At the supply it is from 95 to 105 °C, and at the return - 70 °C. Optimal values in an individual heating system H2_2 Autonomous heating helps to avoid many problems that arise with centralized network, and the optimal coolant temperature can be adjusted according to the season. When individual heating The concept of standards includes the heat transfer of a heating device per unit area of the room where this device is located. The thermal regime in this situation is ensured design features heating devices. It is important to ensure that the coolant in the network does not cool below 70 °C. The optimal temperature is considered to be 80 °C. With a gas boiler, it is easier to control heating, because manufacturers limit the ability to heat the coolant to 90 °C. Using sensors to regulate the gas supply, the heating of the coolant can be adjusted.
Coolant temperature in different heating systems
It, in turn, depends on what minimum and maximum water temperatures in the heating system can be achieved during operation. Measuring the temperature of a heating battery For autonomous heating, the standards are quite applicable central heating. They are set out in detail in Resolution of the PRF No. 354. It is noteworthy that the minimum water temperature in the heating system is not indicated there.
It is only important to observe the degree of heating of the air in the room. Therefore, in principle, the operating temperature of one system may be different from another. It all depends on the influencing factors mentioned above.
In order to determine what temperature should be in the heating pipes, you should familiarize yourself with the current standards. Their contents are divided into residential and non-residential premises, as well as the dependence of the degree of air heating on the time of day:
- In the rooms during the daytime.
Norms and optimal values of coolant temperature
Info
Over time, the maximum water temperature in the heating system will lead to breakdown. Also, a violation of the water temperature schedule in the system autonomous heating provokes the formation air jams. This occurs due to the transition of the coolant from liquid to gaseous state. Additionally, this affects the formation of corrosion on the surface of the metal components of the system.
Attention
That is why it is necessary to accurately calculate what temperature should be in the heat supply batteries, taking into account their material of manufacture. Most often, a violation of the thermal operating conditions is observed in solid fuel boilers. This is due to the problem of adjusting their power. When a critical temperature level in the heating pipes is reached, it is difficult to quickly reduce the boiler power.
Heating in a private house. there are doubts about the correctness of the system made.
For these reasons, sanitary standards prohibit greater heating. To calculate optimal indicators can be used special charts and tables that define the norms depending on the season:
- With an average reading outside the window of 0 °C, the supply for radiators with different wiring is set at 40 to 45 °C, and the return temperature at 35 to 38 °C;
- At -20 °C, the supply is heated from 67 to 77 °C, and the return rate should be from 53 to 55 °C;
- At -40 °C outside the window, all heating devices are set to the maximum permissible values.
Coolant temperature in the heating system: calculation and regulation
According to regulatory documents, the temperature in residential buildings should not fall below 18 degrees, and for children's institutions and hospitals it is 21 degrees Celsius. But it should be borne in mind that depending on the air temperature outside the building, the building through the enclosing structures may lose different sizes heat. Therefore, the temperature of the coolant in the heating system, based on external factors, varies from 30 to 90 degrees.
When heating water above heating structure decomposition begins paint coatings what is prohibited sanitary standards. To determine what the temperature of the coolant in the batteries should be, specially developed temperature charts are used for specific groups of buildings. They reflect the dependence of the degree of heating of the coolant on the state of the outside air.
Heating system water temperature
- In the corner room +20°C;
- In the kitchen +18°C;
- In the bathroom +25°C;
- In corridors and stairwells +16°C;
- In the elevator +5°C;
- In the basement +4°C;
- In the attic +4°C.
It should be taken into account that these temperature standards refer to the period heating season and do not apply to the rest of the time. Also, it will be useful information that hot water should be from +50°C to +70°C, according to SNiP-u 2.08.01.89 “Residential buildings”. There are several types of heating systems: Contents
- 1 With natural circulation
- 2 With forced circulation
- 3 Calculation of the optimal temperature of the heating device
- 3.1 Cast iron radiators
- 3.2 Aluminum radiators
- 3.3 Steel radiators
- 3.4 Warm floor
With natural circulation The coolant circulates without interruption.
Optimal water temperature in a gas boiler
Usually a lattice fence is installed that does not impede air circulation. Cast iron, aluminum and bimetallic devices are common. Consumer choice: cast iron or aluminum The aesthetics of cast iron radiators is the talk of the town.
They require periodic painting, as the rules stipulate that working surface heating device had smooth surface and made it easy to remove dust and dirt. A dirty coating forms on the rough inner surface of the sections, which reduces the heat transfer of the device. But technical specifications cast iron products at height:
- are slightly susceptible to water corrosion and can be used for more than 45 years;
- have high thermal power per section, therefore they are compact;
- are inert in heat transfer, so they smooth out temperature changes in the room well.
Another type of radiator is made of aluminum.
Single-pipe heating system can be vertical and horizontal. In both cases, air pockets appear in the system. The system inlet temperature is maintained at a high temperature to warm all rooms, so the piping system must withstand high pressure water. Two-pipe system heating The principle of operation is to connect each heating device to the supply and return pipelines. The cooled coolant is sent through the return pipeline to the boiler. Additional investments will be required during installation, but there will be no air pockets in the system. Standards temperature regime for premises In a residential building the temperature is within corner rooms should not be below 20 degrees, for interior spaces The standard is 18 degrees, for showers - 25 degrees.
Standard coolant temperature in the heating system
Heating the stairwell Since we're talking about apartment building, then it should be mentioned staircases. The coolant temperature standards in the heating system state: the degree measure at the sites should not fall below 12 °C. Of course, the residents' discipline requires closing the doors tightly entrance group, do not leave the transoms of the staircase windows open, keep the glass intact and promptly report any problems to the management company.
If the management company does not take timely measures to insulate points of probable heat loss and maintain temperature conditions in the house, an application for recalculation of the cost of services will help. Changes in the heating design Replacement of existing heating devices in the apartment is carried out with the obligatory approval of management company. Unauthorized changes in the elements of warming radiation can disrupt the thermal and hydraulic balance of the structure.
Optimal coolant temperature in a private house
This device, shown in the photo, consists of the following elements:
- computing and switching node;
- working mechanism on the hot coolant supply pipe;
- an executive unit designed to mix in the coolant coming from the return. In some cases, a three-way valve is installed;
- booster pump at the supply section;
- The booster pump is not always in the “cold bypass” section;
- sensor on the coolant supply line;
- valves and shut-off valves;
- return sensor;
- outside air temperature sensor;
- several room temperature sensors.
Now you need to understand how the coolant temperature is regulated and how the regulator functions.
Optimal coolant temperature in the heating system of a private house
If the water temperature in the heating system of a private home exceeds the norm, the following situations may occur:
- Damage to pipelines. This is especially true for polymer lines, where the maximum heating can be +85°C. That is why the normal temperature of heating pipes in an apartment is usually +70°C.
Otherwise, deformation of the line may occur and a gust may occur;
- Excessive air heating. If the temperature of the heating radiators in the apartment provokes an increase in the degree of air heating above +27°C, this is outside the normal limits;
- Reduced service life of heating components. This applies to both radiators and pipes.
2.KIT of the boiler at different temperatures entering it
The lower the temperature that enters the boiler, the greater the temperature difference on different sides of the boiler heat exchanger partition, and the more efficiently the heat transfers from exhaust gases(combustion products) into the heat exchanger wall. Let me give you an example with two identical kettles placed on identical burners. gas stove. One burner is set to maximum flame and the other to medium. The kettle that is on the highest flame will boil faster. And why? Because the temperature difference between the combustion products under these kettles and the water temperature for these kettles will be different. Accordingly, the rate of heat transfer at a larger temperature difference will be greater.
In relation to a heating boiler, we cannot increase the combustion temperature, as this will lead to the fact that most of our heat (gas combustion products) will fly out through the exhaust pipe into the atmosphere. But we can design our heating system (hereinafter referred to as CO) in such a way as to lower the temperature entering into, and therefore lower the average temperature circulating through. The average temperature at the return (input) to and supply (outlet) from the boiler will be called the “boiler water” temperature.
As a rule, the 75/60 mode is considered the most economical thermal mode of operation of a non-condensing boiler. Those. with a supply (boiler outlet) temperature of +75 degrees, and a return (boiler inlet) temperature of +60 degrees Celsius. A link to this thermal mode is in the boiler passport, when indicating its efficiency (usually the 80/60 mode is indicated). Those. in a different thermal mode, the efficiency of the boiler will be lower than that stated in the passport.
That's why modern system The heating system must operate in the design (for example 75/60) thermal mode throughout the heating period, regardless of the outside temperature, except when using an outside temperature sensor (see below). Regulation of the heat transfer of heating devices (radiators) during the heating period should be carried out not by changing the temperature, but by changing the flow rate through the heating devices (the use of thermostatic valves and thermoelements, i.e. “thermal heads”).
To avoid the formation of acid condensate on the boiler heat exchanger, for a non-condensing boiler the temperature in its return (inlet) should not be lower than +58 degrees Celsius (usually taken with a margin as +60 degrees).
I will make a reservation that the ratio of air and gas entering the combustion chamber also plays a significant role in the formation of acid condensate. The greater the excess air entering the combustion chamber, the less acid condensate. But we shouldn’t be happy about this, since excess air leads to a large overconsumption of gas fuel, which ultimately “hits our pockets.”
As an example, I’ll give you a photo showing how acid condensate destroys the boiler heat exchanger. The photo shows the heat exchanger of a Vailant wall-mounted boiler, which worked for only one season in an incorrectly designed heating system. Quite severe corrosion is visible on the return (input) side of the boiler.
For condensation systems, acid condensate is not dangerous. Since the heat exchanger of the condensing boiler is made of special high-quality alloyed of stainless steel, which is “not afraid” of acid condensate. Also, the design of the condensing boiler is designed in such a way that the acidic condensate flows through a tube into a special container for collecting condensate, but does not fall on any electronic components and components of the boiler, where it could damage these components.
Some condensing boilers are able to change the temperature at their return (input) themselves due to the boiler processor smoothly changing the power of the circulation pump. Thereby increasing the efficiency of gas combustion.
For additional gas savings, use the connection of an outdoor temperature sensor to the boiler. Most wall units have the ability to automatically change the temperature depending on the outside temperature. This is done so that at an outside temperature that is warmer than the temperature of a cold five-day period (the most very coldy), automatically lower the boiler water temperature. As stated above, this reduces gas consumption. But when using a non-condensing boiler, it is important not to forget that when the temperature of the boiler water changes, the temperature at the return (inlet) of the boiler should not fall below +58 degrees, otherwise acid condensate will form on the boiler heat exchanger and destroy. To do this, during commissioning of the boiler, in the boiler programming mode, such a curve is selected depending on the temperature on the street temperature, at which the temperature in the boiler return would not lead to the formation of acidic condensate.
I would like to immediately warn you that when using a non-condensing boiler and plastic pipes In a heating system, installing an outdoor temperature sensor is almost pointless. Since we can design for the long-term service of plastic pipes the temperature at the boiler supply is not higher than +70 degrees (+74 during the cold five-day period), and in order to avoid the formation of acid condensate, we can design the temperature at the boiler return not lower than +60 degrees. These narrow “frames” make the use of weather-sensitive automation useless. Since such frames require temperatures in the range of +70/+60. Already when using copper or steel pipes in the heating system, it already makes sense to use weather-dependent automation in heating systems, even when using a non-condensing boiler. Since it is possible to design a boiler thermal mode of 85/65, which mode can change under the control of weather-dependent automation, for example, to 74/58 and provide savings in gas consumption.
I will give an example of an algorithm for changing the temperature at the boiler supply depending on the outside temperature using the example of the Baxi Luna 3 Komfort boiler (below). Also, some boilers, for example, Vaillant, can maintain a set temperature not in their supply, but in their return. And if you have set the return temperature maintenance mode to +60, then you do not have to worry about the appearance of acidic condensation. If in this case the temperature at the boiler supply changes up to +85 degrees inclusive, but if you use copper or steel pipes, then such a temperature in the pipes does not reduce their service life.
From the graph we see that, for example, when selecting a curve with a coefficient of 1.5, it will automatically change the temperature at its supply from +80 at an outside temperature of -20 degrees and below, to a supply temperature of +30 at an outside temperature of +10 (in the middle section flow temperature + curve.
But how much will a supply temperature of +80 reduce the service life of plastic pipes (Reference: according to manufacturers, guarantee period The service life of a plastic pipe at a temperature of +80 is only 7 months, so don’t expect 50 years), or a return temperature below +58 will reduce the service life of the boiler; unfortunately, there are no exact data provided by the manufacturers.
And it turns out that when using weather-compensated automation with non-condensing gas, you can save gas, but it is impossible to predict how much the service life of the pipes and boiler will decrease. Those. in the case described above, the use of weather-sensitive automation will be at your own peril and risk.
Thus, it makes the most sense to use weather-compensating automation when using a condensing boiler and copper (or steel) pipes in the heating system. Since weather-dependent automation will be able to automatically (and without harm to the boiler) change the thermal mode of the boiler from, for example, 75/60 for a cold five-day period (for example, -30 degrees outside) to 50/30 mode (for example, +10 degrees outside) street). Those. you can painlessly select the dependence curve, for example, with a coefficient of 1.5, without fear of high boiler supply temperatures in cold weather, and at the same time without fear of the appearance of acid condensate during thaws (for condensation systems, the formula is valid that the more acid condensate is formed in them, the more they save gas). For interest, I will post a graph of the dependence of the CIT of a condensing boiler, depending on the temperature in the boiler return.
3.KIT of the boiler depending on the ratio of the mass of gas to the mass of air for combustion.
The more completely it burns gas fuel in the combustion chamber of the boiler, the more heat we can get from burning a kilogram of gas. The completeness of gas combustion depends on the ratio of the mass of gas to the mass of combustion air entering the combustion chamber. This can be compared to adjusting the carburetor in a car's internal combustion engine. The better the carburetor is tuned, the less for the same engine power.
To adjust the ratio of gas mass to air mass, modern boilers use a special device that meteres the amount of gas supplied to the combustion chamber of the boiler. It is called a gas valve or an electronic power modulator. The main purpose of this device is automatic modulation of boiler power. Also, adjustment of the optimal gas to air ratio is carried out on it, but manually, once during commissioning of the boiler.
To do this, during commissioning of the boiler, you need to manually adjust the gas pressure using a differential pressure gauge on special control fittings of the gas modulator. Two pressure levels are adjustable. For maximum power mode, and for minimum power mode. The method and instructions for setting up are usually set out in the boiler’s passport. You don’t have to buy a differential pressure gauge, but make it from a school ruler and a transparent tube from a hydraulic level or a blood transfusion system. The gas pressure in the gas line is very low (15-25 mbar), less than when a person exhales, therefore, in the absence of open fire This setup is safe. Unfortunately, not all service technicians, when commissioning a boiler, carry out the procedure for adjusting the gas pressure on the modulator (out of laziness). But if you need to get the most gas-efficient operation of your heating system, then you must carry out such a procedure.
Also, during commissioning of the boiler, it is necessary, according to the method and table (given in the boiler passport), to adjust the cross-section of the diaphragm in the air duct pipes of the boiler, depending on the power of the boiler and the configuration (and length) of the exhaust and combustion air intake pipes. The correct ratio of the volume of air supplied to the combustion chamber to the volume of gas supplied also depends on the correct choice of this diaphragm section. The correct ratio ensures the most complete combustion of gas in the combustion chamber of the boiler. And, therefore, it reduces to the necessary minimum gas consumption. I will give (for an example of the methodology correct installation diaphragm) scan from the boiler passport Baksi Nuvola 3 Comfort -
4. KIT of the boiler depending on the temperature of the combustion air entering it.
Also, the efficiency of gas consumption depends on the temperature of the air entering the combustion chamber of the boiler. The boiler efficiency given in the passport is valid for the air temperature entering the boiler combustion chamber of +20 degrees Celsius. This is explained by the fact that when colder air enters the combustion chamber, part of the heat is spent to warm up this air.
There are “atmospheric” boilers, which take combustion air from the surrounding space (from the room in which they are installed) and “turbo boilers” with a closed combustion chamber, into which air is forced into by means of a turbocharger located in the boiler. All other things being equal, a “turbo boiler” will have greater gas efficiency than an “atmospheric” one.
If everything is clear with the “atmospheric” boiler, then with the “turbo boiler” questions arise about where it is better to take air into the combustion chamber from. The “Turbo Boiler” is designed in such a way that the flow of air into its combustion chamber can be organized from the room in which it is installed, or directly from the street (via coaxial chimney, i.e. chimney "pipe in pipe"). Unfortunately, both of these methods have pros and cons. When air enters from the interior of the house, the temperature of the combustion air is higher than when taken from the street, but all the dust generated in the house is pumped through the combustion chamber of the boiler, clogging it. The combustion chamber of the boiler is especially clogged with dust and dirt when carrying out finishing works in the house.
Don't forget that for safe work“atmospheric” or “turbo boiler” with air intake from the premises of the house, it is necessary to organize the correct operation of the supply part of the ventilation. For example, supply valves on the windows of the house must be installed and opened.
Also, when removing boiler combustion products upward through the roof, it is worth considering the cost of manufacturing an insulated chimney with a condensate drain.
Therefore, coaxial chimney systems “through the wall to the street” are becoming most popular (including for financial reasons). Where exhaust gases are emitted through the inner pipe, and outer pipe Combustion air is pumped in from the street. In this case, the exhaust gases heat the combustion air sucked in, since the coaxial pipe acts as a heat exchanger.
5.KIT of the boiler depending on the time of continuous operation of the boiler (lack of “clocking” of the boiler).
Modern boilers themselves adjust their output thermal power, under the thermal power consumed by the heating system. But the limits of power auto-tuning are limited. Most non-condensing ones can modulate their power from about 45 to 100% of rated power. Condenser modulate power in a ratio of 1 to 7 and even 1 to 9. That is. a non-condensing boiler with a rated power of 24 kW will be able to produce at least, for example, 10.5 kW in continuous operation. And condensing, for example, 3.5 kW.
If, however, the temperature outside is much warmer than on a cold five-day period, then there may be a situation where the heat loss at home is less than the minimum possible power generated. For example, the heat loss of a house is 5 kW, and the minimum modulated power is 10 kW. This will lead to periodic shutdown of the boiler when the set temperature at its supply (outlet) is exceeded. It may happen that the boiler turns on and off every 5 minutes. Frequent switching on/off of the boiler is called “clocking” of the boiler. In addition to reducing the service life of the boiler, clocking also significantly increases gas consumption. Let me compare gas consumption in clocking mode with gasoline consumption in a car. Consider that gas consumption during pacing is equivalent to driving in city traffic jams in terms of fuel consumption. And the continuous operation of the boiler means driving on a free highway in terms of fuel consumption.
The fact is that the boiler processor contains a program that allows the boiler, using sensors built into it, to indirectly measure the thermal power consumed by the heating system. And adjust the generated power to this need. But the boiler takes from 15 to 40 minutes for this, depending on the capacity of the system. And in the process of adjusting its power, it does not operate in the optimal gas consumption mode. Immediately after switching on, the boiler modulates maximum power and only over time, gradually using the approximation method, reaches the optimal gas flow. It turns out that when the boiler cycles more often than 30-40 minutes, it does not have enough time to reach the optimal mode and gas consumption. After all, with the start of a new cycle, the boiler begins selecting power and mode again.
To eliminate boiler clocking, install room thermostat. It is better to install it on the ground floor in the middle of the house and, if there is a heating device in the room where it is installed, then the IR radiation of this heating device should reach the room thermostat at a minimum. Also, this heating device must not have a thermocouple (thermal head) installed on the thermostatic valve.
Many boilers are already equipped with a remote control panel. The room thermostat is located inside this control panel. Moreover, it is electronic and programmable by time zones of the day and days of the week. Programming the temperature in the house by time of day, by day of the week, and when you leave for several days, also allows you to save significantly on gas consumption. Instead of a removable control panel, a decorative plug is installed on the boiler. As an example, I will give a photo of the removable Baxi Luna 3 Komfort control panel installed in the hall of the first floor of the house, and a photo of the same boiler installed in the boiler room attached to the house with an installed decorative plug instead of the control panel.
6. Use of a greater proportion of radiant heat in heating devices.
You can also save any fuel, not just gas, by using heating devices with a larger share radiant heat.
This is explained by the fact that a person does not have the ability to feel temperature environment. A person can only feel the balance between the amount of heat received and given out, but not the temperature. Example. If we hold an aluminum block with a temperature of +30 degrees in our hands, it will seem cold to us. If we pick up a piece of foam plastic with a temperature of -20 degrees, then it will seem warm to us.
In relation to the environment in which a person is located, in the absence of drafts, a person does not feel the temperature of the surrounding air. But only the temperature of the surfaces surrounding it. Walls, floors, ceilings, furniture. I will give examples.
Example 1. When you go down to the cellar, after a few seconds you feel chilly. But this is not because the air temperature in the cellar is, for example, +5 degrees (after all, air in a still state is the best heat insulator, and you could not freeze from heat exchange with the air). And because the balance of the exchange of radiant heat with surrounding surfaces has changed (your body has a surface temperature on average of +36 degrees, and the cellar has a surface temperature on average of +5 degrees). You begin to give off much more radiant heat than you receive. That's why you feel cold.
Example 2. When you are in a foundry or steel smelting shop (or just near a big fire), you feel hot. But this is not because the air temperature is high. In winter, with partially broken windows in the foundry, the air temperature in the workshop can be -10 degrees. But you are still very hot. Why? Of course, air temperature has nothing to do with it. The high temperature of surfaces, rather than air, changes the balance of radiant heat exchange between your body and the environment. You begin to receive much more heat than you emit. Therefore, people working in foundries and steel smelting shops are forced to wear cotton pants, quilted jackets and earflap hats. To protect not from cold, but from too much radiant heat. To avoid getting heatstroke.
From here we draw a conclusion that many modern heating specialists do not realize. That it is necessary to heat the surfaces surrounding a person, but not the air. When we heat only the air, first the air rises to the ceiling, and only then, as it descends, the air heats the walls and floor due to the convective circulation of air in the room. Those. at first warm air rises to the ceiling, heating it, then along the far side of the room descends to the floor (and only then the floor surface begins to heat up) and further in a circle. With this purely convective method of heating rooms, an uncomfortable temperature distribution throughout the room occurs. When the highest temperature in the room is at head level, average at waist level, and lowest at foot level. But you probably remember the proverb: “Keep your head cold and your feet warm!”
It is no coincidence that SNIP states that in comfortable home, the temperature of the surfaces of external walls and floors should not be lower average temperature indoors by more than 4 degrees. Otherwise, the effect is that it is simultaneously hot and stuffy, but at the same time chilly (including on the legs). It turns out that in such a house you need to live “in shorts and felt boots.”
So, from afar, I was forced to bring you to the realization of which heating devices are best to use in the house, not only for comfort, but also to save fuel. Of course, heating devices, as you may have guessed, need to be used with the greatest proportion of radiant heat. Let's see which heating devices give us the largest share of radiant heat.
Perhaps, such heating devices include the so-called “warm floors”, as well as “ warm walls"(gaining more and more popularity). But among the usually most common heating devices, steel panel radiators, tubular radiators and cast iron radiators. I am forced to believe that the largest share of radiant heat is provided by steel panel radiators, since the manufacturers of such radiators indicate the share of radiant heat, while the manufacturers of tubular and cast iron radiators keep this secret. I also want to say that aluminum and bimetallic “radiators” that have recently received no right to be called radiators. They are called that only because they are the same sectional as cast iron radiators. That is, they are called “radiators” simply “by inertia”. But according to the principle of their action, aluminum and bimetallic radiators should be classified as convectors, not radiators. Since their share of radiant heat is less than 4-5%.
For panel ones steel radiators The proportion of radiant heat varies from 50% to 15% depending on the type. The largest proportion of radiant heat is found in panel radiators of type 10, in which the proportion of radiant heat is 50%. Type 11 has a radiant heat fraction of 30%. Type 22 has a radiant heat fraction of 20%. Type 33 has a radiant heat fraction of 15%. There are also steel panel radiators produced using the so-called X2 technology, for example from Kermi. It is a type 22 radiator, in which it passes first along the front plane of the radiator, and only then along the rear plane. Due to this, the temperature of the front plane of the radiator increases relative to the rear plane, and consequently the share of radiant heat, since only the IR radiation of the front plane enters the room.
The respected Kermi company claims that when using radiators made using X2 technology, fuel consumption is reduced by at least 6%. Of course, I personally did not have the opportunity to confirm or refute these figures in laboratory conditions, but based on the laws of thermophysics, the use of such technology really allows you to save fuel.
Conclusions. In a private house or cottage, I advise using steel panel radiators across the entire width of the window opening, in descending order of preference by type: 10, 11, 21, 22, 33. When the amount of heat loss in the room, as well as the width of the window opening and the height of the window sill do not allow the use types 10 and 11 (not enough power) and the use of types 21 and 22 is required, then if you have the financial opportunity, I advise you to use not the usual types 21 and 22, but using the X2 technology. If, of course, the use of X2 technology pays off in your case.
Reprinting is not prohibited,
with attribution and a link to this site.
External low-temperature corrosion occurs as a result of the formation of drops or a film of moisture on heating surfaces and reacts with the metal surface.
Moisture appears on heating surfaces during the condensation of water vapor from flue gases due to low water (air) temperature and correspondingly low wall temperature.
The dew point temperature at which water vapor condenses depends on the type of fuel being burned, its humidity, the excess air coefficient, and the partial pressure of water vapor in the combustion products.
It is possible to eliminate the occurrence of low-temperature corrosion on heating surfaces when the surface temperature on the gas side is 5° C higher than the dew point temperature. This dew point temperature value corresponds to the condensation temperature of pure water vapor and appears during fuel combustion.
When burning fuel (fuel oil) that contains sulfur, sulfuric anhydride is formed in the combustion products. Part of this gas, when oxidized, forms aggressive sulfuric anhydride, which, dissolving in water, forms a film of sulfuric acid solution on the heating surfaces, as a result of which the corrosion process sharply intensifies. The presence of sulfuric acid vapors in combustion products increases the dew point temperature and causes corrosion in those areas of the heating surface whose temperature is significantly higher than the dew point temperature and when burning natural gas it is 55 ° C, when burning fuel oil - 125...150 ° C.
In steam boiler houses, for most cases, the temperature of the water entering the economizer exceeds required temperature because the water comes from atmospheric deaerators with a temperature of 102 ° C.
This issue is more difficult to solve for hot water boiler houses, since the temperature of the coolant in the external pipeline of the heating system entering the boilers depends on the outside air temperature.
You can increase the temperature of the incoming water to the boiler using recirculation hot water from the boiler.
The efficiency and reliability of the water heating system of a hot water boiler depends on the coolant flow through recirculation. As the pump supply increases, the temperature of the water entering the boiler increases, and the temperature of the exhaust gases also increases, which means the efficiency of the boiler decreases. In this case, the energy consumption for driving the recirculation pump increases.
The operating instructions for hot water boilers propose to regulate the operation of the heating water heating system so that the temperature of the water entering the boilers when burning natural gas does not fall below 60 ° C. This requirement reduces the efficiency of their operation, since anti-corrosion measures can be ensured to maintain the temperature of the walls of the heating surfaces , if the temperature is below 60° C. But in this case, it is necessary to take into account the temperature of the walls of the heating surface in the calculations.
Analysis of this kind of calculations shows that, for example, for hot water boilers operating on natural gas, at a gas temperature of 140 ° C, the water temperature at the entrance to the boiler must be maintained at least 40 ° C, i.e. below 60°C, which is suggested by the instructions.
Thus, by changing the operating mode of hot water boilers, you can save thermal and electrical energy in the absence of low-temperature corrosion metal surfaces hot water boilers.