I made a temperature control system without PID (just on/off with an offset) to control the temperature in a tank.
I can only cool the tank with a cooling coil inside the tank (so there is no heating element.) However, I can never reach the target temperature 20C due to the remaining cold water inside the coil (although the pump which transfer the cooling water inside the coil is turned off,) so the temperature drops after some hour or hours below 20C.
If I buy a commercial PID controller can I solve the problem?
If not, what can I do?