Diagram for connecting gas boilers to a cascade. Cascade way of connecting boilers. Boilers used in cascade boiler rooms

2007-10-22

Cascading boilers is an effective technique for increasing the unit capacity of a heating device, which has been used by heating specialists for many years. The concept of reception is simple: we divide the total heat load between two or more independently controlled boilers and include in the cascade only those boilers that satisfy the demand for a given load at a certain time. Each boiler represents its own "stage" of heating capacity in total capacity systems. An intelligent controller (microcontroller) constantly monitors the flow temperature of the heating medium and determines which stages of the system should be turned on to maintain the set temperature.

The main advantages of a cascade heating system:

increased reliability (if one boiler fails, the rest can partially or completely cover the required heat load);
increased efficiency (conventional boilers lose quite a lot of efficiency when operating at partial power);
simplification of installation ( individual elements cascade is much easier to deliver and install than one high-capacity boiler).

It is obvious that a system of several boilers instead of one is able to more efficiently ensure the conditions of the design loads. Based on this, it can be assumed that the more steps in a cascade system, the better it will satisfy the load of the heating system. This is especially effective when low power ratings are required.

However, with an increase in the number of steps, the surface area of the system's heat transfer (heat loss through the shells of the boilers), through which heat loss occurs, also increases. This can ultimately "negate" the benefits of the increased efficiency of such a system. Therefore, the use of more than four stages is not always advisable. An inherent limitation of a "simple" cascade system (boilers with one-stage or two-stage burners) is a step-by-step regulation of heat output (system power), and not a continuous controlled process.

Although the use of more than two stages significantly reduces the heating capacity of each boiler, the ideal solution would be a “modulating” cascade system (boilers with modulating burners). Modulating burners allow infinitely variable power regulation depending on the heat demand. The latest trend in cascade systems is the modulated cascade system.

In contrast to the use of staged burners, boilers with modulating burners are able to smoothly change the volume of fuel supply, and, consequently, to control the level of heat output in a wide range of values. On the market today heating equipment widely represented mounted boilers increased power with modulating burners, capable of smoothly changing the boiler performance in the range of 30-100% of the rated thermal power.

The ability of boilers with modulating burners to reduce fuel consumption is often called the burner operating regulation factor (i.e. the ratio of the maximum heat output of the boiler to the minimum). For example, the operating regulation coefficient of a burner of a boiler with a maximum heating power of 50 kW and minimum consumption 10 kW fuel will be equal to 50 kW / 10 kW, or 5: 1.

The total coefficient of operating regulation of the boilers installed in the cascade system significantly exceeds the coefficient of an individual boiler. For example, if three boilers are used in a cascade system with a maximum heat output of 50 kW and a minimum of 10 kW, the total capacity control will be carried out in the range from 150 to 10 kW. Therefore, the operating ratio of such a system would be 15: 1.

Requirements for a "modulated" cascade

There are three important conditions that must be met when designing a “modulated” stage system. First, the piping of mains and controllers must be implemented so that independent regulation of the flow circulation through each boiler is possible. Water should not circulate through a non-operating boiler, otherwise the heat of the heating medium will be dissipated through the heat exchanger or the boiler casing. This also applies to a simple cascade system.

Independent regulation of the heating medium flow is achieved by equipping each boiler with an individual circulation pump. When circulating pumps are installed in parallel, check valves should be installed downstream of the pump to prevent backflow of the heating agent through idle boilers. The supply of heating agent to each boiler using individual circulation pumps allows increasing the pressure in the heat exchanger of the operating boiler in order to prevent cavitation and explosive vaporization.

Secondly, the connection of the flow and return lines for each boiler must be carried out in parallel (especially when using condensing boilers). This allows you to maintain the same water temperature at the inlet to each boiler and, if necessary, exclude the flow of coolant between the circuits. Low temperature The coolant supplied to the boiler contributes to the condensation of water vapor from the combustion products and increases the efficiency of the system.

Some cascade controllers for boilers with modulating burners are equipped with a "time delay" function, i.e. are able to turn on the circulation pump of a specific boiler shortly before turning on the burner. In addition, they can keep the pumps running for a while after the burner has been turned off. The first ensures that the boiler heat exchanger is heated by the warm supplied heat carrier of the system, which prevents thermal shock due to a significant temperature difference (and condensation of flue gases for conventional boilers) when the burner is ignited.

The second is to dispose of the residual heat of the heat exchanger, and not remove it through the ventilation system after the end of the boiler operation. And thirdly, it is very important that the circulation pumps provide an adequate flow of the heating medium through the operating boilers, regardless of the flow rate of the heating system. Natural solution this issue is the use of a low loss header low pressure.

System installation steps

The connection of the cascade system is carried out in three stages:

hydraulic connection of boilers and systems;
connection to a single smoke collector;
cascade automation settings.

Thanks to modular system installation, which can be compared with the collection children's designer, achieved high speed installations and system reliability. The main stages of installation of a cascade heat generating unit are shown in Fig. 2. Naturally, the main way of coordinating several heat-generating units and a heat supply system is a low-pressure hydraulic manifold.

Methods for calculating the selection and installation are well known. The system of hydraulic coordination of boilers consists of several standard connection steps: 1. two boilers in a cascade; 2. the third boiler in the cascade; 3. safety groups of the cascade (fig. 3). Depending on the required power you can assemble a cascade of two or three boilers. The base material is thick-walled nickel-plated pipes, which are connected using quick disconnect couplings(the so-called "American women").

The delivery set includes all the necessary elements, from shut-off valves to gaskets. Such a complete set allows the installation of the cascade to be carried out as quickly and accurately as possible.

Modulated control

A multi-stage controller for a simple cascade system, using proportional-integral-derivative (PID) control, constantly measures the temperature of the heating medium flowing into the system, compares it with a calculated value and determines which burner should be turned on and which one should be turned off. To control a cascade of boilers and achieve an economical fuel consumption, it is necessary to use special automation.

In the event of a fault in the lead boiler, the priority is automatically changed. If the demand for heat does not come from any of the zones, the regulator will turn off all boilers, and when a demand signal is received, it will start them up. After turning off the last boiler, the circulation pump turns off after a certain period of time.

In most "modulated" cascade systems, the control method is different. As a rule, the goal is to increase the operating time of boilers in the low temperature range and at incomplete power. Immergas recommends the use of Honeywell Smile SDC 12-31 controllers for its Victrix 50 boilers (fig. 4). Although different manufacturers offer different systems control, the generally accepted approach is as follows: turning on the boiler, then modulating its operation to the level of heat output that satisfies the required load.

If additional heat is required, the heating capacity of the first boiler is significantly reduced, the second boiler is switched on, and then the heating capacity of both boilers is modulated accordingly to meet the required load. Such a scheme ensures that both boilers operate at lower heating capacities, and therefore in a more gentle mode, in contrast to the operation of one boiler at full power.

This increases the surface area of the heat exchange, therefore, the likelihood of condensation of water vapor from the combustion products increases, as well as the efficiency of the system. Suppose the load continues to increase and two boilers operating at a relatively high level of heating capacity cannot meet its conditions.

Then the second boiler reduces the fuel consumption, the third is switched on, and the heat output of the second and third stages is modulated in parallel. In some systems, the first boiler is also able to reduce fuel consumption when the remaining stages are activated, therefore, all three power stages can be controlled in parallel.

Controller operating modes

Most cascade controllers are capable of at least two operating modes. In heating mode, the weather-dependent control principle is implemented, i.e. The setpoint for the temperature of the heating medium flowing into the system depends on the outside temperature. The lower the outside temperature, the higher the desired flow temperature.

This system eliminates the need for a mixer between the boiler and heating consumers. In DHW mode, software regulation of the system is carried out, when the set value of the supply temperature does not depend on outside temperatures... In other words, a certain, sufficiently high temperature value is set, which ensures high level heat transfer through secondary heat exchanger.

This mode is usually used to ensure a higher temperature of the heat carrier supplied through the heat exchanger to the hot water consumers and anti-icing systems. Modulating the boiler output leads to a significant decrease in the differential between the required and real temperatures of the heating medium, which prevents frequent "clocking" (switching on / off) of the boiler.

Some controllers are also responsible for the operation of the main circulation pump and linked to the dispatching system engineering equipment building. The modern generation of low-power boilers with modulating burners provides space savings, high efficiency, quiet operation and reliability. it perfect solution in low temperature systems; such boilers are ideal for underfloor heating, anti-icing systems, pool heating, hot water systems, as well as heat pump systems, incl. geothermal.

They have already gained a position in the field of private home heating. As part of a cascade system, boilers with modulating burners represent a new alternative to industrial heating systems.

Today, many consumers choose gas heat generators (boilers) as the main source of heat and water supply. There are several types of installation gas equipment:

1 ... One heat generator is installed in the heating system.

2 ... Several heat generators are installed in the heating system.

Consider the option of installing several heat generators in a system to compensate for heat losses. There are several types of control systems with this design: parallel connection of each boiler, when each of the boilers operates separately from each other, but for one system (heating, hot water supply, ventilation, etc.); and the second, cascade switching on of boilers, when the equipment is mounted and connected in one common system thermomechanical and electrical connection.

In this case, the cascade is united by a single control system.

So what is a cascade? The cascade is one of the most effective ways increasing the maximum power or increasing the minimum power of one device, but more on that later, but for now, for example, let's consider the work of an individual heating point.

As practice shows, the equipment operates at maximum heat load from three to five months a year with a nominal heat load from 60 to 100%, while the remaining time the equipment operates at a reduced power (from 40 to 60%). Let us take as a basis the inter-heating period from March to September and the area of the heated room of 1000 m 2 or the heating of water in the hot water supply system. According to average calculations, 1 m 3 of combusted gas provides approximately 10 kW of boiler power. This means that if you have as heater one boiler with a capacity of 100 kW is used, then its minimum load will be 50 kW, which is equal to an average consumption of 5 m 3 of gas per hour. If you have a cascade of three boilers with a capacity of 36 kW each connected in your system, then, as practice shows, one of the heat generators with a minimum load of 10.6 kW will turn on, which equals an average gas consumption of 1.6 m 3 per hour. As a result, when one gas heat generator operates in the system with such a minimum load during the inter-heating period, its gas consumption will be almost three times higher compared to the cascade switching on of boilers, and this is an increase in financial costs.

Typical schemes for installing gas-burning equipment (cascade) are as follows.

The first is a simple cascade. This scheme includes gas equipment with one-stage or two-stage burners. When installing such a scheme, the equipment works according to the following principle: first, the first stage of the burner is turned on with rated power 70% (of the total boiler power), and if this power is not enough to compensate for heat losses, then the second stage with a power of 100% is connected to work.

The second is modulated. This installation scheme is more economical. It integrates equipment with modulating burners. It is possible to smoothly change the volume of fuel supply and the ability to regulate heat output in a fairly wide range. That is, the equipment turns on with a minimum heat load of 40% and, if necessary, smoothly increases it to a power of 100% in 1% steps.

The main advantages of a cascade system with two or more gas boilers over conventional systems in which only one gas boiler is used as heating equipment are as follows.

At first, gas equipment operation should be controlled using a cascade control unit or other automation. A multistage controller for a simple cascade system, using proportional-integral-derivative control (PID), constantly measures the temperature of the heating medium flowing into the system, compares it with calculated value and determines which burner to turn on and which to turn off.

One of the boilers of the cascade plays the role of the "master" and is switched on first, the rest, "slaves", are connected as needed. Automation control allows you to transfer the role of the "master" from one boiler to another, as well as to carry out the sequence of switching on the "slaves". Also, the automation carries out the sequence of switching on the equipment, which guarantees the same number of hours of operation of the gas burner device. As a rule, the automation of the control system is supplied complete with an outdoor temperature sensor, which makes it possible to control the modulation of the gas burner device (power and flow temperature) depending on the temperature environment... For example, at an outside air temperature of 0 ° C, the temperature of the heating medium in the flow line will be 50 ° C. At an outdoor temperature of -10 ° C, the coolant will be supplied to the supply line already at a temperature of 60 ° C, etc. The lower the ambient temperature, the higher the temperature of the heating medium. Automation will turn on the required amount boilers depending on the required power.

Secondly, this is gas saving and, as a result, the preservation of financial resources that can be directed to the reconstruction of your facility. The ability of boilers with modulating burners to reduce fuel consumption is often called the burner operating regulation factor (the ratio of the maximum heat output of the boiler to the minimum). How can this be done? It's very simple, the system will do it for you.

Let us give an example - when the equipment is operating at a capacity of over 70%, an increased gas consumption begins. You have two boilers with a capacity of 24 kW each. First, the first boiler is switched on with a nominal load of 9.4 kW and gradually increases it to 100% power. If one boiler is not enough, then the second boiler is turned on, for example, at a power of 40%. In total, the total load of both boilers will be 32 kW. The second option - the first boiler is also switched on with a nominal load of 9.4 kW and gradually increases to a power of 70%. If this power is not enough, then the second boiler is switched on at a power of also 70%, and the total load will also be 32 kW. When gas equipment operates in the second option, gas savings will be from 15 to 30%.

Thirdly, it is the simplicity of transportation and installation of equipment. Several wall-mounted boilers are much easier to install or assemble than one powerful boiler. The rather small dimensions and weight of wall-mounted boilers make it advantageous to install them in a cascade when installing roof-top boilers, in basements or semi-basements. In particular, when installing such boiler rooms, additional costs are not required for special equipment for lifting or transporting a powerful overall boiler.

Fourthly, this is a reserve. If, for any reason, one of the boilers fails, for example, in the event of a heat generator failure, then the entire system will continue to operate at reduced or medium power. If one boiler operates in the system, and it "goes into an error", then the entire heating system will stop working, and in the cascade each boiler is autonomous, and in the event of an emergency, only the faulty unit will turn off.

Fifth, these are the terms of placement. A cascade of wall-mounted heat generators is allowed to be mounted and operated in attached, built-in, detached, roof-top boiler rooms, etc.

In practice, there are many examples when, during the reconstruction of an object, expansion and addition of additional heat consumers, it was necessary to modernize the boiler house itself (change the existing gas equipment to a more powerful one), which led to large financial losses, and with the option of cascade control, if necessary, you can simply add to the existing system one or more boilers.

There are several options for placing gas equipment: mounting equipment on a wall, on specialized racks (mounts) in a row, or placing gas equipment "back to back".

So, cascade boiler rooms are used in almost all areas, but they are most in demand in systems autonomous heating one or more objects. When installing a cascade control, potential customers and consumers do not need to build a heating main from centralized system heating, which certainly has significant heat losses, especially with the DHW function.

Most a profitable solution cascade regulation is the installation of this equipment in private houses, restaurants, hotels, shops different area etc. If the customer knows how to count his money, wants to be sure of the safety, efficiency, reliability and quality of his equipment, then he will choose a boiler house, consisting of a cascade of boilers.

The cascade method of connecting boilers has been used for many years. The concept is simple: divide the total heat load between two or more independently controlled boilers, and only switch on those boilers that meet the demand for this load at the given time. Each boiler represents its own "step" of heating capacity in the total system capacity. An intelligent controller (microcontroller) constantly monitors the flow temperature of the heating medium and determines which stages of the system should be turned on to maintain the set temperature.

BENEFITS
using a cascade system:

Increased seasonal efficiency of the system compared to using one powerful boiler;
- partial coverage of the load even if one of the boilers is off, for example, for service work. This is especially important in harsh climatic conditions, when, due to low temperatures, an inoperative system can freeze very quickly;
- a cascade system is much easier to install than one large boiler, especially when upgrading the system. In addition, spare parts for less powerful boilers are cheaper;
-the ability to simultaneously provide both high loads for hot water supply or anti-icing, and much less for heating.

We present the performance characteristics of two different cascade systems in relation to a hypothetical load diagram. The first system uses two single-stage boilers, each capable of providing 50% of the design load. The second system uses four single-stage boilers, each capable of providing 25% of the design load. It is obvious that a system of four boilers instead of two is capable of more efficiently ensuring the conditions of the design loads. Based on this, it can be assumed that the more steps in a cascade system, the better it satisfies the loads. This is especially effective at low power requirements. However, with an increase in the number of stages, the heat transfer surface area of the system (boiler casing), through which heat loss occurs, increases, which ultimately can negate the advantages of the increased efficiency of such a system. Therefore, it is not always advisable to use more than four steps. An inherent limitation of the "simple" cascade system (boilers with one-stage or two-stage burners) is a step-by-step regulation of heat output (system power), and not a continuous controlled process. Although the use of more than two stages significantly reduces the heating capacity of each boiler, the ideal solution would be a “modulating” cascade system (boilers with modulating burners). Modulating burners allow stepless power regulation depending on the heat demand without changing the quantitative fuel / air ratio, i.e. when, depending on the volume of supplied air and aerodynamic resistance, the amount of fuel supplied to the combustion chamber changes. This ensures a stable boiler efficiency and minimum concentrations of pollutants in the flue gases at a variable heat load. Next step. The latest trend in cascade systems is the modulated cascade system. In contrast to the use of staged burners, boilers with modulating burners are able to smoothly change the volume of fuel supply, and, consequently, to control the level of heat output in a wide range of values. Today, low-power boilers with modulating burners are widely represented on the heating equipment market, capable of smoothly changing the boiler performance in the range of 30-100% of the nominal thermal power. The ability of boilers with modulating burners to reduce fuel consumption is often referred to as the burner duty ratio (i.e. the ratio of the maximum heat output of the boiler to the minimum). For example, the operating regulation ratio of a burner of a boiler with a maximum heating power of 50 kW and a minimum fuel consumption of 10 kW will be 50 kW / 10 kW or 5: 1. The total coefficient of operating regulation of the boilers installed in the cascade system significantly exceeds the coefficient of an individual boiler. For example, if a cascade system uses four boilers with a maximum heat output of 50 kW and a minimum heat output of 10 kW, the total capacity control will be in the range from 200 kW to 10 kW. Therefore, the operating ratio of such a system would be 20: 1. In conditions of low heat output, the heat exchanger of a modulating burner boiler operates at a relatively low temperature of the heat exchange surfaces of the boiler on the combustion side. When such a boiler is used to satisfy low loads such as underfloor heating, its operation is usually accompanied by continuous condensation of flue gases. To avoid damage to the heat exchanger due to condensation, modern boilers with modulating burners use heat exchangers made of of stainless steel or aluminum. When operating at low temperatures, the efficiency of such boilers can exceed 95%. Small capacity boilers with modulating burners are usually designed with closed chamber combustion, which expands the range of design solutions for air supply and combustion products removal systems, since the chimneys of such boilers do not have to be straight. Chimneys are usually made of galvanized sheet or stainless steel or aluminum. But for some boiler models, for example, for the Vaillant VU 505, a system of flexible polypropylene chimneys is successfully used (they can be laid in old, indirect or unsuitable for normal modes smoke ducts).

System features
There are three important features which should be considered when designing a “modulated” stage system. First. Features of supply lines and controllers should allow independent regulation of the flow circulation through each boiler. Water should not circulate through a non-operating boiler, otherwise the heat of the heating medium will be dissipated through the heat exchanger or the boiler casing. This also applies to a simple cascade system. Independent regulation of the heating medium flow is achieved by equipping each boiler with an individual circulation pump. When circulating pumps are installed in parallel, check valves should be installed downstream of the pumps to prevent backflow of heating medium through idle boilers. Optimal solution this situation - installation of a circulation pump with wet rotor with built-in shut-off valves. The supply of heating agent to each boiler using individual circulation pumps allows increasing the pressure in the heat exchanger of the operating boiler in order to prevent cavitation and explosive vaporization.

Second important point- parallel connection of the supply and return lines for each boiler (especially when using condensing boilers). This allows you to maintain the same water temperature at the inlet to each boiler and, if necessary, exclude the flow of coolant between the circuits. The low temperature of the coolant supplied to the boiler contributes to the condensation of water vapor from the combustion products and an increase in the efficiency of the system. Some cascade controllers for boilers with modulating burners are equipped with a "time delay" function, that is, they are able to turn on the circulation pump of a particular boiler shortly before the burner is turned on. They can also keep the pumps running for a while after the burner is turned off. The first ensures that the boiler heat exchanger is heated by the warm supplied heat carrier of the system, which prevents thermal shock due to a significant temperature difference (and condensation of flue gases for conventional boilers) when the burner is ignited. The second is to dispose of the residual heat of the heat exchanger, and not remove it through the ventilation system after the end of the boiler operation. And thirdly, it is very important that the circulating pumps provide an adequate flow of coolant through the operating boilers, regardless of the flow rate of the system. Closely spaced T-joints (Fig. 2) or low pressure drop manifolds (Fig. 3) ensure that flow is diverted away from the system flow to ensure adequate boiler flow regardless of flow changes in the distribution system. The closely spaced T-pipe joints on the primary / secondary side are used to "relieve" the differential pressure of the circuits.

Modulated control
A multi-stage controller for a simple cascade system using PID (proportional-integral-differential control) constantly measures the temperature of the heating medium flowing into the system, compares it with the calculated value and determines which burner should be turned on and which one should be turned off. To control the boiler cascade and achieve economical fuel consumption, it is necessary to use special automation. One of the boilers of the cascade plays the role of the "master" and is switched on first, the rest - "slaves" - are connected as needed. Automation control allows you to transfer the role of "master" from one boiler to another, as well as to carry out the sequence of switching on the "slave" boilers and temperature differentials of switching on each subsequent stage. In the event of a fault in the lead boiler, the priority is automatically changed. If the demand for heat does not come from any of the zones, the regulator will turn off all boilers, and when a demand signal is received, it will start them up. After turning off the last boiler, the circulation pump is turned off with a time delay. In most "modulated" cascade systems, the control method is different. As a rule, the control is aimed at maximizing the operating time of the boilers in a low temperature range and at partial power. Although different manufacturers offer different control systems, the generally accepted approach is as follows: turn on the boiler, then modulate its operation to a level of heating capacity that satisfies the required load. If additional heat is required, the heating capacity of the first boiler is significantly reduced, the second boiler is switched on, and then the heating capacity of both boilers is modulated accordingly to meet the required load. Such a scheme ensures that both boilers operate at lower heating capacities, and therefore in a more gentle mode, in contrast to the operation of one boiler at full power. This increases the surface area of the heat exchange, and therefore, the likelihood of condensation of water vapor from the combustion products, as well as the efficiency of the system, increases. Suppose that the load continues to increase and two boilers operating at a relatively high level of heating capacity cannot meet its conditions, then the second boiler reduces fuel consumption, the third is turned on, and parallel modulation of the heating capacity of the second and third stages takes place. In some systems, the first boiler is also able to reduce fuel consumption when the remaining stages are activated, therefore, all three power stages can be controlled in parallel.

Working Modes
Most cascade controllers are capable of operating in at least two operating modes. In heating mode, the weather-dependent control principle is carried out, that is, the set value of the temperature of the heating medium supplied to the system depends on the outside temperature. The lower the outside temperature, the higher the desired flow temperature. This system eliminates the need for a mixer between the boiler and heating consumers. In DHW mode, software regulation of the system is carried out when the set value of the temperature of the supply heat carrier does not depend on external temperatures. In other words, a certain, high enough temperature value is set, which ensures a high level of heat transfer through the secondary heat exchanger. This mode is usually used to ensure a higher temperature of the coolant supplied through the heat exchanger to the hot water consumers and anti-icing systems. Modulating the boiler power leads to a significant decrease in the differential between the required and the actual temperature of the heating medium, which prevents frequent "clocking" (switching on / off) of the boiler. Some controllers are also responsible for the operation of the main circulation pump and are linked to the building management system.

Small, quiet and powerful
The ratio of the physical dimensions to the heating capacity of some modulating burner boilers is truly impressive. For example, individual manufacturers provide eight-stage “modulating” cascade systems with a heating capacity range of 30-960 kW. Therefore, the operating regulation ratio of such a system will be 32: 1. Such a system can be placed indoors small area. Additional advantage- low noise of the system. The modern generation of low-power boilers with modulating burners provides space savings, high efficiency, quiet operation and reliability. It is an ideal solution for low temperature systems, such boilers are ideal for underfloor heating, anti-icing systems, pool heating, DHW systems, as well as heat pump systems, incl. geothermal. They have already gained a position in the field of private home heating. As part of a cascade system, modulating burner boilers represent a new alternative to industrial heating systems.

Let's start with what's in modern house located with middle lane, there should be 2 boilers. It is not even necessary 2 boilers, but two independent sources of heat energy - that's for sure.

We have already written about what kind of boilers or energy sources they can be in the article "". It describes in more detail which boiler, which backup is needed and can be selected.

Today we will consider how to connect 2 or more heat generators to a single heating system and how to connect them. Why am I writing about 2 or more units thermal equipment? Because there can be more than 1 main boiler, for example, two gas boilers. And also there can be more than 1 reserve boiler, for example, on different types fuel.

Connection of two or more main heat generators

Let us first consider a scheme in which we have two or more heat generators, which are the main ones and, heating the house, operate on the same fuel.

These are usually connected in a cascade in order to heat rooms from 500 sq.m. total area... Rarely enough they are connected together for main heating or solid fuel boilers.

We are talking specifically about the main heat generators, and about the heating of residential premises. For cascade and modular boiler rooms for heating large industrial premises can include "batteries" of coal-fired boilers or fuel oil in an amount of up to one dozen.

So, as mentioned above, they are connected to a cascade when a second identical boiler or slightly less power complements the first heat generator.

Usually in the off-season and light frosts, the first boiler in the cascade works. In frosts or if it is necessary to quickly warm up the premises, the second boiler in the cascade is connected to help it.

In a cascade, the main boilers are connected in series so that it is heated by the first heat generator. At the same time, of course, in this bundle it is possible to isolate each boiler and bypass, which allows water to bypass the isolated boiler.

In the event of a malfunction, any of the heat generators can be turned off and repaired, while the second boiler will regularly heat the water in the heating system.

There is no particular alternative to the system. As practice shows, it is better and more reliable to have 2 boilers with a capacity of 40 kW than one boiler with a capacity of 80 kW. This makes it possible to repair each individual boiler without stopping the heating system.

It also allows each of the boilers to operate at their full capacity when required. Whereas 1 boiler of high power would work only at half the power and with increased stroke.

Parallel connection of boilers - pros and cons

We examined the main boilers above. Now let's consider the connection of backup boilers, which should be in the system of any modern home.

If backup boilers are connected in parallel, then this option has its pros and cons.

The advantages of parallel connection of reserve boilers are as follows:

Each boiler can be connected and disconnected from each other independently.
You can replace each heat generator with any other equipment. You can experiment with boiler settings.

Disadvantages of parallel connection of reserve boilers:

You will have to work more with the piping of the boilers, more soldering polypropylene pipes, more to cook steel pipes.
As a result, more materials, pipes and fittings, and valves will be consumed.
The boilers will not be able to work together, in unified system, without use additional equipment- hydraulic arrows.
Even after using the hydraulic arrow, there remains the need for complex adjustment and coordination of such a boiler system according to the temperature of the water supply to the system, and.

The indicated advantages and disadvantages of parallel connection can be applied both to the connection of the main and backup heat generator, and to the connection of two or more backup heat generators using any type of fuel.

Series connection of boilers - pros and cons

If two or more boilers are connected in series, they will operate in the same way as the main boilers connected in a cascade. The first boiler will heat the water, the second boiler will heat it up.

In this case, the first is to put the boiler on the cheapest type of fuel for you. It can be wood, coal or waste oil boiler. And behind it in the cascade there can be any reserve boiler - even a diesel one, even a pellet one.

The main advantages of parallel connection of boilers:

In the case of the first operation, the heat exchangers of the second boiler will act as a kind of hydraulic separator, softening the effect on the entire heating system.
The second reserve boiler can be turned on to heat up the water in the heating system in the coldest frosts.

Cons when using a parallel method of connecting backup heat generators in the boiler room:

Longer path of water through a system with more bends and tapers in connections and fittings.

Naturally, you cannot directly start up the supply from one boiler to the inlet of another. In this case, you will not be able to disconnect either the first or the second boiler, if necessary.

Although from the point of view of coordinated heating of boiler water, this method will just be the most effective. It can be realized if bypass bypass loops are installed for each boiler.

Parallel and serial connection of boilers - reviews

And here is a couple of reviews from users about the parallel and serial connection of heat generators in the heating system:

Anton Krivozvantsev, Khabarovsk Territory: I have it, it is the main one and heats the entire heating system. I am satisfied with Rusnit, a normal boiler, for 4 years of operation 1 heating element burned out, I changed it myself, there are all business for 30 minutes with a smoke break.

A KChM-5 boiler is connected to it, into which I built it. The steam locomotive turned out to be a noble one, heats well and, most importantly, the automation of the process is almost the same as that of an automatic pellet boiler.

These 2 boilers work in pairs for me, one after the other. The water that Rusnit did not heat is followed by KChM-5 and the pellet burner Pelletron-15. The system turned out as it should be.

There is one more review, now about the parallel connection of 2 boilers in the boiler room:

Evgeny Skomorokhov, Moscow: My main boiler is, it runs mainly on wood. My reserve boiler is the most common DON, which is included in the system with the first in parallel. It is rarely kindled, and indeed, I inherited it along with the house I bought.

But once or twice a year, in January, the old DON also has to be flooded, when the water in the system almost boils, but the house is still chilly. This is all due to poor insulation, I have not yet finished insulating the walls, and it would be good to insulate the attic ceilings better.

When the insulation is completed, I think I will not heat the old DON boiler at all, but I will leave it as a backup.

If you have any comments on this material, please write them in the comments form below.

Types of connection of two or more boilers

Usage more identical boilers requires a special wiring diagram. You can combine them into one system:

Parallel.
Cascading or sequentially.
According to the scheme of primary-secondary rings.

Parallel Features

There are the following features:

The hot water supply circuits of both boilers are connected to the same line. These circuits must have safety groups and valves. The last can overlap manually or automatically... The second case is possible only when automatics and servos are used.
join another line. These circuits also have valves that can be controlled by the aforementioned automation.
The circulation pump is located on the return line in front of the place where the return pipes of the two boilers join.
Both lines are always connected to hydraulic collectors... There is an expansion tank on one of the collectors. In this case, a make-up pipe is connected to the end of the pipe to which the tank is connected. Of course, at the junction there are check valve and a shut-off valve. The first does not allow hot coolant to enter the make-up pipe.
Branches extend from the collectors to the radiators, warm floors,. Each of them is equipped with its own circulation pump and coolant drain valve.

The use of such a piping arrangement without automation is very problematic, since it is necessary to manually close the valves located on the supply and return pipes of one boiler. If this is not done, then the coolant will move through the heat exchanger of the turned off boiler. And it turns out:

additional hydraulic resistance in the water-heating circuit of the apparatus;
an increase in the "appetite" of circulation pumps (they also have to overcome this resistance). Correspondingly, energy costs rise;
heat losses for heating the heat exchanger of the switched off boiler.

Read also: Heating a house with an air-heating boiler

Therefore, it is necessary to correctly install the automation, which will cut off the switched off device from the heating system.

Cascade connection of boilers

The cascading boiler concept provides for distribution of heat load among several units, which can work independently and heat the coolant as much as the situation requires.

You can cascade like boilers with stepped gas burners, and modulated. The latter, unlike the former, allow you to smoothly change the heating power. It should be added that if boilers have more than two stages of gas supply regulation, then the third and other stages make their performance less. Therefore, it is better to use units with a modulating burner.

With a cascade connection, the main load falls on one of two or three boilers. Additional two or three devices turn on only when needed.

The features of this connection are as follows:

The wiring and controllers are designed so that in each unit it is possible to control the circulation of the coolant... This allows you to stop the flow of water in the switched off boilers and avoid heat loss through their heat exchangers or casings.
Connecting the water supply lines of all boilers to one pipe, and the coolant return lines to the second. In fact, the connection of boilers to the mains occurs in parallel. Thanks to this approach, the coolant at the inlet of each unit has the same temperature. It also avoids the movement of the heated fluid between the disconnected circuits.

The advantage of parallel connection is preheating the heat exchanger before starting the burner... However, this advantage occurs when burners are used which ignite the gas with a delay after the pump is switched on. This heating minimizes the temperature drop in the boiler and avoids the formation of condensation on the walls of the heat exchanger. This applies to a situation where one or two boilers have been turned off for a long time and have had time to cool down. If they have recently turned off, then the movement of the coolant before turning on the burner allows it to absorb the residual heat that has remained in the firebox.

Boiler piping with cascade connection

Its scheme is as follows:

2-3 pairs of pipes from 2-3 boilers.
Circulation pumps, return and shut-off valves... They are on those pipes that are designed to return the coolant to the boiler... The pumps may not be used if the design of the unit includes them.
Shut-off valves on hot water pipes.
2 thick pipes. One is intended for supplying the coolant to the network, the other for returning... They are connected to the corresponding pipes extending from the boiler devices.
Safety group on the coolant supply line. It consists of a thermometer, a test thermometer sleeve, a manually unlocked thermostat, a pressure gauge, a manually unlocked pressure switch, and a backup plug.
Hydraulic low pressure separator... Thanks to him, the pumps can create proper circulation of the coolant through the heat exchangers of their boilers, regardless of what the flow rate of the heating system is.
Heating circuits with shut-off valves and a pump on each of them.
Multi-stage cascade controller. Its task is to measure the indicators of the coolant at the outlet of the cascade (temperature sensors are often located in the zone of the safety group). Based on the information received, the controller determines whether it is necessary to turn on / off and how the boilers combined into one cascade scheme should work.

Without connecting such a controller to the piping, the operation of boilers in a cascade is impossible, because they must work as a whole.

Features of the scheme of primary-secondary rings

This scheme provides organization of the primary ring, through which the coolant must constantly circulate. Heating boilers and heating circuits are connected to this ring. Each circuit and each boiler is a secondary ring.

Another feature of this circuit is the presence of a circulation pump in each ring. The operation of a separate pump creates a certain pressure in the ring in which it is installed. Also, the node has a certain effect on the pressure in the primary ring. So, when it turns on, water comes out of the water supply pipe, falling into the primary circle and changing the hydraulic resistance in it. As a result, a kind of barrier appears on the path of the coolant movement.