The charge is time-based, rather than temperature-based

[Xinfu]

Students pay money to use the air-con, $1 per hour; within this hour you have paid for, you can adjust the temperature up and down from 10 degrees to 26 degrees, without additional charge(s?). So can I say this is?:

-The charge is time-based, rather than temperature-based.

[Rusty]

without additional charge

Yes, your sentence works.

[Xinfu]

Thank you~