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re: cooling the home
10 jul 2002
the_original_ wrote:
>are you really saying a ceiling fan moves 7 times as much air as a whole
>house fan?
something like that, altho a whole house fan can probably work at
a higher static pressure. grainger's 48" 315 rpm 86 w $115 4c853 fan
moves 21k cfm, and their 36" 400 rpm 450 w $385 5m156 (certainteed's
wh362bd-hdx, (800) 527-1924) moves 9700 cfm.
pe norman saunders says a fan's efficiency is about equal to the blade
diameter in inches, and part of a whole house fan's power is used to lift
the shutter beneath. maybe we don't need a shutter in summertime, just
a hole above the fan and some one-way plastic film dampers in basement
windows. this could naturally keep a house cooler in summertime, even
without the fan, letting night air flow in and up when the house is
warmer than outdoor air, and blocking reverse airflow during the day.
>> can we use a $100 90 watt 21k cfm ceiling fan with no louvers instead
>> of a $300 3k cfm noisy whole house fan? warm air rises...
>>
>> we could also tuck 12" poly ductfuls of water under the rafters...
>> 4" of water all over the ceiling would add 22k btu with a 7 h time
>> constant and a materials cost of $300...
the basement and duct mass would have 6144 btu/h-f of airfilm conductance.
adding the fan makes g = 4753, and c = 34.8k makes rc = c/g = 7.3 h, so
tm = 61+(td-61)exp(-6/7.3), (td-tm)c = 18h(73-td)500+2500), td = 16+0.795tm,
tm = 61+(16+0.795tm-61)exp(-6/7.3) = 63.4, and td = 66.4 f :-)
nick
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