Why Does Condensation Not Occur in Air-Conditioned Buses?

[Alan Tam]

We should have experience that when we get off from an air-conditioned bus in the summer, our glasses become misty. It's due to condensation of water vapour on our cooler glasses. But why the condensation doesn't occur in the air-conditioned bus?

 

[chroot]

The air conditioner in the bus has the side effect of reducing the humidity inside the bus. The air inside the bus is both cooler and drier than the air outside.

- Warren

 

[Alan Tam]

Dear Warren, you mean the amount of water vapour in the bus have to reach certain level in order to condense? If the temperature in the bus is further reduced, will the water vapour condense eventally?

Alan

 

[chroot]

For the glasses to become 'misty,' the glasss must be cooler than the surrounding air, and the surrounding air must be of high relative humidity. This occurs when the cooled glasses are taken into the humid air outside.

If the temperature of the bus is further reduced with an air conditioning system, then no, condensation will not occur on the bus. Air conditioning systems necessarily remove water vapor from the air as they cool it, and thus always keep the relative humidity fairly low.

- Warren