Bimetallic Radiator Test

The idea of ​​using two materials with complementary properties is widely used in technology. This is the case with heating equipment. One of the main positions among domestic and foreign radiators and convectors on the market is occupied by bimetallic models. Thanks to the strength of the steel that reinforces the structure, these devices can withstand the high working pressure typical of Russian heating systems. And the steel filling is “quieter” than others related to the alkalinity of water – the pH.

Aluminum, in turn, has a high thermal conductivity, therefore, it significantly improves the heat transfer of the heater and reduces its inertia, that is, the radiator heats up faster and cools accordingly. In addition, this material is high-tech, it can be given any shape, cast ribbing of a complex configuration. In terms of the totality of indicators, “bimetal” is the best choice for extreme Russian conditions. The heat transfer of “combined” models is 1.5-2 times higher than that of the best steel of the same size. Moreover, they are lighter, more elegant. And the design is no worse than aluminum, and the strength is several times greater. All this is true, but it turns out that “bimetal” “bimetal” – strife…

“BIMETAL” CLASSIFICATION

Radiators and convectors. Both are bimetallic. Recall that these devices differ in their principle of operation. Simplified convector diagram – finned tube. The air passing from bottom to top between the ribs heats up and rises upward due to convection. Actually, the device is so named because its main heat flux is convection. The heat flux transmitted by the radiator has not only convection, but also a large radiant component (up to 45%), so heat emanates from it both up and to the sides..

“Bimetal” and “semi-bimetal”. The role of the steel core in a bimetallic radiator is to strengthen the vertical channels. After all, it is the place of their connection to the collectors that is the “weak link” in aluminum devices that cannot withstand high pressure. There are two ways to solve this problem. The first is to make a steel frame and fill it with aluminum. We will call such devices “completely” bimetallic. Their horizontal collectors and vertical channels are steel welded structure, and the water is in contact only with steel, so galvanic steel-aluminum pair cannot occur. The second is to reinforce only vertical channels with steel tubes, so to speak, to solve the problem by half. Let’s call these devices conditionally “semi-bimetallic”, although manufacturers also call them “bimetal”. In principle, this technical solution is quite justified: the thickness of the walls of the aluminum collector is sufficient to withstand high pressure. The problem of a galvanic pair, according to experts from the Scientific Research Institute of Sanitary Engineering, is not as acute as they say. With such a design, the main thing is to ensure the immobility of the steel tabs in the aluminum “shirt”, to securely “glue” them so that they do not inadvertently “fall out” with different thermal expansion of the two metals and block the section of the lower collector.

WHAT WE TESTED

We selected bimetallic sectional radiators with an all-steel core for testing. As it turned out, there are not so many of them on the domestic market. Three brands are widely represented: Global Style (Italy), Bimex (Czech Republic), “Santekhprom BM” (Russia). There is also the Ural development “Ontario” (Yekaterinburg), however, the serial production of this heating device has not yet been established. And yet, most likely next year, Ukrainian bimetallic devices RB and RBP from the Kiev plant “Bolshevik” and LLC “Press” will appear on our market, which are currently undergoing routine tests at the Scientific Research Institute of Sanitary Engineering. Italian and Russian radiators were provided to us for testing by the Terem company and Santekhprom OJSC, Bimex was officially purchased in the Lotos LLC store.

We tested two samples of radiators of each brand with an installation height (center distance) of 500 mm. The test was carried out by specialists in the accredited laboratory of heating devices of the Federal State Unitary Enterprise NIIsantekhniki (the head institute of the Russian Federation for the development and testing of heating devices) and in LLC “Vitaterm”.

HOW TESTED

1. Thermal tests (according to the methodology developed at the Scientific Research Institute of Plumbing). The purpose of testing is to determine the following parameters:

  • nominal heat flux. It characterizes the heat output of the device. In our case, the heat transfer from one section determines the so-called nomenclature step. The smaller it is, the smaller the error in the selection of the heater;
  • heat transfer coefficient. The integral indicator is of interest primarily to specialists. It indirectly reflects the effectiveness of the chosen design;
  • heat density. This parameter will be useful for everyone, since it determines the “stretch” of the radiator. The higher the heat density, the more powerful the “running meter”. By the way, according to the norms of SNiP 2.04.05-91 * for effective heating of the room, it is advisable to install such a device that will cover at least 75% of the length of the window sill;
  • specific gravity. Shows how much the “kilowatt” device weighs. It is important to know this for a business executive organizing the purchase, delivery and installation of heating equipment, say, for an entire facility. When planning private transportation, this information is also not superfluous..
  • According to the methodology, radiators with the most typical thermal power for installation in residential premises in the range of 0.85-1 kW were selected for testing, achieved by a set of the appropriate number of elements: Bimex and Santekhprom BM – 5 sections each, Global Style – 6 sections.

    Each device worked for a week in a specially equipped isothermal chamber (at 18-21 degrees Celsius), simulating real operating conditions. The radiator was installed, as it were, under a window – near a cooled wall with an insulated section a meter high above the floor level. It was connected to a test bench, which ensures the movement of the coolant according to the “top-down” scheme under the so-called normalized (normal) conditions: the average temperature of the coolant is 70 degrees above the air temperature in the chamber, the water flow through the radiator is 0.1 kg / sec. and atmospheric pressure of 760 mm Hg.
    To reduce heat loss, the connecting pipes from the stand to the device were carefully insulated. The heat loss of the stand was estimated during calibration, when the supply and return pipelines were “looped”. As a result, the thermal power of the device was determined as the difference between the heat flux of the system, measured according to the readings of the wattmeter, and the “personal” heat losses of the stand.

    2. Performance tests simulate real heating and cooling processes occurring in heating systems, and allow us to conclude how the device will behave over many years of operation. The fact is that during operation, its thermal characteristics, as a rule, decrease. Different thermal expansion of steel and aluminum in the “bimetal” leads to shifts of the core relative to the aluminum “shirt” and loose fit of materials to each other. This worsens the heat-conducting properties of the radiator, reduces heat transfer.

    A special stand makes it possible to alternately pass hot and cold water with a temperature of + 90-95 and + 5-10 degrees Celsius through the tested device. In addition, each sample was subjected to 360 cycles of sharp temperature “swing”, which, according to the Scientific Research Institute of Sanitary Engineering, corresponds to approximately 20 years of normal operation. Then the thermal tests were repeated. Comparison of the two results (before and after the “swing”) characterizes the thermal stability of the heatsink during the system operation. According to the draft GOST for heating devices (it so happened that there was still no general regulatory document for heating devices and, in particular, for bimetallic sectional radiators), if the decrease in thermal performance after operational tests does not exceed 2%, it can be ignored. If large, the thermal values ​​obtained from the two tests are averaged.

    3. Strength tests. They were carried out according to the method of the Federal State Unitary Enterprise Research Institute of Sanitary Engineering at the RP-50 stand, which develops an overpressure of up to 6 MPa (60 atm.).

    A small educational program on the topic of how the working, test and crimping pressure differ. The working pressure for each type of device is recommended by the manufacturer, taking into account the strength features of the design and materials. It is supposed to choose it with a triple safety factor, that is, the destructive pressure for the device should be at least three times more than the working one. To ensure the safe operation of the radiator there, at the factory, it is tested at a pressure 1.5 times higher than the recommended value. By the way, in Europe the test pressure is only 1.3 times higher than the worker. This is due to the more competent operation of the heating system..

    But the crimping pressure is the maximum pressure in the system when crimping the radiator at the installation site. It should be noted that the calculated maximum excess pressure of the coolant in the heating system is usually determined not by the radiator, but by the weakest element, for example, a thermostat. Pressure testing of the system, according to SNiP 3.05.01-85, is recommended to be carried out at a coolant pressure 1.5 times higher than the working pressure, and according to the rules of technical operation RD 34.20.501-95 – 1.25 times. The above means that after installing the heaters, the plumber must check the tightness of the system by letting in water at a higher pressure than usual. This procedure is carried out not only after the delivery of the construction site, but also before each heating season..

    In our case, the devices were first tested at the maximum pressure recommended by the manufacturer as a working pressure, and the system was visually checked for tightness (leakage). Then the pressure was increased 1.5 times – up to the test one. Then to excess 60-62 atmospheres – everything that could be “squeezed” out of the installation. It should be noted that all the radiators presented had a greater margin of safety, it never came to destruction.

    “Santekhprom BM” RBS-500

    Price: about $ 12 per section (about $ 60 per kilowatt)
    Sectional bimetallic radiator (Russia)

    PURPOSE: installation in heating systems of high-rise buildings with operating pressure up to 16 atm.

    TECHNICAL SPECIFICATIONS
    (according to the manufacturer)

    SECTION DIMENSIONS (VxDxG): 560x80x100 mm; center distance – 500 mm. Weight: 3 kg.
    SECTION CAPACITY: 0.217 L.
    SECTION HEAT DISCHARGE: 195 W.
    PRESSURE: working – 16 atm., Test – 24 atm., Destructive – over 60 atm.
    HEATER TEMPERATURE: up to +130 degrees Celsius. PH value 8.3-9.5.

    TEST RESULTS

    A factory-assembled 5-section bimetallic radiator with a thermal power of about 1 kW was selected for testing..

    CONSTRUCTION: “Santekhprom BM” heater is clearly oriented for installation. It has a steel insert consisting of two horizontal collectors and a vertical duct. The vertical channel is called so conditionally. In reality, it is S-shaped, which is done to reduce the movement of the aluminum shell relative to the steel frame, caused by different temperature elongation of materials.

    The fins are made of AK-12 aluminum alloy (based on secondary aluminum) made by die casting. Each section has six ribs in depth. To prevent overheating along the height of the device, a gap is provided between the front vertical ribs of adjacent sections. At the lower heads of the radiator, it is minimized, and above it is about a centimeter, – the same as between the rear fins.

    Complete instrument painted with high strength powder paint.

    HEAT DISPOSAL: in the course of tests at the Scientific Research Institute of Sanitary Engineering, the nominal heat flux was 198 W and 196 W, respectively, before and after the temperature “buildup” of the device. The manufacturers considered it necessary to provide a large margin for a possible decrease in the heat transfer of the device during operation, therefore, the value of the nominal flux of 195 W. Note that “Santekhprom BM” showed high stability of thermal performance (reduction of only 1%).

    In operational tests, it crackled slightly during the first few cycles. Then he stabilized and did not bother with extraneous sounds.

    STRENGTH: the operating and test pressure declared by the manufacturer for Santekhprom BM is somewhat lower than that of its analogues (16 and 24 atmospheres). However, even at 48 (three times the working pressure) and even at 60 atmospheres, the device did not collapse and did not undergo visible changes. Apparently, the developers with the typical Russians’ craving for reliability were simply reinsured. In any case, a device with a working pressure of 16 atmospheres can be safely installed in heating systems of high-rise buildings and structures..

    INSTALLATION: Santekhprom BM radiators are mounted in the same way as steel heating devices, observing the requirements of SNiP 3.05.01-85 common for sectional radiators. Optimal installation distances: at least 3 cm from the wall and at least 10 cm from the floor and windowsill.

    OPERATION: the radiator is installed in heating systems with steel, copper and plastic pipes, with water as a heat carrier or antifreeze. In this case, you need to adhere to the requirements of RD 34.20.501-95 to its parameters..

    CONCLUSION OF THE LABORATORY: The main advantages of the Santekhprom BM radiator (Russia) are reliability, increased strength, high heat transfer, hygiene, modern appearance and long service life. The heater is characterized by stable thermal performance and high power (195 W). It is used in systems with a coolant temperature of up to 130 degrees Celsius. Due to the large wall thickness of steel pipes, the bimetallic radiator will be used in heating systems with an operating pressure of up to 16 atmospheres and is suitable for installation both in apartments of multi-storey buildings and in private construction.

    Bimex 500

    Price: about $ 13 per section (about $ 65 per kilowatt)
    Sectional bimetallic radiator (Czech Republic)

    PURPOSE: installation in heating systems of high-rise buildings with an operating pressure of up to 25 atm.

    TECHNICAL SPECIFICATIONS
    (according to the manufacturer)

    SECTION DIMENSIONS (HxLxD): 540x80x102 mm; center distance – 500 mm. Weight: 3.07 kg.
    SECTION CAPACITY: 0.23 L.
    SECTION HEAT RELEASE: 201 W.
    PRESSURE: working – 25 atm., Test – 40 atm.
    HEATER TEMPERATURE: up to +110 degrees Celsius. PH 7-8.

    TEST RESULTS

    A factory-assembled 5-section bimetallic radiator with a thermal power of about 1 kW was selected for testing..

    CONSTRUCTION: Bimex sections are symmetrical about vertical and horizontal axes. Each has an outer aluminum fins and a steel welded frame: two collectors and a conventionally vertical channel. The channel is named “conditionally vertical” because it is bent in relation to the construction vertical of the device in the form of a bracket. This is done in order to reduce the movement of the aluminum “shirt” relative to the steel core, caused by the different thermal expansion of the two materials..

    The fins are made of an alloy identical to AK-12 (12% silicon), based on secondary aluminum by injection molding technology, and the outside is painted with high-strength powder enamel. Eight ribs are cast along the depth of the section. To prevent overheating along the height of the radiator, there is a vertical clearance of about a centimeter between the front (front) and rear (rear) ribs of the adjacent sections. This improves both the thermal and hygienic performance of the appliance – it is easier to remove dust between sections.

    THERMAL INDICATORS: in the isothermal chamber of the Scientific Research Institute of Sanitary Engineering, the nominal heat flux values ​​before and after operational tests were obtained: 197.5 W and 190.8 W. Thus, after the “swing”, the heat indicators of the radiator decreased by 3.4%, therefore, according to the draft GOST for heating devices, the nominal value of the heat flux was averaged and taken equal to 194 W. According to the manufacturer, the heat transfer of the section is 201 W, which is explained by different test methods adopted in our country and abroad.

    During the temperature “buildup”, Bimex also crackled at first, which is generally characteristic of new bimetallic devices in the first heating-cooling cycles.

    STRENGTH: the radiator was tested in operation at a coolant pressure of 25 and 40 atmospheres (operating and test). They tried to destroy it by acting on it with 60 atmospheres – it did not work, there was not even a leak. But at such a level of working pressure, 75 atmospheres would be destructive, which could not be verified on the RP-50 stand. However, judging by the design, Bimex is a reliable device and is designed with a large margin of safety..

    INSTALLATION: like other bimetallic radiators with a solid steel core, Bimex is installed according to the rules for steel radiators.

    Thanks to the design feature – symmetry in relation to the front-rear and top-bottom – the installation of the radiator is greatly simplified: twist and turn as you like. If you accidentally scratched or damaged the ribbing of one of the sections, you can always hide the flaw – turn the flaw to the wall, and if necessary, even regroup the sections that are interconnected with steel nipples. Only for this you need to use branded gaskets.

    For more efficient heat transfer during the installation of the device, the general requirements for sectional radiators, regulated by SNiP 3.05.01-85 “Internal sanitary systems”, should be observed, and, in particular, the optimal installation distances: from the wall – at least 3 cm, from the floor and windowsill – at least 10 cm.

    OPERATION: the device is capable of operating both in a hot water heating system and with low-freezing heat carriers, as well as in contact with pipelines made of various materials (when using appropriate adapters). Pay attention to the pH of the coolant. For some reason, the manufacturer proposes to use a radiator in heating systems with a pH of 7-8, recommended for aluminum appliances, while a steel core, according to the conviction of specialists from the Research Institute of Sanitary Engineering, is more suitable for a pH of 8.3-9.5.

    CONCLUSION OF THE LABORATORY: radiators Bimex (Czech Republic) have a modern design, good thermal performance and high strength characteristics. Symmetrical shapes make installation easy. The nominal value of the heat flux of the section is 194 W, which is standard for this standard size (within 200 W), optimal in terms of dimensions, weight, material consumption and price. The high test pressure of 40 atmospheres makes it possible to use bimetallic radiators in heating networks with an operating excess pressure of up to 25 atmospheres, which is typical for high-rise buildings. Bimex is distinguished by high quality workmanship, reliability and durability.

    Global Style 500

    Price: about $ 16.5 per section (about $ 90 per kilowatt)
    Sectional bimetallic radiator (Italy)

    PURPOSE: installation in heating systems of buildings and structures of any number of storeys with a working pressure of up to 35 atm.

    TECHNICAL SPECIFICATIONS
    (according to the manufacturer)

    SECTION DIMENSIONS (WxDxD): 575x80x80 mm; center distance – 500 mm. Weight: 1.97kg.
    SECTION CAPACITY: 0.2 L.
    SECTION HEAT DISPOSAL: 168 W at a temperature difference between the coolant and the air in the heated room of 70 degrees Celsius.
    PRESSURE: working – 35 atm., Test – 52.5 atm., Destructive – over 110 atm..
    HEATER TEMPERATURE: up to +110 degrees Celsius. PH 7-9.5.

    TEST RESULTS

    A factory-assembled 6-section bimetallic radiator with a thermal power of about 1 kW was selected for testing..

    CONSTRUCTION: the Global Style heater is clearly oriented in terms of installation, with top, bottom, front and rear. Each section has an embedded element and outer ribbing. Frame – steel and welded in argon-carbon dioxide environment from three round pipes: two collectors and a vertical channel.

    The shell of the device is die-cast from high quality aluminum alloy. To reduce its movements relative to the steel frame, caused by different temperature elongation of materials (in aluminum, it is twice as high), the shell of the steel pipe is given a special shape.

    Along the depth of the section, there are five “jewelry” vertical ribs (the highest casting technologies are the pride of Italians!). The distance between the front plates of adjacent sections is minimal, but the rear ones have a gap of about a centimeter. A convection window is provided at the top of each section to improve heat removal and prevent overheating of the bimetallic radiator in height.

    The outside of the device is painted with powder enamel by anodic deposition in an electrostatic field. This durable coating reliably protects aluminum from mechanical scratches and moisture.

    HEAT RELEASE: The Global Style has a slightly lower rated heat flux of a section (168 W) than other tested radiators. By the way, both weight and dimensions are the same. This is good and not only from the point of view of compact dimensions: the lower the heat transfer of the section, the more accurately the required thermal power of the device is selected. In accordance with SNiP 2.04.05-91 *, it cannot be underestimated relative to the calculated one by more than 50 W, but it can be overestimated (to the nearest standard size), but I would not want to. After all, overheating of the room is an extra expense. However, the cost of devices with miniature sections of low heat transfer is usually higher..

    Thermal “buildup” showed that the thermal performance of the bimetallic radiator is stable (the decrease was only 1.9%). The first 3-4 cycles, while the “grinding” of the core to the aluminum “shirt” was taking place, it emitted a small crack, which is natural during the operation of a bimetallic device.

    STRENGTH: the tested model belongs to the second generation of Global bimetallic devices, which were developed specifically for Russia taking into account the recommendations of the Scientific Research Institute of Sanitary Engineering (the first were designed for 15 atmospheres) To date, the Global Style radiator has the highest declared operating pressure in its class – 35 atmospheres. (At the RP-50 stand, it is not possible to check the safety factor, which should be at least 105 atmospheres.)

    INSTALLATION: bimetallic radiators with an all steel core are installed in heating systems as steel appliances. However, the mechanical properties of the aluminum fins should be taken into account and protected from damage..

    The radiator sections are connected to each other using steel nipples. For this, the manifolds are provided with a 1-inch pipe thread. When regrouping, use only branded spacers.

    To achieve the calculated heat transfer, when installing Global Style, you need to observe the optimal distances: at least 3 cm from the wall behind the radiator, at least 10 cm – from the floor and window sill.

    OPERATION: it is advisable to strictly adhere to the requirements of RD 34.20.501-95 to the parameters of the coolant. The radiator can be installed in heating systems with steel, copper and plastic pipes, as well as with low-freezing coolant (antifreeze).

    CONCLUSION OF THE LABORATORY: radiators Global Style (Italy) have a modern design (according to experts, the best in their class of devices), compact size, light weight, stable thermal performance and high strength characteristics. The relatively small value of the nominal heat flux of the section (168 W) allows you to more accurately select the required heat output of the heater. The high test pressure of 52.5 atmospheres makes it possible to increase the permissible operating excess pressure of the coolant to 35 atmospheres and to install bimetallic radiators in the heating systems of any high-rise buildings and structures. Global Style devices are distinguished by high quality materials, workmanship, reliability and durability.

    Text: Maria Bagrova

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