HUMIDITY : How do you raise the levels???

[NeoNJ]

As a windowsill grower, I use a Cool-Mist ultrasonic Humidifier. I'm finding it just ain't doin' the job .....and is only able to bring the Humidity level up to 50% (55% on a good day). I have alot of mounted orchids in the windowsill which require HIGH humidity.

I'm at a loss as to what to do other than Mist and Spray the orchids all day long, other than enclosing the entire windowsill in plastic !

Any ideas .....?