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re: should i consider a swamp cooler?
16 jun 2005
desertbob wrote:
>>ragnarkar wrote:
>>
>>>i've just moved to the central valley of california and will be here
>>>for at most 2-3 more years... i'm wondering if it's worthwhile to
>>>invest in a portable swamp cooler...
>>
>>sure. turn it on with a thermostat when the room temp reaches 80, and
>>turn on a window exhaust fan with a humidistat when the rh reaches 65%...
>
>too muggy, and too complex.
well, the ashrae 55-2004 comfort standard says 80 f with w = 0.012 is
comfortable, and 80 f at 100% rh makes pw = 1.033 "hg, and w = 0.012
makes pa = 0.566 "hg, and pa/pw = 0.55, so i shoulda said 55%. imo,
a thermostat and a humidistat and a small exhaust fan are not "too
complex." for "less complex," with no portable swampie, we might
evaporate p = 0.1a(pw-pa) lb/h of water from an a ft^2 floorslab
automatically dampened with a solenoid valve scrounged from an old
washing machine and a thermostat to make 1000p btu/h of cooling.
this is more efficiently done at night, storing coolth in the slab, with
a 58.1 f average daily min and a 93.2 f average daily max in sacramento
in july, then stirring cool air up into the room with a ceiling fan
to keep the room air 80 f when it is occupied during the day, with no
external ventilation. we can store 100k btu of coolth in a 10k btu/f
4" x 1200 ft^2 slab with a 10 f temp swing.
>it's essential for effective adiabatic cooling to maintain positive
>static pressure...
i disagree.
>maintain a good inside air velocity
v = 0.5 vs 0.1 m/s can raise the comfort zone to 82.9 f with w = 0.0121.
>and assure quick air exchange.
removing the water vapor takes c cfm of exhaust air, where
p = 60c0.075(wc-wa) = 4.5c(0.012-0.0087) = 0.01485c, ie c = 67.3p
on an average 75.7 f july day in sacramento.
with a 66.9 f average night temp, moving 100 cfm of outdoor air through
a 70 f house would provide about 100(70-66.9) = 310 btu/h of cooling.
evaporating 0.01485x100 = 1.485 lb/h of water would provide another
1485 btu/h, for a total of 1795 btu/h, with a = 10x1.485/(1.033-0.0566)
= 32 ft^2 of floorslab, approximately. a 90 watt $55 lasko 2155a 16"
2470 cfm window box fan could provide 44.3k btu/h (3.7 tons) of cooling
with 36.7 pounds of water per hour evaporating from a 700 ft^2 slab.
nick
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