When designing a heating system, whether it is an industrial building or a residential building, it is necessary to conduct competent calculations and draw up a circuit of the heating system. Specialists recommend paying special attention at this stage to calculating the possible heat load on the heating circuit, as well as to the amount of fuel consumed and the heat generated.
Thermal load: what is it?
This term refers to the amount of heat given off by heating devices . A preliminary calculation of the heat load allows us to avoid unnecessary expenses for the purchase of components of the heating system and their installation. Also, this calculation will help to correctly distribute the amount of heat generated economically and evenly throughout the building.
These calculations contain many nuances. For example, the material from which the building is built, thermal insulation, the region, etc. Specialists try to take into account as many factors and characteristics as possible 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 areas of an already working structure, which inevitably leads to unplanned expenses. And housing and communal organizations are calculating the cost of services based on data on heat load.
Key factors
An ideally designed and designed heating system should maintain a given room temperature and compensate for the resulting heat loss. When calculating the rate of thermal load on the heating system in a building, you need to take into account:
- Purpose of the building: residential or industrial.
- Description of structural elements of the structure. These are windows, walls, doors, roof and ventilation system.
- The size of the home. The larger it is, the more powerful the heating system should be. Be sure to take into account the area of window openings, doors, exterior walls and the volume of each interior.
- Availability of special rooms (bath, sauna, etc.).
- Degree of equipment with technical devices. That is, the availability of hot water, ventilation systems, air conditioning and the type of heating system.
- Temperature conditions for a single room. For example, in rooms intended for storage, it is not necessary to maintain a temperature that is comfortable for a person.
- Number of hot water points. The more of them, the more the system is loaded.
- The area of glazed surfaces. Rooms with French windows lose a significant amount of heat.
- Additional terms. In residential buildings, this may 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.
- The climatic conditions of the region. When calculating heat losses, street temperatures are taken into account. If the differences are insignificant, then a small amount of energy will go to compensation. While at -40 ° C outside the window will require significant costs.
Features of existing techniques
The parameters included in the calculation of the heat load are in SNiPs and GOSTs. They also have special heat transfer coefficients. From the passports of the equipment included in the heating system, digital characteristics are taken that relate to a particular heating radiator, boiler, etc. And also traditionally:
- heat consumption taken to the maximum for one hour of operation of the heating system,
- maximum heat flux emanating from one radiator,
- total heat consumption in a certain period (most often - season); if you need hourly calculation of the load on the heating network, then the calculation must be carried out taking into account the temperature difference during the day.
The calculations made are compared with the heat transfer 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 thermal energy consumption on weekends and holidays, and in residential premises at night.
Methods for calculating heating systems have several degrees of accuracy. To minimize the error, it is necessary to use rather complex calculations. Less accurate schemes are used if the goal is not to optimize the costs of the heating system.
The main methods of calculation
Today, the calculation of the heat load for heating a building can be carried out in one of the following ways.
Three main
- For the calculation, aggregated indicators are taken.
- The base is taken indicators of structural elements of the building. Here, it will be important to calculate the loss of heat going to warm up the internal volume of air.
- All objects included in the heating system are calculated and summed.
One example
There is a fourth option. It has a sufficiently large error, because the indicators are taken very averaged, or they are not enough. This formula is Q from = q 0 * a * V H * (t - t ), where:
- q 0 - 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 finished tables),
- V H - volume calculated on the outer planes.
Simple calculation example
For a building with standard parameters (ceiling height, room size and good thermal insulation characteristics), you can apply a simple ratio of parameters adjusted for a coefficient that depends on the region.
Suppose that a residential building is located in the Arkhangelsk region, and its area is 170 square meters. m. The thermal load will be equal to 17 * 1.6 = 27.2 kW / h.
Such a determination of thermal loads does not take into account many important factors. For example, structural features of the structure, temperature, number of walls, the ratio of the area of walls to window openings, etc. Therefore, such calculations are not suitable for serious heating system projects.
Calculation of the heating radiator by area
It depends on the material from which they are made. Most often, bimetallic, aluminum, steel, and much less often cast-iron radiators are used today. Each of them has its own indicator of heat transfer (thermal power). Bimetallic radiators with a distance between the axles of 500 mm, on average, have 180 - 190 watts. Aluminum radiators have almost the same performance.
The heat transfer of the described radiators is calculated per section. Steel plate radiators are non-separable. Therefore, their heat transfer is determined based on the size of the entire device. For example, the thermal power of a double-row radiator with a width of 1,100 mm and a height of 200 mm 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 a heating radiator by area includes the following basic parameters:
- ceiling height (standard - 2.7 m),
- thermal power (per sq. m - 100 W),
- one external wall.
These calculations show that for every 10 square meters. m need 1,000 watts of thermal power. This result is divided by the thermal return 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 ones, reducing and increasing coefficients have been developed.
Averaged calculation and accurate
Considering the described factors, the average calculation is carried out according to the following scheme. If for 1 square. m requires 100 watts of heat flow, then a room of 20 square meters. m should receive 2,000 watts. A radiator (popular bimetallic or aluminum) of eight sections emits about 150 watts. Divide 2,000 by 150, we get 13 sections. But this is a fairly enlarged calculation of the heat load.
The exact one looks a bit intimidating. Nothing really complicated. Here is the formula:
Q t = 100 W / m 2 × S ( rooms ) m 2 × q 1 × q 2 × q 3 × q 4 × q 5 × q 6 × q 7 , where:
- q 1 - type of glazing (normal = 1.27, double = 1.0, triple = 0.85);
- q 2 - wall insulation (weak or absent = 1.27, wall lined with 2 bricks = 1.0, modern, high = 0.85);
- q 3 is 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 - outdoor temperature (the minimum value is taken: -35 = 1.5, -25 = 1.3, -20 = 1.1, -15 = 0.9, -10 = 0.7);
- q 5 - the 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 calculation room above the calculation 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.
Approximate calculation
The conditions are as follows. The minimum temperature in the cold season is -20 ° C. The room is 25 square meters. m with triple glazing, double-glazed windows, ceiling height of 3.0 m, two-brick walls and an 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, is divided by 150. As a result, it turns out that in the room with the specified parameters you need to install 16 sections.
If calculation in gigacalories is needed
In the absence of a heat energy meter on an open heating circuit, the calculation of the heat load for heating a building is calculated 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 - a number showing the temperature of hot water, measured in and for calculations the temperature corresponding to a certain pressure in the system is taken. This indicator has its own name - enthalpy. If it is not possible to take temperature indicators in a practical way, resort to an average indicator. It is in the range of 60-65 about C.
- T 2 - temperature of cold water. It is quite difficult to measure it in the system; therefore, constant indicators have been developed that depend on the temperature conditions on the street. For example, in one of the regions, in the cold season, this indicator is taken equal to 5, in the summer - 15.
- 1,000 - coefficient for obtaining the result immediately in gigacalories.
In the case of a closed circuit, the thermal load (gcal / hour) is calculated differently:
Q from = α * q * V * (t in - t . ) * (1 + K . ) * 0,000001, where
- α - coefficient designed to adjust climatic conditions. It is taken into account if the street temperature differs from -30 ° C;
- V is the volume of the building according to external measurements;
- q about - specific heating indicator of the structure at a given t . = -30 , measured in kcal / m 3 * ;
- t in - the estimated internal temperature in the building;
- t - design street temperature for designing a heating system;
- K nr - coefficient of infiltration. It is caused by the ratio of heat losses of the design building with infiltration and heat transfer through external structural elements at street temperature, which is set in the framework of the project.
The calculation of the heat load is somewhat enlarged, but it is this formula that is given in the technical literature.
Thermal Imaging Examination
Increasingly, to increase the efficiency of the heating system, resorting to thermal imaging surveys of the structure.
These works are carried out in the dark. For a more accurate result, you need to observe the temperature difference between the room and the street: it must be at least 15 °. Daylight and incandescent lamps turn off. It is advisable to remove carpets and furniture to the maximum, they knock down the device, giving some error.
The survey is carried out slowly, data are recorded carefully. The scheme is simple.
The first stage of work takes place indoors. The device is moved gradually from door to window, paying particular attention to corners and other joints.
The second stage is a thermal imaging examination of the external walls of the structure. Joints, especially the connection with the roof, are still being thoroughly examined.
The third stage is data processing. First, the instrument does this, then the readings are transferred to the computer, where the corresponding programs complete the processing and produce the result.
If the survey was conducted by a licensed organization, then it will issue a report with mandatory recommendations based on the results of the work. If the work was carried out personally, then you need to rely on your knowledge and, possibly, the help of the Internet.