When should I use a spring-return actuator vs a non-spring-return?

Spring-return actuators should be used in any safety-critical application where the damper or valve must fail to a known safe position upon power loss — this includes smoke control dampers, freeze-protection valves on outdoor air coils, and stairwell pressurization dampers per NFPA and IMC requirements. Non-spring-return actuators are appropriate for general modulating applications where fail-in-place is acceptable, such as VAV box dampers and cooling-only chilled water valves, and they typically offer better energy efficiency since they don't have to continuously overcome a spring. Belimo's spring-return actuators use brushless DC motor technology that reduces holding current to 0.5W in the energized position, making them competitive with non-spring-return designs on energy consumption.