Does the electric heater really have a high resistance
Lexicon> Letter E> Electric heating
Definition: heat generated from electrical energy
More general term: heat
English: electric heat
Categories: electrical energy, heating and cooling
Author: Dr. Rüdiger Paschotta
How to quote; suggest additional literature
Original creation: December 15, 2013; last change: 10/17/2020
If heat is generated directly from electrical energy, it is called electric heat.
In many cases, electrical heat is generated by allowing an electrical current to flow through a conductor with electrical resistance. This principle of Resistance heating comes z. B. used in electric heating rods, also in electric water heaters, heating elements of coffee machines, electric radiant heaters and electrode boilers. Systems for inductive heating (e.g. industrial induction ovens and induction hobs) also work according to this principle, except that the energy is transferred without contact by an oscillating magnetic field. In electric welding and in arc furnaces there is also resistance heating, the resistive conductor being a plasma (ionized gas). Another variant is the electrode boiler, in which electrical current flows directly through water.
In other cases, the electrical energy is first converted into another form of energy, from which heat is then generated. This applies, for example, to microwave ovens, where microwave radiation is first generated, which then z. B. is absorbed by food and thus converted into heat. Another example are infrared emitters, in which the energy is transmitted as infrared light (thermal radiation).
Heat can also be generated with an electric heat pump. Here, however, most of the heat generated comes from another heat source, which is why one usually no longer speaks of electric heat.
Benefits of electric heating
The generation of electrical heat has various advantages, which are more or less effective depending on the purpose:
- Electric heat can be used in a very targeted manner in terms of space and time. B. can be introduced with a small heating element where it is needed, and can be easily switched on and off or the power can be regulated.
- Electric heat enables very high temperatures - often limited only by the resistance of the materials used.
- It is often possible, even at very high temperatures, to apply the heat with almost no loss.
- The technology required for electrical heat generation can usually be implemented very cost-effectively in a very wide range of services.
When evaluating the energy efficiency of electrical heating, various aspects must be taken into account:Is electric heating an efficient solution? It depends on the circumstances!
- The efficiency of the energy conversion is 100%, regardless of the temperature, and because electric heating elements can be very compact and do not require an exhaust pipe through which exhaust gas losses could occur, often little or nothing of the heat generated is lost directly.
- On the other hand, electrical energy is a high-quality form of energy, the generation of which is often a multiple z. B. requires heat - see the article on thermal power plants.
- It must be considered in each case which alternatives may be available.
For some applications, electric heating is ideal, without its disadvantages being important:
- Small amounts of hot water can thus be produced in a relatively targeted and efficient manner, for example for use in a coffee machine; There is hardly an attractive alternative for this.
- A small electric infrared heater can supplement the basic heating in a bathroom in just a few minutes. The energy expenditure for the same level of comfort would be much higher if the bathroom had to be heated more around the clock. Similarly, an electric foot warmer in an office workstation can prevent freezing with much less energy than more room heating would require.
In other cases, the advantages of electric heating are barely exploited, while the disadvantages are strongly felt. This applies in particular to most electrical heaters that are used as basic heating for a building or apartment. Here, namely, the possibility of spatially and temporally targeted heat supply is not used at all, while the poor efficiency of power generation has a very disadvantageous effect, namely leads to a high expenditure of primary energy.
The low efficiency of power generation is less serious when it comes to emergency heating that is rarely required. Such is often used for frost protection purposes; A small electric radiator with a thermostat can prevent pipes from freezing in an otherwise unheated toilet room. However, it should be noted that such radiators always draw electricity on the coldest days, when the load on the power plants and power grids is already greatest; so they make correspondingly larger power reserves necessary.Generating electrical heat from excess electricity (power to heat) can be sensible, v. a. if alternatives were disproportionately expensive or even less efficient (e.g. power to gas).
If electrical heat is specifically generated only from excess electricity, z. B. on days with high wind energy generation and low demand, one speaks of power to heat. Since there are hardly any other options for utilizing such surpluses, low energy efficiency is more likely to be tolerated.
There are hardly any alternatives to electric heat, often when process heat is required at very high temperatures, for example for melting furnaces.
Electric heat is often considered to be safer compared to heat generation by incinerators. Since there are no flames and no openings for air supply and exhaust gas discharge are required, the risk of flames spreading is avoided. However, there are also specific dangers of electrical heat:
- If the heat dissipation is greatly reduced, the unchanged generation of electrical heat leads to very high temperatures, the z. B. can lead to smoldering or self-ignition of materials (when they reach their ignition temperature). Therefore z. B. an electric radiator that is covered too much by fabrics (clothing, curtains, etc.) during operation must have an automatic switch-off in the event of overheating. If this is not available or if it fails in an emergency, serious accidents can result.
- If old power lines in a house are constantly exposed to heavy loads from electric radiators, this can be caused by bad contacts, e.g. B. in junction boxes can lead to fires. (Most other electrical consumers in a household are much less critical in this regard.)
- Touching defective electrical insulation can result in electric shocks.
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See also: heat, process heat, electric energy, electric heating, infrared heating, electric immersion heater, electrode boiler, pipe heating, electric heat pump, power to heat
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