PP&D test question regarding condensation that's a bit confusing.

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6 comments

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    Justin Teufel

    Are you sure C isn't correct?

    I would've guessed C because evaporative coolers need a liquid (water) to evaporate which cools the warmer air. Wouldn't then the water be a refrigerant? I think of some kind of chemical when I see the word refrigerant but I believe its anything that changes phase to help a cooling process. 

    Might be wrong though...

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    Anton Gross

    Yes. C is not correct. Evaporative coolers do not require a refrigerant necessarily.

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    Justin Teufel

    "When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface"

    from wikipedia. So I think your rationalizing it correctly. Was this on a practice test?

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    Luis Burgos

    Simply put, cold air is too dense to hold moisture. Because the air can't hold moisture, it is released and separated from the air. This is why cold air feels drier and why you can see your breath when its cold outside. The water separates from the air into vapor. 

    The colder the air is, the more dense the air is, thus, the more likely it is to lose water vapor to condensation.

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    Adelina Koleva

    B) Roof overhangs on the west facade are typically not the best choice. East and west facades see the sun low on the horizon; an overhang protects from a high altitude or south noon sun. Best protection on east-west facades is vertical fins which would block at low angles (much like ceiling baffles).

    C) This one is interesting. I would say evaporative coolers (also known as swamp coolers) do not require refrigerant, and I'll explain why. A number of reasons. Firstly, it doesn't quite work quite the same way as a refrigeration cycle, which works through either compression and absorption - i.e., forcing a state change through pressure and soluble salts - not evaporation. Secondly, the term "refrigerant" appears throughout the ARE reference texts referring to very specific substances (CFC, HCFC, HFC's). Thirdly, knowing this, my gut tells me water wouldn't be especially efficient at refrigeration. Finally, and most imporantly, evaporative cooling can be a passive system as well as a packaged system; refrigeration itself is not a passive system, it requires an energy source to run.

    That being said there is information out there to support the idea that water does indeed act as a refrigerant but I think the key word here is "require," which should raise a red flag, as definitive wording like that is a typical ARE maneuver for making the answer either completely right or completely wrong.

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    Luis Vargas

    Yes, warm air holds more water proportionally than cold air. That is why we get condensation. So D is True, But the way D is worded is purposely confusing. This question is forcing to eliminate the wrongs rather than pick the right one. Thanks for the info. I will be on the look out for these tricky answers...

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