then releases it during the day when required. Newer storage heaters are able to be used with various tariffs. Whilst they can still be used with economy 7, they can be used with day-time tariffs. This is due to the modern design features that are added during manufacturing. Alongside new designs the use of a thermostat or sensor has improved the efficiency of the storage heater. A thermostat or sensor is able to read the temperature of the room, and change the output of the heater accordingly.
Water can also be used as a heat-storage medium.
Domestic electrical underfloor heating
An electric
Lighting system
In large office towers, the lighting system is integrated along with the heating and ventilation system.
Heat pumps
A heat pump uses an electrically driven compressor to operate a refrigeration cycle that extracts heat energy from outdoor air, the ground or ground water, and moves that heat to the space to be warmed. A liquid contained within the evaporator section of the heat pump boils at low pressure, absorbing heat energy from the outdoor air or the ground. The vapor is then compressed by a compressor and piped into a condenser coil within the building to be heated. The heat from the hot dense gas is absorbed by the air in the building (and sometimes also used for domestic hot water) causing the hot working fluid to condense back into a liquid. From there the high pressure fluid is passed back to the evaporator section where it expands through an orifice and into the evaporator section, completing the cycle. In the summer months, the cycle can be reversed to move heat out of the conditioned space and to the outside air.
Heat pumps may obtain low-grade heat from the outdoor air in mild climates. In areas with average winter temperatures well below freezing,
Liquid heating
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Immersion heater
An immersion heater has an electrical resistance heating element encased in a tube, placed in the water (or other fluid) to be heated. The heating element might be inserted directly into the liquid, or installed inside a metal pipe to protect against corrosion and facilitate maintenance. Portable immersion heaters may not have a control thermostat, since they are intended to be used only briefly and under control of an operator.
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.[5]
Circulation heaters
Circulation heaters or "direct electric heat exchangers" (DEHE) use heating elements inserted into a "shell side" medium directly to provide the heating effect. All of the heat generated by the electric circulation heater is transferred into the medium, thus an electric heater is 100 percent efficient. Direct electric heat exchangers or "circulation heaters" are used to heat liquids and gases in industrial processes.[6][7]
Electrode heater
With an electrode heater, there is no wire-wound resistance and the liquid itself acts as the resistance. This has potential hazards, so the regulations governing electrode heaters are strict.
Environmental and efficiency aspects
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The efficiency of any system depends on the definition of the boundaries of the system. For an electrical energy customer the efficiency of electric space heating is 100% because all purchased energy is converted to heat. However, if a
Variations between countries generating electrical power affect concerns about efficiency and the environment. In 2015 France generated only 6% of its electricity from
In
In
In recent years there has been a major trend for countries to generate low-carbon electricity from renewable sources, adding to
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.[12] 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
Economic aspects
The operation of electric resistance heaters to heat an area for long periods is costly in many regions. However, intermittent or partial day use can be more cost efficient than whole building heating due to superior zonal control.
For example: A lunch room in an office setting has limited hours of operation. During low-use periods a "monitor" level of heat (50 °F or 10 °C) is provided by the central heating system. Peak use times between the hours of 11:00 and 14:00 are heated to "comfort levels" (70 °F or 21 °C). 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.
Industrial electric heating
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Electric heating is widely used in industry.[15]
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 400 °C or 752 °F), medium-temperature (between 400 and 1,150 °C or 752 and 2,102 °F), and high-temperature (beyond 1,150 °C or 2,102 °F). 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.
See also
- Auxiliary power unit
- Central heating
- Diathermy
- Dielectric heating
- Electroslag welding
- Electroslag remelting
- Energy conservation
- Head-end power
- Heater(types of heaters)
- Heating, ventilation, and air conditioning
- Hotel electric power
- Infrared heater
- Microwave oven
- Renewable energy
- Thermal efficiency
- Thermal immersion circulator
- Underfloor heating
References
- ^ "Electric Heater". Britannica.com. The Editors of Encyclopædia Britannica.
- ^ "Energy Efficient Lighting | WBDG Whole Building Design Guide". www.wbdg.org. Retrieved 18 December 2017.
- ^ "Comparison of efficiency of air source heat pumps and ground source heat pumps". Icax.co.uk. Retrieved 20 December 2013.
- ^ "Choosing and Installing Geothermal Heat Pumps - Department of Energy". Energy.gov. Retrieved 16 April 2017.
- ^ "Immersion Heaters - Sigma Thermal". Sigma Thermal. Retrieved 18 December 2017.
- ^ "Gastech News". 12 August 2012. Archived from the original on 22 February 2017.
- ^ "Electric Resistance Heating - Department of Energy". Energy.gov. Retrieved 16 April 2017.
- ^ ISBN 978-0-08-102536-9.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - ^ Hannah Ritchie and Max Roser (2020) - "Fossil Fuels". Published online at OurWorldInData.org. Retrieved from: '[1]; retrieved 2020-05-23
- ^ The Green Electricity Illusion, AECB, published 2005-11-11, accessed 26 May 2007
- ^ Snider, Bradley. Home heating and the environment, in Canadian Social Trends, Spring 2006, pp. 15–19. Ottawa: Statistics Canada.
- ^ "Ground-Source Heat Pumps (Earth-Energy Systems)". NRCan.gc.ca. Archived from the original on 16 April 2017. Retrieved 16 April 2017.
- S2CID 214266085.
- ^ "How to calculate electric energy cost of common household items - McGill's Repair and Construction, LLC". McGill's Repair and Construction, LLC. 19 January 2014. Retrieved 18 December 2017.
- ISBN 0-07-020974-X, pages 21-144 to 21-188