Calculation of the heat load for heating the building: formula, examples

When designing a heating system, whether it is an industrial building or a residential building, you need to conduct competent calculations and draw up a diagram of the heating circuit contour. Special attention at this stage is recommended by specialists to pay attention to the calculation of the possible heat load on the heating circuit, as well as the volume of fuel consumed and the heat generated.

Thermal load: what is it?

By this term we mean the amount of heat given up by the heating devices. Preliminary calculation of the heat load allows to avoid unnecessary expenses for acquiring the components of the heating system and for their installation. Also, this calculation will help to correctly allocate the amount of heat released sparingly and evenly throughout the building.

In these calculations there are many nuances. For example, the material from which the building is built, the thermal insulation, the region, etc. The specialists try to take into account as many factors and characteristics as possible in order to obtain a more accurate result.

Calculation of the heat load with errors and inaccuracies leads to inefficient operation of the heating system. It even happens that you have to redo the sections of the already working design, which inevitably leads to unplanned spending. Yes, and housing and communal services are calculating the cost of services based on data on heat load.

Key Factors

An ideally designed and constructed heating system must maintain the set room temperature and compensate for the resulting heat loss. Counting the heat load on the heating system in the building, you need to take note:

- Purpose of the building: residential or industrial.

- Characteristics of structural elements of the structure. These are windows, walls, doors, roof and ventilation system.

- Dimensions of the dwelling. The more it is, the more powerful the heating system should be. It is necessary to take into account the area of window openings, doors, external walls and the volume of each indoor space.

- Availability of special purpose rooms (sauna, sauna, etc.).

- Degree of equipping with technical devices. That is, the presence of hot water supply, ventilation systems, air conditioning and type of heating system.

- Temperature mode for a single room. For example, in rooms intended for storage, you do not need to maintain a comfortable temperature for a person.

- Number of hot water points. The more of them, the more the system is loaded.

- Area of glazed surfaces. Rooms with French windows lose a significant amount of heat.

- Additional conditions. In residential buildings, this can be the number of rooms, balconies and loggias and bathrooms. In industrial - the number of working days in a calendar year, shifts, the technological chain of the production process, etc.

- Climatic conditions of the region. When calculating heat loss, street temperatures are taken into account. If the differences are insignificant, then a small amount of energy will go into compensation. While at -40 ^o C outside the window will require significant costs.

Peculiarities of existing methods

The parameters included in the calculation of the heat load are found in SNiPs and GOSTs. They also have special heat transfer coefficients. From the passports of equipment included in the heating system, digital characteristics are taken concerning a certain heating radiator, boiler, etc. And also traditionally:

- heat consumption, taken at the maximum for one hour of the heating system,

- the maximum heat flow from one radiator,

- Total heat costs in a certain period (most often - season); If hourly calculation of the load on the heating network is necessary, the calculation should be carried out taking into account the temperature difference during the day.

The performed calculations are compared with the heat output area of the entire system. The indicator is quite accurate. Some deviations happen. For example, for industrial buildings, it will be necessary to take into account the reduction in the consumption of thermal energy on weekends and holidays, and in residential premises - at night.

The methods for calculating heating systems have several degrees of accuracy. To minimize the error, it is necessary to use rather complicated calculations. Less accurate schemes are used if the goal is not to optimize the cost of the heating system.

Basic methods of calculation

To date, the calculation of the heat load for heating the building can be done in one of the following ways.

The three main

1. For calculation, enlarged indicators are taken.
2. Indicators for the structural elements of the building are taken for the base. Here, the calculation of the heat losses going to the heating of the internal volume of air will also be important.
3. All objects entering the heating system are calculated and summed.

One approximate

There is a fourth option. It has a large enough error, because the indicators are very average, or not enough. Here is the formula - Q _from = q ₀ * a * V _H * (t _EH - t _NRO ), where:

• Q ₀ - the specific thermal characteristic of the building (most often determined by the coldest period),
• A - correction factor (depends on the region and is taken from the ready tables),
• V _H is the volume calculated from the outer planes.

Example of a simple calculation

For a building with standard parameters (height of ceilings, room sizes and good thermal insulation characteristics), a simple ratio of parameters with a correction for the coefficient depending on the region can be applied.

Suppose that the house is located in the Arkhangelsk region, and its area is 170 square meters. M. The thermal load will be 17 * 1.6 = 27.2 kW / h.

Such a definition of thermal loads does not take into account many important factors. For example, the structural features of the structure, temperature, the number of walls, the ratio of the areas of walls and window openings, etc. Therefore, such calculations are not suitable for serious projects of the heating system.

Calculation of the heating radiator by area

It depends on the material from which they are made. Most often today used bimetallic, aluminum, steel, much less often cast-iron radiators. Each of them has its own indicator of heat transfer (thermal power). Bimetal radiators with a distance of 500 mm between the axes, on average, have 180 to 190 watts. Radiators from aluminum have practically the same parameters.

The heat transfer of the described radiators is calculated per one section. Radiators steel plate are not folding. Therefore, their heat transfer is determined based on the size of the entire device. For example, the heat output of a double-row radiator of 1 100 mm width and 200 mm height will be 1,010 W, and a panel radiator made of steel with a width of 500 mm and a height of 220 mm will be 1 644 W.

The calculation of the heating radiator for the area includes the following basic parameters:

- height of ceilings (standard - 2,7 m),

- thermal power (per square meter - 100 W),

- one external wall.

These calculations show that for every 10 sq. Km. M needs 1 000 watts of thermal power. This result is divided by the heat output of one section. The answer is the required number of radiator sections.

For the southern regions of our country, as well as for the northern regions, decreasing and increasing coefficients have been developed.

Average calculation and accurate

Taking into account the described factors, the average calculation is carried out according to the following scheme. If the 1 square. M requires 100 watts of heat flow, then a room of 20 square meters. M should receive 2,000 Watts. The radiator (popular bimetallic or aluminum) from eight sections allocates about 150 W. We divide 2,000 by 150, we obtain 13 sections. But this is a rather enlarged calculation of the heat load.

The exact looks a little frightening. In fact, nothing complicated. Here's the formula:

Q _m = 100 W / m ² × S ( _room ) m ² × q ₁ × q ₂ × q ₃ × q ₄ × q ₅ × q ₆ × q ₇ where:

• Q ₁ - type of glazing (conventional = 1.27, double = 1.0, triple = 0.85);
• Q ₂ - wall insulation (weak, or missing = 1.27, wall lined with 2 bricks = 1.0, modern, high = 0.85);
• Q ₃ - the ratio of the total area of window openings to the floor area (40% = 1.2, 30% = 1.1, 20% - 0.9, 10% = 0.8);
• Q ₄ - street temperature (the minimum value is taken: -35 ^о С = 1.5, -25 ^о С = 1.3, -20 ^о С = 1.1, -15 ^о С = 0.9, -10 ^о С = 0.7);
• Q ₅ - number of external walls in the room (all four = 1.4, three = 1.3, corner room = 1.2, one = 1.2);
• Q ₆ - type of settlement room above the settlement room (cold attic = 1.0, warm attic = 0.9, residential heated room = 0.8);
• Q ₇ - ceiling height (4.5 m = 1.2, 4.0 m = 1.15, 3.5 m = 1.1, 3.0 m = 1.05, 2.5 m = 1.3).

By any of the methods described, it is possible to calculate the heat load of an apartment building.

Estimated calculation

The conditions are as follows. The minimum temperature in the cold season is -20 ^о С. Room 25 square meters. M with triple-glazed windows, bicuspid windows, ceiling height 3.0 m, walls in two bricks and unheated attic. The calculation will be as follows:

Q = 100 W / m ² × 25 m ² × 0.85 × 1 × 0.8 (12%) × 1.1 × 1.2 × 1 × 1.05.

The result, 2 356.20, divide by 150. As a result, it turns out that in the room with the specified parameters you need to install 16 sections.

If you need to calculate in gigacalories

If there is no heat meter in the open heating circuit, calculate the heat load for heating the building using the formula Q = V * (T ₁ - T ₂ ) / 1000, where:

• V - the amount of water consumed by the heating system, is calculated in tons or m ³ ,
• T ₁ - the number showing the temperature of hot water is measured in ^o C and for the calculation a temperature corresponding to a certain pressure in the system is taken. This indicator has its own name - enthalpy. If there is no practical way to remove the temperature indexes, resort to the averaged index. It is in the range of 60-65 ° C.
• T ₂ - temperature of cold water. It is difficult to measure it in the system, therefore constant indicators have been developed, depending on the temperature in the street. For example, in one of the regions, in the cold season this figure is taken equal to 5, in the summer - 15.
• 1 000 - the coefficient for obtaining the result immediately in gigacalories.

In the case of a closed circuit, the heat load (gcal / h) is calculated in a different way:

Q _from = α * q _о * V * (t _в - t _н.р ) * (1 + K _н.р ) * 0,000001, where

• Α is a coefficient designed to correct climatic conditions. It is taken into account if the street temperature is -30 ° C;
• V - volume of the structure by external measurements;
• Q _o is the specific heating index of the structure for a given t _H = -30 ° C, measured in kcal / m ³ * C;
• T _в - calculated internal temperature in the building;
• T _н.р - estimated street temperature for the design of the heating system;
• K _n.p is the infiltration coefficient. It is caused by the ratio of the heat losses of the settlement building with infiltration and heat transfer through external structural elements at street temperatures, which is specified in the framework of the project being prepared.

Calculation of the heat load is somewhat enlarged, but this formula is given in the technical literature.

Examination with a thermal imager

Increasingly, in order to increase the efficiency of the heating system, thermal imaging surveys of the structure are used.

These works are carried out in the dark. For a more accurate result, it is necessary to observe the temperature difference between the room and the street: it must be at least 15 ^o . Lamps for daylight and incandescent lamps are turned off. It is advisable to remove carpets and furniture to the maximum, they knock down the device, giving some error.

The examination is slow, the data are recorded carefully. The scheme is simple.

The first stage of the work passes inside the room. The device is moved gradually from the doors to the windows, paying special attention to the corners and other joints.

The second stage is the examination of the external walls of the building by the thermal imager. The joints are also carefully examined, especially the connection to the roof.

The third stage is data processing. First, the device does this, then the readings are transferred to the computer, where the corresponding programs finish processing and produce the result.

If the survey was carried out by a licensed organization, it will issue a report on the results of the work with mandatory recommendations. If the work was done personally, then you need to rely on your knowledge and, perhaps, the help of the Internet.