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re: house ventilation
9 feb 2000
michael tomlinson writes of his
>...very high vaulted ceiling in the entrance hall, equiv. 3 stories.
very dramatic...
>on hot days (it gets very hot in melbourne, australia - 40 deg. centigrade
>== 104 deg. fahrenheit) the lower part of the house stays cool, but the
>vault gets very, very hot!
warmer than the outdoors? sounds like the sun is shining onto the roof
or into the upper windows, and the warm air is rising. perhaps the lower
part of the house has lots of thermal mass, if it stays cooler than
the outdoors during the day.
>our bedroom is on the top floor, and whilst we can close the door there's
>two walls exposed to the hot air, and it does not remain cool.
so you have something like this, seen from above?
north
sun sun sun sun sun sun sun
roof roof roof roof roof roof
w wall
entrance hall door a bedroom
l
roof roof roof roof l roof
peak peak peak peak peak peak
>...i guess what i'm after would be something which could be installed
>in the peak of the roof to pump out the hot air when desired.
when desired... what will replace the hot air that's pumped out?
warmer outdoor air?
>this house does not have a roof cavity, just the actual roof,
>which seems to be insulated reasonably well...
a lighter color might help, or a new indoor roof cavity lined with foil.
dave hatunen reasonably suggests:
> how about an openable skylight?
>ummm....yeh....... i was kinda thinking of something a little more
>sophisticated. we do have windows.....
windows that open...
for more pizzazz, you might replace the roof with two layers of
polycarbonate glazing and fill it with soap bubbles during the day
and air at night, in summertime :-)
>i want a fan at least; with the wind around here the hot air is just as
>likely to come in as out!
a differential thermostat might help.
>otherwise if it's just a passive opening, a temperature actuated system
>would be best; it would only open when the air temp outside was lower than
>inside.
at night? but this sounds like a daytime problem.
>...i don't think that just a hole is going to do it - it's a very big
>space and there's a lot of house to supply hot air :-)
i'm confused. i suppose you'd like to make the upstairs cooler without
warming up the downstairs much. a tall vertical airshaft might help...
a hole might supply lots of airflow if the house is warmer than the
outdoors. you might go look at some fans, and think about buying one
with some airflow rating in cfm (liters per second/2, approximately)
and also look at some openable skylights, and estimate the opening area
av in square feet, and calculate cfm = 16.6avsqrt(hdt), where h is
the height in feet and dt is the f temp diff from top to bottom.
a 4x8' square skylight with a 16 ft^2 opening and 24' of height and a
10 f temperature difference might move 16.6(16)sqrt(24x10) = 4k cfm.
some skylights have electric motors for opening, pizzazz-wise...
nick
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