Weather-dependent control of pumping and mixing units in underfloor heating systems. Principles of building an efficient autonomous heating system
Regulation of the heating system implies bringing the process of consumption of thermal energy in line with the real needs for it. A simple example: the colder it is outside, the more intensively the heating system should work and, conversely, when the air temperature in the house rises above the limit value, the temperature of the coolant in the heating devices should decrease.
The easiest way to regulate the heating system is to manually control the operation of the boiler and heating devices: it is hot in the house, you can turn off the coolant supply valve to the heating device, as a result of which the return water will return to the boiler hot, which will turn off the boiler or reduce fuel consumption.
An even simpler way to regulate the heating system is to temporarily turn off the boiler and turn it on when the room temperature drops. To date, such a "manual control" is outdated and it can only be discussed in relation to heating appliances that do not have automatic control systems, for example, to wood stoves or to some types of wood-burning heating boilers.
Modern heating control systems solve two problems simultaneously:
allow you to create really comfortable conditions in the house, maintaining a predetermined temperature level in it
optimize fuel consumption and, as a result, reduce heating costs
The heating system is adjusted according to one of two parameters
Outdoor temperature
Indoor temperature
It is believed that more comfortable conditions in a private house can be obtained by changing the temperature of the coolant, depending on the conditions inside the room. This is explained simply: heat losses do not always linearly depend on the outdoor temperature: it is necessary to take into account the wind speed and the location of the building relative to the cardinal points.
For apartment buildings and central heating systems, the outdoor temperature is more important, allowing you to obtain average results immediately for all consumers of thermal energy.
Methods for regulating heating systems
As mentioned above, the main task of regulating the heating system is to maintain a certain temperature level in the room. You can do this in several ways:
By changing the speed of movement of the coolant through the heating device using stop valves or with a circulation pump. In this case, there is a change in the amount of coolant passing through the heating device per unit of time. This method is called quantitative.
By changing the heating temperature of the coolant (changing its quality). This method is called qualitative.
It should be noted that both methods are inextricably linked with each other and are used simultaneously in high quality systems.
Practical implementation of method No. 1
The easiest way to control heating is to change the operating modes of the circulation pump depending on the temperature in the room: it is cold, the pump operates at maximum speed, which ensures the most intense heat transfer from heating devices. It became hot: the coolant movement speed is minimal. At night or during the day, when all residents of the house are at work or at school, the heat saving mode can also be used, which provides for a minimum flow rate of water in the heating system.
The disadvantage of heating control with a circulation pump is general approach to all rooms in the house, regardless of the actual need for thermal energy.
More accurate, local regulation of the heating system can be obtained by controlling the operation of a single radiator.
How to control the operation of a heating radiator?
In practice, it is possible to change the flow rate of the coolant using automatic heads, the design of which includes a valve and a temperature sensor that responds to changes in the temperature in the room. The principle of operation of the device is quite simple: the head cavity is filled with liquid, the volume of which depends on temperature: when it gets cold, the volume of liquid decreases, the valve opens, while increasing the flow rate of the coolant. When the temperature in the room rises, on the contrary: the volume of liquid increases, the valve closes, blocking the movement of the coolant.
The disadvantage of automatic heads is their low reliability and frequent failure. More perfect and reliable is the method of heating control using a servo driven and blocking the supply of coolant to the radiator, also depending on the temperature in the room.
Both the automatic head and the servo drive are designed to change the temperature of the coolant not in the entire heating system, but only in one individual radiator. If there are several heaters in the room, each of them will have to be equipped with such automatic control systems. Only in this case can you really regulate the heating.
All heating devices in the house can be combined into one automatic heating control system.
Adjustment during operation
There is also another way - operational regulation. As the name implies, the heating system is regulated while it is running. This is necessary to make adjustments as needed. For example, if there is a need to increase or decrease the amount of heat (depending on the air temperature outside and meteorological conditions). The change in the amount of heat generated by the system is provided by adjusting the temperature or by changing the flow rate of the coolant. Thus, it can be conditionally divided into "qualitative" and "quantitative" options for monitoring the system.
Quality regulation carried out directly at the thermal station. There are local and group. Quantitative has three divisions: group, individual and local.
This method of controlling the system is carried out manually using valves and taps, and automatically when the air temperature in the apartment changes. In branched systems, it is necessary to change the coolant flow rate - this should simplify the adjustment task.
In private homes, it requires knowledge about the features of individual water heating. The main task of the system is to provide optimal microclimate for the whole family. Unfortunately, quite often heating gets out of control. Most often, incorrect operation and untimely adjustment of parameters lead to inefficiency of indicators. The reasons may also be errors made in the design of heating, or poor insulation.
As practice shows, during the heating system, people do not ask themselves the question of calculations. Installation specialists prefer to do everything quickly, due to which accuracy suffers. As a result, it can be cool in one room and too hot in another. Comfort in this case can not be expected.
When evaluating the quality of the system and the efficiency of its operation, all parameters and features of your heating should be taken into account. Regardless of the power source (electric boiler or gas), the system must work smoothly, so proper regulation is the key to a warm and comfortable home.
The easiest way to regulate water circulation is to use thermostat located on the boiler. This is a kind of lever device that will allow you to switch heat costs and in this way the temperature in the house will decrease. Also, if necessary, you can increase the level of heating of the liquid and thereby increase the air temperature in the house.
The efficiency of modern heating is ensured by the controllability of the system and the heat generator, weather-dependent regulation, the ability to program temperature conditions and maintain them separately for different rooms, remote control, and coordinated operation of heat sources.
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Today, the owners of individual houses are making ever higher demands on the efficiency of heating systems, their ability to provide a comfortable temperature in the premises, and ease of use. The article formulates and discloses the basic principles of creating efficient heating using the equipment offered by the modern market.
Efficiency modern heating provide: controllability of the system and the heat generating plant, weather-dependent regulation, the ability to program the change in temperature conditions (thermostating), implement them independently for different rooms, remote control, minimizing the thermal inertia of the system. Coordinated work is also required various sources heat, high- and low temperature heating, DHW.
Consider the noted features and some ways to implement them in more detail.
System manageability - the basic condition for energy-efficient heating. It is necessary to be able to control the temperature of the heating medium depending on the demand for heating.
In the simplest case, use thermostat with a coolant temperature sensor in the boiler flow or return line. The control is carried out by turning the boiler on and off according to the ratio of the set and current temperature.
A step towards improving the system is the installation of a programmable thermostat, which allows you to control the temperature of the coolant not only within the specified limits, but also by hours of the day and days of the week (Fig. 1).
Rice. one. Electronic thermostat with the ability to set heating modes for a week
The use of indoor thermostats, air temperature control and thermostatic radiator valves are effective if it is necessary to control the heating of individual rooms by switching on and off an individual heater or a dependent circuit, for example, heating one room.
To ensure the safety of the system in the boiler flow line, it is necessary thermostat set to the maximum allowable temperature.
Controllability of the heat generator - provision condition automatic regulation heat supply to the heating system, depending on the need for it.
The following methods of boiler power control are implemented: two-position (on-off), step, smooth (modulation) and step-progressive (combination of step and smooth control).
In general, power modulation makes it possible to increase the efficiency of the installation and minimize oscillatory processes in the operation of the system, which is important, for example, when controlling the temperature in individual circuits by means of electrically driven mixing valves.
Weather-compensated regulation consists in adapting the current parameters (power, coolant temperature) of the heating system or its individual circuits to weather conditions. As a rule, external (street) temperature and indoor air temperature are used as external influences. In some cases, humidity and atmospheric pressure are added to them.
The main advantages of the solution are increased comfort of heating, more efficient use of the plant's capacity and energy savings.
The control device is controller with weather compensation function. The regulation is carried out according to the specified dependence of the coolant temperature on the outside air temperature, called the heating curve (Fig. 2).
Rice. 2. Example of a family of heating curves:
the abscissa shows the outside temperature, the ordinate shows the coolant temperature
The steepness of the slope of the curve and its shift along the ordinate axis are determined by the parameters of the heating system (the ratio of the power of the boiler and heating radiators, the thermal resistance of the walls of the building, the presence of additional external sources heat, etc.) and, as a rule, are found experimentally, through numerous observations and analysis of accumulated experience. The more accurately the heating curve is set, the more efficient the system will be and the more energy will be saved. In a number of weather-dependent controllers, in particular, E8 of the German company Kromschroder (Fig. 3), it is possible to automatically adjust the parameters of the heating curve, if the heating mode long time remains constant.
Rice. 3. Kromschroder E8 series controller
An important feature of some controllers with the function of weather compensation - the presence of a channel for proportional-integral (PI) control of the temperature of the coolant according to the temperature of the indoor air of the room. Thanks to electronic temperature sensors, this process can be carried out with high accuracy. IN controllers E8 temperature maintenance accuracy, taking into account the measurement error, is +/-0.3 C.
A number of operating and operational characteristics of the heating system, including efficiency, depend on the accuracy of measuring and setting the temperature settings and control parameters.
It is most convenient to set the gain control parameters in feedback contour (as implemented in the E8 model). So, if the room temperature deviates from the setpoint, the temperature of the heat carrier of the corresponding heating circuit is additionally corrected. As a result, for circuits serving very cold rooms, the coolant temperature will approach the maximum possible (boost mode). As the rooms warm up, the temperature of the heat carrier will decrease proportionally down to the value determined by the heating curve.
The control time constant is taken into account by setting the parameter of the space heating inertia, measured in hours.
The considered method of room temperature control is effective when sharing, for example, electric and furnace heating. With an increase in the room temperature due to the heat transfer of the furnace, the temperature of the coolant in the corresponding circuit decreases (up to its shutdown). This eliminates the need to manually manage the system.
Programmable room temperature control consists in changing the temperature setpoint of the premises heated by the circuit according to a given program. The implementation of this control method allows you to set the temperature of the premises in accordance with the needs for heating at the current time, which makes it possible to significantly reduce energy costs for heating.
The ability to set several programs, quickly change the heating schedule without resetting the temperature settings and time values can be used, for example, if, depending on the conditions of use of the system, the weather, the well-being of people, etc. different modes of space heating are required.
Most of the weather-dependent controllers on the market (manufacturers - Kromschroder, Honeywell, Fantini Cosmi, etc.) provide this.
Organization of separate independent temperature regimes for space heating - the next step in achieving comfort and saving energy spent on heating. The essence of the solution is that the heating of individual premises, their groups or buildings is carried out by its own subsystem (circuit). This is especially true if the serviced premises have different frequency of use, configuration, mass and heat capacity of the building envelope.
Separate heating is carried out due to the device of a multi-circuit system with one boiler or a cascade of heat generators. On fig. 4 shows an example of a simplified functional diagram of a heating system with an independent circuit and outdoor temperature control.
Rice. 4. Simplified functional diagram weather-dependent heating system with independent and dependent circuits: TG - heat generator; Hk - circulation pump collec-lecturer; Pk - heat consumers connected to the collector circuit; CM2, H2 - respectively three-way mixing valve from electric drive and a circulation pump of an independent circuit; P1 - heat consumers of the dependent circuit connected at points a, b; P2 - heat consumers of an independent circuit; Dk - coolant temperature sensor at the outlet of the heat generator; Du - outdoor temperature sensor; D1, Dp1 - coolant temperature sensors at the inlet of an independent circuit and room temperature, respectively; RK - separating valve with electric drive; K - control weather-dependent controller; red lines conditionally show the electrical connection of the system elements to the controller
The system works in the following way. The circulation of the coolant through the collector and the dependent circuit is provided by the Hk pump; through an independent - pump H2. In the heat generator circuit (collector), the coolant flows from both circuits are added. According to temperature sensors on Du Street and in rooms Dp2 and Dp1, the manager controller K calculates the value of the temperature of the coolant in the collector circuit. As a rule, it corresponds to the maximum of those requested by each consumer, taking into account losses for the delivery of the coolant. The temperature of the heat carrier at the boiler outlet is continuously monitored by the Dk sensor, taking into account the readings of which the power of the heat generator (or cascade) is controlled.
The temperature of the heat carrier at the inlet of the independent circuit is also calculated taking into account the temperature outside and in the heated room and is controlled by the D2 sensor. According to the readings of the latter and the calculated temperature of the coolant at the inlet of the circuit, the mixing valve CM2 is controlled by an electric drive. With a large difference between the calculated and actual temperatures of the coolant at the inlet of an independent circuit, the direct branch of the valve is fully open and there is a parallel circulation of liquid through the collector and independent circuits, including the heat generator. As the coolant warms up in an independent circuit, the direct branch of the mixing valve begins to close together with the opening of the inlet connected to the return line, the cooled coolant from which is partially mixed into the circuit entering the inlet. Regardless of the degree of opening of the mixing valve, the circulation through the circuit associated with the latter remains constant. This solution has a significant advantage over the classical one- or two-pipe system heating with parallel circuits. When the direct branch is completely closed, the circulation in the heating circuits is carried out separately; heat consumption is determined only by consumers included in the dependent circuit Pk, and when the required design room temperatures are reached, the heat generator is turned off, the circulation pumps stop. In an independent circuit, the accumulated thermal energy is efficiently spent.
The executive elements of the considered heating system - circulation pumps, mixing, bypass, zone and other valves and drives to them - are widely represented on the domestic market. Examples of these devices are given in Fig. five.
Rice. Fig. 5. Examples of actuators for low power heating systems: a - a three-point control actuator for a rotary mixing valve (ESBE, Sweden); c - three-way rod separating valve (Heimeir, Germany); d - thermoelectric actuator of the stem valve (Honeywell, Germany); d - circulation pump (Grundfos, Denmark)
A controller such as E8.5064 (the "top" model of the E8 series mentioned above) is able to simultaneously control a two-stage boiler, two independent heating circuits with mixing valves and pumps, a DHW circuit, a solid fuel heat generator and solar collector. The temperature is measured and maintained in two separate rooms. When using expansion modules controlled via a digital bus, the number of independent heating circuits can be increased up to 16, and the number of boilers or their power levels - up to eight.
If necessary, the heating system must also take into account requirements for efficient energy consumption at joint work various sources (for example, electrical and solid fuel boilers, heat pump, solar plant) and consumers (radiators, "warm floor", hot water system) of thermal energy.
In modern controllers heating, this is provided as a standard function or through the use of additional expansion modules.
Possibility remote control heating system allows you to achieve additional comfort in case the serviced premises are visited irregularly. The function in question is implemented if the heating system controller has the ability to change the operating mode via an external bus, which is also often used to configure and enter the operating parameters of the device via a personal computer. In controllers from different manufacturers, this is implemented in different ways. For example, in the EV87 regulator from Fantini Cosmi (Italy), the possibility of two-way data exchange is provided using the RS-232 interface and an open data exchange protocol supported by a GSM modem; control is performed by means of SMS-commands.
A number of modern controllers supports remote monitoring of the state of the heated object and the heating system. This is used to track emergency situations in the system operation, register temperatures outside the set values, accumulate statistics for fine-tuning control parameters, and perform scheduled maintenance.
Minimum thermal inertia of the system achieves technical and economic advantages.
The parameter under consideration affects the rate of transient processes (heating and cooling of the coolant) in the boiler and heaters. With high inertia in the heating system, such negative effects as overshoot, oscillatory nature and high duration of transient processes take place. In addition to additional energy costs resulting from inefficient control, these processes reduce the resource of heating equipment.
It is possible to reduce the inertia of the system by optimizing its design based on preliminary thermal and hydraulic calculations, reducing the volume of the coolant and metal consumption - by choosing the optimal sections of the hydraulic lines and installing heat-transfer devices with a minimum capacity.
Magazine "Aqua-Therm" №6(58)
If you turn off the heating system of a non-heat-intensive building at 17:00
at zero outdoor temperature, then the temperature in the premises will drop to + 10 °C only by two in the morning. By this time, the estimated amount of coolant must be supplied to the system for 10 - 15 minutes in order to raise the temperature to 10.5 -11 °C, after which the system must be turned off again for 45 - 55 minutes. In this intermittent heating mode, the system must operate until approximately 6 am, when it must be turned on for continuous operation in order to increase the temperature of the indoor air by the start of the working day. At first, this temperature will rise quickly when the calculated amount of coolant is supplied to the system, because the heat output of the heaters will exceed the calculated value due to lower air temperature, however, as the temperature rises, the rate of temperature increase will decrease, and up to the calculated (18 °C) value this temperature will theoretically increase indefinitely if the heating process is not artificially forced by supplying to the system, starting from 7 hours and 30 minutes, an increased coolant flow rate compared to the calculated value. By 9 o'clock in the morning, that is, by the beginning of the working day, the temperature of the internal air will reach 18 °C, and the coolant flow should be lowered again to the calculated value.
The nature of the relative (in fractions of the calculated values) changes in the coolant flow and heat consumption by hours of the day is shown in fig. 6.
It would be wrong to almost completely stop the supply of coolant at night, because in this case the temperature of the water in the return pipeline of the heating system would not reflect its actual state in any way, and this would not allow using this important parameter as a signal for controlling the operation of automation. Therefore, the minimum flow rate of the coolant should be at a level of 5 to 10% of the calculated value. Then the short-term maximum, during the period of active flooding, the water consumption will not exceed 140% of the calculated value.
The relative values of the hourly heat consumption will be close to the flow rates, however, they will not be exactly equal to them due to the fact that the temperature of the water in the return pipeline will change along with the change in flow. So, if the minimum heat carrier flow rate is set at 5% of the calculated value, then the minimum heat consumption will be about 8%. Taking into account this difference, the decrease in daily heat consumption at a minimum night temperature of 10 °C is estimated at 18-20%.
Thermal point
The main and indisputable criterion for the quality of a modern heating system is its ability to adequately respond by means of automatic control to the changing needs for thermal energy of a heated building, regardless of whether the need changes as a result of external influences on the building or as a consequence. internal factors. In modern heat points, an adequate response is ensured by means of proportional quality regulation, at which the temperature of the coolant changes smoothly, while the water flow in the heating system remains unchanged.
To implement proportional control, circulation pumps are installed in the heat point, and the mixing of water from the supply pipeline of the heating network with water from the return pipeline of the heating system is provided by a control valve installed on the supply pipeline, or a three-way control valve installed at the mixing point. When using microprocessor automation, it is possible to provide in this way a fairly effective central control of heating systems, although it should be noted that any central control of a multi-room building is not able to fully solve the problem of economical energy consumption as efficiently as it could be implemented by means of local control.
In Ukraine, silent circulation pumps that could be installed in the heating points of buildings are not produced, and therefore almost all existing buildings attached to systems district heating, are equipped with an elevator thermal input. Unlike an electric circulation pump, a water-jet pump (elevator) is not capable of providing proportional regulation of thermal power, because with a constant nozzle, mixing occurs in it with a constant proportion of mixing media, while the control process implies the possibility of changing this proportion or, as is commonly called , mixing ratio. For this reason, in the West, the elevator is completely rejected as a device for heating points. Perhaps this happened also because there have been no problems with silent pumps for a long time.
Despite the fact that modern silent pumps are now freely offered by foreign companies on the domestic market of Ukraine, we will have many problems with this equipment, if we evaluate these problems, looking from dark basements and impassable technical undergrounds of millions of residential buildings and kindergartens built over the past decade , schools and other buildings. Therefore, it is worth taking a closer look at the elevator, familiar to everyone, to which flaws are sometimes attributed that are not at all characteristic.
They say that the elevator has a low efficiency, and this would be true if it would require energy to operate. In fact, the existing pressure difference in the heat supply pipelines is used for mixing operation. If it were not for the elevator, then the coolant flow would have to be throttled, and throttling, as you know, is a pure loss of energy. Therefore, in relation to thermal inputs, an elevator is not a pump with low efficiency, but a device for the secondary use of energy spent on driving the circulation pumps of a thermal power plant or a district boiler house.
They say that an elevator is a device that is not capable of providing a given mixing ratio, because the nozzle must be designed for the available pressure in the pipelines of the heating network, and the mixing ratio will be the same as it turns out. Unfortunately, in practice this is often done, but this is a wrong practice. The nozzle must not be designed for the available available pressure. Excessive pressure must be eliminated by a differential pressure regulator or a throttle, and the elevator nozzle must be selected in such a way that the specified water flow in the heating system is ensured. It is worse when there is not enough available pressure at the inlet to operate the elevator. This sometimes happens, but then the elevator should not be used.
The inability to provide proportional control is the only drawback of the elevator, a device, in general, very simple, reliable and unpretentious in operation.
Let us now look again at the nature of the change in the flow rate of the coolant with the program control of the thermal power (Fig. 6). There is no need for any proportional change in the flow of network water, that is, nothing is needed that the elevator could not handle. This immediately opens up real opportunities to reduce heat consumption in public buildings without resorting to a complete and expensive reconstruction of existing heating points, which could be equipped as shown in Fig. 7.
A heat meter (pos. 1-3) is installed on the heat input. The nozzle of the existing elevator 4 is designed to provide design mixing, and the throttle washer 5 is designed to relieve excess pressure. At the end of the working day, the solenoid valve 6 should close, having a calibrated hole for passing 5% of the coolant when the valve is closed. At the same time, the solenoid valve 7 will close, disconnecting the hot water supply system from the heat source for non-working hours. Solenoid valve 8 opens on a short time before the start of the working day in order to intensively heat the premises, 
chilled overnight. The coolant flow through the open valve 8 is limited by a throttle washer installed next to it.
The temperature sensors of the coolant 9 and air 10 provide information for the electronic controller 11, which has a built-in clock (timer). The controller commands the opening and closing of solenoid valves 6, 7 and 8. Commands can be generated based on information received from temperature sensors installed in two control rooms located on different facades of the building, and information about the temperature in the coldest control room should be taken into account. , which is very important for those cases when one of the facades is blown by a strong wind. You can also use information about the temperature of the water in the return pipe in order to calculate the duration of a possible shutdown of the heating system. For example, at outdoor temperatures above +5 °C, the regulator can turn off the heating system for the whole night, and at temperatures of -15 °C and below, the night program control mode can be disabled.
The heat point also includes conventional devices (pos. 12-17) for hot water supply. These devices also include an air collector 15 with a valve 16 for automatic air release.
It is known that in hot water supply systems, oxygen corrosion is a great danger. There are many devices that can suppress this corrosion (eg cathodic protection, silicate water treatment, etc.), but the simplest of these devices is an air collector with a tap installed directly after the water heater. The oxygen liberated from the heated water escapes into the atmosphere before it enters the pipelines.
| free download About the possibility of practical implementation of heat consumption regulation of buildings by periodic interruption coolant flow (page 2 of 3), Gershkovich V.F,
Ph.D. A.G. Batukhtin, director of Technopark Zabaikalsky state university;
M.V. Kobylkin, post-graduate student of the Department of Thermal Power Plants, Trans-Baikal State University, Chita
Currently, technologies aimed at optimizing existing technological solutions in order to save energy are receiving more and more attention in the development of the energy sector. This approach is due both to the political strategy for the development of the Russian energy sector, which is reflected in federal law 261-FZ "On Energy Saving and Increasing Energy Efficiency" and the competition of existing district heating systems under modern market relations in the energy sector. The question of increasing the competitiveness of existing thermal power plants as the basis for heating the Russian Federation is of particular relevance. At the same time, the difficult economic situation and the lack of free financial resources for generating companies it is necessary to find low-cost methods of energy saving.
To date, many methods have been developed to optimize the supply of thermal energy from CHPPs to consumers, taking into account the peculiarities of the functioning of thermal networks, both in systems with open water intake at DHW needs, and closed .
The progressive development of technology, including electronics, has contributed to the development complex systems automatic regulation. The modern automatic control system (ACS) has a number of advantages that were difficult to achieve at the beginning of the last century, when district heating was becoming established. Currently, one of the main advantages of ATS is the ability to implement complex automatic control laws, in addition, in most standard systems the possibility of reprogramming is laid, i.e. changes in the laws of regulation and management of the system. In such conditions, automated control systems become of great relevance, allowing to minimize heat consumption, while creating comfortable temperature conditions for consumers.
Existing automated systems are able to accurately monitor many parameters, both of the heat carrier and the air inside and outside the building, and, as a result, are capable of regulating heat consumption to a sufficient high level. However, such systems include a large number of elements, the installation of which is necessary for each consumer of the system, as a result of which the main disadvantage of such systems is significant capital costs and maintenance costs when introducing automation for a group of consumers.
To solve the problem of equipment costs, it is proposed to introduce a patented automated system for regulating the flow of coolant for heat supply to consumer groups (Fig. 1), in which a complete set of automation is installed only on the consumer with the maximum heat load (automated consumer), on the remaining consumers of the system (non-automated consumers) install only indoor air temperature sensors and coolant flow sensors.
Rice. one. Automated system coolant flow control:
1 - heat source, 2 - automated consumer, 3 - non-automated consumer, 4 - heat and power processor (TEP), 5 - supply pipeline, 6 - return pipeline, 7 - coolant flow sensor, 8 - coolant flow regulator, 9 - automated consumer sensor complex , which includes sensors for flow, temperature and pressure of the coolant, 10 - circulation pump, 11 - indoor air temperature sensor, 12 - outdoor air temperature sensor.
The system operates as follows: when the environmental parameters change in such a way that it becomes necessary to increase the thermal load of consumers, TEC 4 gives a signal to the flow controller 8 to increase the coolant flow to the automated consumer 2, which allows maintaining the preset temperature of the internal air of the automated consumer 2, in at the same time, manual consumer 3 begins to experience a shortage of thermal energy, which leads to a gradual decrease in its internal air temperature monitored by sensor 11. When the temperature of the internal air of manual consumer 3 drops to the lower set limit, TEC 4 sends a signal to flow controller 8 to reduce consumption coolant to the automated consumer 2, which leads to an increase in consumption for non-automated consumer 3 due to an increase in pressure in the heating network. The reduction in consumption for an automated consumer is carried out until the consumption for non-automated consumer 3 reaches the minimum required value.
Using a flow sensor 7, TEC 4 monitors the change in flow to a non-automated consumer, after reaching the minimum required flow rate, TEC 4 stops sending a signal to the flow controller 8, thereby stabilizing the system, after which the non-automated consumer 3 begins to warm up, and the automated consumer 2 gradually cools down , consuming the accumulated heat. As soon as the temperature of the internal air of the non-automated consumer 3 reaches the upper set limit, or the temperature of the internal air of the automated consumer 2 drops to the lower set limit, TEC 4 returns the system to its original state.
Thus, the cycles of reallocation of expenses allow to comply with temperature regime consumers connected to heating networks without installing additional control devices, which saves capital costs for the installation of automation devices and the cost of their maintenance.
Since the principle of operation of the scheme is based on hydraulic dependencies in heating networks, a number of restrictions are imposed on it in use, so for networks with “good” hydraulics, this method will be ineffective due to the insignificant dependence between the coolant flow rate and the pressure drop in the heating network. But, despite this, the scheme takes on particular relevance for dead-end networks with degraded hydraulic performance, which can be shown on the example of the buildings of the Transbaikal State University.
The Trans-Baikal State University has two buildings located on the same branch from the main heating network, with loads of 1.2 and 0.3 Gcal / h, respectively, for the first and second buildings. After carrying out measures to automate the first building, it was noticed that with an increase in the load on the first building, the second building begins to experience a shortage of thermal energy, in connection with which a project was proposed to automate the second building to reduce the resulting deficit, the cost of which is about 900 thousand rubles.
In the course of a series of experiments, it was found that under existing hydraulic conditions and with design parameters, a change in the flow rate of the first consumer by 8 t/h leads to a change in the flow rate of the second consumer by an average of 1 t/h, which, under appropriate loads, gives large range for regulation, thereby allowing the implementation of the above scheme. Moreover, the cost of modernization existing scheme, at which the first building already has a full range of automation, up to the above is about 20 thousand rubles. Thus, the introduction of this automated control system will reduce capital costs by 97.7% of original cost project.
In addition to the local use of the system for specific buildings, the above principle of regulation can be implemented in a wider framework. So, in the conditions of modern urban development, not only single buildings with an automated heating system, but also microdistricts consisting of dozens of buildings with modern automation join the district heating networks. The operation of the automation of such microdistricts in many cases has a rather strong hydraulic effect on the remaining consumers of the system located at a great distance from each other, which can lead to a shortage of heat in some areas of the city. The principle of regulation in such a case can be demonstrated by the example of the heating networks of the city of Chita.
The Oktyabrsky microdistrict with a total heat load of 14 Gcal / h, which has an integrated automation system with single center management for the entire area. When regulating the load on a microdistrict scale, a significant change in costs in the heating networks of the city is inevitable, and taking into account their length, such regulation leads to a change in the available pressure for other consumers (especially for end consumers with insufficient pressure).
The first step, before applying the principle of automatic regulation of consumer groups, is to determine the area to which greatest influence due to changes in load in the Oktyabrsky microdistrict. The influence of the Oktyabrsky microdistrict is determined on the basis of the hydraulic calculation of the heating network of CHPP-1 - City with a variable load on the microdistrict. Having a significant number of consumers in the heat supply system, it is advisable to carry out hydraulic calculation using modern systems mathematical modeling of heating networks. The creation of a mathematical model of the heating network of CHPP-1 - City, as close as possible to the actual hydraulic conditions, made it possible to evaluate and compare the impact of changing the load of the microdistrict for all consumers of the system. According to calculations, Oktyabrsky has the greatest impact on the Sosnovy Bor microdistrict with a total heat load of 26.5 Gcal / h, located at a distance of about eight kilometers from Oktyabrsky. Moreover, a change in the load of Oktyabrsky by 50% in the direction of decrease or increase leads to a change in the available pressure in front of the Sosnovy Bor microdistrict by an average of 20% of the calculated value, which indicates a strong hydraulic dependence of the microdistricts.
The next step is to install a flow sensor in front of the Sosnovy Bor microdistrict, as well as install indoor air temperature sensors in controlled buildings, and provide communication between the sensors in Sosnovy Bor and a single controller in Oktyabrsky. The installation of indoor air temperature sensors is optional for all buildings in the microdistrict, it is enough to install sensors on buildings that are in the worst conditions, thus, having provided these buildings with heat, we will certainly provide heat to the rest of the buildings in the microdistrict. The choice of controlled buildings can also be carried out on the basis of calculations in a mathematical model.
After installing the sensors and creating a connection between them and the controller, it becomes possible to carry out the process of regulating the flow of the coolant, similar to the method described above for a group of buildings.
The use of interconnections between remote consumers (automated and non-automated) allows for high-quality heat supply to the “problem” area of heat consumption. The use of periodic heating, taking into account the unevenness during the day of the influence of automation of the microdistrict. "Oktyabrsky" for the mode of operation of the heating network (6 hours instead of 24) saves about 3.4 million rubles. for the heating season.
In conclusion, it can be noted that the use of this hydraulic dependence in practice for such large areas of heat consumption was a forced measure (although it was characterized by a significant economic effect). Based on the identified thin spots in the district heating system, a number of measures were developed to reduce such a strong impact, as a result, an additional pumping station was installed in Sosnovy Bor (TK-2-27), and the existing one was upgraded. Thus, an automated system for controlling the flow of heat carrier for heat supply to consumer groups, being an alternative solution, can significantly save not only capital costs, but also the costs of further maintenance.
Work on the development of energy-efficient district heating systems is carried out within the framework of the Federal Target Program "Scientific and Scientific and Pedagogical Personnel of Innovative Russia" for 2009-2013, as well as a grant from the President of the Russian Federation to support young scientists, candidates of science.
Literature
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2. Makkaveev V.V. Practical use some methods of optimization of heat supply regimes / V.V. Makkaveev, O.E. Kupriyanov, A.G. Batukhtin// Industrial energy. 2008. - No. 10 - S. 23-27.
3. Batukhtin A.G. Application of optimization models for the operation of heat supply systems to reduce the cost of thermal energy and increase the available power of the station / A.G. Batukhtin, V.V. Makkaveev // Industrial Energy, 2010. - No. 3. P. 7-8.
4. Makkaveev V.V. Mathematical model of a number of subscriber inputs closed systems heat supply / V.V. Makkaveev, A.G. Batukhtin // Scientific and Technical Bulletin of St. Petersburg State Polytechnical University, 2009, No. 3. - St. Petersburg. - S. 200-207.
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C. Deineko
Weather-dependent regulation for heat points of centralized heating systems centralized systems heating of buildings was carried out at the CHPP, boiler houses and elevator units of the central (CTP) and individual (ITP) heating points of buildings. However, due to the large length of the pipelines and the associated inertia of the systems, this did not give a real effect. At the same time, in the TsTP or ITP, elevator nodes, which did not allow quantitative regulation of the coolant. Accordingly, the temperature of the water entering the heating system varied depending on the temperature of the coolant coming from the CHP or boiler house, while the flow rate remained constant. Modern controllers make it possible to carry out qualitative and quantitative regulation of heating systems, and thus save a significant part of energy resources. Consider typical schemes controller applications offered by Honeywell
Modern controllers allow you to control several circuits, each of which can be modified by changing the settings. Consider several schemes for automating the operation of a heat point using weather-dependent regulation.
Scheme independent accession heating system (Fig. 1) allows not only to separate the circuits of the internal heating system from the circuit of the central heating network, to regulate the temperature of the return flow of the primary side (the temperature of the coolant supplied after the heat exchanger to the heat source), but also to carry out weather-dependent temperature control of the internal heating system (secondary side). At the same time, the temperature of the heat carrier in the heating system of the building changes depending on the selected temperature chart and fluctuations in outdoor temperature.
Rice. 1. Scheme of independent connection of the heating system:
SDC7-21N - controller; AF - outdoor air temperature sensor; VFB, WF - coolant temperature sensors; V1 - two-way control valve; DKP - circulation pump of the heating system; SDW - indoor air temperature sensor or room unit for remote control
The heating medium temperature is controlled by a two-way control valve (V1), (the valve can also be installed on the supply line T1), and circulation is carried out by the operation of the heating system circulation pump (DKP). The valve regulates the amount of heat carrier entering the heat exchanger for heating water circulating in the internal heating system, depending on the readings of the heat carrier temperature sensors (WF and VFB). Depending on the outdoor temperature (AF) and the selected temperature curve, the temperature of the heat carrier circulating in the internal heating system (secondary circuit) changes. Among the possible settings for the individual heating characteristics of the system is the choice of the type of task depending on the enclosing structures, the features of the internal heating system, temporary operating modes depending on the time of day and day of the week, the antifreeze function, and the periodic switching on of the circulation pump in summer.
Air temperature control in heated rooms is carried out by using an indoor air temperature sensor or a room unit (SDW), which can be used as a remote control panel.
Malfunctions in the system are displayed on the controller display. This is, for example, a break in the sensor or a situation where it is impossible to reach the set temperature of the coolant. When using a scheme with one circuit of the heating system and one circuit DHW systems(Fig. 2), it is possible to achieve weather-compensated control of the return flow temperature of the primary side and control of the heating circuit depending on the outdoor temperature, as well as maintaining a fixed temperature value in the DHW system.
Rice. 2. Scheme of independent connection of the heating system and the DHW system:
MVC80 - controller; AF - outdoor air temperature sensor; VFB1, VFB2, VF1, SF - coolant temperature sensors; V1, V2 - two-way control valves; P1 - circulation pumps of the heating system; P2 - circulation pumps of the DHW system; PF - make-up pump of the heating system; SV1 - make-up valve of the heating system; PS1 - pressure switch
The control is carried out by means of control valves (V1 and V2), the operation of the heating and DHW circulation pumps (P1 and P2).
Automatic make-up of the heating system is carried out by the installation, make-up pump (PF) and valve (SV1). If the secondary side minimum pressure switch (PS1) generates a non-critical alarm, the make-up valve SV1 opens and the make-up pump PF starts. Setting up user characteristics is carried out similarly to the previous option.
When using a circuit with one heating circuit and a DHW circuit with a two-stage heat exchanger (Fig. 3), it is possible to achieve weather-compensated control of the primary side common return temperature and weather-compensated control of the heating circuit, as well as maintaining a fixed temperature in the DHW system. Heating of cold water for sanitary needs is carried out by using heat from the coolant after the heat exchanger of the heating system, and heating the water to the required temperature and maintaining it in the DHW system - due to the operation of the second stage of heating and the control valve (V2).
Rice. 3. Control scheme of the heating and hot water system with a two-stage heat exchanger:
MVC80 - controller; AF - outdoor air temperature sensor; VFB1, VF1, SF - coolant temperature sensors; V1, V2 - two-way control valves; P1 - circulation pumps of the heating system; P2 - circulation pumps of the DHW system; PF - make-up pump of the heating system; SV1 - make-up valve of the heating system; PS1 - pressure switch
The scheme of independent connection of two heating circuits is shown in fig. 4. It is used for weather-compensated control of the return flow temperature (VFB) of the primary side via valve V1.
Rice. 4. Scheme of independent serial connection of two heating circuits:
SDC9-21N - controller; AF - outdoor air temperature sensor; VFB, WF, VF1 - coolant temperature sensors; V1 - two-way control valve; MK1 - mixing valve actuator; P1 - circulation pump of the mixing circuit of the heating system; DKP - circulation pump of the direct circuit of the heating system; RLF1 - temperature sensor of the heat carrier from the heating system; SDW - indoor air temperature sensor or room module for remote control, TKM - emergency thermostat to prevent overheating of the coolant
This scheme allows to achieve the control of the mixing circuit of the underfloor heating system and the direct circuit of the radiator heating system with weather compensation or with a constant temperature.
The control is carried out by the operation of the two-way control valve V1), the three-way mixing valve (MK1) as well as the circulation pumps (P1) of the mixing circuit and the direct heating circuit pump (DKP). The return water temperature (VFB) is controlled according to an adjustable temperature curve.
To control the temperature of the heat carrier of dependent heating systems (in which network water from the heat source and enters the internal heating system), a three-way mixing valve (MK1) is used (Fig. 5). Before the control valve, a differential pressure regulator is installed, and in the case when the pressure in the return network pipeline (T2) is not enough for normal hydraulic mode operation of the heating system, a pressure regulator "to itself" can be installed at the outlet of the heating system after the mixing bridge. Also, the circulation pump of the heating system (P1) can be installed not on the supply pipe of the heating system (as shown in Fig. 5), but on the return pipe.