Electric heating
Encyclopedia
Electric heating is any process in which electrical energy is converted to heat
. Common applications include space heating
, cooking
, water heating
and industrial processes. An electric heater is an electrical
appliance
that converts electrical energy into heat. The heating element
inside every electric heater is simply an electrical resistor
, and works on the principle of Joule heating
: an electric current
through a resistor converts electrical energy into heat energy.
Alternatively, a heat pump
uses an electric motor
to drive a refrigeration cycle, drawing energy from a source such as the ground or outside air and directing it into the space to be warmed. Some systems can be reversed so that the interior space is cooled and the warm air is discharged outside or into the ground. Heat pumps can deliver two or three units of heating energy for every unit of electricity purchased. For a detailed explanation of heat pumps please see Carnot cycle
.
contain a heating element that reaches a high temperature. The element is usually packaged inside a glass
envelope resembling a light bulb and with a reflector to direct the energy output away from the body of the heater. The element emits infrared radiation that travels through air or space until it hits an absorbing surface, where it is partially converted to heat and partially reflected. This heat directly warms people and objects in the room, rather than warming the air. This style of heater is particularly useful in areas which unheated air flows through. They are also ideal for basements and garages where spot heating is desired. More generally, they are an excellent choice for task-specific heating.
Radiative heaters operate silently and present the greatest potential danger to ignite 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.
than cool air, so it rises due to buoyancy
, allowing more cool air to flow in to take its place. This sets up a constant current of hot air that leaves the appliance through vent holes and heats up the surrounding space. They are ideally suited for heating a closed space. They operate silently and have a lower risk of ignition hazard in the event that they make unintended contact with furnishings compared to radiant electric heaters. This is a good choice for long periods of time or if left unattended. They are very safe heaters and there is a very low chance of getting burned.
to speed up the airflow. This reduces the thermal resistance between the heating element and the surroundings faster than passive convection, allowing heat to be transferred more quickly.
They operate with considerable noise caused by the fan. They have a moderate risk of ignition hazard in the event that they make unintended contact with furnishings. This type of heater is a good choice for quick heating of enclosed spaces.
(also called a radiator
) or are electrically powered.
When a home radiant heat system is turned on, current flows through a conductive heating material. For high-voltage
radiant heat systems, line voltage (110 V or 230 V) current flows through the heating cable. For low-voltage systems, the line voltage is converted to extra low voltage (8 to 30 V) in the control unit (which contains a step-down transformer
) and this low voltage is then applied to the heating element.
The heated material then heats the flooring until it reaches the right temperature set by the floor thermostat
. The flooring then heats the adjacent air, which circulates, heating other objects in the room (tables, chairs, people) by convection
. As it rises, the heated air will heat the room and all its contents up to the ceiling. This form of heating gives the most consistent room temperature from floor to ceiling compared to any other heating system.
by electricity is usually done by an immersion heater mounted in the top of the hot water cylinder. The heater contains an insulated electric resistance heater and a temperature sensor. Domestic immersion heaters (usually rated at 3 kilowatts in the UK) run on the normal domestic electricity supply.
Electric shower and tankless heater also use a immersion heater shielded or naked which is turned on by the water passing and turned off when the tap is closed. A group of heaters working each one or together provide different heating levels. Electric showers and tankless heaters usually have since 3 kilowatts to 7.5 kilowatts according the voltage supply. Industrial immersion heaters (such as those used in electric steam boiler
s) may be rated at 100 kilowatts, or more, and run on a three-phase
supply.
. While it is true that electrical heating loses very little energy to other sources such as chemical reactions, as is the case with oil or gas heating, the system is limited by the temperature difference being created. A more detailed explanation can be found on thermodynamics
or the Carnot cycle.
Apart from the theoretical aspects, one can assume if the power plant supplying electricity is included, the overall efficiency drops. For example, a fossil-fuelled power plant may only deliver 4 units of electrical energy for every 10 units of fuel energy released. Even with a 100% efficient electric heater, the amount of fuel needed for a given amount of heat is more than if the fuel was burned in a furnace or boiler at the building being heated. If the same fuel could be used for space heating by a consumer, it would be more efficient overall to burn the fuel at the end user's building.
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 electric space heating in new buildings for similar reasons.
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 uses electricity for space heating. This can be explained by the fact that more than 90% of all power consumed in Quebec is generated by hydroelectric dams, which have lower greenhouse gases emissions than thermal power station
s and the low and stable rates charged by Hydro-Québec
, the provincially-owned utility.
In order 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 20% of that used by resistive heating and thus reduce the environmental impact.
Electrical space heating can still be economic where electricity supplies are low-cost. Where the primary source of electrical energy is hydroelectric, nuclear, wind, or other carbon-free source, it may not be practical to exploit that resource directly in heating applications but grid electricity can be conveniently used. Electric space heating is useful in places where air-handling is difficult, such as in laboratories.
Doctors recommend electrical space heating for families with a member suffering from multiple chemical sensitivity
, because electricity is the only form of domestic energy that is totally free from indoor domestic pollution. Patients suffering from multiple chemical sensitivity react severely to the very small amounts of indoor pollution coming from any heater using fossil fuels, which are otherwise neutral for healthy people.
Example: A lunch room in an office setting has limited hours of operation. During low use periods a "monitor" level of heat (50 °F (10 °C)) is provided by the central heating system. Peak use times between the hours of 11:00–14:00 are heated to "comfort levels" (70 °F (21.1 °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 cost per kilowatt hour by the number of kilowatts the heater uses.
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 apparatus 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 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 (730 °F)), medium temperature (between 400 °C and 1150 °C (730-2100 °F)), and high temperature (beyond 1150 °C (2100 °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.
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
. Common applications include space heating
Space heating
A space heater is a self-contained device for heating an enclosed area. Space heating is generally employed to warm a small space, and is usually held in contrast with central heating, which warms many connected spaces at once...
, cooking
Cooking
Cooking is the process of preparing food by use of heat. Cooking techniques and ingredients vary widely across the world, reflecting unique environmental, economic, and cultural traditions. Cooks themselves also vary widely in skill and training...
, water heating
Water heating
Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating...
and industrial processes. An electric heater is an electrical
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
appliance
Major appliance
A major appliance, or domestic appliance, is usually defined as a large machine which accomplishes some routine housekeeping task, which includes purposes such as cooking, or food preservation, whether in a household, institutional, commercial or industrial setting...
that converts electrical energy into heat. The heating element
Heating element
A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element....
inside every electric heater is simply an electrical resistor
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
, and works on the principle of Joule heating
Joule heating
Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. It was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature...
: an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
through a resistor converts electrical energy into heat energy.
Alternatively, a heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
uses an electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
to drive a refrigeration cycle, drawing energy from a source such as the ground or outside air and directing it into the space to be warmed. Some systems can be reversed so that the interior space is cooled and the warm air is discharged outside or into the ground. Heat pumps can deliver two or three units of heating energy for every unit of electricity purchased. For a detailed explanation of heat pumps please see Carnot cycle
Carnot cycle
The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot in 1824 and expanded by Benoit Paul Émile Clapeyron in the 1830s and 40s. It can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work, or conversely,...
.
Space heating
Although they all use the same physical principle to generate heat, electric heaters differ in the way they deliver that hot air to the environment. Several types are described in the sections below.Radiative heaters
Radiative heatersRadiator (heating)
Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating. The heating radiator was invented by Franz San Galli, a Prussian-born Russian businessman living in St. Petersburg, between 1855–1857.- Radiation vs...
contain a heating element that reaches a high temperature. The element is usually packaged inside a glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
envelope resembling a light bulb and with a reflector to direct the energy output away from the body of the heater. The element emits infrared radiation that travels through air or space until it hits an absorbing surface, where it is partially converted to heat and partially reflected. This heat directly warms people and objects in the room, rather than warming the air. This style of heater is particularly useful in areas which unheated air flows through. They are also ideal for basements and garages where spot heating is desired. More generally, they are an excellent choice for task-specific heating.
Radiative heaters operate silently and present the greatest potential danger to ignite 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.
Convection heaters
In a convection heater, the heating element heats the air next to it by convection. Hot air is less denseDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
than cool air, so it rises due to buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
, allowing more cool air to flow in to take its place. This sets up a constant current of hot air that leaves the appliance through vent holes and heats up the surrounding space. They are ideally suited for heating a closed space. They operate silently and have a lower risk of ignition hazard in the event that they make unintended contact with furnishings compared to radiant electric heaters. This is a good choice for long periods of time or if left unattended. They are very safe heaters and there is a very low chance of getting burned.
Fan heaters
A fan heater, also called a forced convection heater, is a variety of convection heater that includes an electric fanFan (mechanical)
A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing...
to speed up the airflow. This reduces the thermal resistance between the heating element and the surroundings faster than passive convection, allowing heat to be transferred more quickly.
They operate with considerable noise caused by the fan. They have a moderate risk of ignition hazard in the event that they make unintended contact with furnishings. This type of heater is a good choice for quick heating of enclosed spaces.
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.Domestic electrical underfloor heating
These systems are called radiant heating systems, regardless of whether they include a heat exchangerHeat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
(also called a radiator
Radiator
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...
) or are electrically powered.
When a home radiant heat system is turned on, current flows through a conductive heating material. For high-voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
radiant heat systems, line voltage (110 V or 230 V) current flows through the heating cable. For low-voltage systems, the line voltage is converted to extra low voltage (8 to 30 V) in the control unit (which contains a step-down transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
) and this low voltage is then applied to the heating element.
The heated material then heats the flooring until it reaches the right temperature set by the floor thermostat
Thermostat
A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...
. The flooring then heats the adjacent air, which circulates, heating other objects in the room (tables, chairs, people) by convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. As it rises, the heated air will heat the room and all its contents up to the ceiling. This form of heating gives the most consistent room temperature from floor to ceiling compared to any other heating system.
Heat pumps
A heat pump uses an electrically-driven compressor to operate a refrigeration cycle that extracts heat energy from the outdoor air or from the ground or ground water, and upgrades its temperature to a level high enough to use for space heating. The working fluid boils at a low temperature, absorbing heat in an outdoor heat exchanger, then the resulting vapor is compressed and condenses to liquid form in a condensor inside the building. Heat from the condensor is absorbed by the air in the building (and sometimes also used for domestic hot water). In the summer months the cycle can be reversed to provide air conditioning. 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 extract residual heat stored in the ground at a more constant temperature.Immersion heater
Water heatingWater heating
Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating...
by electricity is usually done by an immersion heater mounted in the top of the hot water cylinder. The heater contains an insulated electric resistance heater and a temperature sensor. Domestic immersion heaters (usually rated at 3 kilowatts in the UK) run on the normal domestic electricity supply.
Electric shower and tankless heater also use a immersion heater shielded or naked which is turned on by the water passing and turned off when the tap is closed. A group of heaters working each one or together provide different heating levels. Electric showers and tankless heaters usually have since 3 kilowatts to 7.5 kilowatts according the voltage supply. Industrial immersion heaters (such as those used in electric steam boiler
Electric steam boiler
An electric steam boiler is a type of boiler where the steam is generated using electricity, rather than through the combustion of a fuel source. They are used to generate steam for process purposes in many locations, for example laundries, food processing factories and hospitals...
s) may be rated at 100 kilowatts, or more, and run on a three-phase
Three-phase
In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are radians offset in time...
supply.
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
The electrical energy is converted into work known as heating and creates an energy difference, either heating or cooling. The overall efficiency of any heating or cooling system is given by the Carnot cycleCarnot cycle
The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot in 1824 and expanded by Benoit Paul Émile Clapeyron in the 1830s and 40s. It can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work, or conversely,...
. While it is true that electrical heating loses very little energy to other sources such as chemical reactions, as is the case with oil or gas heating, the system is limited by the temperature difference being created. A more detailed explanation can be found on thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
or the Carnot cycle.
Apart from the theoretical aspects, one can assume if the power plant supplying electricity is included, the overall efficiency drops. For example, a fossil-fuelled power plant may only deliver 4 units of electrical energy for every 10 units of fuel energy released. Even with a 100% efficient electric heater, the amount of fuel needed for a given amount of heat is more than if the fuel was burned in a furnace or boiler at the building being heated. If the same fuel could be used for space heating by a consumer, it would be more efficient overall to burn the fuel at the end user's building.
In Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
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
Oil phase-out in Sweden
In 2005 the government of Sweden appointed a commission to draw up a comprehensive programme to reduce Sweden's dependence on petroleum, natural gas and other ‘fossil raw materials’ by 2020. In June 2006 the commission issued its report, entitled Making Sweden an OIL-FREE Society...
- while Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
has banned the installation of electric space heating in new buildings for similar reasons.
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
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
however, electric heating is still the most popular form of home heating. According to a 2003 Statistics Canada
Statistics Canada
Statistics Canada is the Canadian federal government agency commissioned with producing statistics to help better understand Canada, its population, resources, economy, society, and culture. Its headquarters is in Ottawa....
survey, 68% of households in the province uses electricity for space heating. This can be explained by the fact that more than 90% of all power consumed in Quebec is generated by hydroelectric dams, which have lower greenhouse gases emissions than thermal power station
Thermal power station
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this...
s and the low and stable rates charged by Hydro-Québec
Hydro-Québec
Hydro-Québec is a government-owned public utility established in 1944 by the Government of Quebec. Based in Montreal, the company is in charge of the generation, transmission and distribution of electricity across Quebec....
, the provincially-owned utility.
In order to provide heat more efficiently, an electrically driven heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
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 20% of that used by resistive heating and thus reduce the environmental impact.
Electrical space heating can still be economic where electricity supplies are low-cost. Where the primary source of electrical energy is hydroelectric, nuclear, wind, or other carbon-free source, it may not be practical to exploit that resource directly in heating applications but grid electricity can be conveniently used. Electric space heating is useful in places where air-handling is difficult, such as in laboratories.
Doctors recommend electrical space heating for families with a member suffering from multiple chemical sensitivity
Multiple chemical sensitivity
Multiple chemical sensitivity is a chronic medical condition characterized by symptoms the affected person attributes to exposure to low levels of chemicals. Commonly suspected substances include smoke, pesticides, plastics, synthetic fabrics, scented products, petroleum products and paints...
, because electricity is the only form of domestic energy that is totally free from indoor domestic pollution. Patients suffering from multiple chemical sensitivity react severely to the very small amounts of indoor pollution coming from any heater using fossil fuels, which are otherwise neutral for healthy people.
Economic aspects
The operation of electric resistance heaters to heat an area for a long period of time is generally considered to be costly. However, intermittent or partial day use can be more cost efficient than whole building heating due to superior zonal control.Example: A lunch room in an office setting has limited hours of operation. During low use periods a "monitor" level of heat (50 °F (10 °C)) is provided by the central heating system. Peak use times between the hours of 11:00–14:00 are heated to "comfort levels" (70 °F (21.1 °C)). Significant savings can be realized in overall energy consumption since infrared radiation losses through thermal radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits 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 cost per kilowatt hour by the number of kilowatts the heater uses.
Industrial electric heating
Electric heating is widely used in industry.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 apparatus 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 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
Arc welding
Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...
), electric current is directly applied to the workpiece. In other processes, heat is produced within the workpiece by induction or dielectric losses
Dielectric heating
Dielectric heating, also known as electronic heating, RF heating, high-frequency heating and diathermy, is the process in which a high-frequency alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is...
. 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 (730 °F)), medium temperature (between 400 °C and 1150 °C (730-2100 °F)), and high temperature (beyond 1150 °C (2100 °F)). Low temperature processes include, baking
Baking
Baking is the technique of prolonged cooking of food by dry heat acting by convection, and not by radiation, normally in an oven, but also in hot ashes, or on hot stones. It is primarily used for the preparation of bread, cakes, pastries and pies, tarts, quiches, cookies and crackers. Such items...
and drying, curing
Curing (chemistry)
Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat...
finishes
Surface finishing
Surface finishing is a broad range of industrial processes that alter the surface of a manufactured item to achieve a certain property. Finishing processes may be employed to: improve appearance, adhesion or wettability, solderability, corrosion resistance, tarnish resistance, chemical resistance,...
, soldering
Soldering
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...
, molding
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
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
Steelmaking
Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Older...
, brazing
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...
, welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
, casting
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
metals, cutting, smelting
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
and the preparation of some chemicals.
See also
- Central heatingCentral heatingA central heating system provides warmth to the whole interior of a building from one point to multiple rooms. When combined with other systems in order to control the building climate, the whole system may be a HVAC system.Central heating differs from local heating in that the heat generation...
- DiathermyDiathermyIn the natural sciences, the term diathermy means "electrically induced heat" and is commonly used for muscle relaxation. It is also a method of heating tissue electromagnetically or ultrasonically for therapeutic purposes in medicine.-Surgical uses:...
- Dielectric heatingDielectric heatingDielectric heating, also known as electronic heating, RF heating, high-frequency heating and diathermy, is the process in which a high-frequency alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is...
- Electroslag weldingElectroslag weldingElectroslag welding ' is a highly productive, single pass welding process for thick materials in a vertical or close to vertical position. is similar to electrogas welding, but the main difference is the arc starts in a different location...
- Electroslag remelting
- Energy conservationEnergy conservationEnergy conservation refers to efforts made to reduce energy consumption. Energy conservation can be achieved through increased efficient energy use, in conjunction with decreased energy consumption and/or reduced consumption from conventional energy sources...
- HeaterHeaterA heater is an object that emits heat or causes another body to achieve a higher temperature. In a household or domestic setting, heaters are usually appliances whose purpose is to generate heating...
(types of heaters) - HVACHVACHVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
- Infrared heaterInfrared heaterAn infrared heater is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the infrared radiation ranges from 780 nm to 1 mm. The relationship...
- Microwave ovenMicrowave ovenA microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
- Renewable energyRenewable energyRenewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...
- Thermal efficiencyThermal efficiencyIn thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...
- Thermal immersion circulatorThermal immersion circulatorA thermal immersion circulator is an electrically powered device that circulates and heats a warm fluid kept at an accurate and stable temperature. It is used in process, environmental, microbiological, hazardous waste, and other laboratories...
- Underfloor heatingUnderfloor heatingUnderfloor heating and cooling is a form of central heating and cooling which achieves indoor climate control for thermal comfort using conduction, radiation and convection...