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Solar Attic Fan Installed. The Verdict is...

Post in 'The Green Room' started by Sandor, Jun 27, 2007.

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  1. Sandor

    Sandor Minister of Fire

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    I installed a new Natural Light solar attic fan on the womens house several weeks ago.

    Last year, on a 95F degree day with full sunshine (like today), I would average about a 158F peak temp in the attic. I have had a remote sensor up there for the last year to see what was going on. The house has a "ridge vent" that is obviously worthless.

    After several of these hot days, with the fan installed, it appears the peak is about 138F. After the sun gets off the roof, things cool down much quicker.

    Also, I installed an Energy Star 9k btu through the wall A/C (heat pump) unit that replaced a old 15k unit. During the same cooling demands, it appears the new (lower btu ouput unit) is averaging about 2 degrees cooler inside the house. This is a 1400 sq/ft ranch house. I know its cooler because the A/C unit will run flat-out during the hot part of the day.

    I know that this is not a "Rhonemas" quality engineering post, but the results were positive and I thought I would share.


    http://www.solaratticfan.com/

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  2. begreen

    begreen Mooderator Staff Member

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    I like the concept and it's proving better than the ridge vent. But I think I'd prefer a hardwired fan because the way our roof is situated, I'd want it running long after the sun isn't on the collector. How long does it take for the attic to drop to ambient? Have you considered adding a second unit?
  3. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Not sure you would need the hardwired BG. I have had a wired gable vent on this place for years. When I installed it the difference was noticable upstairs immediately. It is set to go on and off at 100* and even on these 97* days, and since all of my western shading blew down in the tornado, it still shuts off way before sundown. The recommended on/off is at 120* but I bumped it down a few years ago when the old one crapped and I had to go up and replace it.

    I walked outside at 6:30 and it had already called it a day.
  4. begreen

    begreen Mooderator Staff Member

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    Could be, when I was growing up in the east, we used to leave the attic fan running at night as a whole house fan. There was a ceiling grille to the attic. It was nice to pull the cooler night air into the house.

    The case I was wondering about was with a north/south roof peak. One's house might be oriented so that the sun is on one side of the roof in the morning and the other by the late after noon. I revisited the site and see they have a remote array. It looks like the solution would be to go with the gable mount fan and a remote PV panel facing south.
  5. webbie

    webbie Seasoned Moderator Staff Member

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    I really want to put one or two of them in, but I want roof mounted and my roof is steep - and I'm not the best at pulling up shingles and then setting them back right!

    I think I will have to call the guy who roofed my addition to do it. I know it would make things better both with and without the air conditioning on.

    In my last house I installed a whole house fan - that thing was great, could really blow up a storm. I also had a roof fan with both a thermostat and a humidistat - something that is needed in Southern NJ.
  6. R&D Guy

    R&D Guy New Member

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    I like the idea of a solar powered system - no wiring to do, just a hole in the roof, and what do you know the system gets the most solar power on the hot days. Sure makes sence. I didn't do a lot of digging around on the link you provided, but I noticed that they have a 10 watt system. This may well show how little I know about solar power, but can a small panel like that provide that kind of wattage or are there batteries with this system?
  7. Sandor

    Sandor Minister of Fire

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    BG,

    I had the remote temperature probe up in the attic for the last year to see what was actually happening. What I noticed was this: When the sun is not on the roof, the attic temp tracks the outdoor temp within a degree or two. This was at night, or rainy days.

    My goal was to reduce attic temps at peak - sunny hot days. And by lowering the peak temps, I wanted a quicker attic cool down. Without the fan, the attic would still drop to ambient within 4 hours. Now its looking like about 2 hours. I noted that when the roof starts to shade, the temp drops rather quickly, then cools slowly. (not linear)

    What this told me was that running an attic fan during the evening or cloudy/rainy days was useless.

    I think adding a second unit would help, but these things aren't cheap, and I would run into diminishing returns. I have my array pointing WSW.
  8. Sandor

    Sandor Minister of Fire

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    I got the 10 watt unit. They also make one with a 20 watt array. There is no battery with the system... It runs when its sunny out. (Check my reply to BeGreen above for some observations)

    It still kinda runs when its overcast, but not real fast.
  9. Hogwildz

    Hogwildz Minister of Fire

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    Sandor, do you have vented soffit down at the eaves? That ridge vent should be helping somewhat. Unless there is no venting at the eaves. In that case the ridge vent is useless.
  10. Sandor

    Sandor Minister of Fire

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    Just got back from the Outer Banks, NC.

    Have a "vented" ridge. But it is worthless. Also have vents at the eaves.

    When I re-roof, I will just remove the "vent" at the ridge.
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