Work with a two-stage burner according to the PID law. Domestic boiler control. Classification of gas burners

After getting acquainted with various types gas burners, you can confidently decide on the choice of the burner that is suitable for your purposes.

Manufacturers of modern boilers, constantly improving their products, endow them with new functions and at the same time complicate the selection of the desired boiler and its adjustment. This is not surprising, because the heating system of modern country house consists not only of a boiler, pipes, radiators under the windows, but also includes many heating circuits, the control of which should be entrusted to automatic controllers.

Otherwise, homeowners will have to constantly adjust individual elements manually to ensure a sufficient level of comfort. However, more a complex system management is always a higher price. "Do I need it?" the buyer asks rhetorically.

In this short article, we will try to convey to readers the physics of processes in a working heating system, which is inherent in all heating systems, including complex ones. Having an idea of ​​what you have or are going to buy is very important when choosing a heating system, its operation or modification. into the structure modern systems heating already has functions that require its modification and improvement.

So, two most important functions are assigned to boiler automation: a security system and thermal comfort. Of course, ensuring safety has the highest priority among other tasks. For example, the upper control limit for the boiler water is set in such a way that it never exceeds the limit level due to the temperature overshoot. The value of the possible temperature overshoot depends on the design and material of the boiler and is taken into account by the automation manufacturer when setting the upper temperature control limit in the boiler.

In our article, we focus on the operation of automation to ensure a comfortable temperature in heated rooms.

The feeling of thermal comfort is largely subjective. In this regard, experts in the field climate systems operate with the concept of the Fagner comfort index. It provides seven positions corresponding to subjective feelings.

• -3 "cold"
• -3 "cool"
• -1 "light chill"
• 0 "neutral"
• 1 "light heat"
• 2 "warmth"
• 3 "hot"

This or that temperature in the room is set when a balance is reached between heat losses and heat transfer of devices. At the same time, in order to maintain the set temperature value, any change in heat loss caused by weather changes must be compensated by an appropriate correction of the temperature of the coolant or its volumetric flow through the heating devices.

Let us first consider the second case, namely the regulation of the room temperature by changing the volume flow through the heating devices.

This problem is easily solved with thermostatic valves mounted on radiators or convectors. In this case, the task of boiler automation is to maintain the temperature of the coolant at a given level (simply turn the potentiometer knob on the boiler control panel, setting the desired temperature). In most boilers, this is how everything happens and does not imply anything more. The boiler operation algorithm differs depending on the burner: modulating, one or two-stage.

When operating with a single stage burnerThe temperature controller works as a threshold switch, which switches the burner on and off when the supply temperature reaches the threshold values. A certain difference is set between the on and off thresholds - the “on hysteresis”. As a rule, the switch-on and switch-off thresholds are arranged symmetrically with respect to the set flow temperature, so that the average value of the temperature over a long period coincides with the set value.

Problem occurs when the volume of the coolant is small, and the heat consumption is significant less power burner, the burner temperature will rise too fast. Takes place danger of too frequent burner switching on, which may affect its resource. The problem is overcome different ways. For example, with the help of a time-varying hysteresis value.

At low heat loads and correspondingly short heating-up periods of the boiler, an increased hysteresis value applies. If the switch-off threshold has not been reached within the set hysteresis time, the hysteresis value automatically decreases linearly to the standard 5 deg. Celsius. Buderus uses a different algorithm called "dynamic switching" - when the supply temperature, increasing or decreasing, compares with the set temperature and the system begins to calculate the integral of the function of the difference over time.

The burner is turned on and off when the integral reaches the set value, which means that when the boiler heats up quickly, the switching temperature is higher than when it warms up slowly. Thus, the switching threshold is automatically adjusted to the characteristics of the heating system and the amount of heat demand.

For two stage burner the process does not fundamentally differ from what was discussed above - only there are twice as many switching thresholds.

Modulating burner allows constant proportional control of the flow temperature, when the burner power is linearly dependent on the temperature mismatch. However, such regulation is not always possible, since for many modulating burners the power varies smoothly not from zero, but from 30-40% of the maximum value. If the heat consumption in the heating circuit is below this limit, then we again encounter threshold regulation. Until now, we have considered processes when the preset temperature of the boiler was set manually by a potentiometer on the boiler control panel, and the task of boiler automation was to maintain this temperature.

Maintaining a comfortable room temperature by controlling the boiler water temperature. This happens by introducing a room thermostat into the automation system.

notice, that room thermostat usually not included in the standard equipment of the boiler. The control of the boiler operation in order to maintain the set temperature in the room can be carried out by one of two types of regulation: two-position (on / off) or continuous. In the first case, the control algorithm is the same as for a boiler with a single-stage burner. However, compared to the boiler water temperature, the room temperature changes much more slowly and this can lead to large overshoots. Therefore, on-off control is not usually recommended for heating systems with boilers over 25-30 kW.

With continuous regulation The control variable is the supply temperature, which varies depending on the temperature deviation in the room. The temperature sensor must be located in a specific room (let's call it a reference room) and the temperature in other rooms is set relative to the temperature of this reference room. The comfortable temperature varies from room to room. In the bedroom, for example, it is lower. During the day, the premises are usually empty and maintaining a comfortable temperature is pointless, a waste of money.

It goes without saying that the function of setting and executing a daily temperature schedule in the rooms. Daily temperature programming is often possible for different days of the week (weekdays, holidays, parties, holidays). big problem with this method of control, it becomes the regulation of the temperature in the rooms relative to the reference one, by linking it into a single circuit.

In addition, by increasing comfort in the reference room, we risk reducing it in other rooms tied to the same control loop. In addition, temperature controllers cannot be used in the reference room. heating appliances, since they are independent control systems with the same input parameters as boiler automation.

To control a boiler that heats water for several heating circuits at once with different characteristics, some common input parameter is required for these circuits. Simple and effective solution was found.

Using as an input parameter the air temperature outside the building

Indeed, the flow temperature of any heating circuit required to compensate for heat losses in the rooms is related to the outdoor temperature by well-known relationships, which in the graphical representation are usually called heating curves or heating curves. It remains only to lay these ratios for each specific circuit in the algorithm of the boiler control system. In the automation of most manufacturers, for this it is necessary to select one of the proposed curves. There are other approaches to this problem, for example, it is enough for the Buderus boiler adjuster to set two points, according to which the automation itself will build the entire curve. Note that it is extremely important to locate the temperature sensor on the north side of the house away from heat sources such as windows and chimneys. In this case, weather-dependent automation works as correctly as possible.

What happens if you open the window? System that controls the boiler and heating circuits according to outside temperature, can respond to unforeseen changes in the heat balance in heated rooms. In most cases, this possibility is laid down in the form of automatic adjustment (most often - parallel transfer) of the heating curve of the corresponding circuit based on the readings room sensor temperature.

Moreover, many manufacturers offer, in addition to weather-dependent automation, a room thermostat. When using external and room sensors together, the thermal regime can be adjusted to take into account additional heat sources in the room. Simply put, if the stove is turned on in the kitchen, and due to this it has become warmer there, the controller will “take into account” this fact and correct the indicators of external sensors, or the room is located on the sunny side and requires heating only when the sun “leaves”.

As the cost of automation increases, the ability to control more complex burners (with step, step-progressive and modulation control), a cooking unit is added to its capabilities. hot water, one or more (the number of radiator circuits is growing), low-temperature (warm floor) circuits, implement various other programs (connection of solar water heaters), etc.

To summarize: why all these difficulties with weather-dependent control? How is it better than the elementary circuit "continuous boiler" plus thermostats on all batteries?

Proponents of weather control they say that in the main part of the heating season, the need for heat is much less than the calculated one, therefore, constantly heat the coolant to maximum temperature- waste of money. It works especially effectively during frosts and thaws, thereby achieving the most comfortable room temperature and significant savings in resources, since the inertia of the system is reduced and the boiler does not have to do extra work by burning fuel. In addition, in the case of operation with a constant temperature of the coolant, and it is almost always high, heat losses increase, which are greater, the higher the temperature of the coolant. In general, the efficiency of the boiler decreases as the average temperature of the boiler water increases.

Most Western manufacturers ( « Buderus» , Viessmann) are betting onproduction of low-temperature boilers.

Opponents of weather-independent control appeal to the fact that the price of such automation is too high. And the price of fuel still fully compensates for the costs.

Let's turn to the experts. on the forum, the site clearly says that weather-independent automation saves money and this is not counting the comfort that it brings to the house and ensures longer trouble-free operation.

The Time company offers a programmable controller as a weather-dependent automation calorMATIC 430 West. In fact, it works like a remote control from the boiler. The homeowner does not have to run to the boiler room to make it warmer or colder if he installs a display panel in a convenient place.

Manufacturers of household heating boilers, constantly improving their products and endowing them with new functions, at the same time complicate the selection of the desired boiler and its adjustment. To the greatest extent, this applies to boiler automation - that's already wall boilers, previously controlled by a single potentiometer, are now often supplied with built-in weather-compensated automation. However, a more complex control system is always a higher price. A reasonable question arises: "Is it necessary?". To help consumers answer it, we will try to understand the basic functions of boiler automation.

The purpose of domestic boiler control systems is to ensure safety, proper operation of equipment and comfort for those living in a house or apartment. Comfort in our case is comfortable temperature and no need to take any action to ensure it (for example, go to the boiler room, turn the regulator, etc.).
The most simple and understandable situation is with safety: is the control system built into the boiler, or is it supplied separately - it always has a safety temperature limiter. This device is a thermal relay, the opening of the contacts of which leads to the cessation of fuel supply to the boiler when the safe value of the boiler water temperature is exceeded. Tripping of the safety temperature limiter is a serious abnormal situation, and its elimination, i.e. replacement or reinstallation of the safety device and start-up of the boiler require the intervention of a maintenance specialist.
It goes without saying that safety has the highest priority among other tasks, so the upper limit for the boiler water temperature control is set in such a way that the temperature never exceeds the limit due to the overrun. What temperature runoff are we talking about?
Imagine a sudden power outage situation: the burner has switched off, circulation pump the boiler circuit has stopped. The boiler becomes an isolated system. During the installation process in this system of thermal equilibrium, the temperature of the metal decreases, and the temperature of the water rises by several degrees. If before this increase it was close to the maximum allowable, then a boiler failure during a power outage is guaranteed. The value of the possible temperature overshoot depends on the design and material of the boiler and is taken into account by the automation manufacturer when setting the upper limit for regulating the water temperature in the boiler.
Let's move on to the main purpose of boiler automation: to ensure a comfortable temperature in heated rooms. As you know, one or another temperature in the room is set when a balance is reached between heat losses and heat transfer from heating devices. At the same time, in order to maintain the set temperature value, any change in heat loss caused by a change in the weather must be compensated by an appropriate correction of the temperature of the coolant or its volumetric flow through the heating devices. This problem is most simply solved with the help of thermostatic valves installed on radiators or convectors, while the temperature of the coolant remains constant. In this case, the function of boiler automation is reduced to maintaining the set supply temperature.
I must say that most household boilers have a built-in control unit and do not imply anything more: the supply temperature is set manually, although it is maintained automatically. The control algorithm in this case differs depending on which burner the boiler is equipped with: modulating, one- or two-stage. In boilers with a single-stage burner, the temperature controller works as a threshold switch, which turns the burner on and off when the flow temperature reaches the threshold values. Between the switching thresholds and
switching off, a certain difference is set - the switching hysteresis (Fig. 1). As a rule, the switch-on and switch-off thresholds are arranged symmetrically with respect to the set flow temperature θset so that the average temperature over a long period coincides with the setpoint.
If the volume of the heat carrier in the heating system is small, and the heat consumption is significantly less than the burner power, the temperature will rise too quickly after the burner is turned on. Accordingly, there is a danger of too frequent inclusion of the burner, which can also affect its resource. This problem is overcome in various ways. For example, using a time-varying hysteresis value (Ariston): during the 1st minute after switching on it is 8, during the 2nd minute - 6, and starting from the 3rd minute - 4 K.
The algorithm for changing the hysteresis value depending on the situation is embedded in the Kromschröder automation: at the service level of the control system settings, you can set an increased hysteresis (up to 20 K) and its duration (up to 30 minutes). At low heat loads and correspondingly short heating-up periods of the boiler, an increased hysteresis value applies. If the switch-off threshold has not been reached within the set hysteresis time, the hysteresis value automatically decreases linearly to the standard 5 K.

A fundamentally different approach is used in Buderus boiler automation, where an algorithm is used, called by the developers "dynamic switching". When the supply temperature, increasing or decreasing, is compared with the set temperature θset, the system begins to calculate the integral of the function of the change in the mismatch with time (in Fig. 2 - the shaded area). The burner is turned on or off when the integral reaches the set value. It is obvious that with a fast heating of the boiler, the switching temperature is higher than with a slow one. Thus, the switching threshold is automatically adjusted to the characteristics of the heating system and the amount of heat demand.
Boiler control algorithm with two-stage burner does not fundamentally differ from what was discussed above - only the switching thresholds, respectively, are twice as large (Fig. 3).

Finally, the modulating burner allows constant proportional control of the flow temperature, where the burner output is linearly dependent on the temperature mismatch. However, such regulation is not always possible, since for many modulating burners the power varies smoothly not from zero, but from 30-40% of the maximum value. If the heat consumption in the heating circuit is below this limit, then we again encounter threshold regulation.
So far, we have meant that the flow temperature is set manually by a potentiometer on the boiler control panel and is automatically maintained by its control system. However, the purpose of the heating system is to maintain a comfortable temperature in the room, and it would be logical for this temperature to be a regulated value. The device that maintains the set temperature in the room - the room thermostat - is most often tied to the room itself and is not included in the boiler's main delivery set. However, since the regulation occurs through the control of the boiler, we will consider the room thermostat as an element of boiler automation.
The control of the boiler operation in order to maintain the set temperature in the room can be carried out by one of two types of regulation: two-position (on-off) or continuous. In the first case, the control algorithm is the same as for a boiler with a single-stage burner. However, compared to the temperature of the boiler water, the temperature in the room changes much more slowly when the boiler is turned on and off, which can lead to its large overruns beyond the threshold values. Therefore, on-off control is usually not recommended for heating systems with high (more than 25-30 kW) power boilers. In order to avoid such overruns in Kromschröder automation, for example, at the service level, a time interval for switching on the 2nd stage can be set (Fig. 3), and thus, the 2nd stage does not turn on immediately after reaching the threshold θon.2, but after after the specified time. This gives an additional opportunity to adjust the temperature controller to the characteristics of a particular heating system.

With continuous control, the control variable is the supply temperature, which varies depending on the deviation of the room temperature from the set value (Fig. 4). The room temperature setpoint is the temperature that is comfortable for the user, and it is not always the same - say, the comfortable temperature for sleeping under a blanket is several degrees lower than for morning or evening hours, and during the day the room can be empty and keep it in high temperature also doesn't make sense. The function of setting and executing the daily temperature schedule in the room suggests itself. Daily temperature programming is often possible for different - weekday or weekend - days of the week, as well as for special occasions such as a party or vacation.
The actual temperature value is measured by a sensor located in one of the rooms of the house, which is a reference and determines the heating mode in all other rooms of the house. However, the more other rooms there are, the less feasible the task of comfortable heating becomes by linking them into a single heating circuit controlled by the temperature in the reference room. To control a boiler that heats water for several heating circuits with different characteristics at once, a common input parameter is required for these circuits. It could be calculated from the temperature readings in the reference rooms of all circuits. However, a simpler and more effective solution has become widespread: to use the air temperature outside the building as such a parameter.

And indeed: the supply temperature of any heating circuit, necessary to compensate for heat losses in the premises, is related to the outdoor temperature by well-known relationships, which in graphical representation are usually called heating curves or heating curves (Fig. 5). It remains only to lay these ratios for each specific circuit in the algorithm of the boiler control system. In the automation of most manufacturers, for this it is necessary to select one of the heating curves offered to choose from, but there are other approaches: for example, the Buderus control system installer only needs to set two points, according to which the automation calculates the entire curve.
Can the system that controls the boiler and heating circuits according to the outside temperature react to unforeseen changes in the heat balance in the heated rooms, for example, due to an open window or a lit fireplace? In most cases, this possibility is incorporated in the form of automatic correction (most often - parallel transfer) of the heating curve of the corresponding circuit based on the sensor readings. room temperature. Moreover, meeting the demands of meticulous users who want to take more Active participation in climate control in the house, many manufacturers offer, in addition to weather-dependent automation, a room thermostat. We only note that in this case there is always a risk, by increasing comfort in the reference room, to reduce it in other rooms tied to the same heating circuit. In addition, thermostats on heating devices cannot be used in the reference room, since they are independent control systems with the same input and output parameters as boiler automation.
Why all these difficulties? Why is weather-dependent control better than the elementary circuit that we considered at the very beginning - a “permanent” boiler plus thermostats on all heating devices?

Proponents of weather-dependent automation usually refer to the fact that during the main part of the heating season, the need for heat is much less than the calculated one, therefore, constantly heating the coolant to the maximum temperature is a waste of money. But it's not the temperature that costs money, but the heat produced, and if the same amount of heat is consumed in two cases, then maybe the same amount of it is produced? Unfortunately, no, because in addition to heat consumption, there is always its loss, which is the greater, the higher the temperature of the coolant (Fig. 6). In addition, the efficiency of the boiler decreases with an increase in the average temperature of the boiler water. It is from these percentages that the economic argument in favor of weather-dependent automation is formed. However, with our domestic prices for energy carriers, this argument is easily beaten by the argument of a significantly higher price of the automation itself.
Let us also consider some of the functions of boiler automation, the purpose of which is not to create comfort, but to ensure the longest possible trouble-free operation of the equipment. In addition to the already described ways to prevent too frequent burner starts, this group of functions includes maintaining the minimum temperature of the boiler water. The simplest, but nevertheless effective method The implementation of this function is the so-called pump logic, according to which, when the burner is on, the circulation pump of the boiler circuit stops whenever the temperature of the water in the boiler is below the permissible threshold and does not start until this threshold is exceeded.
But not only the boiler can be taken care of by boiler automation. So, some control systems are equipped with a function to prevent blocking of pumps and three-way valves: once a day (example - Vaillant boilers) or a week (Buderus) all pumps in the system turn on for a short time, and all three-way valves are also fully opened for a short time, after which they return to the state that preceded this procedure.
When reading the documentation of manufacturers, one gets the impression that the developers of boiler control systems act on the principle: “more functions - good and different!”. True, it often turns out that the same functions are hidden under different names, the differences are only in the details.

S. Zotov, Ph.D.
Magazine "Aqua-Therm" №2 (54), 2010

Single-stage, two-stage and modulating burners for heating boilers. Review.

When choosing burners, consumers face a difficult task- which burner to choose . This choice allows them to make a small comparison of burners from different manufacturers according to the type of regulation and the level of automation of the burner device.

We invite you to get acquainted with the opinion of the specialists of our company, based on the experience of using Weishaupt, Elco, Cib Unigas and Baltur combined, oil and gas burners.

Let's define the basic requirements that apply to burners, depending on the application. Depending on the application, burners can be divided into groups.

Group 1. Burners for individual heating systems (in this group we include burners with a capacity of up to 500 - 600 kW, which are installed in boiler rooms of private houses, small industrial and commercial and administrative buildings).

When choosing burners for this group of consumers, it is necessary to take into account the wishes of the buyer in the level of automation of an individual boiler room:

if you do not show elevated technical requirements to the installed equipment and want to have a reliable boiler room that does not require large initial financial investments, then you can opt for burners with single-stage, two-stage operating modes;

if you want to build a heating system with a high level of automation, weather-dependent regulation, as well as low fuel and energy consumption, then you better apply modulating burners or burners with stepless two-stage regulation, which will provide the possibility of programming power and a wide operating range of burner control.

Group 2 Burners for heating systems of large residential complexes (in this group we include burners with a capacity of more than 600 kW for the needs of housing and communal services, central heating, as well as for the heat supply of large industrial and commercial and administrative buildings).

· Sliding two-stage or modulating burners are ideal for this group. This is due to: the large capacity of the boiler houses, the customer’s desire to build a boiler house with a high level of automation, the desire to ensure the lowest possible fuel and electricity consumption (use frequency control of the fan power), as well as to use equipment for automatic control of residual oxygen in flue gases (oxygen control).

Group 3. Burners for use on technological equipment (this group can include burners of any power, depending on the power of the process equipment).

For this group, preferred modulating burners. The choice of these burners is determined not so much by the wishes of the customer, but by the technological requirements of production. For example: for some production processes it is required to maintain a strictly defined temperature schedule and prevent temperature fluctuations, otherwise this may lead to a violation technological process, damage to products and as a result to significant financial losses. Staged burners can also be used in process plants, but only in those cases where slight temperature fluctuations are acceptable and do not entail negative consequences.

Brief description of the principle of operation of burners with different type regulation.

Single stage burners they work only in one power range, they work in a heavy mode for the boiler. During the operation of single-stage burners, frequent switching on and off of the burner occurs, which is regulated by the automation of the boiler unit.

Two stage burners , as the name implies, have two power levels. The first stage, as a rule, provides 40% of the power, and the second - 100%. The transition from the first stage to the second occurs depending on the controlled parameter of the boiler (heat carrier temperature or steam pressure), the on / off modes depend on the boiler automation.

Sliding two-stage burners allow for a smooth transition from the first stage to the second. This is a cross between a two-stage and a modulating burner.

Modulating burners heat the boiler continuously, increasing or decreasing power as necessary. Range of change of a mode of burning - from 10 to 100% of rated power.

Modulating burners are divided into three types according to the principle of operation of modulating devices:

1. burner with mechanical system modulation;

2. burners with pneumatic modulation system;

3. burners with electronic modulation.

Unlike burners with mechanical and pneumatic modulation, burners with electronic modulation provide the highest possible control accuracy, since mechanical errors in the operation of the burner devices are eliminated.

Price advantages and disadvantages

Of course, modulating burners are more expensive than stepped models, but they have in front of them whole line benefits. The smooth power control mechanism makes it possible to reduce the cycling of the boilers on and off to a minimum, which significantly reduces mechanical stresses on the walls and in the nodes of the boiler, which means it prolongs its “life”. Fuel economy in this case is at least 5%, and with proper tuning, you can achieve 15% or more. And, finally, the installation of modulating burners does not require the replacement of expensive boilers, if they function properly, while increasing the efficiency of the boiler.

Against the background of the disadvantages of stepped burners, the advantages of modulating burners are obvious. The only factor that makes managers opt for step models is their lower price. But savings of this kind are deceptive: wouldn't it be better to spend a large sum at a time on more advanced, economical and environmentally friendly burners? Moreover, the costs will pay off in the next few years!

Many buyers understand the benefits of using modulating burners, and now they only have to choose the models they need. Which manufacturers are best to contact? Even with a superficial study of prices for imported and domestic burners, it is clear that the difference is very significant. Some models of foreign manufacturers are more expensive than products Russian production more than twice.

A detailed analysis of the market of burner manufacturers shows that Russian equipment is significantly inferior to imported analogues in terms of automation. In order to achieve high level automation of Russian-made burners, it is necessary to invest a lot of money to purchase necessary systems automation and installation and commissioning of equipment. Based on the results of all the work, it turns out that the cost of retrofitted Russian-made burners is close to the cost of imported burners. But at the same time, you will not have a 100% guarantee that the understaffed Russian burner will provide you with the desired result.

Conclusion of our experts

The right choice of burner is an important step in the construction or modernization of a boiler house. Further work depends on how responsibly you approached this issue. heating equipment. The stable operation of the burner, compliance with environmental regulations, longer service life of the boilers and the possibility of fully automating the operation of the thermal power plant speak of the significant advantages of using modulating burners in boiler rooms. And if the benefit from their exploitation is obvious, it is simply unreasonable not to use it.

Burners Weishaupt / Germany , Elco / Germany , Cib Unigas / Italy, Baltur / Italy have proven themselves as reliable and high-quality equipment. By choosing these burners, you get confidence and profit! In turn, we are ready to provide you with reasonable prices and the shortest delivery time for equipment.