A thermostat is a device that centrally measures and regulates the temperature of an environment, industrial process, or equipment such as a motor. The function of thermostats is to ensure thermal comfort or, in other cases, to promote the safety and protection of people, equipment, and industrial installations.
Thermostats can be classified according to the type of technology used in their construction, the most common being mechanical and electronic. Your choice between these types will depend on your intended use.
Mechanical thermostats have a mechanism that either allows or prevents the passage of a current to maintain the temperature. Within this category, the most commonly used are bimetallic thermostats. Their sensor is a sheet made of two different metals with different coefficients of thermal expansion. Let’s take a space heater as an example. Heating causes greater expansion of one of the metals, leading to deformation of the blade, which triggers the electrical contact and interrupts the passage of current when the pre-set temperature is reached. As it cools down, the blade begins to return to its original shape, once again allowing the passage of electric current and therefore the generation of heat by the device.
Mechanical thermostats can be analog (with a knob that turns to select the desired temperature) or digital (with a numerical display and buttons to set the desired temperature). Although very basic, they are recommended in certain cases, particularly for heating systems with an unstable electrical supply or relays.
The main disadvantage of mechanical thermostats is that they offer less precision in temperature control, which is around 3°C.
Electronic thermostats are the most widely used today. They have integrated circuits that allow precise regulation and continuous temperature measurement to guarantee thermal homogeneity, for example in a room (with a radiator heating system or underfloor heating), inside an oven, etc.
These thermostats have become the most common because they are smart and easy to use. Users can program the desired temperature with great precision and according to the time of day or day of the week. For example, electronic thermostats can be programmed to lower or turn off the heating at night, reducing energy consumption by up to 30%.
There are new connected models with the latest technology that can generate even more significant energy savings.
However, the installation of electronic thermostats must meet certain requirements, namely, it must be carried out by an electrician and the device must be placed at least 1.3 m from the floor, away from draughts, direct sunlight, and heat sources.
IVOR electronic thermostat
STEGO mechanical thermostat
Thermostats can be line voltage or low voltage.
Line voltage thermostats
Line voltage or high voltage thermostats operate on the same electrical circuit as the heating appliance and therefore use the same voltage, which can be 120 or 240 volts. They work like a switch, which either opens or closes an electrical circuit.
They are suitable for controlling the temperature of electric resistance heaters.
Line voltage thermostats offer several advantages:
Low-voltage thermostats
Low-voltage thermostats do not operate in the heating system circuit and use a voltage of less than 30 volts (usually 24 volts). This type of thermostat communicates with the appliance by sending low-voltage signals.
It is suitable for central heating systems (forced-air, boiler, etc.).
Low-voltage thermostats have several advantages:
However, low-voltage equipment requires a transformer to convert the voltage. They cannot be connected directly to the electricial supply with a power cable.
There are different types of thermostats, both mechanical and electronic. They can be preset, differential, or programmable.
SELCO preset thermostat
With preset thermostats, users cannot manually regulate the temperature. These devices are designed to maintain a predefined and constant temperature in an environment or process.
The main advantage of non-adjustable thermostats is their ease of installation and use. On the other hand, they offer little flexibility because they don’t allow you to change the temperature to suit different needs.
Differential thermostats
BMR differential thermostat
These are specifically designed to maintain a temperature difference between two elements. This difference is necessary in HVAC systems or incubators, for example.
Differential thermostats detect the temperature of each element and automatically regulate the heating or cooling system to maintain a constant temperature difference between the two. They can regulate the heat in a room, a building, or an industrial process.
ENDA programmable thermostat
Programmable thermostats automatically adjust the temperature according to the settings programmed by the user. If temperature variations are detected, the thermostat automatically adjusts the heating or cooling system to restore the preset temperature.
Programmable thermostats have several advantages, including the possibility of hourly and/or weekly programming. You can therefore define different temperatures for different times of day (up to 6 events per day in certain models) and/or according to the days of the week. This feature is very practical in heating and air conditioning systems, as it allows you to reduce the energy consumption of such equipment without sacrificing thermal comfort. Some devices can be configured to adjust the temperature depending on whether or not people are in the house. Connected models offer other functionalities, such as issuing maintenance alerts.
However, programmable thermostats are not suitable for all types of equipment. For example, they are not recommended for controlling the temperature of heat pumps that operate in both heating and cooling modes, as they could make the system less effective. They are also not suitable for electric heating systems that operate with a voltage of 120 or 240 volts. For this reason, few brands offer programmable line voltage thermostats.
With the constant development of home and industrial automation, connected and smart thermostats are a major trend in the sector.
Like so many other devices, connected thermostats offer new possibilities:
The new generation thermostats are programmable. If you are planning to buy one, make sure that the equipment (HVAC system, heat pump, etc.) is compatible with these thermostats, in particular the supply voltage.
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