Heating appliances: types, classification, electrical units, requirements for them
In order for the long-awaited warmth to come into the home, it is not enough just to burn the fuel in the furnace and load the coolant with the calories received. It is necessary to transfer the precious cargo to the premises that need it without unjustified losses. This is exactly what heaters do.
The most important place among them is water heating devices. Water as a heat carrier has many advantages: it has high fluidity, it is ecologically impeccable, it is affordable.
Heating appliances hydraulic systems heating - these are radiators, convectors and water (not to be confused with electric!) Underfloor heating. There are also smooth and cast-iron finned tubes, but they are mainly used for heating industrial buildings.
Radiator translated from Latin - "radiating", up to 30% heat flow it gives off in the form of radiation, the rest - in the form of convection. In a convector, the convection phenomenon that gave it its name (from the Latin convectio - bringing, delivery) accounts for over 90% of the heat flow. In city apartments and modern suburban housing, heating devices are the main "acting heroes" of heating systems. In city apartments and modern suburban housing, heating devices are the main elements of heating systems. Heating appliances, with rare exceptions, are always in sight, and design is important for them. According to marketers, he is given priority by up to 50% of buyers. However, beauty that is difficult to ration is an important, but not the only characteristic that the buyer pays attention to.
The choice of heating equipment
First of all, the buyer pays attention to the thermal power of the device. . AT last years noticeably improved thermal insulation of premises. The result is that much less thermal energy is spent on heating them than a decade ago. But during the same time in our apartments, the number of household appliances (computers, microwave ovens, audio systems, etc.) has visibly increased, whose total effect on the air temperature in the room cannot be ignored.
nota bene SINGLE AND TWO PIPE SYSTEMS
In a single-pipe system, heaters are connected in series. As a result, each subsequent coolant comes colder than the previous one. That is, the temperature depends on the distance of the radiator from the heat source. Such a system is difficult to regulate, and the heating devices used in it must have low hydraulic resistance. At two-pipe system heating, the coolant is supplied through one pipe, and discharged through another, which allows parallel, independent connection heating appliances. Another advantage of the "two-tube" is that it allows you to maintain low operating pressures in the system, thereby increasing the service life of communications and making it possible to use cheaper thin-walled radiators. Such schemes are most common in Western Europe. In Russia, however, especially in houses built in the 1950s–80s, single-pipe systems predominate.
Therefore, today the problem of maintaining optimal temperature, the possibility of its correction is relevant. The consumer needs regulated heat. Warmth that can lead to a reasonable compromise between two opposing desires - not to feel discomfort and pay less for the price that rises every year thermal energy. Such heat is brought into the house by easily controlled heaters that adequately respond to changes in air temperature (it’s very good if they work in automatic mode).
It is also an axiom that the consumer should receive absolutely safe heat. That is, completely excluding even the minimal possibility of mechanical and thermal injuries. A modern heater should be pleasant not only externally, but also to the touch. Although the temperature of the water circulating in it may approach 90-95 °C, the temperature of the enclosure should not exceed the absolutely safe 40-45 °C. This is important both for furniture and for electrical appliances that are undesirable to be placed next to heating ones. Modern radiators and convectors have reduced the previously quite extensive "exclusion zone" to zero. And now, in the immediate vicinity of them, you can without any fear place TVs, refrigerators and even expensive leather furniture.
For a modern city dweller, who spends almost twenty-four hours a day within four walls, it is very important that he is also warmed by healthy warmth. Lower than the old conventional batteries, the temperature of the outer surface and an increase in the proportion of convection - these are the two main factors that ensure a more even distribution of air temperature in the room, eliminate the causes of drafts, and also contribute to the natural normalization of humidity, preventing the formation of mold and fungi in the room and, as a result, improve the well-being of the people who live in these premises.
Hot water heating systems tend to shrink in size, which in principle does not affect the heat supply.
The design of heating devices is not only expressive forms or eye-catching coloring, but also small sizes. The evolution of heating devices along the path of reducing their mass and volume does not come from aesthetic considerations alone. The small size is also economical. The heater is smaller (that is, its own mass and the amount of coolant contained in it at a time), which means that its thermal inertia is smaller, it responds faster to temperature changes, changing to the desired mode. For example, a heating system with copper-aluminum radiators JAGA reaches its full capacity in just 10 minutes.
The desire to minimize the volume occupied by the heater, brought to the absolute, is expressed in the production of the mini series, presented in the assortment of many manufacturers. These devices are so small (their height is only 8–10 cm) that they can simply be hidden under the floor, which, however, is not necessary at all - a radiator or convector can serve as an interior decoration no less than a stylish interior door, an original lamp or panel on the wall. But to hide communications (valves and piping) under the casing is quite reasonable for any size.
What are they made from?
Radiators and convectors made of various materials - steel, cast iron, aluminum, a combination of several metals (bimetallic radiators).
When choosing a radiator for your home, you need to pay attention to the following characteristics:
- working and test (or pressure testing) pressure; usually their ratio is in the range of 1.3–1.5;
- nominal heat flow (flow determined under normalized conditions: temperature difference - 70 ° C, coolant flow rate - 0.1 kg / s when it moves in the device according to the "top-down" scheme, atmospheric pressure - 1013.3 GPa);
- dimensions (length, height, depth, center-to-center distance);
- mass and a value derived from it - specific material consumption (measured in kg / kW);
- price.
Radiators
Cast iron radiators. Cast iron has a high thermal conductivity. For these reasons, heaters made from it can be used in systems with large pressure drops and poor water treatment (increased aggressiveness, contamination, scale pieces). Just all these qualities are possessed by single-pipe systems prevailing in multi-storey construction.
Cast iron radiators have been produced for over 100 years. This is a kind of classic, on which more than one generation of our fellow citizens was “brought up”, usually calling this heater a battery. Until the 1960s, almost the entire range of heating appliances in our country was formed from batteries. And today, this heater, prematurely written off by many, still holds up to 70% of the Russian market.
Modern heating radiators have a good design and high heat dissipation.
In our country, cast-iron radiators are most often used, consisting of two-channel sections connected to each other. The number of sections is determined by the calculated heating surface. Single-channel, and abroad multi-channel (up to 9 channels in one section) cast-iron radiators are also used.
Their disadvantages include high weight, a significant percentage of factory defects - cracks and cavities resulting from poor-quality casting and reducing a potentially very long service life. According to the regulations, the warranty period for radiators is 2.5 years from the date of commissioning or sale within the warranty period of storage, and manufacturers and sellers promise at least several decades of flawless service for these devices. Sometimes cast-iron radiators are reproached for the lack of an attractive appearance(remember: “harmonica battery”). However, the use of modern design and powder paints can give charm to these veterans.
Systems in which cast-iron radiators are involved, due to the large thermal inertia, are not easy to regulate. Although there is a way out of this situation, and in some models, by reducing the capacity of the sections, it is possible to effectively use thermostatic elements (such, for example, RTD-G, RTD-N thermostats from Danfoss).
Domestic products prevail in this class of heating devices. Among the foreign ones, cast-iron sectional radiators of firms can be distinguished Roca(Spain), Viadrus(Czech), Biasi(Italy), "Santechlit"(Belarus), Turkish radiators Ridem.
Steel panel radiators formed from two stamped sheets. In our country, their production began in the 1960s. They are distinguished from sectional cast iron ones by their lower weight (specific gravity per 1 kW is approximately three times lower) and thermal inertia. They are considered "sissies" because they are more sensitive to hydraulic shocks that occur when the system is stopped or started and are afraid of corrosion provoked by frequent drains or high oxygen content in the coolant. In systems where there are multiple “higher than normal” pressure surges, it is not necessary to count on the long service life of steel panel radiators. Typically, the operating pressure of devices of this type does not exceed 9 atm.
expert opinion V.V. Kotkov
Commercial Director of HitLine Group of Companies
It can be argued that the proportion of progressive (in relation to the classic cast-iron ones that still prevail) designs of radiators is increasing. Today, up to 5 million sections are produced annually in Europe aluminum radiators. To a large extent, the development of this production is stimulated by the Russian market, where the demand for them annually increases by 5-10%. Therefore, leading Western companies are trying to adapt their products to Russian conditions as much as possible (the problems with water treatment that exist in our country, high unstable pressure in systems central heating etc.). Although, by tradition, many Russian construction companies give priority to cast-iron radiators, the number of firms working with aluminum is steadily increasing. After all, an aluminum radiator is not just a private technical solution, but the solution to a whole range of problems related to efficiency, safety and design. He is able to fit into modern interior, it does not need to be masked, spending a lot of money on it.
Wide application steel panel radiators found in low-rise buildings. They are especially appropriate for a two-pipe heating system, which is preferred in cottage construction. AT high-rise buildings it is reasonable to install them if there is an individual heating point, i.e., a boiler room. Three-quarters of steel panel radiator sales are from the private developer, high-end residential and civil buildings. The most famous models of firms in our country are: VSZ(Slovakia), Dia Norm, Preussag, Kermi(Germany), Korado(Czech), DeLonghi(Italy), Stelrad(Holland), Purmo(Poland), Roca(Spain), DemirDokum(Turkey), Impulse West(England, but assembly in Italy), Dunaferr(Hungary).
Tubular and sectional the radiators are outwardly similar, although they are structurally different - there are no tubular sections as such, and the tubes are connected by two monolithic collectors. Both have an attractive appearance and organically fit into almost any interior. The streamlined shape of the radiator eliminates the possibility of injury to a person. The small capacity of the sections contributes to effective thermoregulation. And if some of its elements are made of a finned tube, then it is possible, without changing the linear dimensions, to significantly increase the power of the radiator.
The working pressure of tubular steel radiators is higher than that of panel radiators - 10 or more atm.
In our market, this type of radiators is represented mainly by German brands Bemm, Arbonia, Kermi.
Aluminum called radiators made of an alloy of aluminum with silicon (the content of aluminum itself is from 80 to 98%). Aluminum is a material with high thermal conductivity, but with high requirements for chemical composition coolant. The disadvantage of radiators made of aluminum-silicon alloy with a high content of silicon is the generation of hydrogen upon contact with water. The excellent design of most radiators somewhat spoils the automatic air release valve installed on each device, since active hydrogen evolution occurs during operation.
A significant part of the Russian market of aluminum radiators is occupied by products of Italian companies: Rovall, Industrie Pasotti, Global, Alugas, Aural, Fondital, Giacomini, Nova Florida. There are also Spanish radiators Roca, Czech Radus, English Wester, etc.
Bimetal radiators. They look like aluminum. The sections consist of two thin-walled steel pipes (channels for the passage of the coolant), pressed under pressure with a high-quality aluminum alloy. The logic of this symbiosis is based on the fact that aluminum has a high thermal conductivity, and steel has strength, which guarantees the operation of the device at excess pressure. Italian firms are the actual monopolists in the production of bimetallic radiators. The most famous brand is Sira.
Bimetal radiators are both durable and efficient.
Convectors. The basis of the convector design is a heating element enclosed in a casing. Leaking to it from below, the cooled room air heats up and rises up. Due to this, more than 90% of the heat is transferred by convection.
Most widespread convectors received in autonomous systems. They are especially effective at low coolant temperatures. So, they are able to warm up the room at a water temperature of only 40 ° C. For the convenience of the user, the convector is equipped with an air valve and a drain tube. The built-in thermostat and the regulator of a pressure of water do its operation economic.
The convector fits especially harmoniously into the modern architectural environment, which actively uses large windows, bay windows, winter gardens, etc.
Structurally, it can have four solutions. Radiator convectors are a combination of two devices, reflected in the name itself. They are installed near windows, on the floor or on small stands. Plinth convectors are located in the floor under large windows. The low height (90–100 mm) does not require niches, and a weak convective flow can be increased by a slowly rotating fan. Convectors recessed into the floor are the best option for residential premises on the first floors. The device is placed in a kind of shaft, cold air passing along the window freely enters the convector, and the flow of warm air provides natural circulation in room. And finally, convectors covered with a decorative screen. Unlike radiators, a closed convector does not lose heat transfer at all, on the contrary, the screen helps to increase traction.
Pipes for water heating
The functioning of heating devices of hydraulic systems is impossible without pipes. The first polymer (polyvinyl chloride) pipes were made in 1936 in Germany. The first pipeline of them was built in the same place in 1939. But the active introduction of polymer pipes in water supply and heating systems began in the mid-1950s, and in our country since the early 1970s.
Both for systems using classic radiators and for underfloor heating, pipes made of cross-linked polyethylene are best suited. They are not afraid of short-term temperature rise up to +110 °C ( normal temperature their operation is usually +95 °C). With all the advantages, they have one minus - a high price.
Used in heating systems propylene pipes. But at the same time, the high coefficient of thermal expansion of the material should be taken into account. The service life of polymer pipes can reach 30 years or more. The gasket must be hidden: they are hidden in skirting boards, shafts, channels or floor structures. If polymer pipes are used in heating systems, then in order to protect them from exceeding the parameters of the coolant, it is necessary to provide for the installation of automatic control devices.
The advantages of plastic and metal combine metal-plastic pipes. They are combined with other materials, do not allow oxygen to pass through, and due to the smooth inner surface, they have less resistance to leakage than steel, which, in conditions of mass use, saves a lot of energy. The warranty period is at least 20 years, but, as a rule, in reality it reaches 30–50 years. For comparison, according to the State Construction Committee of the Russian Federation, galvanized steel pipes in internal systems serve an average of 12-16 years, and the "black" - half as much.
Competing devices for hot water heating systems
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Warm floors
It is logical to make a smooth transition from pipes to water heated floors. This heating system has many advantages. Firstly, low (40–55 °C) coolant temperature contributes to energy savings. Secondly, due to the participation in the heat emission of the entire floor surface, an almost ideal horizontal and close to ideal vertical temperature distribution is ensured. So, if the floor surface temperature is 22-25 ° C, then the air temperature at head level is 19-22 ° C. People, according to research by hygienists, feel most comfortable if their head is a little colder than their feet. In the hot season, running water with a temperature of 10–12 ° C through pipelines can effectively cool the room. Thirdly, water warm floor make it possible to rationally use the living space.
In new buildings with bulk concrete floors system floor heating consists of several layers: concrete slab, hydro, sound and heat insulation, film, pipes, concrete screed(the most common concrete grade not lower than M-300 is used), a cement layer for leveling the floor and coating. In old buildings, the dry laying method is used, when the heating pipes are installed in the insulation of the carrier layer in special metal plates that ensure uniform heat distribution.
A water heated floor can also be installed under a wooden floor mounted on beams. To do this, a subfloor is made from a board, chipboard, moisture-resistant plywood or DSP (cement-bonded particle board with a thickness of at least 20 mm).
Fastening pipes in circuits is carried out using reinforcing mesh and wire, fastening tape and mounting brackets.
In accordance with Russian regulations, the average temperature of the heated floor should not exceed 26 °C. Therefore, before instructing the water warm floor the role of the main heating system, it is necessary to carefully calculate whether the heat "removed" from it is enough for the room or whether a backup system is still needed.
AT heating system heating devices are used, which serve to transfer heat to the room. Manufactured heating devices must meet the following requirements:
- Economic: low cost of the device and small consumption material.
- Architectural and construction: the device must be compact and match the interior of the room.
- Production and installation: mechanical strength of the product and mechanization in the manufacture of the device.
- Sanitary and hygienic: low temperature surface, small horizontal surface area, easy to clean surfaces.
- Thermotechnical: maximum heat transfer to the room and controllability of heat transfer.
Instrument classification
The following indicators are distinguished in the classification of heating devices:
- - the value of thermal inertia (large and small inertia);
- - the material used in the manufacture (metal, non-metal and combined);
- — method of heat transfer (convective, convective-radiation and radiation).
Radiation devices include:
- ceiling emitters;
- sectional cast iron radiators;
- tubular radiators.
Convective-radiation devices include:
- floor heating panels;
- sectional and panel radiators;
- smooth tube devices.
Convection devices include:
- panel radiators;
- ribbed tubes;
- plate convectors;
- tubular convectors.
Consider the most applicable types of heaters.
Aluminum sectional radiators
Advantages
- high efficiency;
- light weight;
- ease of installation of radiators;
- efficient operation of the heating element.
Flaws
- 1. not suitable for use in old heating systems, as heavy metal salts destroy the protective polymer film of the aluminum surface.
- 2. long-term operation leads to the unusability of the cast structure, to rupture.
Mainly used in central heating systems. Operating pressure of radiators from 6 to 16 bar. Note that the greatest loads can withstand the radiators, which were cast under pressure.
Bimetal Models
Advantages
- light weight;
- high efficiency;
- the possibility of prompt installation;
- heat large areas
- withstand pressure up to 25 bar.
Flaws
- have a complex structure.
These radiators will last longer than others. Radiators are made of steel, copper and aluminum. The material aluminum conducts heat well.
Cast iron heating appliances
Advantages
- not subject to corrosion;
- transfer heat well;
- withstand high pressure;
- it is possible to add sections;
- the quality of the heat carrier does not matter.
Flaws
- significant weight (one section weighs 5 kg);
- brittleness of thin cast iron.
The operating temperature of the heat carrier (water) reaches 130°C. Cast iron heaters serve for a long time, about 40 years. Heat transfer performance is not affected by mineral deposits inside the sections.
There is a wide variety cast iron radiators: single-channel, double-channel, three-channel, embossed, classic, enlarged and standard.
In our country, the economical version of cast iron appliances has received the greatest use.
Steel panel radiators
Advantages
- increased heat transfer;
- low pressure;
- easy cleaning;
- simple installation of radiators;
- small weight compared to cast iron.
Flaws
- high pressure;
- metal corrosion, in the case of using ordinary steel.
The steel radiator of the present time heats up better than cast iron.
Steel heaters have built-in thermostats that provide constant temperature control. The design of the device has thin walls and responds quickly enough to the thermostat. Inconspicuous brackets allow you to mount the radiator on the floor or wall.
The low pressure of the steel panels (9 bar) does not allow them to be connected to the central heating system with frequent and significant overloads.
Steel tubular radiators
Advantages
- high heat transfer;
- mechanical strength;
- aesthetic look for interiors.
Flaws
- high price.
Tubular radiators are quite often used in interior design because they decorate the room.
Due to corrosion, conventional steel radiators are currently not produced. If the steel is subjected to anti-corrosion treatment, this will significantly increase the cost of the device.
Radiator made of galvanized steel is not subject to corrosion. It has the ability to withstand a pressure of 12 bar. A radiator of this type is often installed in multi-storey residential buildings or organizations.
Heating appliances of convector type
Advantages
- small inertia;
- small mass.
Flaws
- low heat transfer;
- high demands on the coolant.
Convector-type appliances quickly heat the room. They have several manufacturing options: in the form of a plinth, in the form of a wall block and in the form of a bench. There are also floor convectors.
This heater uses a copper tube. A coolant moves through it. The tube is used as an air stimulator (hot air goes up and cold air goes down). The process of air change takes place in a metal box, which does not heat up.
Convector type heaters are suitable for rooms with low windows. Warm air from a convector installed near the window prevents the incoming cold air.
Heating appliances can be connected to a centralized system, as they are designed for a pressure of 10 bar.
Towel dryers
Advantages
- variety of shapes and colors;
- high pressure indicators (16 bar).
Flaws
- may not perform its functions due to seasonal interruptions in water supply.
Steel, copper and brass are used as manufacturing materials.
Towel dryers are electric, water and combined. Electric ones are not as economical as water ones, but allow buyers not to depend on the availability of water supply. Combined heated towel rails must not be used if there is no water in the system.
Radiator selection
When choosing a radiator, it is necessary to pay attention to the practicality of the heating element. Next, you need to remember the following characteristics:
- overall dimensions of the device;
- power (per 10 m2 of area 1 kW);
- working pressure (from 6 bar - for closed systems, from 10 bar for central systems);
- acidic characteristics of water as a heat carrier (this heat carrier is not suitable for aluminum radiators).
After clarifying the main parameters, you can proceed to the choice of heating devices according to aesthetic indicators and the possibility of its modernization.
According to 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.
Metal appliances are made of cast iron (from gray cast iron) and steel (from sheet steel and steel pipes).
Combined appliances use a concrete or ceramic array in which steel or cast iron heating elements (heating panels) are embedded, or ribbed 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.
In terms of 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 five types of heaters are shown in Fig. III.
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 with radiation).
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 skirting heaters without a casing.
A finned tube is an openly installed convective type heating device, in which the area of \u200b\u200bthe external heat-giving surface is at least 9 times greater than the area of \u200b\u200bthe internal heat-receiving surface.
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
in the form of blocks, have a pleasant appearance, have a smooth, lay down
surface to be cleaned of dust. They have sufficiently high
logistic indicators
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 used in low-rise construction, used as non-pressure heating devices.
2. Cast iron radiators - widely used heating
burs - cast from gray iron in the form of separate sections and can
be assembled into devices of various sizes by connecting sections
on nipples with gaskets made of heat-resistant rubber. Known differently
figurative designs of one-, two- and multi-column radiators
personal height, but the most common two-column (III.2)
medium and low radiators.
Radiators are designed for maximum operational (usually the term is used - working) coolant pressure of 0.6 MPa (6 kgf / cm2) and have relatively high thermal performance
However, the significant metal consumption of radiators and other disadvantages lead to their replacement with lighter and less metal-intensive devices. It should be noted their unattractive appearance when installed outdoors 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 pressure up to 0.6 MPa (6 kgf/cm2) and have high thermal performance
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 m2 of steel radiators instead of 1.5 million m2 enp of cast-iron radiators per year. Finally, when using steel panels, labor costs during installation are reduced due to a decrease in the mass of metal to 10 kg/m2 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.
Stamped steel panels and radiators of 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:
a) with concreted coil heating elements
or columnar form from steel pipes with a diameter of 15 and 20 mm;
b) with concrete, glass or plastic channels of various
noy configuration (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/cm2).
I have concrete panels! thermotechnical indicators close to those of other smooth devices, 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, for some types of convectors up to 0.6. Nevertheless, their production in many countries is growing (with a reduction in the production of cast-iron heaters) due to ease of manufacture, the possibility of mechanization and automation of production, ease of installation (weight is only 5-8 kg / m2 enp). Low metal consumption contributes to an increase in the thermal stress of the metal of the device. M=0.8-1.3 W/(kg-K) . The devices are designed for the operating pressure of the coolant up to 1 MPa (10 kgf/cm2).
Convectors can have steel or cast iron heating elements. At present, convectors with steel heaters are produced in the USSR:
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 finning 90 (80) mm high with a pitch of 20 mm, made of sheet steel 0.5 mm thick, 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 dY = 20 mm, through which the heat carrier flows in series, and vertical finning elements (height 300 mm) made of 1 mm thick sheet steel, 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 shell
Jacketed convectors are mainly used for space heating in public buildings (for example, in Moscow they are installed in the buildings of the Palace of Congresses, the Rossiya and Intourist hotels, and the Oktyabr cinema).
The low convector with Comfort casing consists of a steel heating element, a demountable casing made of steel panels, an air outlet grille and an air regulation valve (Sh.Z). In the heating element, rectangular fins are mounted on two pipes dy = 15 or 20 mm in increments of 5 to 10 mm. The total mass of the heater metal is 5.5-7 kg/m2 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. Finned tubes are made of gray cast iron and are used at operating pressures up to 0.6 MPa (6 kgf/cm2). 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 surface temperature 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 thermal engineering. 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 used in industrial premises in which there is no significant dust emission, and in auxiliary premises 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-cast ribbed tubes are being developed, which include a ribbed tube of the RK type with rectangular ribs 70X XI30 mm. This pipe is easy to manufacture and relatively light in weight. The base is a steel pipe d?y = 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 working pressure up to 1 MPa (10 kgf/cm2).
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).
Devices are welded from pipes cfy = 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
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; they are used for air space heating in local and central systems. Directly in rooms, heaters are used as part of air-heating units of various types or for recirculation air heaters (see § 72-73). The heaters are designed for the operating pressure of the coolant up to 0.8 MPa (8 kgf/cm2); 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/(m2-K) [from 8 to 30 or more kcal/(h-m2-°C)].
In table. II 1.3 shows the indicators of heating devices of various types; conditionally noted the fulfillment or non-fulfillment of the requirements for devices.
What are water heating systems? This article is an introductory excursion designed to acquaint you with the main types and components of heating systems. In addition, we will get acquainted with the basic principles of creating home heating schemes with our own hands.
Classification
It is clear that, by definition, water or a coolant based on it with a lower freezing point is used as a coolant. Are there alternatives?
- Steam heating. The heat carrier is superheated high-pressure steam. Temperature allows heaters to be made smaller or more efficient for the same size.
Please note: the reverse side of efficiency is a greater risk of accidents (steam heating is not used in residential premises) and faster corrosion of pipes and registers made of corrosion-resistant steels.
- . Heated air is diluted by heat-insulated air ducts, at the same time performing ventilation functions.
- Decentralized heating implies that instead of any coolant a separate heat source is used for each room or even for each zone of the room. This is how electric and gas convectors, infrared panels and oil coolers work.
Let us return, however, to the use of water as a coolant. On what grounds is it possible to classify water heating systems?
Dependents and Independents
In a dependent system, the heat carrier from the outside (as a rule, from the heating main) enters directly into the heating system. It can be used exclusively for heating; much more often it is possible to select hot water for household needs. It is according to this scheme that heating works in the vast majority of city houses.
The thermal unit of an independent system includes a heat exchanger, through which the water of the heating main gives off thermal energy to the heat carrier in a closed circuit. The scheme can be applied if antifreeze is used as a coolant in a private house. In the presence of heat meters, such a connection will allow you to turn off the heating for the duration of a long departure, without risking the system defrosting.
open and closed
An open water heating system operates without excess pressure and opens to the atmosphere. An open expansion tank is mounted at its upper point, where all air plugs are forced out.
In a closed system, a constant overpressure is maintained from 1 (in private houses) to 6 (in multi-apartment buildings) atmospheres.
Forced and natural circulation
Systems with natural circulation in our time are used relatively rarely. However, this is a great solution for small houses, allowing you to make heating independent of electricity.
The principle of operation of the so-called gravitational systems is based on the fact that when heated, the density of water decreases. In a closed volume, colder water displaces heated water masses to the upper part of the circuit. With a certain configuration, it is possible to ensure continuous movement of the coolant.
The instructions for creating a gravity system are, in general, relatively simple:
- The boiler is placed as low as possible. In houses without a basement, a recess in the floor is often made under it.
- From the boiler, the filling rises vertically upwards to the highest point of the circuit, forming the so-called accelerating collector.
- At the top point, in the case of an open system, an open-type expansion tank is mounted, as already mentioned. In the case of a closed circuit, an air vent is installed there - automatic or manual; the expansion tank of the membrane type can be located in any part of the circuit.
- From the top point, the filling returns to the boiler with a constant slight slope, necessary for the movement of the cooling water by gravity. Along the way, the coolant gives off heat to radiators or other heating devices.
A feature of gravitational systems is stringent requirements for the hydraulic resistance of the circuit. A pipe is used no thinner than DN 32 and a minimum of shutoff valves. Throttles of any type are categorically not put on bottling.
For reference: the hydraulic resistance of a modern ball valve is ten times less than that of a cast-iron or brass screw valve. A comparison of this and a number of other characteristics leads to a simple thought: it is better to completely forget about screw valves when purchasing materials.
In a system with forced circulation, an external (from the heating main) difference or its own circulation pump is used to create it. At the same time, pumps can work in systems of both closed and open types.
An excellent solution is a circuit with a circulation pump, which, in the absence of electricity, can work as a gravity one. To ensure this possibility, filling is carried out with a pipe of large cross section and is broken at one point by a valve. Before and after the valve, a pump with a sump cuts in.
What gives such a scheme?
- With the bypass closed and the pump on, the system operates with forced circulation. The bypass is blocked so that the pump does not drive water in a circle.
- With an open bypass, the system, due to the minimum hydraulic resistance, is able to work as a gravitational one.
Why forced circulation forced gravity systems to make room? After all, by definition, it makes heating more fail-safe, right?
- allows you to lay the bottling strictly according to the level and get by with a pipe of a smaller diameter. In addition to saving, this greatly affects the aesthetics of the room.
However: in houses with an attic and a basement, the bottling of the supply and return can be taken out of the residential part of the house.
- Forced circulation provides faster and more uniform heating of heaters. In a gravity system, the radiators farthest from the boiler are always noticeably colder than the nearest ones.
One-pipe and two-pipe
The difference is easier to explain with examples.
The simplest one-pipe scheme (barrack type, or Leningradka) is arranged as follows:
- A bottling ring runs along the contour of the room.
- In parallel to it or, opening it, heating devices are mounted.
The minimum consumption of materials and maximum fault tolerance are undoubted advantages. The disadvantage is a large temperature spread between the first and last radiators. However, it is easy to level it with a different number of sections or throttling valves on each radiator (of course, in this case they should not break the main filling ring).
In the case of a two-pipe scheme, which is quite logical, we will need two fillings - supply and return. Each heater is a jumper between them. What is the result?
- You do not need an inextricable contour around the entire perimeter. It is possible, for example, not to surround a door or a panoramic window with pipes.
- The temperature of the heating devices can be the same. In practice, however, there is variation.
- Balancing with chokes or thermal heads is MANDATORY. Otherwise, the situation is quite real when the entire mass of the coolant moves along a short circuit - through the nearest heating devices, and the far part of the filling and batteries in the cold will simply be defrosted.
Horizontal and vertical wiring
How these schemes of water heating systems differ is easy to understand intuitively. For example, the notorious Leningradka is a typical horizontal scheme, but the heating riser in a modern five-story building is vertical.
In practice, however, it is much more common to see combined circuits that include horizontal and vertical wiring sections:
- In the standing system in Soviet-built houses, in addition to risers, there are also horizontally located bottlings.
- In new buildings, an even more complex combination is used: bottlings are connected by vertical risers, from which horizontal wiring inside a single apartment is powered on each floor.
Dead-end and passing schemes
Dead-end water heating systems are two-pipe schemes in which the directions of water in the supply and return spills are opposite. The coolant reaches the distant radiators and returns back. But if it continues to move towards the boiler or heating unit, keeping the same direction, our scheme becomes passing.
Note: a passing wiring diagram has very few advantages over a single-pipe one in the case of a one-story house. Only a slightly more uniform heating of the radiators speaks in its favor.
Connecting heating devices
Different connection types can be used primarily for sectional radiators of different types.
The convectors are equipped with connections, and the direction of circulation in them is determined by the manufacturer. What options are available when connecting batteries?
- Lateral connection is most popular in urban apartments. The hoses go into two plugs on one side of the radiator. The main advantage of such a scheme is that the length of the connections leading from the riser is minimal. Disadvantages - uneven heating of the far and near sections and, much worse, the inevitable silting of the end of the battery.
- Diagonal connection(the top plug on one side of the radiator and the bottom plug on the other) will make the radiator heat evenly throughout the entire volume. Under the top connection, however, the bottom of the sections will silt up in this case as well. Periodic flushing is required.
- Finally, connection from the bottom down means both uniform heating along the entire length and absolutely clean sections. The price of this is an air pocket in the heater: you will need to install a Mayevsky crane or, better, an automatic air vent.
Main elements
What does the water heating system in a private house consist of? If we move into a city apartment, as a rule, into housing with already functioning heating, then here we will have to draw up a project from scratch.
Boiler
A source of heat that converts the energy of burning fuel or electricity into thermal energy transported by a coolant. The list of main types of boilers looks like this:
- Gas provide currently the lowest operating costs. Of course, when working on main gas: bottled gas will increase the cost of a kilowatt-hour of heat by several times.
- Solid fuel boilers are in second place in terms of low cost of heating. Firewood, coal, peat, sawdust, etc. are used as fuel. The main problem is the need for frequent fuel loads.
- Solar boilers can operate in a fully automatic mode; however, solariums are very expensive and continue to rise in price.
- Finally, electricity is the most convenient, safest and ... expensive way to heat your home.
In addition: the very idea of using a coolant in this case seems strange. Separate electric radiators or convectors look like a much more sensible solution.
Pipes
Black steel pipes are still used in the installation of central heating; however, when independently transferring radiators and designing heating systems for cottages, the emphasis is, as a rule, on other materials.
- Galvanized steel has the strength of black steel pipes and is devoid of their main drawback - susceptibility to corrosion.
- Corrugated stainless steel, in addition to strength, is also easy to bend. Connections are made with silicone seal fittings, without threads, which makes assembly quick and easy.
- Polypropylene pipes are cheap and are mounted using a simple low-temperature soldering iron. Usually, pipes reinforced with aluminum or fiber are used for hot water and heating: they are stronger and have a much lower coefficient of thermal expansion.
- Cross-linked polyethylene is an excellent material for beam wiring with laying in a screed. Temperature resistance and tensile strength combined with flexibility and availability in coils up to 500 meters long.
fittings
- If you need to turn off the water, the best tool for this is a modern ball valve. Reliability is combined with ease of use and low hydraulic resistance in the open state.
- Chokes are used for manual adjustment of heat transfer of heating devices and their balancing.
- After calibration, thermostatic heads are able to adjust the throughput in such a way that the set temperature is maintained in the room with acceptable accuracy.
- For air removal, automatic air vents are most convenient. However, instead of them, both Mayevsky taps and conventional valves and even taps can be used.
Safety
It is provided by devices that are called so - a security group:
- Expansion tank compensates for the increase in the volume of the coolant during heating. Water is practically incompressible and can easily break pipes or radiators; but the air, separated from the water by a rubber membrane, is compressed easily. The volume of the membrane tank is taken approximately equal to 10% of the amount of coolant in the system.
- Safety valve needed in case the capacity of the expansion tank is not enough with strong heating. When the critical pressure is reached, it releases excess water.
- pressure gauge allows you to control the current pressure in the system.
Heating appliances
- Cast iron radiators quite heat-resistant and not subject to corrosion. The sections have a large internal volume and, due to the slow movement of the coolant, they are easily silted up when connected to the side.
- Steel heating appliances are divided into several types: lamellar, tubular, convectors and registers. The execution of corrosion-resistant steels makes them vulnerable to rust, and the thin walls of plate radiators are also extremely fragile mechanically.
- Aluminum radiators they are cheap and have excellent heat dissipation, but they are afraid of excess pressure and galvanic processes, which are generated by the combination of different metals in one circuit (in particular, aluminum and copper).
- Bimetal heating devices- these are aluminum radiators with steel cores that increase tensile strength, and copper-aluminum convectors. The latter are a copper tube with aluminum plates pressed to increase heat transfer.
Heating appliances for water and steam heating systems
1. Modern requirements for heating appliances
Heaters are the main element of the heating system and must meet certain heat engineering, sanitary and hygienic, technical and economic, architectural, construction and installation requirements.
Thermal requirements consist mainly in the fact that heating devices must transfer heat well from the coolant (water or steam) to the heated premises, i.e. so that their heat transfer coefficient is as high as possible, not less than 9-10 W / (m 2 -K), given that for modern designs of heating devices it is in the range of 4.5-17 W / (m 2 -K).
sanitary and hygienic requirements, requirements for heating appliances are that the design and shape (type) of their surface do not lead to the accumulation of dust and allow it to be easily removed.
Technical and economic requirements the following: minimum factory cost; minimum consumption of metal; compliance of the device design with the requirements of the technology of their mass production; sectionality, which allows to arrange the device with the required heating surface area.
The criterion for the thermotechnical and technical and economic evaluation of metal heating appliances is thermal stress metal appliance a M, W / (kg-K), which is the ratio of the heat flux of the device at a difference in the average temperatures of the surface of the device and the ambient air of the room in 1C, related to the mass of the metal of the device:
M=Q n p /Gt(8.1)
where Q n p - the amount of heat given off by the device, W; G is the mass of the device, kg; A / - the difference between the average temperatures of the surface of the device and the surrounding air (t P r-tv).
The greater the thermal stress of the metal of the heater, the more profitable it is. Modern devices operate with a thermal stress of metal 0.19-1.6 W / (kg-K).
Architectural and construction requirements include reducing the space occupied by heaters and making them look pleasing. To meet these requirements, heating appliances must be compact, with a surface that is easily accessible for inspection and cleaning from dust, and must correspond to the interior of the room.
Mounting Requirements primarily reflect the need to increase labor productivity in the manufacture and installation of heating appliances. Their design should favor the automation of production and be easy to install. The devices must be durable, convenient for transportation and installation, and their walls must be vapor- and water-tight, temperature-resistant.
A large variety of types and types of heating devices is explained by the fact that it is very difficult to satisfy all the considered requirements at the same time.
2. Types and designs of heating devices and their technical and economic indicators
Heating appliances used in central heating systems are divided into: according to the predominant method of heat transfer- on radiation (suspended panels), convective-radiation (devices with a smooth outer surface) and convective (convectors with a ribbed surface and finned tubes); in appearance material- for metal appliances (cast iron from gray cast iron and steel from sheet steel and steel pipes), low-metal (combined) and non-metallic (ceramic radiators, concrete panels with embedded glass or plastic pipes or with voids, no pipes at all, etc.); the nature outer surface- on smooth (radiators, panels, smooth-tube appliances), ribbed (convectors, finned tubes, heaters).
Consider the main types of heating devices widely used in residential, public and industrial buildings.
2.1 Cast iron and steel stamped radiators
The industry produces sectional and block cast-iron radiators. Sectional radiators are assembled from separate sections, block - from blocks into two to four sections. Sections of radiators, depending on the number of vertical channels, are divided into one-, two- and multi-channel. In the USSR, mainly two-channel sections are manufactured, since they better meet sanitary and hygienic requirements.
Separate blocks or sections are interconnected by means of ductile iron nipples having external right and left threads and inside two protrusions for a key. The nipples are screwed simultaneously at the top and bottom into two sections or into two blocks. To seal the joints between the sections of the radiator, a gasket is placed: for water heating (t g up to 100 ° С) - from a gasket cardboard moistened with water and boiled in natural drying oil, and for steam or overheated water (t g > 100 ° С) - from pa-ronite dipped in hot water.
A gasket made of heat-resistant rubber and other heat-resistant materials is allowed, ensuring the tightness of the joints. Ordinary rubber is not allowed to be used for gaskets.
The most common cast-iron radiators are MS-140, MS-90, M-90 (GOST 8690-75 *) with two column-mm in depth. The mounting height - the distance between the centers of the nipple holes of the radiators - is h = 500 mm, the total height is H=582-588 mm, the construction depth b = 140 mm and the construction length of the section is H=98-108 mm.
Radiators MS-140 and MS-90 are designed for coolant overpressure up to 0.9 MPa, which expands the scope of their application, and all other cast-iron radiators - up to 0.6 MPa. All of these radiators, in contrast to the discontinued M-140-AO radiator, do not have inter-column fins, which, along with other design features, determines their improved hygienic and aesthetic qualities.
According to the mounting height, radiators are divided into high - 1000 mm, medium - 500 mm, low - 300 mm. The most widely used medium radiators. Each radiator has four cast-iron plugs screwed into the nipple holes of the outer sections; two of them - through, with an internal thread of 15-20 mm - are used to connect devices to the heat pipe.
The production of cast-iron radiators requires a large amount of metal, they are labor-intensive in manufacturing and installation. This complicates the manufacture of panels due to the arrangement of niches in them for installing radiators. In addition, the production of radiators leads to pollution environment. Therefore, despite such important advantages of radiators as corrosion resistance, well-established manufacturing technology, ease of changing the power of the device by changing the number of sections, etc., their production in our country is reduced due to an increase in the output of devices made of steel, aluminum and its alloys.
In the USSR, single-row and double-row steel panel radiators are manufactured: stamped columnar type RSV1 and stamped coil type RSG2. A single-row stamped steel radiator of the RSV1 type (Fig. 8.2, a) consists of two stamped steel sheets 1.4-1.5 mm thick, interconnected by resistance welding and forming a series of parallel vertical channels, united above and below by horizontal collectors. Steel radiator panel type RSG2 (Fig. 8.2, b) as well as the RSV1 radiator, it consists of two steel sheets 1.4-1.5 mm thick, interconnected by contact welding and forming a number of horizontal channels for the passage of the coolant.
Steel radiators of the RSV1 and RSG2 types, compared to cast iron ones, have approximately half the weight, are 25-30% cheaper, and require less transportation and installation costs. Due to their low construction depth, they are conveniently installed openly under windows and against the wall. The scope of steel radiator-panels is limited to heating systems using treated heating water, the corrosive effect of which is insignificant.
2.2 Finned tubes
Finned tubes are made of cast iron 0.5 long; 0.75; one; 1.5 and 2 m with round ribs and heating surface 1; 1.5; 2; 3 and 4 m 2. At the ends of the pipe, flanges are provided for attaching them to the flanges of the heat pipe of the heating system.
The finning of the device increases the heat-releasing surface, but makes it difficult to clean it from dust and lowers the heat transfer coefficient. Finned tubes are not installed in rooms with a long stay of people.
2.4 Convectors
In recent years, convectors have become widely used - heating devices that transfer heat mainly by convection.
Let's look at some of their types. Convector "Accord" is designed for heating systems of residential, public and industrial buildings with a coolant temperature up to 150°C and pressure up to 1 MPa. Convector "Akkord" consists of two electric-welded pipes with a diameter of 20 mm and U-shaped finning plates made of sheet steel 0.8 mm thick. The surface of convectors is covered with PF-115 enamel. The industry produces eight standard sizes of convectors (through and end) in a single-row version with a surface area of 0.98-3.26 m 2 and eight standard sizes of convectors (end) in a two-row version in height with a heating surface area of 1.95-6.50 m 2 . The height of the convectors is 300 mm (single-row) and 645 mm (double-row).
In "Sever" convectors, the design of which is similar to the design of "Akkord" convectors, U-shaped plates are stamped from duralumin tape or sheet 1 mm thick. The Sever convector is the lightest device, so it is advisable to use it for heating buildings for various purposes, mainly in the northern and other remote regions of the country, in order to reduce transportation costs for its transportation. There are 18 standard sizes of convectors "North" (through passage and end). More advanced heating devices with a finned heating element are a floor convector with a casing, low "Rhythm", intended for public buildings. The high island convector type KB is used for heating public and industrial buildings, as well as a convector with a casing of the "Comfort" type, designed for residential, public and industrial buildings. These steel appliances have high thermal, technical, economic and operational qualities. Convectors "Comfort-20" are produced by the industry with a heating surface area of 0.71-4.26 m 2. They allow the air damper to change the heat flow within 70% without installing shut-off and control valves.
In 1984-1985. The Novokuznetsk plant "Santekhlit" has mastered the serial production of convectors of shallow depth "Universal" (Fig. 8.7, table 8.1) and medium depth of the "Universal C" type. This will allow designers to fulfill one of the basic rules for installing heaters, which consists in the need to cover at least 60% of the window sill length with them (according to MNIITEP, according to foreign data - at least 75-85%). This placement of heaters allows you to neutralize the cold air streams falling from the windows. Thus, the new appliances differ significantly from the Comfort-20 convectors, which covered less than 50% of the window sill length.
The convectors "Universal" have connecting pipes located one above the other with an assembly height of 80 mm, which reduces the amount of procurement work for heating systems by 35-40% compared to systems that use convectors "Comfort-20". The regulation of the heat flow of convectors "Universal" is carried out by an air valve, the actuator of which is placed on the top panel of the device. The residual heat flow with the valve fully closed is less than half of the nominal value. As a disadvantage of the "Universal" convectors in comparison with the "Comfort" convectors, one should note their somewhat lower heat transfer coefficient due to the location of the heat-releasing tubes one above the other (the upper tube, as it were, "shields" the lower one). The use of new convectors instead of Comfort-20 convectors and Akkord double-row convectors will provide an economic effect of about 4 rubles / kW.
2.5 Concrete heating panels
These devices are currently installed in buildings for various purposes. A device of this type is a coil and, more rarely, a register of steel water and gas pipes with a diameter of 15 or 20 mm, embedded in a flat concrete slab 40-50 mm thick. They are manufactured from concrete M200 or M250 with a density of 2200-2500 kg / m 3 in the factory and can be attached to the outer wall with one-sided heat transfer , with double-sided heat transfer , as well as with double-sided heat transfer and with a supply channel . The prototype of concrete devices are “tubular devices with a concrete jacket”, invented in 1905 by engineer. V. A. Yakhimovich.
Table 8.1 Basic technical data of some heaters
a 8.1 Basic technical data of some heaters | |||||||
Section heating surface area f : , m 2 | Nominal heat flux density? nom, Bt / m g |
Device connection diagram | Consumption of body-carrier through the device G np , kg/s | Indicator! AT P | i degree and coefficient of formula (8.2) G \ with pr |
||
Cast iron sectional radiators: MS-140-108 MS-140-98 MS-90-108 |
0,244 0,240 0,187 | 753 . 725 802 | Top down | 0,005-0,014 | 0,3 | 0,02 | 1,039 |
0,015-0,149 | 0,3 | 0 | 1 | ||||
M-90 | 0,2 | 700 | 0,15-0,25 | 0,3 | 0,01 | 0,996 | |
Single-row steel panel radiators type RSV1: RSV1-1 RSV1-2 |
0,71 0,95 | 710 712 | Upwards | 0,005-0,017 | 0,25 | 0,12 | 1,113 |
RSV1-3 RSV1-4 RSV1-5 | 1,19 1,44 1,68 | 714 712 714 | 0,018-0,25 | 0,25 | 0,04 | 0,97 | |
The same, double row: 2RSV1-1 2RSV1-2 |
1,42 1,9 | 615 619 | Bottom down | 0,005-0,032 | 0,15 | 0,08 | 1,09/ |
: 2RSV1-4 2RSV1-5 |
2,38 2,88 3,36 | 620 618-620 | 0,033-0,25 - | 0.15 | 0 | 1 |
Name of the device, its type, brand | Section heating surface area /, m* | Nominal heat flux density? nom, W / m 2 | Device connection diagram | Coolant flow through the device 0 |
Exponents and coefficients! in formula (8.2) | ||
P | R | s p R | |||||
Wall-mounted convectors with a casing of shallow depth such as "Universal": | |||||||
KN20-0.918 | 2,570 | 357 | |||||
KN20-1.049 | 2,940 | 357 | 0,01-0,024 | 0,3 | 0,18 | 1 | |
KN20-1.180 | 3,300 | 358 | Any | ||||
"KN20-1.311 | 3,370 | 389 | 0,025-0,25 | 0,3 | 0,07 | 1 | |
KN20-1,442 | 4,039 | 357 | |||||
KN20-1.573 | 4,410 | 357 | |||||
KN20-1.704 | 4,773 | 357 | |||||
KN20-1.835 | 5,140 | 357 | |||||
KN20-1.966 | 5,508 | 357 | |||||
Convectors without casing type "Accord": КА-0,336 | 0,93 | 343 | |||||
KA-0.448 | 1,3 | 345 | |||||
KA-0.560 | 1,63 | 344 | |||||
KA-0.672 | 1,96 | 343 | |||||
KA-0.784 | 2,28 | 344 |
Of great interest are devices with a heating element made of heat-resistant glass and plastic, as well as tubeless devices made of waterproof concrete and ordinary concrete with channels impregnated with waterproof compounds. Such heaters are still in the research stage. More detailed description concrete heating panels is given in §41.
3. Selection, placement and installation of heating devices. Connecting them to heat pipes
Heaters of the central heating system are placed near the outer walls (Fig. 8.9), mainly under the windows, since as a result cold air currents near the windows decrease. In order to minimize the protrusion of appliances into the room in the wall, niches up to 130 mm deep are often used. At such a depth, the heat transfer coefficient of the device is assumed to be the same as for a device installed without a niche.
The type of heater is chosen in accordance with the nature and purpose of the given building, structure and premises. With increased sanitary and hygienic requirements, devices with a smooth surface are recommended, best of all panel, combined with building structures; with normal sanitary and hygienic requirements, you can use devices with a smooth and ribbed surface, and you should choose no more than one or two types of devices for the entire building; with reduced sanitary and hygienic requirements in rooms intended for short-term stay of people, devices of any kind are used, preference should be given to devices with high technical and economic indicators.
Heating appliances installed in stairwells should not protrude from the plane of the walls at the level of people's movement and reduce the width of marches and platforms required by the standards. According to SNiP 2.04.05-86, heaters in stairwells should be installed at the entrance and some of them should not be transferred to the landings. To prevent the water in the heat pipeline from freezing, it is not allowed to install heaters in the vestibules of staircases that communicate with the outside air, as well as at the entrance external single doors. Stairwells of multi-storey buildings are recommended to be heated with recirculating air heaters (convectors), installing them on the ground floor and connecting them to the high-temperature water heat pipeline.
In rooms of great height, in the presence of lanterns or a second tier, in order to prevent moisture condensation on the building envelope, it is sometimes necessary to install 1/3-1/4 of the surface of heating devices in the upper zone. Appliances should not be blocked by furniture, as this reduces their heat transfer and makes it difficult to clean from dust. Decorative screens (grilles) may be provided for heaters (except for convectors with casings) in public buildings, providing access to heaters for cleaning.
Painting heaters in light colors reduces heat transfer by 1-2% compared to unpainted ones, and when coated with aluminum paint - up to 25%; when painting devices in dark colors, heat transfer increases by 3-5%. Heating appliances are placed in the room so that the system has smallest number risers and branches to them had a short length.
The connection of heating devices to heat pipelines can be carried out according to three schemes (schemes for supplying and discharging water from devices), which are briefly called: “from top to bottom”; "bottom down" and "bottom up". The scheme of water movement in the device, due to the scheme of connection to heat pipelines, affects the calculated surface area of the device. The most efficient top-down scheme, in which the heat flux density of the heater qnp always higher due to the most uniform and high temperature surface of the device than with the “bottom down” and especially “bottom up” scheme. Therefore, with the “top-down” connection scheme, the required surface area of the device F p will be the smallest [see. formula (8.8)], and this scheme is preferable to others.
In two-pipe and single pipe systems with the upper laying of the supply line, it is most advisable to place the devices in relation to the risers in such a way that each riser has a two-sided load (Fig. 8.11, a). Devices from other rooms cannot be connected to the risers that feed the stairwell devices. It is recommended to power the stairwell devices according to a single-pipe flow scheme. Connection of heating devices on the "hitch" (Fig. 8.11,6,0) is allowed only within the same room, with the exception of kitchens, corridors, toilets, washrooms and other auxiliary premises, where they can be connected to the appliances of the next room and on the "hitch" . The most expedient is a versatile adaptation to the instrument stack on the "hitch" (see Fig. 8.11, c). Devices on the "coupling" in the heat engineering and hydraulic calculation are considered as one device.
Versatile connection of heat pipes to heater with the “top-down” scheme, it is used in cases where the horizontal return line of the system is located under the device (Fig. 8.11, d), above the device (Fig. 8.11,<3) и при внутренней установке крупного прибора (рис. 8.11,е).
Although the thermotechnical advantage has a versatile connection of heat pipelines, in practice one-sided connection is more often used, which makes it possible to unify the “piping” unit of the device, which is important for mass construction buildings. Connection of devices according to the “bottom down” scheme is most often carried out in the upper floor of vertical one-pipe and two-pipe systems with the bottom laying of both lines (Fig. 8.11, g, h) and in a horizontal one-pipe system (Fig. 8.11, and). The connection of devices according to the “bottom-up” scheme is used in single-pipe (Fig. 8.11, j) and two-pipe heating systems with the bottom laying of both lines.
In bathrooms and shower rooms where towel dryers are not connected to the hot water supply system, they should be connected to the heating system in accordance with SNiP 2.04.01-85.
Finned tubes are installed in one or, if necessary, in two or three rows in a vertical plane and attached to the heat pipeline using flanges. At high parameters of the coolant (steam, superheated water), it is necessary to provide the possibility of free extension of the branches to the devices.
Heating appliances (radiators, finned pipes, convectors) are attached to building structures using brackets, which are fixed with dowel-nails or sealed with cement mortar at a depth of at least 100 mm, not counting the thickness of the plaster. With the number of sections in the radiator n=3-9 its fastening is carried out on one upper and two lower brackets; at n=10-14 - on the two upper and lower diuh; at n=15-20 - on the two upper and three lower.
When fixing radiators to the wall, instead of the upper brackets, you can install radiator strips 3 located at a height equal to 2/3 of the radiator height; instead of the bottom brackets - 4 stands attached to the floor. Ribbed tubes are mounted on the wall with brackets, convectors - with brackets 7 . Steel panel radiators are mounted on two brackets Kr2-RS, the axis of which is at a distance of 200 mm from the side ends of the radiator. Devices are hung only after plastering the surfaces of the wall niches at the installation sites of the devices. The connection of heating devices to heat pipelines is carried out by welding, threading or flanges.
4. Determination of the surface area and the number of elements of heating devices
The surface area of heating appliances F p is currently measured only in m 2 . To calculate F p, first of all, it is necessary to determine the value of the heat flux of the heater, due to surface density, i.e., the value of the heat flux q pr transferred from the coolant to the environment through 1 m 2 of the surface area of the device.
As follows from the basic heat transfer equation (2.55), the heat flux density of devices, being the product of the heat transfer coefficient and the temperature difference, depends on the same factors as the heat transfer coefficient. Therefore, in practice, to simplify the calculations, the heat flux density of the heater q ave is determined taking into account all factors at once. For this, the so-called nominal heat flux density is used.
Rated heat flux density q nom , W / m 2, obtained by thermal testing of the heater for standard operating conditions in a water heating system, when the average temperature difference ∆tst / cf = 70 ° C, the water flow in the device is G st / pr \u003d 0.1 kg / s, and atmospheric pressure p b \u003d 1013.3 hPa.
Under these standard conditions, the relative water flow in the device (the ratio of the actual water flow in the device to the nominal flow rate adopted during its thermal tests).
Standard temperature difference with the coolant water, in which thermal tests of heating devices are carried out, is obtained by the formula
∆tst / cf = tav - tin = 0.5 (tin + tout) - tin = 0.5 (105 + 70) - 18 = 69.5 ≈ 70 ° С,
where the temperature of the water entering the device from above tin = 105°C; coming out from below tout = 70°С; air temperature in the room tv = 18°С.
The value of the nominal heat flux density, W / m 2, the main types of heaters, see table. 8.1. As can be seen from this table, the q nom values of panel radiators are 1.5-2 times higher than q nom convectors, which reflects the thermal engineering advantages of the former.
Having the value q nom , can be defined design heat flux density heater q pr , W / m 2, for working conditions other than standard, according to the formulas:
a) for the coolant - water
(8.2),
tav - temperature difference equal to the difference between the half-sum of the temperatures of the coolant at the inlet and outlet of the heater and the room air temperature, ∆ tav = , о С
Gpr - the actual water flow in the heater, kg / s, Gpr \u003d Q /;
n, p - experimental values of exponents (Table 8.1),
Spr - coefficient taking into account the connection scheme of the heater and the change in the exponent p in different ranges of coolant flow (Table 8.1).
b) for the coolant - steam
, (8.3)
where q nom is the nominal heat flux density of the heater under standard operating conditions, W / m 2 (accepted according to Table 8.1),
∆tn - temperature difference equal to the difference between the temperature of saturated steam and the temperature of the room air (tp-tv)
If the surface heat flux density of the heater q pr, W / m2 is known, then the heat flux of the device Qnp, W, proportional to the area of its heating surface, will be:
Qnp \u003d q pr Fр (8.4)
From here , estimated area Fr, m2, heater regardless of the type of coolant
Fr \u003d Qnp / q pr (8.5)
When additional factors affecting the heat transfer of devices are taken into account, formula (8.5) takes the form
Fр = Qnp/q prβ1β2 (8.6)
where Qnp is the heat transfer of the heater to the heated room, is determined by the formula
Qnp - Qnotrp - 0, 9Qtrp, (8.7)
Where Qnotp is the heat demand of the room, equal to its heat loss minus heat gains, W;
Qtp - total heat transfer of openly laid within the riser room, wiring, to which the device is directly connected (coefficient 0.9 takes into account the share of heat flow from heat pipes, useful for maintaining the air temperature in the room.
Taking into account expression 8.7, formula 8.6 takes the form
where Qnotrp, Qtrp - the same as in formula 8.7, q pr -
the same as in formulas (8.2) and (8.3).
The total heat transfer of heat pipes Qtr, W can be determined by the formula
Qtr \u003d ∑ktrpdnl (tt-tv), (8.9)
where ktr, dn and l are, respectively, the heat transfer coefficient, W / (m 2 -K), outer diameter, m, and length, m, of individual heat pipes; t 1 and t B- temperature of the heat carrier and air in the room, m.
In practice, heat transfer from heat pipes is determined by a simplified formula
Qtr \u003d qvlv + qrlr (8-10)
In this case, reference tables are used, where values are given q B and q r- heat transfer of 1 m of vertically and horizontally laid pipes, W / m, based on their diameter and temperature difference (tt-tv); l and lr. - the length of vertical and horizontal heat pipes within the premises, m.
In formula (8.8) β 2 - coefficient for accounting for additional heat losses by heating devices near external fences (taken according to Table 8.3).
Table 8.2 The value of the coefficient β 1
Note. For space heaters with a rated heat flux of more than 2.3 kW, instead of β 1, the coefficient β 1 ’ = 0.5 (1+ β 1) should be taken.
The estimated number of sections of cast iron radiators is determined by the formula
(8.11),
Where f 1 is the heating surface area of one section, m2, depending on the type of radiator accepted for installation in the room (accepted according to Table 8.1),
β 4 - coefficient taking into account the way the radiator is installed in the room with an open installation
Table 8.3 The value of the coefficient β 2
β 4 =1.0; β 3 - coefficient that takes into account the number of sections in one radiator and is taken for a radiator of the MS-140 type equal to the number of sections from 3 to 15 - 1, from 16 to 20 - 0.98, from 21 to 25 - 0.96, and for the rest of the cast iron radiators is calculated by the formula
β 3 \u003d 0.92 + 0.16 / Fp (8.12)
Since the calculated number of sections according to the formula (8.11) rarely turns out to be an integer, it has to be rounded up to obtain the number of sections N mouths accepted for installation. At the same time, according to clause 3.49, the heat flux Qpr is allowed to decrease by no more than 5% (but not more than 60 W). As a rule, the nearest larger number of radiator sections is accepted for installation.
For all other heaters β 3 = 1.
If a panel radiator of the RSV1 and RSG2 types or a convector with a casing of a certain area /i, m 2 are accepted for installation, then their number (placed openly in the room) will be
N-F p /f 1 . (8.13)
The number of convectors without casing or finned tubes vertically and in a row horizontally is determined by the formula
N = F p /nf 1 (8.14)
Where n is the number of tiers and rows of elements that make up the device; f \ - area of one convector element or one ribbed tube, m g,
In the process of determining the required surface area of heating devices, the initial and resulting data are entered in the form (Table 8.4).
Table 8.4
During the heating period, the heat loss of the premises changes, as the outside temperature changes, the wind and solar radiation act, as well as household and technological heat emissions change.
To bring the heat output of appliances installed in individual rooms in line with heat losses, it is necessary to change both the amount of water passing through the appliances and its temperature, i.e., to regulate the heating system qualitatively and quantitatively.
High-quality regulation is achieved by changing the temperature of the water supplied to the heating devices from the thermal center (boiler house, CHP). This is central regulation.
Quantitative local regulation of the heat transfer of devices is carried out by changing the amount of water entering the device, for which double adjustment valves are used in two-pipe systems (see Fig. 7.12, G), three-way valves (KRTP and KRPSH Fig. 7.12, e) used on connections to devices of single-pipe water heating systems.
Adjusting valves are installed to carry out diukh not one from the other stages of regulation: installation - during the commissioning and start-up of the system and operational - during the operation of the system. Control valves are not installed at appliances located in stairwells and in other places where water can freeze. It is not allowed to install shut-off and control valves on the "scenes" of devices.
For convectors with air control valves, the installation of control valves on the inlets is not provided according to.
In steam heating systems, the limit of quality regulation is very limited, therefore, central and local quantitative regulation is used in these systems: when the outdoor temperature changes, the amount of steam entering the system changes, or steam is supplied with a certain interruption (regulation by "passes").
In recent years, automatic control devices have been used. They automatically close the valves on the heat pipes when the room temperature rises and reopen them when the temperature drops.
test questions
1. What are the basic requirements for heating appliances?
2. What types of heating devices are used for residential, public and industrial buildings?
3. Where are the heating devices located and how are they installed?
4. In what units is the surface area of heating devices measured?
5. For what operating conditions were the values of the nominal heat flux density of heating appliances obtained?
6. How are additional factors that affect the heat transfer of heating devices taken into account?
7. In what cases and to what extent is it necessary to take into account the heat transfer of the heat pipes of the heating system? What is the method for doing this calculation?
8. Why is it necessary to regulate the heat transfer of heating devices? What are the heat transfer control methods?
9. How is the heat output of Universal convectors regulated?