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gone-ot · 06-07-2013, 11:18 PM

Swamp Cooler Theory 102

It's ALL about LOTs of surface area with evaporative coolers. With mister's, yes, there are lots of droplets, but they're tiny and they're w-i-d-e-l-y separated and thus provide surprisingly small amount of surface area.

The aspen excelsior pads are usually 1"-2" thick, with the wood fibers oriented perpendicular to the airflow through them, so the air has to flow OVER / UNDER / THROUGH / BETWEEN lots and lots of wetted wood shaving fibers.

However, the OTHER major player in how well (or not) the evap cooler "works" is: (a) the DEW POINT temperature (Tdp) and (b) it's cohort, WET BULB temperature (Twb).

When the outside dry bulb temperature (Tdb) is above 95ºF and the dewpoint temperature (Tdp) exceeds 50-54ºF (just 22-25%RH!), the wet bulb temperature (Twb) will NOT be lower than 67-69ºF...and although this number LOOKS like really cool air, it is NOT, unfortunately, what you actually GET from the evaporative cooler.

With most evaporative coolers you only achieve about 80%-saturation, so you only "get" 80% of the Wet Dulb Depression temperature (WBD = Tdb - Twb):

T(cooler) ~ Tdb - 0.8*WBD

T(cooler) ~ Tdb - 0.8*(Tdb - Twb)

So, if Tdb is 95ºF and Twb is 67-69ºF, the air blowing from the cooler [ T(cooler) ] will only get down to about 73-74ºF...at almost 80%RH! But, your body wants to see/free something below 72ºF and closer to 30-50%RH!

This is when / why they're called "swap" coolers, because when it's HUMID you feel like you're in a tepid "sweat" sauna in a swamp!

06-07-2013, 11:18 PM	#18 (permalink)
gone-ot ...beats walking... Join Date: Jul 2009 Location: . Posts: 6,190 Thanks: 179 Thanked 1,525 Times in 1,126 Posts	Swamp Cooler Theory 102 It's ALL about LOTs of surface area with evaporative coolers. With mister's, yes, there are lots of droplets, but they're tiny and they're w-i-d-e-l-y separated and thus provide surprisingly small amount of surface area. The aspen excelsior pads are usually 1"-2" thick, with the wood fibers oriented perpendicular to the airflow through them, so the air has to flow OVER / UNDER / THROUGH / BETWEEN lots and lots of wetted wood shaving fibers. However, the OTHER major player in how well (or not) the evap cooler "works" is: (a) the DEW POINT temperature (Tdp) and (b) it's cohort, WET BULB temperature (Twb). When the outside dry bulb temperature (Tdb) is above 95ºF and the dewpoint temperature (Tdp) exceeds 50-54ºF (just 22-25%RH!), the wet bulb temperature (Twb) will NOT be lower than 67-69ºF...and although this number LOOKS like really cool air, it is NOT, unfortunately, what you actually GET from the evaporative cooler. With most evaporative coolers you only achieve about 80%-saturation, so you only "get" 80% of the Wet Dulb Depression temperature (WBD = Tdb - Twb): *T(cooler) ~ Tdb - 0.8WBD T(cooler) ~ Tdb - 0.8(Tdb - Twb)* So, if Tdb is 95ºF and Twb is 67-69ºF, the air blowing from the cooler [ T(cooler) ] will only get down to about 73-74ºF...at almost 80%RH! But, your body wants to see/free something below 72ºF and closer to 30-50%RH! This is when / why they're called "swap" coolers, because when it's HUMID you feel like you're in a tepid "sweat" sauna in a swamp! Last edited by gone-ot; 10-20-2014 at 06:56 PM..