evaporative air coolers?

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wrote:

I used a Master Cool Plus located on a flat roof for 8 years in the Tucson, AZ area. Worked like a charm, did not need air conditioning except during the monsoon season, mid June to Sept approx. It used very, very little water and electricity; it just had to be disconnected in the winter to prevent freezing. Big 4x4 filter was hosed down once a year;, no mold, etc. In southern parts of New Mexico, they are in use for most of the year. Las Cruces comes to mind. The picture of the unit y'all supplied probably operates on the same principle, however I have no experience with it. I doubt if it would be effective above 15% humidity, as indicated above. hth
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...

A 16'x16'x8' room with R20 insulation all round and a thermal conductance of 768ft^2/R20 = 38.4 Btu/h-F would only need Q = 10x38.4 = 384 Btu/h of net cooling to lower the room temp 10 F.
If it's Ta (F) outdoors with a wa humidity ratio and 80 F indoors with wi = 0.012 pounds of water per pound of dry air (an efficient corner of the ASHRAE comfort zone), evaporating P lb/h of water while ventilating with C cfm of 0.075 lb/ft^3 outdoor air makes P = 60C0.075(0.012-wa) and 1000P = Q+(Ta-80)C. Dagget CA in August with Ta = 87.1 F and wa = 0.0077 makes P = 0.0194C and 1000P = 384+7.1C, so P = 0.61 lb/h and C = 31 cfm.
Fresh air might come from 2 vents with an 8' height difference. If 31 cfm = 16.6Asqrt(8'x(87.1-80)) (an empirical chimney formula), A = 0.25 ft^2, eg 6"x6" vents. Outdoor air with Pa = 29.921/(1+0.62198/wa) = 0.366"Hg, and Pw = 0.566"Hg indoors and 0.61 = 0.1A(Pw-Pa) (an ASHRAE pool formula) makes A = 30 ft^2, eg an 8'x8" diameter 2-sided porous shower curtain below the upper vent with a 10 watt fountain pump moving 1 gpm from a sump with a float valve up over the curtain whenever the room temp rises to 80 F.
Or maybe a 5' tall x 8" diameter nuclear bong cooler (see wiki :-)
20 PI=4*ATN(1) 30 AS'screen evap area (ft^2) 40 CW=2*8.33*60'water flow rate (lb/h) 50 TW(0)p'initial water temp (F) 60 CAf5'inlet airflow (cfm) 70 FA=PI*(8/24)^2'duct free area (ft^2) 80 VA/FA/88'air velocity (mph) 90 UA=2+VA/2'airfilm conductance (Btu/h-F-ft^2) 100 TA(0)0'inlet air temp (F) 110 PA=.1*EXP(17.863-9621/(100+460))'air vapor pressure ("Hg) 120 W(0)=.62198/(29.921/PA-1)'inlet air humidity ratio 140 QTC=0:QTE=0'initialize total heatflows (Btu/h) 150 FOR S=0 TO 9'evap screen number (0 is first) 160 QC=(TW(S)-TA(S))*UA*AS'water-air convective heatflow (Btu/h) 170 QTC=QTC+QC'total convective heatflow (Btu/h) 180 PW=EXP(17.863-9621/(TW(S)+460))'water vapor pressure ("Hg) 190 PA).921/(1+.62198/W(S))'air vapor pressure ("Hg) 200 BOWEN.4*(PW-PA)/(TW(S)-TA(S))'Bowen's ratio ("Hg/F) 210 QE=QC*BOWEN'water-air evaporative heatflow (Btu/h) 220 QTE=QTE+QE'total evaporative heatflow (Btu/h) 230 W(S+1)=W(S)+QE/(60*CA*.075*1000)'hum rat leaving screen 240 TA(S+1)=TA(S)+QC/CA'exit screen air temp (F) 250 TW(S+1)=TW(S)-(QC+QE)/CW'exit screen water temp (F) 260 NEXT 270 TW(0)=TW(0)-(QTC+QTE)/CW'new water temp (F) 280 IF ABS(QTE-QTEL)>.01 THEN QTEL=QTE:GOTO 140 290 FOR S=0 TO 10 300 PRINT TW(S),TA(S) 310 NEXT S 320 PRINT QTE
water temp (F) air temp (F)
62.82701 100 62.68013 92.83129 62.66226 87.01672 62.68551 82.32003 62.71742 78.53357 62.74708 75.48347 62.77165 73.02729 62.7911 71.04951 62.80624 69.4569 62.81795 68.17434 62.82701 67.14138
21850.99 Btu/h
Nick
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On Aug 1, 7:42 am, snipped-for-privacy@ece.villanova.edu wrote:

Thanks Nick. It's a long time since I've seen a BASIC program listing. I shouldn't have thrown out that Commodore VIC-20.
;-)
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Dave wrote:

I live in Phoenix, and coolers are fine through about June, but once the relative humidity exceeds 20% they become lousy. Here's a table showing the best temperature you can expect from a cooler, depending on the humidity and outdoor temperature:
www.swampy.net/humevap.html
Also coolers aren't necessarily cheaper to operate than newer air conditioners ( < 15 years old), and it was found that people who had combination cooler-A/C units spent more on cooling than did people who have only A/C.
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