Calculation of the power of the heating boiler. Heating system
The selection of a gas boiler of optimal power is possible only after calculations have been made. The technical documentation for boiler equipment indicates its thermal power - TMK. This parameter means the power that the boiler is able to transmit to external devices (heating, ventilation, DHW preparation), taking into account its efficiency. But this value does not in any way inform the user what area can be heated using a particular boiler model.
The problem is that any building, even insulated, gives off part of the heat to the outside air through structures such as walls, ceilings, floors, windows and doors. Therefore, without a thermal calculation of the building, it is difficult not to make a mistake in choosing the right boiler.
In this article:
What parameters need to be taken into account
Heat loss of a private house
When choosing boiler equipment for heating a house, it is necessary to consider:
- climatic conditions of the region (the calculation formula includes the value of the average temperature for the coldest week of the year);
- the set air temperature inside the heated premises;
- the need for organizing hot water supply;
- heat loss from forced ventilation (if any in the house);
- number of storeys of the building;
- ceiling height;
- construction and materials of floors;
- the thickness of the outer walls and the materials from which they were built;
- geometric dimensions of the outer walls;
- floor construction (layer thickness and materials from which they are built);
- dimensions, number of windows and doors and their type (glass thickness, number of chambers, etc.).
Heat loss at home
The amount of heat loss of a building is greatly influenced by:
- type of attic (insulated, non-insulated);
- the presence or absence of a basement.
To clearly show dependence of heat loss at home on materials used in its construction, we suggest considering a small comparative table.
The table shows that a wooden house loses less heat than a brick house, respectively, and the boiler in the first case will require less power than for a brick house.
In building codes, thermal conductivity indicators for all building materials are painted.
Something similar happens with windows..
Only they are characterized not by thermal conductivity, but, on the contrary, by the heat transfer resistance coefficient: the higher the figure, the less heat the window will release from the house (in another way, this indicator is called the R-factor).
As you can see, the more chambers in the window design, the higher its resistance to heat loss. An important role is also played by the gas mixture, which fills the chambers of double-glazed windows.
How to calculate the TMK of a gas boiler
First of all - the thermal calculation of the building itself
The heat output of a heating boiler can be calculated in two ways:
- complete;
- simplified.
The first method involves making calculations taking into account the thermal properties of all building materialsinvolved in the construction of the house and its decoration. It can be seen from the data in the above tables how important it is to complete the calculation.
But this work is not easy, in the absence of certain experience, it is difficult to cope with it.
This is usually done by designers in design organizations. Although with a strong desire, you can arm yourself with SNiPs and try to do everything yourself.
Thermal conductivity coefficient of building materials
Thermal conductivity coefficients of common building materials
To determine the amount of heat loss through the building envelope, it is necessary to calculate the thermal conductivity of the building materials of which they are composed.
The initial data for the calculation are:
- a(vn)- coefficient that determines the intensity of heat transfer from the air in the room to the ceiling and walls. This is a constant value of 8.7.
- a(nr)- another constant coefficient equal to 23. It characterizes the intensity of heat transfer from the walls and ceiling to the outside air.
- To- thermal conductivity of building materials that make up the ceiling and walls. Data is taken from building codes. For some materials, the thermal conductivity is given in the table of building materials (see above).
- D- the thickness of the layers of building materials.
After collecting all the initial data, you can begin to calculate the heat transfer coefficient using the formula:
Kt = 1/
Kt is calculated for the ceiling and walls separately.
The principle of calculating the Kt of the floor is the same, but there are some nuances here: the correct approach requires dividing the floor area into 4 zones, located from the outer walls to the center. To simplify the calculations, heat losses through the floor structure without heating can be taken equal to 10%.
Calculation of heat loss through windows and doors
The initial data for this part of the calculation are:
- kst- the heat transfer coefficient of a double-glazed window or glass (indicated by the manufacturer).
- F Art.- the area of the glazed surface of the window.
- Cr- heat transfer coefficient of the window frame (specified by the manufacturer).
- F p- the area of the window frame.
- R- the perimeter of the glazed surface of the window.
The heat transfer coefficient of windows (Ko) is calculated by the formula:
Kst. x F Art. + Кр х F р + Р/F, where F is the window area.
The same formula is used to calculate the heat transfer coefficient of doors.
In this case, instead of the values of glass and frames, the values of the materials from which the doors are made are substituted.
To simplify the calculations, you can use the following data:
To determine heat loss, the conditional coefficient is multiplied by the total area of \u200b\u200bthe house.
This method gives only an approximate result. It does not take into account the number of windows, the configuration of the house and its location. But for a preliminary assessment of heat loss, it is quite suitable.
Simplified Method
The power of the heating boiler is determined as the sum of the powers required to heat each heated room. That is, the calculations described in the previous sections are carried out for each room separately.
At the same time, designers are required to take into account the number of lamps, people in the room, and even the operation of household appliances.
Fortunately, in most cases it is possible to do without such complex and expensive thermal engineering calculations. Residential buildings are usually built taking into account the climatic conditions of a particular region, so you can choose the required amount of TMK according to a simplified scheme.
This calculation is based on the assumption that the specific power of the entire house is equal to the sum of the specific power of each room. In this case, when performing calculations, they operate with experimental values of the specific power of the house, depending on the region.
These tables are valid for well-insulated wooden and reinforced concrete houses with a standard ceiling height of 2.7 meters.
Boiler power per 10 sq. m is calculated by the formula:
- W \u003d S x W beats / 10, where
- W is the design power of the boiler
- S - the sum of the areas of the premises
- Wsp - specific power of the house (see table above)
Example
Typical house plan for 300 sq.m (for example)
For example, let's calculate the power of a gas boiler for a house located in the Moscow region. The total building area is 300 sq. m.
We take the value of specific power (according to the fourth table) equal to 1.5.
- W \u003d 300 x 1.5 / 10 \u003d 45 kW
For high ceilings
If the ceiling height differs from the standard values, in this case the power of the heating boiler is calculated by the formula:
- Mk \u003d TxKz, where
- Mk - boiler power
- T - estimated heat loss
- Kz - safety factor
Heat losses T are calculated by the formula:
- T \u003d VxRxKr / 860, where
- V is the volume of the room (in cubic meters)
- P - the difference between the external and internal temperatures
- Kp - dispersion coefficient
For buildings made of bricks, Kp is 2 - 2.9, for poorly insulated buildings - 3-4.
And the last thing: if you assume that the boiler will provide the house with hot water, increase the calculated power by 25%.
Despite the abundance of modern heating options for private homes, most consumers stop at a traditional and proven gas boiler over the years. They are durable and reliable, do not require frequent and complex maintenance, and the breadth of the model range allows you to choose the unit for any room.
The main characteristic of a gas boiler is its power, for the correct determination of which a large number of factors should be taken into account. The comfort of the climate in the house, the efficiency of the boiler, and its service life depend on the right choice of power.
Why is an accurate calculation of the boiler power necessary?
A competent approach should be based on clear measurements that will allow you to see a complete picture of the heat loss of a private house. Buying a unit with excess capacity will lead to unreasonably high gas consumption, and, consequently, to unnecessary expenses. At the same time, the lack of boiler power can cause it to fail quickly, because in order to heat the house, it will have to work at high speeds all the time.
The easiest way to calculate the power of a gas boiler, which has been used for quite a long time, is 1 kW for every 10 square meters of a dwelling, plus 15-20%. That is, from this simple formula it follows that for a private house with an area of 100 m², a boiler with a capacity of about 12 kW is required.
This calculation is very rough and is only suitable for houses with good thermal insulation and windows, low ceilings and in a fairly mild climate. Practice shows that not all private houses meet these criteria.
What data is needed to calculate the power of a gas boiler
For private houses built according to a standard project, with a ceiling height of about 3 meters, the calculation formula looks quite simple. In this case, it is necessary to take into account the building area (S) and the boiler specific power index (UMK), which varies depending on the climatic zone. He hesitates:
- From 0.7 to 0.9 kW in the southern regions of the country
- From 1 to 1.2 kW in the regions of the middle lane
- From 1.2 to 1.5 kW in the Moscow region
- 1.5 to 2 in the north of the country
Thus, the formula for calculating the power of a gas boiler for a typical private house will look like this:
M=S*UMK/10
80*2/10 = 16 kW
If the consumer, whose task, in addition to heating the home, will also be heating water, experts recommend adding another 20% to the figure obtained using the formula.
What other heat losses should be taken into account?
Even taking into account the climate zone cannot give a complete picture of the heat loss of a private house. Someone has double plastic windows installed, and someone else has not bothered to change the old wooden frames, someone, and someone has only one layer of brick between the street and the room.
According to averaged data, based on experts' calculations, the largest heat losses occur on non-insulated walls and amount to about 35%. A little less, 25% of the heat is lost due to a poorly insulated roof. Ideally, there should be a warm attic above the house. The bad one can take up to 15% of the heat generated by the boiler, like old wooden windows. We should also not forget about ventilation and open windows, which account for 10 to 15% of heat loss.
Thus, it turns out that the generally accepted formula is far from suitable for every residential building. For such cases, there are their own counting systems.
The concept of dissipation factor
The dissipation coefficient is one of the important indicators of heat exchange between the living space and the environment. Depending on how well, there are such indicators that are used in the most accurate calculation formula:
- 3.0 - 4.0 is the dissipation factor for structures in which there is no thermal insulation at all. Most often in such cases we are talking about makeshift houses made of corrugated iron or wood.
- A coefficient from 2.9 to 2.0 is typical for buildings with a low level of thermal insulation. This refers to houses with thin walls (for example, one brick) without insulation, with ordinary wooden frames and a simple roof.
- The average level of thermal insulation and a coefficient from 1.9 to 1.0 are assigned to houses with double plastic windows, insulation of external walls or double masonry, as well as with an insulated roof or attic.
- The lowest dispersion coefficient from 0.6 to 0.9 is typical for houses built using modern materials and technologies. In such houses, the walls, roof and floor are insulated, good windows are installed and the ventilation system is well thought out.
Table for calculating the cost of heating in a private house
The formula in which the value of the dissipation coefficient is used is one of the most accurate and allows you to calculate the heat loss of a particular building. It looks like this:
Qt \u003d V * Pt * k / 860
In the formula Qt – is the level of heat loss, V – is the volume of the room (the product of length, width and height), Pt – this is the temperature difference (to calculate it is necessary to subtract from the desired temperature in the room the minimum air temperature that can be in this latitude), k – is the scattering coefficient.
Let's substitute the numbers into our formula and try to find out the heat loss of a house with a volume of 300 m³ (10 m * 10 m * 3 m) with an average level of thermal insulation at a desired air temperature of + 20 ° C and a minimum winter temperature of - 20 ° C.
300*48*1,9/860 ≈31,81
Having this figure, we can find out what power the boiler needs for such a house. To do this, the obtained value of heat loss should be multiplied by a safety factor, which is usually from 1.15 to 1.2 (the same 15-20%). We get that:
31, 81* 1,2 = 38,172
Rounding the resulting number down, we find the desired number. To heat a house with the conditions we set, a boiler of 38 kW is required.
Such a formula will allow you to very accurately determine the power of the gas boiler required for a particular house. Also, to date, a wide variety of calculators and programs have been developed that allow you to take into account the data of each individual building.
Technical consultants of the Termomir company, who have been working with gas boiler equipment for more than a year, often hear the question - How to choose a gas boiler according to the area of \u200b\u200bthe house. Let's deal with this topic in more detail.
A heating gas boiler is a device that, by means of the combustion of fuel (natural or liquefied gas), heats the coolant.
The device (design) of a gas boiler: burner, heat exchanger, thermally insulated housing, hydraulic unit, as well as safety and control devices. Such gas-fired boilers require a chimney to be connected to remove combustion products. The chimney can be either a conventional vertical or coaxial (“pipe in pipe”) for boilers with a closed combustion chamber. Many modern boilers are equipped with built-in pumps for forced circulation of water.
The principle of operation of a gas boiler- the heat carrier, passing through the heat exchanger, heats up and then circulates through the heating system, giving off the received thermal energy through radiators, underfloor heating, heated towel rails, and also providing water heating in an indirect heating boiler (if it is connected to a gas-fired boiler).
Heat exchanger - a metal container in which the coolant (water or antifreeze) is heated - can be made of steel, cast iron, copper, etc. The reliability and durability of a gas boiler depends on the quality of the heat exchanger in the first place. Cast iron heat exchangers are resistant to corrosion and have a long service life, but are sensitive to sudden temperature changes and are quite heavy. Steel containers can suffer from rust, so their internal surfaces are protected with various anti-corrosion coatings that prolong the “life” of the device. Steel heat exchangers are the most common in the manufacture of boilers. Corrosion is not terrible for copper heat exchangers, and due to the high heat transfer coefficient, low weight and dimensions, such heat exchangers are often used in wall-mounted boilers, but of the minuses, it should be noted that they are more expensive than steel ones.
In addition to the heat exchanger, an important part of gas boilers is a burner, which can be of various types: atmospheric or fan, single-stage or two-stage, with smooth modulation, double.
To control the gas boiler, automation is used with various settings and functions (for example, a weather-compensated control system), as well as devices for programming operation and remote control of the boiler.
The main technical characteristics of gas heating boilers are: power, number of heating circuits, type of fuel, type of combustion chamber, burner type, installation method, pump and expansion tank, boiler control automation.
To determine required power gas heating boiler for a private country house or apartment, a simple formula is used - 1 kW of boiler power for heating 10 m 2 of a well-insulated room with a ceiling height of up to 3 m. If heating is required for a basement, glazed winter garden, rooms with non-standard ceilings, etc. the gas boiler output must be increased. It is also necessary to increase the power (about 20-50%) when providing a gas boiler and hot water supply (especially if water heating in the pool is necessary).
The peculiarity of calculating the power of gas boilers: the nominal gas pressure at which the boiler operates at 100% of the power declared by the manufacturer, for most boilers is from 13 to 20 mbar, and the actual pressure in gas networks in Russia can be 10 mbar, and sometimes even lower . Accordingly, a gas boiler often only works at 2/3 of its capacity, and this must be taken into account when calculating. In more detail with a table for calculating the power of a heating boiler, you can
Most gas boilers can switch from natural gas to LPG(ballooned propane). Many models switch to liquefied gas at the factory (check these characteristics of the model when purchasing), or nozzles (jets) are additionally supplied to the gas boiler to switch to bottled gas.
Pros and cons of gas boilers:
Boiler piping- These are devices for the full operation of the heating and water supply system. It includes: pumps, expansion tanks, filters (if necessary), manifolds, check and safety valves, air valves, valves, etc. You will also need to purchase radiators, connecting pipes and valves, thermostats, a boiler, etc. The issue of choosing a boiler is quite serious, so it is better to entrust the selection of equipment and its complete set to professionals.
What is the best boiler? The Russian market of gas boiler equipment has its own leaders in quality and reliability. The best manufacturers and brands of gas boilers are presented in the assortment:
"Premium" or "Lux"- the most reliable and durable, easy to manage, the kit is assembled as a "constructor", more expensive than the others. These manufacturers include German companies
In terms of power, the comfort of living in the house depends. This also affects the depreciation of boiler equipment, the duration of its operation and fuel consumption, that is, the monthly cost of operating the cottage.
Autonomous home heating is a complex system that requires detailed calculation. One of the important variables is heating boiler power. This article is about how to calculate it correctly, what parameters you should pay attention to and why do it at all - calculate the boiler power. Let's start with the "why" question.
If the capacity of the boiler exceeds the needs, then, of course, it will perform its function of heating the building and preparing hot water. But, firstly, the cost of boiler equipment depends on the power. Therefore, making a purchase without preliminary calculations, you will certainly spend more money in vain.
Secondly, excess power, which exceeds the needs of the building's heat loss, leads to an increased load on the entire hydraulic system. Excessive load leads to unbalanced operation of the system, failures in automation and, ultimately, to a rapid failure of equipment.
Partially, this problem can be overcome if the boiler is equipped with a multi-stage modulating burner, when the flame burning intensity is regulated depending on the requested power. Another option is to install a hydraulic switch in the system, perhaps in addition to a multi-stage burner.
But in this way the issue is only partially solved: if the difference between the required and generated power is significant, then the modulating burner will not work in a multi-stage mode. Therefore, the operation of the boiler will be pulsed, as in equipment with a single-stage burner.
Thirdly, the burner of a powerful boiler, heating the coolant, turns off too quickly, does not have time to completely burn out, but warms up. As a result, we get increased soot deposition in the chimney and on the heat exchanger (the need for frequent cleaning), as well as the formation of excessive condensate. And all the same possible failures in the heating system.
What parameters affect the choice of the boiler
In addition to the financial issue and the type of fuel available, the main parameter when choosing a heating boiler is its power. That is, how much heat does it generate, and is this heat enough for heating and hot water preparation, if hot water supply (hot water supply) is also assigned to this boiler.What affects the ability of heating equipment to heat a house?
Heat loss
The most important parameter that determines whether the house will have a comfortable temperature is heat loss building. No matter how powerful the boiler is and has a high efficiency, if the house is not, then do not expect comfort in it.Most of the heat escapes through the roof and the ventilation system, including chimneys: approximately 25-30% each. Through the outer walls and windows, 10-15% is lost, the junction of the foundation to the ground also takes about 15%, another 10-15% falls on the floor of the first floor and unheated. Therefore, the task of insulating a building is closely related to the choice of heating equipment: it is better to insulate - a boiler will be required for less power.
Simplified boiler power calculation scheme
In practice, a simplified scheme of heat engineering calculations based on the building area is often used. If the building has standard insulation of walls and other enclosing structures, that is, it has calculated heat loss, then it is assumed that 1 kW of power is required for heating every 10 m² of space.To correct calculations for different regional climatic conditions, the following coefficients are used:
- for central Russia - 1-1.5;
- for the northern regions - 1.5-2;
- for the southern regions - 0.7-0.9.
In case of severe abnormal frosts, when calculating, we add a power reserve of 10%, and if the boiler also heats hot water, then we add an additional 25%.
Let's count on specific examples
To make it easier to understand the methodology for calculating the required power of the boiler, consider a specific example. Let's say we have a brick house with walls 2 bricks thick, located in the Kaluga region.House area - 160 m². The height of the ceilings in the rooms is higher than the standard - 3500 mm. And the boiler, in addition to the heating system, is also supposed to be used for hot water supply.
So, let's start the calculations. Our house is with brick walls 500 mm thick (2 bricks). According to building codes, these walls have standard heat loss. We assume that other building envelopes are also made in accordance with standard requirements. We divide the area of \u200b\u200bthe house by ten (160/10 \u003d 16) and we get that a boiler with a capacity of 16 kW is required for heating. Now we use all the coefficients and corrections.
Since the Kaluga region is the middle zone of Russia, we will use a coefficient of 1. Our ceilings are higher than the standard ones, so we calculate the correction factor: 3500/2700 = 1.29. Rounding up to the first digit after the decimal point, we get 1.3. We apply the coefficients: 16 kW * 1 * 1.3 \u003d 20.8 kW. We round up to 21 kW.
Since the boiler will, in addition to heating, also heat hot water, let's add another 25%: 21 + 5.3 = 26.3 kW. For abnormal winter temperatures, we add another 10%: 26.3 + 2.1 = 28.4 kW. We round up and look at which model of boilers the power value most closely matches the calculated one.
To finally understand, consider another example.
Log house in the Pskov region. House area - 72 m², ceiling height - 2500 mm. The house is built from a thickness of at least 220 mm. The boiler is not supposed to be used to heat water.
If non-brick is used as the material for the walls, then we correlate the thermal conductivity of the existing structures with the same parameter of a brick wall 500 mm thick. The walls of our house correspond to the standard thermal conductivity of a brick wall of 2 bricks. A log house, given the thickness of the log, is even warmer than a brick house (wood has a lower thermal conductivity than brick). But since the house is old, we will consider that in terms of heat loss, they are the same.
Although the Pskov region belongs to the middle lane, it is still its north, so we will use a regional coefficient of 1.5. So, 72/10=7.2 kW, 7.2*1.5=10.8 kW. Since the ceilings in the house are below standard, we will not use the correction factor, as well as add 25% for hot water supply. We take into account only possible severe frosts: 10% is 1.08 kW. This means that we need to purchase a boiler with a capacity of at least 12 kW.
The above simplified power calculation scheme justifies itself in the selection of heating equipment only for standard projects of detached houses. If your house is blocked, part of a townhouse or an apartment, then the calculations will be different, because the neighbors on the side, below or above reduce the heat loss of the premises. Separate heat engineering calculations will also be required if the house is built according to an individual project.
When choosing a boiler, it is sometimes difficult to determine its compliance with the heating requirements of a particular house. It seems that there is data on the size, internal volume. But this is not enough. The modern definition requires knowledge of the heat loss characteristic of this house. It is with heat losses that the possibility of choosing the power of the future boiler is associated, which should compensate for them in the course of its work.
Incorrectly selected boiler power leads to additional fuel costs(gas, solid and liquid). Each option will be discussed below, but for now it must be taken into account that, as a first approximation, insufficient boiler power leads to a low temperature in the heating system, due to its slow and insufficient heating. Power that exceeds the required leads to the operation of the system in a pulsed mode. It causes a sharp increase in gas consumption, wear of the gas valve. The right choice of boiler power and calculation of the heating system can help reduce heating costs.
Method for calculating heat losses
Calculation of heat losses is carried out according to certain methods, different from the climatic zone of the country. Having such calculations on hand, it is much easier to navigate in the choice of all the devices of the future heating system. The abundance of incoming data, basic and auxiliary, as well as the formalization of calculations, made it possible to introduce automation and carry them out using computer programs. Thanks to this, such calculations have become available for individual execution on the websites of construction companies.
Of course, only a specialist can determine the exact results. But an independent determination of the magnitude of heat loss will give quite visible results with the determination of the required power. By entering the data requested by the program, according to the parameters of the house(cubic capacity, materials, insulation, windows and doors, etc.), after performing the proposed actions, the value of heat losses is obtained. The resulting accuracy is sufficient to determine the required power of the boiler.
Using house ratios
The old way of determining the amount of heat loss was use of house coefficients of 3 types for an individual calculation of the power of a gas boiler using a simplified method:
- from 130 to 200 W / m2 - houses without thermal insulation;
- from 90 to 110 W / m2 - houses with thermal insulation, 20-30 years;
- from 50 to 70 W/m2 - heat-insulated house with new windows, 21st century.
Knowing the value of your coefficient and the area of \u200b\u200bthe house, by multiplying, the desired value is obtained. The required power was even easier to determine during the Soviet era. Then it was believed that 10 kW per 100 meters of area is just right.
However, today such accuracy is no longer enough.
What affects the power of the boiler
If it is too small, then a powerful solid fuel boiler will not “burn out” the remaining fuel due to lack of air supply, the chimney will quickly become clogged, and fuel consumption will be excessive. Gas or oil fired (LF) boilers will quickly heat a small amount of water and turn off the burners. This burning time will be the shorter, the more powerful the boilers. In such a short time, the removed combustion products will not have time to warm up the chimney, and condensate will accumulate there. Acids formed quickly will render unusable like a chimney, and the boiler itself.
Long burner operation allows the chimney to warm up and the condensate to disappear. Frequent turning on of the boiler leads to wear of it and the chimney, as well as increased fuel consumption due to the need to warm up the chimney channel and the boiler itself. To calculate the power of a liquid fuel (diesel) boiler, you can use calculator program, taking into account many of the features described above (designs, materials, windows, insulation), but express analysis can be performed using the above method.
It is believed that 1-1.5 kW of boiler power is needed to heat 10 square meters of a house. DHW is not taken into account in a house with high-quality insulation, without heat loss, with an area of 100 sq. m. Coefficients for the level of insulation used to calculate the required power of the boiler ZhT:
- 0,11 - apartment, 1st and last floors of an apartment building;
- 0,065 - an apartment in an apartment building;
- 0,15 (0,16) - a private house, a wall of 1.5 bricks, without insulation;
- 0,07 (0,08) - private house, wall 2 bricks, 1 layer of insulation.
For calculation, an area of 100 sq. m. is multiplied by a factor of 0.07 (0.08). The received power is 70-80 W per 1 sq. m. area. The boiler power is reserved by 10–20%, for hot water supply the reserve increases to 50%. This calculation is very approximate.
Knowing the heat losses, we can say about the required amount of heat generated. Usually, for comfort in the house, the value is taken +20 degrees Celsius. Since there is a period of minimum temperatures in the year, the demand for heat increases sharply on these days. Taking into account the periods when temperatures fluctuate around the average for the winter, the boiler power can be taken equal to half of the previously obtained value. In this case, compensation for heat losses due to other heat sources is taken into account.
Solving the problem of excess power
In the case of low heat demand, the boiler output becomes obviously high. There are several solutions. Firstly, during this period, the use of 4-way mixing valves in hydraulic systems is proposed. Can be applied thermohydraulic distributor. That allows you to regulate the heating of water without changing the boiler power, due to valves and circulation pumps. This ensures optimal operation of the boiler.
Due to the high cost of the method, a budget option is being considered. multi-stage burners in inexpensive gas and LT boilers. With the onset of the specified period, a stepwise transition to reduced combustion reduces the boiler power. A variant of smooth transition is modulation or smooth adjustment, commonly used in wall-mounted gas appliances. This possibility is almost not used in the designs of LT boilers, although a modulating burner is a more advanced option than a mixing valve. Modern pellet boilers are already equipped power control system and automatic fuel supply.
For the inexperienced consumer the presence of a modulating burner system may seem like a sufficient reason to abandon the calculation of heat losses at home, or at least limit themselves to an approximate definition. By no means, the presence of such a function cannot solve all the problems that arise: if, when the boiler is turned on, it starts working at maximum power, then after a while the machine reduces it to the optimum.
At the same time, a powerful boiler in a small system has time heat water and turn off even before the transition of the modulating burner, I needed the desired level of combustion. The water cools down quickly enough, the situation will repeat itself “to a blot”. As a result, the operation of the boiler takes place in impulses as with a single-stage powerful burner. The change in power can reach no more than 30%, which will eventually lead to failures with a further increase in the external temperature. It is worth remembering that it is about relatively cheap devices.
In more expensive condensing boilers, the modulation limits are wider. ZhT boilers can cause tangible difficulties when trying to use in small and well-insulated houses. In such a house, about 150 sq. m, 10 kW of power is enough to cover heat losses. In the line of ZhT boilers offered by manufacturers, the minimum power is twice as much. And here an attempt to use such a boiler can lead to a situation even worse than that described above.
ZhT (diesel fuel) is burning in the furnace, everyone saw a black plume behind an unheated and unregulated diesel engine. And here in the products of incomplete combustion, soot falls abundantly, it and unburned products are thoroughly clog the combustion chamber. And now the brand new boiler needs to be urgently cleaned so as not to reduce the efficiency and restore heat transfer. And after all, if you first select the correct power of the boiler, there would not be all the problems described.
In practice, you should choose the boiler power slightly lower than the heat losses of the house. Popularity and practical use have gained boilers with TsOGVS, i.e. double-circuit, heating water for heating and hot water supply. And among these two functions, the required capacity for CH is less than for DHW. Of course, this approach made the choice of boiler power more difficult.
The method of obtaining hot water in a 2-circuit boiler - flow heating. Since the time of contact (heating) of running water is insignificant, the power of the boiler heater must be high. Even for low-power double-circuit boilers, the DHW system has 18 kW of power and this is only the minimum, which makes it possible to take a normal shower. The presence of a modulating burner in such a device will make it possible to work with a minimum power of 6 kW, almost equal to the heat loss in a 100-meter house with high-quality thermal insulation.
In real life, average, for the heating season, the needs will be no more than 3 kW. That is, although the situation is not ideal, it is acceptable. A way to reduce the required capacity of the DHW system is to use a DHW storage tank. And it is very similar to a single-circuit boiler equipped with a boiler. The boiler connected through the heat exchanger to the boiler has a capacity at least 100 liters. This is a minimum, designed for several points of water intake and their simultaneous use.
This scheme allows reduce boiler output combined with a water heater. As a result, the task is completed and the boiler power is sufficient to compensate for heat losses (CH) and hot water (boiler). At first glance, as a result, during the operation of the boiler to the boiler, hot water will not go into the heating system and the temperature in the house will drop. In fact, for this to happen, the boiler must turn off for 3 - 4 hours. The process of replacing heated water from the boiler with cold water occurs gradually. The practice of using heated water says that even draining half the volume, which is 50 liters at a temperature of about 85 degrees Celsius and the same amount of cold to use, leads to the remainder in the tank of half the volume of hot and the same amount of cold. The heating time will be no more than 25 minutes. Since such a volume is not consumed at a time in the family, the heating time of the boiler will be much less.
An example of determining the boiler power
An approximate method for determining the power of a gas boiler based on its specific power (Rud) per 10 sq. m and taking into account the conditions of climatic zones, heated area - P.
- 0.7−0.9 - south;
- 1.2−1.5 kW - middle band;
- 1.5−2.0 kW - north
Boiler power is determined Pk \u003d (P * Rud) / 10; where Rud = 1;
The volume of water in the system Osist \u003d Pk * 15; where 1 kW is accepted for 15 liters of water
So for the house from the example with a LT boiler, in the north, the calculation will look like this:
Pk \u003d 100 * 2/10 \u003d 20 (kW);