Thermomizers are automatic temperature controllers. Automatic temperature control systems

According to the principle of regulation, everything automatic control systems are divided into four classes.

1. Automatic stabilization system - a system in which the regulator maintains a constant set value of the controlled parameter.

2. Program control system - a system that ensures a change in the controlled parameter according to a predetermined law (in time).

3. Tracking system - a system that ensures a change in the controlled parameter depending on some other value.

4. Extreme control system - a system in which the regulator maintains the value of the controlled variable that is optimal for changing conditions.

To regulate the temperature regime of electric heating installations, systems of the first two classes are mainly used.

Automatic temperature control systems can be divided into two groups according to the type of action: intermittent and continuous regulation.

Automatic regulators for functional features are divided into five types: positional (relay), proportional (static), integral (astatic), isodromic (proportional-integral), isodromic with anticipation and with the first derivative.

Position regulators belong to intermittent ACS, and other types of regulators belong to ACS continuous action. Below we consider the main features of positional, proportional, integral and isodromic controllers that have greatest application in automatic temperature control systems.

(Fig. 1) consists of a control object 1, a temperature sensor 2, a program device or temperature level setter 4, a controller 5 and an actuator 8. In many cases, a primary amplifier 3 is placed between the sensor and the program device, and between the controller and the actuator - secondary amplifier 6. Additional sensor 7 is used in isodromic control systems.

Rice. 1. Functional diagram of automatic temperature control

Positional (relay) temperature controllers

Positional regulators are those in which the regulatory body can occupy two or three specific positions. In electric heating installations, two- and three-position regulators are used. They are simple and reliable to use.

In Fig. Figure 2 shows a schematic diagram of two-position air temperature control.

Rice. 2. Schematic diagram two-position air temperature control: 1 - control object, 2 - measuring bridge, 3 - polarized relay, 4 - electric motor excitation windings, 5 - electric motor armature, 6 - gearbox, 7 - heater.

To control the temperature in the control object, a thermal resistance of the vehicle is used, connected to one of the arms of the measuring bridge 2. The values ​​of the bridge resistances are selected in such a way that at a given temperature the bridge is balanced, that is, the voltage in the diagonal of the bridge is equal to zero. When the temperature rises, polarized relay 3, included in the diagonal of the measuring bridge, turns on one of the windings 4 of the electric motor direct current, which with the help of gearbox 6 closes air valve in front of the heater 7. When the temperature drops, the air valve opens completely.

With two-position temperature control, the amount of heat supplied can be set at only two levels - maximum and minimum. The maximum amount of heat should be greater than that required to maintain a given controlled temperature, and the minimum amount should be less. In this case, the air temperature fluctuates around a given value, that is, the so-called self-oscillating mode(Fig. 3, a).

The lines corresponding to temperatures τ N and τ V define the lower and upper boundaries of the dead zone. When the temperature of the controlled object, decreasing, reaches the value τ n, the amount of heat supplied instantly increases and the temperature of the object begins to increase. Having reached the value τ in, the regulator reduces the heat supply and the temperature drops.

Rice. 3. Time characteristic of two-position control (a) and static characteristic of two-position controller (b).

The rate of temperature increase and decrease depends on the properties of the controlled object and its time characteristics (acceleration curve). Temperature fluctuations do not go beyond the dead zone if changes in heat supply immediately cause temperature changes, that is, if there is no delay of the controlled object.

As the dead zone decreases, the amplitude of temperature fluctuations decreases down to zero at τ n = τ v. However, this requires that the heat supply be varied at an infinitely high frequency, which is extremely difficult to achieve in practice. All real objects of regulation have a delay. The regulatory process in them goes something like this.

When the temperature of the controlled object decreases to the value τ n, the heat supply instantly changes, however, due to the delay, the temperature continues to decrease for some time. Then it increases to the value τ in, at which the heat supply instantly decreases. The temperature continues to rise for some time, then due to the reduced heat supply, the temperature drops and the process repeats again.

In Fig. 3, b is given static characteristic of a two-position regulator. It follows from it that the regulatory impact on an object can take only two values: maximum and minimum. In the example considered, the maximum corresponds to the position at which the air valve (see Fig. 2) is completely open, the minimum - when the valve is closed.

The sign of the regulatory effect is determined by the sign of the deviation of the controlled variable (temperature) from its set value. The magnitude of the regulatory impact is constant. All two-position regulators have a hysteresis zone α, which arises due to the difference in the operating and releasing currents of the electromagnetic relay.

Example of using two-position temperature control:

Proportional (static) temperature controllers

In cases where high control accuracy is required or when a self-oscillating process is unacceptable, use regulators with continuous control process. These include proportional controllers (P-controllers), suitable for regulating a wide variety of technological processes.

In cases where high control accuracy is required or when a self-oscillatory process is unacceptable, regulators with a continuous control process are used. These include proportional controllers (P-controllers), suitable for regulating a wide variety of technological processes.

In automatic control systems with P-regulators, the position of the regulator (y) is directly proportional to the value of the controlled parameter (x):

y=k1х,

where k1 is the proportionality coefficient (controller gain).

This proportionality continues until the regulator reaches its extreme positions (limit switches).

The speed of movement of the regulator is directly proportional to the rate of change of the controlled parameter.

In Fig. Figure 4 shows a schematic diagram of a system for automatically regulating air temperature in a room using a proportional controller. The room temperature is measured by a resistance thermometer connected to the measuring bridge 1 circuit.

Rice. 4. Scheme of proportional control of air temperature: 1 - measuring bridge, 2 - control object, 3 - heat exchanger, 4 - capacitor motor, 5 - phase-sensitive amplifier.

At a given temperature the bridge is balanced. When the controlled temperature deviates from the set value, an unbalance voltage appears in the diagonal of the bridge, the magnitude and sign of which depend on the magnitude and sign of the temperature deviation. This voltage is amplified by a phase-sensitive amplifier 5, the output of which is connected to the winding of the two-phase capacitor motor 4 of the actuator.

The actuator moves the regulating body, changing the flow of coolant into heat exchanger 3. Simultaneously with the movement of the regulating body, the resistance of one of the arms of the measuring bridge changes, as a result of which the temperature at which the bridge is balanced changes.

Thus, each regulation of the regulatory body, due to the strict feedback corresponds to its equilibrium value of the controlled temperature.

A proportional (static) controller is characterized by residual unevenness of regulation.

In the case of an abrupt deviation of the load from the set value (at time t1), the controlled parameter will, after a certain period of time (moment t2), reach a new steady value (Fig. 4). However, this is only possible with a new position of the regulatory body, that is, with a new value of the controlled parameter that differs from the specified value by δ.

Rice. 5. Timing characteristics of proportional control

The disadvantage of proportional regulators is that each parameter value corresponds to only one specific position of the regulator. To maintain a given parameter value (temperature) when the load (heat consumption) changes, it is necessary that the regulator takes a different position corresponding to the new load value. This does not happen in a proportional controller, resulting in a residual deviation of the controlled parameter.

Integral (astatic regulators)

Integral (astatic) These are called regulators in which, when a parameter deviates from the set value, the control element moves more or less slowly and all the time in one direction (within the working stroke) until the parameter again takes on the set value. The direction of travel of the regulator changes only when the parameter passes through the set value.

In integral regulators electrical action Usually, a dead zone is artificially created, within which a change in the parameter does not cause movement of the regulator.

The speed of movement of the regulating body in an integral regulator can be constant or variable. A feature of the integral regulator is the absence of a proportional relationship between the established values ​​of the controlled parameter and the position of the regulator.

In Fig. Figure 6 shows a schematic diagram of an automatic temperature control system using an integral controller. In it, unlike the proportional temperature control circuit (see Fig. 4), there is no strict feedback.

Rice. 6. Scheme of integrated air temperature control

In an integral regulator, the speed of the regulator is directly proportional to the deviation of the controlled parameter.

The process of integral temperature control with abrupt changes in load (heat consumption) is shown in Fig. 7 using timing characteristics. As can be seen from the graph, the controlled parameter during integral regulation slowly returns to the set value.

Rice. 7. Time characteristics of integral regulation

Isodromic (proportional-integral) controllers

Isodromic regulation has the properties of both proportional and integral regulation. The speed of movement of the regulatory body depends on the magnitude and speed of deviation of the controlled parameter.

If the controlled parameter deviates from the set value, regulation is carried out as follows. Initially, the regulator moves depending on the deviation of the controlled parameter, that is, proportional regulation takes place. Then the regulating body makes additional movement, which is necessary to eliminate the residual unevenness (integral regulation).

An isodromic air temperature control system (Fig. 8) can be obtained by replacing rigid feedback in the proportional control circuit (see Fig. 5) with elastic feedback (from the regulator to the feedback resistance engine). Electrical feedback in an isodromic system is carried out by a potentiometer and is introduced into the control system through a circuit containing resistance R and capacitance C.

During transient processes, the feedback signal, together with the parameter deviation signal, affects subsequent elements of the system (amplifier, electric motor). When the control element is stationary, no matter what position it is in, as capacitor C charges, the feedback signal fades out (in steady state it is equal to zero).

Rice. 8. Scheme of isodromic air temperature control

It is characteristic of isodromic regulation that the unevenness of regulation (relative error) decreases with increasing time, approaching zero. In this case, the feedback will not cause residual deviations of the controlled variable.

Thus, isodromic regulation leads to significantly best results than proportional or integral (not to mention position control). Proportional regulation, due to the presence of strict feedback, occurs almost instantly, while isodromic regulation occurs slowly.

Software automatic temperature control systems

To implement program regulation, it is necessary to continuously influence the setting (setpoint) of the regulator so that the controlled value changes according to a predetermined law. For this purpose, the controller setting unit is equipped with a software element. This device serves to establish the law of change of a given value.

With electric heating actuating mechanism The ACS can influence the switching on or off of electrical sections heating elements, thereby changing the temperature of the heated installation in accordance with the specified program. Software control of temperature and air humidity is widely used in artificial climate systems.

Temperature controls in individual rooms

Thanks to the Danfoss radiator thermostat, only required amount energy, and the room temperature is constantly maintained at the required level. The thermostat measures the room temperature and automatically adjusts the heat supply.

It allows you to avoid overheating of premises during transitional and other periods of the year and to ensure the minimum required level of heating in rooms with periodic occupancy (system freezing protection).

Short name for radiator thermostatRTD(Danfoss Radiator Thermostat). What is a radiator thermostat?

1 - combination of room temperature sensor and water valve,

2 - independent pressure regulator (works without an additional energy source)

3 - a device that constantly maintains a set temperature.



Operating principle of a radiator thermostat:

The principle of operation is the balance between the force of the medium (in this case: gas) and the force of the pressure spring, the magnitude of which depends on the setting of the head (to the required temperature). Thus, the amount of flow through the valve depends on the head setting and temperature external environment, which is perceived by the sensor.

If the temperature rises, the gas expands and thus closes the valve slightly. If the temperature drops, the gas is compressed accordingly, which leads to the opening of the valve and access of the coolant to heating device.

Gas usage is provided by Danfoss big advantage over other manufacturers: a small value of the time constant, which is expressed in better use free heat through a quick response to changes in room temperature (reaction time).

Today, only Danfoss radiator thermostats use the principle of gas expansion and compression. The reason is that using gas requires very modern technology and, accordingly, high quality requirements. However, Danfoss is willing to incur additional costs in order to achieve high-quality and competitive products.

The choice of radiator thermostat depends on the following conditions:

sensor type Y valve location

valve type Y radiator size (heat demand), temperature drop across the heating element, type of heating system (1- or 2-pipe system)

Why is it necessary to use a radiator thermostat?

1 - because it allows you to save money thermal energy(15-20%), allows the use of free, “free” heat (solar radiation, additional heat from people and devices), its payback period< 2 лет.

2 - provides high level indoor comfort.

3 - ensures hydraulic balance - it is very important to create hydraulic balance in heating system, which means supplying available thermal energy to each consumer according to his needs.

RTD thermostatic heads (20% heat saving)




Heads for radiator thermostats are manufactured in the following versions:

RTD 3100 / 3102 - standard sensor, built-in or remote, temperature range 6-26° C, limiting and fixing temperature settings.

RTD 3120 - tamper-proof sensor, built-in, temperature range 6 - 26° C, frost protection.

RTD 3150 / 3152 - sensor with maximum temperature limitation, built-in or remote, temperature range 6 - 21 ° C, frost protection, temperature setting fixation.

series RTD 3160 - element remote control, capillary tube length 2 / 5 / 8 m, maximum temperature 28 ° C with limitation and fixation of temperature settings (for radiators and convectors inaccessible to the user).

The remote sensor must be used if the built-in sensor will be affected by a draft or if it is hidden behind curtains or decorative grilles.

The thermostatic head itself is easily secured to the valve using a union nut. The head can be protected against unauthorized removal using a screw (ordered separately as an additional accessory).


Valves RTD-N and RTD-G

When Danfoss began expanding into markets outside Western Europe, then the company’s specialists carried out numerous analyzes of water quality in different countries. As a result of this experience, it became clear that poor water quality is common in heating systems in some countries. For this reason, a new series of valves has been developed for the markets of Eastern Europe- RTD series.

The materials used in the RTD remain particularly resistant to low water quality (compared to valves produced for Western European markets, we replaced all tin bronze parts with more resistant brass ones). This means that the service life of the valve is significantly increased, even in difficult conditions Ukraine. From experience we know that average term The valve service life reaches 20 years.

Type control valvesRTD-N(diameters 10-25 mm) are intended for use in two-pipe pump water heating systems and are equipped with a device for preliminary (installation) adjustment of their throughput.

In 2 pipe system heating, adding water in excess of the calculated volume leads to an increase in heat transfer and an imbalance in the system. The valve preset feature allows the installer to limit the valve capacity so that hydraulic resistance in all radiator circuits was the same and thus regulate the amount of flow.

Simple and precise bandwidth adjustment is easily done without additional tool. The number stamped on the setting scale must be aligned with the mark located opposite the valve outlet. The valve capacity will change according to the numbers on the setting scale. In position “N” the valve is fully open.

Protection against unauthorized changes to the setting is provided by a thermostatic element installed on the valve.

High Capacity Control ValvesRTD-G(diameters 15-25 mm) are intended for use in pump single-pipe water heating systems. They can also be used in two-pipe gravity systems. Valves have fixed capacity values ​​depending on the valve diameter.

Example of radiator thermostat calculation:

Heat demand Q = 2,000 kkal/h

temperature difference D T = 20 ° C

existing pressure loss D P = 0.05 bar

We determine the amount of flow (water flow) through the device:

Water flow G = 2,000/20 = 100 l/h

We determine the valve capacity:


Valve capacity Kv = 0.1/C 0.05 = 0.45 m3/bar



The value Kv = 0.45 m3/h means that for the RTD-N 15 mm valve you can select the preset “7” or “N”.

When choosing a radiator thermostat, it is necessary to ensure adjustment in the range from 0.5 ° C to 2 ° C for given dimensions, which will ensure good conditions regulation. In our case, it is necessary to select the preset “7” or “N”. However, if there is a danger of contaminated water in the heating system, we do not recommend using a preset lower than “3”.

Using our technical description “Radiator thermostats RTD”, you can select the valve size directly from the diagrams through the pressure loss across the valve D P, or through the flow value through the valve G. The selection of the size of the RTD-G valves (for a 1-pipe system) is carried out identically.


New construction

In new buildings we recommend the use of a 2-pipe system with RTD-N valves, with pre-adjustment to maintain hydraulic balance in the system, DN 10-25 mm, straight and angled versions.



Reconstruction

The vast majority of older buildings use a 1-pipe system, for which we recommend RTD-G valves with increased capacity (fixed capacity values ​​​​depending on diameter), DN 15-25 mm, straight and angled versions.

Especially for RTD-N valves with presetting, the use of a filter is very important to prevent interference with the normal functioning of the valve.


Balancing valves ASV series

Because the radiator systems heating are dynamic systems (different falls pressure by reducing the heat load), then radiator thermostats must be combined with pressure regulators (automatic balancing valves ASV-P for a 2-pipe system) and a shut-off valve MV-FN.

The ASV series of regulators includes two types of automatic and manual balancing valves:

automatic valve ASV-PV - differential pressure regulator with variable setting 5 - 25 kPa

valve ASV-P - regulator with fixed setting at 10 kPa

ASV-M - manual shut-off valve

ASV-I - shut-off and metering valve with adjustable capacity

ASV ensures optimal distribution of coolant throughout the heating system risers and normal functioning the latter, regardless of pressure fluctuations in the system. They also allow you to close and empty the riser. Maximum operating pressure becomes 10 kPa, maximum operating temperature 120° C.

The styrofoam packaging in which the valve is transported can be used as a heat-insulating shell at coolant temperatures up to 80° C. At maximum operating temperature coolant 120° C, a special heat-insulating shell is used, which is available upon additional order.



Automatic flow regulator ASV-Q

For hydraulic balancing of 1-pipe heating systems, automatic flow limiting valves ASV-Q are used - diameters 15, 20, 25 and 32 mm (setting range from 0.1-0.8 m3/hour to 0.5-2.5 m3 /hour). They are used to automatically limit the maximum value of water flow through the riser, regardless of fluctuations in pressure and coolant flow in the system and for optimal distribution of coolant along the risers of the heating system

These valves are especially useful for balancing heating systems for which hydraulic performance data is not available. ASV-Q always provides the coolant flow for which the valve is set. When the system characteristics change, the controller automatically adjusts.

Installing ASV-Q valves eliminates the need for traditionally complex commissioning work in new construction and reconstruction of heating systems, including expansion of systems without hydraulic calculation pipelines.



Application (examples 1 - 2 pipe systems)

When reconstructing a single-pipe system without bypass ( flow system) it is necessary to install radiator thermostats on heat radiation sources (RTD-G and RTD heads) and install a bypass line (bypass), the cross-section of which should be one size smaller than the main pipe of the system (bypass of 1/2” for the main pipe of 3 /4").

With the help of a bypass, the coolant flow through the heat radiation source is reduced to 35 - 30%, which also depends on the diameter of the main pipes in the system. By studying the heat transfer curve of a radiator of a single-pipe system, we are convinced that reducing the coolant flow from 100% to even 30% will lead to a decrease in the heat transfer of the radiator by only 10%.

This means that in the vast majority of cases, installing a bypass will have only a minor effect on heat transfer. In many cases, the dimensions of the heat emitter (radiator, convector) have already been selected with a margin, and therefore the heat emitters can continue to provide the required amount of heat. If the radiator is low-power, then to solve the problem you need to:

- Increase the coolant temperature

- Increase the performance of the circulation pump

- Increase heating surfaces of radiators

-Insulate the building envelope (walls)

RTD-G high flow valves are used in single-pipe heating systems with circulation pumps and in two-pipe systems ah gravitational (gravity).

To maintain hydraulic balance in the heating system, it is necessary to install an automatic flow regulator ASV-Q on each riser, which will limit the flow through each riser. In this way, the heat will be distributed evenly across all risers, especially in the case of changing heat loads, or if there is an insufficient heat supply. The ASV-M shut-off and metering valve allows you to shut off each individual riser and, if necessary, drain water from it, while simultaneously measuring the flow through the riser.

Heat emitters (radiators and convectors) can be equipped with radiator thermostats (RTD-G and RTD heads) without any restrictions. The selection of the RTD-G valve is carried out in accordance with the previous example (see also the example of the selection of RTD-G in technical description). In this case, the risers must be equipped with flow limiters ASV-Q and ASV-M shut-off and metering valves.

In the case of a 2-pipe system, heat emitters can be equipped with radiator thermostats (RTD-N and RTD sensors) without any restrictions. The selection of the RTD-N valve is carried out in accordance with the examples given above for the RTD-N. In this case, each riser should be equipped with an ASV-P pressure regulator (and an ASV-M shut-off and metering valve), which will provide a constant D P on each riser, thereby compensating for changes in the thermal load and changes in D P. Moreover, reducing the risk noise in radiator thermostats, the differential pressure regulator will thereby ensure their durability


This solves the issue of adjusting the temperature in individual rooms.

Temperature is an indicator of the thermodynamic state of an object and is used as an output coordinate when automating thermal processes. The characteristics of objects in temperature control systems depend on the physical parameters of the process and the design of the apparatus. That's why general recommendations It is impossible to formulate temperatures based on the choice of ACP and a careful analysis of the characteristics of each specific process is required.

Temperature regulation in engineering systems ah is performed much more often than the regulation of any other parameters. The range of adjustable temperatures is small. The lower limit of this range is limited by the minimum value of the outside air temperature (-40 ° C), the upper limit - maximum temperature coolant (+150 °C).

TO general features Temperature ASR can be attributed to the significant inertia of thermal processes and temperature meters (sensors). Therefore, one of the main tasks when creating a temperature control system is to reduce the inertia of sensors.

Let us consider, as an example, the characteristics of the most common manometric thermometer in a protective case in engineering systems (Fig. 5.1). Block diagram such a thermometer can be represented in the form serial connection four thermal tanks (Fig. 5.2): protective cover/, air gap 2 , thermometer walls 3 and working fluid 4. If we neglect the thermal resistance of each layer, then the equation heat balance for each element of this device can be written in the form

G,Cpit, = a p? Sjі ( tj _і - tj) - a i2 S i2 (tj -Сн), (5.1)

Where Gj- the mass of the cover, air gap, wall and liquid, respectively; C pj - specific heat; tj- temperature; a,i, a/2 - heat transfer coefficients; S n , S i2 - heat transfer surfaces.

Rice. 5.1. Schematic diagram of a manometric thermometer:

• 1 - protective cover; 2 - air gap; 3 - thermometer wall;
• 4 - working fluid

Rice. 5.2.

As can be seen from equation (5.1), the main directions for reducing the inertia of temperature sensors are;

• increased heat transfer coefficients from the medium to the cover as a result of the correct choice of the sensor installation location; in this case, the speed of movement of the medium should be maximum; all other things being equal, it is more preferable to install thermometers in the liquid phase (compared to the gaseous phase), in condensing steam (compared to condensate), etc.;
• reducing the thermal resistance and thermal capacity of the protective cover as a result of the choice of its material and thickness;
• reducing the time constant of the air gap due to the use of fillers (liquid, metal shavings); for thermocouples, the working junction is soldered to the body of the protective cover;
• selection of the type of primary transducer: for example, when choosing, it is necessary to take into account that the low-inertia thermocouple has the least inertia, and the manometric thermometer has the greatest inertia.

Each temperature control system in engineering systems is created for a very specific purpose (regulating the temperature of indoor air, heating or cooling fluid) and, therefore, is designed to operate in a very small range. In this regard, the conditions for using one or another ACP determine the device and design of both the sensor and the temperature controller. For example, when automating engineering systems, temperature controllers are widely used direct action with pressure measuring devices. So, to regulate the air temperature in administrative and public buildings When using ejection and fan coils of a three-pipe heating and cooling circuit, a direct-acting regulator of the RTK direct type is used (Fig. 5.3), which consists of a thermal system and a control valve. The thermal system, which proportionally moves the control valve rod when the temperature of the recirculation air at the inlet to the closer changes, includes a sensing element, a set point and an actuator. These three nodes are connected by a capillary tube and represent a single sealed volume filled with a heat-sensitive (working) fluid. A three-way control valve controls the supply of hot or cold water to the ejection heat exchanger

Rice. 5.3.

a - regulator; b - control valve; c - thermal system;

• 1 - bellows; 2 - set point; 3 - tuning knob; 4 - frame;
• 5, 6 - regulators of hot and cold water respectively; 7 - rod; 8 - actuating mechanism; 9 - sensing element

closer and consists of a housing and regulatory bodies. As the air temperature rises, the working fluid of the thermal system increases its volume and the valve bellows moves the rod and the regulating body, closing the passage hot water through the valve. When the temperature increases by 0.5-1 °C, the regulating bodies remain motionless (hot and cold water passages are closed), and with more high temperature Only the cold water passage opens (the hot water passage remains closed). The set temperature is ensured by rotating the adjustment knob connected to the bellows, which changes the internal volume of the thermal system. The regulator can be adjusted to temperatures ranging from 15 to 30 °C.

When regulating the temperature in water and steam heaters and coolers, RT type regulators are used, which differ slightly from RTK type regulators. Their main feature is the combined design of a thermal cylinder with a set pointer, as well as the use of a double-seat valve as a regulating body. Such pressure regulators are available in several 40-degree ranges ranging from 20 to 180 °C with a nominal diameter from 15 to 80 mm. Due to the presence of a large static error (10 °C) in these controllers, they are not recommended for high-precision temperature control.

Manometric thermal systems are also used in pneumatic P-regulators, which are widely used for temperature control in engineering air conditioning and ventilation systems (Fig. 5.4). Here, when the temperature changes, the pressure in the thermal system changes, which, through the bellows, acts on the levers that transmit force to the pneumatic relay rod and membrane. When the current temperature is equal to the set one, the entire system is in equilibrium, both pneumatic relay valves, supply and bleed, are closed. As the pressure on the rod increases, the supply valve begins to open. Pressure is supplied to it from the power supply compressed air, as a result of which a control pressure is formed in the pneumatic relay, increasing from 0.2 to 1 kgf/cm2 in proportion to the increase in the temperature of the controlled environment. This pressure activates the actuator.

Thermostatic valves from an American company have begun to be widely used to automatically control the air temperature in rooms. Honeywell and radiator thermostats (thermostats) RTD produced by the Moscow branch

Rice. 5.4.

with manometric thermosystem:

• 1 - pneumatic relay rod; 2 - unevenness node; 3, 9 - levers;
• 4, 7 - screws; 5 - scale; 6 - screw; 8 - spring; 10 - bellows;
• 11 - membrane; 12 - pneumatic relay; 13 - thermal cylinder; 14 - nourishing

valve; 15 - bleed valve

Danish company Danfoss, the required temperature is set by turning the adjusted handle (head) with a pointer from 6 to 26 °C. Lowering the temperature by 1 °C (for example, from 23 to 22 °C) allows you to save 5-7% of the heat consumed for heating. Thermostats RTD make it possible to avoid overheating of premises during transitional and other periods of the year and to ensure the minimum required level of heating in premises with periodic occupancy. In addition, radiator thermostats RTD provide hydraulic stability for a two-pipe heating system and the possibility of its adjustment and coordination in case of errors during installation and design without using throttle washers and other design solutions.

The thermostat consists of a control valve (body) and a thermostatic element with a bellows (head). The connection between the body and the head is made using a threaded union nut. For ease of installation on the pipeline and connection of the thermostat to the heating device, it is equipped with a union nut with a threaded nipple. The room temperature is maintained by changing the water flow through the heating device (radiator or convector). The change in water flow occurs due to the movement of the valve stem by a bellows filled with a special mixture of gases that change their volume even with a slight change in the temperature of the air surrounding the bellows. The elongation of the bellows as the temperature rises is counteracted by an adjustment spring, the force of which is regulated by turning the handle with an indicator of the desired temperature value.

To better suit any heating system, two types of regulator housings are available: RTD-G with low resistance for single-pipe systems and RTD-N with increased resistance for two-pipe systems. Housings are manufactured for straight and angle valves.

Thermostatic elements of the regulators are manufactured in five versions: with a built-in sensor; with remote sensor (capillary tube length 2 m); with protection against inept use and theft; with the setting range limited to 21 °C. In any design, the thermostatic element ensures that the set temperature range is limited or fixed at the required air temperature in the room.

Regulator service life RTD 20-25 years, although at the Rossiya Hotel (Moscow) the service life of 2000 regulators is registered for more than 30 years.

Regulating device (weather compensator) ECL(Fig. 5.5) ensures maintenance of the coolant temperature in the supply and return pipelines heating systems depending on the outside air temperature according to the corresponding specific repair and specific object heating schedule. The device acts on an electrically driven control valve (if necessary, also on circulation pump) and allows for following operations:

• maintaining settlement heating schedule;
• night decline temperature chart according to weekly (2-hour intervals) or 24-hour (15-minute intervals) programmable clocks (in the case of electronic clocks, 1-minute intervals);
• flooding the room within 1 hour after an overnight drop in temperature;
• connection via relay outputs of a control valve and a pump (or 2 control valves and 2 pumps);

Rice. 5.5. EU weather compensator/. with setting,

available to the consumer:

1 - programmable clock with the ability to set periods of operation at a comfortable or reduced temperature on a daily or weekly cycle: 2 - parallel movement of the temperature graph in the heating system depending on the outside air temperature (heating graph): 3 - operating mode switch; 4 - space for operating instructions: 5 - power-on signaling, current operating mode,

emergency modes;

O - heating is turned off, the temperature is maintained to prevent freezing of the coolant in the heating system;) - work with a reduced temperature in the heating system; © - automatic switching from mode comfortable temperature to a mode with a reduced temperature and back in accordance with the task on the programmable clock;

O - work without lowering the temperature on a daily or weekly cycle; - manual control: the regulator is turned off, the circulation pump is constantly on, the valve is controlled manually

• automatic transition from summer mode in winter and back according to a given outside temperature;
• stopping night temperature reduction when outside temperatures drop below a set value;
• protection of the system from freezing;
• correction of the heating schedule based on room air temperature;
• transition to manual control of the valve drive;
• maximum and minimum restrictions on supply water temperature and the possibility of fixed or proportional

temperature limitation return water depending on the outside temperature;

• self-testing and digital indication of temperature values ​​of all sensors and states of valves and pumps;
• setting the dead band, proportional band and accumulation time;
• the ability to work on accumulated funds for a given period or current values temperatures;
• setting the thermal stability coefficient of the building and setting the influence of the return water temperature deviation on the supply water temperature;
• protection against scale formation when working with gas boiler. Automation schemes for engineering systems use

also bimetallic and dilatometric thermostats, in particular electric two-position and pneumatic proportional.

The electrical bimetallic sensor is intended mainly for two-position temperature control in rooms. The sensitive element of this device is a bimetallic spiral, one end of which is fixedly fixed, and the other is free and meets moving contacts that close or open with a fixed contact depending on the current and set temperature values. The set temperature is set by turning the setting scale. Depending on the setting range, thermostats are available in 16 modifications with a total setting range from -30 to + 35 °C, and each regulator has a range of 10, 20 and 30 °C. Operation error ±1 °C at the middle mark and up to ±2.5 °C at the extreme marks of the scale.

The pneumatic bimetallic regulator, as a converter-amplifier, has a nozzle-flap, which is acted upon by the force of the bimetallic measuring element. These regulators are available in 8 modifications, direct and reverse acting, with a total adjustment range from +5 to +30 °C. The setting range for each modification is 10 °C.

Dilatometric regulators are designed using the difference in the linear expansion coefficients of an Invar (iron-nickel alloy) rod and a brass or steel tube. These thermostats, in terms of the operating principle of the control devices, do not differ from similar regulators using a manometric measuring system.

Automatic regulation is very convenient. Using a thermostat for greenhouses, you can maintain the required air temperature in the building.

Types of thermostats and their characteristics

There are many types of thermostats. To do right choice, you need to know their features. There are 3 main types.

1. Electronic thermostat. It has a liquid crystal display, which makes it possible to obtain accurate information about the status.
2. Touch devices. They are good because you can set a work program in them, which makes it possible to create different temperatures at different times of the day.
3. Mechanical product. Most easy installation, allowing you to control soil temperature. In this case, the temperature is set once, and then you simply adjust it. Perfect option for small greenhouses.

How to choose a thermostat

When choosing a thermostat, you should be guided by what you ultimately want to achieve. First of all, you should pay attention to the following characteristics:

• installation features;
• control method;
• appearance;
• power;
• presence or absence of additional functions.

When choosing thermostats for greenhouses, special attention should be paid to power. It must be greater than the required soil heating power. Take plenty! In this case, all work is controlled by a sensor. He can be:

• external;
• hidden.

A circuit may consist of several elements. The appearance of thermostats also varies. Installation can be either mounted or hidden.

Installation Features

When installing the system with your own hands, it is worth knowing that the regulator operates from sensors - light and temperature. The temperature in the building will be higher during the day and lower at night. Depending on this, heating also changes. The parameters for the thermostat are as follows:

• illumination limit - from 500 to 2600 lux;
• deviation in the power supply of the device - up to 20%;
• temperature range - from +15 to 50 degrees;

• when crossing the illumination limit, the temperature difference is up to 12 degrees;
• accuracy is about 0.4 degrees.

When installing the system yourself, you should know that the thermostat includes an adjustment unit and a temperature control unit. They can be performed using transistors. A switch allows you to vary the temperature. The relay can be combined with a heating device for the stove using contacts. The regulator may have an output relay that controls the heating.

The sensors include photoresistors and thermistors. They respond to various changes in environment. Settings can be made according to the instructions provided by the manufacturer.

You should set up the installation yourself, starting with calibrating the resistor scale. First, the sensors are lowered into heated water and then the temperature is determined. Next, the light sensor is calibrated. It is allowed to assemble the temperature regulator inside greenhouses. It is placed near a heating device, which can be a stove.

Thermostat review (video)

How to work with a thermostat

Thermostats, regardless of whether they are made by hand or purchased in a store, are very similar in principle of operation. Because of this, it is easy to work with them. What are the characteristics of working with the device?

• A special button helps you scroll through the menu.
• Temperature adjustment is done manually.
• You can save settings in the device's memory for quick startup.
• Application special buttons allows you to control the operation of the boiler and stove and set heating characteristics.
• If there is a display with readings, you can find out what the heating is like at a given time.

Among other things, thermostats make it possible to control the boiler for heating the greenhouse.

1. Once power is applied to the controller, the sensors are polled for real-time information. Then the controller compares the readings and already recorded information for day or night and selects the necessary settings for the thermostat.
2. After 5 minutes, the thermostat is activated and the boiler starts working.
3. If heating is insufficient, the heater and pump begin to function. A command is given to increase the fuel supply, which increases heating.

Thermostats are multifunctional. With their help, you can heat the greenhouse and set the required temperature for the air in the building, as well as heat the soil and water.

The regulator is capable of maintaining optimal environmental conditions in any environment. Some devices turn on and work independently, which is very convenient. They are connected to the controller, heat sensors, stove and boiler. Ultimately, control temperature conditions fully possible.

Making a simple regulator with your own hands

You can make the regulator yourself using a standard household thermometer. However, it will have to be modified.

• First disassemble the device, but remember to proceed carefully.
• A hole is made in the scale at the location of the area of ​​the required control limit. Its diameter should be less than 2.5 millimeters. A phototransistor is fixed opposite it. Sheet aluminum is taken, a corner is made in which a 2.8 mm hole is drilled. The phototransistor is glued to the socket using Moment glue.
• Below the hole, a corner is fixed so that if the temperature exceeds (during the day), the arrow does not have the opportunity to pass through the hole. This will prevent the heating from turning on when it is not needed.
• A 9-volt light bulb is installed on the outside of the thermometer. A hole is drilled for it in the thermometer body. A lens is placed inside between the scale and the light bulb. It is needed for the device to work accurately.
• The wires from the light bulb are routed through a hole in the housing, and the wires from the phototransistor are routed through a hole in the scale. The common tourniquet is placed in a vinyl chloride tube and secured with a clamp. A 0.4 mm hole is drilled opposite the light bulb.

• In addition to the sensor, the thermostat must have a voltage stabilizer. A photo relay is also required. The stabilizer is powered from a transformer. A modified transistor of the GT109 type serves as a photocell for the photo relay. All you need to do is remove the cap from its body and break off the base terminal.
• A mechanism made from a factory-made relay is used as a load. The work in this case follows the principle of an electromagnet, where a steel armature goes inside the coil and influences the microswitch, which is fixed with 2 brackets. And the microswitch activates the electromagnetic starter, through the contacts of which the supply voltage goes to the heating device.
• The photo relay along with the power subunits is placed in a housing made of insulating material. A thermometer is attached to it on a special rod. On the front side there is a neon light (it will signal the start of the heating elements) and a toggle switch.
• In order for the regulator to work accurately, it is necessary to achieve a clear focus of the light emanating from the light bulb onto the photocell.

How to make a thermostat with your own hands (video)

Thus, despite the complexity of the work, installing a thermostat significantly simplifies maintenance. Crops that receive an optimal microclimate develop better, which means the harvest will be significantly larger.