Thermostat for heating boilers

Control of the operation of heating equipment, automation of processes associated with heating a house is impossible without temperature controllers. With the development of technology and technology, thermostats for heating boilers (thermostats) of various designs and even with a different principle of operation have appeared.

When designing a heating system, it is important to pay attention to the selection of an automation unit, which will determine the comfort in the house.

Temperature is the main physical quantity, moreover, sufficient to control the operation and control of the boiler and the entire heating system in the house. It is enough to know how much the coolant is heated in order to automate the operation of the boiler to a minimum extent.

If you add a thermometer installed in the room, you can already talk about energy-efficient boiler control and greater comfort for residents.

For the user, the most important thing is to choose the best version of the room thermostat so that it is convenient to regulate the temperature in the room. You have to choose from mechanical or electronic devices.

Electronic thermostats provide greater accuracy and convenience, but mechanical devices still find applications, mainly due to its cheapness, simplicity and, most importantly, energy independence.

Operating principle

Any thermostat has three functional blocks:

  • Temperature sensitive element;
  • Regulator;
  • functional block.

The temperature-sensitive element reacts to changes in the temperature of the working medium (coolant, indoor or outdoor air) and changes a number of its physical, mechanical properties, to which the control unit reacts.

The regulator is needed to set the target value with which the data received from the sensor will be compared. Boundary conditions are taken into account when the sensor value is greater or less than the controller setting. The result is used:

  • Sending a digital or analog control signal;
  • Management of the electromagnetic relay;
  • Opening or closing a mechanical valve;
  • Closing or opening electrical contacts

The method of use, installation and the main purpose of the thermostat also depends on this. During the selection of the optimal model, this is the determining factor for narrowing down the list of suitable devices.

The exact choice is made according to the performance characteristics:

  • Installation method, dimensions;
  • Thermoelement sensitivity;
  • Temperature measurement range;
  • Regulator setting range;
  • Version of the thermosensitive element (remote, built-in)
  • Availability of additional functions (programming, installation of several temperature-sensitive elements).

Mechanical

The work is based on the physical phenomenon of thermodynamic expansion of gases, liquids and the change in the elasticity of metals. The gas or liquid is enclosed in a special flask, a bellows, which is connected through a thin channel with an adjustable valve fitting or a contact group. As matter expands or contracts in the bellows, the pressure exerted on the valve stem changes.

In this case, the controller determines the boundary condition by which the valve operates. A temperature-sensitive element can be connected to a control valve with a sufficiently long channel, a tube with a small cross section, but the connection is very unreliable and fragile.

The result of the operation of the thermostat can be not only the actuation of the valve, but also the adjustment of the gate, a mechanical control unit for the air supply draft in solid fuel boilers.

The most practical solution is a three-way thermostatic valve. With it, you can control the heating system in conjunction with any heating boiler that has built-in protection against overheating of the coolant.

Advantages:

  • simple design, reliability (subject to high-quality assembly and coordination of functional parts);
  • relatively low cost;
  • energy independence.

Flaws:

  • large dimensions of the thermostat;
  • low sensitivity, the ability to adjust with an error of up to 1-2ºС.

You will have to choose either from the solutions offered by the boiler manufacturer, or from such popular manufacturers as: Regulus, Kg Elektronik, ICMA. The cost of regulators starts from 900 rubles and above.

Temperature controllers based on an elastic metal plate that reacts to temperature changes are used only in conjunction with a contact group. Under the influence of temperature elasticity changes. It, deforming, opens or closes electrical contacts.

Advantages:

  • compact design;
  • low cost.

Flaws:

  • only local installation without the possibility of removing the temperature-sensitive element;
  • a large error in measurements reaching 2-3ºС.

Electromechanical

The temperature-sensitive element is a thermocouple, a bundle of two plates of specially selected metals. Under the influence of temperature at the boundary of two metals, a microEMF of up to 50 mV arises, which is quite enough to control a mechanical valve using an electromagnetic relay.

However, for the sensor to operate, a significant heating of the thermoelement is required. Electromechanical thermostats are used mainly in gas and solid fuel boilers to determine the presence of a flame and, accordingly, in the safety unit.

Electronic

In principle, any electronic thermostat uses two functional parts: a temperature sensor and a microcontroller that takes sensor readings and performs a given action.

The sensor for the electronic temperature controller is not physically connected to the control unit except for connecting wires.

That is why the sensor itself can be located at a considerable distance from the controller or boiler, up to 100 meters or even more.

According to the method of execution, they distinguish:

  • Analog thermostats;
  • Digital.

Analog devices are designed with rigid logic and have limited functionality. Their advantage is low cost, reliability. They repeat the capabilities of simple mechanical thermostats with the difference that their accuracy is an order of magnitude higher, the error reaches only 0.2-0.5 ºС.

Digital thermostats can be closed or open logic. In the first case, a direct alternative to analog devices is obtained, however, it is possible to expand the functionality due to the presence of a digital interface for connecting to a digital boiler control unit.

Open logic thermostats are programmable microcontrollers. It is possible to set target values ​​according to the schedule or according to one of the additional conditions, creating an effective boiler control program.

Advantages:

  • High accuracy of setting the target temperature, error - 0.1ºС;
  • Temperature measurement with a remote sensor;
  • Large selection of control options (mechanical regulator, dial pad, interactive menu, etc.);

Flaws:

  • The greater the functionality of the thermostat, the more expensive it is, moreover, significantly.
  • The performance of the device depends on the condition of the batteries or the presence of an external power supply.

In addition to solutions from the boiler manufacturer, you can use thermostats from manufacturers such as: VENTS, DS Electronics, Quantrax, Salus, Vaillant, Auraton.

Wireless

The main difference between electronic thermostats is that they can be installed at almost any distance from the boiler. In addition to this, you can even get rid of the need to lay wires from the thermostat to the boiler. Any electrical communication can be transferred to a wireless mode, for which radio waves are used.

Popular models of manufacturers: EUROSTER, SAKUS, Watts. The price of wireless solutions starts from 2100 rubles and can reach 10-15 thousand rubles. if there is a GSM module and an extended list of functions.

For electric boilers

There are three ways to control an electric heating boiler:

  • Interruption of the power line of the entire boiler;
  • Management of the work of only heating elements;
  • Transmission of control signals to the built-in control controller.

In the first case, the main regulator unit is installed in the break of the boiler supply line or only heating elements. The sensor is used built-in or remote, fixed in residential heated premises.

Execution options:

  • Socket block. It is vented into the socket, the power cord of the boiler is inserted into the regulator;
  • Outdoor unit for mounting on a DIN rail. It is mounted in a separate protected shield near the boiler, together with a circuit breaker and RCD. Supplemented with a remote wired or wireless temperature sensor;
  • Microcontroller or room thermostat in a wall-mounted or built-in housing for installation directly in residential areas. At the boiler, a block is mounted in the break of the power circuit.

What you should pay attention to when choosing:

  • Permissible rated switching current. Depending on the power of the heating boiler, it can be from 3 to 25 amperes and above. It is important that the current tolerance of the thermostat is at least 20% higher than the boiler consumption;
  • Temperature setting accuracy;
  • Temperature sensors are selected in strict accordance with the requirements of the thermostat manufacturer. The type of sensor (resistive, capacitive or thermocouple), the permissible current and the range of the measured temperature are important.

Many manufacturers supply their electric boilers with a digital control unit with the ability to connect an external thermostat. The choice is limited to special offers from the manufacturer or recommended third-party solutions with an identical connection interface.

For gas boiler

For a gas boiler, the solution is often similar to an electric heating boiler. It is enough to install the thermostat in the break of the power circuit and set the target temperature. When the desired heating of the air in the room is reached, the thermostat cuts off the power supply to the boiler, and it automatically turns off. However, this is not true for all types of gas boilers.

The requirements for thermostats in this case are as follows:

  • Permissible switching current. For gas boilers, a value of 1.5-2 A is often sufficient, since the consumption of a gas boiler is much less than that of an electric one;
  • Temperature setting accuracy and adjustment range.

In gas boilers with power supply, a special standardized interface is more often used to connect an external thermostat.

For non-volatile heating boilers, mechanical thermostats are used, more often with an external temperature-sensitive element connected to the control unit with a long copper tube. The automation unit is often equipped with a standard remote thermostat, so it will not be possible to supplement or replace it.

solid fuel

For solid fuel boilers, the use of an external thermostat is possible in two versions:

  • Connecting the thermostat to the automatic boiler control unit. Depending on the controller model, it is possible to use electronic or mechanical plate thermostats;
  • Using a mechanical temperature controller with a bellows filled with gas or liquid. The working part of the thermostat for solid fuel boilers is specially designed to control the damper on the air supply and / or adjust the draft.

There is no particular choice among thermostats for solid fuel boilers. You will have to look for a ready-made solution from the manufacturer of boiler equipment or complete the boiler with an automation unit complete with a thermostat.

Wiring diagram

A universal option is the use of a three-way valve with a thermostatic head in combination with a heating boiler, which has built-in protection against overheating of the coolant. By means of the valve, a bypass is formed parallel to the main heating circuit.

Scheme of connecting the thermostat to the boiler

When it is necessary to reduce the heating power, the valve redirects the entire flow of coolant from the boiler through the bypass to the return line, closing the circuit on a short circuit. Hot water does not enter the main circuit, and the boiler automatically stops working after warming up to the maximum temperature.

For electric and gas boilers with electronic control, but without a programmable controller, a simple outlet thermostat or a block thermostat for a DIN rail is perfect. The regulator is installed in the break of the power line and actually takes over the role of the main control.

However, it is important to mount the equipment so that the circulation pump continues to work in any case during the heating season.

Even if the maximum return from the boiler is not needed and the thermostat turns it off, the coolant must circulate, comparing the temperature throughout the circuit.

Basic rules for installing a room thermostat. A remote sensor or thermostat with a built-in temperature sensor should be located in the living room:

  • away from drafts and heating radiators;
  • recommended installation height indicated in the instructions by the manufacturer of the thermostat;
  • it is desirable that the sun's rays do not fall on the thermostat during the day;
  • it is not allowed to block the access of air to the thermostat with curtains or other elements of decor and furnishings.

As a result, when using a thermostat, the operation of the boiler is optimized, and the room will always have a comfortable temperature.