Cascade or Direct Fill

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luis
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Re: Cascade or Direct Fill

Fri Sep 08, 2017 6:39 pm

You have to be careful taking any air directly out of an air-conditioner duct.

The air at the outlet of an air-conditioner duct is at 100% relative humidity. It does have lower absolute humidity than the surrounding, but it can still create issues. Let’s see how I can explain this, without getting too deep into thermodynamics.

An air-conditioner dehumidifies by dropping the air temperature below its dew point (condensing air temperature) and therefore the humidity condensates out of the air. But, it only condensates because at that temperature the air is saturated (or 100% humidity).

Sometime in some window units you may occasionally see water droplets right at the outlet vent fins of an air-conditioner. That is because that air is still cold and saturated at 100% relative humidity.

As soon as the air comes out of the duct and mixes with the room air, the combined air temperature is up a bit and the relative humidity drops immediately.

Since moisture has been condensed out of that air, the absolute humidity in that air is lower, and when mixed with the room air, the average humidity goes down.

I hope I explain this well and it is clear.


The point is that if you want to feed air-conditioned air into a compressor, you need to be a bit careful not to carry any condensate with it. This can be avoided by not taking air directly after the condensing unit or mixing just a small amount of warmer air with it. Some un-insulated length of duct may be all you need to allow the air to re-warm just enough to drop the relative humidity enough.
Luis

Buceador con escafandra autónoma clásica.

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