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Old 03-09-16, 05:54 PM   #18
jeff5may
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Quote:
Originally Posted by Robaroni View Post
Hi,
My thinking is if one fan's rpms pick up appreciably when the other fan comes on that you might get more benefit with two fans as the single fan is loading trying to pull air through the tube.

Usually fans have CFM ratings on them. If you can find a number and do a search you might find a data sheet to give you the info you need. Then knowing the room area you could get a ratio of air moved to time and then calculate how long it takes for enough temp differential to take place to make it worth turning on the fan.

After a specific point it becomes a null. The air at the ceiling isn't warming fast enough for the air moved so you're just spinning your wheels (and fan) which consumes extra power so I would think balancing the system as best as possible is something to work toward.

Rob
This is very true. Being basically very large air pumps, all but the cheapest will have charts and graphs like a well or sump pump. Absolute maximum ratings, graphs plotted against static pressure, current draw, and the like. Most computer fans also have these ratings published (even many cheap chinese models).

The whole counterflow current-inducing process is another one of those processes the HVAC industry knows well, but holds close to the shirt. When asked, quickly point out that this a game of diminishing returns that quickly becomes uneconomical, due to the "low grade" heat source. Same story that used to be told about PV solar, low temperature hydronic heating, variable speed compressors, etc.

I don't agree.
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