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Re: Heat engine

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Posted by nicksanspam on March 1, 2005, 12:15 pm
 


NREL data indicate July is the worst-case month for AC in Mobile, when
1770 Btu/ft^2 hits the ground on an average 82.3 F day with a 73.2 F min
and humidity ratio w = 0.0169 pounds of water per pound of dry air.
Very humid...
 

The techniques in that book won't help much. Baruch Givoni's 1998 Climate
Consderations in Building and Urban Design has more on design for hot and
humid climates, but that book won't help much either, compared to serious
air conditioning.


That won't help, in humid climates. Offgridman might enjoy ceiling fans
and an airtight house with a LiCl solar still on the roof, which might
also heat water for showers. I could help, if he wants to get into that.
We've proposed another all-day workshop on solar heating and natural
cooling for the 2005 ISES/ASES conference in Orlando in August. It would
be nice to have a working example of this new liquid desiccant technique.

Nick


Posted by Offgridman on March 2, 2005, 2:33 am
 
Hi ya Nick,
I have ceiling fans, three in the cabin now. One in the bedroom and two
in the living area. You are dead on that evaporative cooling is
virtually nonfunctional here due to the humid climate. I would like to
learn more of your LiCl solar still on the roof idea. Sounds
interesting.  Liquid desiccant cooling hmmmm. Very interesting idea.
Cabin is 24ftX24ft R 19 ceiling with a air channel in between the
rafters of 1inch in depth below the metal roofing between the 24 inch
on center ceiling joists. This channel funnels air from the 24inch
overhanging eaves to the ridge vent. The cabin has running full length
down the inside continous ridge vent that allows hot air to vent freely
up through the roof and out under the ridge.
The ceilings are cathedral and the peak is 17.5 ft and the exterior
side walls are 10 ft tall. The building  gable end faces SSW with two
8x6 glass doors and one 3x5 window. All insulated glass. there are two
windows on the east wall 2x5 and one 2x2 window on the north wall.
Now, where can I learn about the system you described.
Thanks
Offgridman


Posted by nicksanspam on March 2, 2005, 1:00 pm
 

Hi ya Offgridman,


Good. You might add occupancy sensors.


The basic idea is to distill water out of a LiCl solution during the day and
let it absorb water vapor from house air at night. This could dehumidify an
airtight house, with some potential for cooling as water evaporates indoors.


So that keeps the roof cooler, without exchanging indoor and outdoor air?
What color is the roof?


With overhangs or other shading? How much insulation in the walls?
How airtight is your cabin? I'd blower-door test it before LiCling.

Nick


Posted by Offgridman on March 3, 2005, 3:10 am
 Walls are R13 plus 5/8 plywood  R14 maybe total or so.  Roof is silver
galvanized tin. large overhangs east and west walls.
plan on installing roof over deck to shade south windows later, right
now I have vertical blinds.
and reflective tint on doors and windows.
Cabin has sill plate caulked to sub floor and is tighter than most
average homes. Patio Doors are lousy if I need a tight structure  to do
this.
Offgridman


Posted by nicksanspam on March 3, 2005, 11:01 am
 

So it runs north and south, with a atan((17.5-10)/12) = 32 degree pitch?


The LiCl still might be on top of that flattish roof.


You do, for dehumidification. Say 30 cfm max. Insulation is less important.

NREL says the average humidity ratio wo = 0.0154 pounds of water per pound
of dry air in Mobile in June, on an average 80.4 F day with an average 70.7
daily min. If the average outdoor temp is 75 F for 12 hours on a June night
and Pso = e^(17.863-9621/(460+75)) = 0.887 "Hg and Pao = 29.921/(1+0.62198/w)
= 0.723 "Hg, the average RH would be about 100Pao/Pso = 82%.

If the average indoor temp is 80 F with an average 50% indoor RH, Psi = 1.047
and Pai = 0.5Psi = 0.524 and wi = 0.62198/(29.921/Pai-1) = 0.0111. With 30 cfm
of air leakage, you might collect N = 12hx60m/hx30cfmx0.075lb/ft^3(wo-wi)
= 7 pints in 12 hours from a dehumidifer...

Nick


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