Thermostats: The difference between an ON/OFF and Modulated
Source: September 10, 2021 - Thermostats https://www.comwo.nl/nl/blog/artikel/wat-is-het-verschil-tussen-aanuit-en-moduleren/
What is the difference between on/off and modulate?
In this blog you will find an explanation about the differences between on/off thermostats and modulating thermostats. We use examples to explain how the relevant thermostat work. We also provide more information about the communication protocols OpenTherm and EMS (Energy Management System).
Example: on/off thermostat: red traffic light
An on/off thermostat can be compared to accelerating a car at the turn of a green traffic light and braking/stopping at a red traffic light, every time.
An on/off thermostat work the same as driving a car full throttle towards the next traffic light when the light turns green. You continue to drive full throttle until a new red light traffic light appears and you need to brake to a stop. As soon as the light turns green you begin to drive full throttle again to the next red traffic light. In addition to being an uncomfortable ride, this style of driving is also energy inefficient and ensures a high fuel consumption.
An on/off thermostat can also be compared to a light switch, but then for your central heating boiler. The thermostat can only be 'on' and 'off'. If the temperature in the room is cooler than the set temperature of the thermostat, the thermostat switches to 'on'. At that moment the boiler starts up. The central heating boiler operates at a high temperature so that the temperature requested by the thermostat is quickly reached. When the desired temperature is attained the thermostat switches the central heating boiler to ‘off’.
Example: modulating thermostat: green wave effect
A modulating thermostat can also be compared to driving a car. Instead of continuously accelerating to the next traffic light and braking hard at the traffic light, the modulating thermostat ensures that you accelerate and drive to the next light at a speed that is more economical for the car. This is similar to driving along city blocks at exact speed that enables you to catch every green light. This is called the ‘green wave’. This method of driving ensures less energy consumption and a more comfortable ride in the car. The modulating thermostat ensures that it handles the current temperature in the room and the requested temperature in a smart way. The communication between the central heating boiler and modulating thermostat ensures better efficiency, energy savings and less impact on the environment.
In addition to the on/off function, a modulating thermostat can send other signals to your central heating boiler. A modulating thermostat does not heat up your central heating system to unnecessarily high temperatures. If your home needs to be heated by 1 °C, the thermostat ensures even heating. Your central heating boiler in combination with the modulating thermostat ensures that the system heats your house with the lowest possible temperature. This means the amount of heat provided is sufficient to keep your house warm, but your central heating boiler will not switch on and off unnecessarily wasting energy.
What is OpenTherm?
Your thermostat communicates with the central heating boiler via a communication protocol. One of the communication protocols is called OpenTherm. A major advantage of OpenTherm products is that central heating boilers and thermostats from different brands can communicate with each other. OpenTherm controls the central heating boiler with modulation. OpenTherm communication uses the normal two-wire thermostat cable. With this connection the boiler and the thermostat provide each other with the necessary information in two directions for an accurate and energy-efficient control. The thermostat is also powered by the same two-wire connection. The information that is given to the thermostat from the boiler control unit depends on the particular boiler.
Do all modulating boilers work with OpenTherm?
No, not all modulating boilers work with OpenTherm. Manufacturers such as ATAG, Nefit and Vaillant use their own communication protocol. As a result an OpenTherm modulating thermostats cannot be connected to these boilers. If you are unsure consult the manufacturer of the central heating boiler.