What is the heat load for heating a building

To heat the room, heating devices of the appropriate power are required. Calculation of the heat load on heating a building allows you to accurately determine how much boiler power is required, what size radiators need to be installed and which heating scheme will be most effective. Many factors are taken into account in the calculations.

Thermal load concepts

Heating a room is a compensation for heat loss. Heat is gradually released through walls, foundations, windows and doors. The lower the outside temperature, the faster the heat transfer to the outside takes place. To maintain a comfortable temperature inside the building, heaters are installed. Their performance must be high enough to cover the heat loss.

Heat load is defined as the sum of the building's heat loss, equal to the required heating power. Having calculated how much and how the house loses heat, they find out the power of the heating system. The total is not enough. A room with 1 window loses less heat than a room with 2 windows and a balcony, so the indicator is calculated for each room separately.

When calculating, be sure to take into account the height of the ceiling. If it does not exceed 3 m, the calculation is performed according to the size of the area. If the height is from 3 to 4 m, the flow rate is calculated by volume.

Factors affecting TN

Many factors affect heat loss:

• Foundation - the insulated version retains heat in the house, the non-insulated one allows up to 20% to pass through.
• Wall - aerated concrete or wood concrete has a much lower throughput than a brick wall. Red clay bricks retain heat better than silicate bricks. The thickness of the partition is also important: a wall made of 65 cm thick brick and 25 cm thick foam concrete has the same level of heat loss.
• Thermal insulation - thermal insulation significantly changes the picture. External insulation with polyurethane foam - a sheet of 25 mm thick - is equal in efficiency to the second brick wall 65 cm thick. Finishing with a cork inside - a sheet of 70 mm - replaces 25 cm of foam concrete. It is not in vain that experts say that effective heating begins with proper insulation.
• Roof - pitched structure and insulated attic reduce losses. A flat roof made of reinforced concrete slabs allows up to 15% of heat to pass through.
• Glazing area - the thermal conductivity of glass is very high. No matter how airtight the frames are, heat escapes through the glass. The more windows and the larger their area, the higher the thermal load on the building.
• Ventilation - the level of heat loss depends on the performance of the device and the frequency of use. The recuperation system makes it possible to somewhat reduce losses.
• The difference between the temperature outside and inside the house - the greater it is, the higher the load.
• Heat distribution inside the building - affects the performance for each room. The rooms inside the building cool down less: when calculating a comfortable temperature here, they consider the value of +20 C. The end rooms cool down faster - the normal temperature here will be +22 C.In the kitchen, it is enough to heat the air up to +18 C, since there are many other heat sources here: stove, oven, refrigerator.

When calculating the thermal load of an apartment building, the material, thickness and insulation of partitions and ceilings are taken into account.

Object characteristics for calculation

Heat load for heating and heat loss at home are not the same thing. A technical building does not need to be heated as intensively as living quarters. Before proceeding with the calculations, the following is established:

• The purpose of the object is a residential building, apartment, school, gym, shop. Heating requirements are different.
• Features of architecture are the size of window and balcony openings, roof arrangement, the presence of attics and basements, the number of storeys of the building, etc.
• Temperature standards - they are different for living rooms and an office.
• Purpose of the premises - this parameter is important for production facilities, since each workshop or even a site requires a different temperature regime.
• Construction of external fences - external walls and roofs.
• Maintenance level - hot water supply reduces heat loss, intensive ventilation increases.
• The number of people who are constantly in the house - for example, affects the indicators of temperature and humidity.
• The number of points of intake of the coolant - the more there are, the greater the heat loss.
• Other features - for example, the presence of a pool, sauna, greenhouse or the number of hours when people are in the building.

When calculating heat loss in a store or in a catering center, the amount of equipment that generates heat is taken into account - showcases, refrigerators, kitchen appliances.

Types of heat loads

Heat loads are of a different nature. There is some constant level of heat loss associated with wall thickness, roof structure. There are temporary ones - with a sharp drop in temperature, with intensive ventilation. The calculation of the entire heat load takes this into account as well.

Seasonal loads

This is the name of the heat loss associated with the weather. This includes:

• the difference between the temperature outside and inside the room;
• wind speed and direction;
• the amount of solar radiation - with high insolation of the building and a large number of sunny days, even in winter, the house cools less;
• air humidity.

Seasonal load is distinguished by a variable annual schedule and a constant daily schedule. Seasonal heat demand is heating, ventilation and air conditioning. The first 2 species are referred to the winter ones.

The formulas use not short-term sharp changes in temperature and humidity - maximum, but averaged: the values ​​observed over the 5 coldest days of the 5 coldest winters in 50 years.

Permanent thermal

Hot water supply and technological devices are referred to year-round. The latter is important for industrial enterprises: digesters, industrial refrigerators, and steaming chambers emit a gigantic amount of heat.

In residential buildings, the hot water load becomes comparable to the heating load. This value changes little during the year, but fluctuates greatly depending on the time of day and day of the week. In summer, the consumption of FGP is reduced by 30%, since the water temperature in the cold water supply system is 12 degrees higher than in winter. During the cold season, hot water consumption increases, especially on weekends.

Dry heat

Comfort mode is determined by air temperature and humidity. These parameters are calculated based on the concepts of dry and latent heat. Dry is a value measured with a special dry bulb thermometer. It is affected by:

• glazing and doorways;
• sun and heat loads for winter heating;
• partitions between rooms with different temperatures, floors over empty spaces, ceilings under attics;
• cracks, crevices, gaps in walls and doors;
• air ducts outside heated areas and ventilation;
• equipment;
• people.

Floors on a concrete foundation, underground walls are not taken into account in the calculations.

Latent warmth

This parameter determines the humidity of the air. The source is:

• equipment - heats the air, reduces humidity;
• people are a source of moisture;
• air currents passing through cracks and crevices in the walls.

Usually ventilation does not affect the dryness of the room, but there are exceptions.

Methods for calculating the heat load on heating a building

To calculate the required heat load, data on the norms of temperature and humidity are taken from GOST and SNiP. There is also information about the heat transfer coefficients of different materials and designs. When calculating, the passport data of radiators, heating boiler, and other equipment must be taken into account.

Calculations include:

• heat flow of the radiator - maximum value;
• maximum consumption for 1 hour when the heating system is operating;
• heat costs for the season.

The approximate value gives the ratio of the calculated data to the area of ​​the house or rooms. However, this approach does not take into account the structural features of the building.

Calculation of heat loss using aggregated indicators

The method is used when the exact characteristics of the building cannot be determined. To calculate the heat load, use the formula.

Qfrom = α * qо * V * (tv-tn.r); Where:

• q ° - specific thermal index of the building according to the project or standard table. For buildings of different purposes - a residential apartment building, a garage, a laboratory - it is different.
• a is a correction factor that is different for different climatic zones.
• Vн - external volume of the building, m³.
• TVn and Tnro - temperature inside and outside the house.

The method allows you to calculate indicators for the entire building and for each zone or room. However, the formula does not include data on the thermal conductivity of the materials from which the house is built, and the indicators for wood, foam concrete and stone are very different.

Determination of heat transfer from heating and ventilation equipment

To get a more reliable result, use the calculation for walls and windows and additionally calculate the heat load of ventilation. Calculations are made in several stages:

• calculate the area of ​​the walls and glazing;
• calculate the resistance to heat transfer using data from the directory;
• the coefficient is calculated by the type of insulation - the data is also in the building reference book, it can be specified in the product passport;
• calculate the level of heat loss through the windows;
• the calculated values ​​are multiplied by the sum of the temperatures (inside and outside the building) and the total heat consumption is obtained.

The calculation of the thermal ventilation load is performed according to the formula Qv = c * m * (Tv-Tn)where:

• Qv - heat consumption by ventilation;
• from - heat capacity of air;
• m - air mass: on average, for normal ventilation, an air volume equal to three times the quadrature of the room is required; the mass is obtained by multiplying the value by the density of the air;
• Tv-Tn - the difference between outside and inside temperature.

The overall indicator is obtained by summing the calculated heat loss of the building and the loss through ventilation.

Calculation of values ​​taking into account various elements of the building envelope

If you use theoretical data for calculations - indicators for heat loss of each material - the result is still not entirely accurate. In calculations, it is impossible to take into account the number and size of cracks and gaps, the work of lighting, and so on.

The most accurate result is provided by a thermal imaging survey of the building. The procedure is performed in the dark, with the lights off.It is recommended to remove carpets and furniture for a while so as not to distort the readings.

The survey is performed in 3 stages:

• using a thermal imager, they study the room from the inside, carefully examine the corners and joints;
• measure losses from the outside - this is how all the features of materials and architecture are taken into account;
• the device data is transferred to a computer, the result is calculated.

Based on the results of the survey, recommendations are made: for insulation, reconstruction, the choice of heating devices.

Modern boilers are equipped with power regulators. These are devices that maintain performance at a set level, but prevent surges and dips during operation. There are limits on the use of energy resources: if the set value is exceeded, the payment for gas or electricity increases. PTH limits the energy consumption of the fuel.