Preliminary calculation of thermal loads example. How is the calculation of the heat load for heating

On the initial stage arrangement of the heat supply system of any of the real estate objects, the design of the heating structure and the corresponding calculations are carried out. It is imperative to perform a heat load calculation to find out the amount of fuel and heat consumption required to heat the building. These data are required to decide on the purchase of modern heating equipment.

Thermal loads of heat supply systems

The concept of heat load determines the amount of heat that is given off by heating devices installed in a residential building or at an object for other purposes. Before installing the equipment, this calculation is carried out in order to avoid unnecessary financial expenses and other problems that may arise during operation heating system.

Knowing the main operating parameters of the heat supply design, it is possible to organize the efficient functioning of heating devices. The calculation contributes to the implementation of the tasks facing the heating system, and the compliance of its elements with the norms and requirements prescribed in SNiP.

When the heat load for heating is calculated, even the slightest mistake can lead to big problems, because based on the data obtained, the local housing and communal services department approves limits and other consumption parameters that will become the basis for determining the cost of services.

The total amount of heat load on a modern heating system includes several basic parameters:

• load on the heat supply structure;
• load on the floor heating system, if it is planned to be installed in the house;
• load on the natural and/or forced ventilation system;
• load on the hot water supply system;
• load associated with various technological needs.

Characteristics of the object for calculating thermal loads

Correctly calculated heat load on heating can be determined, provided that absolutely everything, even the slightest nuances, will be taken into account in the calculation process.

The list of details and parameters is quite extensive:

• purpose and type of property. For the calculation, it is important to know which building will be heated - a residential or non-residential building, an apartment (read also: ""). The type of building depends on the load rate determined by the companies supplying heat, and, accordingly, the cost of heat supply;
• architectural features. The dimensions of such external fences as walls, roofing, flooring and the dimensions of window, door and balcony openings are taken into account. The number of storeys of the building, as well as the presence of basements, attics and their inherent characteristics are considered important;
• norm temperature regime for every room in the house. The temperature is implied for a comfortable stay of people in a living room or area of ​​\u200b\u200bthe administrative building (read: "");
• features of the design of external fences, including the thickness and type of building materials, the presence of a heat-insulating layer and the products used for this;
• purpose of premises. This characteristic is especially important for industrial buildings, in which for each workshop or section it is necessary to create certain conditions regarding the provision of temperature conditions;
• availability of special premises and their features. This applies, for example, to pools, greenhouses, baths, etc.;
• degree of maintenance. Presence/absence of hot water supply, centralized heating, air conditioning system, etc.;
• number of points for the intake of heated coolant. The more of them, the greater the thermal load exerted on the entire heating structure;
• the number of people in the building or living in the house. From given value directly dependent on humidity and temperature, which are taken into account in the formula for calculating the heat load;
• other features of the object. If this is an industrial building, then they can be the number of working days during the calendar year, the number of workers per shift. For a private house, they take into account how many people live in it, how many rooms, bathrooms, etc.

Calculation of heat loads

The heat load of the building is calculated in relation to heating at the stage when a real estate object of any purpose is being designed. This is required in order to prevent unnecessary spending and to choose the right heating equipment.

When making calculations, norms and standards are taken into account, as well as GOSTs, TCH, SNB.

In the course of determining the value of thermal power, a number of factors are taken into account:

The calculation of the thermal loads of the building with a certain degree of margin is necessary in order to prevent unnecessary financial costs in the future.

The need for such actions is most important when arranging heat supply country cottage. In such a property, installation additional equipment and other elements of the heating structure will be incredibly expensive.

Features of the calculation of thermal loads

The calculated values ​​of the temperature and humidity of the air in the premises and the heat transfer coefficients can be found in special literature or from technical documentation applied by manufacturers to their products, including heating units.

The standard method for calculating the heat load of a building to ensure its efficient heating includes the consistent determination of the maximum heat flow from heating devices (heating radiators), the maximum heat energy consumption per hour (read: ""). It is also required to know the total consumption of heat power during a certain period of time, for example, during the heating season.

The calculation of thermal loads, which takes into account the surface area of ​​the devices involved in heat exchange, is used for various real estate objects. This calculation option allows you to most correctly calculate the parameters of the system, which will provide efficient heating, as well as to conduct an energy survey of houses and buildings. This is an ideal way to determine the parameters of the on-duty heat supply of an industrial facility, which implies a decrease in temperature during non-working hours.

Methods for calculating thermal loads

To date, the calculation of thermal loads is carried out using several main methods, including:

• calculation of heat losses using aggregated indicators;
• determination of heat transfer of heating and ventilation equipment installed in the building;
• calculation of values ​​taking into account various elements of enclosing structures, as well as additional losses associated with air heating.

Enlarged heat load calculation

An enlarged calculation of the thermal load of the building is used in cases where there is not enough information about the designed object or the required data do not correspond to the actual characteristics.

To carry out such heating calculations, a simple formula is used:

Qmax from.=αxVxq0x(tv-tn.r.) x10-6, where:

• α is a correction factor that takes into account the climatic features of a particular region where the building is being built (it is used when the design temperature differs from 30 degrees below zero);
• q0 - specific characteristic of heat supply, which is chosen based on the temperature of the coldest week during the year (the so-called "five days"). See also: "How is the specific heating characteristic of a building calculated - theory and practice";
• V is the outer volume of the building.

Based on the above data, an enlarged calculation of the heat load is performed.

Types of thermal loads for calculations

When making calculations and choosing equipment, different thermal loads are taken into account:

1. Seasonal loads with the following features:

   They are characterized by changes depending on the ambient temperature in the street;
   - the presence of differences in the amount of heat energy consumption in accordance with the climatic features of the region where the house is located;
   - change in the load on the heating system depending on the time of day. Since external fences have heat resistance, this parameter is considered insignificant;
   - heat consumption of the ventilation system depending on the time of day.

2. Permanent thermal loads. In most objects of the heat supply and hot water supply system, they are used throughout the year. For example, in the warm season, the cost of thermal energy in comparison with winter period are reduced somewhere by 30-35%.
3. dry heat. Represents thermal radiation and convection heat exchange due to other similar devices. This parameter is determined using the dry bulb temperature. It depends on many factors, including windows and doors, ventilation systems, various equipment, air exchange due to the presence of cracks in walls and ceilings. Also take into account the number of people present in the room.
4. Latent heat. It is formed as a result of the process of evaporation and condensation. The temperature is determined using a wet bulb thermometer. In any intended room, the level of humidity is affected by:

   The number of people who are simultaneously in the room;
   - availability of technological or other equipment;
   - flows of air masses penetrating through cracks and cracks in the building envelope.

Thermal Load Controllers

The set of modern boilers for industrial and household purpose includes RTN (thermal load regulators). These devices (see photo) are designed to maintain the power of the heating unit at a certain level and do not allow jumps and dips during their operation.

RTH allow you to save on heating bills, since in most cases there are certain limits and they cannot be exceeded. This is especially true for industrial enterprises. The fact is that for exceeding the limit of thermal loads, penalties should be imposed.

It is quite difficult to independently make a project and calculate the load on systems that provide heating, ventilation and air conditioning in a building, therefore this stage works are usually trusted by specialists. True, if you wish, you can perform the calculations yourself.

Gav - average consumption hot water.

Comprehensive heat load calculation

In addition to the theoretical solution of issues related to thermal loads, a number of practical activities are carried out during the design. Comprehensive thermal surveys include thermography of all building structures, including ceilings, walls, doors, windows. Thanks to this work, it is possible to identify and fix various factors that affect the heat loss of a house or industrial building.

Thermal imaging diagnostics clearly shows what the real temperature difference will be when a certain amount of heat passes through one “square” of the area of ​​the enclosing structures. Thermography also helps to determine

Thanks to thermal surveys, the most reliable data regarding heat loads and heat losses for a particular building over a certain period of time is obtained. Practical activities allow you to clearly demonstrate what theoretical calculations cannot show - problem areas future building.

From the foregoing, we can conclude that the calculations of heat loads for hot water supply, heating and ventilation, similarly to the hydraulic calculation of the heating system, are very important and they should certainly be performed before the start of the arrangement of the heat supply system in your own home or at an object for other purposes. When the approach to work is done correctly, the trouble-free operation of the heating structure will be ensured, and at no extra cost.

Video example of calculating the heat load on the heating system of a building:

Ask any specialist how to properly organize the heating system in the building. It doesn't matter if it's residential or industrial. And the professional will answer that the main thing is to accurately make calculations and correctly carry out the design. We are talking, in particular, about the calculation of the heat load on heating. The volume of consumption of thermal energy, and hence fuel, depends on this indicator. I.e economic indicators stand next to the technical specifications.

Performing accurate calculations allows you to get not only full list the documentation necessary for the installation work, but also to select the necessary equipment, additional components and materials.

Thermal loads - definition and characteristics

What is usually meant by the term "heat load on heating"? This is the amount of heat that all heating devices installed in the building give off. To avoid unnecessary expenses for the production of work, as well as the purchase of unnecessary devices and materials, a preliminary calculation is necessary. With it, you can adjust the rules for installing and distributing heat in all rooms, and this can be done economically and evenly.

But that's not all. Very often, experts carry out calculations, relying on accurate indicators. They relate to the size of the house and the nuances of construction, which takes into account the diversity of building elements and their compliance with the requirements of thermal insulation and other things. It is precisely the exact indicators that make it possible to correctly make calculations and, accordingly, obtain options for the distribution of thermal energy throughout the premises as close to the ideal as possible.

But often there are errors in the calculations, which leads to inefficient operation of the heating as a whole. Sometimes it is necessary to redo during operation not only the circuits, but also sections of the system, which leads to additional costs.

What parameters affect the calculation of the heat load in general? Here it is necessary to divide the load into several positions, which include:

• System central heating.
• Underfloor heating system, if one is installed in the house.
• Ventilation system - both forced and natural.
• Hot water supply of the building.
• Branches for additional household needs. For example, a sauna or a bath, a pool or a shower.

Main characteristics

Professionals do not lose sight of any trifle that can affect the correctness of the calculation. Hence the rather large list of characteristics of the heating system that should be taken into account. Here are just a few of them:

1. The purpose of the property or its type. It can be a residential building or an industrial building. Heat suppliers have standards that are distributed by type of building. They often become fundamental in carrying out calculations.
2. The architectural part of the building. This can include enclosing elements (walls, roofs, ceilings, floors), their overall dimensions, thickness. Be sure to take into account all kinds of openings - balconies, windows, doors, etc. It is very important to take into account the presence of basements and attics.
3. Temperature regime for each room separately. This is very important because the overall temperature requirements for a house do not give an accurate picture of heat distribution.
4. Appointment of premises. This mainly applies to production shops, which require stricter compliance with the temperature regime.
5. Availability of special premises. For example, in residential private houses it can be baths or saunas.
6. Degree technical equipment. The presence of a ventilation and air conditioning system, hot water supply, and the type of heating used are taken into account.
7. The number of points through which hot water is taken. And the more such points, the greater the heat load the heating system is exposed to.
8. The number of people on the site. Criteria such as indoor humidity and temperature depend on this indicator.
9. Additional indicators. In residential premises, one can distinguish the number of bathrooms, separate rooms, balconies. IN industrial buildings- the number of working shifts, the number of days in a year when the shop itself works in the technological chain.

What is included in the calculation of loads

Heating scheme

The calculation of thermal loads for heating is carried out at the design stage of the building. But at the same time, the norms and requirements of various standards must be taken into account.

For example, the heat loss of the enclosing elements of the building. Moreover, all rooms are taken into account separately. Further, this is the power that is needed to heat the coolant. We add here the amount of thermal energy required to heat the supply ventilation. Without this, the calculation will not be very accurate. We also add the energy that is spent on heating water for a bath or pool. Specialists must take into account the further development of the heating system. Suddenly, in a few years, you will decide to arrange a Turkish hammam in your own private house. Therefore, it is necessary to add a few percent to the loads - usually up to 10%.

Recommendation! It is necessary to calculate thermal loads with a "margin" for country houses. It is the reserve that will allow in the future to avoid additional financial costs, which are often determined by amounts of several zeros.

Features of calculating the heat load

Air parameters, or rather, its temperature, are taken from GOSTs and SNiPs. Here, the heat transfer coefficients are selected. By the way, the passport data of all types of equipment (boilers, heating radiators, etc.) are taken into account without fail.

What is usually included in a traditional heat load calculation?

• Firstly, maximum flow thermal energy coming from heating devices (radiators).
• Secondly, the maximum heat consumption for 1 hour of operation of the heating system.
• Thirdly, the total heat costs for a certain period of time. Usually the seasonal period is calculated.

If all these calculations are measured and compared with the heat transfer area of ​​the system as a whole, then a fairly accurate indicator of the efficiency of heating a house will be obtained. But you have to take into account small deviations. For example, reducing heat consumption at night. For industrial facilities Weekends and holidays must also be taken into account.

Methods for determining thermal loads

Underfloor heating design

Currently, experts use three main methods for calculating thermal loads:

1. Calculation of the main heat losses, where only aggregated indicators are taken into account.
2. The indicators based on the parameters of the enclosing structures are taken into account. This is usually added to the losses for heating the internal air.
3. All systems included in heating networks are calculated. This is both heating and ventilation.

There is another option, which is called the enlarged calculation. It is usually used when there are no basic indicators and building parameters required for a standard calculation. That is, the actual characteristics may differ from the design.

To do this, experts use a very simple formula:

Q max from. \u003d α x V x q0 x (tv-tn.r.) x 10 -6

α is a correction factor depending on the region of construction (table value)
V - the volume of the building on the outer planes
q0 - characteristic of the heating system by specific index, usually determined by the coldest days of the year

Types of thermal loads

Thermal loads that are used in the calculations of the heating system and the selection of equipment have several varieties. For example, seasonal loads, for which the following features are inherent:

1. Changes in outdoor temperature throughout the heating season.
2. Meteorological features of the region where the house was built.
3. Jumps in the load on the heating system during the day. This indicator usually falls into the category of "minor loads", because the enclosing elements prevent a lot of pressure on the heating in general.
4. Everything related to the thermal energy associated with the ventilation system of the building.
5. Thermal loads that are determined throughout the year. For example, the consumption of hot water in the summer season is reduced by only 30-40% when compared with winter time of the year.
6. Dry heat. This feature is inherent in domestic heating systems, where a fairly large number of indicators are taken into account. For example, the number of window and door openings, the number of people living or permanently in the house, ventilation, air exchange through various cracks and gaps. A dry thermometer is used to determine this value.
7. Latent thermal energy. There is also such a term, which is defined by evaporation, condensation, and so on. A wet bulb thermometer is used to determine the indicator.

Thermal Load Controllers

Programmable controller, temperature range - 5-50 C

Modern heating units and devices are provided with a set of different regulators, with which you can change the thermal loads, in order to avoid dips and jumps in thermal energy in the system. Practice has shown that with the help of regulators it is possible not only to reduce the load, but also to bring the heating system to rational use fuel. And this is a purely economic side of the issue. This is especially true for industrial facilities, where quite large fines have to be paid for excessive fuel consumption.

If you are not sure about the correctness of your calculations, then use the services of specialists.

Let's look at a couple more formulas that relate to different systems. For example, ventilation and hot water systems. Here you need two formulas:

Qin. \u003d qin.V (tn.-tv.) - this applies to ventilation.
Here:
tn. and tv - air temperature outside and inside
qv. - specific indicator
V - external volume of the building

Qgvs. \u003d 0.042rv (tg.-tx.) Pgav - for hot water supply, where

tg.-tx - temperature of hot and cold water
r - water density
c - the ratio of the maximum load to the average, which is determined by GOSTs
P - the number of consumers
Gav - average hot water consumption

Complex calculation

In combination with settlement issues, studies of the thermotechnical order are necessarily carried out. For this, various devices are used that give accurate indicators for calculations. For example, for this, window and door openings, ceilings, walls, and so on are examined.

It is this examination that helps to determine the nuances and factors that can have a significant impact on heat loss. For example, thermal imaging diagnostics will accurately show the temperature difference when a certain amount of thermal energy passes through 1 square meter of the building envelope.

So practical measurements are indispensable when making calculations. This is especially true for bottlenecks in the building structure. In this regard, the theory will not be able to show exactly where and what is wrong. And practice will show where to apply different methods protection against heat loss. And the calculations themselves in this regard are becoming more accurate.

Conclusion on the topic

Estimated heat load is a very important indicator obtained in the process of designing a home heating system. If you approach the matter wisely and spend everything necessary calculations correctly, you can guarantee that the heating system will work perfectly. And at the same time, it will be possible to save on overheating and other costs that can simply be avoided.

The topic of this article is thermal load. We will find out what this parameter is, what it depends on and how it can be calculated. In addition, the article will provide a number of reference values ​​\u200b\u200bof thermal resistance different materials that may be needed for the calculation.

What it is

The term is essentially intuitive. The heat load is the amount of heat energy that is necessary to maintain a comfortable temperature in a building, apartment or separate room.

The maximum hourly heating load is thus the amount of heat that may be required to maintain normalized parameters for an hour under the most unfavorable conditions.

Factors

So, what affects the heat demand of a building?

• Wall material and thickness. It is clear that a wall of 1 brick (25 centimeters) and a wall of aerated concrete under a 15-centimeter foam coat will allow VERY different amounts of thermal energy to pass through.
• Material and structure of the roof. Flat roof from reinforced concrete slabs and an insulated attic will also differ quite noticeably in terms of heat loss.
• Ventilation is another important factor. Its performance, the presence or absence of a heat recovery system affects how much heat is lost to the exhaust air.
• Glazing area. Significantly more heat is lost through windows and glass facades than through solid walls.

However: triple-glazed windows and glass with energy-saving spraying reduce the difference by several times.

• The level of insolation in your area, the degree of absorption of solar heat by the external coating and the orientation of the planes of the building relative to the cardinal points. Edge cases- a house that is shaded by other buildings all day long and a house oriented with a black wall and a black sloping roof with maximum area South.

• temperature delta between indoor and outdoor determines the heat flow through the building envelope at a constant resistance to heat transfer. At +5 and -30 on the street, the house will lose a different amount of heat. It will, of course, reduce the need for thermal energy and lower the temperature inside the building.
• Finally, a project often has to include prospects for further construction. Say, if the current heat load is 15 kilowatts, but in the near future it is planned to attach an insulated veranda to the house, it is logical to purchase it with a margin of thermal power.

Distribution

In the case of water heating, the peak heat output of the heat source must be equal to the sum of the heat output of all heating appliances in the house. Of course, wiring should not become a bottleneck either.

The distribution of heating devices in rooms is determined by several factors:

1. The area of ​​​​the room and the height of its ceiling;
2. Location inside the building. Corner and end rooms lose more heat than those located in the middle of the house.
3. Distance from heat source. In individual construction, this parameter means the distance from the boiler, in the central heating system apartment building- by the fact that the battery is connected to the supply or return riser and by the floor you live on.

Clarification: in houses with a lower bottling, the risers are connected in pairs. On the supply side, the temperature decreases as you rise from the first floor to the last, on the opposite, respectively, vice versa.

It is also not difficult to guess how the temperatures will be distributed in the case of top bottling.

1. Desired room temperature. In addition to filtering heat through external walls, inside the building with an uneven distribution of temperatures, the migration of thermal energy through partitions will also be noticeable.

1. For living rooms in the middle of the building - 20 degrees;
2. For living rooms in the corner or end of the house - 22 degrees. A higher temperature, among other things, prevents the walls from freezing.
3. For the kitchen - 18 degrees. It usually contains a large number of own heat sources - from the refrigerator to the electric stove.
4. For a bathroom and a combined bathroom, the norm is 25C.

In the case of air heating, the heat flow entering a separate room is determined throughput air sleeve. Usually, simplest method adjustments - manual adjustment of the positions of adjustable ventilation grilles with temperature control by thermometer.

Finally, if we are talking about a heating system with distributed heat sources (electric or gas convectors, electric underfloor heating, infrared heaters and air conditioners) the required temperature regime is simply set on the thermostat. All that is required of you is to ensure that the peak thermal power of the devices is at the level of the peak heat loss of the room.

Calculation methods

Dear reader, do you have a good imagination? Let's imagine a house. Let it be a log house from a 20-centimeter beam with an attic and a wooden floor.

Mentally draw and specify the picture that has arisen in my head: the dimensions of the residential part of the building will be equal to 10 * 10 * 3 meters; in the walls we will cut 8 windows and 2 doors - to the front and inner courtyards. And now let's place our house ... let's say, in the city of Kondopoga in Karelia, where the temperature at the peak of frost can drop to -30 degrees.

Determining the heat load on heating can be done in several ways with varying complexity and reliability of the results. Let's use the three most simple ones.

Method 1

The current SNiP offer us the simplest way to calculate. One kilowatt of thermal power is taken per 10 m2. The resulting value is multiplied by the regional coefficient:

• For southern regions(Black Sea coast, Krasnodar region) the result is multiplied by 0.7 - 0.9.
• The moderately cold climate of Moscow and Leningrad regions will force you to use a coefficient of 1.2-1.3. It seems that our Kondopoga will fall into this climate group.
• Finally, for the Far East of the Far North, the coefficient ranges from 1.5 for Novosibirsk to 2.0 for Oymyakon.

Instructions for calculating using this method are incredibly simple:

1. The area of ​​the house is 10*10=100 m2.
2. The base value of the heat load is 100/10=10 kW.
3. We multiply by the regional coefficient 1.3 and get 13 kilowatts of thermal power needed to maintain comfort in the house.

However: if we use such a simple technique, it is better to make a margin of at least 20% to compensate for errors and extreme cold. Actually, it will be indicative to compare 13 kW with values ​​obtained by other methods.

Method 2

It is clear that with the first method of calculation, the errors will be huge:

• The height of the ceilings in different buildings varies greatly. Taking into account the fact that we have to heat not an area, but a certain volume, and with convection heating, warm air is collected under the ceiling - an important factor.
• Windows and doors let in more heat than walls.
• Finally, it would be a clear mistake to cut one size fits all city ​​apartment(and regardless of its location inside the building) and private house, which below, above and behind the walls does not warm apartments neighbors, and the street.

Well, let's correct the method.

• For the base value, we take 40 watts per cubic meter of room volume.
• For each door leading to the street, add to base value 200 watts. 100 per window.
• For corner and end apartments in apartment building we introduce a coefficient of 1.2 - 1.3 depending on the thickness and material of the walls. We also use it for the extreme floors in case the basement and attic are poorly insulated. For a private house, we multiply the value by 1.5.
• Finally, we apply the same regional coefficients as in the previous case.

How is our house in Karelia doing there?

1. The volume is 10*10*3=300 m2.
2. The base value of thermal power is 300*40=12000 watts.
3. Eight windows and two doors. 12000+(8*100)+(2*200)=13200 watts.
4. Private house. 13200*1.5=19800. We begin to vaguely suspect that when selecting the power of the boiler according to the first method, we would have to freeze.
5. But there is still a regional coefficient! 19800*1.3=25740. In total, we need a 28-kilowatt boiler. The difference with the first value obtained in a simple way is twofold.

However: in practice, such power will be required only on a few days of peak frost. It is often a smart decision to limit the power of the main heat source to a lower value and buy a backup heater (for example, an electric boiler or several gas convectors).

Method 3

Do not flatter yourself: the described method is also very imperfect. We very conditionally took into account the thermal resistance of the walls and ceiling; the temperature delta between the internal and external air is also taken into account only in the regional coefficient, that is, very approximately. The price of simplifying calculations is a big error.

Recall that in order to maintain a constant temperature inside the building, we need to provide an amount of thermal energy equal to all losses through the building envelope and ventilation. Alas, here we will have to somewhat simplify our calculations, sacrificing the reliability of the data. Otherwise, the resulting formulas will have to take into account too many factors that are difficult to measure and systematize.

The simplified formula looks like this: Q=DT/R, ​​where Q is the amount of heat lost by 1 m2 of the building envelope; DT is the temperature delta between indoor and outdoor temperatures, and R is the resistance to heat transfer.

Note: we're talking about heat loss through walls, floors, and ceilings. On average, another 40% of heat is lost through ventilation. For the sake of simplifying the calculations, we will calculate the heat loss through the building envelope, and then simply multiply them by 1.4.

Temperature delta is easy to measure, but where do you get data on thermal resistance?

Alas - only from directories. Here is a table for some popular solutions.

• A wall of three bricks (79 centimeters) has a heat transfer resistance of 0.592 m2 * C / W.
• A wall of 2.5 bricks - 0.502.
• Wall in two bricks - 0.405.
• Brick wall (25 centimeters) - 0.187.
• Log cabin with a log diameter of 25 centimeters - 0.550.
• The same, but from logs with a diameter of 20 cm - 0.440.
• A log house from a 20-centimeter beam - 0.806.
• A log house made of timber 10 cm thick - 0.353.
• Frame wall 20 centimeters thick with insulation mineral wool — 0,703.
• A wall of foam or aerated concrete with a thickness of 20 centimeters - 0.476.
• The same, but with a thickness increased to 30 cm - 0.709.
• Plaster 3 cm thick - 0.035.
• Ceiling or attic floor — 1,43.
• Wooden floor - 1.85.
• Double door made of wood - 0.21.

Now let's get back to our house. What options do we have?

• The temperature delta at the peak of frost will be equal to 50 degrees (+20 inside and -30 outside).
• Heat loss through a square meter of floor will be 50 / 1.85 (heat transfer resistance of a wooden floor) \u003d 27.03 watts. Through the entire floor - 27.03 * 100 \u003d 2703 watts.
• Let's calculate the heat loss through the ceiling: (50/1.43)*100=3497 watts.
• The area of ​​the walls is (10*3)*4=120 m2. Since our walls are made of a 20 cm beam, the R parameter is 0.806. The heat loss through the walls is (50/0.806)*120=7444 watts.
• Now let's add the obtained values: 2703+3497+7444=13644. This is how much our house will lose through the ceiling, floor and walls.

Note: in order not to calculate the shares square meters, we neglected the difference in the thermal conductivity of walls and windows with doors.

• Then add 40% ventilation losses. 13644*1.4=19101. According to this calculation, a 20-kilowatt boiler should be enough for us.

Conclusions and problem solving

As you can see, the available methods for calculating the heat load with your own hands give very significant errors. Fortunately, excess boiler power will not hurt:

• Gas boilers at reduced power operate with virtually no drop in efficiency, and condensing boilers even reach the most economical mode at partial load.
• The same applies to solar boilers.
• Electric heating equipment of any type always has an efficiency of 100 percent (of course, this does not apply to heat pumps). Remember physics: all the power not spent on making mechanical work(that is, the movement of mass against the vector of gravity) is ultimately spent on heating.

The only type of boilers for which operation at less than nominal power is contraindicated is solid fuel. Power adjustment in them is carried out in a rather primitive way - by limiting the flow of air into the furnace.

What is the result?

1. With a lack of oxygen, the fuel does not burn completely. More ash and soot are formed, which pollute the boiler, chimney and atmosphere.
2. The consequence of incomplete combustion is a drop in boiler efficiency. It is logical: after all, often the fuel leaves the boiler before it burns out.

However, even here there is a simple and elegant way out - the inclusion of a heat accumulator in the heating circuit. A heat-insulated tank with a capacity of up to 3000 liters is connected between the supply and return pipelines, opening them; in this case, a small circuit is formed (between the boiler and the buffer tank) and a large one (between the tank and heaters).

How does such a scheme work?

• After ignition, the boiler operates at nominal power. At the same time, due to natural or forced circulation, its heat exchanger gives off heat to the buffer tank. After the fuel has burned out, the circulation in the small circuit stops.
• The next few hours, the coolant moves along a large circuit. The buffer tank gradually releases the accumulated heat to radiators or water heated floors.

Conclusion

As usual, some additional information For more information on how the heat load can be calculated, see the video at the end of the article. Warm winters!

In district heating systems (DH) heat networks supply heat to various heat consumers. Despite the significant diversity of the heat load, it can be divided into two groups according to the nature of the flow in time: 1) seasonal; 2) all year round.

Changes in seasonal load depend mainly on climatic conditions: outdoor temperature, wind direction and speed, solar radiation, air humidity, etc. The main role is played outdoor temperature. The seasonal load has a relatively constant daily pattern and a variable annual load pattern. Seasonal heat load includes heating, ventilation, air conditioning. None of these types of load has a year-round character. Heating and ventilation are winter heat loads. For air conditioning in summer period artificial cold is required. If this artificial cold is produced by the absorption or ejection method, then the CHPP receives an additional summer heat load, which contributes to an increase in the efficiency of heating.

The year-round load includes process load and hot water supply. The only exceptions are certain industries, mainly related to the processing of agricultural raw materials (for example, sugar), whose work is usually seasonal.

The technological load schedule depends on the profile of industrial enterprises and their mode of operation, and the hot water supply load schedule depends on the improvement of residential and public buildings, the composition of the population and its working day, as well as on the operating mode of public utilities - baths, laundries. These loads have a variable daily schedule. Annual graphs of technological load and load of hot water supply also depend to a certain extent on the season. As a rule, summer loads are lower than winter ones due to the higher temperature of the processed raw materials and tap water, as well as due to lower heat losses of heat pipelines and industrial pipelines.

One of the primary tasks in the design and development of the mode of operation of district heating systems is to determine the values ​​and nature of heat loads.

In the event that when designing district heating installations there is no data on the estimated heat consumption based on the projects of heat-consuming installations of subscribers, the calculation of the heat load is carried out on the basis of aggregated indicators. During operation, the values ​​of the calculated thermal loads are adjusted according to the actual costs. Over time, this makes it possible to establish a proven thermal characteristic for each consumer.

The main task of heating is to maintain the internal temperature of the premises at a given level. To do this, it is necessary to maintain a balance between the heat losses of the building and the heat gain. The condition of thermal equilibrium of a building can be expressed as an equality

where Q- total heat loss of the building; Q T- heat loss by heat transfer through external enclosures; QH- heat loss by infiltration due to cold air entering the room through leaks in the external enclosures; Qo- supply of heat to the building through the heating system; Q TB - internal heat dissipation.

The heat loss of the building mainly depends on the first term Q r Therefore, for the convenience of calculation, the heat losses of the building can be represented as follows:

(5)

where μ= Q And /QT- infiltration coefficient, which is the ratio of heat loss by infiltration to heat loss by heat transfer through external fences.

Source of internal heat QTV, in residential buildings are usually people, cooking appliances (gas, electric and other stoves), lighting fixtures. These heat releases are largely random in nature and cannot be controlled in any way in time.

In addition, heat dissipation is not distributed evenly throughout the building.

To ensure a normal temperature regime in residential areas in all heated premises, the hydraulic and temperature regimes of the heating network are usually set according to the most unfavorable conditions, i.e. according to the mode of space heating with zero heat emissions (Q TB = 0).

To prevent a significant increase in the internal temperature in rooms where internal heat generation is significant, it is necessary to periodically turn off some of the heaters or reduce the flow of coolant through them.

A qualitative solution to this problem is possible only with individual automation, i.e. when installing autoregulators directly on heating devices and ventilation heaters.

The source of internal heat release in industrial buildings is various types of thermal and power plants and mechanisms (furnaces, dryers, engines, etc.). Internal heat dissipation industrial enterprises quite stable and often represent a significant proportion of the calculated heating load Therefore, they should be taken into account when developing the mode of heat supply for industrial areas.

Heat loss by heat transfer through external enclosures, J/s or kcal/h, can be determined by calculation using the formula

(6)

where F- surface area of ​​individual external fences, m; to- heat transfer coefficient of external fences, W / (m 2 K) or kcal / (m 2 h ° С); Δt - air temperature difference from internal and outer sides building envelopes, °С.

For a building with an external dimension V, m, perimeter in plan R, m, area in plan S, m, and height L m, equation (6) is easily reduced to the formula proposed by prof. N.S. Ermolaev.

Whether it is an industrial building or a residential building, you need to make competent calculations and draw up a diagram of the heating system circuit. At this stage, experts recommend paying special attention to the calculation of the possible heat load on the heating circuit, as well as the amount of fuel consumed and heat generated.

Thermal load: what is it?

This term refers to the amount of heat given off. The preliminary calculation of the heat load made it possible to avoid unnecessary costs for the purchase of components of the heating system and for their installation. Also, this calculation will help to correctly distribute the amount of heat generated economically and evenly throughout the building.

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

The 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 sections of an already working structure, which inevitably leads to unplanned expenses. Yes, and housing and communal organizations calculate the cost of services based on data on heat load.

Main Factors

An ideally calculated and designed heating system must maintain the set temperature in the room and compensate for the resulting heat losses. When calculating the indicator of the heat load on the heating system in the building, you need to take into account:

Purpose of the building: residential or industrial.

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

Housing dimensions. The larger it is, the more powerful the heating system should be. Area must be taken into account window openings, doors, exterior walls and the volume of each interior space.

The presence of rooms for special purposes (bath, sauna, etc.).

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

For a single room. For example, in rooms intended for storage, it is not necessary to maintain a comfortable temperature for a person.

Number of points with hot water supply. 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 terms. 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, technological chain production process etc.

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 be spent on compensation. While at -40 ° C outside the window it will require significant expenses.

Features of existing methods

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 regarding a specific heating radiator, boiler, etc. And also traditionally:

The heat consumption, taken to the maximum for one hour of operation of the heating system,

The maximum heat flow from one radiator,

Total heat costs in a certain period (most often - a season); if you need an hourly calculation of the load on 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 index is quite accurate. Some deviations happen. For example, for industrial buildings, it will be necessary to take into account the reduction in heat energy consumption on weekends and holidays, and in residential buildings - at night.

Methods for calculating heating systems have several degrees of accuracy. To reduce the error to a minimum, 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.

Basic calculation methods

To date, the calculation of the heat load on the heating of a building can be carried out in one of the following ways.

Three main

1. Aggregated indicators are taken for calculation.
2. The indicators of the structural elements of the building are taken as the base. Here, the calculation of the internal volume of air going to warm up will also be important.
3. All objects included in the heating system are calculated and summarized.

One exemplary

There is also a fourth option. It has a fairly large error, because the indicators are taken very average, or they are not enough. Here is the formula - Q from \u003d q 0 * a * V H * (t EH - t NPO), 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 ready-made tables),
• V H is the volume calculated from the outer planes.

Example of a simple calculation

For a building with standard parameters (ceiling heights, room sizes and good thermal insulation characteristics) you can apply a simple ratio of parameters, corrected by a factor depending on the region.

Suppose that a residential building is located in the Arkhangelsk region, and its area is 170 square meters. m. The heat load will be equal to 17 * 1.6 \u003d 27.2 kW / h.

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

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

The heat transfer of the described radiators is calculated for one 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 two-row radiator 1100 mm wide and 200 mm high will be 1010 W, and a steel panel radiator 500 mm wide and 220 mm high will be 1644 W.

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

Ceiling height (standard - 2.7 m),

Thermal power (per sq. m - 100 W),

One outer wall.

These calculations show that for every 10 sq. m requires 1,000 W of thermal power. This result is divided by the heat output of one section. The answer is required amount radiator sections.

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

Average calculation and exact

Given the factors described, the average calculation is carried out according to the following scheme. If for 1 sq. m requires 100 W of heat flow, then a room of 20 square meters. m should receive 2,000 watts. The radiator (popular bimetallic or aluminum) of eight sections allocates about Divide 2,000 by 150, we get 13 sections. But this is a rather enlarged calculation of the thermal load.

The exact one looks a little intimidating. Actually, nothing complicated. Here is the formula:

Q t \u003d 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 (ordinary = 1.27, double = 1.0, triple = 0.85);
• q 2 - wall insulation (weak or absent = 1.27, 2-brick wall = 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 - outdoor temperature (the minimum value is taken: -35 o C = 1.5, -25 o C = 1.3, -20 o C = 1.1, -15 o C = 0.9, -10 o C = 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).

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

Approximate calculation

These are the conditions. Minimum temperature in the cold season - -20 o C. Room 25 sq. m with triple glazing, double-leaf windows, ceiling height of 3.0 m, two-brick walls and an unheated attic. The calculation will be as follows:

Q \u003d 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 16 sections need to be installed in a room with the specified parameters.

If calculation is required in gigacalories

In the absence of a heat energy meter on an open heating circuit, the calculation of the heat load for heating the building is calculated by the formula Q \u003d V * (T 1 - T 2) / 1000, where:

• V - the amount of water consumed by the heating system, calculated in tons or m 3,
• T 1 - a number showing the temperature of hot water, measured in o C, 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 remove temperature indicators in a practical way, they resort to an average indicator. It is in the range of 60-65 o C.
• T 2 - temperature of cold water. It is quite difficult to measure it in the system, so constant indicators have been developed that depend on the temperature regime on the street. For example, in one of the regions, in the cold season, this indicator is taken equal to 5, in summer - 15.
• 1,000 is the coefficient for obtaining the result immediately in gigacalories.

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

Q from \u003d α * q o * V * (t in - t n.r.) * (1 + K n.r.) * 0.000001, where

The calculation of the heat load turns out to be somewhat enlarged, but it is this formula that is given in the technical literature.

Increasingly, in order to increase the efficiency of the heating system, they resort to buildings.

These works are carried out at night. For a more accurate result, you must observe the temperature difference between the room and the street: it must be at least 15 o. Fluorescent and incandescent lamps are switched 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, the data are recorded carefully. The scheme is simple.

The first stage of work takes place indoors. The device is moved gradually from doors to windows, giving Special attention corners and other joints.

The second stage is the examination of the external walls of the building with a thermal imager. The joints are still carefully examined, especially the connection with the roof.

The third stage is data processing. First, the device does this, then the readings are transferred to a computer, where the corresponding programs complete the processing and give 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.