When choosing a boiler, it is sometimes difficult to determine its compliance with the heating requirements of a particular home. There seems to be data on dimensions and internal volume. But this turns out to be not enough. The modern definition requires knowledge of the heat loss rate characteristic of this house. It is with heat losses that the possibility of choosing the power of the future boiler is associated, which must compensate for them during its operation.
Incorrectly selected boiler power leads to additional fuel costs(gas, solid and liquid). Each option will be discussed below, but for now you need to take 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 results in the system operating in pulse mode. It causes sharp increase in gas consumption, wear of the gas valve. Reducing heating costs can be achieved by choosing the correct boiler power and calculating the heating system.
Method for calculating heat losses
Calculation of heat losses is carried out according to certain techniques differing from the climatic zone of the country. Having such calculations in hand, it is much easier to navigate the choice of all devices for 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 independent determination of the amount 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 house parameters(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 boiler power.
Using house odds
The old way of determining the amount of heat loss was use of house coefficients of 3 types for 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 - thermally insulated house with new windows, 21st century.
Knowing the value of your coefficient and the area of the house, the desired value is obtained by multiplication. The required power was determined even more simply during Soviet times. Then it was believed that 10 kW per 100 meters of area was just right.
However, today such accuracy is no longer enough.
What does boiler power affect?
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 liquid fuel boilers will quickly heat a small amount of water and turn off the burners. This burning time will be shorter as more powerful boilers. In such a short time, the removed combustion products will not have time to warm up the chimney, and condensation will accumulate there. Acids formed quickly will fall into disrepair like a chimney, and the boiler itself.
Long burner operating time allows the chimney to warm up and the condensation will disappear. Frequent switching on of the boiler leads to wear and tear on the boiler and the chimney, as well as increased fuel consumption due to the need to heat up the chimney duct 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 (structures, materials, windows, insulation), but express analysis can be carried out using the given methodology.
It is believed that to heat 10 square meters of house area you need 1-1.5 kW of boiler power. DHW in a house with high-quality insulation, without heat loss, and an area of 100 square meters is not taken into account. m. Coefficients for the level of insulation used to calculate the required power of the ZhT boiler:
- 0,11 - apartment, 1st and last floors apartment building;
- 0,065 - apartment in an apartment building;
- 0,15 (0,16) - a private house, wall 1.5 bricks, without insulation;
- 0,07 (0,08) - private house, wall 2 bricks, 1 layer of insulation.
For calculation, the area is 100 sq. m. is multiplied by a factor of 0.07 (0.08). The resulting power is 70-80 W per 1 sq. m. area. The boiler power is reserved by 10−20%, for DHW the reserve increases to 50%. This calculation is very approximate.
Knowing the heat losses, we can say about the required amount of heat generated. Typically, comfort in the home is taken to mean +20 degrees Celsius. Since there is a period of minimum temperatures throughout the year, the need for heat increases sharply on these days. Taking into account periods when temperatures fluctuate around winter averages, the boiler power can be taken equal to half of the previously obtained value. In this case, the calculation includes compensation for heat losses from other heat sources.
Solving the problem of excess power
In case of low heat demand, the boiler power becomes obviously high. There are several solutions. Firstly, during this period, it is proposed to use 4-way mixing valves in hydraulic systems Oh. Can be applied thermohydraulic distributor. This allows you to regulate water heating without changing the boiler power, due to valves and circulation pumps. This ensures optimal boiler operation.
Due to the high cost of the method, it is considered a budget option multi-stage burners in inexpensive gas and HT boilers. With the onset of the specified period, a stepwise transition to reduced combustion reduces the boiler power. An option for a smooth transition is modulation or smooth adjustment, commonly used in wall gas appliances. This possibility is almost never used in the designs of HT boilers, although a modulating burner is a more advanced option than a mixing valve. Modern boilers on pellets are already equipped power control system and automatic fuel supply.
For the inexperienced consumer presence of a modulation burner system may seem like a sufficient reason to refuse to calculate the heat losses of a house, or at least limit ourselves to their approximate determination. 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 automatic machine reduces it to the optimum.
At the same time, a powerful boiler in a small system manages to heat the water and switch off Even before the transition of the modulating burner, I had the desired level of combustion. The water cools down quickly enough, the situation will repeat itself “until a blot”. As a result, the boiler operates in pulses as with a single-stage powerful burner. The change in power can reach no more than 30%, which will ultimately lead to failures with a further increase in external temperature. It is worth remembering that we are talking about relatively cheap devices.
In more expensive condensing-type boilers, the modulation limits are wider. ZhT boilers can cause tangible difficulties when trying to use it 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 large. And here an attempt to use such a boiler can lead to a situation even worse than the one described above.
Diesel fuel (diesel fuel) is burning in the firebox; everyone has seen the black plume behind the unheated and unregulated diesel engine. And here soot falls out abundantly in the products of incomplete combustion; it and the unburned products are completely clog the combustion chamber. And now the brand new boiler urgently needs to be cleaned so as not to reduce efficiency and heat exchange must be restored. And after all, if you had first selected the correct boiler power, all the problems described would not have arisen.
In practice, you should choose a boiler power slightly lower than the heat loss of the house. Boilers with COGVS, i.e. double-circuit, heating water for heating and hot water supply, have gained popularity and practical use. And among these two functions, the required power for central heating is less than for domestic hot water. Of course, this approach made choosing the boiler power more difficult.
Method for producing hot water in a 2-circuit boiler - flow heating. Because contact time (heating) running water insignificantly, the boiler heater power must be high. Even with low-power double-circuit boilers, the hot water 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 modulation burner in such a device will make it possible to work with a minimum power of 6 kW, almost equal to the heat losses in a 100-meter house with high-quality thermal insulation.
IN real life, average, for the heating season, 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 power of a DHW system is to use a storage tank for DHW. And this is very similar to a single-circuit boiler equipped with a boiler. The boiler connected through a heat exchanger to the boiler has a capacity not less than 100 liters. This is a minimum designed for several water points and their simultaneous use.
This scheme allows reduce boiler power, 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 DHW (boiler). At first glance, as a result, while the boiler is running, hot water will not flow 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 in a family at one time, the heating time of the boiler will be significantly shorter.
An example of determining boiler power
An approximate method for determining the power of a gas boiler based on its specific power (Rud) per 10 square meters. 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 Rk = (P*Rud)/10; where Rud = 1;
Volume of water in the system Osist = Pk*15; where 1 kW is taken for 15 liters of water
So for the house from the example with an HT boiler, in the north, the calculation will look like this:
Pk = 100*2/10 = 20 (kW);
Selection of a gas boiler of optimal power is possible only after calculations. The technical documentation for boiler equipment indicates its thermal power– TMK. This parameter means the power that the boiler is capable of transmitting to external devices (heating, ventilation, domestic hot water preparation), taking into account its efficiency. But this value in no way informs the user what area can be heated using a specific boiler model.
The problem is that any building, even insulated, transfers some 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 making the right choice boiler
In this article:
What parameters need to be taken into account
Heat loss of a private house
When choosing boiler equipment for heating your home, you must consider:
- climatic conditions of the region (the calculation formula includes the average temperature for the coldest week of the year);
- set air temperature inside heated rooms;
- the need to organize hot water supply;
- heat loss from forced ventilation (if there is one in the house);
- number of storeys of the building;
- ceiling height;
- design and materials of floors;
- the thickness of the external walls and the materials from which they were built;
- geometric dimensions of external walls;
- floor construction (thickness of layers and materials from which they are constructed);
- sizes, number of windows and doors and their type (glass thickness, number of cameras, etc.).
Heat loss at home
The amount of heat loss from a building is greatly influenced by:
- type of attic (insulated, non-insulated);
- the presence or absence of a basement.
To clearly show dependence of house heat loss 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 in the first case a boiler will be required less powerful than for brick house.Building codes specify thermal conductivity indicators for all building materials.
Something similar is observed in relation to windows..
Only they are not characterized by thermal conductivity, but, on the contrary, by the heat transfer resistance coefficient: the higher the number, the less heat the window will release from the house (this indicator is also called the R-factor).
As you can see, the more chambers in a window design, the higher its resistance to heat loss. The gas mixture that fills the chambers of double-glazed windows also plays an important role.How to calculate the TMC of a gas boiler
First of all, the thermal calculation of the building itself
The thermal power of a heating boiler can be calculated in two ways:
- full;
- simplified.
The first method involves carrying out calculations taking into account the thermal properties of all building materials involved in the construction of the house and its finishing. From the data shown in the tables above, you can see how important it is to perform a complete calculation.
But this work is not easy, and in the absence of certain experience, it is difficult to cope with it.
This is usually done by designers in design organizations. Although, if you really want to, 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 coefficient of the building materials from 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 equal to 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, thermal conductivity is given in the table of building materials (see above).
- D– thickness of layers of building materials.
After collecting all the initial data, you can begin to calculate the heat transfer coefficient using the formula:
Kt = 1/
CT is calculated for the ceiling and walls separately.
The principle of calculating the floor CT is the same, but there are some nuances: the right approach requires dividing the floor area into 4 zones, located from the outer walls to the center. To simplify calculations, heat loss 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– heat transfer coefficient of a double glazing unit or glass (indicated by the manufacturer).
- F st.– area of the glazed surface of the window.
- Kr- heat transfer coefficient window frame(specified by the manufacturer).
- F r– area of the window frame.
- R– the perimeter of the glazed surface of the window.
The heat transfer coefficient of windows (Ko) is calculated using the formula:
Kst. x F st. + Кр x F р + Р/F, where F is the area of the windows.
Using the same formula, the heat transfer coefficient of doors is calculated.
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 calculations, you can use the following data:
To determine heat loss, the conditional coefficient is multiplied by the total area of the 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 a heating boiler is defined as the sum of the power 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 you can do without such complex and expensive thermal calculations. Residential buildings are usually built taking into account the climatic conditions of a particular region, so you can select the required TMC value using a simplified scheme.
The basis for this calculation is 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 kW. m is calculated by the formula:
- W = S x W beats/10, where
- W – boiler design power
- S - sum of premises areas
- Wud – 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 area of the building is 300 sq. m. m.
Let us take the value of specific power (according to the fourth table) equal to 1.5.
- W = 300 x 1.5/10 = 45 kW
For high ceilings
If the ceiling height is different from standard values, in this case, the power of the heating boiler is calculated using the formula:
- Mk = TxKz, Where
- Mk – boiler power
- T – estimated heat loss
- Кз – safety factor
Heat losses T are calculated using the formula:
- T = VхРхКр/860, Where
- V – volume of the room (in cubic meters)
- P – difference between external and internal temperatures
- Kr – dissipation coefficient
For buildings made of brick, Kr is 2 - 2.9, for poorly insulated buildings - 3-4.
And lastly: if you assume that the boiler will provide the house and hot water, increase the design power by 25%.
In any heating system using coolant liquid, its “heart” is the boiler. It is here that the energy potential of fuel (solid, gaseous, liquid) or electricity is converted into heat, which is transferred to the coolant, and is already distributed throughout all the heated rooms of the house or apartment. Naturally, the capabilities of any boiler are not unlimited, that is, they are limited by its technical and operational characteristics specified in the product data sheet.
One of the key characteristics is the thermal power of the unit. Simply put, it must be able to generate in a unit of time such an amount of heat that would be sufficient to fully heat all the rooms of a house or apartment. Selection suitable model“by eye” or according to some overly generalized concepts can lead to an error in one direction or another. Therefore, in this publication we will try to offer the reader, although not professional, but still with a fairly high degree of accuracy, an algorithm on how to calculate the power of a boiler for heating a house.
A trivial question - why know the required boiler power?
Despite the fact that the question really seems rhetorical, there is still a need to give a couple of explanations. The fact is that some owners of houses or apartments still manage to make mistakes, going to one extreme or another. That is, purchasing equipment either of obviously insufficient thermal performance, in the hope of saving money, or greatly overestimated, so that, in their opinion, they are guaranteed to provide themselves with heat in any situation with a large margin.
Both are completely wrong and have a negative impact on both the provision of comfortable conditions residence, and on the durability of the equipment itself.
- Well, with insufficient calorific value everything is more or less clear. When winter cold sets in, the boiler will begin to operate at full capacity, and it is not a fact that there will be a comfortable microclimate in the rooms. This means that you will have to “bring up the heat” with the help of electric heating devices, which will entail significant extra costs. And the boiler itself, operating at the limit of its capabilities, is unlikely to last long. In any case, after a year or two, homeowners will clearly realize the need to replace the unit with a more powerful one. One way or another, the cost of an error is quite impressive.
- Well, why not buy a boiler with a large reserve, what can this hinder? Yes, of course, high-quality heating of the premises will be provided. But now let’s list the “cons” of this approach:
Firstly, a higher-power boiler itself can cost significantly more, and it’s difficult to call such a purchase rational.
Secondly, with increasing power, the dimensions and weight of the unit almost always increase. These are unnecessary difficulties during installation, “stolen” space, which is especially important if the boiler is planned to be placed, for example, in the kitchen or in another room in the living area of the house.
Thirdly, you may encounter uneconomical operation of the heating system - part of the expended energy resources will be spent, in fact, in vain.
Fourthly, excess power means regular long shutdowns of the boiler, which, in addition, are accompanied by cooling of the chimney and, accordingly, abundant formation of condensate.
Fifth, if powerful equipment is never properly loaded, it does not benefit it. Such a statement may seem paradoxical, but it is so - wear becomes higher, the duration of trouble-free operation is significantly reduced.
Prices for popular heating boilers
Excess boiler power will be appropriate only if it is planned to connect a water heating system to it for economic needs– boiler indirect heating. Well, or when it is planned to expand the heating system in the future. For example, the owners plan to build a residential extension to the house.
Methods for calculating the required boiler power
In truth, it is always better to trust specialists to carry out thermal engineering calculations - there are too many nuances to take into account. But, it is clear that such services are not provided free of charge, so many owners prefer to take responsibility for choosing the parameters of boiler equipment.
Let's see what methods of calculating thermal power are most often offered on the Internet. But first, let’s clarify the question of what exactly should influence this parameter. This will make it easier to understand the advantages and disadvantages of each of the proposed calculation methods.
What principles are key when carrying out calculations?
So, the heating system faces two main tasks. Let us immediately clarify that there is no clear division between them - on the contrary, there is a very close relationship.
- The first is creating and maintaining a comfortable temperature in the premises. Moreover, this level of heating should extend to the entire volume of the room. Of course, due to physical laws, temperature gradation in height is still inevitable, but it should not affect the feeling of comfort in the room. It turns out that it should be able to warm up a certain volume of air.
The degree of temperature comfort is, of course, a subjective value, that is, different people can evaluate it in their own way. But it is still generally accepted that this indicator is in the range of +20 ÷ 22 °C. Typically, this is the temperature that is used when carrying out thermal calculations.
The same is true of the standards established current GOST, SNiP and SanPiN. For example, the table below shows the requirements of GOST 30494-96:
Room type Air temperature level, °C optimal acceptable Living spaces 20÷22 18÷24 Residential premises for regions with minimum winter temperatures of - 31 °C and below 21÷23 20÷24 Kitchen 19÷21 18÷26 Toilet 19÷21 18÷26 Bathroom, combined toilet 24÷26 18÷26 Office, recreation and study areas 20÷22 18÷24 Corridor 18÷20 16÷22 Lobby, staircase 16÷18 14÷20 Storerooms 16÷18 12÷22 Residential premises (the rest are not standardized) 22÷25 20÷28
- The second task is the constant compensation of possible heat losses. Creating an “ideal” house in which there would be no heat leaks is a problem that is practically unsolvable. You can only reduce them to the bare minimum. And almost all elements of a building’s structure become leakage paths to one degree or another.
Building design element Approximate share of total heat losses Foundation, plinth, floors of the first stage (on the ground or above an unheated basement) from 5 to 10% Joints building structures from 5 to 10% Passage sections engineering communications through building structures (sewage pipes, water supply, gas supply, electrical or communication cables, etc.) up to 5% External walls, depending on the level of thermal insulation from 20 to 30% Windows and doors to the street about 20÷25%, of which about half is due to insufficient sealing of boxes, poor fit of frames or canvases Roof up to 20% Chimney and ventilation up to 25÷30% Why were all these rather lengthy explanations given? But only so that the reader has complete clarity that when making calculations, willy-nilly, it is necessary to take into account both directions. That is, the “geometry” of the heated rooms of the house, and the approximate level of heat loss from them. And the amount of these heat leaks, in turn, depends on a number of factors. This is the difference in temperatures outside and in the house, and the quality of thermal insulation, and the features of the entire house as a whole and the location of each of its rooms, and other evaluation criteria.
You might be interested in information about which ones are suitable
Now, armed with this preliminary knowledge, let's move on to consider various methods for calculating the required thermal power.
Calculation of power based on the area of heated premises
It is proposed to proceed from their conditional relationship that for high-quality heating of one square meter of room area it is necessary to consume 100 W of thermal energy. Thus, it will help to calculate which one:
Q =Stotal / 10
Q- the required thermal power of the heating system, expressed in kilowatts.
Stotal- the total area of the heated premises of the house, square meters.
However, reservations are made:
- First, the ceiling height of the room should be on average 2.7 meters, a range from 2.5 to 3 meters is allowed.
- Secondly, you can make an adjustment for the region of residence, that is, take not a rigid standard of 100 W/m², but a “floating” one:
That is, the formula will take a slightly different form:
Q =Stotal ×Qud / 1000
Qud - The value of the specific thermal power per square meter of area taken from the table shown above.
- Third - the calculation is valid for houses or apartments with an average degree of insulation of enclosing structures.
However, despite the mentioned reservations, such a calculation cannot be called accurate. Agree that it is largely based on the “geometry” of the house and its premises. But heat loss is practically not taken into account, except for the rather “blurred” ranges of specific thermal power by region (which also have very vague boundaries), and remarks that the walls should have an average degree of insulation.
But be that as it may, this method is still popular precisely for its simplicity.
It is clear that the operating power reserve of the boiler must be added to the obtained calculated value. You should not overestimate it - experts advise staying in the range from 10 to 20%. This, by the way, applies to all methods for calculating the power of heating equipment, which will be discussed below.
Calculation of the required thermal power by volume of premises
By by and large, this method of calculation largely repeats the previous one. True, the initial value here is not the area, but the volume - essentially the same area, but multiplied by the height of the ceilings.
And the norms of specific thermal power adopted here are:
- for brick houses – 34 W/m³;
- For panel houses– 41 W/m³.
Even based on the proposed values (from their wording), it becomes clear that these standards were established for apartment buildings, and are used mainly to calculate the heat energy demand for premises connected to central system department or to an autonomous boiler station.
It is quite obvious that “geometry” is again being put at the forefront. And the entire system for accounting for heat losses comes down to only differences in the thermal conductivity of brick and panel walls.
In a word, this approach to calculating thermal power is also no different in accuracy.
Calculation algorithm taking into account the characteristics of the house and its individual premises
Description of the calculation method
So, the methods proposed above give only a general idea of required quantity thermal energy for heating a house or apartment. They have a common weak point - almost complete ignorance of possible heat losses, which are recommended to be considered “average”.
But it is quite possible to carry out more accurate calculations. The proposed calculation algorithm will help with this, which is also embodied in the form of an online calculator, which will be offered below. Just before starting the calculations, it makes sense to consider step by step the very principle of their implementation.
First of all, an important note. The proposed methodology involves assessing not the entire house or apartment by total area or volume, but each heated room separately. Agree that rooms of equal area, but differing, say, in the number of external walls, will require different quantities heat. It is impossible to put an equal sign between rooms that have a significant difference in the number and area of windows. And there are many such criteria for evaluating each of the rooms.
So it would be more correct to calculate the required power for each room separately. Well, then a simple summation of the obtained values will lead us to the desired indicator of the total thermal power for the entire heating system. That is, in fact, for her “heart” - the cauldron.
One more note. The proposed algorithm does not pretend to be “scientific”, that is, it is not directly based on any specific formulas established by SNiP or other governing documents. However, it has been tested by practical application and shows results with a high degree of accuracy. The differences with the results of professionally carried out thermal engineering calculations are minimal and do not in any way affect the correct choice of equipment based on its rated thermal power.
The “architecture” of the calculation is as follows: the basic, already mentioned above value of specific thermal power, equal to 100 W/m², is taken, and then a whole series of correction factors is introduced, to one degree or another reflecting the amount of heat loss in a particular room.
If we express this in a mathematical formula, it will turn out something like this:
Qк= 0.1 × Sc× k1 × k2 × k3 × k4 × k5 × k6 × k7 × k8 × k9 × k10 × k11
Qк- the required thermal power required for full heating of a specific room
0.1 - conversion of 100 W to 0.1 kW, just for the convenience of obtaining the result in kilowatts.
Sk- area of the room.
k1 ÷k11- correction factors to adjust the result taking into account the characteristics of the room.
Presumably, there should be no problems with determining the area of the room. So let’s immediately move on to a detailed consideration of correction factors.
- k1 is a coefficient that takes into account the height of the ceilings in the room.
It is clear that the height of the ceilings directly affects the volume of air that the heating system must warm up. For the calculation, it is proposed to take the following values of the correction factor:
- k2 is a coefficient that takes into account the number of walls of the room in contact with the street.
How larger area contact with the external environment, the higher the level of heat loss. Everyone knows that a corner room is always much cooler than one with only one external wall. And some rooms of a house or apartment may even be internal, having no contact with the street.
In your mind, of course, you should take not only the number of external walls, but also their area. But our calculation is still simplified, so we will limit ourselves to only introducing a correction factor.
The coefficients for various cases are given in the table below:
We do not consider the case when all four walls are external. This is no longer a residential building, but just some kind of barn.
- k3 is a coefficient that takes into account the position of external walls relative to the cardinal points.
Even in winter, one should not discount the possible effects of solar energy. On a clear day, they penetrate through the windows into the rooms, thereby joining the general heat supply. In addition, the walls also receive a charge of solar energy, which leads to a reduction total number heat loss through them. But all this is true only for those walls that “see” the Sun. There is no such influence on the northern and northeastern sides of the house, for which a certain correction can also be made.
The values of the correction factor for the cardinal directions are in the table below:
- k4 is a coefficient that takes into account the direction of winter winds.
This amendment may not be mandatory, but for houses located in open areas, it makes sense to take it into account.
You might be interested in information about what they are
In almost any area there is a predominance of winter winds - this is also called the “wind rose”. Local meteorologists are required to have such a diagram - it is compiled based on the results of many years of weather observations. Quite often, the local residents themselves are well aware of which winds most often bother them in winter.
And if the wall of the room is located on the windward side, and is not protected by any natural or artificial barriers from the wind, then it will cool down much more. That is, the heat loss of the room increases. This will be less pronounced near a wall located parallel to the direction of the wind, and to a minimum - located on the leeward side.
If you don’t want to “bother” with this factor, or there is no reliable information about the winter wind rose, then you can leave the coefficient equal to one. Or, on the contrary, take it as maximum, just in case, that is, for the most unfavorable conditions.
The values of this correction factor are in the table:
- k5 - coefficient taking into account the level winter temperatures in the region of residence.
If you carry out thermal calculations According to all the rules, the assessment of heat losses is carried out taking into account the difference in temperatures indoors and outdoors. It is clear that the colder the climatic conditions of the region, the more heat is required to be supplied to the heating system.
Our algorithm will also take this into account to a certain extent, but with an acceptable simplification. Depending on the level of minimum winter temperatures falling on the coldest ten-day period, the correction factor k5 is selected .
It would be appropriate to make one remark here. The calculation will be correct if temperatures that are considered normal for a given region are taken into account. There is no need to remember the abnormal frosts that happened, say, a few years ago (and that’s why, by the way, they were remembered). That is, the lowest but normal temperature for the given area should be selected.
- k6 is a coefficient that takes into account the quality of thermal insulation of walls.
It is quite clear what more efficient system insulation of walls, the lower the level of heat loss will be. Ideally, what we should strive for, thermal insulation should generally be complete, carried out on the basis of thermal calculations performed, taking into account the climatic conditions of the region and the design features of the house.
When calculating the required thermal power of the heating system, the existing thermal insulation of the walls should also be taken into account. The following gradation of correction factors is proposed:
In theory, an insufficient degree of thermal insulation or its complete absence should not be observed in a residential building. Otherwise, the heating system will be very expensive, and even without a guarantee of creating truly comfortable living conditions.
You may be interested in information about the heating system
If the reader wants to independently assess the level of thermal insulation of his home, he can use the information and calculator that are posted in the last section of this publication.
- k7 andk8 – coefficients taking into account heat loss through the floor and ceiling.
The following two coefficients are similar - their introduction into the calculation takes into account the approximate level of heat loss through the floors and ceilings of the premises. There is no need to describe in detail here - both the possible options and the corresponding values of these coefficients are shown in the tables:
For starters, the k7 coefficient, which adjusts the result depending on the characteristics of gender:
Now - the coefficient k8, which corrects for the proximity from above:
- k9 is a coefficient that takes into account the quality of windows in the room.
Here, too, everything is simple - the better the quality of the windows, the less heat loss through them. Old wooden frames, as a rule, do not have good thermal insulation characteristics. This situation is better with modern window systems equipped with double-glazed windows. But they can also have a certain gradation - according to the number of cameras in a double-glazed window and according to other design features.
For our simplified calculation, we can apply the following values of the k9 coefficient:
- k10 is a coefficient that corrects for the glazing area of the room.
The quality of windows does not yet fully reveal all the volumes of possible heat loss through them. The glass area is very important. Agree, it’s difficult to compare a small window and a huge one panoramic window almost the entire wall.
To make adjustments for this parameter, you first need to calculate the so-called glazing coefficient of the room. This is not difficult - you simply find the ratio of the glazing area to the total area of the room.
kw =sw/S
kw- room glazing coefficient;
sw- total area of glazed surfaces, m²;
S- room area, m².
Anyone can measure and sum up the area of windows. And then it’s easy to find the required glazing coefficient by simple division. And it, in turn, makes it possible to go into the table and determine the value of the correction factor k10 :
Glazing coefficient value kw k10 coefficient value - up to 0.1 0.8 - from 0.11 to 0.2 0.9 - from 0.21 to 0.3 1.0 - from 0.31 to 0.4 1.1 - from 0.41 to 0.5 1.2 - over 0.51 1.3
- k11 is a coefficient that takes into account the presence of doors to the street.
The last of the considered coefficients. The room may have a door leading directly to the street, to a cold balcony, to an unheated corridor or entrance, etc. Not only is the door itself often a very serious “cold bridge” - when it is opened regularly, a fair amount of cold air will penetrate into the room each time. Therefore, an allowance should be made for this factor: such heat losses, of course, require additional compensation.
The values of the coefficient k11 are given in the table:
This coefficient should be taken into account if the doors are winter time use regularly.
You might be interested in information about what it is
* * * * * * *
So, all correction factors have been considered. As you can see, there is nothing super complicated here, and you can safely move on to the calculations.
One more tip before starting the calculations. Everything will be much simpler if you first draw up a table, in the first column of which you sequentially indicate all the sealed rooms of the house or apartment. Next, place the data required for calculations in columns. For example, in the second column - the area of the room, in the third - the height of the ceilings, in the fourth - the orientation to the cardinal points - and so on. It’s not difficult to create such a sign if you have a plan of your residential property in front of you. It is clear that the calculated values of the required thermal power for each room will be entered in the last column.
The table can be compiled in an office application, or even simply drawn on a piece of paper. And don’t rush to part with it after making the calculations - the resulting thermal power indicators will still be useful, for example, when purchasing heating radiators or electric heating devices, used as a backup heat source.
To make the task of carrying out such calculations extremely simple for the reader, a special online calculator is located below. With it, with the initial data pre-collected in a table, the calculation will take literally a matter of minutes.
Calculator for calculating the required heating power for the premises of a house or apartment.
A boiler for autonomous heating is often chosen based on the same principle as your neighbor’s. Meanwhile, this is the most important device on which comfort in the home depends. Here it is important to choose the right power, since neither its excess, nor even its shortage will bring any benefit.
Boiler heat transfer - why calculations are needed
The heating system must completely compensate for all heat loss in the house, which is why the boiler power is calculated. The building constantly releases heat to the outside. Heat loss in a house varies and depends on the material of the structural parts and their insulation. This affects the calculated performance of the heat generator. If you take the calculations as seriously as possible, you should order them from specialists; based on the results, a boiler is selected and all parameters are calculated.
It is not very difficult to calculate heat loss yourself, but you need to take into account a lot of data about the house and its components, and their condition. More the easy way is the use of a special device for detecting heat leaks - a thermal imager. The screen of a small device displays not calculated, but actual losses. It clearly shows the location of leaks, and measures can be taken to eliminate them.
Or maybe no calculations are needed, just take a powerful boiler and the house will be provided with heat. Not so simple. The house will really be warm and comfortable until it’s time to think about something. The neighbor has the same house, the house is warm, and he pays much less for gas. Why? He calculated the required boiler capacity, which is one third less. The understanding comes that a mistake has been made: you should not buy a boiler without calculating the power. Extra money is spent, some of the fuel is wasted and, what seems strange, an underloaded unit wears out faster.
A boiler that is too powerful can be reloaded for normal operation, for example, by using it to heat water or by connecting a previously unheated room.
A boiler with insufficient power will not heat the house and will constantly work with overload, which will lead to premature failure. And it will not only consume fuel, but eat it, and still there will not be good heat in the house. There is only one way out - install another boiler. Money went down the drain - buying a new boiler, dismantling the old one, installing another - everything is not free. And if we also take into account moral suffering due to a mistake made, perhaps a heating season experienced in a cold house? The conclusion is clear - buy a boiler without preliminary calculations it is forbidden.
We calculate power by area - the basic formula
The simplest way to calculate the required power of a heat generation device is by the area of the house. When analyzing calculations carried out over many years, a pattern was identified: 10 m 2 of area can be heated properly using 1 kilowatt of heat energy. This rule is valid for buildings with standard specifications: ceiling height 2.5–2.7 m, average insulation.
If the housing fits into these parameters, we measure its total area and approximately determine the power of the heat generator. We always round up the calculation results and increase them a little in order to have some power in reserve. We use a very simple formula:
W=S×W beats /10:
- here W is the required power of the thermal boiler;
- S – total heated area of the house, taking into account all residential and domestic premises;
- W beat – specific power required to heat 10 square meters, adjusted for each climate zone.
For clarity and greater clarity, let’s calculate the power of a heat generator for a brick house. It has dimensions of 10 × 12 m, multiply and get S - the total area equal to 120 m 2. Specific power – Wsp is taken as 1.0. We make calculations using the formula: area 120 m2 multiplied by specific power 1.0 and we get 120, divide by 10 - the result is 12 kilowatts. A heating boiler with a capacity of 12 kilowatts is suitable for a home with average parameters. These are the initial data that we will adjust in the course of further calculations.
There are a lot of units on the market with similar characteristics, for example, solid fuel boilers from the “Kupper Expert” line from the Teplodar company, the power of which varies from 15 to 45 kilowatts. You can get acquainted with the other characteristics and find out the price on the official website of the manufacturer https://www.teplodar.ru/catalog/kotli/.
Correcting calculations - additional points
In practice, housing with average indicators is not very common, so additional parameters are taken into account when calculating the system. About one determining factor - climatic zone, the region where the boiler will be used has already been discussed. We present the values of the coefficient Wsp for all areas:
- the middle band serves as a standard, power density is 1–1.1;
- Moscow and Moscow region - multiply the result by 1.2–1.5;
- for southern regions – from 0.7 to 0.9;
- for the northern regions it rises to 1.5–2.0.
In each zone we observe a certain spread of values. We do it simply - the further south the area in the climate zone, the lower the coefficient; the further north, the higher.
Here is an example of adjustments by region. Let's assume that the house for which the calculations were carried out earlier is located in Siberia with frosts up to 35°. We take W beat equal to 1.8. Then we multiply the resulting number 12 by 1.8, we get 21.6. Rounding to the side greater value, comes out to 22 kilowatts. The difference with the original result is almost double, but only one correction was taken into account. So it is necessary to adjust the calculations.
In addition to the climatic conditions of the regions, other corrections are taken into account for accurate calculations: ceiling height and heat loss of the building. The average ceiling height is 2.6 m. If the height differs significantly, we calculate the coefficient value - divide the actual height by the average. Let's assume that the ceiling height in the building from the previously considered example is 3.2 m. We calculate: 3.2/2.6 = 1.23, round up, it comes out to 1.3. It turns out that to heat a house in Siberia with an area of 120 m2 with ceilings of 3.2 m, a boiler of 22 kW × 1.3 = 28.6 is required, i.e. 29 kilowatts.
It is also very important for correct calculations take into account the heat loss of the building. Heat is lost in any home, regardless of its design and type of fuel. 35% can escape through poorly insulated walls. warm air, through windows – 10% or more. An uninsulated floor will take 15%, and the roof will take all 25%. Even one of these factors, if present, should be taken into account. A special value is used by which the resulting power is multiplied. It has the following indicators:
- for a brick, wooden or foam block house that is more than 15 years old, with good insulation, K = 1;
- for other houses with non-insulated walls K=1.5;
- if the house, in addition to uninsulated walls, does not have an insulated roof K = 1.8;
- for a modern insulated house K=0.6.
Let's return to our example for calculations - a house in Siberia, for which, according to our calculations, a heating device with a capacity of 29 kilowatts will be needed. Let's assume that this is a modern house with insulation, then K = 0.6. Let's calculate: 29×0.6=17.4. We add 15–20% to have a reserve in case of extreme frosts.
So, we calculated the required power of the heat generator using the following algorithm:
- 1. Find out the total area of the heated room and divide by 10. The specific power number is ignored; we need average initial data.
- 2. We take into account the climate zone where the house is located. We multiply the previously obtained result by the region coefficient.
- 3. If the ceiling height differs from 2.6 m, we also take this into account. We find out the coefficient number by dividing the actual height by the standard height. The boiler power obtained taking into account the climate zone is multiplied by this number.
- 4. We make allowances for heat loss. Previous result multiply by the heat loss coefficient.
Above we discussed exclusively boilers that are used exclusively for heating. If the device is used to heat water, the calculated power should be increased by 25%. Please note that the heating reserve is calculated after correction taking into account climatic conditions. The result obtained after all calculations is quite accurate, it can be used to select any boiler: gas , liquid fuel, solid fuel, electric.
We focus on the volume of housing - we use SNiP standards
Counting heating equipment for apartments, you can focus on SNiP standards. Building codes and the rules determine how much thermal energy is needed to heat 1 m 3 of air in standard buildings. This method is called calculation by volume. SNiP provides the following standards for thermal energy consumption: for panel house– 41 W, for brick – 34 W. The calculation is simple: we multiply the volume of the apartment by the rate of heat energy consumption.
Here's an example. An apartment in a brick house with an area of 96 sq.m., ceiling height - 2.7 m. Let's find out the volume - 96 × 2.7 = 259.2 m 3. Multiply by the norm - 259.2 × 34 = 8812.8 W. Converting to kilowatts, we get 8.8. For a panel house, we carry out the calculations in a similar way - 259.2×41 = 10672.2 W or 10.6 kilowatts. In heating engineering, rounding is carried out upward, but if you take into account energy-saving packages on windows, you can round down.
The obtained data on equipment power are initial. For a more accurate result, correction will be needed, but for apartments it is carried out according to different parameters. The first step is to take into account the presence of an unheated room or its absence:
- if a heated apartment is located on the floor above or below, we apply an amendment of 0.7;
- if such an apartment is not heated, we do not change anything;
- if there is a basement under the apartment or an attic above it, the correction is 0.9.
We also take into account the number of external walls in the apartment. If one wall faces the street, we apply an amendment of 1.1, two - 1.2, three - 1.3. The method for calculating boiler power by volume can also be applied to private brick houses.
So, you can calculate the required power of a heating boiler in two ways: by total area and by volume. In principle, the data obtained can be used if the house is average, multiplying it by 1.5. But if there are significant deviations from the average parameters in the climate zone, ceiling height, insulation, it is better to correct the data, because the initial result may differ significantly from the final one.
To answer this question, data on its cubic capacity alone is not enough. To choose the right heating equipment, you need information about heat loss at home.
To ensure proper comfort in using the DHW system, the power of a double-circuit boiler must be significantly greater than in the case when the boiler only heats the house.
When building or reconstructing a house, it becomes necessary to select the boiler power to provide the home with heat and hot water.
Without mathematics - not a step.
The main information required to select the boiler power is the heat loss of the house, which it must compensate. They need to be calculated. Each country has adopted a certain method for calculating heat loss, which takes into account local climatic conditions.
In Ukraine, the methodology set out in DBN B 2.6-31:2006 “ Thermal insulation structures”, which contains requirements for thermal performance indicators of enclosing structures of houses and structures and the procedure for their calculation.
When ordering a house project from an architect, you have the right to demand that the project contain the results of such calculations. Based on them, you can choose not only a boiler, but also heating equipment for all rooms. Using a computer program. Calculation of heat loss is facilitated by computer programs, free versions which are distributed by many installation companies. Thanks to advanced additional functions, the program allows you to perform calculations even for people who have never encountered design before. But due to the lack of relevant experience, they will most likely need much more time to carry out the calculation. Based on the results of such calculations, it is better to consult a specialist.
Using a questionnaire. If you do not have a project with heat losses calculated by the architect (designer), you can try to determine them yourself using simplified calculation methods. The questionnaires, which are not yet very common in our country, but very practical, are quite accurate for small private houses.
They raised questions regarding: the cubic capacity of the house, the material of the walls and their thickness; insulation material and its thickness; number of windows and their sizes, number of chambers in double-glazed windows and others. For each of the questions posed, several answer options are presented. You need to choose the one that best describes your home. Each answer corresponds to a specific number. By performing mathematical operations with these numbers according to the attached instructions, we obtain a value that describes the heat loss of your home. Its accuracy is quite acceptable for selecting boiler power. Filling out the form and making payments takes only a few minutes. Approximately. The simplest method for calculating heat loss at home is to determine it using a conditional coefficient, which is approximately:130-200 W/m - for houses without thermal insulation;
90-110 W/m - for houses with thermal insulation, built in the 80-90s of the XX century;
50-70 W/m2 - for houses with modern windows, well insulated and built since the late 90s of the 20th century.Heat loss is determined by multiplying the coefficient value by the area of the house. These calculations are very rough and do not take into account the number and size of windows, the shape of the house and its location - factors that significantly affect the heat loss of the house. Such calculations should not be the main criterion when choosing a boiler; they can be used to evaluate the designer's calculations. Unfortunately, the difference between these results can be significant, so this way only a gross error can be identified.
« Approximately" Just recently, when fuel was cheap, houses were practically not insulated, the windows were not airtight and no one thought about the concept of energy saving - installers selected the boiler power very simply - 1 kW for every 10 m2 of the house area. But today you need to select a boiler based on strict calculations.
More comfort means more power.
A double-circuit boiler with a power of 18 kW allows only one person to comfortably use hot water. Opening the second tap at this time will lead to a significant decrease in pressure and temperature hot water. A large family will experience discomfort from the hot water supply provided by such a boiler. Purchasing a boiler with a higher power, for example 28 kW, may eliminate the discomfort when using hot water, but you need to weigh whether the minimum power of such a boiler will be too high compared to the heat required to heat the house.
In order for the boiler to operate in the most suitable mode, that is, with constant [approximately the same] power, hydraulic systems with a four-way mixing valve are used.
A similar effect, but for less money, can be achieved by installing a so-called thermo-hydraulic distributor
Heat loss and boiler power.
The calculated heat loss of a house is equal to its maximum heat requirement necessary to maintain a comfortable temperature in the house - usually +20°C. The maximum heat demand occurs on the coldest days, when the outside temperature drops (depending on the temperature zone) to -22°C. It should be borne in mind that such frosts occur only a few days a year, and sometimes are not observed for several years in a row. However, the boiler must function efficiently throughout the entire heating season when the temperature fluctuates most often near zero. In this case, to heat the house, a boiler with half the power (than the calculated one) is sufficient. Therefore, often buying a boiler of higher power does not make sense - not only due to its higher price, but also taking into account the decrease in the efficiency of its operation when the heat demand is significantly lower than the calculated one. The lack of heat on cold days can be made up by other sources, such as a fireplace or electric heaters.
How to combine high power with low demand.
It is best if the boiler operates at a constant, rated power throughout the entire time. But the need for thermal energy (depending on outside temperature) changes all the time. How to solve this problem? Mixing valves. One way to achieve this is to use hydraulic systems with a four-way mixing valve or a thermo-hydraulic distributor. In such systems, the temperature of the water entering the radiators is regulated not by changing the boiler power, but by changing the position of the control valve and the performance of the circulation pumps. Thanks to this, the boiler constantly operates at optimal conditions. This is a very good, but quite expensive solution.Multistage burners.
In small and not very expensive systems with gas or liquid fuel boilers, the issue of adapting the boiler performance to the current heat demand is solved with the help of multi-stage burners. When full power is not needed, a boiler equipped with such a burner operates at a lower power (lower burner stage). A more advanced option are burners with smooth power control, the so-called modulation. They are widely used in wall-hung gas boilers. IN liquid fuel boilers they are much less common. A boiler with a modulating burner is a cheaper and less troublesome option than a system with a mixing valve. No additional elements are required - all the necessary fittings are mounted in the boiler body. Power adjustment is also possible in modern solid fuel boilers that operate on pellets and are equipped with an automated fuel supply system (unfortunately, expensive).
Modulation is not a perfect solution.
A boiler with a modulating burner produces energy equal to the current heat demand. At first glance, one might assume that when choosing such a boiler there is no need to accurately determine the heat loss of the house. After all, knowing them only approximately, you can buy a boiler of greater power, which in any case will work with the power required at a certain moment. Unfortunately, in practice, boiler power modulation does not completely solve all issues. Immediately after switching on, the boiler begins to operate at maximum power; after some time, its automation begins to reduce power to optimal level. If a powerful boiler operates in a small system, then in conditions where the heat demand is small (i.e., the outside temperature is around zero or above), the water in the system will heat up even before the burner reaches the required modulation level and the boiler turns off. The water in the system will quickly cool down and the situation will repeat. The boiler will operate in pulse mode - as if it were equipped with a single-stage high-power burner. Power modulation is only possible within a limited range, which is usually no less than 30% of the maximum power. Therefore, too high a maximum boiler output will lead to difficulties in adapting its performance at higher outside temperatures. There are boilers with more wide range power modulation, but these are more expensive condensing boilers.
An oil-fuel boiler is not for a small house.
Quite big difficulties arise when selecting a liquid fuel boiler for small house. To compensate for the heat loss of a well-insulated house with an area of about 150 m2, a boiler with a power of no more than 10 kW is usually sufficient, and the power of liquid fuel boilers on the market is at least twice as high. Operating an oil-fuel boiler in pulse mode (that is, frequently turning it on and off) is even more unfavorable for it than for a gas boiler. Immediately after turning on the liquid fuel burner, a lot of soot and products of incomplete combustion are released from the combustion products, which clog the combustion chamber of the boiler. Therefore, it will have to be cleaned frequently, otherwise the soot layer will impede heat transfer, and the efficiency of the boiler will decrease, that is, it will consume more fuel.
Central heating is just the beginning.
Most of the described problems that arise can theoretically be avoided by selecting a boiler with a power that does not exceed, and even slightly lower than, the calculated heat loss of the house. But in practice, the boiler energy is usually used not only for the central heating system, but also for heating water in the DHW system. In small, well-insulated houses, the power required to heat the house is much less than that needed to quickly heat the required amount of water from the domestic hot water system. This complicates the problem optimal choice boiler
Boiler power and hot water.
A double-circuit boiler heats water for the DHW system using a flow-through method. The time for water to flow through the heat exchanger is short, so the boiler must have high power so that during this time it can heat a sufficient amount of water. The lowest power double-circuit boilers have a power of 18 kW, because this is the minimum that still allows you to prepare a sufficient amount of hot water (for taking a shower). If such a boiler is equipped with a modulating burner, it will be able to operate with a minimum power of about 6 kW, that is, close to the maximum heat loss in a well-insulated house with an area of about 100 m2. In practice, during most of the heating season, the power requirement for heating such a house will most likely be around 3 kW. Therefore, this is not an ideal situation, but it is an acceptable situation.
One of the ways to reduce the required power of a double-circuit boiler is to use a storage tank for hot water in the DHW system. The boiler can then heat the water more slowly, because after opening the tap there is a supply of warm water available in the storage tank. The larger its volume, the longer it can replenish the missing amount of water prepared by the boiler in the DHW system. Therefore, the boiler output may be lower.
Single-circuit boiler with boiler.
The volume of an indirect heating boiler (storage water heater with a heat exchanger), which is connected to a single-circuit boiler, is usually more than 100 liters. Thanks to this, the simultaneous use of hot water by several consumers does not lead to the depletion of its supply within several minutes, therefore, the power of a boiler operating in conjunction with a water heater may be lower than the power of a double-circuit boiler. Therefore, we can assume that the boiler power, which is necessary to compensate for heat loss at home, is also sufficient to heat the water in the boiler. However, when selecting the power of a single-circuit boiler, it is better to calculate how long it will take to heat the water in the boiler. This can be done using the formula:
T = mc B (t 2 - t 1) / P,
where: T - water heating time (s); m is the mass of water in the boiler (kg); c B - specific heat capacity of water - 4.2 kJ/(kg x K); t2 is the temperature to which the water should be heated (°C); t 1 — initial water temperature in the boiler (°C); P - boiler power (kW).
For example: the time for heating water at a temperature of 10°C (it is generally accepted that this is the temperature of cold water entering the water heater) to 50°C in a 200-liter boiler with a 12 kW boiler will be: 200 x 4.2 x (50 - 10J/12 = 2800 (s) = 46.7 (min).
It's long enough, especially considering that during heating of water in the boiler, warm water does not flow from the boiler operating at full capacity to the central heating system. During this time, the rooms may become cool.
However, it should be noted that a situation in which the entire volume of water has a temperature of 10°C can only occur after the boiler is turned off for at least several hours. On practice cold water enters the boiler as hot water is consumed. Even with intensive use, for example, with very fast filling bathtubs to the brim, about half of the hot water from such a large boiler will be used. After this, the temperature of the water (hot mixed with cold) in the boiler will be about 30°C. In this case, the water heating time will be 23 minutes and can be considered satisfactory. The one-time consumption of hot water in a single-family home is usually much lower, so the water in the boiler will heat up even faster.
Option to solve the problem. The problem of sharing boiler power for the central heating system and for preparation DHW water can be solved in a radical way: by purchasing two independent devices - a boiler for the central heating system and a water heater for domestic hot water. But this is definitely an expensive solution.
Why not more powerful?
What happens if the boiler has too much power?
Its performance can be adjusted only by changing the amount of air entering the firebox. When working with less than rated power (that is, with a lack of air), the fuel will not burn completely, so its consumption will be greater. In addition, unburnt compounds will flow into the chimney, causing it to clog more quickly.
Gas or liquid fuel boiler, working with modern system The central heating system (containing a small amount of water), after turning on the burner, very quickly heats the water in the system to desired temperature and turns off the burner. The higher the boiler power, the shorter the burner operating time. It may happen that it is too short and the combustion products will not be able to heat the chimney to normal temperature. Then condensation will form in the chimney, which, combining with other combustion products, forms acids that destroy the chimney, and sometimes the boiler itself.
If the burner operates for a long time, the exhaust gases heat the chimney to a high temperature, due to which condensation will not form, and the condensate that arises in the initial phase of burner operation will evaporate.
When switching on and off frequently, the boiler consumes more fuel than during continuous operation, because each time it is switched on, part of the energy will be spent on heating the boiler and chimney elements. In addition, frequent temperature changes negatively affect its strength.
A solid fuel boiler that is too powerful uses more fuel, and the thermal energy in any case will not be fully used for heating
A gas boiler that is too powerful will turn on frequently, which reduces its energy efficiency and accelerates wear of the elements.
How to use excess boiler power?
If you nevertheless bought a boiler, the power of which is significantly higher than the estimated heat requirement for heating the house, its operating conditions can be significantly improved by installing an accumulator tank (also called a buffer tank).
This solution, used in systems with solar collectors, it is recommended to use primarily in systems with solid fuel boilers. Thanks to the battery tank, regardless of short-term heat demand, the boiler can operate at its rated power, at which it has the highest efficiency. The accumulator tank is completely filled with water.
In systems with a solid fuel boiler its optimal volume can be determined from the calculation: 10 liters for each square meter of heated area. When it is relatively warm outside, automatic control valves restrict the flow of hot water into the radiators, directing it to the heat exchanger of a well-insulated storage tank, heating the water there. Its large volume (for a house with an area of 100 m2: it should be 1000 liters) accumulates a large amount of excess thermal energy from the system during the operation of the boiler.
When the fuel in the boiler burns out and its firebox cools down, warm water from the buffer tank will begin to flow into the radiators. This will ensure that the heating system continues to function properly.
Heating systems with a large amount of water have significant thermal inertia, due to which the burners of gas and liquid fuel boilers operate at higher temperatures. favorable conditions. The periods of burner operation and breaks between them are longer - it takes longer to heat more water, which then takes longer to cool. However, the system's response to changes in outside temperature is slower, making it more difficult to maintain a comfortable indoor temperature.
