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re: a.c. house holds heat?
3 sep 2001
kasper  wrote:

>>>many modern houses cannot be cooled just by opening the windows.

>>warm air only rises in older houses?

> ... got nothing to do with the warm air rising. more to do
>with situating older pre-a/c houses so they can take advantage of
>breezes, if any, to bring the cooler outside air into the house
>without mechanical devices.

steve baer writes (in cooling with night air, sunpaper, january, 1984):

  many books mention placing windows for "cross ventilation" and talk at
  great length about catching the breeze to cool the house. such schemes are
  fine if there is a wind, but a house designed to depend on the wind is a
  miserable failure when the wind stops. the only sure way to ventilate a
  house is to use natural convection [warm air rising] or to use exhaust fans. 

  exhaust fans or whole house fans, as they are called, are well worth the
  power they consume when you consider the cooling they provide, but their
  noise is irritating and it is still cheaper to use natural ventilation.

  the equation for natural ventilation in the ashrae handbook can help
  size the vents: v = 9.4sqrt(ti-ta)e), where v is the velocity in ft./min,
  ti is the temperature averaged over the different elevation between the
  entrance and the exit, ta is the ambient temperature, and e is the
  difference in elevation [in feet] between the entrance and the exit. 

  if we assume that the inlet vents are at floor level and the exit vent
  10' above and the average temperature inside is 10 f above ambient,
  we have v = 9.4sqrt(10x10) = 94 ft/min. [so a 1 ft^2 vent moves 94 cfm,
  4 ft^2 moves 376 cfm, and 16 ft^2 moves 1504 cfm.]

>since i plan to replace my sick central air conditioning unit, my
>house will be plenty cool again when the work is done .. which is why
>i am not thinking of putting a whole house fan in the attic.  it is
>the humidity i hate, not the heat.

you might use a licl pond in a solar attic or trickle licl over a south
roof during the day...

nick




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