Dehumidify with a Waterfall? - Short #259

In this short podcast episode, Bryan talks about history and HVAC science: how to dehumidify the air with a waterfall and how cold water became the first air conditioner.

In 1902, Willis Carrier worked for a printing company in Brooklyn, New York. There was a huge humidity problem during the summer: the printing plant got damp, causing paper to swell and ink to smudge. Carrier realized that he could wring water out of the air if he brought the air's temperature below the dew point. His solution was to spray chilled water into the airstream; he filed a patent for an invention that would pass air through a mist of cool water, which caused it to cool down and shed its moisture. He called it the "apparatus for treating air."

This invention applies basic psychrometric principles. Air holds water vapor up to a certain point. The dew point defines that point. If the air is full of water vapor and its temperature drops below that dew point, excess water vapor condenses to liquid water (such as when it passes over an evaporator coil). In the case of Carrier's invention, the cold water in the spray chamber acted as a giant cooling coil. However, if the water is warm, the opposite effect would happen.

We do NOT dehumidify with liquid water due to the requirement for water treatment (to prevent algae and scale buildup). Cold water is less prone to bacterial and algal growth than warm water, but it's still essentially an indoor science experiment. Water is also messy and causes corrosion, and pumping it is expensive. Carrier's experiment evolved to the chilled water coil, which then evolved to the DX coils we see today.

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