Hi: the short answer is that it outputs a high impulse voltage (22 to 24V DC) when opening a valve, then it quickly drops to the input voltage (7 to 9V DC) after the valve is energized. More technical details can be found here:
Because of the way many solenoid valves work (and relays, and similar inductive load as well), OpenSprinkler DC can drive many of them, including standard 24V AC valves and 12V DC valves. It’s important to understand that OpenSPrinkler DC does NOT output 24V AC, NOR can it be powered by 24V AC.
Do you have a link to your 24V thermoelectric positioners? I don’t know what a thermoelectric positioner is and am curious to learn about it.