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Old 05-13-13, 03:51 PM   #21
jeff5may
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Higgy,

It all depends on your floor plan and where the small unit would do the most good. In my place, the top floor is just one long room. It has windows at each end wall of the house. I put my unit in the end where the stairwell comes out. When it runs, the cooler air fills up the stairwell first, then fills up the whole story with cooled air. It is set warmer than the central unit below, so it won't try to cool the whole house. It functions as a dehumidifier more than anything.

When the central unit downstairs kicks on, the dried return air from upstairs takes much less capacity to cool because the central unit doesn't have to condense liters of humidity. The central unit runs for less time each cycle and cycles less often. It saves energy because even though the upstairs window unit isn't as efficient, it's not cooling the air upstairs to the same lower temperature as the larger unit downstairs. I'm not trying to "freeze" the air upstairs.

This is kind of the opposite of the original idea of moving cool basement air to a higher level of the house. If you have a basement which occupies a large portion of the footprint of your house and can circulate this cooler air to the top story of your house efficiently, you would achieve a similar result for much less energy. However, Ryland found that his circulator fan consumed as much energy to run as a small window ac unit and did not dehumidify as well as he wished. As for me, I don't even have a basement...

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