A controller assembly controls water flow through individual emitters of a heating/cooling system based on a temperature setpoint and room temperature indicator obtained from an associated thermostat. The controller assembly provides delta temperature room control using a high precision movement actuator fitted with two pipe temperature sensors to power modulate individual radiators, underfloor heating circuits or fan-coils to provide energy efficiency for individual room heating/cooling control. Based on the temperature difference between the room temperature and the setpoint the controller assembly controls water flow through the emitter by adjusting a valve to attain a target temperature delta between the inlet and outlet of the emitter. As the room temperature approaches the setpoint so that the temperature difference decreases, the power output of the emitter is modulated to achieve desirable performance characteristics.