Threshold - why and when to use?

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Threshold for differential thermostat is introduced in 2.3.3 version.


Standard definition for differential thermostat is that this is a type of automatic thermostat (used on solar heating systems) that responds to temperature differences (between collectors and the storage components) so as to regulate the functioning of appliances (to switch transfer fluid pumps on and off).


Here as an image of typical (simple) solar heating system:





Condition for switching Pump in this case will be:


"Turn ON Relay(Pump) if T1(Collector) > T2(Tank)", which means that the pump will be activated if temperature of Collector(T1) is greater then temperature of Tank(T2) even for 0,1 degree. Accordingly, the pump will be switched off if  temperature of Collector(T1) is lesser then temperature of Tank(T2) even for 0,1 degree.


With threshold option, condition for switching pump will be:


"Turn ON Relay(Pump) if T1(Collector) > T2(Tank)+Threshold". In this way, we are avoiding unnecessary pump activation especially on higher temperatures in Collector and Tank with small temperature differences. Sometimes, with weather(sun light intensity) changes or in sunset, it is possible that Collector temperature will be always slightly higher than Tank temperature, pump will work without interruption, which will lead to Tank water cooling.