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Heat transfer is the heat exchange between two media separated by a surface. Its intensity is characterized by a coefficient. When installing a heating main, the problem of energy saving should be taken into account. Therefore, old heating mains are being replaced with new ones, which use pipes equipped with thermal insulation, which makes it possible to reduce heat losses by almost 80%.

In everyday life, the need to determine the heat transfer coefficient arises in two situations:

if you need to calculate heating devices;
if it is required to estimate heat losses in the pipeline.

In both the first and second cases, it is necessary to determine how much heat a steel pipe for a heating main gives off to space, if the temperature of the heat carrier and the temperature of the medium are known. An additional parameter is the absence or presence of thermal insulation.

Calculation of heat transfer of steel pipes

The steel pipe has a very high thermal conductivity - 74 W / m x K. But the thermal conductivity characterizes the material, that is, steel. Heat transfer, of course, depends on thermal conductivity, but not only. The shape of the pipe, its surface area, color, environmental characteristics, and coolant flow rate are also important.

The formula is used to calculate:

Heat transfer = K*F*dT, where:

K - coefficient (8 - 12.5), which depends on the number of threads in the heater, pipe diameter and temperature difference;
F is the surface area;
dT - temperature difference - half the sum of the coolant temperatures at the inlet outlet, from which the temperature of the medium is subtracted.

If the pipe is insulated, then the result is multiplied by the efficiency of the insulating material. The initial parameters are determined, for example, there are three threads in the heater, the length of each is one meter, the diameter is 10 mm, the room temperature is +20 degrees, the temperature at the entrance is 81 degrees, at the exit - 79 degrees.

First you need to calculate the surface area of the heater using the formula for calculating the area of a cylinder:

S=2πrh, that is, multiply the circumference by the height. It turns out:

F= 2*3.14*0.05*3= 0.94 m2.

dT= (79+81)/2-20=60

K for such a device can be, for example, 9.

Heat transfer \u003d 9 * 0.94 * 60 \u003d 507.6 W / (m² * K).

Heating appliances

warm floor;
registers (radiators);
heated towel rails.

Warm floor

Pipes are used for a water-heated floor, but steel pipes are rarely used. They are not resistant to corrosion, tend to accumulate deposits (which reduces clearance), require welding. When using threaded connections, a leak invariably appears during operation. And this is not at all desirable when laying the system under the screed, as it will entail wet ceiling neighbors from below or destruction of the ceiling. Based on this, metal-plastic products are most often used for underfloor heating.

Registers

The register is several pipes of large diameter with welded ends, which are connected in parallel. This is the cheapest heating device. But the registers can also include trunk lines, consisting of smooth-bore pipes, radiators, heated towel rails, tubular - radiators. The most primitive registers can still be seen in old warehouses and shops, where the heat is felt from a few thick pipes on the wall. The register can also be considered as a thick pipe, which is stretched along the perimeter of the room.

But a simple register is less efficient than, for example, an aluminum radiator equipped with metal plates. The aesthetic side of a simple steel register is not even worth talking about. But in Soviet times, such a heater was a simple and cheap solution, which also had the advantage of not needing to clean the inner surface, since it generated enough heat even after it was overgrown with corrosion products and other deposits.

You can increase the heat transfer of the register by attaching metal plates. In this case, it will also play a decorative role, turning into a design radiator that carries a certain load in the interior of the room.

The register can only be mounted by welding, which limits the scope of application. However, if the correct scheme is created and the welding work is carried out outdoors, the final assembly is possible without welding work.

Towel dryers

Towel rails made of steel pipes are still found in houses that were built in Soviet times. Then they were mounted using threaded connections and heated up only at a time when the residents used hot water. That is, they either heated up or cooled down, which led to leaks.

Later, heated towel rails were made part of the heating risers and mounted by welding. They began to heat up continuously, but the size of the devices decreased significantly.

Ways to increase heat transfer

The shape of the material does not affect the heat index at all, as it has an unfortunate surface-to-volume ratio. In order for the heating devices to still heat, it is used:

black coloring, which increases the amount of infrared radiation;
finning (welding of metal plates) - increases the area;
thermal insulation that reduces heat loss on the way to the devices.

A few simple tricks are enough:

clean the radiators from accumulated dust;
clean their inner surface from rust and scale;
attach a screen to the wall at the back - a foil reflector that redirects heat;
install aluminum casings on the devices, increasing the heat transfer area;
redirect heat with a fan.

The easiest way to reduce the heat transfer of the pipeline is to insulate. For a couple of decades, they were wrapped with glass wool or rags for this purpose. Now there is no need for this - steel pipes with insulation are produced, there are foam linings, split casings and mineral wool.

But this all applies to houses that are built on this moment. The limited funds of the budgets of housing and communal enterprises forces them to use all the same rags.

One of the main stages in planning a heating system in a house or apartment is the calculation of heating pipes. At this stage of project development, the type of pipes, as well as their diameter, are determined. The duration and quality of its functioning will depend on the correct selection of all starting materials for creating a heating system.

Diameters of heating pipes and features of their choice

When starting to solve such a problem as calculating the diameter of the pipes of a heating system, it should be taken into account that there are several concepts united by the general term "pipe diameter". Each pipe can be characterized by the following parameters:

The inner diameter is the main characteristic of the pipe, indicating its throughput.
Outer diameter - not less than important characteristic, which must be taken into account when designing the heating system.
Nominal diameter (nominal bore) - a certain rounded value, which is indicated when marking.

We should also not forget that pipes made of different materials have a number in their marking corresponding to one or another of its diameters:

Steel and cast iron pipes are marked by the size of their inner diameter.
Pipes made of copper or plastic - according to the size of the outer diameter.

That is why, when calculating the cross section of a heating pipe, it is imperative to take into account the material of the pipes. Especially if it is supposed to create a system that is a combination of different pipes.

One of the features that influence the choice of the size of any pipes is the unit of measure adopted to assess the size of their diameter, and therefore their marking. The basic unit for pipe size is an integer or fraction of an inch. To convert inches into the usual measurement system for us, you should remember that 1 inch = 25.4 mm.

How to calculate the required diameter of heating pipes

Starting the calculation of the diameter of the pipe for heating a dwelling, one more important parameter should be taken into account. This is the heat load. In accordance with the standards, comfortable conditions for living in a room with a ceiling height of 2.5 m provide 0.1 kW of thermal power per 1 m 2 of its area. Therefore, it is very easy to calculate how much heat is required to heat, for example, a room of 20 m 2:

20 * 0.1 = 2.0 (kW).

In accordance with the table, the diameter of the pipes that can provide comfortable heat is selected. In our example, according to the table presented, in order to keep the room always warm, pipes with an internal diameter of 1/2 inch are quite suitable.

Characteristics of heating pipes: heat transfer and slope

Thermal conductivity of pipes and heating radiators

Having installed an autonomous heating system in his house, everyone decides for himself what the temperature of the water flowing through these pipes will be. It all depends on the wishes of the household, external climatic conditions and the type of radiators installed in the house. Since there is no standard and restriction on such a parameter as the temperature of the coolant, the heat transfer of the heating pipes should be the determining value here.

The lower the thermal conductivity of the pipes, the less heat loss will occur before the direct delivery of the coolant to the radiator. Consider which pipes have less heat transfer:

Here, polypropylene pipes are seen as the best option, since their thermal conductivity coefficient is the smallest among other types of pipes used in heating systems.
Metal-plastic and reinforced polymer pipes have somewhat higher thermal conductivity, although they are also a good option for installing a heating pipeline.
And, finally, steel pipes, laid in the vast majority of houses built in the last century, give off heat the fastest.

When installing a heating system, it is not recommended to use steel pipes in their pure form without insulation, since they will significantly contribute to reducing the efficiency of the system.

As for radiators, here, on the contrary, products made from materials with the highest heat transfer are welcome. The rating in ascending order of the quality of radiators in relation to their heat transfer will look like this:

Radiators made of cast iron have the lowest heat transfer coefficient among modern heating appliances.
They are followed by bimetallic radiators.
Aluminum batteries have the highest coefficient of heat transfer from the carrier to the environment, so it is recommended to use them to increase the efficiency of the system.

In addition, there is a parameter that will help determine the number of radiator sections. This is their thermal power, which must be indicated in the product passport. Usually it corresponds to the value set on the basis that the water flowing through the heating pipes will have a temperature of 75 ° C. To maintain comfort and save energy in the house, this value can be varied by changing in one direction or another.

To create an optimal microclimate, it is not necessary to raise the water temperature in polypropylene pipes above 95 ° C in order to avoid their deformation and failure. It is best to increase the total working surface of the batteries.

Also, for the normal operation of the house heating system, it is important to know what the pressure is in the pipes that heat the house. The standard indicator is 1.5-2 atm. Increasing the pressure above the specified values \u200b\u200bmay lead to the fact that the wall thickness of the pipe for heating will be insufficient. In this case, depressurization and equipment failure will inevitably occur. To avoid such a nuisance, you should use pressure gauges to control the pressure in the system.

Organization of the slope of heating pipes

When creating an autonomous water heating system at home, one should not forget that it should be arranged with a slight slope that helps its proper functioning. This is especially true for the system of natural circulation of the coolant through the pipes. Rules for choosing the slope of heating pipes:

A correctly selected slope of the heating pipes will ensure unhindered circulation of the coolant through the system. The slope in the direction of the water flow should be 10 mm per 1 m of pipe both in the direction from the heating boiler to the heating radiators, and when withdrawing from the system.

To pre-mark the angle of inclination of the heating pipes, use a water level - spirit level or hydro level.

In systems using forced circulation of the coolant using a pump, it is not necessary to arrange a slope. Typically, in such systems, pipes are laid horizontally or with a minimum slope towards the drain valves of 2-3 mm. This helps to drain water from the pipes for repair work or to prevent rupture of the pipeline when the system is not used for a long time during the cold season.
A horizontal outlet for connecting to a battery from vertical pipeline systems with a length of more than 0.5 m is arranged with a slope of 10 mm in the direction of water movement. If this branch has a shorter length, it is not necessary to arrange a slope.

Designing and installing a heating system in a house is a complex task. Therefore, it is best to entrust its solution to professionals who know exactly how to calculate pipes for heating, choose the right materials. They will carry out the necessary thermal and hydraulic calculations to ensure that the heating system in your home will last reliably and for a long time. If the heating system in your apartment or house is compact, following the instructions of our portal, you will surely be able to perform all the necessary work no worse, but at the same time much cheaper.

There are a considerable number of different kinds of heating devices on the market. However, home-made radiators are still used. And the most common registers are from pipes. Heating registers are welded or prefabricated structures made of horizontally located pipes interconnected by jumpers for the circulation of the coolant.

What are

Heating registers are made of different materials, they have different shape. Each has pros and cons.

What are they made of

If we talk about materials, then the most common is steel, or rather steel electric-welded pipes. Steel does not have the best heat transfer, but this is offset by a low price, ease of processing, availability and a large selection of sizes.

It is very rare to find stainless pipes - decent power requires a large number of pipes, and how much stainless steel products cost, you have an idea. If they did, it must have been a long time ago. They also use “galvanizing”, but it is more difficult to work with it - it will not work to cook.

Sometimes they make copper registers - they are used in those networks where the wiring is done. Copper has a high heat dissipation (four times greater than that of steel), therefore, their dimensions are much more modest (both in length and in diameter of the pipes used). In addition, the wiring pipes themselves (if they are not) give off a sufficient amount of heat. At the same time, the plasticity of this metal allows pipes to be bent without any special tricks and efforts, and welding can be used only at the junctions of different pieces. But all these pluses are offset by two big minuses: the first is the high price, the second is the capriciousness of copper to operating conditions. For the price, everything is clear, but for the operation there are a few explanations:

requires a neutral and clean heat transfer fluid, free of solid particles
the presence of other metals and alloys in the system is undesirable, except for compatible ones - bronze, brass, nickel, chromium, therefore all fittings and fittings will need to be sought from these materials;
carefully performed grounding is mandatory - without it, in the presence of water, electrochemical corrosion processes begin;
the softness of the material requires protection - casings, etc. are needed.

There are registers made of cast iron. But they are too bulky. In addition, they have a very large mass, under them you need to make no less massive racks. Plus, cast iron is brittle - one blow, and it can crack. It turns out that this type of registers also needs protective covers, and they reduce heat transfer and increase the cost. Moreover, installing them is a difficult and hard job. The advantages include high reliability and chemical neutrality: this alloy does not care what coolant to work with.

In general, copper and cast iron are not easy. So it turns out that the best choice is steel registers.

Types of registers

The most common type is registers made of smooth pipes, and most often - steel electric-welded ones. Diameters - from 32 mm to 100 mm, sometimes up to 150 mm. They are made of two types - serpentine and register. Moreover, register ones can have two types of connections: a thread and a column. A thread is when the jumpers, through which the coolant flows from one pipe to another, are installed either on the right or on the left. It turns out that the coolant sequentially runs around all the pipes, that is, the connection is serial. When connecting the "column" type, all horizontal sections are interconnected at both ends. In this case, the movement of the coolant is parallel.

Any type of registers can be used for any type of system: with single pipe and, with vertical and horizontal type of supply. With any system, a large heat transfer will be when the supply is connected to the upper pipe.

In the case of use in systems with natural circulation, it is required to observe a slight slope towards the movement of the coolant of the order of 0.5 cm per meter of pipe. Such a small slope is explained by a large diameter (low hydraulic resistance).

These products are made not only of their round, but also of square pipes. They are practically no different, only it is more difficult to work with them, and the hydraulic resistance is slightly greater. But the advantages of this design include more compact dimensions with the same volume of coolant.

There are also registers made of pipes with fins. In this case, the area of \u200b\u200bcontact of the metal with air increases, and heat transfer increases. Actually, until now, in some budget new buildings, builders install just such heating devices: the well-known “pipe with fins”. With not the best appearance, they heat the room well.

If you insert a heating element into any register, you can get a combined heater. It can be standalone, unrelated to the system, or used as additional source heat. If the radiator is insulated with heating only from the heating element, it is necessary to install an expansion tank at the top point (10% of the total coolant volume). When heated from the expansion tank, it is usually built into the structure. If it is not there (often happens in), then in this case it is also necessary to install an expansion tank. If the material for the registers is steel, then the tank needs a closed type.

Electric heating can come in handy in the most severe cold, when there is not enough. Also, this option can help out in the off-season, when it makes no sense to load and overclock the system “to the fullest”. You just need to warm up the room a little. This is not possible with solid fuel boilers. And such a fallback option will help warm up in the offseason.

Calculation of registers from smooth pipes

Steel heating registers are easy to do with your own hands. The cost of such a heating system will depend on who will cook them. If you own the welding technique yourself, the option is the most low-budget, if the welder needs to be paid, there will not be much difference in cost with inexpensive ones.

At the same time, the registers will occupy larger areas than standard heaters: due to the insignificant surface of contact with air, their efficiency is low. They increase heat transfer by installing a more powerful pump, but there are speed limits due to possible noise in the system. About,

Diameters, as mentioned - from 32 mm to 100-150 mm. Large pipe sizes lead to an increase in the volume of the system. When starting and accelerating the system, this is a minus - until the coolant heats up, a decent amount of time will pass. When working, a large volume is rather a plus: softer conditions for the boiler. On the other hand, at in large numbers coolant to regulate the temperature is difficult.

Table of heat transfer of steel pipes of different diameters for different operating conditions of the system (click on the picture to enlarge it)

The distance between the two pipes in the register should not be small: this reduces heat transfer. Therefore, they are located at a distance of not less than 1.5 radius. The number of rows and the length of the register depend on the required power, as well as on the diameter of the selected pipes. In the general case (for central Russia, for rooms with medium thermal insulation and a ceiling height of 3 m), it can be calculated from the heat transfer of a meter of steel pipe. These values are shown in the table. Using it, you can find the size and number of registers by the area of \u200b\u200bthe room.

Heat transfer of one meter of steel pipes of different diameters - for calculating the heating register by area

To calculate the heat losses of the premises, there are averaged data on the heat output of a linear meter of a steel pipe. You can use them for standard conditions. If the system operates at other temperatures, adjustments up or down are required.

If these tables did not help you, you can calculate the register using the formula.

Substituting the appropriate values, you will find the heat transfer of one pipe under your conditions. The heat transfer of all subsequent (second and more) will be slightly less. The found value must be multiplied by 0.9. So you will calculate and be able to make a register of smooth pipes with your own hands.

How to install

There are two installation options: hang on the wall or put on a rack. The choice depends on the dimensions and weight of the resulting structure, as well as on the type of walls.

Quite often they make a combined installation: they cook racks, which are then attached to the wall. Even very massive registers can be installed in this way. Also, this installation option provides a high level of security.

Each such heater at the top point must have. It is needed to bleed air from the system.

Advantages and disadvantages

The advantages include a simple design and simple calculation, the availability of materials. All this together allows you to make registers for heating with your own hands.

The next positive is most of heat is transmitted with the help of radiant energy, and it is perceived by a person as more pleasant.

The next plus is the smooth surface, which ensures easy cleaning.

Excellent quality - compatible with any system - both with natural and forced circulation.

There are also disadvantages: low heat transfer, susceptibility to corrosion, not the most attractive appearance, the need for regular painting ().

Results

Registered heating in private homes is rarely used today: there is big choice heating appliances for different conditions. The price range is also quite wide. But registers made of smooth pipes and pipes with fins are often used for heating industrial, warehouse and auxiliary premises, greenhouses, garages, greenhouses, etc. That is, where external attractiveness does not matter.

The calculation of the heat transfer of the pipe is required when designing heating, and is needed to understand how much heat is required to warm the premises and how long it will take. If the installation is not carried out according to standard projects, then such a calculation is necessary.

What systems need calculation?

The heat transfer coefficient is calculated for a warm floor. Increasingly, this system is made of steel pipes, but if products from this material are chosen as coolants, then it is necessary to make a calculation. The coil is another system, during the installation of which it is necessary to take into account the heat transfer coefficient.

Registers - are presented in the form of thick pipes connected by jumpers. The heat output of 1 meter of this design is on average 550 watts. The diameter ranges from 32 to 219 mm. The structure is welded so that there is no mutual heating of the elements. Then the heat transfer increases. If you correctly assemble the registers, you can get a good room heating device - reliable and durable.

How to optimize the heat transfer of steel pipe?

During the design process, specialists face the question of how to reduce or increase the heat transfer of 1 m of steel pipe. To increase, you need to change the infrared radiation to big side. This is done with paint. Red color enhances heat dissipation. Better if the paint is matte.

Another approach is to install fins. It is mounted outside. This will increase the heat transfer area.

In what cases is it necessary to reduce the parameter? The need arises when optimizing a pipeline section located outside the residential area. Then experts recommend insulating the site - isolating it from the external environment. This is done by means of foam, special shells, which are made from special foamed polyethylene. Mineral wool is also often used.

We make a calculation

The formula for calculating heat transfer is as follows:

Q = K*F*dT, where

K - coefficient of thermal conductivity of steel;
Q is the heat transfer coefficient, W;
F is the area of the pipe section for which the calculation is made, m 2 dT is the temperature pressure (the sum of the primary and final temperatures, taking into account room temperature), ° C.

The thermal conductivity coefficient K is selected taking into account the area of the product. Its value also depends on the number of threads laid in the premises. On average, the value of the coefficient lies in the range of 8-12.5.

dT is also called temperature difference. To calculate the parameter, you need to add the temperature that was at the outlet of the boiler with the temperature that was recorded at the inlet to the boiler. The resulting value is multiplied by 0.5 (or divided by 2). The room temperature is subtracted from this value.

dT \u003d (0.5 * (T 1 + T 2)) - T to

If the steel pipe is insulated, then the value obtained is multiplied by the efficiency of the thermal insulation material. It reflects the percentage of heat that was given away during the passage of the coolant.

We calculate the return for 1 m. of the product

Q \u003d 0.047 * 10 * 60 \u003d 28 W.

K = 0.047, heat transfer coefficient;
F \u003d 10 m 2, pipe area;
dT = 60° C, temperature difference.

It's worth remembering

Do you want to make the heating system competently? Do not pick up pipes by eye. Heat transfer calculations will help optimize construction costs. In this case, you can get a good heating system that will last for many years.

In the construction of heating systems for private houses and apartment buildings, steel pipes are used as the most commonly used material. Many consumers have questions: how good are these traditional products in their technical characteristics? It is about such a significant parameter for heating systems as heat transfer that we will describe in more detail.

When the heat transfer coefficient of a steel pipe matters

It is required to take into account the heat transfer coefficient of a steel pipe when designing heating systems to determine the required number of heating devices and the choice of boiler equipment. This setting also matters:

in the calculation of possible losses during the movement of the coolant through pipelines of central and individual heating systems;
to select the optimal and most efficient working dimensions of heating devices made of steel pipes (coils (towel dryers), registers).

The heat transfer coefficient is a calculated value that characterizes the intensity with which steel pipes give off heat to the environment. To calculate the heat transfer of steel pipes, a formula is used in which the surface area and ambient temperature are taken into account as initial data. The desired parameter is obtained from the ratio of the heat flux density given off by the surface and the temperature difference on it with the environment.

What is important to consider when calculating the heat transfer of steel pipes

The average specific thermal conductivity of steel pipes is taken as 74 W / m x K, where K is the heat transfer coefficient. Please note that this is precisely the average indicator, since for a more detailed calculation it is necessary to take into account other criteria, including:

pipe shape,
Surface area (depending on diameter),
Coating pipes with paint, its color,
Properties of heat-insulating materials planned for use,
Environmental characteristics: temperature, thermal conductivity,
Temperature and speed of movement of the coolant.

To calculate the surface area of steel pipes, the mathematical formula used in determining the area of a cylinder is used.

To perform the calculation, you will need to use the formula: Q = K x F x dT . In this formula:

Q- heat transfer, measured in Watts (W),

F- the area of the measured pipes (for convenience, it is recommended to initially calculate the heat transfer of 1 m of steel pipe, multiply the result by the lengths of pipes of the same diameter in the system and get the average value of pipes of different diameters),

dT- temperature pressure. There is also a calculation rule to get this value. This value corresponds to the sum of the pipe inlet and outlet temperatures divided by 2, from which the ambient temperature is subtracted.

When using thermal insulation, the results of the calculation according to the above formula must be multiplied by the thermal insulation efficiency index indicated by the material manufacturer.

What to do in order to reduce heat transfer

Reducing heat transfer is necessary in areas that are not used for useful purposes. This is necessary to save the cost of heating the coolant and will save you money on paying for it. You hardly agree to literally throw your money away.

To prevent the coolant from cooling in such problem areas, the construction market offers a fairly large selection of heat-insulating, efficient and environmentally friendly materials. A description of their entire range and properties is beyond the scope of this article and should be the subject of a separate study. General recommendation is that their use should be considered mandatory both in private and multi-storey construction.

Ways to increase heat transfer

Heat transfer from steel pipes and heaters made from them can be increased in several ways. Here are some practical and inexpensive tips to follow:

Paint the heater or pipes with a warm matt paint. So you increase the infrared radiation.
Install fins made of flat metal plates or hollow pipes of smaller diameter between the pipes.

Heating appliances made of steel pipes

The most common heating devices made of steel pipes are:

Coils (towel dryers),
Warm floor,
Heating registers.

Towel rails made of steel pipes in their classic form, connected to the heating system and operating only during the heating season, are not particularly popular today. Consumers prefer autonomous devices with a special coolant and electric heating. The industry produces a fairly large assortment with various technical characteristics and designs, which have a low cost. Therefore, the issue of making towel warmers from steel pipes in a handicraft way has long ceased to be relevant.

For the installation of underfloor heating, steel pipes are also gradually becoming a thing of the past. The main reason for this is the development and improvement of technologies that are more efficient in all significant characteristics.

The situation is somewhat different with efficient registers made of steel pipes. These heaters continue to be highly popular in private residential buildings, they are used for heating in the entrances of apartment buildings and in industrial buildings. The reason is their maximum heat transfer with at the same time low cost of materials for their manufacture. Appearance registers are pipes interconnected by jumpers of a smaller diameter. Their high heat transfer coefficient is achieved due to the increased total area of thermal study.