Another DIY radiation shield (FARS of better: SFARS)

[henkg]

The standard mini radiation shield of my WH-1080 does not suffice. Temperature spikes of up to two degrees, quite noticable when it is partly sunny. I read about the plastic bowls screens, as well as the louvre doors screens, but I wanted something smaller, cheaper, easier to build. (SFARS= Solar Fan aspirated Radiation Shield.)

Parts list:
- PVC pipe 80 mm
- 90 degree PVC female/male connector (elbow).
- PVC strap
- Solar fan: many ebay suppliers, e.g. http://www.ebay.com/itm/Solar-Cell-Fan- ... 4606955802
Total costs: about EUR 11,-

First tests are promising: With a little sun, the fan starts immediately and runs fast enough, even in this time of year. No / much less temperature spikes when the sun shines on the shield.
The lab setup (after first tests I will paint the PVC white, find a better way to attach the screen to the standard mount and the wall, and a better way to attach the solar panel). The solar fan fits exacty, in this lab setup I did not even glue anything. The fan blows the air out, from bottom to top. When not running, the fan blades do not block passive airflow. For a better airflow the standard shield of the sensor is removed, the DIY PVC shield should protect against rain.

After a while, I will report my experiences, and post a more detailed description. But real testing has to wait until may/june next year. Will this fan survive frost, fog? I will wait, and see ...

The setup:


After testing, I will find a better way to attach to base and wall; insulate the wiring. But for now, it is easy to make adjustments:


The PVC rainhood mounted (I might replace this version with one with a more "horizontal" angle):


Solar fan images:
(Panel Size: 42x30mm | Fan diameter: 73mm | Blade diameter: 6 cm)



YOUTUBE: The fan running, at a very overcast moment in october. The noise is caused by the wind, the fan itself is silent:
http://www.youtube.com/watch?v=L-sjmaz0lNg
At that moment, the sun was about 45 degrees to the solar panel, and did not hit the panel directly. So I expect the fan will run much faster in bright sun (hope not too fast ).

My idea was inspired by:
- http://n8vhf.com/2011/05/21/fan-aspirat ... on-shield/
- http://www.frohling.org/temp-probe.jpg
- and a post about the used fan, can't find it anymore.

[nitrx]

Looks great is he fan silent ?

[beteljuice]

Have you seen any of the 'pipe' designs on the web ?

One of the more common designs is like an inverted uppercase 'J' (with the complete T type bar) - I believe this is to assist passive airflow and to stop static or reverse flows when wind goes accross the end of (one) of the pipes.

PS. I experimented with those cap fans, but I used two of the SP to one fan - almost ran in the dark

[henkg]

@nitrx: Yes, the fan is silent. Driven by a 300 Watt halogen bulb I could hear it spinning, indoors of course. Outside, even in bright sunlight, the sound should be unnoticable.

@beteljuice:
- Yes, I have seen a picture of an inverted J design. With only MY common sense I cannot think of a reason why this would increase the airflow from inlet to outlet, especially when the fan is inactive. However, I will keep this in mind. Replacing the current rainhood with a 90 degree elbow will be easy, the hood isn't glued.
- About cap fans: I also own a cap with an integrated dual panel and fan. Given the performance, I did not even try using that for a SFARS. Sizes of both fan and panels are very much smaller than the one I used for my SFARS. I was surprised by the build quality and performance. In my OP, I added a Youtube video link, taken in low light conditions.

And, even if it stops working (too) soon, I will report this here. But for only USD 3.31, I will order a spare one. Put it on my cap if not needed ....

[NO0C]

Hi henkg,

I like your design and ingenuity.

How about adding another elbow to your BOM and making it undeniably waterproof ?



Just a brain storm.

Regards,

[henkg]

@all: thanks for advice. This is my first prototype, based only on Google and my common sense, so any advice is welcome ....
Adding a down pipe, or a down elbow to my design?
The shield is mounted in a shady place. The outlet points to my house, no fierce winds from that direction. Because the fan only runs during sunshine (13:00-20:00h in summer), I think that with the current construction there will be a better passive airflow. When using a 24h operated fan (using external AC current), I would add the elbow. I hope the current hood will protect against rain enough. Will let you know if it does or doesn't. Air humidity worries me more. These fans, as well as PC fans, are not constructed to operate under damp conditions.

[henkg]

An update: my SFARS is finished.
- Painted and mounted.
- Nothing is glued, except for the solar panel on the elbow.
- I removed the base plate of the panel because it wasn't water resistant. After soldering the wires to the panel, I painted the back of it for isolation.
- All solar fan components are within the elbow. In wintertime I might swap the elbow with a plain one, and keep the vented one indoors.





Does it work? For now I see less or even no spikes. However, real testing will have to wait until May next year.

[nitrx]

I've just ordered two fans in China today (will be delevired in 3 weeks) how did you place the fan inside the pvc tube ?

Ron

[henkg]

The fan fits exactly inside the male part of the 80mm elbow. I just squeezed it in. To be sure, take the fan with you when visiting the hardware store.
(For US (and UK?) readers: A 3 inch elbow probably is too small to fit the fan without adjustments).

[nitrx]

Ok thanks for the tip.

[nitrx]

Well finally I received the solarfans from China

I've made almost the same construction as henkg an 90 degrees angle PVC diameter 80 mm , the pipe attached to the bottom is shorter I don't want to measure the groundtemperature.

Until now I've had no sun but I've tried the fan with a 25 watt lightbulb and it starts to rotate, when I'm sure it works the pvc will be painted white or I wrap tinfoil (with bubbles around it)

I will let you know my results hopefully we get some sun these days.



First image fan blows out to the west (when sun shines
Second image solarcell focussed to the south

[henkg]

So the fans did work
Tinfoil might give problems with the transmitter range.
And I do not see a rain hood to protect the fan from rain, when wind is blowing in the direction of the fan outlet.
(Last week I swapped the vented elbow with a plain one, to protect the fan from humidity. I will refit the vented elbow in February. Until then it will not get any sun.)
Anyway, looking forward to your results.

[mcrossley]

Foil is just about the worst possible surface, white paint is about the best.

[nitrx]

Yes they do both Henk, well I see I've to do something to the rain indeed

I never had issues with the foil.

Mark I thought that tinfoil should reflect radiation better ( for radioactive I should use lead )

I didn't mean the kitchen tinfoil but isolationfoil (dutch sample site http://www.sbr.nl/producten/infobladen/ ... latiefolie ) this foil should claim a high reflection of infra-red light.

Do you have sources for comparisions ?

[mcrossley]

OK, the reason shiny foil is bad is because whilst it has a high coefficient of reflectivity, it has a very low coefficient of emissivity. So the heat it does absorb it hangs on to and radiates it very slowly, it does however conduct heat quite efficiently to whatever it is attached to. In simple terms it is the ratio of the reflectivity to emissivity that determines how hot things will get in the sun.

You can see this effect yourself if you have ever left a shiny spanner out in the sun - it gets very hot despite reflecting most of the heat that hits it. It is also why children's slides in parks are no longer installed in a south facing position, the shiny surface gets hot enough to burn bare legs, even in the UK (when we get some sunshine! ).

Things that need to be kept cool like astronomers telescopes and observatories, Stevenson screens etc are almost invariably painted white and not shiny metal for this same reason.