Author Topic: A Comparison of Solar Radiation Shields  (Read 6863 times)

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Offline CW2274

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Re: A Comparison of Solar Radiation Shields
« Reply #50 on: May 21, 2015, 01:26:32 AM »
I think its too big though.
Yep, I just drew it out and it's indeed too big. Now if one was to cut all the corners off, it might fit.
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Offline BCJKiwi

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Re: A Comparison of Solar Radiation Shields
« Reply #51 on: May 21, 2015, 03:36:35 AM »
Hi,
I have an 80mm fan in my system but want to replace it soon. What I did not do was measure the inside diameter of the tubular section where the whole fan module fits. Just cut off the corners of the one that is in there now before it was installed.

The diameter I'm referring to is somewhere around 90 to 95mm diameter - approx. 3.5 to 3.75".

Does someone have the actual diameter?
Want to sort out how best to fit a 90mm fan if possible before taking the station off line.

Thanks.

Offline ValentineWeather

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Re: A Comparison of Solar Radiation Shields
« Reply #52 on: May 21, 2015, 07:39:25 AM »
I'll look for the Davis fan today and post dimensions. The 80mm fan draws plenty of air 4-5x more than the solar Davis as long as its sealed. Remember its pulling air through the narrowed down triple wall tube. At one time I had all the dimensions for calculating air flow, but don't have handy after changing computers.
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Offline BCJKiwi

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Re: A Comparison of Solar Radiation Shields
« Reply #53 on: May 21, 2015, 07:47:47 AM »
Thanks,
But the Davis Fan is much smaller in Diameter as it fits inside another molding - it is the OD of that other molding/ID of the white plastic body - not the OD of the fan itself that I am looking for.

Offline aweatherguy

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Re: A Comparison of Solar Radiation Shields
« Reply #54 on: May 21, 2015, 02:50:34 PM »
Wow, this discussion really took off. This reply is a little late so go back to the bottom of the first page for context.

I've plotted the test data from JCA433 (attached). The upper plot is all three temperature columns and the bottom one is the last two columns relative to the first column.

It is fairly obvious in the bottom plot that the nearby FAWN data is not well correlated with the two sets of shield data. I'm guessing that the FAWN station is too far away to be meaningful for a test like this and/or sited differently.

Taking kcidwx's comments on calibration a little further: The data from the two shields is showing a difference of roughly 0.5F to 1.0F. If the sensors in question are calibrated to +-0.2F accuracy (not impossible but a tall order) then consider this. If the true temperature is 70F, one sensor could read 69.8F and the other could read 70.2F and they would both be within the +-0.2F spec limit. However, comparing the readings, they are 0.4F apart. So, if they are reading different by 0.5F then that is just barely enough to be a significant difference in light of the calibrated accuracy.

I am guessing that the sensors used by JCA433 are the Ambient F007TH units (right?). If so, they are specified by Ambient to be accurate to +-1.0F. I don't know if Ambient claims NIST traceability or over what time period the calibration would be valid (one year is typical). Anyway, my point is that these sensors would need to be further calibrated for the data from JCA433 to be meaningful. He mentioned having calibrated the sensors but now I am curious as to how they were calibrated.
« Last Edit: May 21, 2015, 02:53:43 PM by aweatherguy »

Offline CW2274

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Re: A Comparison of Solar Radiation Shields
« Reply #55 on: May 21, 2015, 03:10:58 PM »
Thanks,
But the Davis Fan is much smaller in Diameter as it fits inside another molding - it is the OD of that other molding/ID of the white plastic body - not the OD of the fan itself that I am looking for.
As I measure my spare housing, it is exactly 4 1/8", or 104.78mm. That's measuring at the base of the fan housing, not the curled portion on top. That being said, one could safely extrapolate that the diameter of the ISS portion of where the fan housing sits is approx. 106mm.
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Offline CW2274

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Re: A Comparison of Solar Radiation Shields
« Reply #56 on: May 21, 2015, 03:14:22 PM »
And if it helps, the depth at which the fan housing sits in the ISS is 1 1/4", or 31.75mm.
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Offline BCJKiwi

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Re: A Comparison of Solar Radiation Shields
« Reply #57 on: May 21, 2015, 04:52:05 PM »
Thanks a lot!

That is bigger than I thought it would be going by the work I had to do to get an 80mm fan in there.

Offline CW2274

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Re: A Comparison of Solar Radiation Shields
« Reply #58 on: May 21, 2015, 07:13:05 PM »
Well, I'm part of the a/c club now! Went out to the local parts store, picked up an 80mm, cut the 4 ends off at the bottom right through the screw holes, and it dropped in like it was meant to be. The top of the fan's uncut portion rested on the top of the ISS's hole perfectly. Then at Randy's suggestion, I used rope putty to fill in the rest of the square peg in a round hole, hole. That thing's suckin' like nobody's business. Problem for me is I now have my ISS in the yard to power it, but it's not in an aesthetic place. #-o. Anyway, lets see if I notice a difference. ;)
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Offline ValentineWeather

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Re: A Comparison of Solar Radiation Shields
« Reply #59 on: May 21, 2015, 07:54:20 PM »
Well, I'm part of the a/c club now! Went out to the local parts store, picked up an 80mm, cut the 4 ends off at the bottom right through the screw holes, and it dropped in like it was meant to be. The top of the fan's uncut portion rested on the top of the ISS's hole perfectly. Then at Randy's suggestion, I used rope putty to fill in the rest of the square peg in a round hole, hole. That thing's suckin' like nobody's business. Problem for me is I now have my ISS in the yard to power it, but it's not in an aesthetic place. #-o. Anyway, lets see if I notice a difference. ;)

Good deal should work like a charm, If you have a GFI plug just in case wouldn't be a bad idea. I'm plugged into one but when I tested it, it failed to see a ground fault so I'm sol until I rewire this house built in 1953.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline CW2274

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Re: A Comparison of Solar Radiation Shields
« Reply #60 on: May 21, 2015, 08:06:19 PM »
Well, I'm part of the a/c club now! Went out to the local parts store, picked up an 80mm, cut the 4 ends off at the bottom right through the screw holes, and it dropped in like it was meant to be. The top of the fan's uncut portion rested on the top of the ISS's hole perfectly. Then at Randy's suggestion, I used rope putty to fill in the rest of the square peg in a round hole, hole. That thing's suckin' like nobody's business. Problem for me is I now have my ISS in the yard to power it, but it's not in an aesthetic place. #-o. Anyway, lets see if I notice a difference. ;)

Good deal should work like a charm, If you have a GFI plug just in case wouldn't be a bad idea. I'm plugged into one but when I tested it, it failed to see a ground fault so I'm sol until I rewire this house built in 1953.
Yes sir, porch outlet GFI protected. Now I must consider whether to wire out to it's normal sitting place, or go back to d/c, :-( cause it ain't stayin' were it's at forever.
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Offline ValentineWeather

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Re: A Comparison of Solar Radiation Shields
« Reply #61 on: May 21, 2015, 08:19:55 PM »
Well, I'm part of the a/c club now! Went out to the local parts store, picked up an 80mm, cut the 4 ends off at the bottom right through the screw holes, and it dropped in like it was meant to be. The top of the fan's uncut portion rested on the top of the ISS's hole perfectly. Then at Randy's suggestion, I used rope putty to fill in the rest of the square peg in a round hole, hole. That thing's suckin' like nobody's business. Problem for me is I now have my ISS in the yard to power it, but it's not in an aesthetic place. #-o. Anyway, lets see if I notice a difference. ;)

Good deal should work like a charm, If you have a GFI plug just in case wouldn't be a bad idea. I'm plugged into one but when I tested it, it failed to see a ground fault so I'm sol until I rewire this house built in 1953.
Yes sir, porch outlet GFI protected. Now I must consider whether to wire out to it's normal sitting place, or go back to d/c, :-( cause it ain't stayin' were it's at forever.

Well my weather station comes first. The bird spikes are a little ugly but whats more important.  :grin:
Randy, the Aviator is my father in 1963 with his Indian bike

Offline CW2274

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Re: A Comparison of Solar Radiation Shields
« Reply #62 on: May 21, 2015, 08:34:26 PM »
Well, I'm part of the a/c club now! Went out to the local parts store, picked up an 80mm, cut the 4 ends off at the bottom right through the screw holes, and it dropped in like it was meant to be. The top of the fan's uncut portion rested on the top of the ISS's hole perfectly. Then at Randy's suggestion, I used rope putty to fill in the rest of the square peg in a round hole, hole. That thing's suckin' like nobody's business. Problem for me is I now have my ISS in the yard to power it, but it's not in an aesthetic place. #-o. Anyway, lets see if I notice a difference. ;)

Good deal should work like a charm, If you have a GFI plug just in case wouldn't be a bad idea. I'm plugged into one but when I tested it, it failed to see a ground fault so I'm sol until I rewire this house built in 1953.
Yes sir, porch outlet GFI protected. Now I must consider whether to wire out to it's normal sitting place, or go back to d/c, :-( cause it ain't stayin' were it's at forever.

Well my weather station comes first. The bird spikes are a little ugly but whats more important.  :grin:
I truly hear you. Mine is now stuck in a pool fence post next to the gate. Works beautifully, pool water far enough away not to influence the dew pt., but really doesn't belong.
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Offline JCA433

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Re: A Comparison of Solar Radiation Shields
« Reply #63 on: May 22, 2015, 04:30:27 AM »
Wow, this discussion really took off. This reply is a little late so go back to the bottom of the first page for context.

I've plotted the test data from JCA433 (attached). The upper plot is all three temperature columns and the bottom one is the last two columns relative to the first column.

It is fairly obvious in the bottom plot that the nearby FAWN data is not well correlated with the two sets of shield data. I'm guessing that the FAWN station is too far away to be meaningful for a test like this and/or sited differently.

Taking kcidwx's comments on calibration a little further: The data from the two shields is showing a difference of roughly 0.5F to 1.0F. If the sensors in question are calibrated to +-0.2F accuracy (not impossible but a tall order) then consider this. If the true temperature is 70F, one sensor could read 69.8F and the other could read 70.2F and they would both be within the +-0.2F spec limit. However, comparing the readings, they are 0.4F apart. So, if they are reading different by 0.5F then that is just barely enough to be a significant difference in light of the calibrated accuracy.

I am guessing that the sensors used by JCA433 are the Ambient F007TH units (right?). If so, they are specified by Ambient to be accurate to +-1.0F. I don't know if Ambient claims NIST traceability or over what time period the calibration would be valid (one year is typical). Anyway, my point is that these sensors would need to be further calibrated for the data from JCA433 to be meaningful. He mentioned having calibrated the sensors but now I am curious as to how they were calibrated.


I am going to redo the test with some NIST traceability sensors. 

Offline JCA433

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Re: A Comparison of Solar Radiation Shields
« Reply #64 on: May 22, 2015, 07:23:25 AM »
I calibrated the sensors by measuring the readings of the sensors relative to the indoor air temperature at different temperatures  and then calculating the difference and adding this to the high temperature measurements.  All of the temperature calibration measurements were within the range of the temperature data provided.  I spent a lot of time recording a lot of data calibrating those sensors to make sure they were as accurate as possible.
« Last Edit: May 22, 2015, 11:02:56 AM by JCA433 »

Offline JCA433

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Re: A Comparison of Solar Radiation Shields
« Reply #65 on: May 22, 2015, 10:31:16 AM »
The reason I did these tests was because I was getting somewhat high temperature readings in the afternoon during the past winter season.   My delta T for high temperatures was about 0.9 F relative to the most reliable weather station.   I am not sure if the other weather stations on Weather Underground are mounted properly 4 to 6 feet above ground and well away from concrete surfaces and buildings.  The FAWN station has a very similar micro climate to mine  and most near my property and the temperature there is measured about 2 meters above ground and   away from buildings and pavement.  The sensors used in these tests are NOT DAVIS sensors and NOT ideal for the Davis shield 7714.  I plan to buy a better sensor and then test it in the Davis shield 7714.  I am growing tropical plants so accurate low temperature measurements are important.  The high temperature measurements are not really relevant for my work.  It would  be nice though to have reasonably accurate high temperature measurements. 

Offline ct

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Re: A Comparison of Solar Radiation Shields
« Reply #66 on: June 04, 2015, 11:54:06 PM »
I built a weather station using a modified Davis passive radiation shield turned into a fan aspirated one.  The fan reaches full speed even with moderate sunlight and battery takes over when not enough power supplied from the 12v solar panel. 

Inside the radiation shield is a dual PVC pipe sensor chamber that allows air to pass between the 2 pipes, hopefully reducing any heat transmitted from the shield to the temperature sensor.  Air intake is from the bottom of shield, similar to a Davis Vantage Pro.

I haven't done any scientific analysis on the accuracy, but compared to the nearest official bureau station about 3km away the daily maximum is very often identical. 

Weather station http://imgur.com/LK79VtZ
Sensor chamber http://imgur.com/RDylwsE

Offline CW2274

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Re: A Comparison of Solar Radiation Shields
« Reply #67 on: June 05, 2015, 12:52:35 AM »
I built a weather station using a modified Davis passive radiation shield turned into a fan aspirated one.  The fan reaches full speed even with moderate sunlight and battery takes over when not enough power supplied from the 12v solar panel. 

Inside the radiation shield is a dual PVC pipe sensor chamber that allows air to pass between the 2 pipes, hopefully reducing any heat transmitted from the shield to the temperature sensor.  Air intake is from the bottom of shield, similar to a Davis Vantage Pro.

I haven't done any scientific analysis on the accuracy, but compared to the nearest official bureau station about 3km away the daily maximum is very often identical. 

Weather station http://imgur.com/LK79VtZ
Sensor chamber http://imgur.com/RDylwsE
Very nice!
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Offline jerryg

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Re: A Comparison of Solar Radiation Shields
« Reply #68 on: June 09, 2015, 11:13:42 PM »
I have been running a shield comparison for the last few months, comparing the Davis 24 hr solar shield with the 24 hr shield running on a 3 volt wall wart and a 24 hr davis using a 12 volt computer fan using a RM Young shield as the reference shield. The results have been very interesting so far. I am waiting for late June and July to see how they compare with the Texas heat. The motor in the earlier post is the motor used in the Davis fan setup. To answer the sensor question asked earlier about the Davis fitting in the RM Young, i used an sht15 breakout board from Sparkfun and added the cable and connector plus the factory sf1 filter over the sensor and it fits just fine in the rmy shield plus i made it alittle longer to allow me to plug it into the iss board. I got four of the boards and calibrated them against each other using 2 tm99 temperature meters. So far the results have surprised me. Will pass along the results later on.

Offline djwiktor

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Re: A Comparison of Solar Radiation Shields
« Reply #69 on: August 23, 2017, 05:31:32 AM »
Nothing beats the old Stevenson screen  :grin:


So far based on my tests of new radiation shield from Barani - MeteoShield, I can say to this only - " until 2017"   :)

See the discussion here: https://www.wxforum.net/index.php?topic=31346.0

The radiation shield from Barani shows a significant improvement in ambient temperature measuring, and I think it may even smack down the stevenson screen.  So far I know, Mr. Barani is already doing a real comparison between Stevenson screen and MeteoShield.