Heating devices, the principle of which is based on induction heating, are called induction heaters. They are used both in industry and in everyday life, and in industry the importance of their use can hardly be overestimated.
Let’s take a closer look at these devices.
The device and principle of operation of the induction heater
Simplified, the induction heater consists of three components:
- alternator (1);
- inductor (2);
- core (3).
A conductive (metal, graphite) rod is placed in a coil, consisting of a certain number of turns of a conductor of a given cross-sectional area, without direct contact with it, after which voltage is applied to the coil contacts from an alternator. An electromagnetic field is formed around the turns of the coil, under the influence of which Foucault eddy currents arise in the rod, heating the core. Thus, there is no heat transfer to the core, heat is generated by it independently under the influence of currents wandering in it, and can be transferred using a coolant. The temperature of the rod rises not simultaneously throughout the mass, but from the surface layers to the center, depending on the thermal conductivity of the core material. At the same time, increasing the frequency of the alternating current reduces the depth of inductive heating, but increases its intensity. Particularly noteworthy is the fact that the coil around the core remains almost cold during operation.
Visually, this process looks like this:
Areas of use
In industry, induction heaters are used to perform the following complex processes:
- ultra-pure melting of metals (produced in channel — non-contact induction furnaces);
- bending steel pipes of large diameter;
- performance of surface hardening of steel products (building fittings, details of transmission mechanisms of machine tools, etc.);
- heat treatment of small parts of complex configuration;
In everyday life, induction heating devices are also quite widespread. Their areas of application:
- household autonomous heating systems (for summer cottages, apartments, private houses);
- induction hobs and tiles for the kitchen;
- crucible furnaces of small volume for domestic metal smelting;
- jewelry craft.
Since the main topic of the article is an induction heater, we will dwell in detail on a heating boiler, the basis of which is the idea of inductive heating of the coolant.
Induction heater — heating boiler
Since homeowners began to install autonomous heating systems in their homes, the issue of the efficiency of heating boilers remains one of the most important for them. According to this indicator, at least among devices that generate heat from electricity, induction heating boilers are in the lead. At the same time, their power, which is not comparable with the identical parameter of such a device as a plinth heater, allows the units to be used as the main heating method in large areas.
Induction heating boilers consist of two circuits — primary (electromagnetic) and secondary (heat exchange piping). The first circuit, consisting of a voltage converter and a heat generator with an induction type heater, creates an electromagnetic field, eddy currents and generates heat. The second circuit, which includes a heat exchanger with a piping system, transfers this heat through the circulation of the coolant to the radiators of the heating system. Pure water or with additives is used as a heat carrier.
In addition to these two circuits, the heating system includes automation responsible for the operation of individual units of the unit.
Modern induction heating boilers are installed only in a closed-type heat exchange circuit, which has a membrane-type expansion tank and a forced circulation pump in its design. The use of a circulation pump is a forced measure and is due to the small volume of the coolant at a high heat exchanger heating intensity. The possibility of natural circulation in such a system is excluded — without a pump, water will boil before it begins to move through the pipes.
Important! The induction boiler must be grounded. In addition, when installing the heating system, for safety reasons, the heat carrier distribution circuit must be mounted from plastic pipes, or the heating unit must be isolated from the steel circuit by inserting polypropylene fittings.
Induction heating boilers are classified identically to other heating electric units — in terms of power, design, parameters of electricity consumed. But these devices also have a classification according to the design solution of the electrical part.
Varieties of induction boilers
There are the following types of induction-type heating boilers, designated both by the principle of operation and by the brand of the manufacturer:
- SAV — a variety and at the same time a trademark of a new generation of boilers with a capacity of 2.5 to 100 kW, since 2007 produced by the European company CJSC NPK INERA;
- VIN — the abbreviation is not only an abbreviation for the name of the type of induction devices (vortex induction heaters), but also the patented name of the boilers produced by the Izhevsk company Alternative Energy.
SAV induction heaters
The operation of SAV units does not require the use of an inverter, a current with a frequency of 50 Hz is supplied to the inductor. The electromagnetic field induced by the primary winding causes the formation of vortex flows in the secondary winding, the role of which in boilers of this type is performed by a section of a closed loop of pipes with a coolant. This section of the pipe — the secondary winding is intensely heated under the influence of Foucault currents and transfers heat to the coolant, which is forcibly circulated in the heating system using a circulation pump.
The device of the heating system is carried out using radiators or in a labyrinth way, reminiscent of baseboard heating, in order to increase the total area of u200bu200bthe outer surface (heat transfer) of the pipes — the heating circuit, at least, should not be minimal in length.
SAV boilers are produced for voltages of 220V and 380V. They use water as a coolant (in pure form or with antifreeze additives), as well as antifreeze. The output of the unit at full capacity takes about 5–20 minutes (depending on the volume of the coolant), the efficiency of the heaters of such devices is at least 98%. For efficient heating of rooms up to 30 sq. m. a 2.5 kW induction device is enough, the purchase of which, complete with automation and control systems, will cost approximately 300 $.
Boilers of this type are more perfect in terms of the principle of operation and design, which, of course, is reflected in their cost. For the operation of VIN-devices, an inverter is required — a device for increasing the frequency of the incoming current. The high frequency current causes the formation of an electromagnetic field of high intensity, which, in turn, causes the occurrence of more powerful eddy currents in the secondary winding. In addition, the heat exchanger and the boiler body are made of ferromagnetic alloys that have their own magnetic field. The result of all these processes is a high heating intensity of the heat exchanger and, of course, the coolant.
A VIN-unit with a capacity of 3 kW is sufficient for heating a room with an area of 35–40 sq. m. (depending on climatic conditions and the quality of thermal insulation of external building structures).
VIN units, due to their higher productivity, can be used not only in residential heating systems, but also for hot water supply. To do this, additional storage tanks are inserted into the coolant circuit, equipped with protective automation, the capacity of which is calculated depending on the number of hot water intake points. These containers are provided with hot water by circulating it in a system with direct-flow heating by an induction heater.
Evaluation of marketing characteristics-statements
Many advantages are attributed to induction heating boilers, often without arguments. We list these characteristics and give an assessment of the degree of conformity of the statements to the fact:
Electricity consumption by induction boilers is 20–30% less than other electric heaters.
All heating electrical appliances that do not perform mechanical work convert 100% of the energy of the electric current into heat, their efficiency is always below 100%, but differs in magnitude for different devices in different conditions. To generate 1 kW of thermal energy, it is necessary to spend more than 1 kW of electricity, but how much more depends on the parameters of the dispersion medium. Inside the boiler, of course, there are also losses — for example, for heating the coil, since any conductor material has resistance, but all these losses remain indoors
Important! Old-style meters (bakelite) will record a lower (1.6 — 1.8 times) electricity consumption than modern electronic ones, since they are not designed to take into account the reactive power of induction boilers.
Perhaps this fact determines the statement about the efficiency of induction boilers.
High reliability and long service life of equipment — more than 25 years.
Indeed, the absence of moving parts eliminates the mechanical wear of induction boilers. But the heating system with a VIN unit includes a circulation pump, the resource of which is much more modest. In addition, the control and automation system includes mechanisms, also consisting of many components subject to wear.
The core of the induction heater operates under conditions of constant cyclic heating and cooling, temperature deformations, which are also a negative factor. Therefore, to call the resource of induction boilers almost unlimited is an exaggeration. However, it is actually many times higher than heating element heaters.
Consistency of characteristics for the entire period of operation
The absence of the formation of scale on the inner surface of the pipes determines the constant efficiency of the heater and heat exchanger.
Scale is a deposit of salts contained in water (coolant). The amount of these impurities in a limited volume of the coolant is also limited and small, so the effect of scale on the efficiency of the heater is insignificant. And in an induction boiler, the secondary winding is under almost constant vibration, and scale formation does not occur at all. So the statement is true, only its significance is exaggerated.
The operation of induction heating boilers is silent, which distinguishes them from other electric heaters.
The statement is true, but — all electric boilers do not make noise during operation, since acoustic waves are not included in the range of their oscillations. Only the circulation pump can make noise, but if you wish, you can choose a model of silent action.
Induction boilers are compact, which is convenient when choosing a place for their installation.
This is true if you do not use a cascade of induction boilers and do not install intermediate tanks if there are several points of hot water intake in the hot water supply system, since an induction heater is, by and large, a small piece of pipe with a winding.
The safety of the device is absolute.
Absolutely safe electric heaters do not exist. During the operation of induction devices, the possibility of a coolant leakage from the system is not ruled out, and the electromagnetic field generator will continue to operate, and the empty pipe system will heat up. To prevent the occurrence of such a situation, the boiler design provides for an automatic shutdown device, but it can also fail.
Therefore, induction heaters, while outperforming rivals in some safety criteria, are not completely safe.
Disadvantages of induction heaters
- The high cost of devices.
- Significant weight with compactness.
- The presence of a factor in the influence of the electromagnetic field on the body and devices.
Let’s take a closer look at the last point.
The electromagnetic field affects living organisms in much the same way as food in a microwave oven — it warms them up to a certain depth, and this can have consequences. The intensity of the impact of the field, including on a person, is determined by such an indicator as the energy flux density (PEF), which grows with an increase in the frequency of the current supplied to the primary winding. When operating induction heaters, it is necessary to comply with the sanitary limit value of the PES, which is established in SanPiN 2.2.4 / 2.1.8.055–96, depends on the duration of the field exposure and is, for example, for an 8‑hour exposure — 25 μW / sq. cm, one-hour — 200 μW / sq. cm.
In addition, the radiation of the inductor adversely affects the electronics and radio equipment located nearby, creating interference during operation.
Important! To protect yourself from the effects of an electromagnetic field, you can surround the boiler with a fine-mesh (1x1, 2x2 mm) metal mesh (Faraday cage), which is not in contact with the boiler body and is grounded.
The safe operation of induction heating boilers, like any other technical devices, is ensured by the implementation of a number of rules regarding both their installation and use after installation:
- The boiler must be earthed.
- The distance from the device to the walls on the sides must be at least 30 cm, from the bottom point of the boiler to the floor — 80 cm, from its top point to the ceiling — 80 cm.
- Induction boilers are installed only in a closed circuit with a membrane-type expansion tank.
- The system must include a block of safety devices (pressure gauge, air valve, overpressure relief valve, automatic overheat shutdown system).
Overview of well-known manufacturers
- Edison — induction-type heaters with a capacity of 4.7 to 500 kW, produced by the of the world plant “SibTechnoMash”, for domestic and industrial needs;
- Miratron — products of the European manufacturer of induction heating equipment NPK Miratron for domestic use, featuring an advanced design that allows you to use the equipment without damaging the interior of the room;
- Teco-House — induction heating boilers with a unique control system, produced by the Ukrainian company of the same name according to the standards of the EU and the EU.
The modern market of boilers for the installation of autonomous heating systems is represented by hundreds of models of various types of units. The objectivity of the price / quality criterion of each variety is different. The choice in favor of induction heating devices in terms of the risk of subsequent disappointment in the purchase is the most reasonable.