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re: is airconditioning necessary?
28 dec 1997
newton ellison  rants:

>i am looking for comments from people who... are concerned, like me,
>about how much electricity it uses... [and care] about being very
>productive inside when it is hot and humid outside... those who need
>a.c. to sleep when it's hot and humid... working and low income people...
>i want to ask you if you know there is a better way to cool and dehumidify
>our houses, apartments, schools, shops, churches, libraries and malls?

>       what's the answer?

dig a hole in the ground? san antonio, tx has an average annual (underground) 
temperature of 68.6 f. cool enough? the hottest month is july, on the average,
with a 24 hour average temp of 85 and a daily min and max of 75 and 95, and a
humidity ratio of 0.0157 pounds of water per pound of dry air, corresponding
to a dew point of about 70 f. too humid? the average daily amount of sun that
falls on a horizontal surface in july is 2170 btu/ft^2, enough to make a dandy
liquid licl absorption system regenerator with a small roof pond or a little 
pond on the south side of a house, with a poly film cover and a vent, even
simpler than the "unglazed collector/regenerator performance for a solar
assisted open cycle absorption cooling system" described by m. n. a. hawlader,
k. s. novak, and b. d. wood of the center for energy system research, college
of engineering and applied sciences, arizona state university, tempe, az
85287-5806 usa, in solar energy, vol. 50, pp 59-73, 1993:

  "an ordinary black shingled roof [was] used as a collector/regenerator for
  the evaporation of water to obtain a strong solution of [lithium chloride]
  absorbent... results [using a 36' x 36' roof] show a regeneration efficiency
  varying between 38 and 67%, and the orresponding cooling capacities ranged 
  from 31 to 72 kw (8.8 to 20 tons)", ie about 1 ton per 100 square feet of
  roof area, ie 1 ton per square :-)

  in the house "water [the refrigerant] is sprayed into an evaporator,
  evacuated to about 5 mmhg of pressure, where it immediately flashes
  into vapor... cold water, pumped from the bottom of the evaporator,
  flows through a fan coil... that blows cool air into the conditioned
  space. the absorber acts as a vapor compressor and condenser for the
  system. water vapor from the evaporator flows over the absorber where
  it is absorbed by the concentrated absorbent. the continuous absorption
  of water vapor maintains a low pressure in the system and permits
  flashing of water in the evaporator... the product of the absorption
  process, a weak absorbent solution, collects at the bottom of the
  absorber to be pumped [up over the roof] for concentration."

  "the dilute licl solution was delivered to the collector surface through
  a spray header spanning the top of the roof and made from 50.8 mm (2 in)
  diameter cpvc pipe fitted with 35 evenly spaced brass nozzles. the
  concentrated solution collected at the bottom... in a pvc rain gutter, and
  returned via gravity feed to a 1608 l (425 gallon) fiberglass tank... in
  the event of of a rain, fluid flowing off the collector could be manually 
  diverted to a 946 l (250 gallon) wash tank or to a roof drain. during the
  initial phase of the rain, residual salt would be washed from the roof
  and collected in the wash tank to be stored for later regeneration. after
  sufficient rainfall, the rainwater is diverted to the roof drain."

one might add a layer of plastic film spaced up over the roof shingles
to avoid losing or contaminating the licl. the open system described in the
paper worked best in low winds, about 2 mph. warm humid air rising might
provide such a wind, and draw in fresh air through a counterflow plastic
film air-air heat exchanger, eg the outer glazing cavity, to make this
thermally more efficient, especially with outgoing condensation.

foote mineral sells licl for about $4/pound, and 50 pounds might be plenty.
in-line plastics in texas (800) 364-7688 sells pond liners for 10 cents per
square foot, made to your sketch and shipped by ups in a day or so, and a
20x20' pond might provide a peak of 48,000 btu/h of ac or dehumidification,
on the days when you need it most.

so what are you waiting for, newton?

nick




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