Abstract: A method of controlling an orifice of a valve in an HVAC system to regulate a flow of a primary fluid through a primary side of a thermal energy exchanger of the HVAC system and thereby adjust a thermal energy transfer by the thermal energy exchanger from the primary fluid to a secondary fluid, flowing through a secondary side of the thermal energy exchanger, includes adjusting, by one or more electronic circuits, the orifice of the valve by applying an efficiency control algorithm to a control setpoint for the valve, the efficiency control algorithm processing the control setpoint for the valve to maintain energy-efficient thermal energy transfer. The method further includes the one or more electronic circuits determining the control setpoint for the valve, using current performance values of the HVAC system and recorded historical data of the HVAC system.