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re: cool tower alternatives
24 nov 2005
abby normal wrote:
>>you want to rely on your ceiling fans then lets see you develop some
>>some convection coefficients, then crunch some numbers...
ok.
>>> slow ceiling fans use very little energy. let's say 0, for now.
>>>
>>> how much heat moves from the room to the slab by radiation?
if the linearized radiation conductance between an ordinary ceiling
and slab is about 4x0.1714e-8x(460+80)^3 = 1.1 btu/h-f-ft^2 at 80 f,
a 2000 ft^2 slab could collect 10k btu/h of heat by radiation with
a 5 f temperature difference, so a 75 f slab might need no fans, but
how would we turn the coolth off during unoccupied times?
>>> grainger's 4c853 48" fan moves 21k cfm at full speed at 315 rpm
>>> with 86 watts. how much air do we need to move up from the slab
>>> to the room to keep it comfy?
with low-e ceiling and wall surfaces, we could keep the room 80 f with
a 75 f slab with a 1.5x2000 = 3k btu/h-f film conductance and c cfm of
airflow if 10k = (80-75)(1/(1/c+1/3k)), which makes c = 6000 cfm.
>>> how much power does that require, according to fan laws?
...(6k/21k)^3x86 = 2 watts.
nick
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