I'm not familiar with the .setDescription function and typically use the following for double arguments:

Arguments Method

 fan_rise = OpenStudio::Ruleset::OSArgument::makeDoubleArgument("fan_rise", true)
 fan_rise.setDisplayName("Pressure Rise {inH2O}")
 fan_rise.setDefaultValue(-1)
 args << fan_rise

This is from a measure I wrote to Set Fan Inputs which allows the user to select a fan type and change any or all of the inputs. I use a negative default value as a flag to check whether the user wants to change a field. Not the most elegant solution but it works.

Run Method fans.each do |fan|

fans.each do |fan|

  if fan.name.to_s.include? string or string == "*.*"

    # set common inputs
    if fan_eff_tot > 0
      fan.setFanEfficiency(fan_eff_tot)
    end
    if fan_rise > 0
      fan.setPressureRise(fan_rise_si)
    end
    ...

I'm not familiar with the .setDescription function and typically use the following for double arguments:

fan_rise = OpenStudio::Ruleset::OSArgument::makeDoubleArgument("fan_rise", true)
 fan_rise.setDisplayName("Pressure Rise {inH2O}")
 fan_rise.setDefaultValue(-1)
 args << fan_rise
fan_rise

fans.each do |fan|
|fan|
  
  if fan.name.to_s.include? string or string == "*.*"

    # set common inputs
    if fan_eff_tot > 0
      fan.setFanEfficiency(fan_eff_tot)
    end
    if fan_rise > 0
      fan.setPressureRise(fan_rise_si)
    end
    ...