Kirchhoff's loop rule (otherwise known as Kirchhoff's voltage law (KVL), Kirchhoff's mesh rule, Kirchhoff's second law, or Kirchhoff's second rule) is a rule pertaining to circuits, and is based on the principle of conservation of energy.
ECM stands for Electronically Commutated Motor. Basically, circulator pumps with ECM motors offer intelligent speed control. Speed-controlled pumps automatically adjust their output to changing demand, whether it be due to outside temperature, level of sunlight, overall activity, and other heating sources. The benefit of having a more efficient ECM motor pump is substantial energy savings, which directly relates to cost savings.
An ECM motor is some times referred to an a variable speed motor. In one sense, this is true, it does vary its RPM of the motor, but only in response to changing conditions in the system. But in the truest sense, all it trying to do is maintain a programmed CFM. ECM stands for Electronically Commutated Motor.