nronronronro...
Hello again!
I live in Arizona, and am also a cheapskate, so I've wrestled
with this very issue for the last 2 years. Here's what I've
found:
Denco-ga makes a good point about drawing the air from the
shaded part of the house, however, in my situation, it would
be frustratingly slow. The north side of the house is shaded,
and thus cooler, but drawing the air from there to the hottest
part of the house, the southern end, where I spend my time,
would take too long, as it's the furthest away. I would have
to replace all the air in the house before I felt any
difference. Obviously, the layout of your house may be a
strong determining factor in this regard.
What I have found to work best is to blow the hot air out of
the house from any convenient location (the most convenient
for me is a part of the house where I can't hear the fan
running).
Now, I have observed some interesting phenomena. Once the
outside temperature is lower than the inside, it seems
logical to turn the fan on (I have a variable-speed fan
which isn't as powerful as yours).
The first thing I notice is that, even with the temperature
outside being lower than the inside, with the fan on low,
I can see an *increase* in the inside temperature in the
room where the cooler air is coming directly in. I believe
this is due to the heat which has been absorbed by the walls
and ceiling spaces of the structure during the day continuing
to be spread into the air of the structure at night.
Turning the fan up higher helps to counteract this.
Secondly, I notice that a small difference in temperature
between the outside and inside is not sufficient. When
you consider that the test of a healthy air conditioner
is that the temp at the outlet is 20 degrees cooler than
the room temp, and considering how long the AC must run
(and how often) to cool the space, you can see that a
smaller difference in temp will have little effect.
With a higher-volume fan, there will be a corresponding
increase in the air exchange, so you won't need a 20
degree difference, but I wouldn't start until there's
at least a 5 degree difference.
Thirdly, as omnivorous-ga notes, replacing low-humidity
air with high-humidity, but cooler, air, will not feel
any cooler, so make sure the outside humidity is fairly
low, or it won't be worth the effort. Additionally,
should you give up on the fan, on a particular evening,
and turn on the AC, realize that the AC provides most
of its cooling effect precisely by removing humidity
from the air in your house. If you have imported
significantly humid air from the outside, your AC will
have to work that much harder to remove the humidity.
This can get expensive.
Given all that, here's what I would recommend:
Allow the intake of air to come into the room you will
be spending the most time in during the cooling period.
For me, that is my living room, and the point of intake
is the fireplace. With the flue open, this is ideal,
since it draws in air from a higher altitude than any
window I have in that room, and that air is cooler than
outside air coming from a lower altitude (hot air rises,
cold air descends). And it doesn't have to travel through
any warm air before arriving in my living room (versus air
coming into a second story window, which must then travel
through the hotter air in that part of the house).
Set the fan up for exhaust, preferably from either the
*quietest* location in the house, or if that's not an
issue, from the *hottest* place in the house, which,
for you, will surely be on the second floor, since,
again, hot air rises, cold descends. The higher you
can place the exhaust fan in that space, the better.
In short, exhaust from the space with the hottest air,
and intake into the space where you will be spending
time, from the highest intake point possible.
By the time you go to bed, the temperature in your
bedroom *should* have averaged out with the rest of
the house, but realize that, if the exhaust fan is
*in* your bedroom, it may end up being the hottest
space in your house, since that's the exit point for
the heat. If the fan is not exhausting from your
bedroom, you can experiment with opening a window
in the bedroom to just the right amount to cool that
space to the perfect temperature by the time you go
to bed, without significantly detracting from the
cooling effect on your main living space.
Two fans *can* work more effectively. One at the
exhaust and one at the intake would be most effective,
however, if the one at intake is, as I recommended,
in your main living space, it will likely be too
noisy. Two fans exhausting from the two hottest
spaces in the house (upstairs) would be quieter
and more effective all around.
Finally, place a thermometer in the main living space,
and use it to gauge the success of your arrangement.
This will help you determine exactly how much of a
difference in temperature, between inside and outside,
is workable. It will also help you to know when & if
it's time to turn off the fan and turn on the AC.
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sublime1-ga |
