A brief overview of electrical heating appliances. Heating equipment
One of the main elements of water heating systems - a heater - is designed to transfer heat from heat carriers to a heated room.
To maintain the required room temperature, it is required that at each moment of time the heat loss of the room Qp be covered by the heat transfer of the heater Qpp and pipes Qtp.
The scheme of heat transfer of the heater Qpr and pipes to compensate for the heat loss of the room Qp and Qdop during heat transfer Qt from the side of the water coolant is shown in fig. 24.
Rice. 24. Scheme of heat transfer of a heater located at the outer fence of the building
The heat Qt supplied by the coolant for heating this room should be greater than the heat loss Qp by the amount of additional heat loss Qadd caused by increased heating of the building structures.
Qt \u003d Qp + Qadd
The heating device is characterized by the area of the heating surface Fpr, m2, calculated to ensure the required heat transfer of the device.
According to the predominant method of heat transfer, heating devices are divided into radiation (ceiling radiators), convective-radiation (devices with a smooth outer surface) and convective (convectors with a ribbed surface).
When heating rooms with ceiling radiators (Fig. 25), heating is carried out mainly due to radiant heat exchange between heating radiators (heating panels) and the surface of the building structures of the room.
Rice. 25. Suspended metal heating panel: a - with a flat screen; b - with a wave-shaped screen; 1 - heating pipes; 2 - visor; 3 - flat screen; 4 - thermal insulation; 5 - wavy screen
The radiation from the heated panel, falling on the surface of fences and objects, is partially absorbed, partially reflected. In this case, the so-called secondary radiation arises, which is also eventually absorbed by the objects and enclosures of the room.
Radiant heat transfer raises the temperature inner surface fences compared to the temperature during convective heating, and the surface temperature of the internal fences in most cases exceeds the temperature of the air in the room.
With panel radiant heating, due to the increase in the temperature of the surfaces in the room, an environment favorable for humans is created. It is known that a person's well-being improves significantly with an increase in the proportion of convective heat transfer in the total heat transfer of his body and a decrease in radiation to cold surfaces (radiative cooling). This is exactly what is provided with radiant heating, when the heat transfer of a person by radiation decreases due to an increase in the temperature of the surface of the fences.
With panel radiant heating, it is possible to lower the normal (normative for convective heating) air temperature in the room (on average by 1-3 ° C), and therefore the convective heat transfer of a person increases even more. It also improves a person's well-being. It has been established that under normal conditions, people's well-being is ensured at an indoor air temperature of 17.4 ° C with wall heating panels and at 19.3 ° C with convective heating. Hence, it is possible to reduce the consumption of thermal energy for space heating.
Among the disadvantages of the panel-radiant heating system, it should be noted:
Some additional increase in heat loss through external fences in those places where heating elements are embedded in them; -
The need for special fittings for individual control of heat transfer of concrete panels;
Significant thermal inertia of these panels.
Devices with a smooth outer surface are sectional radiators, panel radiators, smooth-tube devices.
Devices with a ribbed heating surface - convectors, ribbed tubes (Fig. 26).
Rice. 26. Schemes heating appliances various kinds(cross section): a - sectional radiator; b - steel panel radiator; c - smooth-tube device of three pipes; g - convector with a casing; D - a device of two finned tubes: 1 - channel for the coolant; 2 - plate; 3 - rib
According to the material from which heating devices are made, metal, combined and non-metallic devices are distinguished. Metal appliances are mainly made of gray cast iron and steel (sheet steel and steel pipes). Also apply copper pipes, sheet and cast aluminum and other metals.
In combined appliances, a heat-conducting material (concrete, ceramics, etc.) is used, into which steel or cast-iron heating elements (panel radiators) or finned metal pipes are embedded, and a non-metallic (for example, asbestos-comeptpy) casing (convectors).
Non-metallic appliances include concrete panel radiators with embedded plastic or glass pipes or with voids, as well as ceramic, plastic and other radiators.
By height, all heaters are divided into high (more than 650 mm high), medium (more than 400 to 650 mm), low (more than 200 to 400 mm) and plinth (up to 200 mm).
According to the magnitude of thermal inertia, devices of small and large inertia can be distinguished. Low-inertia devices have a small mass and contain a small amount of water. Such devices based on metal pipes small sections (for example, convectors) quickly change heat transfer to the room when adjusting the amount of coolant admitted into the device. Devices with large thermal inertia - massive, containing a significant amount of water (for example, concrete or sectional radiators), heat transfer is changed slowly.
For heating appliances, in addition to economic, architectural and construction, sanitary and hygienic and production and installation requirements, thermal engineering requirements are also added. The device is required to transfer from the coolant through a unit area to the room of the largest heat flow. To fulfill this requirement, the device must have an increased value of the heat transfer coefficient Kpr, in comparison with the value of one of the types of sectional radiators, which is taken as a standard (cast iron radiator type H-136).
In table. 20 shows thermal performance and conventional signs mark other indicators of devices. The plus sign indicates positive indicators of the devices, the minus sign - negative ones. Two pluses indicate indicators that determine the main advantage of any type of device.
Table 20
Design of heating devices
A sectional radiator is a device of a convective-radiation type, consisting of separate columnar elements - sections with round or elliptical channels. Such a radiator emits about 25% of the total heat flux transmitted from the coolant into the room with radiation (the remaining 75% - by convection) and is called a "radiator" only by tradition.Radiator sections are cast from gray cast iron, they can be combined into devices of various sizes. Sections are connected on nipples with gaskets made of cardboard, rubber or paronite.
Various designs of one-, two-, and multi-column sections of various heights are known, but the most common are two-column sections (Fig. 27) of medium (installation height hm = 500 mm) radiators.
Rice. 27. Two-column radiator section: hp - full height; hm - mounting height (construction); b - building depth
The production of cast-iron radiators is laborious, installation is difficult due to the bulkiness and significant mass of the assembled devices. Radiators cannot be considered to meet sanitary and hygienic requirements, since cleaning the intersection space from dust is difficult. These devices have significant thermal inertia. Finally, it should be noted that their appearance does not correspond to the interior of the premises in buildings. modern architecture. These disadvantages of radiators make it necessary to replace them with lighter and less metal-intensive devices. Despite this, cast-iron radiators are the most common heating device at present.
At present, the industry produces cast-iron sectional radiators with a construction depth of 90 mm and 140 mm (type "Moscow" - abbreviated M, type IStandardI - MS and others). On fig. 28 shows the designs of manufactured cast-iron radiators.
Rice. 28. Cast iron radiators: a - M-140-AO (M-140-AO-300); b - M-140; c - RD-90
All cast iron radiators are designed for operating pressure up to 6 kgf/cm2. The heating surface meters of heating devices are a physical indicator - a square meter of the heating surface and a thermotechnical indicator - an equivalent square meter (ekm2). equivalent square meter called the area of the heating device, giving off 435 kcal of heat in 1 hour with a difference in the average temperature of the coolant and air of 64.5 ° C and a water flow rate in this device of 17.4 kg / h according to the flow pattern of the coolant from top to bottom.
Technical characteristics of radiators are given in table. 21.
Heating surface of cast iron radiators and finned tubes
Table 21
Continuation of the table. 21
Steel panel radiators consist of two stamped sheets forming horizontal manifolds connected by vertical columns (column form) or horizontal channels connected in parallel and in series (serpentine form). The coil can be made from a steel pipe and welded to a single profiled steel sheet; such a device is called sheet-tube.
Rice. 29. Cast iron radiators
Rice. 30. Cast iron radiators
Rice. 31. Cast iron radiators
Rice. 32. Cast iron radiators
Rice. 33. Cast iron radiators
Rice. 34. Schemes of channels for the coolant in panel radiators: a - columnar; b - two-way coil, c - four-way coil
Steel panel radiators differ from cast iron ones in their lower mass and thermal inertia. With a decrease in weight by about 2.5 times, the heat transfer rate is no worse than that of cast-iron radiators. Them appearance meets architectural and construction requirements, steel panels are easy to clean from dust.
Steel panel radiators have a relatively small heating surface area, which is why sometimes it is necessary to install panel radiators in pairs (in two rows at a distance of 40 mm).
In table. 22 shows the characteristics of manufactured steel stamped radiator panels.
Table 22
Continuation of the table. 22
Continuation of the table. 22
Concrete panel radiators (heating panels) (Fig. 35) can have concrete heating elements of a serpentine or register shape made of steel pipes with a diameter of 15-20 mm, as well as concrete, glass or plastic channels of various configurations.
Rice. 35. Concrete heating panel
Concrete panels have a heat transfer coefficient close to those of other devices with a smooth surface, as well as a high thermal stress of the metal. Devices, especially combined type, meet strict sanitary-hygienic, architectural and construction and other requirements. The disadvantages of combined concrete panels include the difficulty of repair, large thermal inertia, which complicates the regulation of heat supply to the premises. The disadvantages of attachment-type devices are the increased costs of manual labor in their manufacture and installation, and the reduction in the usable floor area of the room. Heat losses through additionally heated external fences of buildings also increase.
A smooth-tube device is called a device made of several steel pipes connected together, forming channels for a coil or register-shaped coolant (Fig. 36).
Rice. 36. Forms of connecting steel pipes to smooth-tube heaters: a - serpentine form; b - register form: 1 - thread; 2 - column
In the coil, the pipes are connected in series in the direction of movement of the coolant, which increases the speed of its movement and the hydraulic resistance of the device. When the pipes are connected in parallel in the register, the coolant flow is divided, the speed of its movement and the hydraulic resistance of the device decreases.
The devices are welded from pipes DN = 32-100 mm, located from each other at a distance of 50 mm greater than their diameter, which reduces mutual exposure and, accordingly, increases heat transfer to the room. Smooth-tube appliances have the highest heat transfer coefficient, their dust-collecting surface is small and they are easy to clean.
At the same time, smooth-tube devices are heavy and bulky, take up a lot of space, increase the consumption of steel in heating systems, and have an unattractive appearance. They are used in rare cases when other types of devices cannot be used (for example, for heating greenhouses).
Characteristics of smooth-tube registers are given in table. 23.
Table 23
The convector is a convective type device, consisting of two elements - a finned heater and a casing (Fig. 37).
Rice. 37. Schemes of convectors: a - with a casing; b - without casing: 1 - heating element; 2 - casing; 3 - air valve; 4 - pipe fins
The casing decorates the heater and increases heat transfer due to the increase in air mobility at the surface of the heater. A convector with a casing transfers up to 90-95% of the total heat flux into the room by convection (Table 24).
Table 24
A device in which the functions of the casing are performed by the fins of the heater is called a convector without a casing. The heater is made of steel, cast iron, aluminum and other metals, the casing is made of sheet materials(steel, asbestos cement, etc.)
Convectors have a relatively low heat transfer coefficient. However, they are widely used. This is due to the ease of manufacture, installation and operation, as well as low metal consumption.
The main technical characteristics of convectors are given in Table. 25.
Table 25
Continuation of the table. 25
Continuation of the table. 25
Note: 1. When installing KP skirting convectors in multiple rows, a correction for the heating surface is introduced depending on the number of rows vertically and horizontally: with a two-row vertical installation 0.97, a three-row installation - 0.94, a four-row installation - 0.91; for two rows horizontally, the correction is 0.97. 2. The indicators of the end and passage models of convectors are the same. Passage convectors have an index A (for example, Hn-5A, H-7A).
A finned tube is a convective-type device, which is a flanged cast-iron pipe, the outer surface of which is covered with jointly cast thin ribs (Fig. 33).
Area outer surface ribbed tube is many times larger than the surface area of a smooth tube of the same diameter and length. This gives the heater a particularly compact design. In addition, the reduced surface temperature of the fins when using a high-temperature coolant, the relative ease of manufacture and low cost determine the use of this thermally inefficient, heavy device. The disadvantages of finned tubes also include an outdated appearance, small mechanical strength fins and the difficulty of cleaning from dust. Ribbed tubes are usually used in auxiliary premises(boiler rooms, warehouses, garages, etc.). The industry produces round ribbed cast-iron pipes 1-2m long. They are installed horizontally in several tiers and connected according to the serpentine scheme with bolts using "kalachi" - flanged cast-iron double taps and counterflanges.
For a comparative thermal performance of the main heating devices in table. 25 shows the relative heat transfer of devices 1.0 m long under equal thermal and hydraulic conditions when using water as a heat carrier (heat transfer of a cast-iron sectional radiator 140 mm deep is taken as 100%).
As you can see, sectional radiators and convectors with a casing are distinguished by high heat transfer per 1.0 m of length; convectors without a casing and especially single smooth pipes have the lowest heat transfer.
Relative heat output of heaters with a length of 1.0 m Table 26
Selection and placement of heating devices
When choosing the type and type of heating device, the purpose, architectural layout and features are taken into account. thermal regime premises, place and duration of stay of people, type of heating system, technical, economic and sanitary-hygienic indicators of the device.
Rice. 38. Cast iron ribbed tube with round ribs: 1 - channel for the coolant; 2 - ribs; 3 - flange
To create a favorable thermal regime, devices are chosen that provide uniform heating of the premises.
Metal heaters are installed mainly under the light openings, and under the windows the length of the device is desirable not less than 50-75% of the length of the opening, under the shop windows and stained-glass windows the devices are placed along their entire length. When placing devices under windows (Fig. 39a), the vertical axes of the device and the window opening must match (a deviation of not more than 50 mm is allowed).
Devices located at the outer fences contribute to an increase in the temperature of the inner surface in the lower part outer wall and windows, which reduces the radiation cooling of people. Rising currents of warm air created by devices, prevent (if there are no window sills blocking appliances) from the ingress of cooled air into working area(Fig. 40a). In the southern regions with a short warm winter, as well as for a short stay of people, heating devices can be installed near the internal walls of the premises (Fig. 39b). This reduces the number of risers and the length of heat pipelines and increases the heat transfer of devices (by about 7-9%), but there is an unfavorable movement of air with a low temperature near the floor of the room (Fig. 40c).
Rice. 39. Placement of heating devices in rooms (plans): a - under the windows; b - at the inner walls; p - heater
Rice. 40. Schemes of air circulation in rooms (sections) at different locations of heating devices: a - under windows without a window sill; b - under the windows with a window sill c - y inner wall; p - heater
Rice. 41. Location under the window of the heater room: a - long and low (preferably); b - high and short (undesirable)
Vertical heating devices are installed as close as possible to the floor of the premises. With a significant rise of the device above the floor level, the air near the floor surface may be supercooled, since the circulation flows of heated air, closing at the level of the device, do not capture and do not warm up the lower part of the room in this case.
The lower and longer the heater (Fig. 41a), the more even the temperature of the room and the better the entire volume of air warms up. A tall and short device (Fig. 41b) causes an active rise of a jet of warm air, which leads to overheating of the upper zone of the room and the lowering of cooled air on both sides of such a device into the working area.
The ability of a tall heater to cause an active upward flow of warm air can be used to heat rooms of increased height.
Vertical metal appliances, as a rule, are placed openly against the wall. However, it is possible to install them under window sills, in wall niches, with special fencing and decoration. On fig. 42 shows several methods for installing heaters in rooms.
Rice. 42. Accommodation heating appliances- in a decorative cabinet; b - in a deep niche; c - in a special shelter; g - behind the shield; d - in two tiers
Instrument shelter decorative wardrobe, having two slots up to 100 mm high (Fig. 42a), reduces the heat transfer of the device by 12% compared to its open installation near a blank wall. To transfer a given heat flux to the room, the area of the heating surface of such a device must be increased by 12%. Placing the device in a deep open niche (Fig. 42b) or one above the other in two tiers (Fig. 42e) reduces heat transfer by 5%. However, hidden installation of devices is possible, in which the heat transfer does not change (Fig. 42c) or even increases by 10% (Fig. 42d). In these cases, it is not required to increase the area of the heating surface of the device or even reduce it.
Calculation of the area, size and number of heating devices
The area of the heat-releasing surface of the heating device is determined depending on the type of device adopted, its location in the room and the connection scheme to the pipes. In residential premises, the number of devices, and therefore the necessary heat transfer of each device, is usually determined by the number window openings. IN corner rooms add another device placed in a blank end wall.The task of the calculation is, first of all, to determine the area of the external heating surface of the device, which, under the calculated conditions, provides the necessary heat flow from the coolant to the room. Then, according to the catalog of devices, based on the estimated area, the nearest trade size of the device is selected (the number of sections or the brand of the radiator (the length of the convector or finned tube). The number of sections of cast-iron radiators is determined by the formula: N=Fpb4/f1b3;
where f1 is the area of one section, m2; type of radiator accepted for indoor installation; b4 - correction factor, taking into account the way the radiator is installed in the room; b3 is a correction factor that takes into account the number of sections in one radiator and is calculated by the formula: b3=0.97+0.06/Fp;
where Fp is the calculated area of the heater, m2.
Often with choice of heaters are limited only to radiators, without thinking about the existence of other heating devices. And modern trends in the development of the interior of the room require much more attention for decoration.
After all, you must admit that a radiator under the window would not be entirely appropriate if the window is stained glass, that is, in height from floor to ceiling. For this, convectors are used, which are located in the floor and do not spoil the view of the main interior. It is possible to use designer radiators in the form of a comfortable chair or bench. Modern technologies very successful in the manufacture of various types of heating devices, we will consider the most common of them separately.
Technical parameters of heating devices
Before buying any type of heater, you need to select several parameters. One of the options is pressure maintained by the heater. If you have your own system, then, for example, choosing a radiator can reduce the cost of the entire home heating procedure. Since you maintain the pressure in the system yourself, this will allow you to use radiators with lower pressure ratings, which are cheaper than radiators with thick material walls.
When connected to a central heating system, you do not have the ability to control the composition of the coolant and its pressure. Therefore, it is worth choosing radiators with a margin. Pressure can also be divided into several types: working, installation and burst pressure. As a rule, the working pressure is 8 atm., the installation pressure is 1.5 times more, and the burst pressure is 3 times the working pressure.
Our centralized heating systems are very unstable, so you should pay great attention to the pressure parameter of heating devices and fittings. After all, judge for yourself how the pressure jumps in the system after the repair work carried out in centralized system heating.
The next parameter of the heater is thermal power. talking plain language, the thermal power of the heater is the amount of heat given off to the room from the coolant. According to the method of heat transfer, the heater is divided into radiation (50%), convective-radiation (50-75%) and convective (75-95%).
Radiator device
As a rule, two control valves are installed on one heating device, this allows not only to regulate the temperature of the device, but also to remove it for washing or replacing it with a new one. Previously, only one tap was installed on the heater, which made repair work difficult, since it was necessary to turn off the entire heating system and drain the coolant. In modern conditions, the device of two cranes has become simply necessary.
So, the radiator remains the most common heating device, but the installation conditions are not always observed. Please note that radiators are installed mainly under windows. This is done in order to create thermal curtain, which will prevent big losses heat from the room, because windows are the best conductors of cold.
The size of the heater should be half the width of the window opening in residential premises, and in children's rooms - 75% of the width of the opening. It is also necessary to observe the installation distances to the floor, wall and window sill:
- wall - 20-50 mm;
- floor - 120 mm;
- window sill - 100 mm.
If you still neglect these dimensions of the installation of the heater, then be prepared for the fact that the room will not receive about 15% of heat. The same losses are possible when installing a decorative screen or painting the radiator in several layers. If the device decorative lattice is a necessity, then use a foil heat insulator on the wall behind the radiator. This will slightly increase the amount of heat supplied to the room and compensate for its loss.
When choosing radiators, you should pay attention to corrosion, since corrosion can very quickly damage the heater. When using aluminum radiators, copper should not be present in the heating system, as this causes the formation of a copper-aluminum galvanic pair and the radiators are susceptible to severe corrosion.
As a rule, it is very difficult to exclude copper from the system, since most pumps, boilers, valves, thermostats contain copper or brass in their construction. Although an aluminum radiator is a good heat exchanger, its use in a heating system is fraught with a number of problems during operation.
To solve the problem of corrosion, they invented bimetallic radiators, which are aluminum on the outside and metal on the inside. But such heating devices did not receive their calling because of their cost, especially if metal tubes inside covered with a special anti-corrosion coating.
From the foregoing, it becomes clear that the most rational choice there will be a cast iron radiator. Cast iron is inexpensive and easily withstands high pressures in systems. Modern production technologies make it possible to produce an almost smooth surface that will be easy to wipe from dust.
Convector
In simple terms, the convector is a U-shaped horizontal pipe on which the plates are pressed. Thus, the surface area of the heater is increased. To increase the rate of heat transfer, convectors are supplied with forced airflow, if you plan to install this type of convector, then you need to take care of the supply electric cable to power the fan. There are also options for the device of the control panel and software, which will allow you to program the heater to the desired temperature and at the right time.
The convector is installed in a niche in the floor, so its entire structure is hidden in the floor, and is decorated with a wooden or metal grate on top.
It is hard not to mention the use of water heated floors, which are gaining more and more popularity. You can read more about it in one of the articles on our website. Such a system can also be used on walls or behind a false wall made of. But it will be difficult to hang something on such walls without damaging the heating pipeline, so it is most rational to use it in the floor.
There is also such a heating device as a plinth, the coolant of which is water. Such a device is easy to install and convenient during operation, but due to its cost, it is inferior to other heating devices. Do your right choice from all the variety on the market.
The types of heating devices are determined by their design, which determines the method of heat transfer (convective or radiative heat transfer may prevail) from the outer surface of the devices to the room.
There are six main types of heating appliances, radiators, panels, convectors, finned tubes, smooth tube appliances and heaters.
By the nature of the outer surface, heating devices can be with a smooth (radiators, panels, smooth-tube devices) and ribbed surface (convectors, finned pipes, heaters).
According to the material from which heating devices are made, metal, combined and non-metallic devices are distinguished.
Schemes of heating devices
a - a radiator, b - a panel, c - a convector, e - a finned tube, e - a smooth-tube device.
Metal appliances are made of cast iron (from gray cast iron) and steel (from sheet steel and steel pipes).
In combined appliances, a concrete or ceramic mass is used, in which steel or cast iron heating elements (heating panels) are embedded, or finned steel pipes placed in a non-metallic (for example, asbestos-cement) casing (convectors).
Non-metallic appliances are concrete panels with embedded glass or plastic pipes or with voids without pipes at all, as well as porcelain and ceramic radiators.
By height, all heaters can be divided into high (more than 600 mm high), medium (400-600 mm) and low (<400 мм). Низкие приборы высотой менее 200 мм называются плинтусными.
Schemes of heaters of five types are shown in the figure. Heater used primarily for heating air in ventilation systems.
It is customary to call a radiator a device of a convective-radiation type, consisting of separate columnar elements - sections with channels of a round or elliptical shape. The radiator emits about 25% of the total amount of heat transferred from the coolant into the room with radiation, and is called a radiator only by tradition.
The panel is a device of a convective-radiation type of relatively shallow depth, which does not have gaps along the front. The panel transmits by radiation a somewhat larger part of the heat flux than the radiator, however, only the ceiling panel can be classified as radiation-type devices (radiating more than 50% of the total amount of heat).
The heating panel can have a smooth, slightly ribbed or wavy surface, columnar or serpentine channels for the coolant.
The convector is a convective type device consisting of two elements - a finned heater and a casing. The convector transfers at least 75% of the total amount of heat into the room by convection. The casing decorates the heater and increases the rate of natural air convection at the outer surface of the heater. The convectors also include baseboard heaters without casing.
A finned tube is an openly installed convective-type heating device, in which the area of \u200b\u200bthe outer heat-releasing surface is at least 9 times greater than the area of \u200b\u200bthe internal heat-receiving one.
Section of a two-column radiator
hp - total height, hm - assembly (construction) height, l - depth; b - width.
A smooth-tube device is called a device consisting of several steel pipes connected together, forming channels of a columnar (register) or serpentine (coil) shape for the coolant.
Consider how the requirements for heating devices are met.
1. Ceramic and porcelain radiators are usually made in the form of blocks, they are distinguished by a pleasant appearance, have a smooth surface that is easy to clean from dust. They have sufficiently high thermal performance: kp p \u003d 9.5-10.5 W / (m 2 K); f e /f f >1 and lower surface temperature in comparison with metal devices. When using them, the consumption of metal in the heating system is reduced.
Ceramic and porcelain radiators are not widely used due to insufficient strength, unreliable connection with pipes, difficulties in manufacturing and installation, and the possibility of water vapor penetrating through ceramic walls. They are applied in low-rise construction are used as non-pressure heating devices.
2. Cast iron radiators - widely used heating devices - are cast from gray cast iron in the form of separate sections and can be assembled into devices of various sizes by connecting sections on nipples with heat-resistant rubber gaskets. Various designs of one-, two- and multi-column radiators of various heights are known, but two-column medium and low radiators are most common.
Radiators are designed for maximum operational (the term is usually used - working) coolant pressure of 0.6 MPa (6 kgf / cm 2) and have relatively high thermal performance: k pr \u003d 9.1-10.6 W / (m 2 K) and f e /f f ≤1.35.
However, the significant metal consumption of radiators [(M = 0.29-0.36 W / (kg K) or 0.25-0.31 kcal / (h kg ° C)] and other disadvantages cause their replacement with lighter and less metal-intensive devices It should be noted their unattractive appearance when open installation in modern buildings. In sanitary and hygienic terms, radiators, except for single-column ones, cannot be considered to meet the requirements, since cleaning the intersection space from dust is quite difficult.
The production of radiators is laborious, installation is difficult due to the bulkiness and significant mass of the assembled devices.
Corrosion resistance, durability, layout advantages with good thermal performance, well-established production contribute to a high level of production of radiators in our country. At present, a two-column cast-iron radiator of the M-140-AO type with a section depth of 140 mm and inclined inter-column finning is being produced, as well as of the S-90 type with a section depth of 90 mm.
3. Steel panels differ from cast-iron radiators in their lower weight and cost. Steel panels are designed for operating pressures up to 0.6 MPa (6 kgf / cm2) and have high thermal performance: k pr \u003d 10.5-11.5 W / (m 2 K) and f e / f f ≤1.7 .
The panels are made in two designs: with horizontal collectors connected by vertical columns (columnar shape), and with horizontal channels connected in series (serpentine shape). The coil is sometimes made of steel pipe and welded to the panel; the device in this case is called sheet-tube.
The panels meet the architectural and construction requirements, especially in buildings made of large building elements, are easily cleaned of dust, and allow their production to be mechanized using automation. On the same production areas, it is possible to produce up to 5 million m 2 of steel radiators instead of 1.5 million m 2 enp of cast-iron radiators per year. Finally, when using steel panels, labor costs are reduced during installation due to a decrease in the mass of metal to 10 kg/m 2 enp. Reducing the mass increases the thermal stress of the metal to 0.55-0.8 W / (kg K). The spread of steel panels is limited by the need to use high quality cold-rolled steel sheet with a thickness of 1.2-1.5 mm, resistant to corrosion. When manufactured from ordinary sheet steel, the service life of the panels is reduced due to intense internal corrosion. Steel panels, except for sheet-pipe panels, are used in heating systems with deoxygenated water.
Steel stamped panels and radiators various designs are widely used abroad (in Finland, USA, Germany, etc.). In our country, medium and low steel panels are produced with columns and serpentine channels for single and paired (in depth) installation.
4. Concrete heating panels are manufactured:
- with concreted serpentine or columnar heating elements made of steel pipes with a diameter of 15 and 20 mm;
- with concrete, glass or plastic channels of various configurations (metal-free panels).
These devices are located in the enclosing structures of the premises (combined panels) or attached to them (attached panels).
When using steel heating elements concrete heating panels can be used at a working coolant pressure of up to 1 MPa (10 kgf / cm 2).
Concrete panels have thermal performance close to those of other smooth devices: k pr \u003d 7.5-11.5 W / (m 2 K) and f e / f f ≈1, as well as high thermal stress of the metal. Panels, especially combined ones, meet strict architectural, construction, sanitary and hygienic and other requirements.
However, concrete panels, despite their compliance with most of the requirements for heating devices, are not widely used due to operational shortcomings (combined panels) and installation difficulties (attached panels).
5. Convectors have relatively low thermal performance k pr \u003d 4.7-6.5 W / (m 2 K) and f e / f f<1, для отдельных типов конвекторов до 0,6. Тем не менее их производство во многих странах растет (при сокращении производства чугунных отопительных приборов) из-за простоты изготовления, возможности механизации и автоматизации производства, удобства монтажа (масса всего 5-8 кг/м 2 энп). Малая металлоемкость способствует повышению теплового напряжения металла прибора. M=0,8-1,3 Вт/(кг К) . Приборы рассчитаны на рабочее давление теплоносителя до 1 МПа (10 кгс/см 2).
Convectors can have steel or cast iron heating elements. Currently, convectors with steel heaters are produced:
- skirting convectors without casing (type 15 KP and 20 KP);
- low convectors without a casing (such as "Progress", "Accord");
- low convectors with casing (Comfort type).
Skirting convector type 20 KP (15 KP) consists of a steel pipe with a diameter of dy = 20 mm (15 mm) and closed fins 90 (80) mm high with a step of 20 mm, made of sheet steel with a thickness of 0.5 mm, tightly fitted on the pipe . Convectors 20 KP and 15 KP are produced in various lengths (every 0.25 m) and are assembled at the factory into units consisting of several convectors (in length and height), pipes connecting them and control valves.
It should be noted such an advantage of using skirting convectors as improving the thermal regime of rooms when they are placed in the lower zone along the length of windows and outer walls; in addition, they take up little space in the depth of the premises (building depth is only 70 and 60 mm). Their disadvantages are: the cost of sheet steel, which is not efficiently used for heat transfer, and the difficulty of cleaning the fins from dust. Although their dust-collecting surface is small (less than that of radiators), they are still not recommended for heating rooms with increased sanitary and hygienic requirements (in medical buildings and children's institutions).
The low convector of the "Progress" type is a modification of the 20 KP convector, based on two pipes connected by common fins of the same configuration, but of greater height.
The low convector of the Akkord type also consists of two parallel steel pipes d y = 20 mm, through which the coolant flows in series, and vertical finning elements (height 300 mm) made of sheet steel 1 mm thick, mounted on pipes with 20 mm gaps. Ribbed elements forming the so-called front surface of the device are U-shaped in plan (rib 60 mm) and open to the wall.
Convector type "Accord" is manufactured in various lengths and installed in one or two rows in height.
In a convector with a casing, air mobility increases, which contributes to an increase in the heat transfer of the device. The heat transfer of convectors increases depending on the height of the casing.
Jacketed convectors are mainly used for space heating in public buildings.
The low convector with Comfort casing consists of a steel heating element, a detachable casing made of steel panels, an air outlet grille and an air regulation valve. In the heating element, rectangular ribs are mounted on two pipes d y =15 or 20 mm in increments of 5 to 10 mm. The total mass of the heater metal is 5.5-7 kg/m 2 enp.
The convector has a depth of 60-160 mm, is installed on the floor or on the wall and can be through the movement of the heat carrier (for connecting horizontally with another convector) and end (with a coil).
The presence of a valve for air control allows you to connect the convectors in series along the coolant without installing fittings to control its amount. Convectors can also be with artificial convection when installed in a fan casing of a special design.
6. Ribbed tubes are made of gray cast iron and are used at operating pressures up to 0.6 MPa (6 kgf / cm 2). The most widespread are flanged cast-iron pipes, on the outer surface of which thin cast round ribs are placed.
Due to the high coefficient of finning, the outer surface of a finned tube is many times larger than the surface of a smooth tube of the same diameter (inner diameter of the finned tube 70 mm) and length. The compactness of the device, the reduced temperature of the surface of the fins when using a high-temperature coolant, the relative ease of manufacture and low cost determine the use of this device, which is inefficient in terms of heat engineering: k pr \u003d 4.7-5.8 W / (m 2 K); f e / f f \u003d 0.55-0.69. Its disadvantages also include unsatisfactory appearance, low mechanical strength of the ribs and the difficulty of cleaning from dust. Finned tubes also have a very low thermal stress of the metal: M = 0.25 W / (kg K).
They are applied in industrial premises where there is no significant dust emission, and in auxiliary rooms with temporary stay of people.
Currently, round finned tubes are produced in a limited range of lengths from 0.75 to 2 m for horizontal installation. Steel-iron finned tubes are being developed, which include PK-type finned tube with 70 X 130 mm rectangular fins. This pipe is easy to manufacture and relatively light in weight. The base is a steel pipe d y \u003d 20 mm, poured into cast-iron fins 3-4 mm thick. Two longitudinal plates are cast over the ribs to protect the main fin from mechanical damage. The device is designed for operating pressure up to 1 MPa (10 kgf / cm 2).
Scheme of a convector with a casing
1 - heating element, 2 - casing, 3 - air valve.
For a comparative thermal performance of the main heating devices, the table shows the heat transfer of devices 1 m long.
Heat transfer of heating devices with a length of 1 m at Δt cf = 64.5 ° and a water flow rate of 300 kg / h.
| Heating appliances | Instrument depth, mm | Heat transfer | |
| W/m | kcal/(h m) | ||
| Radiators: | |||
| - type M-140-AO | 140 | 1942 | 1670 |
| - type S-90 | 90 | 1448 | 1245 |
| Steel panels type MZ-500: | |||
| - single | 18 | 864 | 743 |
| - paired | 78 | 1465 | 1260 |
| Convectors type 20 KP: | |||
| - single row | 70 | 331 | 285 |
| - three-row | 70 | 900 | 774 |
| Convectors: | |||
| - type "Comfort" H-9 | 123 | 1087 | 935 |
| - type "Comfort-20" | 160 | 1467 | 1262 |
| Finned tube | 175 | 865 | 744 |
As can be seen from the table, deeper heating devices are characterized by high heat transfer per 1 m of length; The cast-iron radiator has the greatest heat transfer, the smallest - the plinth convector.
7. Smooth-tube devices are made of steel pipes in the form of coils (the pipes are connected in series according to the movement of the coolant, which increases its speed and the hydraulic resistance of the device) and columns or registers (parallel connection of pipes with reduced hydraulic resistance of the device).
The devices are welded from pipes d y =32-100 mm, located at a distance from one another of at least a selected pipe diameter to reduce mutual exposure and, accordingly, increase heat transfer to the room. Smooth-tube devices are used at operating pressures up to 1 MPa (10 kgf / cm 2). They have high thermal performance: k pr \u003d 10.5-14 W / (m 2 K) and f e / f f ≤1.8, and the highest values \u200b\u200bare related to smooth steel pipes with a diameter of 32 mm.
Indicators of heating devices of various types
positive | pressure | Requirements for devices | |||||||||
Technical | architecturally Construction | sanitary hygienic | production Mounting |
||||||||
labor |
|||||||||||
| Radiators: | |||||||||||
Physical and | 2-4 | >1 | - | ++ | + | - | + | ++ | - | - | |
| - cast iron | 6 | Up to 1.35 | - | - | - | + | - | - | - | - | |
| Panels: | |||||||||||
| - steel | 6 | Up to 1.7 | ++ | + | + | - | - | ++ | ++ | + | |
| - concrete | 10 | ~ 1 | + | ++ | + | ± | ++ | + | - | ± | |
| - without casing | |||||||||||
| - with casing | 10 | <1 | ± | + | ± | ± | + | - | ++ | + | |
| 6 | + | - | - | ++ | + | - | - | - | |||
| 10 | Up to 1.8 | - | - | - | - | - | ++ | - | - | ||
| 8 | >1 | - | + | - | ++ | + | - | + | - | ||
Note: The sign + indicates the fulfillment, the sign - non-fulfillment of the requirements for devices; the ++ sign marks the indicators that determine the main advantage of this type of heater.
Smooth-tube devices meet sanitary and hygienic requirements - their dust-collecting surface is small and easy to clean.
The disadvantages of smooth-tube devices include their bulkiness due to the limited area of the outer surface, the inconvenience of placing under windows, and the increase in steel consumption in the heating system. Given these shortcomings and unfavorable appearance, these devices are used in industrial premises in which there is a significant emission of dust, as well as in cases where other types of devices cannot be used. In industrial premises, they are often used to heat skylights.
8. Heaters - compact heating devices of a large area (from 10 to 70 m2) of the outer surface formed by several rows of finned tubes; apply them to air heating premises in local and central systems. Directly in the premises, heaters are used as part of air-heating units various types or for recirculating air heaters. The heaters are designed for the operating pressure of the coolant up to 0.8 MPa (8 kgf/cm 2); their heat transfer coefficient depends on the speed of movement of water and air, therefore it can vary widely from 9 to 35 or more W / (m 2 K) [from 8 to 30 or more kcal / (h m 2 ˚C)].
The table shows the indicators of heating devices of various types; conditionally noted the fulfillment or non-fulfillment of the requirements for devices.
heating device- this is an element of the heating system, which serves to transfer heat from the coolant to the air of the heated room.
1. Registers from smooth pipes represent a bundle of pipes located in two rows and united on both sides by two pipes - collectors, equipped with fittings for supplying and discharging the coolant.
Registers from smooth pipes are used in rooms where increased sanitary and technical and hygiene requirements, as well as in industrial buildings with an increased degree of fire hazard, where a large accumulation of dust is unacceptable. The devices are hygienic, easy to clean from dust and dirt. But not economical, metal-intensive. Estimated heating surface of 1m smooth pipe.
2. Cast iron radiators. The block of cast-iron radiators consists of cast iron sections interconnected by nipples. They are 1-2 and many channel. In Russia, mainly 2-channel radiators. According to the mounting height, radiators are divided into high 1000 mm, medium - 500 mm and low 300 mm.
M-140-AO radiators have inter-column finning, which increases their heat transfer, but reduces aesthetic and hygienic requirements.
Cast iron radiators have a number of advantages. This:
1. Corrosion resistance.
2. Fine-tuned manufacturing technology.
3. Ease of changing the power of the device by changing the number of sections.
The disadvantages of these types of heaters are:
1. Big expense metal.
2. The complexity of manufacturing and installation.
3. Their production leads to environmental pollution.
3. Finned tubes. They are a cast iron pipe with round fins. The fins increase the surface of the instrument and reduce the surface temperature.
Ribbed tubes are mainly used in industrial plants.
Advantages:
1. Cheap heaters.
2. Large surface heating.
Disadvantages:
Do not meet sanitary and hygienic requirements (difficult to clean from dust).
4. Stamped steel radiators. They are two putty steel places, interconnected by contact welding.
There are: columnar radiators RSV 1 and serpentine radiators RSG 2.
Column radiators: form a series of parallel channels, interconnected at the top and bottom by horizontal collectors.
Serpentine radiators form a series of horizontal channels for the passage of the coolant.
Steel plate radiators made in single and double rows. Double-row are made of the same standard sizes as single-row, but consist of two plates.
Advantages:
1. Small weight of the device.
2. Cheaper than cast iron by 20-30%.
3. Less transportation and installation costs.
4. Easy to install and meet sanitary and hygienic requirements.
Disadvantages:
1. Small heat dissipation.
2. Special treatment of heating water is required, since ordinary water corrodes with metal. Found wide application in housing in public buildings. Due to the rise in the price of metal, the release is limited. High price.
5. Convectors. They are a series of steel pipes through which the coolant moves and steel finning plates mounted on them.
Convectors are available with or without casing. They are made of various types: For example: Comfort convectors. They are divided into 3 types: wall-mounted (hung on a wall h = 210 m), island (installed on the floor) and ladder (built into the building structure).
Convectors are made end and through. Convectors are used for heating buildings for various purposes. Used mainly in central Russia.
Non-metallic heating devices
6. Ceramic and porcelain radiators. They are a panel cast in porcelain or ceramic with vertical or horizontal channels.
Such radiators are used in rooms with increased sanitary and hygienic requirements for heating devices. Such devices are used very rarely. They are very expensive, the manufacturing process is laborious, short-lived, subject to mechanical stress. It is very difficult to connect these radiators to metal pipelines.
7. Concrete heating panels. Represent concrete plates with coils of pipes embedded in them. Thickness 40-50 mm. They are: window sill and partition.
Heating panels can be attached and built into the construction of walls and partitions. Concrete panels meet the most stringent sanitary and hygienic requirements, architectural and construction requirements.
Disadvantages: difficulty of repair, large thermal inertia, which complicates the regulation of heat transfer, increased heat loss through additionally heated external structures of buildings. Used mainly in medical institutions in operating rooms and in maternity hospitals in children's rooms.
Plumbing heaters must meet the heat engineering, sanitary and hygienic and aesthetic requirements.
Thermal engineering assessment heating appliances is determined by its heat transfer coefficient.
Sanitary and hygienic assessment- characterized constructive solution appliance to make it easier to keep clean.
The temperature of the outer surface of the heater must meet sanitary and hygienic requirements. In order to avoid intense burning of dust, this temperature should not exceed 95 ° C for residential and public buildings, and 85 ° C for medical and children's institutions.
Aesthetic evaluation- the heater must not spoil internal view rooms, should not take up much space.