Author Topic: A Comparison of Solar Radiation Shields  (Read 7248 times)

0 Members and 1 Guest are viewing this topic.

Offline aweatherguy

  • Senior Contributor
  • ****
  • Posts: 284
    • Weather Station Data Logger
A Comparison of Solar Radiation Shields
« on: April 18, 2015, 05:17:28 PM »
I've just concluded a comparison of the performance of four different radiation shielding devices for measuring outdoor temperature. This post is a work in progress and I plan to eventually turn this into a report in PDF format. Comments are welcome and there could easily be errors in here so please let me know if you find one. Raw data is available on request, as are Matlab scripts used in my processing of the raw data.

Hardware Information
--------------------

This comparison was performed using the following radiation shields:

1) Home-built fan aspirated shield (FARS)
2) Davis #07714 naturally aspirated shield
3) Ambient Weather LX100 naturally aspirated shield
4) AcuRite VN1TX (aka 5n1) shield

The VN1TX unit is fan aspirated when there is enough solar energy on the solar cell to run the fan; at other times it is passive. This is the version that only has a single solar cell. It uses a Sensirion SHT21 temperature sensor which has a typical accuracy of +-0.3C (+-0.54F).

All other shields are fitted with custom-built sensors whose (NIST traceable) accuracy is +-0.08C (+-0.15F).

The test location is at approximately 38 degrees north latitude. Sensors are shaded by trees in the early morning so sun appears rather suddenly on them around 10:30Am local time.

Test Setup
----------
As shown in the photograph, the passive shields and AcuRite sensor were mounted in one cluster while the FARS unit was separately mounted nine feet away from the passive cluster. The VN1TX was oriented approximately north as per AcuRite installation instructions. The FARS air inlet and passive shield temperature sensors were all 64-inches above ground level, and the bottom of the VNT1X (where the temperature sensor is located) was 78 inches above ground level.

All sensors are wireless, with the exception of a DC fan power connection to the FARS. Data was recorded to a CSV log file using the WeatherStationDataLogger (WSDL) windows application.

Discussion
----------

While in many cases it is desirable to locate a weather station's anemometer separate from temperature measurement, in this case having the anemometer integrated with the temperature sensor in the VN1TX is fortuitous. This allows for an examination of the effect of wind on solar shielding effectiveness.

The first six days of the test run were dominated by clear skies, day and night. There was a significant negative offset on VN1TX temperatures at night and I knew from past experience that some of this might be due to radiational cooling to the clear night sky. On the last night of the test run, a thick layer of low stratus moved in, eliminating the effect of cooling to a clear night sky. This provided a 3.6 hour period over which a calibration comparison between sensors was made.

Each of the sensors in this experiment has a different time lag in its response to temperature changes. This results in a difference between readings whenever the air temperature is changing (which is pretty much all the time). It is just a matter of how much and how fast the air temperature is changing. However, on average these differences will average out to zero if one is careful to avoid certain situations such as a time segment where the temperature is only increasing.

Several graphs of results are presented below. The time axis on each graph is in days, UTC relative to 00 UTC on the first day of the test run. The test location is in the Pacific time zone and daylight savings time was in effect, so midnight UTC occurs at 5PM local time. Temperatures are in degrees Farenheit and wind speed is in knots (MPH = knots * 1.15).

In analyzing overall effects (including that of wind), subsets of data are extracted and averaged for separate day and night periods. The morning and evening intervals where the lack of fan rotation in the VN1TX creates large errors is intentionally excluded from these averages. Obviously, including those times would result in a significant increase in average differences between the VN1TX and FARS readings.

Data extracted for the night period runs from 11PM through 6AM and the day period is from 11AM to 4PM local daylight savings time.

Results
-------

The first data graph image contains two sub-plots. This is the 3.6 hour calibration interval with a thick stratus layer overhead. The top graph shows the temperatures reported by the four sensors. The lower graph shows temperatures reported by the VN1TX, LX100 and Davis units relative to the FARS temperature. The mean differences are also shown in the graph legend. As luck would have it, this particular VN1TX unit has an SHT21 sensor with a very small temperature difference compared to FARS. With this difference being so small, no adjustments were made to the VN1TX temperatures for calibration purposes. The remaining graphs below are all showing raw temperatures from each sensor. It is also worth pointing out that a fair portion of the up-and-down variation seen in the lower graph is probably due to differing time lags in each sensors' response to changes.

The next graph shows the test run over one full day with clear skies.

Most obvious in the VN1TX data are the "bat ears" at x-axis locations of about 1.73 and 2.0 where the aspirating fan turns off and on. Because morning sun is shaded by trees until about 10:30AM local time, the morning bat-ears are less pronounced -- when the sun finally hits the VN1TX sensor, it is already strong enough to start the fan running. Remember that this is the smaller 5n1 AcuRite sensor with a single solar cell -- the daytime performance of dual-solar cell unit is going to be different (hopefully better). Once the fan is running, solar heating bias is between 4 and 6 degrees F on average on this day. At night, there is somewhere between 2 or 2.5F of cooling bias due to the clear night sky.

The Davis and LX100 passive shields are very close in performance here, running between perhaps 1.7F and 3F of solar heating during the day. At night, these shields are exhibiting a minimal amount of cooling (less than 0.5F) to the clear night sky.

The next graph shows six consecutive days of the test run. Temperatures compared to the FARS and 30-minute averaged wind speed are the two sub-plots here. From this data, numerical averages of day and night temperature differences have been computed and are tabulated below. The day and night time intervals for which data is extracted for numerical averages are shown with green and blue boxes respectively on the graph.

Wind clearly (and not unexpectedly) has a significant effect here. For example compare the daytime performance of day 1 to day 2. Average wind is nearly double (1.10 on day 2 versus 0.65 on day 1) and the temperature difference between FARS and all othere sensors is much less on day 2 compared to day 1. The effect is especially noticeable with the VN1TX where the difference drops from 5F to 3.5F with the higher average wind.

At night, wind is also well correlated with temperature differences in all sensors and is especially obvious with the VN1TX sensor. Differences are typically around 2 to 2.5F on calm nights and drop to 1F with only 0.65 knots of average wind.

Here is the tabulated average data extracted for day and night periods on each of the six days (average wind speed in knots):

======================================
Daytime Average Differencs (Farenheit)
--------------------------------------
Day   Wind   VN1TX     LX100     Davis
 1   0.65   +5.02       +2.55   +1.85
 2   1.10   +3.48       +1.38   +0.84
 3   0.75   +4.98       +2.34   +1.71
 4   0.90   +4.51       +2.22   +1.50
 5   1.01   +4.30       +2.20   +1.31 
 6   0.89   +4.74       +2.49   +1.48


========================================
Nighttime Average Differencs (Farenheit)
----------------------------------------
Day   Wind   VN1TX      LX100     Davis
 1   0.00   -2.08       -0.28   -0.24
 2   0.00   -2.55       -0.49   -0.40
 3   0.00   -2.03       -0.40   -0.37
 4   0.01   -1.57       +0.09   -0.04
 5   0.65   -1.01       +0.08   -0.08
 6   0.30   -1.55       -0.01   -0.10




Offline nincehelser

  • Forecaster
  • *****
  • Posts: 1966
    • nincehelser.com
Re: A Comparison of Solar Radiation Shields
« Reply #1 on: April 18, 2015, 05:52:11 PM »
Quote
The VN1TX was oriented approximately north as per AcuRite installation instructions.

in my experience getting it dead-on to true north is critical for proper operation of the fan.

Offline aweatherguy

  • Senior Contributor
  • ****
  • Posts: 284
    • Weather Station Data Logger
Re: A Comparison of Solar Radiation Shields
« Reply #2 on: April 18, 2015, 06:06:58 PM »
Thanks for the input. I'll re-check the north alignment and see what difference it makes. Was this just in regards to the times for fan on/off or did it also make a difference during the middle of the day?

Offline nincehelser

  • Forecaster
  • *****
  • Posts: 1966
    • nincehelser.com
Re: A Comparison of Solar Radiation Shields
« Reply #3 on: April 18, 2015, 06:27:43 PM »
Thanks for the input. I'll re-check the north alignment and see what difference it makes. Was this just in regards to the times for fan on/off or did it also make a difference during the middle of the day?

In my case it makes a difference in the start time of the fan.  A few degrees off to the east and I'll get a small spike in the morning.  It's due to my mounting pole sometimes slipping, probably due to high winds coming from the west.  I'll repoint it to true north, and the problem goes away.

I'm not sure what to make of your night temperatures.  I've never noticed a problem with the temperature being too cold when compared to other stations or other nearby thermometers.


Offline CW2274

  • Forecaster
  • *****
  • Posts: 3078
    • Conditions @ CW2274
Re: A Comparison of Solar Radiation Shields
« Reply #4 on: April 18, 2015, 06:31:48 PM »
Quote
The VN1TX was oriented approximately north as per AcuRite installation instructions.

in my experience getting it dead-on to true north is critical for proper operation of the fan.
How could that be? My Davis can literally be in the shade when there's full sun and still run on the panel alone. I understand having our solar panels point south in our hemisphere, but I would certainly think being EXACT is totally unnecessary.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline nincehelser

  • Forecaster
  • *****
  • Posts: 1966
    • nincehelser.com
Re: A Comparison of Solar Radiation Shields
« Reply #5 on: April 18, 2015, 06:37:23 PM »
]How could that be? My Davis can literally be in the shade when there's full sun and still run on the panel alone. I understand having our solar panels point south in our hemisphere, but I would certainly think being EXACT is totally unnecessary.

The 5n1 has a very small solar panel, and it seems just barely enough to keep the fan going, which is all it is meant to do.

As for pointing North, I'm referring to alignment with the embossed arrows on the 5n1 chassis.  If you align the north arrow true north, the panels will obviously point true south.


Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 4098
Re: A Comparison of Solar Radiation Shields
« Reply #6 on: April 18, 2015, 06:37:52 PM »
First of all thanks for doing this test. Its a lot work to determine what testing has already shown many times, even though some still believe passive works just as well as fan aspirated.
I realized the benefit and started using fan aspiration when I had the original white washed cotton region shelter many years ago. In the desert Southwest the difference was like day and night during low wind conditions.
   
Today and over the last decade I've use the well designed 24 hour FARS Davis triple walled shield but modified with a much higher velocity AC powered fan instead of the standard solar. I would put it up against the best professional FARS units out there, and bet it would do just as well.

Appreciate your passion for doing this test.  =D> Good idea to use some of the more popular selling stations for the test.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline DoctorKnow

  • Forecaster
  • *****
  • Posts: 1084
Re: A Comparison of Solar Radiation Shields
« Reply #7 on: April 18, 2015, 06:51:42 PM »
This test matches my known experience with Acurite 5 in 1. It is an excellent test, and a great comparison. The acurite needs to be painted with a glossy white, and then it will run much closer to the other stations. It does run colder at night for me, especially when the sky is clear and it is below 50 F

Offline CW2274

  • Forecaster
  • *****
  • Posts: 3078
    • Conditions @ CW2274
Re: A Comparison of Solar Radiation Shields
« Reply #8 on: April 18, 2015, 06:56:02 PM »
First of all thanks for doing this test. Its a lot work to determine what testing has already shown many times, even though some still believe passive works just as well as fan aspirated.
I realized the benefit and started using fan aspiration when I had the original white washed cotton region shelter many years ago. In the desert Southwest the difference was like day and night during low wind conditions.
   
Today and over the last decade I've use the well designed 24 hour FARS Davis triple walled shield but modified with a much higher velocity AC powered fan instead of the standard solar. I would put it up against the best professional FARS units out there, and bet it would do just as well.

Appreciate your passion for doing this test.  =D> Good idea to use some of the more popular selling stations for the test.
I remember way back when Davis put their new (then) 24hr FARS up against RM Young and it fared VERY well. IIRC only .5F difference at full solar noon.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline DoctorKnow

  • Forecaster
  • *****
  • Posts: 1084
Re: A Comparison of Solar Radiation Shields
« Reply #9 on: April 18, 2015, 07:01:09 PM »
I would ask about humidity, but if the temp is wrong on the acurite, then so is the humidity readings, and the only good test would be the Davis and Ambient.

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 4098
Re: A Comparison of Solar Radiation Shields
« Reply #10 on: April 18, 2015, 07:02:22 PM »
First of all thanks for doing this test. Its a lot work to determine what testing has already shown many times, even though some still believe passive works just as well as fan aspirated.
I realized the benefit and started using fan aspiration when I had the original white washed cotton region shelter many years ago. In the desert Southwest the difference was like day and night during low wind conditions.
   
Today and over the last decade I've use the well designed 24 hour FARS Davis triple walled shield but modified with a much higher velocity AC powered fan instead of the standard solar. I would put it up against the best professional FARS units out there, and bet it would do just as well.

Appreciate your passion for doing this test.  =D> Good idea to use some of the more popular selling stations for the test.
I remember way back when Davis put their new (then) 24hr FARS up against RM Young and it fared VERY well. IIRC only .5F difference at full solar noon.

Yes, that was with the very low volume solar fan. Fan I'm running is as high or higher velocity & volume of air than the RM Young is why I'm confident it would hold its own the way its setup.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline CW2274

  • Forecaster
  • *****
  • Posts: 3078
    • Conditions @ CW2274
Re: A Comparison of Solar Radiation Shields
« Reply #11 on: April 18, 2015, 07:14:04 PM »
First of all thanks for doing this test. Its a lot work to determine what testing has already shown many times, even though some still believe passive works just as well as fan aspirated.
I realized the benefit and started using fan aspiration when I had the original white washed cotton region shelter many years ago. In the desert Southwest the difference was like day and night during low wind conditions.
   
Today and over the last decade I've use the well designed 24 hour FARS Davis triple walled shield but modified with a much higher velocity AC powered fan instead of the standard solar. I would put it up against the best professional FARS units out there, and bet it would do just as well.

Appreciate your passion for doing this test.  =D> Good idea to use some of the more popular selling stations for the test.
I remember way back when Davis put their new (then) 24hr FARS up against RM Young and it fared VERY well. IIRC only .5F difference at full solar noon.

Yes, that was with the very low volume solar fan. Fan I'm running is as high or higher velocity & volume of air than the RM Young is why I'm confident it would hold its own the way its setup.
I replaced my OEM motor with this;http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&pa=2158442&productId=2158442&keyCode=WSF&CID=GOOG&gclid=CP3F1subxbMCFeuPPAod4GgA3Q Any idea how it compares to the original?
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline ValentineWeather

  • Forecaster
  • *****
  • Posts: 4098
Re: A Comparison of Solar Radiation Shields
« Reply #12 on: April 18, 2015, 07:28:01 PM »
Sorry I don't.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline CW2274

  • Forecaster
  • *****
  • Posts: 3078
    • Conditions @ CW2274
Re: A Comparison of Solar Radiation Shields
« Reply #13 on: April 18, 2015, 07:38:25 PM »
Sorry I don't.
Thank you anyway. Perhaps someone else knows.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline aweatherguy

  • Senior Contributor
  • ****
  • Posts: 284
    • Weather Station Data Logger
Re: A Comparison of Solar Radiation Shields
« Reply #14 on: April 18, 2015, 09:48:12 PM »
DoctorKnow: Thanks for asking about humidity...that's another dimension to this that I left out at first because the study is mostly about temperature.

So, if the SHT-21 is working correctly, what would we expect to see? I think it is safe to assume that the dew point experienced by the SHT-21 is very close to the same as seen by the FARS. When you heat up a parcel of air w/o adding or removing moisture, the dew point does not change. So if the SHT-21 is seeing warmer air with the same dew point, then it should see a lower RH value because warmer air can hold more water vapor. The change in RH should be in accordance with well known physics and formulas for converting between temperature and dew point.

The custom sensors used in this experiment also have SHT-15 humidity sensors so I put together a plot comparing computed dew points from FARS data to the VN1TX data. The data is quite noisy, especially during the day but on average has close to the expected behavior.

This confirms one of two things: either the SHT15 and SHT21 sensors are decent humidity sensors, or at least they track well together. Anyway, I was pleasantly surprised to see that the dew point data is relatively insensitive to temperature variations.

Offline CW2274

  • Forecaster
  • *****
  • Posts: 3078
    • Conditions @ CW2274
Re: A Comparison of Solar Radiation Shields
« Reply #15 on: April 18, 2015, 10:11:50 PM »
DoctorKnow: Thanks for asking about humidity...that's another dimension to this that I left out at first because the study is mostly about temperature.

So, if the SHT-21 is working correctly, what would we expect to see? I think it is safe to assume that the dew point experienced by the SHT-21 is very close to the same as seen by the FARS. When you heat up a parcel of air w/o adding or removing moisture, the dew point does not change. So if the SHT-21 is seeing warmer air with the same dew point, then it should see a lower RH value because warmer air can hold more water vapor. The change in RH should be in accordance with well known physics and formulas for converting between temperature and dew point.

The custom sensors used in this experiment also have SHT-15 humidity sensors so I put together a plot comparing computed dew points from FARS data to the VN1TX data. The data is quite noisy, especially during the day but on average has close to the expected behavior.

This confirms one of two things: either the SHT15 and SHT21 sensors are decent humidity sensors, or at least they track well together. Anyway, I was pleasantly surprised to see that the
Quote
dew point data is relatively insensitive to temperature variations.
Quote
That's exactly as it should be.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline JCA433

  • Member
  • *
  • Posts: 29
Re: A Comparison of Solar Radiation Shields
« Reply #16 on: May 19, 2015, 02:23:35 AM »
I see two problems with this test.

1.   Some of the shields are clustered together.   The shields should be at least 10 feet apart.

2.  The sun altitude is too low at 38 N in  April.  This test should be done in the tropics during summer.
     The sun altitude at solar noon should be at least 80 degrees.

Offline JCA433

  • Member
  • *
  • Posts: 29
Re: A Comparison of Solar Radiation Shields
« Reply #17 on: May 19, 2015, 08:42:06 AM »
I did a test of the DAVIS shield and found that it read a bit high even with moderate wind speed.   At first I had the shields  mounted to the same tripod and wanted to see if there was a difference mounting them about 10 feet apart at the same elevation and same sun exposure.   The Delta was 0.4 F.  I am south of Miami ,Florida.

Offline aweatherguy

  • Senior Contributor
  • ****
  • Posts: 284
    • Weather Station Data Logger
Re: A Comparison of Solar Radiation Shields
« Reply #18 on: May 19, 2015, 08:38:06 PM »
I based my arrangement of shields closer than 10 feet on this paper from Davis:

"Comparisons of Solar Heating in Five Radiation Shields", Application Note 24, November 17, 1999

http://davisnet.com/product_documents/weather/app_notes/AN_24-temp-radiation-shield-comparison.pdf

It would be possible to re-run these test with shields farther apart and I would consider it if you could point me at some published literature that discusses or explains the need for more spacing. The folks at Davis obviously thought that clustering of the shields was okay.

Regarding latitude and sun angle...you've got me there. Sorry but I'm not moving to the tropics just to conduct another experiment. I do intend to keep this running over the summer and will post an update if things change very much (sun elevation at solar noon should be around 75 degrees then). Obviously this test is valid for folks living at 38N latitude in April and I would expect that Florida residents will get different results. That's why I was careful to state the latitude and month of the test.

Can you share data from your tests? You mentioned testing the Davis shield but you did not mention what you were testing it against. It would be nice to see some more test data with higher sun angles.

Offline JCA433

  • Member
  • *
  • Posts: 29
Re: A Comparison of Solar Radiation Shields
« Reply #19 on: May 20, 2015, 02:26:01 AM »
   The weather conditions here are often  windy so I have not been able to repeat your weather with such low wind speeds.   I did not expect to get a larger error with the radiation shields clustered together and the error is very small only about 0.3 to 0.4 F.   It is possible that somehow radiation reflected from one weather station got into the other radiation shield or maybe something elsewhere caused it.  I was surprised by this error.  I rather have them apart though so I can rule out radiation reflected from one shield entering the other.


My weather stations are about 70 inches above the ground and mounted over grass.  When we finally get some days when the wind is near calm for long periods then the data can be more meaningful.  Right now we have wind nearly every day.  Over the past month I have found the Davis shield to be about 0.7F higher than a modified shield that has no fan with winds about 10 to 15 MPH though much of the day.  I plan to get an aspirated shield to compare both of these weather stations with calm winds.

It would be nice to see the results from exposure to  sun altitude  to near 90 degress so the maximum error can be found.  Even down here the sun altitude does not quite get to 90 degrees only about 88 degrees in June.

There is a great paper that discuss solar radiation errors in radiation shields.  I will try to find the link and post it in this tread.
« Last Edit: May 20, 2015, 02:40:24 AM by JCA433 »


Offline JCA433

  • Member
  • *
  • Posts: 29
Re: A Comparison of Solar Radiation Shields
« Reply #21 on: May 20, 2015, 09:48:56 AM »
Did you use the Ambient weather SRS100LX?


I am using the Davis 7714 shield and a modified Davis 7714 shield.  The modified shield is painted flat black inside and a quarter inch plywood painted white on top is bolted across the top of the shield extending about one inch from the end of louvered sides to shade it from the highest sun altitude.  The shields are mounted 10 feet apart  about 70 inches above the ground with a grass surface.   Both sensors in the shields are ambient weather sensors for the  WS-11 weather station in same position in the radiation shields and have been calibrated.  This weather data was compared to the Florida Automated Weather Network station or FAWN very nearby. 
Sensor 3 was installed in modified shield and Sensor 2 in the unmodified shield.  This data was collected on May 8 2015.

May 8 data below:

Time         S3          S2                FAWN       Sun Altitude
9:15 AM    78.4 F     79.2 F           77.6 F            33.2
9:30 AM    79.3 F     80.2 F           78.9 F            36.5
9:45 AM    80.1 F     81.0 F           79.9 F            39.9
10:00 AM  80.2 F     81.3 F            80.9 F           43.3
10:15 AM  80.8 F     81.9 F            81.4 F           46.7
10:30 AM  82.2 F     83.1 F            81.9 F           50.1
10:45 AM  83.1 F     83.8 F            82.3 F           53.4
11:00 AM  83.5 F     84.2 F            83.2 F           56.8
11:15 AM  83.8 F     84.7 F            84.1 F           60.1
11:30 AM  84.2 F     84.9 F            84.4 F           63.4
11:45 AM  84.7 F     85.8 F            82.3 F           66.7
12:00 PM  85.1 F     85.8 F            85.8 F           69.9
12:15 PM  85.5 F     86.4 F            85.4 F           73.1
12:30 PM  86.0 F     86.9 F            86.1 F           76.0
12:45 PM  87.3 F     88.3 F            86.7 F           78.6
1:00 PM   88.2 F     89.2 F             87.2 F           80.6
1:15 PM   87.4 F     88.2 F             87.8 F           81.6
1:30 PM   87.6 F     88.3 F             88.1 F           81.2
1:45 PM   86.0 F     86.7 F             87.6 F           79.6
2:00 PM   86.0 F     86.5 F             85.2 F           77.2
2:15 PM   86.2 F     86.9 F             86.0 F           77.4
2:30 PM   85.3 F     86.0 F             86.3 F           71.4   


The weather condition on May 8 was party cloudy with winds generally in the 5 to 15 MPH range with minimum wind of only 0.4 MPH at 9:15 AM
« Last Edit: May 20, 2015, 10:23:06 AM by JCA433 »

Offline kcidwx

  • Senior Contributor
  • ****
  • Posts: 287
Re: A Comparison of Solar Radiation Shields
« Reply #22 on: May 20, 2015, 11:05:29 AM »
The important thing in doing tests like this is knowing your sensors are accurate and that you account for any sensor corrections needed in your data. That means you must use NIST traceable certified sensors and not ones that were certified more than a year ago. If you don't use certified sensors, the data is as good as useless. The first thing I ask someone when they say "calibrated" is, show me the certificate. I had one guy argue with me one time about the accuracy of his thermometer. He said he went to Radio Shack and bought a $10 LCD thermometer and compared it to his weather station and it matched. I just started laughing.

I did a similar test that aweatherguy did using the Davis 7714 (passive) and the RM Young 43502 (FARS) from June through August and pretty much got identical results. I did the test out of my own curiosity as to whether I really needed a FARS or not for my temperature sensor. I concluded I don't need one at my location. The average wind speed here in summer is 14 mph and there's low to moderate solar insolation. As long as my average ΔT is under 1.5°F I'm fine with it. The Davis FARS is known to be a poor performer anyway.

« Last Edit: May 20, 2015, 11:48:17 AM by kcidwx »
[Retired] Key West, FL
Supervisor Meteorological Technician
NWS Certified Aviation Weather Observer
B.S. Meteorology

Offline JCA433

  • Member
  • *
  • Posts: 29
Re: A Comparison of Solar Radiation Shields
« Reply #23 on: May 20, 2015, 01:12:28 PM »
What is your opinion of the Young shield?  What size fan does it have?  I have never purchased Young weather instrumentation.    Davis seems to be a very popular brand. 

Offline Jáchym

  • Meteotemplate Developer
  • Forecaster
  • *****
  • Posts: 8531
    • Meteotemplate
Re: A Comparison of Solar Radiation Shields
« Reply #24 on: May 20, 2015, 01:55:55 PM »
Nothing beats the old Stevenson screen  :grin:

 

anything