Electric heating is any process in which electrical energy is converted to heat. Common applications include heating of buildings, cooking, and industrial processes.
An electric heater is an electrical appliance that converts electrical energy into heat. Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature The heating element inside every electric heater is simply an electrical resistor, and works on the principle of Joule heating: an electric current flowing through a resistor converts electrical energy into heat energy. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | Joule heating is the process by which the passage of an Electric current through a conductor releases Heat. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere.
A heat pump uses an electric motor to drive a refrigeration cycle, drawing heat from a source such as ground water or outside air and directing it into the space to be warmed. A heat pump is a machine or device that moves Heat from one location (the 'source' to another location (the 'sink' or 'heat sink' using work. Such systems can deliver two or three units of heating energy for every unit of purchased energy.
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Design variations
Although they all use the same physical principle to generate heat, electric heaters differ in the way they deliver that heat to the environment. Several types are described in the sections below.
Radiative heaters or "space heaters"
Radiative heaters 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 incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general 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. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of 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.
They operate silently. Radiant heaters present the greatest potential danger to ignite nearby furnishings due to the focused intensity of their output and lack of overheat protection.
Convection heaters
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In a convection heater, the heating element heats the air next to it by conduction. A convector heater is a Heater which operates by air Convection currents circulating through the body of the appliance and across its Heating element. Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower 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. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is 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.
In the United Kingdom, these appliances are sometimes called electric fires, because they were originally used to replace open fires. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located
Fan heaters or "forced convection heaters"
A fan heater is a variety of convection heater that includes an electric fan to speed up the airflow. A fan heater is a heater that works by using a fan to pass air over a Heating element. A mechanical fan is an electrically powered device used to produce an airflow for the purpose of creature comfort (particularly in the heat ventilation, exhaust This reduces the thermal resistance between the heating element and the surroundings, allowing heat to be transferred more quickly. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat.
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; however, they should not be left unattended.
Storage heating
A storage heating system takes advantage of cheaper electricity prices, sold during low demand periods such as overnight. A storage heater is an electrical Appliance which stores Heat at a time when Base load electricity is available at a low price usually during the night In the United Kingdom, this is branded as Economy 7. Economy 7 is the name of a tariff provided by United Kingdom Electricity suppliers that uses Base load generation to provide cheap night-time electricity The storage heater stores heat in clay bricks, then releases it during the day when required. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and
Domestic electrical underfloor heating
These systems are called radiant heating systems, regardless of whether they include a heat exchanger (also called a radiator) or are electrically powered. Underfloor heating is a form of Central heating which utilizes Heat conduction and Radiant heat for indoor climate control, rather than forced A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media Radiators and convectors are types of Heat exchangers designed to transfer Thermal energy from one medium to another for the purpose of cooling
When a home radiant heat system is turned on, current flows through a conductive heating material. In Science and engineering, a conductor is a material which contains movable Electric charges. For high-voltage radiant heat systems, line voltage (110 V or 230 V) current flows through the heating cable. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical For low-voltage systems, the line voltage is converted to 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. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors
The heated material then heats the flooring until it reaches the right temperature set by the floor thermostat. A thermostat is a device for regulating the Temperature of a System so that the system's temperature is maintained near a desired setpoint The flooring then heats the adjacent air, which circulates, heating other objects in the room (tables, chairs, people) by convection. Convection in the most general terms refers to the movement of molecules within Fluids (i 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.
Immersion heater
Water heating by electricity is usually done by an immersion heater. Water heating is a thermodynamic process using an energy source to heat Water above its initial Temperature. This consists of a metal tube containing an insulated electric resistance heater. Domestic immersion heaters (usually rated at 3 kilowatts in the UK) run on the normal domestic electricity supply. Industrial immersion heaters (such as those used in electric steam boilers) may be rated at 100 kilowatts, or more, and run on a three-phase supply. Electric steam boilers are used to generate steam for process purposes in many locations e This article deals with the basic mathematics and principles of three-phase electricity
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 [1].
Environmental and efficiency aspects
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 can be 100% because all purchased energy is converted to building heat. However, 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 electical 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. A furnace is a device used for Heating The name derives from Latin fornax, Oven. A boiler is a closed vessel in which Water or other Fluid is 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. Not all fuels are suitable for building heating; for example, emissions controls required for coal combustion are too expensive for household-scale furnaces.
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. "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. In 2005 the Government of Sweden announced their intention to make Sweden the first country to break its dependence on Petroleum, Natural gas The Kingdom of Denmark ( ˈd̥ænmɑɡ̊ (archaic ˈd̥anmɑːɡ̊ commonly known as Denmark, is a country in the Scandinavian region of northern Europe [2] 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 Passive House standard. Generically a low-energy house is any type of house that uses less energy than a regular house The term passive house ( Passivhaus in German) refers to the rigorous voluntary Passivhaus standard for energy use in buildings
In order to use electricity to provide heat efficiently, a heat pump driven by electricity can boost the temperature of the heat in the ground, in the outside air, or in waste streams such as exhaust air in order to use it as a heat source. A heat pump is a machine or device that moves Heat from one location (the 'source' to another location (the 'sink' or 'heat sink' using work. This can cut the electricity consumption down to as little as 20% and can reduce the environmental impact.
Electrical space heating can still be economic where electicity 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.
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 since there savings 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 °C). Significant savings can be realized in overall energy consumption since infrared radiation losses through thermal conductivity 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. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat.
Mathematical analysis
According to Joule's Law, the heat power produced by a resistor is:
- P = IV
where
and according to Ohm's Law I and V are related as follows:
- V = IR
where
- R is the resistance of the heating element, in ohms. Joule's laws are a pair of laws concerning the heat produced by a current and the energy dependence of an Ideal gas to that of pressure volume and temperature respectively The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. Ohm's law applies to Electrical circuits it states that the current through a conductor between two points is directly proportional to the The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance,
We can combine these two formulae to obtain the heat output from the heating element in terms of either current or voltage: 
For heaters powered by AC mains, I and V are the root mean square (RMS) values of current and voltage. In Mathematics, the root mean square (abbreviated RMS or rms) also known as the quadratic mean, is a statistical measure of the
Industrial electric heating
See also Induction furnace, Electric arc furnace
See also
References
- ^ http://www.tlc-direct.co.uk/Book/7.11.2.htm
- ^ The Green Electricity Illusion, AECB, published 2005-11-11, accessed 2007-05-26
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