This mixing unit is controlling the supply water to radiators 24/7 to keep the right room temperature at any times.
Mixing unit also known as loading unit is combined of circulation pump, 3-way valve, thermometers, regulating valve. 3-way valve can be controlled with different heating controllers (such as Automix AM10, AM20, 30 etc) which combines a perfect water temperature measuring either outside, inside or both temperatures. That way the motor will rotate the 3-way valve position. When outside temperature decreases, loading unit regulates 3-way valve, that more hot water will move into the system, ensuring needed temperature inside the building. When outside temperature increases, it does the opposite. This will avoid any overheating of the building, ensuring the best possibile economical use of heat.
See the figure below how the system works.