Thermal calculation of devices consists in determining the required nominal heat flux, brand panel radiator or convector and the number of sections or columns of sectional and tubular radiators. The calculation of heating devices is carried out according to the recommendations of VITATERM LLC. Heating specifications are taken for a device with a center distance of 500 mm (except for the convector).
The required nominal heat flux of the device, W, is determined by the formula
,
(11)
where Q etc - the required heat transfer of the device, W;
- complex coefficient of reduction to nominal conditions.
Heat dissipation device Q etc , W, is calculated by the formula
Q etc = Q p – Q tr , (12)
where Q p - heat loss of the room, determined in the calculation of the heat balance (from table 3) W;
Q tr - total heat transfer of pipes laid within the premises, W.
In the course work, useful heat transfer from pipes Q tr , W, is taken as a fraction of the heat losses of the room: in a two-pipe vertical heating system for the upper floor, the heat transfer of the pipes is 5% of the heat losses of the room and 15% for the remaining floors; for apartment wiring in the floor structure - 5% of the heat loss of the room is taken.
The complex coefficient of reduction to nominal conditions is determined by the formula
,
(13)
where n, m, с - empirical numerical indicators, taking into account the influence of the coolant flow pattern on the heat flow and the heat transfer coefficient of the device, are given in the recommendations of VITATERM LLC with the most optimal water flow pattern “from top to bottom”;
p - the coefficient takes into account the direction of movement of the coolant in the device;
b - coefficient of accounting for atmospheric pressure in a given area;
Δ t - the difference between the average temperature of the water in the device and the temperature of the ambient air in the room;
G etc - water consumption through the device, kg / h.
The temperature difference in the device is determined by the formula
,
(14)
where t in , t out - the temperature of the water entering and leaving the device, ºС, for a two-pipe water heating system with steel pipes should be taken t in \u003d 95 ºС, t out \u003d 70 ºС; with a distribution of polymer pipes, the temperature is selected depending on the characteristics of their material. For metal-polymer pipes, t in \u003d 90 ºС and t out \u003d 70 ºС; for polypropylene t in \u003d 85 ºС and t out \u003d 65 ºС.
Water flow through the heater 
, kg / h, is determined by the formula
,
(15)
where 
- heat loss of the room from table 3, W;
β 1 - coefficient depending on the step of the nomenclature range of the device;
β 2 - coefficient depending on the type of device and installation method.
Both coefficients are selected according to the table.
Number of sections heater determined by the formula
,
(16)
where 
- the nominal heat flux of one section, W, is given in the recommendation for calculating the heater, table;
- coefficient characterizing the dependence of heat transfer of the radiator on the number of sections, table.
Thermal calculation of heating devices should be performed in tabular form.
Table 4 - Thermal calculation of heating devices
|
Riser No., room No. |
Heat loss of the room Qcalculated, W |
Heat transfer of pipes Q tr, W |
Required heat transfer of the device Qpr, W |
Coefficient β 1 |
Coefficient β 2 |
Room air temperature t in, 0 С |
Water temperature at the inlet to the device t in, 0 С |
Water temperature at the outlet of the device t out, 0 С |
Temperature head Δt, 0 С |
Water consumption through the device G pr, kg / h |
The question of the efficient operation of the heating system largely depends on how the heat transfer of the radiators is calculated. These appliances are the main heat source for heating indoor air. Therefore, even at the design stage, engineers carry out a calculation, on the basis of which a radiator with a certain number of sections is installed in each room. These calculations are not so simple, because they have to take into account a large number of criteria.
What should be considered when calculating?
Calculation of heating radiators
Be sure to take into account:
- The material from which the heating battery is made.
- Its size.
- The number of windows and doors in the room.
- The material from which the house is built.
- The side of the world in which the apartment or room is located.
- The presence of thermal insulation of the building.
- Type of piping routing.
And this is just a small part of what needs to be considered when. Do not forget about the regional location of the house, as well as the average outdoor temperature.
- Regular - using paper, a pen and a calculator. The calculation formula is known, and it uses the main indicators - the heat output of one section and the area of \u200b\u200bthe heated room. Coefficients are also added - decreasing and increasing, which depend on the previously described criteria.
- Using an online calculator. It is an easy-to-use computer program that loads specific data about the dimensions and construction of a house. It gives a fairly accurate indicator, which is taken as the basis for the design. heating system.
For a simple man in the street, both options are not the easiest way to determine the heat transfer of a heating battery. But there is another method for which a simple formula is used - 1 kW per 10 m² of area. That is, to heat a room with an area of \u200b\u200b10 square meters, you will need only 1 kilowatt of thermal energy. Knowing the heat transfer rate of one section of a heating radiator, you can accurately calculate how many sections need to be installed in a particular room.
Let's look at a few examples of how to correctly carry out such a calculation. Different types of radiators have a wide range of sizes, depending on the center distance. This is the dimension between the axes of the lower and upper manifold. For the bulk of heating batteries, this indicator is either 350 mm or 500 mm. There are other parameters, but these are more common than others.
This is the first thing. Second, there are several types of heating devices made of various metals on the market. Each metal has its own heat transfer, and this will have to be taken into account when calculating. By the way, everyone decides for himself which one to choose and put a radiator in his home.
Heat transfer from cast iron radiators
The range of heat transfer of cast iron batteries ranges from 125 to 150 W. The spread depends on the center distance. Now the calculation can be done. For example, your room has an area of \u200b\u200b18 m². If the installation of a 500 mm battery is planned in it, then we use the following formula: (18: 150) x100 \u003d 12. It turns out that a 12-section heating radiator must be installed in this room.
It's simple. Similarly, you can calculate cast iron radiator with a center distance of 350 mm. But this will only be an approximate calculation, because the coefficients must be taken into account for accuracy. There are not so many of them, but it is with their help that you can get the most accurate indicator. For example, the presence of not one, but two windows in the room increases heat loss, so the final result must be multiplied by a factor of 1.1. We will not consider all the coefficients as it will take a long time. We have already written about them on our website, so find the article and check it out.
Heat dissipation of aluminum radiators
To compare the two opposing metals, an aluminum battery was chosen. For aluminum radiators
Heat dissipation of Global radiators is calculated according to EN-442
heat dissipation is greater, and one section emits 200 watts of heat. Substituting this figure in the formula, we determine how many sections need to be used in an 18 m² room.
(18: 200) x100 \u003d 9. The number of sections has decreased only due to the high heat transfer of aluminum devices. So you can choose a radiator not only by size, but also by model.
Connection method
Not everyone understands that the piping of the heating system and the correct connection affect the quality and efficiency of heat transfer. Let us examine this fact in more detail.
There are 4 ways to connect a radiator:
- Lateral. This option is most often used in city apartments. multi-storey buildings... There are more apartments in the world than private houses, so manufacturers use this type of connection as a nominal way to determine the heat transfer of radiators. A factor of 1.0 is used to calculate it.
- Diagonal. Perfect connection, because the heating medium flows throughout the device, evenly distributing heat throughout its volume. Usually this type is used if there are more than 12 sections in the radiator. The calculation uses a multiplying factor of 1.1–1.2.
- Lower. In this case, the supply and return pipes are connected from the bottom of the radiator. Usually this option is used when hidden wiring pipes. This type of connection has one drawback - heat loss is 10%.
- One-pipe. This is essentially a bottom connection. Usually it is used in the Leningrad pipe distribution system. And here it was not without heat loss, however, they are several times more - 30-40%.
Conclusion on the topic
Radiator power table
You yourself were able to see that you can correctly calculate the heat transfer of the radiator in a simple wayhowever, it is not very accurate. In addition, it is necessary to take into account the large variation in the dimensional parameters of batteries, the materials from which they are made, plus additional factors. So everything is complicated.
Therefore, we advise you to do it easier. Take as a basis the very formula with the ratio of the area of \u200b\u200bthe room and the required amount heat. Make a calculation and add up to 10% to it. If your home is in the northern region, add 20%. Even 10% is very generous, but there is no extra warmth. Moreover, it is possible, using various devices, to control the supply of coolant to the radiators. You can reduce, but you can increase. The only drawback of such an increase is the initial cost of purchasing radiators with big amount sections. This is especially true for aluminum and bimetallic heating appliances.
The generally accepted temperature for apartment comfort is considered to be 21 0 Celsius. In order for it to be in the apartment at this level even in winter cold, various heating systems are used, including autonomous and central heating systems. Common sense and competent calculation of heat transfer from a radiator of heating batteries allows you to set the required number of heating devices, including heating radiators.
Goals and objectives of calculating heating radiators
Calculations of radiators are carried out to ensure the effective functioning of the heating system for heating a specific living space, and, in the calculations, thermal comfort is interpreted not only as a positive temperature of an arbitrary value, but also the maximum allowable one. It makes no sense to install an exorbitant number of heaters, if at the same time it is necessary to open the vents wide open for the sake of fresh air (recall that too hot batteries "burn" oxygen). That is, the calculations determine the boundaries of low-temperature and high-temperature heating.
Another task of thermal calculations is to determine the parameters of heat transfer, which make it possible to evenly distribute heat fluxes throughout the room. In this case, heat losses must be taken into account, depending on the presence of a basement and an attic in the room, the type of wall material, wall thickness, window sizes and many other related factors.
When designing a building object, special programs are used; thermal imagers can be used to calculate radiators in an apartment. But for approximate calculations, simple algorithms are used, which are usually called a calculator for calculating heating batteries. Their methods are based mainly on the ratio of the required heat output of the heater and the area of \u200b\u200bthe heated room.
Radiator area calculation method
The basis of the conditional calculation for the area is based on the regulated sanitary standards value of heating power per 1 sq. meter of the area of \u200b\u200bthe room. For a temperate climate at the latitude of Moscow, this figure is from 50 to 100 W. For the northern regions above 60 0 north latitude, it is higher and is taken in the range from 150 to 200 W per 1 sq. meter. Passport value of heat transfer of one cast iron section indicated in the size from 125 to 150 W. 
We determine the required power for 15 sq. meters:
100 x 15 \u003d 1500 W.
Determine the number of sections:
1500/125 \u003d 12 sections, which can be thought of as two six-section cast iron batteries.
This calculation is equivalent for a bimetallic radiator, since its heat transfer has practically the same values.
Ceiling norms were used in calculations standard height 270 cm. For higher ceilings, radiator calculations are performed based on the parameters of the room volume.
Method for calculating a radiator by volume
In this case, the technique, or, as they say, a calculator for the selection of kW batteries, operates with such concepts as the nominal heat flux Qnom of a particular type of radiator and the amount of heat energy Qnom required to heat 1 cubic meter. meter of the room. The value of Qnom must be indicated in the radiator passport. The value of Qpom for a standard room of a panel house is 0.041 kW. For brick house this figure is reduced to 0.034 kW per 1 cu. meter. For residential premises with good thermal insulation, thermal power even less - 0.02 kW.
The number of radiator sections is determined in the same way as the heating radiator calculator by area, that is, by multiplying the volume of the room by the specific volumetric heat energy and then dividing by the value of the nominal heat flux of the radiator:
N \u003d V x Qnom / Qnom, pcs. The result is rounded up.
It is important! Since these calculations are rather approximate and do not take into account the heat losses of the building, rounding up will allow you to make some margin for improving the comfortable heating conditions.
Consideration of additional factors in thermal calculations of radiators
Additional factors affecting the heat transfer of radiators are correction factors that correct deviations from standard conditionsaccepted in the basic calculations.
Height adjustment
The standard room height is 270 cm. For higher room heights, the correction factor is determined by dividing the room height by standard value 270 cm.That is, for a room height of 324 cm, the coefficient will be 324/270 \u003d 1.2. Accordingly, the specific thermal power is 100 W per 1 sq. meter must be increased by 1.2 times, that is, it will already be 120 W per kV. meter.
The heat transfer of radiators depends on the location, since convective flows are mixed in different ways at different distances between the radiator fins and the floor or window sill. The correction factors are shown in the diagram. It should be borne in mind that for corner rooms the heat loss is twice as large, since there are two windows in such rooms. 
The correction factor to the nominal value of the heat transfer of the radiator is most optimal when the heating pipes are connected diagonally. But the specific conditions for installing batteries do not always allow the use of this scheme. 
Summary
It is difficult to take into account all the factors affecting the heat transfer of the radiator. According to plumbers, if the house has perfect thermal insulation, you can do without heating. There is enough heat from electrical appliances and a stove. It is also very important to be able to calculate heat loss, depending on the size of windows, doors and vents. However, the considered averaged values \u200b\u200bof the thermal characteristics of rooms and radiators make it possible with a certain accuracy to determine the required number of radiator sections and not miss the room temperature.
