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Posted by Don Ocean on May 28, 2009, 1:32 am
W wrote:
> Attic temperature depends on the amount of solar radiation, construction
> details and the rate of ventilation. Calculations indicate that on a July
> day in Texas, a ventilation rate of one air change per minute for a typical
> attic using 95-degree F air will lower the peak attic temperature to about
> 101 degrees F. Providing half air change per minute will lower the
> temperature to about 106 degrees F. Thus, the first half change per minute
> is most effective and a doubling of this rate only achieves about 5 degrees
> F additional cooling. Studies indicate that further increases in ventilation
> are not effective in significantly reducing attic temperatures.
>
> Calculate the required summer ventilation rate by determining the volume of
> attic space and dividing by 2. This will be the cfm (cubic feet per minute)
> of ventilation air needed. The volume is determined approximately for a
> rectangular house by multiplying the height from the ceiling to the
> peak/ridge (H) times the width of the house (W) times the length (L) and
> dividing by 2 -- ( H x W x L / 2 ). For a gable roof, this will be
> reasonably accurate. For a hip roof house, the volume will be overestimated
> but adequate.
Why bother to have an attic at all? If the damned thing needs a fan to
cool that wasted space it is just a ridiculous expenditure of energy.
>
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> details and the rate of ventilation. Calculations indicate that on a July
> day in Texas, a ventilation rate of one air change per minute for a typical
> attic using 95-degree F air will lower the peak attic temperature to about
> 101 degrees F. Providing half air change per minute will lower the
> temperature to about 106 degrees F. Thus, the first half change per minute
> is most effective and a doubling of this rate only achieves about 5 degrees
> F additional cooling. Studies indicate that further increases in ventilation
> are not effective in significantly reducing attic temperatures.
>
> Calculate the required summer ventilation rate by determining the volume of
> attic space and dividing by 2. This will be the cfm (cubic feet per minute)
> of ventilation air needed. The volume is determined approximately for a
> rectangular house by multiplying the height from the ceiling to the
> peak/ridge (H) times the width of the house (W) times the length (L) and
> dividing by 2 -- ( H x W x L / 2 ). For a gable roof, this will be
> reasonably accurate. For a hip roof house, the volume will be overestimated
> but adequate.