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

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...

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

...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

A 32'x32' greenhouse with a larger fan might double this:

20 DATA 78.1,86.6,0.0158,1550
30 DATA 69.1,79.4,0.0114,1370
40 CFM=3560'fan airflow (cfm)
50 L=32:W=32'greenhouse length and width (feet)
60 GH=800'house conductance (Btu/h-F)
70 FOR MONTH = 1 TO 2'September and October in New Orleans
80 READ TAVG,TMAX,WA,HSUN'Tavg, Tmax, humidity ratio, sun on ground
90 TD=(TAVG+TMAX)/2'average daytime temp (F)
100 SUNPOWER=.9*L*W*HSUN/8'sun power (Btu/h)
110 TG=TD+SUNPOWER/CFM'greenhouse temp (F)
120 T=80'initial house temp est (F)
130 TERM1=17.863-LOG(29.921)
140 TERM2=(2*CFM+GH)/1000
150 TERM3=60*CFM*.075
160 TERM4=(CFM*TG+TD*(CFM+GH))/1000
170 T1=(TERM4+TERM3*WA)/TERM2
180 T2=T1+TERM3*.62198/TERM2
190 TH=9621/(TERM1-LOG((T1-T)/(T2-T)))-460
200 IF ABS(T-TH).01 THEN T=TH:GOTO 190
210 PI=EXP(17.863-9621/(460+T))
220 WI=.62198/(29.921/PI-1)
230 P=4.5*CFM*(WI-WA)
240 PRINT TG,T,WI,P
250 NEXT MONTH

Greenhouse Indoor Humidity Pounds
temp (F) temp (F) ratio per hour

132.5073 84.19831 2.602676E-02 163.8327 September
118.5826 76.60541 2.008044E-02 139.0606 October

Greenhouse polyethyelene film comes in 32'x100' rolls with a 4-year
guarantee. It costs about 5 cents/ft^2. A lot of it's made in Texas.
To minimize the greenhouse heat loss, we might put black plastic on
the ground and hang a layer of shadecloth above, with the fan above
that, pushing outdoor air into the greenhouse which warms as it passes
down through the shadecloth and flows into the lower house windows.

Nick