Users of our portal have a unique opportunity to follow how, as part of the project with FORUMHOUSE, we, with our partners, are building a comfortable and energy-efficient country house in the Moscow region. For this purpose, when constructing a cottage, the most modern materials and technology.
USHP was chosen as the foundation, and the heating system was underfloor heating. In addition, the boiler room was equipped with a wall-mounted condensing gas boiler. A technical specialist from the company will tell you in a master class format why this particular equipment was chosen for our project and what the advantages of its operation are.
- Operating principle of a condensing gas heat generator.
- Advantages of using condensing gas boiler.
- In which heating system is it best to use this equipment?
- What to pay attention to when operating a condensing gas boiler.
Operating principle of a condensing gas heat generator
Before we talk about the nuances of condensation technology, we note that an energy-efficient, and therefore comfortable and economical, country house is a balanced structure. This means that, in addition to the closed thermal insulation loop, all elements of the cottage, including engineering system, must be optimally matched to each other. Therefore, it is so important to choose a boiler that fits well with a low-temperature heating system “warm floor”, and will also reduce the cost of purchasing energy in long term.
Sergey Bugaev Ariston technical specialist
In Russia, unlike European countries, condensation gas boilers less common. In addition to environmental friendliness and greater comfort, this type equipment allows you to reduce heating costs, because such boilers operate 15-20% more economically than conventional ones.
If you look specifications condensing gas boilers, then you can pay attention to the efficiency of the equipment - 108-110%. This contradicts the law of conservation of energy. While, indicating the efficiency of a conventional convection boiler, manufacturers write that it is 92-95%. Questions arise: where do these numbers come from, and why does a condensing gas boiler work more efficiently than a traditional one?
The fact is that this result is obtained thanks to the thermotechnical calculation method used for conventional gas boilers, which does not take into account one important point: evaporation/condensation. As is known, during the combustion of fuel, for example, main gas (methane CH 4), thermal energy, and also produces carbon dioxide (CO 2), water (H 2 O) in the form of steam and a number of others chemical elements.
In a conventional boiler the temperature flue gases after passing through the heat exchanger it can reach 175-200 °C.
And water vapor in a convection (ordinary) heat generator actually “flies into the chimney,” taking with it part of the heat (generated energy) into the atmosphere. Moreover, the amount of this “lost” energy can reach up to 11%.
To increase the efficiency of the boiler, it is necessary to use this heat before it is lost and transfer its energy through a special heat exchanger to the coolant. To do this, you need to cool the flue gases to the so-called temperature. “dew point” (about 55 °C), at which water vapor condenses and useful heat is released. Those. - use the energy of phase transition to maximize the use of the calorific value of the fuel.
Let's return to the calculation method. Fuel has a lower and higher calorific value.
- The gross calorific value of a fuel is the amount of heat released during its combustion, taking into account the energy of water vapor contained in the flue gases.
- The net calorific value of a fuel is the amount of heat released without taking into account the energy hidden in water vapor.
The boiler efficiency is expressed in the amount of thermal energy obtained from fuel combustion and transferred to the coolant. Moreover, when indicating the efficiency of a heat generator, manufacturers can by default calculate it using the method using the lower calorific value of the fuel. It turns out that real efficiency of a convection heat generator is actually about 82-85% , A condensation(remember the 11% additional heat of combustion that it can “take away” from water vapor) – 93 - 97% .
This is where condensing boiler efficiency figures appear that exceed 100%. Due to its high efficiency, such a heat generator consumes less gas than a conventional boiler.
Sergey Bugaev
Condensing boilers provide maximum efficiency if the coolant return temperature is less than 55 °C, and these are low-temperature heating systems “warm floor”, “ warm walls"or systems with an increased number of radiator sections. In conventional high temperature systems the boiler will operate in condensing mode. Only in very coldy we will have to maintain a high coolant temperature, the rest of the time, with weather-dependent regulation, the coolant temperature will be lower, and due to this we will save 5-7% per year.
The maximum possible (theoretical) energy savings when using condensation heat is:
- when burning natural gas – 11%;
- when burning liquefied gas (propane-butane) – 9%;
- when burning diesel fuel (diesel fuel) – 6%.
Advantages of using a condensing gas boiler
So, we have dealt with the theoretical part. Now we’ll tell you how the design features of a condensing boiler affect its operating efficiency and durability. At first glance, it seems that it is possible to use the additional energy of water vapor hidden in the flue gases in a conventional boiler, specially “driving” it into a low-temperature operating mode. For example, by connecting the boiler (this is incorrect) directly to the underfloor heating system or by significantly lowering the temperature of the coolant circulating in the radiator heating system. But, we already wrote above that during the combustion of main gas a whole “bouquet” of chemical elements is formed. Water vapor contains: carbon dioxide and carbon monoxide, nitrogen oxides, and sulfur impurities. During condensation and the transition of steam from a gaseous to a liquid state, these impurities end up in water (condensate) and the output is a weak acidic solution.
Sergey Bugaev
The heat exchanger of a conventional boiler will not withstand prolonged operation in an aggressive chemical environment; over time it will rust and fail. The condensing boiler heat exchanger is made of materials that are corrosion resistant and resistant to acidic environments. The most resistant material is stainless steel.
In the manufacture of the condensing boiler, only durable and wear-resistant materials are used. This increases the service life and reliability of this equipment, and also reduces maintenance costs.
In addition, increased demands are placed on other structural elements condensing heat generator, because it is necessary to cool the flue gases to the required temperature. For this purpose, the boiler is equipped with a forced-air burner with high degree modulation. This burner operates over a wide power range, which allows you to optimally regulate water heating. Condensing boilers are also equipped with automatic equipment that ensures precise maintenance of the combustion mode, temperature of the exhaust gases and water in the return line. Why are they placed? circulation pumps, smoothly changing the pressure force of the coolant flow, and not like simple 2- and 3-speed ones. With a conventional pump, the coolant flows through the boiler at a constant speed. This leads to an increase in the temperature in the “return”, an increase in the temperature of the flue gases above the dew point, and, consequently, a decrease in the efficiency of the equipment. It is also possible for the heating system (warm floor) to overheat and reduce thermal comfort.
Important nuance: the burner of a conventional boiler cannot operate at a power lower than 1/3 of the maximum (rated) power of the heat generator. The condensing boiler burner can operate at a power of 1/10 (10%) of the maximum (rated) power of the heat generator.
Sergey Bugaev
Consider the following situation: started heating season, outside temperature -15 °C. The power of a conventional boiler installed in a house is 25 kW. The minimum power (1/3 of the maximum) at which it can operate is 7.5 kW. Let's assume that the building's heat loss is 15 kW. Those. The boiler, continuously operating, compensates for these heat losses, plus there remains a power reserve. A few days later there was a thaw, which, you see, often happens during the winter. Eventually outside temperature now around 0°C or slightly below. The heat loss of the building, due to the increase in outside temperature, has decreased and is now approximately 5 kW. What will happen in this case?
An ordinary boiler will not be able to working continuously, produce the 5 kW of power necessary to compensate for heat loss. As a result, it will go into the so-called cyclic mode of operation. Those. the burner will constantly turn on and off, or the heating system will overheat.
This mode is unfavorable for the operation of the equipment and leads to its accelerated wear.
A condensing boiler, with the same power and in a similar situation, in continuous operation will quietly produce 2.5 kW of power (10% of 25 kW)¸ which directly affects the service life of the heat generator and the level of comfort in a country house.
The condensing boiler, complemented by weather-compensating automation, flexibly adapts to changes temperature regime throughout the heating season.
Modern automation makes it possible to significantly simplify the process of boiler control, including remotely, using a special mobile application for smartphones, which increases the ease of use of the equipment.
Let us add that the heating season in Russia, depending on the region, is on average 6-7 months, starting in the fall, when it is not very cold outside, and lasting until spring.
Approximately 60% of this time, average daily temperatures outside remain around 0 °C.
It turns out that the maximum boiler power may be required only in a relatively short period of time (December, January), when real frosts have set in.
In other months, the boiler is not required to reach maximum operating mode and increase heat output. Consequently, a condensing boiler, unlike a conventional one, will work effectively even with temperature changes and slight frost. At the same time, gas consumption will be reduced, which, in tandem with a low-temperature heating system (warm floor), will reduce the cost of purchasing energy.
Even when using a condensing boiler together with high-temperature radiator heating, this equipment works 5-7% more efficiently than traditional ones.
Sergey Bugaev
In addition to efficiency, an important advantage of condensing boilers is the ability to obtain high power with compact equipment sizes. A wall-mounted condensing gas boiler is especially relevant for small boiler houses.
In addition, the condensing boiler has a turbocharged burner, which allows you to abandon the standard expensive chimney and simply remove the coaxial chimney pipe through a hole in the wall. This simplifies the installation of equipment or the installation of a new condensing boiler to replace the old - conventional one, when renovating an existing heating system.
Features of operation of a condensing gas boiler
Frequently asked questions from consumers: what to do with the condensate obtained during the operation of the boiler, how harmful it is, and how to dispose of it.
The amount of condensate can be calculated as follows: per 1 kW*h there are 0.14 kg. Consequently, a condensing gas boiler with a power of 24 kW when operating at 12 kW of power (since most of the heating period the boiler operates with modulation, and the average load on it, depending on conditions, can be below 25%) on a fairly cold day produces 40 liters of condensate at low temperature.
Condensate can be drained into the central sewer, provided that it is diluted in a ratio of 10 or better 25 to 1. If the house is equipped with a septic tank or local treatment plant, neutralization of the condensate is required.
Sergey Bugaev
The neutralizer is a container filled with marble chips. Filler weight – from 5 to 40 kg. It must be changed manually on average once every 1-2 months. The condensate, usually passing through the neutralizer, flows by gravity into the sewer system.
Summarizing
This is modern equipment that is reliable, economical and efficient. Emissions of harmful substances into the atmosphere are also reduced, which is especially important when environmental standards are tightened. In addition, the installation of this type of heat generator, by reducing gas consumption, will reduce heating costs in the long term and increase the level of comfort in a country house.
Conventionally, the installation diagram (we are considering the Victrix 50 boiler as an example) can be divided into several connection stages:
- safety kit;
- storage boiler;
- solar collector;
- hydraulic separator.
Let's look at each stage in detail.
Safety kit
When connecting a boiler with a power of more than 35 kW, European legislation requires paying closer attention to safety issues. Therefore, a special safety kit is provided, which includes a safety thermostat, a maximum water pressure switch (4 bar), a pressure gauge and a system filling valve (sleeve for connecting the thermal cylinder of the gas shut-off valve).
There are also fittings for connecting expansion tank and a sleeve for an immersion alcohol thermometer. The pressure switch and overheating thermostat have manual unlocking and are connected in series to the boiler power circuit (Fig. 2). The response limit of safety devices is adjustable and is 3 bar and 105 °C, respectively. This kit allows you to produce a compact, fast and reliable installation safety devices, and also guarantees reliable protection against emergency situations under any circumstances.
Storage boiler
Since the boilers are single-circuit, it is proposed to use a storage type boiler to meet the needs for hot water. Several standard sizes of boilers are offered, with a capacity from 80 to 200 liters. Boilers have a rectangular body white. The material used to make the boiler body and coil is high quality food grade stainless steel. To reduce heat loss, the boiler is enclosed in highly efficient polyurethane foam insulation.
The boilers are equipped with spiral heat exchangers with a large heat exchange surface, which are connected in a counterflow circuit (Fig. 3). This allows you to quickly heat the accumulated water supply. To ensure the preparation of a large volume of hot water, you can use two 200 l boilers, in which the coolant circuits and sanitary water connected in parallel. To connect the boiler to the boiler, you must use a special kit, which consists of adapters and a three-way valve. As with all other mounted boilers, operation in hot water supply mode is based on the principle of strict DHW priority.
Connecting solar collectors
A special feature of 200-liter boilers is the ability to work with solar collectors. In Fig. Figure 4 shows an example of connecting solar collectors to a heat supply system based on a condensing boiler. High-quality solar collectors and a home heating system coordinated with them make it possible to consider the economic use of solar energy as a necessary condition for building an effective system.
In our latitudes, the total radiation (reflected and direct) under optimal conditions (cloudless clear sky, middle of the day) is a maximum of 1000 W/m2. Solar collectors, depending on their type, allow the use of up to 75% of the total radiation. It only remains to note that, from our point of view, the combination of a condensing boiler + solar collector (heat pump) is the most promising direction for the further development of autonomous heat supply systems.
Hydraulic separator
Since the boiler is designed to carry a significant heat load, this requires the presence of separate heating system circuits with zone control. Therefore, the issue of independent control of circuits becomes relevant. There is a possibility of a change in the amount of coolant circulating through the boiler, which adversely affects its hydraulic mode.
A natural solution in this situation is the use of a hydraulic separator (hydraulic arrow). At the same time, the transition to pipes is carried out larger diameter, which allows you to connect the “hydraulic arrow” directly to the supply and return distribution manifolds. For one boiler, a compact solution for this unit is proposed, in the form of a rectangular pipe (Fig. 5).
This unit is located directly under the boiler, which makes it possible to significantly reduce the dimensions of the installation. Since the collector is installed horizontally, to remove sludge from the heating system, it is necessary to install a sediment filter on the return line, in front of the collector.
From the design instructions for condensing Buderus boilers(Germany).
Compliant SNiP 41-01-2003 clause 6.4.1 PIPELINES
: "...Polymer pipes used in heating systems together With metal pipes(including in external heat supply systems) or with devices and equipment that have restrictions on the content of dissolved oxygen in the coolant, must have an oxygen permeability of no more than 0.1 g/(m3
∙day)..."
VITODENS Gas condensing boilers
Design instructions
Bosch Condens 3000W
- Possibility of direct connection to the underfloor heating system
Other model
BoschCondens 5000 W Maxx
Possibility of direct connection to the underfloor heating system
Without the required minimum circulation water flow
High-quality components such as a plasma-cured aluminum heat exchanger and robust construction make the Condens 5000 W Maxx not only extremely reliable, but also extremely durable. Thanks to innovative Flow Plus technology there is no minimum value of water pressure through the heat exchanger . For this reason, complete hydraulic system not required.
About the anti-diffusion layer (oxygen barrier):
"... This result once again confirms the fallacy of the widespread statement: “Pipes of small diameters do not necessarily need to be reinforced or protected from the ingress of oxygen into the coolant, since the flow of oxygen through the wall of such pipes can be neglected.” Proponents of this point of view urge not to reinforce with aluminum and not to cover with an AVOH layer (anti-diffusion layer for PEX pipes). and small diameter PPR pipes. However, it is precisely these pipes that stand, for example, in front of steel panel radiators (steel wall thickness is 1.2 mm). Therefore, to reinforce small and large pipes with aluminum large diameter necessary for heating systems. Moreover, for small-diameter pipes this rule is more important than for large-diameter pipes, where calculation and reference to a specific application scheme is necessary.
For example, with D = 2x10-11 m2/s (oxygen permeability of polypropylene) and ∆сО2 MAX = 270 g/m3 (approximate oxygen content in the atmosphere)
Q/V=1.9٠10-8/DN2 (g/s٠m3) or 1.6٠10-3/DN2 (g/day٠m3)
for DN20mm, we get 4 g/m3 of oxygen per day - in other words, the formation of 30 g of rust is possible. One meter of pipe DN20 PN20 (SDR=6) contains 2.2x10-4 m3; accordingly, through this linear meter pipes into the coolant will pass a maximum of 8.8x10-4 g/day. oxygen.
For example, if the heating system is made of PN20 polypropylene pipe (unreinforced or fiberglass reinforced), the volume of the heating system is 100 liters, there is a wall-mounted boiler with an aluminum-copper heat exchanger and a heating temperature of 80 C° and steel panel radiators, and the pipe capacity is 50 liters, then per day for a typical set of pipes of different diameters with SDR = 6 will pass into the coolant about 0.1 g of oxygen; in terms of per year this amounts to 37 g of oxygen, or 250 g of rust obtained in steel panel radiators(which will very likely leak after a year or two of use).
The scope of this article does not include an exact quantitative analysis of oxygen permeability, but the example given allows us to resolve the frequently asked question: “How much oxygen does a plastic pipe allow through? Is it a lot or a little? I think we have given a very specific answer. In conclusion, we note that many informative works have been written on this topic, but the conclusions of readers or companies supplying similar products to the market do not always correspond to the analysis carried out in these articles..."
The chimney is one of the most important parts in the design of a boiler room based on any boilers that burn fuel, including condensing ones. Proper design, choice of material and high-quality installation of the chimney - the necessary conditions long and efficient operation boiler room as a whole.
The main feature of flue gases from condensing boilers is their low temperature compared to flue gases from traditional boilers. In turn, low temperature leads to the obligatory formation of a certain amount of condensate in the chimney. It is these two factors - low temperature and condensation - that are decisive when choosing a chimney material for a condensing boiler. In addition, the need to ensure constant removal of condensed moisture must be taken into account in the design and geometry of chimneys.
Against the background of the above, we will analyze three main aspects regarding chimneys for condensing boilers:
- Materials used;
- Design features;
- Basic installation diagrams.
Materials for the manufacture of chimneys for condensing boilers
The two most common materials used to make chimneys for condensing boilers are fire-resistant polypropylene and stainless steel.
Flame retardant polypropylene (PPs)
IN household use PPs chimneys are the most affordable and convenient in terms of installation. Generally speaking, polypropylene chimneys are also used with traditional boilers most modern designs, but still the service life in this case is limited due to the relatively high temperature of the flue gases.
In the case of condensing boilers, the exhaust temperature is low enough to have no effect on the strength of the chimneys. In addition, polypropylene is inert to the acidic composition of the condensate formed during the combustion of hydrocarbon fuels. That is, from the point of view of durability, this material is ideal for use with condensing boilers.
Another feature of chimneys for condensing boilers is the requirement for operation under excess pressure. That is, the connections of the elements must be sealed. Typically, silicone seals are used to provide a seal. Polypropylene is convenient here because, due to its elasticity, it does not require the use of additional clamps, unlike stainless steel.
The main disadvantage of this material is its vulnerability to ultraviolet radiation, that is, such chimneys cannot be laid outdoors in the open.
It is also important to note that polypropylene must be fire resistant. This fact is usually indicated by the letter “s” in the material designation (PPs). This type of polypropylene is more resistant to high temperatures and, no less important from a safety point of view, does not support combustion.
In past years, it was a fairly common mistake to use sewer pipes for chimney installation. pressure pipes from ordinary polypropylene in order to reduce the cost of the material. This should not be done under any circumstances for the reasons stated above.
Stainless steel
Acid-resistant grades of stainless steel are the second most popular material for condensing boiler chimneys in domestic use, and the main one in the industrial and commercial segment!
The basic requirements are still the same: operation under excess pressure and resistance to the chemical composition of condensate. In terms of temperature, stainless steel provides a huge margin of safety.
Types of chimneys
There are three main structural types of chimneys, each of which has a specific area of application:
- single wall;
- double-walled (sandwich);
- coaxial.
Single wall chimney
From the name it is clear that these are simply pipes and shaped elements made of the appropriate material. Can only be used indoors or in thermally insulated ducts (for example chimneys during reconstruction). Typically used for the emission of flue gases when air is taken from the boiler room.
It is often also used to make a channel for supplying combustion air from the street. These air ducts, of course, do not have any special requirements for temperature and chemical resistance and tightness. That is, they can be made from almost any available material. However, from the point of view of uniformity and ease of installation, the same type of single-wall chimney is usually used as for the exhaust of flue gases.
Single-wall chimneys can under no circumstances be used outdoors. The main problem is the constant formation of condensation in the channel. From the point of view of chemical resistance, as noted above, this is not terrible, but there is a great danger of freezing of the liquid inside the chimney and, as a result, a narrowing of the pipe’s flow area. The drop in natural draft due to the cooling of flue gases is not critical for this type of boiler, since they are equipped with powerful fans that provide a high value of residual pressure.
Double wall chimney (sandwich)
Elements of this type of chimney consist of two concentric pipes various diameters, the space between which is filled with heat-insulating material, usually stone wool non-flammable.
There are no special requirements for the outer pipe in terms of acid and heat resistance; only resistance to atmospheric conditions (precipitation, ultraviolet) and mechanical strength. Therefore, in the case of double-walled stainless steel chimneys, the inner and outer pipes are usually made of different grades of steel to optimize cost. There are options with an outer pipe made of aluminum.
Double-walled chimneys can be used both indoors and outdoors.
Due to the low temperature of the flue gases and the absence of the risk of burns, in the case of condensing boilers, the double-walled version is usually used only for the outer part of the chimney, and for the inner part a regular single-walled pipe can be used.
Coaxial chimney
Again, based on the name, it is clear what this chimney is: two concentric pipes with empty space between them.
The main feature of this type is that it is used both for the emission of flue gases (through the internal pipe) and for the intake of combustion air (through the space between the pipes). Accordingly, when using it, it is not necessary to constantly ensure the supply of combustion air to the boiler room. In addition, the incoming air is heated from flue gases, thereby increasing the overall efficiency of the boiler room.
Laying coaxial chimneys is also only allowed indoors; the length of the external section in our conditions should be no more than one meter. A common problem in cold winter conditions is ice freezing at the end of the chimney. This happens due to the sharp cooling of the flue gases at the outlet upon contact with cold air entering the combustion through the gap between the pipes. To solve this problem, you can trim a section of the external pipe in the area where the chimney ends in order to separate the exhaust of flue gases from the air intake; or use the factory winter options for ending the coaxial pipe.
This type of chimney is made from both plastic and stainless steel.
Basic installation diagrams for chimneys for condensing boilers
All chimney schemes for condensing boilers are divided into two main types: with combustion air intake from the room and from the street. Naturally, domestic regulatory documentation describes these types of smoke removal and the requirements for them, but in the documentation for boilers, names are usually found in accordance with European standards. A chimney with air intake from the boiler room is designated as “Bxx”, from the street - as “Cxx”. The first index varies depending on the specific circuit, the second - on the location of the fan relative to the boiler heat exchanger. In all modern condensing boilers the fan is located in front of the heat exchanger, which is indicated by the index “3”. Below are the basic diagrams using the example of wall-mounted boilers:
For domestic power, chimney calculations are usually not necessary; it is enough to follow the boiler manufacturer’s recommendations for maximum length taking into account shaped elements (elbows, tees, etc.). In the case of industrial boiler houses, a smoke exhaust calculation is required; you can contact the chimney manufacturer for this.
Combustion air intake from the room
| The simplest way to organize the removal of flue gases. Almost always used for high-power boiler houses: industrial or commercial, when floor-standing boilers are used. It is also often found in household use. Two main requirements when using such schemes: ensuring the necessary air flow into the boiler room and its cleanliness. For large-capacity boiler houses this is usually not a problem, since these points are carefully taken into account at the design stage. In private boiler houses, a situation often occurs when sufficient air flow is not provided; or carried out through adjacent rooms, where after starting the boiler they continue Finishing work, which contributes to the presence of fine dust in the air and clogging of the internal elements of the boiler. Naturally, this state of affairs should be avoided or special air filters should be used on boilers. |
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In this case, the chimney must be installed above the roof level and out of the so-called “wind surge” zone.
This is necessary in order to eliminate the influence of air pressure fluctuations on the smoke removal process.
Combustion air intake from the street
In this case, two main subtypes of chimney are used: coaxial and separate.
Coaxial chimney
As mentioned above, it is widespread mainly in household use with wall-mounted boilers. In a private house, a coaxial chimney is especially convenient in that it is quite easy to install it horizontally behind the wall, without constructing a vertical trunk extending beyond the roof level. This is possible due to the fact that the air intake and smoke emission areas are located nearby in the same pressure zone, and are thus not exposed to wind.
However, the issue of flue gas dispersion into the atmosphere remains. The emissions of modern condensing boilers are environmentally friendly, but the chimney must comply with standards for distances to windows, doors, ventilation grilles and neighboring land plots. In order to combine the convenience of installing a coaxial chimney indoors and using a double-walled pipe outdoors, you can use special transition kits.
In case of modernization of an existing boiler house with brick chimneys there is an option with coaxial pipe to the area of this chimney. Next, it is laid inside it new pipe made of stainless steel (single-walled can be used). Air intake is carried out through the gap between the steel pipe and the brick chimney.
The most diverse option for organizing a chimney in terms of design options. However, it is rare in private construction and industrial boiler houses. Since for condensing boilers in the first case it is usually easier to use a coaxial chimney, in the second case it is easier to take air from the room.
Often found in apartment buildings with separate heat generators for each apartment, according to the following scheme: 
Regarding the selection and purchase of a chimney for a condensing boiler, please contact our
.