How can I control a loop by relative humidity?

I'm going to control airloop by air relative humidity... There are a zone and an air loop containing 1 humidifier and 1 fan. The fan is always on and I try to turn it off when humidifier is off...

how can I turn loop off?

I try to use EMS and turn the fan off when humidifier power is 0 but it didn't work...and also I've tried to change loop availability by using a sensor for humidifier power but it doesn't work also... what must I do?

Option 1 - Wrap the fan with an AirLoopHVAC:UnitarySystem object. It is a multipurpose system object which can be set to use LatentOnlyLoadControl. It should cycle the fan on whenever there is a latent load.

Option 2 - Since you already have an EMS program in place, change the sensor to "Zone Predicted Moisture Load to Humidifying Setpoint Moisture Transfer Rate".