Connecting several boilers in a cascade. Features of cascade connection of gas boilers Cascade control unit of boilers and connection diagram

The cascade method of connecting boilers has been used for many years. The concept is simple: divide the total heating load between two or more independently controlled boilers, and turn on only those boilers that satisfy the demand for a given load in given time. Each boiler represents its own “stage” of heating output in the total power of the system. An intelligent controller (microcontroller) constantly monitors the temperature of the coolant supply and determines which stages of the system should be turned on to maintain the set temperature.

ADVANTAGES
using a cascade system:

Increased seasonal efficiency of the system compared to using one powerful boiler;
-partial coverage load even if one of the boilers is switched off, for example, for maintenance work. This is especially important in harsh conditions climatic conditions when, due to low temperatures, an idle 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 lower loads for heating.

We present the performance characteristics of two different cascade systems in relation to a hypothetical load diagram. The first system uses two boilers with single-stage burners, each capable of supplying 50% of the design load. The second system uses four boilers with single-stage burners, each of which can supply 25% of the design load. It is obvious that a system of four boilers instead of two is able to more effectively provide the conditions of the design loads. Based on this, it can be assumed that the more stages in the cascade system, the better it satisfies the loads. This is especially effective when the required power is low. However, as the number of stages increases, the heat transfer surface area of ​​the system (boiler casing) through which heat loss occurs increases, which can ultimately negate the benefits of the increased efficiency of such a system. Therefore, it is not always advisable to use more than four stages. An inherent limitation of a “simple” cascade system (boilers with single-stage or two-stage burners) - step-by-step regulation of heating output (system power), rather than a continuous controlled process. Although the use of more than two stages significantly reduces the heating output of each boiler, the ideal solution would be a “modulated” cascade system (boilers with modulating burners). Modulating burners allow you to continuously adjust the power 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 stable boiler efficiency and minimal concentrations of pollutants in the flue gases under variable heat load. Next step. Latest trend in solving cascade systems - a modulated cascade system. Unlike the use of staged burners, boilers with modulating burners are able to smoothly change the volume of fuel supply, and therefore control the level of heating output over a wide range of values. Today, the heating equipment market is widely represented by low-power boilers 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 control coefficient (i.e., the ratio of the boiler’s maximum thermal output to its minimum). For example, the operating regulation coefficient of a boiler burner with a maximum thermal power of 50 kW and minimum consumption 10 kW of fuel will be equal to 50 kW/10 kW or 5:1. The total operating regulation coefficient of boilers installed in a cascade system significantly exceeds the coefficient of an individual boiler. For example, if a cascade system uses four boilers with a maximum heating output of 50 kW and a minimum of 10 kW, the total output control will be in the range from 200 kW to 10 kW. Consequently, the operating regulation ratio of such a system will be 20:1. In conditions of low heat output, the heat exchanger of a boiler with a modulating burner 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 in 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%. Low-power boilers with modulating burners are usually designed with closed camera combustion, which expands the set design solutions for air supply and combustion product removal systems, since the chimneys of such boilers do not necessarily have to be straight. Typically, chimneys are 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 installed in old, indirect or unsuitable normal modes smoke channels).

System Features
There are three important features, which should be taken into account when designing a “modulated” cascade system. First. Features of the supply lines and controllers should allow independent adjustment of the flow circulation through each boiler. Water should not circulate through an idle boiler, otherwise the heat from the coolant will be dissipated through the heat exchanger or boiler casing. This also applies to the simple cascade system. Independent regulation of the coolant flow is achieved by equipping each boiler with an individual circulation pump. When installing circulation pumps in parallel, to prevent the reverse flow of coolant through idle boilers, downstream pumps should be installed check valves. Optimal solution this situation - installation circulation pump with wet rotor with built-in shut-off valves. Supplying coolant to each boiler using individual circulation pumps makes it possible to increase the pressure in the heat exchanger of an operating boiler in order to prevent cavitation and explosive steam formation.

The second important point is parallel connection 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, eliminate the flow of coolant between the circuits. The low temperature of the coolant supplied to the boiler promotes the condensation of water vapor from combustion products and increases 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 turning on the burner. They can also keep the pumps running for some time after the burner is turned off. The first ensures that the boiler heat exchanger is heated by the warm supplied coolant 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 utilize the residual heat of the heat exchanger, and not remove it through the ventilation system after the boiler has finished operating. And thirdly, it is very important that circulation pumps ensure adequate coolant flow through operating boilers, regardless of the system flow rate. Closely spaced T-junctions (Figure 2) or low pressure drop manifolds (Figure 3) provide flow diversion from the system flow to ensure adequate boiler flow regardless of flow changes in the distribution system. Closely spaced T-tube joints on the primary/secondary circuit are used to “shave off” the pressure differential of the circuits.

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

Operating modes
Most cascade controllers are capable of at least two operating modes. In heating mode, a weather-dependent control principle is implemented, that is, the set temperature value of the coolant supplied to the system depends on the external temperature. The lower the external temperature, the higher the set value for the supply temperature. This system eliminates the need to use a mixer between the boiler and heating consumers. In DHW mode, software control of the system is carried out when the set value of the temperature of the supplied coolant does not depend on external temperatures. In other words, a certain, sufficiently high temperature value is set, which ensures high level heat transfer through the secondary heat exchanger. This mode is usually used to provide more high temperature coolant supplied through a heat exchanger to DHW consumers and anti-icing systems. Modulating the boiler power leads to a significant reduction in the differential between the required and actual coolant temperatures, which prevents frequent “clocking” (turning on/off) of the boiler. Some controllers are also responsible for the operation of the main circulation pump and are connected to the dispatch system engineering equipment building.

Small, quiet and powerful
The ratio of physical size to heating output of some modulating burner boilers is truly impressive. For example, some manufacturers provide eight-stage “modulated” cascade systems with a heating output 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 benefit- low noise system. The modern generation of low-power boilers with modulating burners provides space savings, high efficiency, quiet operation and reliability. This is an ideal solution in low temperature systems, such boilers are ideal for underfloor heating, anti-icing systems, swimming pool heating, DHW systems, as well as heat pump systems, incl. geothermal. They have already gained a position in the field of heating private houses. As part of a cascade system, boilers with modulating burners represent a new alternative to industrial heating systems.

Practice shows that 80% of the heating season, the boiler capacity is used at only 50%. This means that on average only 30% of the boiler power is consumed throughout the year. Such a weak load often leads to low efficiency of its use. Therefore, rational use of energy often requires A complex approach. Great solution can become a cascade boiler system. It provides the consumer with the amount of heat required at the moment, gradually connecting several small boilers one after another.

What are the advantages of such a system?

• Firstly, high reliability. If one of the boilers fails, this does not mean that the entire system has stopped - the remaining boilers will fill the necessary load.
• Secondly, increasing the overall service life of boilers. In the warm season, you can use only part of the boilers, turning off the rest manually or using the built-in automation.
• Thirdly, economical energy consumption due to less loss of efficiency when operating at partial power.
• Fourthly, ease of installation. Several small-capacity boilers are easier to transport and install than one powerful, large-sized boiler.
• Fifthly, affordable repair and maintenance. Parts for high-power boilers are much more problematic to obtain due to lower production volumes.

The advantages of such a system also include the ability to vary the location of the boilers and the installation location itself.

Principle cascade connection boilers

The principle of cascade connection is to combine several boilers in order to increase the power of each piece of equipment.
To implement a cascade, it is necessary to divide the total heat load between several boilers and include in the cascade only those whose power corresponds to the required load in a certain period. In this case, one of the boilers acts as a “leader” and starts working first, and the remaining boilers are turned on as needed.
The entire process is controlled by automatic control, which can transfer the role of the main boiler, as well as regulate the order and need to connect secondary boilers to maintain a given mode. In a cascade system, each boiler represents a certain “stage” of heat output. Control system supports required level temperature by connecting or disconnecting individual stages. In the event of a malfunction of one boiler, the automation distributes the load to the rest of the system. If there is no need for heat, the automation turns off all boilers, restoring operation on demand.
A stepped cascade connection system makes it possible to replenish the heating system loads with great efficiency. However, one cannot assume that the more boilers in the system, the more efficient their operation. In proportion to the increase in the number of units, heat loss through the surfaces of idle boilers increases, so experts advise choosing a cascade of a maximum of four boilers. For uninterrupted operation of the system, it is necessary to install a hydraulic separator between the heating and boiler circuits. It will ensure a reduction in hydraulic resistance and hydraulic balance of the boiler and heating circuits.

What types of boiler cascades are there?

Types of cascades are usually distinguished by the type of burner devices used in them:

• "Simple" the cascade includes boilers with single-stage or two-stage burners. Such a system increases the boiler power levels - for example, combining two boilers with single stage burner forms a more economical two-stage system.


• Cascade "mixed" type combines boilers, one of which is equipped with a modulating burner. It is on this boiler that a control system is installed that regulates the temperature of the boiler water.


• Part "modulating" The cascade includes boilers with modulating burners. Unlike the “simple” and “mixed” cascades, this system is capable of changing the volume of fuel supply in a smooth mode and adjusting the heating output over a wide range.

How to calculate and assemble a cascade

The calculation of the cascade boiler house project is based on determining the rated thermal power of the heat source. This value represents thermal power, necessary to replenish the heat consumed by the object and the power of heat consumption by other objects of the system.
The productivity of a boiler room is not determined by the sum of all consumed powers, but is calculated for each system individually.
The ČSN 06 0310 standard defines calculations for the following objects:

• Heating with intermittent water heating and ventilation:

Qtotal=0.7xQOtop+0.7QVent+QDHW (W, kW.)

• Heating with continuous process heating and constant ventilation:

Qtotal=QOtop+QTechnical(W, kW.)

• Heating and water heating flow method with the advantage of the DHW circuit:

Qtot = maximum value of heat consumption for heating or DHW heating

Qtotal – total boiler power

Qotop– heat loss of the object at the external design temperature

Qvent– heat demand of ventilation equipment

QDHW– heat requirement for heating the DHW circuit

Qtechn– heat demand for ventilation or process heating

Calculation of the boiler room requires serious and professional approach, otherwise errors in calculations can lead to ineffective and uneconomical operation of the system.

Assembly and installation of the system

The cascade boiler system consists of the following main parts:

• Hydraulic cut-off;
• Hydraulic connection of boilers;
• Security Group;
• Heating of the DHW circuit;
• Additional components.

Connecting the cascade system is carried out in several stages:

• Installation of fixtures and boilers;
• Installation of hydraulic manifolds, gas mains and drainage lines;
• Connection of safety group and hydraulic separator;
• Connecting the smoke collector

First, two boilers are connected in a cascade, then the rest are connected. After combining the boilers, the security group is connected and the automation is configured.

It's no secret that centralized provision of heat to existing and newly built facilities is becoming more and more problematic every year. In particular: the lack of the possibility of objective accounting, large heat losses during transportation, subjectivity in determining the cost, the monopolistic nature of the activities of heat suppliers, the impossibility of increasing existing capacity, and, consequently, the ban on connecting additional consumers - these are just some of the problems due to which Experts' views are turning towards autonomous heating and hot water supply.
In this regard, in recent years, block boiler rooms, modular boiler rooms or cascade boiler rooms have become increasingly popular in our country.
The Termona-Bel company promotes on the domestic market heating equipment Czech Thermona(Termona), which has been working for many years towards improving equipment for autonomous heating. 13 years ago, specialists from Thermona were one of the first in the world to come up with the idea of ​​creating cascade boiler houses with a capacity from 8 to 1440 kW based on wall-mounted gas boilers.

A cascade based on THERM boilers is a sequential connection of several boilers (up to 16 units) into a single heating system with program controlled. The peculiarity of the connection and design of Therm boilers allows you to smoothly regulate the total power of all boilers in the cascade from the minimum power of one of the boilers. For example, when installing a cascade of 16 THERM TRIO 90 boilers, the total power of the boiler room will be 1440 kW, and the minimum – 36 kW, i.e. 2.5% of its maximum. For comparison, a modern boiler with a power of 1500 kW provides a control range from 1050 kW to 1500 kW, which is from 70 to 100% of power.
In heating system technology, the cascade boiler room based on THERM boilers is an innovative method for optimizing the operation of high-power heating systems. It is quite obvious that the heat loss of the facility, and accordingly the power of the boiler house, is calculated based on the lowest temperatures in the given region, and the actual load on the boiler house is significantly lower than the established one.
Practice has confirmed that in heating season approximately 80% of the operating period, the boiler room capacity is used at no more than 50%, and during the operating season, the load is, on average, 25-45%. Consequently, with such an uneven and often low load, one high-power boiler (traditional system) will unnecessarily consume energy resources and ineffectively compensate for heat costs. In contrast, the cascade system smoothly ensures that the boiler room operates at the required power (over a wide range) regardless of the time of year by connecting several small boilers one after the other in series. With help cascade regulation with program control, the problem of determining the optimal ratio of the power of the boiler room and the heating system is solved. Thus, in the off-season and during warm winters, a cascade boiler house can operate for a long time at low coolant temperatures, which reduces heat radiation costs and system standby periods. At the same time, the temperature conditions of the object improve, that is, the comfort of the user.
The use of THERM DUO, TRIO and KD boilers in a cascade makes it possible to achieve an optimal ratio of occupied area to installed capacity boiler room while maintaining one of the main advantages of cascade connection - an incomparably wide range of smooth power modulation. In the organization of the boiler room, single-circuit wall-mounted boilers with a capacity of 20, 28, 45 and 90 kW are used. From 2 to 16 units can be assembled in a cascade, depending on the required power. All boilers are modern, technically advanced gas appliances, having an efficiency of up to 94%, with a service life of at least 15-20 years.
A significant advantage of a cascade boiler house based on THERM boilers over traditional boiler houses is its high reliability and extended service life. High reliability of the boiler room is achieved through the joint operation of several boilers in one system, and the failure of one of the boilers does not stop the operation of the heating system as a whole. The software underlying the operation of the cascade boiler house is designed in such a way that the boiler startup sequence changes daily. Consequently, if today the boiler is started first, then the next day it becomes the last in line and will start only if the boiler room needs to operate at full capacity. Due to this, the operational life of each boiler increases, which leads to an increase in the service life of the boiler room as a whole. An undoubted advantage in a cascade boiler room is the ability to connect a boiler indirect heating to each boiler (except for the manager). Thus, in a boiler room of 16 boilers, you can connect 15 boilers from 200 to 1000 liters each and thereby satisfy any need for hot water supply. The boiler automation gives preference to the preparation of domestic hot water, and if there is no need for its preparation, the boiler proceeds to work in the heating system together with other boilers. When the operation of a cascade boiler house changes from winter to summer mode operation, the DHW preparation mode remains, the heating system pumps are started automatically once a day, driving the coolant through the system, and the anti-freeze function remains active. The advantages of cascade connection of boilers undoubtedly include the ability to choose many options for the boiler room: location and placement. You can install a boiler room almost anywhere: in the basement or attic space, in a specially made extension.
In the case of organizing a boiler room on the roof, the huge advantage of a cascade of wall-mounted boilers over stationary floor-mounted ones is light weight and ease of delivery to the installation site. There is no need to use special cranes to lift equipment during installation or dismantling. There is no need to disassemble the roof when replacing the boiler. Faulty boiler components are replaced on site. The light weight of the equipment and its placement on the wall help avoid unwanted loads on the building’s floors. Retraction flue gases when using boilers in the “turbo” version, it is possible directly through the wall on which the boiler is mounted. This allows you to save on the construction of an expensive stainless steel chimney. An undeniable advantage is the automatic regulation of the boiler room. The programmer provides control in accordance with the room temperature set for a given period of time. It brings to work the required number of boilers from the cascade and at the power that is really needed. The absence of the “human factor” eliminates management errors. In general, a universal building climate control system is created. When the temperature in the room increases above the set one, the programmer turns off the operation of the boiler room, and if necessary, the thermostat of the air conditioning system turns on the air conditioning system. If the temperature drops, everything happens in the reverse order. Boiler room control devices allow the dispatcher of a service organization to see the current state of all equipment from his computer via a modem.
Termona-Bel company is official dealer Czech company Termona in the territory of the Republic of Belarus. The main activities of the Termona-Bel company are wholesale and retail trade of boiler houses, training of interested specialists, installation and commissioning of boilers, warranty and service maintenance boiler houses, supply of spare parts for boilers and other activities aimed at promoting equipment in the territory of the Republic of Belarus.
The main advantages of cascade boiler houses based on THERM boilers can be briefly formulated as follows:
profitable investment;
economical operation due to a wide range of smooth power modulation (minimum threshold from 20% when installing 2 boilers and from 3% when installing 16 boilers);
full automation of control;
weather-dependent regulation;
remote control and control of the boiler room operation via a programmer or PC;
no need to maintain full-time workers in the boiler room;
high operational reliability due to the operation of several boilers in one system;
increased service life of boiler equipment;
simplicity and clarity of the technical solution;
ease of installation and commissioning;
simple and intuitive controls;
small footprint;
use of the floor for other components of the boiler room;
convenient connection of external tanks for DHW preparation;
the possibility of installing a high-power boiler room without installing an expensive chimney;
careful attitude towards environment.
Choosing the right heat source will help you save a lot of money while maintaining the required comfort. When comparing the economic indicators of exploited residential buildings and other facilities before and after installing Therm cascade systems, users often achieve incredible energy savings of up to 40% per year, so the return on investment is very quick and obvious!

Today, the heating problem is very acute and is often considered, paying great attention to it. Both professionals and ordinary consumers are involved in the process. In this material you are invited to consider the solution of heat production from a new perspective. Options and selection of boilers will be considered, taking into account the opportunities that can be provided modern technology, implemented in the Therm boiler cascade systems. Optimal choice heat generating equipment will help to significantly reduce costs without skimping on comfort requirements.

If you compare the cost of operating residential buildings or other facilities before and after installing Thermona cascade boiler houses, then the cost savings can reach an incredible amount - up to 40% per year. The return on investment comes very quickly. In addition to high efficiency and smooth power modulation over a very wide range, the cascade boiler room can be located directly in the heated object. The cascade boiler system reacts accurately and quickly to changing heating requirements of the facility and does not have inertial losses characteristic of clumsy central systems heating, as well as for boiler rooms with one massive and bulky boiler.

What is a boiler cascade

The boiler cascade is special system connecting several boilers, allowing them to work as a single whole. The design feature of Therm boilers and their automation allows you to smoothly increase the generated power from 24% of the rated power of one boiler used. If increased power is required (up to 1440 kW), cascading boilers will provide great advantages. First of all, the installation of Therm DUO 50T, DUO 50FT, DUO 50, TRIO 90T, TRIO 90 and 45KD boilers makes efficient use of the required space. The boiler room has the highest ratio of occupied area to installed power, while maintaining all the advantages of cascade connection and stepless power modulation.

It is not necessary to include boilers of the same type KD, DUO or TRIO in the cascade. Boilers can be combined with different powers, which allows the system to be adapted to the actual heat loss of the facility and to the required hot water supply performance. In the heating industry, the cascade has become an innovative way to optimize high-capacity heat-generating facilities. One high-power boiler would work even with a low heat demand, overheating the system; using cascade switching, you can turn on exactly the number of boilers that are needed at the moment, which is regulated by electronic microprocessor automation.

It has been confirmed in practice that during the heating season, 80% of the time, only 50% of the boiler power is in demand. That is, for the season as a whole, the boiler is used only at 30% of its maximum capacity. This means that most of the time it operates at minimum power with low efficiency. While the cascade circuit provides required power at a given time, connecting one after another required quantity boilers and bringing them to optimal, economy mode. Cascade regulation, controlled by software, removes the impact of the factor of imbalance of heat generation power and the need for heat from consumers. The range of power changes in a cascade allows you to constantly work with a low heating water temperature, which reduces radiation losses even during system downtime. Availability is increased and heating temperature conditions are optimized to improve comfort of use.

Until recently, the operation of a cascade boiler house could only be supported by expensive equipment with completely changed automation of the leading boiler. A breakthrough was the communication interfaces developed for boilers, connected to standard boards and making it possible to transfer information between boilers and smoothly change the power of all boilers connected in a cascade. This made it possible to install optimal parameters power at any time of operation and gain access to information about the actions performed by each boiler, for example, when diagnosing faults or during commissioning of a cascade boiler house. Cascade boiler room is " intelligent system"with a fully automated operating mode without the presence of the human factor.

Today, a technical solution using standardized hardware and software available for very budget-conscious owners.

Why cascade

Boilers currently on the market can be of different designs - boilers with one constant power, boilers with two constant powers and boilers with continuously variable power control (from approximately 40% to 100% power). Usually, control units for sequential switching of boilers ("cascade switches") are offered, which can alternately switch the boilers on and off. The standard switching scheme is up to 4 boilers in a cascade. In practice, this corresponds to an input power step of 100 kW, with a total maximum of 400 kW, i.e. jumps of 25%. In contrast, the THERM boiler cascade operates at minimum power, e.g. 13 kW (45 KD) continuously up to max. power 400 kW. Naturally, in this case, gas consumption will be significantly less. The advantages of cascading boilers include a large number of options for possible boiler houses. You can change both the location of the boilers and the layout of the boiler room itself. The boiler room can be placed almost anywhere - in the basement, a separate extension or in the attic. Separate boilers and the cascade boiler room equipment can be installed arbitrarily so that the boiler room, like the children's designer, will fit exactly into the allotted space.

Why a cascade of THERM boilers

THERM wall-mounted boilers, when used alone, smoothly regulate their own power from approx. 23% to 100% (depending on the type of boilers used) of rated power. The THERM cascade of boilers in a unique, but at the same time simple way, makes it possible to increase the range of smooth changes in boiler room performance from the minimum power produced by one boiler to the maximum power of all 16 boilers connected in cascade. This extends the control range from 1.8% to 100% power for up to 16 cascaded boilers. The implementation is very simple - a switching interface board is installed in each connected boiler, connected via two wires to other boilers, and a full-fledged cascade is ready. Without the use of an expensive cascade switch. Managing the cascade as a whole is also simple. You need to turn on all the boilers, and then set the heating temperature on the first one. The boilers will do the rest themselves. There is no need for time-consuming and complex setup of each boiler, setting up the control of the leading boiler, etc. If it is necessary to increase the number of boilers, it must be connected to heating system another boiler, install an interface in it, connect two wires and start the cascade.

Everything is very simple. It is enough to install switches on all interfaces, in accordance with the serial number of the boiler in the cascade, set the switch located in the main boiler, according to total number boilers and the cascade will start working. This initial setting must be carried out by a service technician to avoid complications. In the future, such settings will no longer be made. In the case of heating water heating control outside temperature(equithermal regulation), it is enough to install only one additional sensor and the cascade boiler room will operate depending on weather conditions. Equithermal regulation is strongly recommended to be used in boiler rooms heating industrial or office buildings to completely eliminate errors associated with the actions of untrained personnel.

Another advantage of THERM boilers is manifested in solving the issue of hot water supply (DHW). One or more boilers are hydraulically connected through a three-way valve to the boiler in the cascade, and the tank thermostat is connected with two wires to the corresponding boiler in the cascade and the DHW issue is resolved. Any THERM boiler connected to the THERM cascade, except the control boiler, can heat water for hot water supply. Thus, the maximum number of boilers connected to the cascade that can heat water for domestic hot water is up to 15 units.

Briefly the main advantages of THERM boilers:
1. exceptional investment efficiency;
2. economical and highly efficient cascade communication solution;
3. greater cost savings compared to other heat sources;
4. fully automated operation;
5. excellent operating economy;
6. wide modulation of the power of the boiler house as a whole (for example, from 13 to 720 kW);
7. high operational reliability;
8. simple installation and commissioning;
9. simple and clear technical solution;
10. simple and intuitive controls;
11. optimal adaptation for connecting a DHW boiler;
12. small footprint;
13. remote diagnostics and monitoring of boiler rooms;
14. respect for the environment.

Boilers used in cascade boiler houses

Most often, Therm DUO 50, DUO 50 T, DUO 50 FT, TRIO 90, TRIO 90 T boilers or Therm 45 KD boilers are used for inclusion in the cascade. Boilers with a capacity of 28, 20, 17 or 14 kW can also be included in the cascade. The technical solution of the boiler cascade system allows all THERM boilers with DIMS automatic control to be included in the cascade, and these are boilers with a digital display, with the exception of boilers with instantaneous heating of the DHW circuit. For large cascade boiler houses, first of all, you can use boilers TRIO 90 or a version with forced removal of combustion products - TRIO 90T (advantages of DUO 50 FT). A separate topic is cascade boiler rooms made from Therm 45 KD condensing boilers.

Combination of Thermona intelligent boiler control and condensation principle boilers leads to sharp decrease heating costs and heating the DHW circuit while maintaining very low emission parameters as a result of the gas combustion process. The first impetus for development condensing boiler THERM 45 KD was mainly used in cascade boiler houses. When developing a cascade boiler system from condensing boilers, Thermona specialists used their own experience gained in designing cascade boiler systems from traditional boilers. The cascade boiler system as a whole is designed to provide the end user with a comprehensive, intelligent heating and domestic hot water solution. Therefore, a cascade of Therm 45 KD boilers will fulfill all the requirements for a heat source, and not only that. At the same time, the cascade boiler room allows the use of fully compatible equithermal control without the need to install additional control systems or regulators. Today, not all manufacturers can offer such a solution.

The same cascade as from THERM gas boilers can be assembled using Therm electric boilers. All THERM electric boilers can be connected together. Intelligent Control cascade of electric boilers allows you to use a cascade with smooth power control as a heat source. A cascade of THERM electric boilers allows you to heat water for households. boiler needs. Only control systems for cascades of gas and electric boilers cannot be connected to each other.

Boiler characteristics

Possibility of connecting THERM boilers in cascade

Characteristics of boilers THERM DUO 50, DUO 50T

Characteristics of boilers THERM DUO 50FT

Characteristics of boilers THERM TRIO 90, TRIO 90T

Characteristics of THERM 28 boilers

Characteristics of combustion products of THERM boilers

A. Boyko

The use of several gas boilers for one heating system is a fairly popular solution among installation and design organizations. Let's consider practical issues regarding the installation and use of such cascade installations

The decision to use several gas (two or more) boilers for one heating system is justified with a heat load of 40 kW. This can be either a large heated area or the presence of thermal loads in the form of swimming pools, garages, bathhouses, greenhouses, etc.

Using several boilers for one heating system has a number of advantages compared to one boiler, which has the same total power. Firstly, several small boilers of smaller size and weight are much easier and cheaper to deliver to the boiler room and install there instead of one large and heavy boiler. This point becomes especially relevant when installing roof or semi-basement cascade boilers.

In addition, system reliability is significantly increased. If one of the boilers is forced to stop, the system will continue to operate, providing at least 50% of the power (if two boilers are installed).

Other factors in favor of a cascade installation include ease of maintenance due to the smaller size of each boiler (maintenance of each boiler can be carried out without stopping the entire system); increase in the total lifespan of boilers (in autumn and spring time You can operate only part of the boilers by turning off the other part manually or using cascade automation).

In addition, if in the future it becomes necessary to replace a part, then it is generally known that parts for lower-capacity boilers are more accessible and cheaper due to greater serial production.

Control of boiler operation in a cascade

Most often, to simplify the schemes when boilers are used together, no cascade automation is provided, and the required outlet temperature is set on each boiler. But, if desired, you can use cascade control units that are connected to contacts intended for connecting individual room thermostats.

Connecting boilers in a cascade using a cascade control unit is comprehensive solution and has more high efficiency. This unit ensures alternate operation of all boilers and guarantees the same number of operating hours for each heat generator. The block optimizes the functioning of the system and ensures that only required quantity heat generators, depending on the required power.

When working with modulating burners, the cascade control unit, in addition to the principle described above, strives to ensure that the boilers operate in partial power mode (modulation mode). The most effective is to use a cascade control unit together with condensing boilers. In this case, the power supplied by the boilers most closely matches the power consumed. For example, when using together three wall-mounted boilers of the LUNA Duo-tec MP series with a power of 100 kW (BAXI (Italy)), the power released smoothly changes from 30 to 300 kW depending on the needs of the system. This means that the operating regulation coefficient of such a system will be 1:10. Schematic diagram such a system is shown in Fig.

Rice. Diagram of a heating system with a cascade of Luna Duo-Tec MP boilers, one high-temperature circuit, two low-temperature circuits and a DHW boiler:
QAC 34 - sensor outside temperature; AVS 75 - external programmable expansion module; AGU 2.550 - internal expansion module; OCI 345 - interface board for connecting other regulators via LPB bus; QAD 36 - clamp-on temperature sensor; QAZ 36 - water temperature sensor in DHW boiler; QAA 55 - room temperature sensor; QAA 75 - remote control climate regulator; MV - mixing valve; RT - room mechanical thermostat

Condensation

Condensing boilers thanks to low consumption fuels are currently the most economical installations that consume gas. As part of a cascade system they represent a new alternative to industrial heating systems.

The use of condensing boilers with a power of 45 to 150 kW in cascades makes it possible to: provide greater power in limited space; facilitate the installation of roof boiler rooms due to the small specific gravity equipment (per unit of power). In addition, condensing technology provides lower vibration and noise levels compared to traditional boilers with forced-air burners, and the presence of a built-in fan allows the use of small-diameter chimneys (you can do without large, expensive chimneys).

Environmental friendliness of condensing boilers, namely very low CO and NO x content in comparison with other boilers in the traditional types fuel allows the use of such systems in major cities and environmental zones. Among the disadvantages of condensation technology are high price(which, however, is compensated short term payback due to increased gas tariffs), the need to organize the removal and neutralization of condensate.

Taking into account the errors that often occur when installing and servicing boilers, we can determine the basic recommendations regarding this.

In particular, it should be noted that when working together several boilers for one heating system with variable water flow (several separately adjustable heating zones), it is recommended to use a hydraulic separator (“hydraulic arrow”).

In addition, when using a boiler to heat a small area (less than 100 m2), it is strongly recommended to use a room thermostat together with the boiler (to reduce the number of boiler switches on/off). It is also recommended to carry out a separate adjustment of the heating circuit power.

Otherwise, recommendations for installing cascade boilers do not differ from recommendations for installing other boilers. So, before connecting the heat generator to the heating system, it is necessary to thoroughly flush all the pipes of the boiler and heating system to remove possible foreign particles. It is strongly recommended to install a filter on the heating system return pipe and shut-off valves on the supply and return pipes of the heating system.