I am a do it yourselfer and I am working on a solar heater to help heat my unattached garage. I found a couple of dc 12v .235 computer cabinet type fans and would like to use them to blow the heat from the solar heater into the garage. Not being much into electronics I need help on finding the most economical way to run the fans. My initial thought was to have them hooked up to a solar panel to provide to power and to have a thermal switch of some sort to turn them on only when it gets warm enough inside the heater. Any help would be appreciated.

 

passive solar I assume.. Great way to heat a garage IMO..
I built one 2ft x 4ft using an aluminum gutter plenum and its amazing the amount of heat it can put off. Too bad my house/windows are at all the wrong angles and I couldn't find a spot where it would work efficiently and I didn't have to cut a hole/route tubing through walls,etc...

yes a solar panel with a simple off the shelf thermal switch would be a simple way..
I had mine attached to a microcontroller (arduino) so I could see the actual temp input/output,etc.. and be able to turn on a fan as needed.
But even just a solar panel on its own is more than likely sufficient.. If there is enough sun to turn on the fan there is enough to have the heat you need in the box.

 

A solar heating panel will move it's own air by convection because the optimum installation is always at an angle. You should be thinking about a back-flow preventer for cold nights.

 

Hi Cebsix,
Is it a solar water heater?

Only if the unattached garage is water tight.

 

It's too easy to do with air, and cheaper, as you said.

 

Is the .235 current in mA? If so about 5 W or a solar panel of about 10 W. I have a 15 W from Harbor Freight @ about US $ 60. An old fasion thermostat could work or electronic detection with a variety of sensors, thermister, diode , LMxx with comparator & motor driver. A large capacitor ( 1000 u F ) in parallel with panel would aid in starting fans.

 

I would size the panel so that it can run the fans directly (no battery) on lightly shaded sunlight. Then the fans should always be available when there is enough sun to make significant heat, and your system is simplified by not having a battery with charging control. All you need is a thermostat to keep the fans off if the heat isn't there. Even that might be dispensed with.

 

A motor of any sort is problematic when driven off a solar panel. Motors require a higher starting for them to run. Typically what happens is they tend to stall which shorts the solar cell, then just sit there shorted as the voltage times current is not enough to get them to turn.

I have seen some schemes to make this work so it is not impossible. I would provide a link but I have not seen a scheme I think is excellent, or even good, the ones I have seen are amateur designs.

 

There are pneumatic vent openers for greenhouses. Open when too hot. That might work for you.

 

Found 10 W on Ebay for around $ 25.

 

passive solar I assume.. Great way to heat a garage IMO..
I built one 2ft x 4ft using an aluminum gutter plenum and its amazing the amount of heat it can put off. Too bad my house/windows are at all the wrong angles and I couldn't find a spot where it would work efficiently and I didn't have to cut a hole/route tubing through walls,etc...

yes a solar panel with a simple off the shelf thermal switch would be a simple way..
I had mine attached to a microcontroller (arduino) so I could see the actual temp input/output,etc.. and be able to turn on a fan as needed.
But even just a solar panel on its own is more than likely sufficient.. If there is enough sun to turn on the fan there is enough to have the heat you need in the box.

What size solar panel would you suggest for the two fans?

 

A solar heating panel will move it's own air by convection because the optimum installation is always at an angle. You should be thinking about a back-flow preventer for cold nights.

It would take quite a while for the heater to warm the garage without help.

 

Hi Cebsix,

Is it a solar water heater?

Regards,

Nandu.

No, not a water heater. Just air.

 

Found 10 W on Ebay for around $ 25.

Does it have to be wired to a rechargeable battery or will it be directly to the fans?

 

You think a 10 watt fan is going to help when the insolation of a sunny day is 79 watts per square foot?
It might help stratification, but it doesn't add much heat.

 

You think a 5 watt fan is going to help when the insolation of a sunny day is 79 watts per square foot?
It might help stratification, but it doesn't add much heat.

I don't know what you just said but all of the solar heaters I have seen are rigged with fans to force the warm air into the area to be heated.

 

I would size the panel so that it can run the fans directly (no battery) on lightly shaded sunlight. Then the fans should always be available when there is enough sun to make significant heat, and your system is simplified by not having a battery with charging control. All you need is a thermostat to keep the fans off if the heat isn't there. Even that might be dispensed with.

After considering the comment posted, I decided to go the cheapest route and run the fans using a transformer. I figure the power drawn for a .235 a fan will be minimal and still cheaper than running a kerosene heater full time. Thanks for all your help.

 

What I said was, a tiny fan is not going to produce much heat compared to even a single square foot of solar collector.

You simply have not read the same books that I have read. A direct-to-air solar heater can work by convection if you provide large enough ducts at the top and bottom.

Signed,
Number Twelve,
Florida State Certified Heating contractor since 1985

 

Re # 16, no battery required. Small computer fans start easily with graduat increase in solar power but if needed a" Solar Gleaner " would help, designed by an amature & field tested.

 

What I said was, a tiny fan is not going to produce much heat compared to even a single square foot of solar collector.

You simply have not read the same books that I have read. A direct-to-air solar heater can work by convection if you provide large enough ducts at the top and bottom.

Signed,
Number Twelve,
Florida State Certified Heating contractor since 1985

Notice he puts "Florida" where heat is the last thing they typically want ha ha

A fan to force air through the system does increase the efficiency.
Its not considered a "passive" system anymore but rather "active" and even just a small 100 cfm fan really does help it move that hot/cold air around much better and heat the area up faster. These little boxes can heat up air so quickly you can increase the airflow over natural convection and see decent benefits.