5. When do temperature control units heat and cool? Do they do it automatically?

There are 3 basic cases of heating and cooling:

    1. Heating to production temperature: The unit heats only. 

    2. Production: Due to changes in the ambient temperature, cycle time, etc., the temperature of the consumer also changes. If it rises, the unit will cool; if it drops, the unit will heat. 

    3. Production interruption: Generally, the consumer must be heated to prevent its temperature from dropping.

Method: Heating and cooling take place in on/off mode, i.e. either completely on or completely off. Due to its PD behaviour, the controller cycles, with heating or cooling pulses becoming shorter as the temperature nears its set point. Cycling prevents under and overshooting.
Because of the inertia of the control loop, on/off mode (cycling) provides the same control accuracy as control valves, for example, which are significantly more technically demanding and much more likely to break down. The controller is a three-step controller with the positions "heating - neutral - cooling".

Further information: Temperature Control by Means of Fluid Media, 5th Edition, p. 58, Section “Control Engineering”. To order the book, see Answer 21.

FAQ overview