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PVC Pipe Fan Aspirated Radiation Shield FARS

For discussion of DIY weather equipment - sensors, accessories, improvements to existing kit etc
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Buford T. Justice
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PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Sun Sep 22, 2013 12:30 pm

I am new to building radiation shields. I came across this and decided to build one for my Fine Offset weather station and a second for my Sky Scan Atomic Clock which has a similar-designed temperature sensor:

http://n8vhf.com/2011/05/21/fan-aspirat ... on-shield/
http://n8vhf.com/wp-content/uploads/201 ... _N8VHF.pdf

I bought the pipe, connectors, and caps with a few exceptions:

1) I made sure to get everything in bright white to reflect the sunshine so nothing would need to be painted on the outside. I did decide to paint the inside of the 4" cap and the inside of the 3" pipe flat/matte black which was a pain (I am not sure if that really helped or not).

2) Instead of two 3" drain inserts, I used one 4" drain insert on the bottom which slips over the 3" pipe nicely.

3) I cut the 3" pipe into 13" sections.

4) I made a 9" stud and attached it to the bottom of the 4" drain insert then zip-tied my temperature sensor to that so it is in the middle of the pipe.

5) I used 80 mm CPU fans after shaving down the corners with an electric work bench grinder and let the power cables come down to the drain insert and hooked up a 9 volt battery.

So far so good. During the day yesterday, the temperatures seemed to be in agreement with other nearby weather stations. I went to bed happy. No more crappy OEM solar shield!

I woke up at 5:30 AM and looked at my temperatures. My weather station says 45.0 °F (7.2 °C) and my Sky Scan says 43.2 °F (6.2 °C). I looked at nearby temperatures again and they are in the 53-57 °F (11.7-13.9 °C) range.

Something is not right. I wonder if it has to do with dew as there is a coat of it on the outside of both tubes. Maybe it's the fans as it makes no sense to have them running when it is dark does it? I ordered solar-powered fans which should fit this radiation shield kit just fine, but they will not be here from China until another week or two:

http://www.ebay.com/sch/i.html?_odkw=So ... n&_sacat=0

Remember, each has:

(1) 4" PVC cap.
(1) 3" coupler.
(1) 3" pipe cut to 13".
(1) 4" drain insert.
(1) 9" stud connected to the bottom of the 4" drain insert sticking up the inside of the 3" PVC pipe with the temperature sensor zip-tied to the stud.
(1) 80 mm CPU fan with corners shaved down to fit inside the top section of the 3" coupler hooked to a 9 volt battery (soon to be replaced by solar fan linked above).
(4) 5/16" bolts to connect the 4" cap to the top of the 3" coupler above the fan which also hold every together.
(1) 3" 1/4" bolt to attach to the bracket.

Here is a picture of the one i made for my weather station:
IMAG0065.jpg
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BCJKiwi
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by BCJKiwi » Sun Sep 22, 2013 11:28 pm

Others have done a similar build but with maybe a longer pipe and no fan.
The top half or so of the pipe is painted black to provide a thermal updraft through the pipe to replace the fan.
Keeping the lower section where the sensor is white ensures that does not get heated.

moe3
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by moe3 » Sun Sep 22, 2013 11:35 pm

Your first link was posted over at wxforum.net shortly after he put that link together. I built one like it and it did work pretty well. I had used a Davis fan (custom cut to fit) and a Davis ISS solar panel. Then I came accross some plastic bowls at the local 'Dollar Store' and built 3 or 4 radiation shields for some 'homemade' Davis inventions. Still have the parts, so it may come back into play some day.

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Buford T. Justice
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Mon Sep 23, 2013 4:45 pm

I changed out the 13" section of 3" PVC pipe I had painted the inside of flat/matte black for an unpainted one. That seems to be working better so far temperature-wise. Looking inside the assembled FARS, it is very dark inside even with the Sun shining on the side of it.

The 9-volt batteries don't last but maybe 1 day. I am going to see if I can get rechargeable ones at a local store and use those until my solar-powered fans arrive. Definitely need a fan during the day. Maybe during the night too depending on conditions.

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Buford T. Justice
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Sat Oct 05, 2013 6:41 pm

So far these two FARS have been working very well. I wound up using a 12-volt 80 mm CPU fan that I ground the corners of down with a bench grinder and slid into the 3" coupler. I then stripped a USB cable and used crimps to connect the red/black wires to the fan (the others I cut off and wrapped the exposed remains in electrical tape to be safe. I had a USB wall socket adapter from an Android phone which you plug the USB cable into giving the CPU fan 5 volts which seems to be enough to keep the inside of the radiation shield cool. I heard the Apple version may output a few more volts so I am looking into getting a couple of those instead so the fans spin a bit faster.

When the Sun shines on the FARS, my temperature readings are roughly 2-3 °F hotter. Today I decided to paint the outside of the 3" pipe (minus where the coupler and screen slide on) and the 4" cap a very bright, glossy white. It hasn't been sunny here today due to rain, but I am hopefully this will get the difference in temperature down a bit more. I want to be no more than 1 °F off from the local airport readings. I think this glossy white spray paint for plastic will do it.

I had found some plastic bowls and used a 3.5" hole saw to cut the centers out of them. The hole was just big enough to slide the bowls onto the PVC pipe, but the bowls didn't help with cooling whatsoever. Don't waste your time trying this.

I still have not received my China Solar Fans. I think they are coming across the Pacific to me via sailboat. That or the USA government shutdown is affecting imports. Regardless, the CPU fans on USB power are fine and working well in both of the FARS I built.

So here is what not to do I found out by trial and error so far along with some other advice someone new to building may make:

1) Don't use a hand saw to cut the PVC pipe if you want nice, clean cuts. Some people have a gift for cutting PVC pipe perfectly with a hand saw, but I am not one of them. A pipe cutter or a miter saw work best for the rest of us. I used a miter saw to cut mine.

2) Don't paint the inside of the PVC pipe or anything else flat/matte black. It does no good and is a waste of time.

3) Don't use a 1/4" drill bit to drill a 1/4" hole for a 1/4" screw. You need to make a slightly smaller hole so the screws can thread into the plastic of the 4" cap. Use a 3/16" bit first. If the hole is too small, use a 7/32" drill bit.

4) Don't use 9-volt batteries. A new one of good quality lasts maybe one day before it no longer has enough power to spin the fan.

5) Don't use bowls. They may have worked if I made the hole bigger so air could blow between them and the PVC pipe and used long crews to keep them together, but that would add more weight to everything.

6) Don't place your temperature sensor too close to the ground. Make sure your temperature sensor is 4-6 feet from the ground and make sure the ground below it is grassy. Concrete, bricks, and rocks reflect heat. I now have mine hanging under the eve of my garage:
WS62694 Thermometer FARS Painted.jpg
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Buford T. Justice
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Sat Oct 05, 2013 7:35 pm

LOL! I type the previous post and then the China Solar Fans arrive in the mail. They are too small to fit inside the 3" coupler without major modification so I will not use them. They do spin up somewhat on an overcast day though, but not powerful enough to offer any cooling for a FARS which needs 24/7/365 fanning. The product literature is hilarious. They say China has the most English speakers on the planet. That may be true, but they need to work on their spelling and grammar:
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by henkg » Sun Oct 06, 2013 7:11 am

Buford T. Justice wrote:the China Solar Fans .. / .. They are too small to fit inside the 3" coupler without major modification so I will not use them.
Too small? A different model? The one I own: Solar Panel Size: 42x30mm | Fan diameter: 73mm | Blade diameter: 6 cm (http://sandaysoft.com/forum/viewtopic.php?f=16&t=8445).
So for 3" this one is slightly too big. However, the plastic cage around the fan blade can be removed easlily.
They do spin up somewhat on an overcast day though, but not powerful enough to offer any cooling for a FARS which needs 24/7/365 fanning.
I wonder if any active cooling is necessary when the sun isn't shining. A solar panel certaintly doesn't work 24/7/365.
With even a faint sun my fan works OK: http://sandaysoft.com/forum/viewtopic.p ... 5&start=17
Image

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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Sun Oct 06, 2013 11:07 am

henkg wrote:Too small? A different model? The one I own: Solar Panel Size: 42x30mm | Fan diameter: 73mm | Blade diameter: 6 cm (http://sandaysoft.com/forum/viewtopic.php?f=16&t=8445).
So for 3" this one is slightly too big. However, the plastic cage around the fan blade can be removed easlily.
I cannot find my metric tape measure at the moment, but the cage appears to be right around 7 cm. There are no numbers on the packaging. It looks identical to yours.
I wonder if any active cooling is necessary when the sun isn't shining. A solar panel certaintly doesn't work 24/7/365.
With even a faint sun my fan works OK: http://sandaysoft.com/forum/viewtopic.p ... 5&start=17
I think it is vital actually and probably yields the most accurate readings obtainable. Buildings can add radiant heat to the night air they absorbed during the day. I remember reading something that the Davis solar-powered FARS can read colder at night if installed out in the open and no wind is blowing. To me, it just makes sense to have air constantly blowing across the temperature sensor.

I am between two very small airports with AWOS equipment reporting to NOAA I compare my temperature readings to. One of these days, I want to go to one or both of them with permission and see their AWOS equipment. I imagine I would see either the SARS or MARS model listed on the link below:

http://www.allweatherinc.com/meteorolog ... #tabs=1153

The MARS looks funny. I see the point of the design which is essentially the same as our PVC pipe versions. I would almost bet the MARS is made out of PVC pipe as well. Since the fan air in ours escapes from the top or the side, distancing the entrance and exit holes as done on the MARS seems unnecessary for our needs I would think.

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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by MickinMoulden » Fri Oct 11, 2013 2:20 am

I think you are missing the point of going through all that effort. It is so that you can mount it out in the sun and not have the Sun effect the temperatures. The point of mounting it out in the open is so that you get the night time cool air and not get heat radiating from the house. Even with a fan blowing all night, if it is under the eve of the house it won't get the night time cool as well. I would suggest mounting it even just 5 inches out from the eve. Other than that, it is a brilliant job.
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Buford T. Justice
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Fri Oct 11, 2013 5:09 am

MickinMoulden wrote:I think you are missing the point of going through all that effort. It is so that you can mount it out in the sun and not have the Sun effect the temperatures. The point of mounting it out in the open is so that you get the night time cool air and not get heat radiating from the house. Even with a fan blowing all night, if it is under the eve of the house it won't get the night time cool as well. I would suggest mounting it even just 5 inches out from the eve. Other than that, it is a brilliant job.
I can tell you that the Sun still affects it, but night time temperatures are fine.

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Buford T. Justice
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Sun Dec 08, 2013 6:30 pm

I have an idea I am currently trying. I bought some 2" PVC pipe. I disassembled the FARS I made and cut both the 3" and 2" pipe to 10" long. I then drilled holes into the 3" pipe for screws to hold the 2" pipe inside and in the middle so the fan could suck any hot air radiating through the 3" pipe hopefully before coming into contact with the 2" pipe. I am hoping the heat will stay away from the temperature sensor now inside the 2" pipe. I have no real way to test it since it is now Winter, lol. I'll report back once Spring/Summer comes back. I have a hunch this should fix a lot of issues.

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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by MickinMoulden » Wed Jan 14, 2015 4:52 am

I had to insulate mine due to the high amount of solar radiation. UV hits 17 here. Here is mine: https://www.facebook.com/29759796028273 ... =1&theater
Michael, Palmerston, NT Australia www.Palmerston-WeatherImageNo image? I'm offline!
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by BillW » Wed Jan 28, 2015 11:21 am

Hi,

I posted this elsewhere but I've forgotten exactly where....
low cost temp shields.pdf
It is an interesting read for those looking at aspirated housings using pipe as discussed.

cheers,
Bill.

PS. On the aspiration issue, after a recent big blow and seeing the demise of another screen posted on the forum, I thought I'd check my home made one. The primitive "flow director" seems to be doing the trick. What surprised me is that the fan, which has run without a hitch for 6 months, has lots of green fungus, bacteria or whatever organic compound it is!, growing along the edge of the blades. Exactly the same as you see when you clean out a dusty PC. Anyway, scrapped it off and away it goes for another 6 months I hope. Using a 40w solar panel and huge battery has paid off. Total overkill but flawless running right through winter. :D
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Buford T. Justice
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Re: PVC Pipe Fan Aspirated Radiation Shield FARS

Post by Buford T. Justice » Mon Jun 15, 2015 6:15 am

This design has been working great since I built it especially after putting the 2" PVC pipe inside the 3" PVC pipe. The only other modification I plan to do is to spray the space between the pipes with foam insulation and remove the screws holding the inner pipe in place since the foam insulation can do the job.

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