Drew Cutter wrote:

I understand that dehumidifiers will be hard to come by because of
Katrina. Demand for these have gone way up.

Solar-assisted fans might work faster with less electrical energy.
NREL says 1550 Btu/ft^2 of sun falls on the ground on an average
78.1 F September day in New Orleans, with an 86.1 daily max and
humidity ratio wa = 0.0158 pounds of water per pound of dry air.

With 8 hours of sun and an average 82 F daytime temp, a $100 16'x16'
plastic film greenhouse with 1x3 bows and a $50 Lasko 16" 90 W window
fan could collect 0.9x1550x256ft^2/8h = 44.6K Btu/h, heating 2470 cfm
of 82 F air to 82+44.6K/2470 = 100 F.

With temp T and vapor pressure Pi and w in a house with an 800 Btu/h-F
conductance, we could remove P = 60x2470x0.075(w-0.0158) = 11115w-176
pounds of water per hour. If (100-T)2470 = (T-82)(2470+800)+1000P, ie
247-2.47T = 3.27T-268-P, P = 5.74T - 515 = 11115w-176, so T = 120.4-1936w.
Pi = e^(17.863-9621/(460+T)) "Hg and w = 0.62198/(29.921/Pi-1) makes
T = 120.4-1204/(29.921/Pi-1), ie Pi = 29.921((120.4-T)/(1324-T)), so
T = 9621/(14.46-ln((120.4-T)/(1324-T)))-460. Plugging in T = 80 F on
the right makes T = 74 on the left. Repeating makes T = ... 78.79.

20 TD=(78.1+86.6)/2'average daytime temp (F)
30 WA=.0158'outdoor humidity ratio
40 CFM=2470'fan airflow (cfm)
45 SUNPOWER=.9*256*1550/8'solar heat (Btu/h)
50 TG=TD+SUNPOWER/CFM'greenhouse temp (F)
60 GH=800'house conductance (Btu/h-F)
70 T=80'initial house temp est (F)
80 TERM1=17.863-LOG(29.921)
90 TERM2=(2*CFM+GH)/1000
100 TERM3=60*CFM*.075
105 TERM4=(CFM*TG+TD*(CFM+GH))/1000
110 T1=(TERM4+TERM3*WA)/TERM2
120 T2=T1+TERM3*.62198/TERM2
130 TH=9621/(TERM1-LOG((T1-T)/(T2-T)))-460
140 IF ABS(T-TH).01 THEN T=TH:GOTO 130
150 PI=EXP(17.863-9621/(460+T))
160 WI=.62198/(29.921/PI-1)
170 P=4.5*CFM*(WI-WA)
180 PRINT T,PI,WI,P

Indoor Vapor Humidity Pounds
temp pressure ratio per hour

78.79059 1.006362 2.164776E-02 64.99785 September
71.0885 .7767595 1.657717E-02 57.5442 October

So it looks like we can remove about 8 gallons per hour or 64 gallons
per day this way in September, and 57 in October, with 1370 Btu/ft^2
of sun and a 69.1 average and 79.4 max and wa = 0.0114.

Nick