Infrared heater

Infrared heaters are independently functioning components or devices that produce infrared radiation, which are used for heating or drying purposes. Areas of application are, for example, animal husbandry, electric sauna, indoor heating, residential space heating or in medicine. As energy source for infrared radiator combustible gas or electrical current is used. The principle of infrared radiation is the same for electrically operated as well as with gas infrared heaters.

In contrast to other heating systems operate primarily above the infrared radiator heating of the illuminated surface, not heating the air of the radiator.

Besides infrared heaters, so the devices emit broadband infrared radiation, there are also devices the infrared radiation only in a relatively narrow range emit, including infrared laser (especially carbon dioxide laser ) and an infrared light emitting diode.

• 4.1 Luminous Heaters 4.1.1 plates
• 4.1.2 reflectors
• 4.1.3 Infrared power
• 4.1.4 Areas of application
• 4.1.5 rules for exhaust system
• 4.1.6 control

• 4.2.1 structure
• 4.2.2 Infrared power
• 4.2.3 exhaust system
• 4.2.4 Areas of application
• 4.2.5 control

Principle of infrared heaters

The principle of the device is simple and can best be explained by the sun on a glacier. Although the ambient temperature is below 0 ° C, it is warm in the sun. This is due to the thermal radiation of the sun. Where these impacts, it is (partly) absorbed and converted into heat, for example on our skin.

Infrared radiation is only a small part of the electromagnetic spectrum dar. radiation with wavelengths shorter than visible or infrared is in the harmful range ( ionizing radiation) and is therefore undesirable. Radiation with longer wavelength, however, becomes progressively worse absorbed (eg, radar, radio ).

Radiation has the property of heat only the body to which it applies. The heat transfer occurs directly and clearly differs from the convection, ie the heating of the ambient air. The aim is to keep the convective loss ( rising warm air) as low as possible.

In contrast to most solid materials the air is limited, especially by water present, to absorb infrared radiation in the area. Therefore air heats up less and also in the non-irradiated region it remains cold.

Infrared heating

Infrared heaters are among the most radiation or heat wave heaters and are used primarily in warehouses, where conventional convection heating would be uneconomical, the warm air would depend largely useless under the hall roof. This advantage is more pronounced with the light radiator systems working at a higher temperature and a lower surface of the radiator. From dark radiator systems comes from a lower fire risk. Variants for the living area are located on an area behind a protective layer to prevent burns with brief contact of (80-100 ° C with panel radiators, infrared heaters much more) hot heating. The heaters are used in many different variations as surface, mirrors, picture or ball, fixed or produced transportable.

Electrical operation

Basically light sources are divided by type of emission: infrared lamps, as well as normal light bulbs and most light sources are among the thermal emitters, that is, they emit radiation due and according to their temperature. See also Black Body. Black in this context means that radiation is emitted only because of the body's own temperature, not " distorted " due to reflection or the like is. Conversely, that every body emits thermal radiation at a temperature above zero Kelvin.

After the Wien's displacement law the " main color" of radiation from a ( black ) body depends only on its temperature: the colder it is, the low frequency is the maximum of the radiation emitted by this. For example, a moderately heated iron wire glows dark red ( low frequency ); when the wire is heated further, increases the frequency which is accompanied by a bright red, orange, yellow or even bluish- white color. Hand, has the wire for example, only room temperature, its radiation is still " under" the darkest red, what human eyes can still be seen, in other words, not to shine Such a wire appears by itself.

Thus, it depends on the type of the lamp and thus the annealing temperature, as much as visible light and infrared light it emits much. Seen in relatively cool lamps would therefore be quite efficient infrared lamps, but decreases the total radiation power of a body with the fourth power of its temperature due to the Stefan- Boltzmann law.

Last, let us briefly refer to the Planck's radiation law. It describes the entire frequency distribution of the radiation of a black body, not only the maximum. One known exception to the group of the thermal emitter ( light source ), the light-emitting diode: the emitted radiation is generated from an electronic transition which ideally has nothing to do with the internal temperature of the diode.

Quartz heater

In a quartz heater, the electric current flowing through it from the heating resistor is in an inflated with inert quartz tube. Therefore, the temperature of the wire can be selected to be higher than in a conventional heater.

Infrared lamps

Infrared lamps (also called red light lamps or heat lamps ) are lamps that emit predominantly invisible heat radiation. To a red filter is generally mounted to the remaining ( non- red ) to filter out visible light in the air. The lights used can contain these filters in their glass envelope directly. The emitted radiation has then alongside the (still visible ) red light fraction mainly just called near infrared radiation ( NIR).

Infrared lamps are used for example in chick rearing stations and terrariums. They emit infrared radiation in the area that felt by many living things as pleasant. This can be explained by the high proportion of NIR radiation, the most energetic infrared with the same time highest penetration depth (of still only a few millimeters, see penetration depth of IR radiation): The heat is thus generated by the incident radiation just below the skin surface, and not directly on the skin surface, which sometimes people feel at least as unpleasant (skin drying out and burning sensation ). At the same time, these infrared lamps not escape reflex in animals trigger in spite of their performance by their mild and deep red radiation that would otherwise avoid direct sunlight.

The intensity of modern infrared lamps can be dimmed. The filament then glows no more glaring white to light yellow, but only reddish. The intensity of the infrared light is thus - due to the shift of the radiation maximum (see Wien's law ) - only slightly lower.

There are also modified infrared lamps, which are more adapted as an infrared radiator. In these, the proportion of visible radiation is further reduced and emits it proportionately more middle infrared ( MIR). Lamps on the basis of filaments to reach a wavelength range of 5-10 microns or so. This type of infrared light is used when the body to be heated, the (largely) are for the NIR region invisible, i.e., the corresponding radiation can pass without hindrance. An example is water ice: it is in the visible range and substantially transparent in the NIR and only the far-infrared (FIR) is opaque and ice takes all of the energy of the radiation, and is thus heated. " Ice -thawing infrared heaters " are therefore only really effective if they would like to leave a high proportion of FIR radiation.

Even in industrial heating processes are electrical infrared heaters, such as thermoforming, used.

Gas operation

Heater in the industry and when camping, however, are usually operated with fuel gas, usually with LPG, in steady use of rare and natural gas. The gas flame heats the filament. Industrial heaters can be used for the sole hall heating. For the gas lamps that are valid for Boiler installation regulations must be observed. Due to these properties, they are hardly suitable for the living area. In recent years, more and more came patio heater (also called " patio heaters " called ) in outdoor areas such as street cafes to use. These outdoor heaters are because of their " aesthetic " and a postulated climate impact in the review, but are still allowed in most German cities. In essence, today there are two types of infrared heaters with direct gas-fired appliances: Light spotlights and dark radiator.

Bright spotlights

Light emitters are heated directly by an atmospheric burner and runs on natural gas, kerosene or LPG. They are installed on the wall or ceiling. They are called light 'illuminators because the generation of infrared rays vonstattengeht by a visible combustion of a gas -air mixture at the bottom. This glow ceramic plates " bright". The perforated ceramic plates simultaneously form the core of the light radiator. It flows through the gas-air mixture and burned to their surfaces. The ceramic plate surface it heats up to 950 ° C and emits infrared radiation. Reflectors reflect the radiation down into the occupied zone.

Plates

Previously, the ceramic plates were relatively simple. On average, they had some 1200 holes and reached only a quarter of the size of today's disks. The surface of the rectangular plates was flat. Developers already began in the 1970s to perfect the ceramic plate. They had recognized that power output and emissions to a large extent on the surface properties and the structure of the disk are dependent. Today there are between 3,000 and 4,000 holes with 1-1.3 mm in diameter on a blackboard. The surface, the so-called low- effect structure, developed by Schwank, similar to an evenly spaced honeycomb. Through them, the specific surface area and thus the heat transfer surface and the radiation yield by about 60 % increased. In each hole quasi burns a small flame. This creates a very hot ceramic surface, although the actual flames remain relatively cool. This reduces the nitrogen oxide levels (NOx ) to a barely measurable range. The carbon monoxide values ​​( CO) are in the range of modern boilers, often use the same ceramic plate and the effect of hot surface and cold flame. A high quality ceramic plate has an unlimited life. By advanced manufacturing process, they have an extremely dense and homogeneous structure. This is especially with the myriad interactions cold / hot, caused by switching on and off of many years of operation, important.

Reflectors

To meet the demands of high power output, there is next to non-insulated devices also fully insulated. The insulation causes the heat transfer to the reflector outside is very low, thus arises in the spotlight a hot air cushion, the reflectors are hot and in turn gives off heat. This effect is called Combined radiation. Another " reflector ", but in grid form, the so-called radiation grid, sits just below the ceramic plates. It means that the radiation is reflected to them from the ceramic plates to some extent. The radiation is converted into heat on the surface and the temperature of the ceramic plate begins to rise, a " ping-pong " of the radiation.

Infrared power

The performance of the devices has increased rapidly in recent years. Achieved earlier devices an average of only 40-50 %, the radiated power ( radiation factor) is now between 65 % and 77 %. Each percentage point more means more heat in the occupied zone. The radiation factor is, therefore, a direct indicator of the energy yield and thus a direct indicator of how much heating costs can be saved.

Areas of application

Light emitters are particularly suitable for higher buildings with ceiling heights above 6 m, for heating poorly insulated buildings or outdoor heating. In industry, workshops, exhibition halls, museums, warehouses, aircraft hangars, churches and many more areas of application light emitters are used millions of times in Europe. As special applications, the heating of bearings for condensate control systems and the heating of football stadiums can be mentioned.

Regulations for exhaust system

The exhaust gases of light radiators can be discharged due to the almost non-polluting combustion indirectly via the ambient air. It is necessary to ensure a fresh air supply of 10 m³ / (h · kW).

Control

The spotlights can be either in stages or modulating control. Depending on the design and temperature profile of the room at different temperatures can be realized in a room. How can respond flexibly to the individual needs of individual temperature zones or jobs. The instruments are operated by simple switches or complex control systems that govern the buying and shutdown procedures with radiation sensors. Modern control systems determine autonomously when to start. PC connection or connection to the building control system is also easily possible.

Tube Heaters

Tube heaters produce heat also by combustion of oxygen -gas mixture, but closed torches with nozzles. The combustion is therefore not visible, hence the name dark radiator. Through the generated hot gases the surface of the beam tubes is heated, which supply heat primarily as radiation. As fuel, natural gas and LPG used.

Construction

Tube heaters are relatively simple construction equipment consisting of a burner, a fan, a radiant tube and arranged above reflectors. A linear or U-shaped tube serves as reflecting surface. The burner is mounted on one end of the jet pipe, generates a flame that extends relatively far into the tube. Modern devices work with a oppressive system. That is, the fan is located at the same position of the burner and "pushes" the flame radiation far into the tube. Thus, a long and a laminar flame is obtained, which heats the emitter over the entire length evenly. In addition, the fan is not exposed to the hot exhaust gases. Older designs still use the exhaust fan at the other end of the pipe. The fans thereby produce a negative pressure which transports the gas through the lance. However, here, the fans are always exposed to the hot gases, which has a shorter life of the fans result. The radiant tube is covered by a reflector, which directs the heat radiation in the desired range. To increase the radiation factor, the reflector plate can be deposited with a thermal insulation made of mineral fiber. Some manufacturers, however, this insulation is not needed, since the reflector is so good edged that the best radiation factor is given.

Infrared power

The pipe surface temperature is depending on performance and execution 300-650 ° C. Depending on the type and burner technology work dark radiator due to the relatively low temperatures with radiation factors between 45% and 55%. The radiation level of modern insulated devices ( radiation factor to 77 %) is difficult to increase it and will never reach the high level of light radiators. By complying with statutory emission levels, the developers come up against their limits.

Exhaust system

Dark radiator will have to pay their exhaust directly out of the hall. These are discharged through appropriate exhaust pipes either individually per unit or collected from multiple devices directly over a fireplace out of the hall. The exhaust system requires an annual audit by the chimney sweep.

Areas of application

Dark radiators radiate at a lower intensity than the light radiator, but provide due to its length a larger radiation field per unit. Due to the lower surface temperature, it can already be used in rooms above a ceiling height of about 4 m. For use in high halls or for outdoor heating, they are unsuitable.

Control

The scheme corresponds to that of light radiators. Only the exhaust fans must be additionally controlled for collecting exhaust systems.

Benefits

From the function has already had the advantages of equipment. Infrared rays do not need a " carrier medium " to transport their energy. That is, they get virtually no loss from the device to the body and also cause fewer drafts than conventional systems. In principle, of course, continue to apply the laws of thermodynamics, so that all bodies that have been heated, for example within a hall by infrared radiation, and in turn heat the air by heat conduction. This effect is, however, significantly lower than would be the case with the conventional systems, in most circumstances.

Because infrared heaters primarily the surfaces and only secondarily heat the air, the air temperature can average 2-3 ° C below the temperature felt by the people, but is still perceived as cozy. These factors have a positive effect on the indoor climate - the quality of work increases, allergy symptoms are reduced.

Since the air is not heated directly, no expensive hot bubble formed under the roof. Depending on the device type and manufacturer can be proven up to 50 % energy savings compared to conventional heating systems. Bright spotlights case have the greater advantage, because their efficiency, so what arrives proven to heat the floor, opposite tube heaters is higher.

Efficiency of the infrared radiators

Operated with electric power infrared heaters give up to 86% of the supplied energy as radiation. The filaments emit heat by infrared radiation. The loss of energy due to the pipes and convection.

In principle, the efficiency of an infrared radiator is a function of the emitted wavelength with respect to the absorption spectrum of the material to be heated (see infrared radiation). A careful selection of appropriate infra-red radiator is required to increase the efficiency.

Mid or classic (standard ) infrared (MIR; Wavelength: 3-50 micron ): for example, water has an absorption spectrum with a peak of about 3.0 microns. This means that the emission radiation of medium wave emitters or carbon infrared heaters of water and water - based coatings ( human body ) is better absorbed than the short-wave radiation. The same is true for a number of plastics such as polyvinyl chloride ( PVC) or polyethylene. Their absorption peak is around 3.5 microns.

Near-infrared (NIR; wavelength: 0.78 to 3.0 microns): Conversely, absorbed a variety of metals infrared radiation only in the short wave and shows a high reflection at long and medium waves. Ceramic heating elements operate at a temperature between 300-700 ° C and generate infrared radiation in the wavelength range already from 2 to 10 microns. Most plastics, and many other materials absorb the infra-red radiation at the best in this range, therefore, the ceramic heating element are preferably used for these materials.

Depth effect

The infrared spectral region is divided into the following sections (DIN 5031 ). Crucial for efficient use in outdoor areas the depth effect is under the skin layers that can be felt in spite of movements of air as heat.