Why Does Condensation Not Occur in Air-Conditioned Buses?

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Discussion Overview

The discussion centers on the phenomenon of condensation in air-conditioned buses, specifically why condensation does not occur inside the bus while it does on glasses when exiting into humid air. The scope includes conceptual understanding of humidity, temperature, and the mechanics of air conditioning systems.

Discussion Character

  • Conceptual clarification, Technical explanation, Debate/contested

Main Points Raised

  • Some participants note that when exiting an air-conditioned bus, glasses become misty due to condensation from humid air outside.
  • Warren proposes that the air conditioning reduces humidity inside the bus, making it cooler and drier compared to outside air.
  • Alan questions whether a certain level of water vapor must be reached for condensation to occur and wonders if further cooling could lead to condensation inside the bus.
  • Warren clarifies that for condensation to occur, the temperature of the glass must be lower than the surrounding air, which must also have high relative humidity, and asserts that air conditioning removes water vapor, keeping relative humidity low.

Areas of Agreement / Disagreement

Participants express differing views on the conditions necessary for condensation to occur, with some agreeing on the role of humidity and temperature, while others question the thresholds for condensation in relation to air conditioning effects.

Contextual Notes

The discussion does not resolve the specific conditions under which condensation might occur in air-conditioned environments, nor does it clarify the exact thresholds of temperature and humidity involved.

Alan Tam
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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?
 
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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
 
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
 
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
 

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