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? Whole-House fans for flat roof house? DonC 10-06-2007
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Posted by willshak on October 7, 2007, 1:24 am
on 10/7/2007 12:47 AM DonC said the following:
>
>>
>>> But we're talking about a different animal here. A WH fan "moves"
>>> existing cool air supplementing AC at a much, much cheaper cost.
>>>
>>>
>> I hope you mean instead of AC, not supplementing. You don't run both at
>> the same time do you?
>>
>> As for the flat roof, how much space do you have up there above the
>> joists? How much venting? It may be possible, but you may be better off
>> looking at the mushroom cap type of roof ventilator.
>>
>>
>
> I guess I wasn't very clear on that. By supplementing I meant using cool
> air during the night and early morning so as to delay turning the AC on --
> if turning it on at all. If the wind is blowing the fan isn't really needed.
> But that's not usually the case. The fan just gets things moving.
>
> There's 2x12s so I guess that's 11 1/2" +/-. I'm not sure a typical
> ventilator pulls enough CFM. A typical WH fan is rated 3000 to 4000 CFM.
>
> An example of the economies of a WH fan using Atlanta as an example (The
> savings would be much greater here -- south of Tucson):
>
> .. Operating a properly sized 2-ton air
> conditioner with a seasonal energy
> efficiency ratio (SEER) of 10 in Atlanta,
> Georgia, costs over $250 per cooling
> season (1,250 hours), based on
> 8.5¢/kWh, or roughly 20¢ per hour
> of runtime.
>
> .. By contrast, a whole house fan has a
> motor in the 1/4 to 1/2
> hp range, uses 120
> to 600 watts, and costs around 1¢ to 5¢
> per hour of use.
>

I have a whole house fan and CA, and we use the fan for a number of
reasons other than getting cool night air in the house. Did you ever
burn something in the kitchen and the whole house smells or fills with
smoke? The fan will clean out the smell and smoke in a short time.
I let the dog (large Golden Retriever) out one night and she came back
in after having an encounter with a skunk. This was 12 AM at night and
we spent the next hour washing her in the tub with tomato sauce, tomato
soup, ketchup, or anything else we could find with tomatoes in it. The
fan cleaned 'most' of the smell out.
In the case of having an accessible attic. In the summer, when the attic
is about 130º F (I have a black roof with no rafter insulation, but
soffit and gable vents), I turn the fan on and blow the hot air out of
the attic before going up there, and leave it on while I'm up there. It
saves getting drenched with sweat and having to take another shower.


.--

Bill
In Hamptonburgh, NY
To email, remove the double zeroes after @

Real Goods Solar, Inc.
Posted by Edwin Pawlowski on October 7, 2007, 1:34 am

>
> There's 2x12s so I guess that's 11 1/2" +/-. I'm not sure a typical
> ventilator pulls enough CFM. A typical WH fan is rated 3000 to 4000 CFM.
>
> An example of the economies of a WH fan using Atlanta as an example (The
> savings would be much greater here -- south of Tucson):

There may be space between the ceiling and the roof. In my last house, it
was pitched from about 3 feet+ at the front to 1 foot + at the back. If
yours is like that, you can vent the fan into the space by adding enough
venting to it. Worth checking out.



Posted by DonC on October 7, 2007, 1:14 pm

>
>>
>> There's 2x12s so I guess that's 11 1/2" +/-. I'm not sure a typical
>> ventilator pulls enough CFM. A typical WH fan is rated 3000 to 4000 CFM.
>>
>> An example of the economies of a WH fan using Atlanta as an example (The
>> savings would be much greater here -- south of Tucson):
>
> There may be space between the ceiling and the roof. In my last house, it
> was pitched from about 3 feet+ at the front to 1 foot + at the back. If
> yours is like that, you can vent the fan into the space by adding enough
> venting to it. Worth checking out.
>

Nice thought but there is only the width of a 2x12 : ( IIRC the fans
require at least 2 clear feet above the fan blades. The fans I previously
installed had 4 to 8+ feet thanks to the pitched roofs.



Posted by DanG on October 7, 2007, 10:45 am
An exhaust fan will require intake air. This can be as simple as
opening a window or using operable louvers opened when the fan
unit comes on. The exhaust fan can be mounted in a window, cut
into a sidewall, punched through a roof. A roof penetration
requires the most to keep it rain tight.

Knock your lights out here:
http://www.grainger.com/Grainger/wwg/start.shtml

Roof mount:
<http://www.grainger.com/Grainger/wwg/productIndex.shtml?from=Search&newSrch=yes&operator=keywordSearch&search_type=keyword&action=Go%21&QueryString=roof+top+exhaust&submit.x=0&submit.y=0>

Wall mount:
<http://www.grainger.com/Grainger/wwg/productIndex.shtml?operator=prodIndexRefinementSearch&originalValue=exhaust+fan&L1=Wall-Mount>
--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgriff237@7cox.net



>
>> DonC wrote:
>>> Hi all,
>>>
>>> In every house I've owned, until now, I've installed a
>>> whole-house fan. They significantly reduce AC costs and make
>>> for comfortable living. Alas, that was while I lived in
>>> Michigan in houses that had attics. My typical unit included
>>> a twist timer and variable speed motor.
>>>
>>> Now we live in southeastern AZ in a condo with a flat built-up
>>> roof so a typical attic unit won't work. But we still have
>>> frequent cool nights that would we could benefit from.
>>>
>>> Anybody here have any experience with WH fans in a similar
>>> setting? My research so far has been disappointing -- no
>>> variable speed fans and fewer available units : (
>>>
>>> Thanks
>>>
>>>
>>
>> Being in AZ I would consider a swamp (evaporative) cooler. A
>> downdraft model would easily install on a flat roof, and give
>> you cooling when needed, not just at night. I'll bet most of
>> your neighbors have one, (or A/C).
>
> Yes we have AC. Some -- but closer to a "few" rather than
> most -- have swamp coolers but they're simply a form of air
> cooling limited to about 20 degrees of cooling. When temperature
> get over 100, 20 degrees isn't enough.
>
> But we're talking about a different animal here. A WH fan
> "moves" existing cool air supplementing AC at a much, much
> cheaper cost.
>



Posted by DonC on October 7, 2007, 1:49 pm

> An exhaust fan will require intake air. This can be as simple as opening
> a window or using operable louvers opened when the fan unit comes on. The
> exhaust fan can be mounted in a window, cut into a sidewall, punched
> through a roof. A roof penetration requires the most to keep it rain
> tight.
>
> Knock your lights out here:
> http://www.grainger.com/Grainger/wwg/start.shtml
>
> Roof mount:
>
<http://www.grainger.com/Grainger/wwg/productIndex.shtml?from=Search&newSrch=yes&operator=keywordSearch&search_type=keyword&action=Go%21&QueryString=roof+top+exhaust&submit.x=0&submit.y=0>
>
> Wall mount:
>
<http://www.grainger.com/Grainger/wwg/productIndex.shtml?operator=prodIndexRefinementSearch&originalValue=exhaust+fan&L1=Wall-Mount>
> --
> ______________________________
> Keep the whole world singing . . . .
> DanG (remove the sevens)
> dgriff237@7cox.net

Good stuff! Variable speed too! Only negative I see off-hand is the price.
The roof top unit I'd need would run about $450 + shipping. I'd also need a
speed controller ($20?) -- they've discontinued offering them! And
shutters, ductwork and roof curb. But it's certainly doable.

Thanks

>
>
>
>>
>>> DonC wrote:
>>>> Hi all,
>>>>
>>>> In every house I've owned, until now, I've installed a whole-house fan.
>>>> They significantly reduce AC costs and make for comfortable living.
>>>> Alas, that was while I lived in Michigan in houses that had attics. My
>>>> typical unit included a twist timer and variable speed motor.
>>>>
>>>> Now we live in southeastern AZ in a condo with a flat built-up roof so
>>>> a typical attic unit won't work. But we still have frequent cool
>>>> nights that would we could benefit from.
>>>>
>>>> Anybody here have any experience with WH fans in a similar setting? My
>>>> research so far has been disappointing -- no variable speed fans and
>>>> fewer available units : (
>>>>
>>>> Thanks
>>>>
>>>>
>>>
>>> Being in AZ I would consider a swamp (evaporative) cooler. A downdraft
>>> model would easily install on a flat roof, and give you cooling when
>>> needed, not just at night. I'll bet most of your neighbors have one, (or
>>> A/C).
>>
>> Yes we have AC. Some -- but closer to a "few" rather than most -- have
>> swamp coolers but they're simply a form of air cooling limited to about
>> 20 degrees of cooling. When temperature get over 100, 20 degrees isn't
>> enough.
>>
>> But we're talking about a different animal here. A WH fan "moves"
>> existing cool air supplementing AC at a much, much cheaper cost.
>>
>
>



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