Review of 15 leading manufacturers of double-circuit gas boilers

Factors affecting boiler operation

They are:

1. Design. The equipment may have 1 or 2 circuits. It can be mounted on a wall or on the floor.
2. Normative and actual efficiency.
3. Proper heating arrangement. The power of the equipment is comparable to the area that needs to be heated.
4. Technical conditions of the boiler.
5. Gas quality.

Question about the design.

The device may have 1 or 2 circuits. The first option is complemented by an indirect heating boiler. The second one already has everything you need. And the key mode in it is the provision of hot water. When water is supplied, heating ends.

Models mounted on the wall have less power than those placed on the floor. And they can heat a maximum of 300 sq.m. If your living space is larger, you will need a floor-mounted unit.

P.2 efficiency factors.

The document for each boiler reflects the standard parameter: 92-95%. For condensation modifications it is approximately 108%. But the actual parameter is usually 9-10% lower. It decreases even more due to heat losses. Their list:

1. Physical underburning. The reason is excess air in the apparatus when gas is burned, and the temperature of the exhaust gases. The larger they are, the more modest the efficiency of the boiler.
2. Chemical underburning. What is important here is the volume of CO2 oxide produced when carbon is burned. Heat is lost through the walls of the apparatus.

Methods for increasing the actual efficiency of a boiler:

1. Removing soot from pipelines.
2. Elimination of scale from the water circuit.
3. Limit chimney draft.
4. Adjust the position of the blower door so that the coolant reaches its maximum temperature.
5. Removing soot from the combustion compartment.
6. Installation of a coaxial chimney.

P.3 Questions about heating. As already noted, the power of the device necessarily correlates with the heating area. A competent calculation is needed. The specifics of the structure and potential heat losses are taken into account. It is better to entrust the calculation to a professional.

If the house is built according to building codes, the formula works: 100 W per 1 sq.m. This results in a table like this:

It is better to purchase foreign-made boilers. Also in advanced versions there are many useful options that help you achieve the optimal mode. One way or another, the optimal power of the device is in the spectrum of 70-75% of the highest value.

The optimal operating mode of a gas boiler to save gas is achieved by eliminating clocking. That is, you need to set the gas supply to the lowest value. The attached instructions will help with this.

Accurate calculation is the key to the longevity of a gas boiler

Please note: the roughly averaged “10 m² of area per 1 kW of power” has nothing to do with a correct calculation.
It is imperative to take into account the multi-component factors that characterize the heat loss of a room. You cannot ignore the number of floors, cubic footage, type of ventilation, and “outboard” temperature. Don’t forget about the expected effect of the boiler. Difficult? Use an online calculator. Where, by indicating the data you know about the dimensions of the building, the material of the walls, your preferences and the climatic characteristics of the region, you get a fairly accurate calculation of the power of the gas boiler. Then you can move on to specific offers from manufacturers. Summary table of models of gas double-circuit boilers

Adjustment

Automatic control is provided by the heating regulator.

It includes the following parts:

1. Computing and matching panel.
2. Actuating device on the water supply section.
3. An actuator that performs the function of mixing liquid from the returned liquid (return).
4. Boost pump and sensor on the water supply line.
5. Three sensors (on the return line, on the street, inside the building). There may be several of them in the room.

The regulator closes the liquid supply, thereby increasing the value between return and supply to the value specified by the sensors.

To increase the flow, there is a boost pump and a corresponding command from the regulator. The incoming flow is controlled by a "cold bypass". That is, the temperature decreases. Some of the liquid that has circulated along the circuit is sent to the supply.

Sensors collect information and transmit it to control units, resulting in a redistribution of flows that provide a rigid temperature scheme for the heating system.

Sometimes, a computing device is used that combines hot water and heating regulators.

The hot water regulator has a simpler control scheme. The hot water sensor regulates the flow of water with a stable value of 50°C.

Advantages of the regulator:

1. The temperature scheme is strictly maintained.
2. Elimination of overheating of the liquid.
3. Fuel and energy efficiency.
4. The consumer, regardless of the distance, receives heat equally.

Table with temperature graph

The operating mode of boilers depends on the environmental weather.

If we take various objects, for example, a factory building, a multi-storey building and a private house, they will all have an individual thermal diagram.

In the table we show the temperature diagram of the dependence of residential buildings on outside air:

There are certain standards that must be observed in the creation of projects for heating networks and the transportation of hot water to the consumer, where the supply of water steam must be carried out at 400°C, at a pressure of 6.3 Bar. It is recommended that the heat supply from the source be released to the consumer with values ​​of 90/70 °C or 115/70 °C.

Regulatory requirements must be met in compliance with the approved documentation with mandatory approval from the Ministry of Construction of the country.

Link to download the chart

• 110 - for industrial premises of categories B, D and D with emissions of flammable dust and aerosols;
• 130 - for industrial premises without the release of flammable dust and aerosols.

The maximum temperature, °C, of ​​the heating surface should be taken as follows:

• c) for low-temperature panels for radiant heating of workplaces - 60.
• d) for high-temperature radiant heating devices - 250.
• e) for building structures with built-in heating elements:
• — 26 — for floors of rooms with constant occupancy;
• — 30 ​​— for bypass paths, benches of swimming pools;
• — 31 — for floors of premises with temporary occupancy;
• - 28, 30, 33, 36, 38 for ceilings with a room height not exceeding 2.8, 3.0, 3.5, 4 and 6 m, respectively.

Thermona spol. s ro

All activities of the Czech company Thermona, spol. s ro is aimed at developing its own production base. The refusal to cheaply assemble gas boilers abroad indicates a desire to maintain the achieved quality indicators. Thanks to which reliable mounted and highly productive floor models are widespread in the Russian Federation. Each device features automatic flame modulation and equithermal (taking into account the main climatic factors of the external environment) regulation. There are options with open and closed chambers. The installation, configuration and maintenance of these devices can be entrusted to one of the two hundred authorized service centers in Russia. Some models of gas boilers Thermona, spol. s ro

Watch a video about Thermona, spol. s ro:

What happens when hot water is turned on simultaneously at two points of intake

The scheme becomes more complicated if, while using hot water at one point of intake, it becomes necessary to turn it on at another point, for example: when the shower is turned on in the bathroom, it becomes necessary to wash your hands in the toilet washbasin. In this case:

• the rate of hot water use increases sharply, its consumption increases,
• weak pressure of hot water appears;
• the flow of cold water into the boiler increases,
• a drop in the temperature of the boiler heat exchanger leads to the fact that the water temperature at the first intake point ceases to be comfortable,
• a few seconds are required to turn on the boiler automation for heating,
• a few more seconds for both users at two points of collection to be able to use water at a comfortable temperature.

All this time, both users cannot fully use hot water. It arrives intermittently. The unproductive consumption of water, which goes uselessly into the sewer system, increases sharply.

What if one of the users turned off the water? In this case, the consumption of hot water drops sharply. A temperature jump occurs on the heater of a double-circuit gas boiler. As a result, the temperature of hot water increases sharply at the point of intake that continues to operate. The user cannot fully use the water; it goes down the drain until the automation on the boiler is activated and water at the required temperature begins to flow to the user in a stable manner.

Since such situations are repeated several times every day, the unproductive consumption of hot water increases every day. At the same time, we should not forget about the discomfort that users experience when the supply of hot water is unstable.

Types of double-circuit gas boilers

The type of gas boilers is divided according to several criteria:

1. According to the principles of using combustion products:
   convection;
2. condensation
3. According to the design provided in the heat exchanger:
   separate;
4. bithermic.
5. By type of combustion chamber:
   closed;
6. open.

The first type has a number of advantages and disadvantages, namely the fact that thermal energy is not used to its full potential is attributed to the disadvantages. The advantages include relative ease of use and budget price.

The advantages of the second type include a separate design, since if any of the parts fails, it can be replaced - this will be very problematic with a monolithic block. The disadvantages include the following: when a person takes a shower, the water must be turned on a little in advance, because it heats up to such an extent that you can get a thermal burn.

For combustion chambers, a closed type chamber is preferable, as it is safer.

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 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.

LLC "GAZLUX Trade"

Heating equipment from GAZLUX Trade LLC has been on sale since 2006. The boilers, developed by three Russian companies, were found to be profitable in a highly competitive environment. Today, models with bithermic and separate heat exchangers, open and closed combustion chambers are available in the Russian Federation. The control panel is available with an information board or LED display. The modulating burner determines a wide range of settings. Auto-ignition and flame control functions bring these boilers to a decent level of comfort and safety. Some models of gas boilers LLC "GAZLUX Trade"

Watch the promotional video of GAZLUX Trade LLC:

Coordination of coolant and boiler temperatures

Regulators help coordinate the temperature of the coolant and the boiler.
These are devices that create automatic control and adjustment of return and supply temperatures. The return temperature depends on the amount of liquid passing through it. Regulators cover the liquid supply and increase the difference between the return and supply to the level required, and the necessary indicators are installed on the sensor.

If the flow needs to be increased, a boost pump can be added to the network, which is controlled by a regulator. To reduce the heating of the supply, a “cold start” is used: that part of the liquid that has passed through the network is again transported from the return to the inlet.

The regulator redistributes the supply and return flows according to the data collected by the sensor, and ensures strict temperature standards for the heating network.

Viessmann

The international company Viessmann Werke GmbH & Co. KG offers on the Russian market more than 50 modifications of 3 basic models of gas boilers. Automatic ignition of the burner, flame control and many sensors involved determine safety and ease of use. The boilers are programmed for periodic self-diagnosis. Well-thought-out device systems eliminate frequent interference with its operation. Service center specialists are invited to prepare for the first start-up and conduct annual maintenance. Some models of Viessmann gas boilers

Watch a video about Viessmann:

What is the difference between heating flow and return?

And so, let’s summarize the differences between supply and return in heating:

• Supply – coolant that flows through water pipes from a heat source. This could be an individual boiler or central heating of the house.
• Return water is water that, having passed through all the heating radiators, goes back to the heat source. Therefore, at the input of the system there is supply, and at the output there is return.
• It also differs in temperature. The feed is hotter than the return.
• Installation method. The water conduit that is attached to the top of the battery is the supply; the one that connects to the bottom is the return line.

After installing the heating system, it is necessary to adjust the temperature regime. This procedure must be carried out in accordance with existing standards.

Requirements for coolant temperature are set out in regulatory documents that establish the design, installation and use of engineering systems of residential and public buildings. They are described in the State Building Codes and Rules:

• DBN (V. 2.5-39 Heat networks);
• SNiP 2.04.05 “Heating, ventilation and air conditioning.”

For the calculated supply water temperature, the figure is taken that is equal to the water temperature at the outlet of the boiler, according to its passport data.

For individual heating, deciding what the coolant temperature should be should take into account the following factors:

1. The beginning and end of the heating season based on the average daily outdoor temperature of +8 °C for 3 days;
2. The average temperature inside heated premises of housing, communal and public importance should be 20 °C, and for industrial buildings 16 °C;
3. The average design temperature must comply with the requirements of DBN V.2.2-10, DBN V.2.2.-4, DSanPiN 5.5.2.008, SP No. 3231-85.

According to SNiP 2.04.05 “Heating, ventilation and air conditioning” (clause 3.20), the coolant limit values ​​are as follows:

Depending on external factors, the water temperature in the heating system can be from 30 to 90 °C. When heated above 90 °C, dust and paintwork begin to decompose. For these reasons, sanitary standards prohibit greater heating.

To calculate optimal indicators, special graphs and tables can be used, which define standards 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. On the supply side it is from 95 to 105 °C, and on the return side it is 70 °C.

Gas double-circuit wall-mounted boiler: how to choose

The desire of many apartment owners to achieve maximum autonomy and independence from city utilities is quite understandable. One of the main issues in this regard is creating your own heating system. This allows you to independently determine the start and end dates of your “local heating season”, setting the desired temperature in the premises at any time of the year, without freezing if the cold in the fall came too early or the arrival of spring was too long, and without suffering from the heat if the situation develops in a diametrically opposite way. And from the point of view of payment for services, it turns out to be much more profitable. Therefore, the installation of individual heating boilers is becoming an increasingly popular trend among homeowners.

Gas double-circuit wall-mounted boiler: how to choose

Well, if the owners plan to create their own autonomous heating system, then it would be quite reasonable, in parallel with this, to immediately resolve the issue of independent hot water supply. It is no secret that almost everywhere with the supply of hot water various “surprises” occur throughout the year, and in addition, prices for utilities tend to constantly increase. Thus? own heating and hot water supply system means not only “technical”, but also, to a certain extent, financial independence. In addition, an important aspect is the gas consumption in the boiler.

Of course, the limited space conditions of apartments in multi-storey buildings limit the owners in the choice of boiler equipment. However, there is a way out - this is a double-circuit wall-mounted gas boiler, how to choose which will be discussed in this publication.

Operating principle of double-circuit boilers

Today, in cities, network gas remains the most inexpensive source of energy. If a multi-storey building is connected to a gas main, then for sure, despite certain administrative and technological difficulties in installing the appropriate equipment, such a heating and hot water supply system will become the most profitable. By paying bills only for the actual consumption of “blue fuel”, the owners receive in return both independent heating and an uninterrupted supply of hot water for household needs. Moreover, the timing of switching on and the heating temperature all depend on the wishes of the apartment owners.

With a certain simplification, the principle of connecting a double-circuit boiler can be schematically depicted as follows:

Approximate connection diagram for a double-circuit boiler

The boiler itself (item 1) is placed on the wall in the most convenient place, where there will be a connection to the gas main (item 2) and to the combustion product removal system.

Hot water circuit. A cold water supply pipe is connected to the boiler (item 3, blue arrows). Heated water is distributed (pos. 4, red arrows) through a collector or corner circuit to points of consumption - in the bathtub (pos. 5), shower stall (pos. 6), kitchen sink (pos. 7), etc.

The heating circuit is closed. The circulation pump (most often it is a structural unit of the boiler itself) ensures the movement of the coolant through the supply pipes (item and return pipes (item 9). Depending on the specific features of the heating system, ordinary radiators (item 9) can be connected to the heating circuit. 10), water heated floors (pos. 11), convectors of one type or another (pos. 12). If desired, other devices can be embedded here, for example, heated towel rails (pos. 13).

Thus, five pipes fit and connect to the wall-mounted double-circuit boiler:

• Gas main.
• Supply of the heating circuit with further distribution to priors or heat exchange systems.
• "Return" of the heating circuit.
• Cold water inlet
• The outlet of the heated water supply system for domestic needs with subsequent distribution to water intake points.

Inside the boiler itself, both circuits - heating and hot water supply - do not directly intersect, which makes it possible, if desired or necessary, to use a special coolant in the heating circuit.

By and large, this is a fundamental difference with single-circuit boilers, many of which have the ability to connect to a hot water supply system, but only through an indirect heating boiler.

Differences in the connection diagram of a boiler with an indirect heating boiler

Look at the diagram. Everything seems to be the same, but the points of consumption of hot domestic water are connected to an indirect heating boiler. And this, in turn, is connected to a dedicated boiler circuit, through which the same coolant circulates as in the heating system.

Even if such a boiler has four water pipes at the outlet - two for heating circuits, and two for an indirect heating boiler, it will still not be considered double-circuit. It’s just that its internal design provides for rational redistribution of coolant flows with the necessary automation of this process. But the heat exchanger is used alone, and the composition of the liquid circulating in both circuits is no different.

A system using an indirect heating boiler has a number of significant advantages. In particular, it is possible to organize local closed recirculation of hot water supply - at any time, whenever the tap is opened, hot water at the set temperature will immediately flow out of it.

You may be interested in information on how to choose a voltage stabilizer for a gas boiler

But there are also several negative aspects. Firstly, the cost of such a kit is always quite high. And secondly, and for small apartments, perhaps the most important thing, installing a boiler and boiler will require a considerable area, which is not always possible.

It is in such conditions that a double-circuit wall-mounted boiler will help out. Its main advantages:

• Compactness - it does not take up much space, and at the same time, as a rule, does not disharmonize with the kitchen interior.

Wall-mounted boilers fit well into the interior

• Two problems are solved at once - heating the apartment and meeting the needs for hot water. The owners largely get rid of the “whims” of public utilities.
• Such boilers, when installed correctly and with a well-thought-out, balanced autonomous heating system, are very economical - this will certainly be immediately noticeable in the amount of monthly utility costs.
• The total cost of purchasing and installing a double-circuit boiler will be significantly lower than for a single-circuit boiler with an indirect heating boiler.

However, double-circuit boilers are not without significant disadvantages:

• These devices operate in only one mode at a time. For example, if it is necessary to heat domestic water, the boiler switches completely to water supply, temporarily turning off the heating circuit.
• As in the case of a gas water heater, there is a certain “inertia” - when you open the tap, you will have to wait until the cold water remaining in the pipes flows out and until the boiler “accelerates” to the desired heating temperature.
• Many double-circuit boilers are very limited in the volume of heating running water. So, taking a shower and washing dishes at the same time will either not always be possible or uncomfortable - when you close one tap, a temperature jump will inevitably occur in the other. True, many modern devices are equipped with an internal boiler, which eliminates this disadvantage.

Overgrowth of heat exchanger channels

• If in a single-circuit boiler the purity of the coolant can be achieved, then in a double-circuit boiler, tap water is also heated, which is not always and not always of different quality. This poses a certain risk of overgrowth of the heat exchanger tubes, which will either have to be cleaned regularly or replaced with new ones.

Which double-circuit wall-mounted boiler should I choose?

The boiler connection diagram shown above is very arbitrary, and in no way covers the variety of these devices. So in order to correctly determine the right model, it is necessary to take a closer look at the main selection criteria.

Boiler power and performance

• The boiler must fully cope with its main task - to ensure the operation of an autonomous heating system. This means that one of the basic selection criteria is its thermal power.

Experts calculate the total amount of heat required by an apartment or house based on many factors - from the area and volume of the premises to the material of the walls, the degree of insulation of the building and the climate zone of residence. To independently determine the required boiler power, you can, with acceptable simplification, proceed from the standard of 10 m² of area of ​​sealed premises per 1 kW. this rule will be valid with an average ceiling height of up to 2.5 - 3 m, and if the rules of proper thermal insulation are still followed in the house (apartment).

It is clear that the heating device should not operate at the peak of its capabilities, so it is better to provide a certain reserve, especially in the case when the insulation of a high-rise building still does not inspire complete confidence. Plus, the boiler needs additional power to heat water. In a word, it would not be a mistake to add another 30 ÷ 35% to the obtained value.

Most modern double-circuit boilers have a fairly wide power range. Technical documentation usually indicates its minimum and maximum values. For example, useful thermal power: 9.3 ÷ 14 kW.

• The second component of the problem is the performance of the device for heating water for domestic needs. If there is no boiler, then heating will be carried out according to a flow-through circuit, and the selection parameter depends on the number of water points that can operate simultaneously. It is clear that the more liters per minute the boiler can heat, the better.

Typically, the technical documentation of double-circuit boilers indicates several performance values, with different indicators of the temperature difference at the inlet and outlet. Usually they operate with the values ​​Δt° = 25 and 35 degrees. This is not the temperature of the water at the outlet, but rather the increase in its value compared to the input. For example, in the summer, the water in the water supply may be 15° C, and at Δt° = 25°, 40° will flow into the taps, which is quite enough for taking a shower.

In principle, a productivity of about 10 ÷ 11 l/min at Δt° = 25°C, and 7 ÷ 8 l/min at Δt° = 35°C is considered very good performance.

All these considered characteristics will be valid only if the gas pressure in the main and water in the water supply correspond to the parameters specified by the manufacturer. You should also pay close attention to this.

Type and number of heat exchangers

According to the principle of heating water for domestic hot water, boilers can vary significantly. So, there are two main types of such devices - with a secondary heat exchanger and with a bithermic one. Each type has its own characteristics.

The main heat exchanger of the boiler, which is responsible for the most energy-intensive function, heating, is always located above the gas burners. And water heating can take place in the same place, or with heat transfer from the heated coolant through an additional device - a secondary heat exchanger.

Double-circuit boilers with a secondary heat exchanger

The primary heat exchanger itself is a metal structure - a curved pipe, the turns of which are united by plate ribs to increase the heat exchange area from the hot combustion products to the circulating coolant. In this version of the boiler, such a heat exchanger has two pipes - inlet and outlet.

Boiler primary heat exchanger

Heating of water for domestic needs is carried out in a secondary heat exchanger, which is located below the combustion chamber and has no contact with the burner flame. Typically this element has a compact plate design.

Secondary heat exchanger - more compact, plate type

There are already four pipes here, and inside there are two circuits for counter-flow of liquid. In one way, the heated coolant circulates, giving off heat, in the second, tap water receives it.

The operating principle of such a boiler is shown in more detail in the diagrams.

• The boiler is operating in heating mode.

Boiler operation in heating mode

Above the gas burner (item 1) there is a primary heat exchanger (item 3). The combustion of gas supplied through the line (yellow arrow) leads to heating of the coolant in the circuit. The circulation pump (item 5) ensures the movement of liquid through the heating pipes. The three-way valve with a servo drive (item 7) is in a position in which the valves open the flow from the return of the heating circuit and at the same time close the entrance to the secondary heat exchanger.

Prices for Baxi gas boilers

gas boiler Baxi

As a result, circulation occurs “in a large circle”, through heating collectors and installed heating devices.

The diagram additionally shows the built-in expansion tank (item and safety group - safety valve and automatic air vent (item 9).

• What happens when you open a hot water tap?

Operation in water heating mode for DHW

Water flow begins through the pipes of the DHW circuit. This causes the flow sensor turbine (position 6) to rotate. The signal from the sensor enters the automation unit, where a control pulse is generated to the three-way valve (item 7). The valve moves to the position in which the valve closes the inlet from the heating return, but opens the inlet to the secondary heat exchanger. In this case, the pump does not turn off, ensuring the circulation of the heated coolant in a “small circle”.

While using hot water, the circulation of coolant through the heating circuit is suspended.

In the event that this happens during a period when the heating is completely turned off, when the hot water tap is turned on, the flow sensor will transmit a signal to the control unit, which will start the circulation pump, open the gas valve and trigger the electronic igniter (item 2). The gas heaters (item 3) are ignited, and the circulation of the coolant begins through the secondary heat exchanger, transferring thermal energy to the water.

Advantages of boilers with a secondary heat exchanger:

• Double heat exchange eliminates the possibility of getting burned by overheated water. Under any circumstances, if the temperature in the primary circuit can reach 80 ° C, then in the secondary circuit it will not rise above 60.
• For the same reason, and also because heating occurs exclusively during circulation in both circuits at the same time, the build-up of scale in the secondary heat exchanger is much less than in boilers with a bithermal heat exchanger.
• The primary heat exchanger tubes can be made thicker and are less at risk of clogging or fouling.
• Even a clogged primary heat exchanger can be washed and cleaned.
• Such a boiler is more maintainable - each unit can be removed, cleaned or even replaced. The cost of each heat exchanger separately is not so high.

Disadvantages of boilers with secondary heat exchange in the DHW circuit

• The price of such equipment is higher than with a bithermal heat exchanger.
• The presence of an additional electromechanical valve (three-way valve) is an extra vulnerable point for breakdown.

Video: a short “lecture” on the construction of a wall-mounted double-circuit boiler

Boilers with bithermal heat exchanger

In these types of boilers, both heat exchange circuits are combined into one structural unit.

Bithermal heat exchanger - outside view...

Externally, the heat exchanger seems to be similar to the primary one, which was already mentioned above. But there are only four pipes - a pair each for heating and hot water supply.

... and he is in the cross-section

If you look at a cross-section of such a heat exchanger, you can see that the tubes have a cellular structure. Hot water circulation circulates through the central channel. External channels (in this case, four) are intended for circulation of the heating system coolant.

If only the heating is turned on, the circulation pump ensures the movement of the coolant, and the water in the central channel is motionless.

Scheme of operation of a boiler with bithermal heat exchange

When you open the hot tap on the mixer, under the influence of the water supply pressure, water begins to move through the inlet pipe (item 1) towards the outlet pipe (item 2). The flow sensor through the control unit turns off the circulation pump of the heating system, and the movement of the coolant stops. The heat from the burners is taken over by the heated water. When the tap is turned off, the pump resumes operation, and the heating system becomes the main one.

Advantages of such a scheme:

• One heat exchanger takes up much less space. In addition, there is no three-way valve with a servo drive or additional piping. This makes the entire structure of the double-circuit boiler much lighter and more compact.
• Although a bithermal heat exchanger is a rather complex part in terms of manufacturing technology, its cost is still lower than two separate heat exchangers. This also affects the price of the boiler.

The disadvantages are very significant:

• In any mode, in one of the heat exchanger circuits the liquid is stationary, but is subject to heating. This leads to fairly rapid scale formation and overgrowing of the channels.
• The relatively narrow clearance of all channels also leads to the same consequences. Overgrowth of at least one of them leads to a decrease in boiler performance and the appearance of unpleasant noises.
• While the hot water supply circuit is closed, the water continues to heat up and reaches the same temperatures as the heating fluid. When you open a tap, very hot water may initially flow, which can scald your skin. To minimize such a risk, they try to limit the overall heating temperature using hardware and software methods (not higher than 70 ÷ 75 ° C, although this is already too much). But such a reduction simultaneously entails a reduction in the possible thermal output of the boiler for the heating system.
• A bithermal heat exchanger is more difficult to manufacture, and the presence of a large number of joints greatly increases the likelihood of leaks. Cleaning such a structure from scale is much more difficult. Well, if a leak occurs (especially between the external and internal circuits), such a heat exchanger is practically beyond repair and requires mandatory replacement. But its cost is much higher than both primary and secondary in other types of boilers.

Thus, in terms of these positions, a boiler with secondary heat exchange in the hot water supply circuit still looks preferable.

Prices for Vaillant gas boilers

Vaillant gas boiler

There is another innovative type of double-circuit boilers - with a condensation-type primary heat exchanger. They are designed with an eye to a fairly serious effect of saving gas consumption at the same or even higher thermal power levels.

Double-circuit condensing boiler

The fact is that one of the combustion products of natural gas is always water vapor. In conventional boilers, it is simply released into the atmosphere, and meanwhile its thermal energy (temperature reaches 110 - 140 ° C) can additionally be used to heat the coolant.

One of the models of condensation type heat exchangers

A special heat exchanger device ensures steam condensation with heat release. Studies have shown that steam potentially stores up to 11% of the total heat generated by the boiler, and if their unreasonable losses are returned to heat exchange, then gas savings over the season can reach 30% of the usual consumption level.

Of course, such energy-saving boilers are the future, and in many countries they have taken leading positions in popularity. The only thing that still holds them back from widespread use in our area is the very high price.

Type of combustion products exhaust system

Boilers are divided into two large subgroups - with an open combustion chamber and with a closed one. Accordingly, they are spilled into systems for supplying the air necessary for gas combustion and for removing combustion products into the atmosphere.

Chimney boilers with an open combustion chamber

An open combustion chamber assumes that air enters the burners naturally, from the room in which the boiler is located. The combustion products, also naturally rising upward, are redirected to the pipe to which the chimney pipe is connected. In a word, the effect of natural draft is used, based on the difference in the density of cold and heated gases.

This is what a boiler with an open chamber looks like with the casing removed

The advantages of such a boiler:

• The operation does not require a special fan. This means the absence of noise and lower power consumption of the boiler.
• The contraction does not have complex air injection and control elements (pneumatic relays), therefore, the overall reliability of the device is higher.
• A chimney assembled in accordance with all the rules solves the problem of condensation formation.
• Chimney boilers are cheaper than turbocharged boilers.

Flaws:

• Air enters the combustion chamber directly from the room. This means that the issues of constant supply ventilation should be considered. And this very often leads to excessive heat loss in the premises and the appearance of drafts.
• There are special, fairly strict rules for the design and installation of a chimney. This often leads to large-scale repair and construction work and serious expenses - otherwise you will not be able to obtain permission to install the boiler.
• Installing a chimney is not possible in principle in all buildings.

Flueless boilers with a closed combustion chamber.

Such boilers are often called turbocharged. The air for them is supplied from the street forcibly, using a special fan-turbine; accordingly, combustion products are also thrown out into the street by the created pressure.

A turbocharged boiler always indicates the presence of a fan

The chamber itself is completely closed, and exhaust gases cannot enter the room.

The supply of air and the emission of combustion products can be carried out through two separate pipes, but the vast majority of modern boilers of this type provide for the installation of a coaxial system - a “pipe in a pipe”, which is discharged through the wall to the outside.

Coaxial chimney

Inside the outer pipe, usually 100 mm in diameter, a second pipe with a diameter of 60 mm is located coaxially. Through the space between the outer wall and the inner pipe, air is forcedly drawn in from the street. The internal channel serves for the exit of combustion products.

Advantages of such a system:

• There are practically no significant restrictions on its installation.
• There is no need to provide fresh ventilation in the room.
• The cost of such boilers is slightly higher, but it is fully justified by the absence of large-scale work on the design and construction of the chimney.

The disadvantages are the following:

• A significant temperature difference in the outer and inner pipes is accompanied by the formation of condensation. In severe frosts, this can lead to icing, impairing the permeability of the chimney and, accordingly, insufficient vacuum in the chamber for the automation to operate.
• Mandatory elements of the system are a pneumatic relay, a fan and a fan switch relay. All of them have a certain resource, and failure of any of them leads to failure of the boiler.
• The fan creates noise when operating. In addition, this is an additional energy consumption.

Conclusion: a boiler with an open combustion chamber and a conventional chimney looks more reliable in operation. But turbocharged boilers are easier to install and have no special restrictions on the installation location.

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Controls, automation, protection levels

The boiler must be fairly easy to use, have clear controls, be equipped with the necessary functions to optimize operation and several degrees of protection against emergency circumstances.

Modern boilers are equipped with convenient display and control panels

Leading manufacturing companies are constantly improving their models, thereby creating competition between brands, so new developments are constantly appearing. Thus, modern boilers can be equipped with the following options:

• Flame modulation in heating and water heating modes. The flame level is electronically regulated, ensuring smooth starts, which is especially important for models with instantaneous heating of DHW water. The automation independently selects the height of the flames depending on the set temperature and the specific current water flow.

In some models, the last 5 degrees to the set heating temperature of the heating system are gained at a reduced combustion intensity. This allows you to make the operation of the device smoother, reduce the number of starts, and therefore increase the service life of the equipment.

• Similar goals are pursued by a smooth electronic ignition system, when after the appearance of a minimum flame on the burners, it gradually grows to a given combustion intensity within 30 - 40 seconds.

When the boiler operates as a water heater, this option does not apply - what is important here, on the contrary, is the speed of heating the water to a given level.

• Weather-compensated boiler automation. This innovation, when installing an external street sensor, allows the equipment to monitor the level of external temperature and make adjustments to maintain an optimal microclimate in the apartment.

More advanced equipment of this type also has an automatic self-adaptation function. Electronics not only compares graphs of changes in external and internal temperatures, but also conducts an analysis, making adjustments to the operation of the boiler, which leads to maximum comfort and significant gas savings.

• Pump post-circulation. A useful function that, when a room thermostat is installed, can significantly reduce energy consumption. Once the required heating temperature has been reached in the heating system, the boiler turns off and the pump continues to operate for another three minutes. When it is necessary to resume operation, both the boiler and the pump are started simultaneously.
• Naturally, all modern electronically controlled boilers allow you to accurately set the temperature in both the heating circuit and the DHW. In addition, some models provide two switchable ranges in heating mode - for conventional radiators and for heated floors.
• The electronics allow programming of the boiler operation for a certain period of time, with the programs being stored in memory for reuse.
• Any gas equipment has several degrees of protection - in case of insufficient draft, in case of heater extinguishing, in the absence or insufficient water pressure in the circuits, etc. In addition, modern models are equipped with other safety functions. So, if the temperature in the circuits drops to +5 degrees, the boiler will start on its own to bring the heating level of the coolant and water to a safe value, in order to avoid freezing. In addition, some control systems also monitor the condition of the boiler elements. If the device has not been used for more than a day, the processor will turn on the pump for a short time or switch the position of the three-way valve back and forth. This allows you to avoid blocking or “sticking” of these units and extends their service life.

Panel with push-button control and combined, arrow and LCD indication

Control panels can have push-button, touch or electromechanical control, and are equipped with dial or digital indicators of temperature and pressure in the system.

Prices for popular gas boilers

Dimensions, “appearance”, manufacturing company

A mandatory evaluation criterion should be the dimensions of the boiler - they must correspond to the dimensions of the place where it is planned to be installed. This takes into account both the location of the gas main and the possibility of connecting to a chimney or installing a coaxial system. There are certain restrictions in these matters, for example, on the length of the coaxial pipe - this must be clarified in the product passport.

Boiler with built-in boiler

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Perhaps, if the installation area allows, it makes sense to purchase a boiler with a built-in boiler - its dimensions are certainly larger, but its ease of use is incomparably higher - this has already been mentioned.

For many owners, an important selection criterion is the design of the boiler. It is difficult to give advice here - the main thing is that the device does not spoil the interior. Most of the boilers have a matte white finish, which fits perfectly into any style.

No matter how much you like a particular model on sale, you should always give preference to reputable brands. Leading manufacturing companies provide a solid guarantee for their equipment, and since the boiler can be considered an expensive purchase, this fact is very important.

Very popular modern model “Baxi - Luna3″

European companies, Beretta, Baxi, Vaillant, Bosch, enjoy well-deserved authority and an untarnished reputation. Protherm, Buderus, Ariston and other companies have proven themselves well. You can completely trust the products of Korean, Daewoo, Celtic, Kiturami - in terms of equipment with modern electronics, they are sometimes superior to Europeans.

Video: wall-mounted double-circuit gas boilers Daewoo

You should be careful with Chinese technology, despite its relatively low price. Well, a brand “unknown to science” should be discarded immediately, no matter how attractive the model may seem.

When choosing between manufacturers, you should clarify whether there are service centers in the region, how difficult it will be to send equipment for maintenance or for replacement due to a complaint. Probably, you should not purchase a boiler from even the most popular manufacturer, if in a given area it is “exotic”, and the search for any trifling detail will be difficult.

You may be interested in information about what types of wall-mounted double-circuit gas heating boilers are available, prices, reviews

So, in order to choose a truly high-quality wall-mounted double-circuit boiler that is fully suitable in all respects, you should evaluate many criteria, understand the device, carefully study the technical documentation for the model you like, and compare its technical characteristics with the existing conditions of the planned operation. You should not chase the cheap - this purchase is made with the expectation of many years of service, and the stingy, as we know, pays twice.

Dependence of coolant temperature on outside air temperature

The specific table of the relationship between outdoor temperature and coolant depends on factors such as climate, boiler room equipment, and technical and economic indicators. Reasons for using a temperature schedule The basis for the operation of each boiler house serving residential, administrative and other buildings during the heating season is a temperature schedule, which indicates the standards for coolant indicators depending on what the actual outside temperature is.

• Drawing up a schedule makes it possible to prepare the heating for a drop in outside temperature.
• It also saves energy resources.

ATTENTION! In order to control the temperature of the coolant and have the right to recalculate due to non-compliance with the thermal regime, a heat sensor must be installed in the centralized heating system

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, since the rules require that the working surface of the heating device have a smooth surface and allow dust and dirt to be easily removed. A dirty coating forms on the rough inner surface of the sections, which reduces the heat transfer of the device. But the technical parameters of cast iron products are excellent:

• 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. A single-pipe heating system can be vertical or 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 water pressure. Two-pipe heating system 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. Temperature standards for premises In a residential building, the temperature in corner rooms should not be lower than 20 degrees, for interior spaces the standard is 18 degrees, for showers - 25 degrees.

How is it calculated

A control method is selected, then a calculation is made

The calculated winter and reverse order of water supply, the amount of outside air, and the order at the break point of the diagram are taken into account. There are two diagrams: one of them considers only heating, the second considers heating with hot water consumption

For an example of calculation, we will use the methodological development of Roskommunenergo.

The input data for the heat generating station will be:

1. Tnv – the value of outside air.
2. TV - indoor air.
3. T1 – coolant from the source.
4. T2 – reverse flow of water.
5. T3 – entrance to the building.

We will look at several heat supply options with values ​​of 150, 130 and 115 degrees.

At the same time, at the exit they will have 70°C.

The results obtained are compiled into a single table for subsequent construction of the curve:

So, we have three different schemes that can be used as a basis. It would be more correct to calculate the diagram individually for each system. Here we examined the recommended values, without taking into account the climatic features of the region and the characteristics of the building.

To reduce energy consumption, it is enough to select a low temperature setting of 70 degrees and uniform heat distribution throughout the heating circuit will be ensured. The boiler should be taken with a power reserve so that the system load does not affect the quality operation of the unit.

Types of gas boilers with two circuits

The operating features of gas equipment are largely determined by the design version of the heating device. Modern boilers are available in two form factors - floor-mounted and wall-mounted.

When choosing a design option, you need to focus on the size of the heated area and the activity of using the hot water system. You need to understand that wall-mounted boilers are more compact, but at the same time they have much less power.

The double-circuit wall-mounted gas boiler has a compact size and modern design, but is only effective when heating small areas with moderate hot water consumption

The choice of a wall-mounted double-circuit boiler may be justified if the heated area does not exceed 200 sq.m, and the total productivity of the hot water system does not exceed 14 l/min.

The small size of a wall-mounted boiler, although it seems like an advantage, actually hides many disadvantages. Compactness is achieved through the use of thinner heat exchanger tubes. In addition to the fact that they have a shorter service life, there is a possibility of clogging.

In floor-standing installations, more massive and reliable cast iron heat exchangers are used. This not only increases the reliability of the heating device, but also extends its service life.

Protection against low coolant temperature in the return of a solid fuel boiler.

What will happen to a solid fuel boiler if its return temperature is below 50 °C? The answer is simple - a tarry coating will appear on the entire surface of the heat exchanger. This phenomenon will reduce the performance of your boiler, make it much more difficult to clean, and most importantly, can lead to chemical damage to the walls of the boiler heat exchanger. To prevent such a problem, it is necessary to provide appropriate equipment when installing a heating system with a solid fuel boiler.

The task is to ensure the temperature of the coolant that returns to the boiler from the heating system at a level not lower than 50 °C. It is at this temperature that the water vapor contained in the flue gases of a solid fuel boiler begins to condense on the walls of the heat exchanger (transition from a gaseous state to a liquid one). The transition temperature is called the “dew point”. The condensation temperature directly depends on the moisture content of the fuel and the amount of hydrogen and sulfur formations in the combustion products. As a result of a chemical reaction, iron sulfate is obtained - a substance useful in many industries, but not in a solid fuel boiler. Therefore, it is quite natural that manufacturers of many solid fuel boilers remove the boiler from warranty if there is no return water heating system. After all, here we are not dealing with the burning of metal at high temperatures, but with chemical reactions that no boiler steel can withstand.

The simplest solution to the problem of low return temperature is to use a thermal three-way valve (anti-condensation thermostatic mixing valve). The thermal anti-condensation valve is a thermomechanical three-way valve that ensures the admixture of coolant between the primary (boiler) circuit and the coolant from the heating system in order to achieve a fixed boiler water temperature. In essence, the valve releases the coolant that has not yet been heated in a small circle and the boiler heats itself. After reaching the set temperature, the valve automatically opens the coolant to the heating system and operates until the return temperature again drops below the set values.

Solid fuel boiler piping - Anti-condensation valve

Simple calculation by area

The simplest rough calculation of the power of a water supply boiler can be performed based on the thermal energy needs of the house at 100 watts per square meter. For a house with an area of ​​100 m2, 10 kW is therefore required.

100 watts of heat is taken per square heated area

Additionally, a safety factor of 1.2 is introduced, compensating for unaccounted heat losses and helping to maintain a comfortable temperature in the room during extreme frosts. What adjustments does hot water supply from the boiler make to this scheme?

This can be provided in two ways:

1. Storage water heater (indirect heating boiler) . In this case, an additional coefficient of 1.1 is introduced: the boiler takes a relatively small amount of heat from the heating system;

Water supply diagram for a solid fuel boiler with an indirect heating boiler

1. Flow-through heater of a double-circuit boiler . The coefficient used here is 1.2. Taking into account the safety factor, the thermal performance of the boiler should exceed the estimated heat demand of the house by 40 percent. In our example with a 100-meter cottage, when connecting the heating and hot water supply system, the boiler should produce 14 kW.

Connecting the heating system and water supply diagram for a double-circuit boiler

Please note: in the latter case, a small reserve of power for DHW needs is associated with short-term operation of the flow-through heater. Hot water is rarely consumed for more than half an hour a day, and the heating system has a certain inertia, so the coolant parameters do not go beyond standard values.

Simple calculation of a boiler with hot water supply based on the area of ​​the house.
This calculation scheme is simple, but has several serious shortcomings:

• It takes into account the area of ​​the heated room, not its volume. Meanwhile, the heat requirement for cottages with ceiling heights of 2.5 and 4 meters will be very different;

A room with a high ceiling needs more heat

• It ignores differences between climate zones. As is known, the heat loss of a building is directly proportional to the temperature difference between the interior and the street and will vary greatly in Crimea and Yakutia;
• It does not take into account the quality of the building's insulation. For brickwork and a façade insulated with foam plastic, the heat loss will differ significantly.

Insulating the facade can greatly reduce heat loss

Briefly about return and flow in the heating system

The water heating system, using a supply from the boiler, supplies heated coolant to the radiators, which are located inside the building. This makes it possible to distribute heat throughout the house. Then the coolant, that is, water or antifreeze, having passed through all available radiators, loses its temperature and is supplied back for heating.

The most simple heating structure consists of a heater, two lines, an expansion tank and a set of radiators. The conduit through which heated water from the heater moves to the batteries is called the supply. And the water conduit, which is located at the bottom of the radiators, where the water loses its original temperature and returns back, will be called return. Since water expands when heated, the system provides a special tank. It solves two problems: a supply of water to saturate the system; accepts excess water, which is obtained during expansion. Water, as a heat carrier, is directed from the boiler to the radiators and back. Its flow is ensured by a pump, or natural circulation.

Supply and return are present in one and two pipe heating systems. But in the first there is no clear distribution into the supply and return pipes, and the entire pipe line is conditionally divided in half. The column that leaves the boiler is called the supply, and the column that comes out from the last radiator is called the return.

In a single-pipe line, heated water from the boiler flows sequentially from one battery to another, losing its temperature. Therefore, at the very end the batteries will be the coldest. This is the main and probably the only disadvantage of such a system.

But the single-pipe version will have more advantages: lower costs for purchasing materials are required compared to a 2-pipe; the diagram looks more attractive. It is easier to hide the pipe, and you can also lay pipes under doorways. The two-pipe system is more efficient - two fittings are installed in parallel into the system (supply and return).

This system is considered more optimal by experts. After all, its work revolves around supplying hot water through one pipe, and cooled water is discharged in the opposite direction through another pipe. In this case, the radiators are connected in parallel, which ensures uniform heating. Which of them establishes the approach must be individual, taking into account many different parameters.

There are only a few general tips to follow:

1. The entire line must be completely filled with water; air is a hindrance; if the pipes are airy, the heating quality is poor.
2. It is necessary to maintain a sufficiently high fluid circulation rate.
3. The difference in supply and return temperatures should be about 30 degrees.

Optimal values ​​in an individual heating system

Autonomous heating helps to avoid many problems that arise with a centralized network, and the optimal temperature of the coolant can be adjusted according to the season.
In the case of 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 by the design features of the heating devices. It is important to ensure that the coolant in the network does not cool below 70 °C. 80 °C is considered optimal

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.

It is a little more difficult with solid fuel devices; they do not regulate the heating of the liquid, and can easily turn it into steam. And it is impossible to reduce the heat from coal or wood by turning the knob in such a situation. Control of heating of the coolant is quite conditional with high errors and is carried out by rotary thermostats and mechanical dampers.

Electric boilers allow you to smoothly regulate the heating of the coolant from 30 to 90 °C. They are equipped with an excellent overheat protection system.

Protherm

The Slovakian manufacturer Protherm has been supplying domestic and industrial gas boilers to the Russian market since 1997. Equipment with a power range from 11 to 40 kW consists of models of different lines. There are both floor-standing and wall-mounted models. With integrated boilers and heating water for domestic hot water in flow-through mode. This allows each buyer to choose the most optimal equipment for a bathhouse, small country house, apartment or cottage. The boilers have proven themselves in terms of safety and economical operation. The manufacturer provides a maximum 5-year warranty for condensing models. Some models of Protherm gas boilers

Watch the Protherm video:

The influence of temperature on the properties of the coolant

In addition to the factors described above, the temperature of the water in the heating pipes affects its properties. This is the basis of the operating principle of gravity heating systems. As the heating level of water increases, it expands and circulation occurs.

However, if antifreeze is used, exceeding the normal temperature in the radiators can lead to different results. Therefore, for heating with a coolant other than water, you should first find out the permissible heating rates. This does not apply to the temperature of central heating radiators in the apartment, since such systems do not use antifreeze-based liquids.

Antifreeze is used if there is a possibility that low temperatures will affect radiators. Unlike water, it does not begin to change from a liquid to a crystalline state when it reaches 0°C. However, if the heat supply operation exceeds the norms of the temperature table for heating to a greater extent, the following phenomena may occur:

• Foaming
  . This entails an increase in the volume of coolant and, as a result, an increase in pressure. The reverse process will not be observed when the antifreeze cools;
• Formation of limescale
  . Antifreeze contains a certain amount of mineral components. If the heating temperature in the apartment is violated, they begin to precipitate. Over time, this will lead to clogged pipes and radiators;
• Increasing the density index.
  Malfunctions of the circulation pump may occur if its rated power was not designed for such situations.

Therefore, it is much easier to monitor the water temperature in the heating system of a private home than to control the degree of heating of antifreeze. In addition, when evaporating, ethylene glycol-based compounds emit gas that is harmful to humans. Currently, they are practically not used as a coolant in autonomous heat supply systems.