Replies

1. 
   xMikeSmith | Jul 03, 2002 05:23am | #1

   yes.. Suntunnel makes one of the solar attic fans.. her's why they don't have battery backup..

   when the sun is out they operate and "keep the attic cooler"

   when the sun is not out , the attic isn't hot..so they don't need to operate.. it's different than a boat.. the only heat source is teh sun.. on a boat, there are other heat sources

   Mike Smith   Rhode Island : Design / Build / Repair / Restore

1. 
   4Lorn1 | Jul 03, 2002 08:44am | #2

   I agree with Mike. It would be nice if they had a small back up battery. The roof deck will not cool for some time after the sun sets. In the mean time it continues to radiate heat down into the house. A thermostat would also be nice when the temperatures are too low to worry about and would provide energy to charge the batteries that wouldn't compete with the motor.

   I checked them out at Suntunnel. At $350 a pop they seem to be very proud of them. I wonder if I could cobble something similar together for far less.

   I also noticed that they used polycrystaline photocells. Cheap and reasonably effective but they may have to be replaced in ten years or so. Monocrystaline cells would last far longer and have more output. For $350 I would think that they would go for better quality.

   Edit 07/03/2002 Added last block of text.

   Edited 7/3/2002 1:49:43 AM ET by 4LORN1

1. 
   MHubert55 | Jul 04, 2002 02:26am | #4

   Thx for your reply 4lorn1.  I'm actually considering purchasing one of the sailboat units to take apart and use as a chinese blueprint if you know what I mean.  From what I've read they will actually run for several hours just on battery juice which would really give enough time for the roof deck to cool.  So all I have to do is apply the proper voltages and probably some relays or switches and incorporate them into the house solar vent.  Maybe someone out there has already done something like that. 

1. 
   4Lorn1 | Jul 04, 2002 03:57am | #5

   Just off the top of my head. I would think that 11 solar cell in series, I'm assuming 1.2v/cell and the ni-cads would charge at 13.2v (Double check these figures), battery in parallel to both solarcells and motor and a diode placed between the solarcells and the batteries, to prevent the batteries from discharging in the photocells, would be a start.

   I would probably add a bimetal thermostat between the motor and the photocells to give the batteries time to charge without competition from the motor. I would use a ballbearing 18v motor, they use a 36v, and a balanced fan.Patch it together and lay it in the sun. Resize or modify to get good function and a holdover of 45 minutes or so and full charging of the batteries. Sounds so fun I may end up cobbling one together myself.

2. 
   BossHog | Jul 03, 2002 02:54pm | #3

   Why not use passive/gravity vents?

   They're not expensive, work anytime the attic is hot regardless of the sun, and don't wear out.

   All those who believe in psychokinesis, raise my hand.

3. 
   ahneedhelp | Jul 08, 2002 02:34am | #6

   Although solar assisted venting make a lot of sense, it seems like an expensive solution even if you cobble something together yourself.

   And it seems to me it accomplishes basically the same thing as a passive setup would.

1. 
   4Lorn1 | Jul 08, 2002 12:26pm | #7

   I tend to agree. Passive thermosyphon between soffit and a good ridge vent have been shown, DoE, to be the most cost effective solution in the majority of cases. It is only my inner Toolman Taylor seeking more power that interests me in the power vent idea. Maybe I could fit a 302 with a 6' prop and.....

   Still the solar powered vent fan seems like a nice little project. I doubt I will get around to the design but I have it on the list. I could spend the same time in a bar. Spend more money have less fun and accomplish very little.