It is a particular application of flow meters where incorporating the temperature difference between the flow sent and the fluid returned the thermal energy released in the heating or cooling of the liquid is calculated.
Insertion devices for small pipes (up to 2”) that measures directly the flow and temperature of the returning pipe and have an auxiliary sensor for the measurement of sent temperature, are available
For bigger pipes and also when a non-intrusive system is needed, ultrasonic flow meters with two incorporated sensors PT100 for the measure of temperature and with energy calculation, are available. They can be applied in pipes from 15to 700 mm.