Topic: Barani pro passive shield

[Jorginho]

Well I can't argue with testresults, but.....But: the Vaisala screen is not too different and does not record such errors. It too has a roof of two closed plates. Much like the Davis. I wonder if the radiation errors could be in part at least explained by the Davis being white inside versus black. I must say that the vaisala has a much more open construction so I guess it is more connected with the surrounding air and radiation errors that should come with it are taken care of by the black, absorbing inside. I remember the  white Barani (inside) performed less well than  the current black version.

it is very easy to paint the Davis black inside in fact, like I said, I have on such here lying around for 5 years when I had the intention to test it but never did. Who knows, next summer....

[Jasper3012]

Can you show me a picture of that Vaisala screen? I'm not talking about the structure of the VP2 shield itself, I'm talking about the black rain gauge right above it, that is what is blocking long wave radiation.

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[Jasper3012]

That rain gauge is effectively functioning as a blanket, reflecting outward going heat back onto the shield, so it loses its heat slower at night and lags behind the true air temp.

[Jorginho]

Can you show me a picture of that Vaisala screen? I'm not talking about the structure of the VP2 shield itself, I'm talking about the black rain gauge right above it, that is what is blocking long wave radiation.

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Thx, I know how it looks. But something on top is not necessarily blocking anything to that degree. But in this case, it obviously (research is available) is.

This is the Vaisala screen. As you can see it has no double louvres. I am not saying it is the best option, but it is what is used by the KNMI hence to me given my stationsiting the preferable solution.

The KNMI modified Vaisala screen is on page 8. Interesting research, sadly no Barani to compare.

https://bibliotheek.knmi.nl/stageverslagen/traineereport_Proksch.pdf

[Jasper3012]

Can you post a screenshot of the screen instead? The link isn’t safe according to my pc.

[raffaello.dimartino]

The VP2 cools down too slow at night due to the large rain gauge right above the shield blocking outgoing long wave radiation (heat). By day, because the rain gauge is directly above the radiation shield, it shades the shield substantially so it keeps the error lower. Removing the rain gauge would expose the shield to direct sunlight, which would create a much higher error. So pretty much, if you removed the rain gauge you'd get a cooler min temp but a much higher max temp, if you get what I mean.

The study, where they compare the Stevenson screen vs VP2, came to the same conclusion. Over a yearly period, the VP2 recorded a slightly higher avg min temp than the Stevenson screen and a slightly cooler avg max temp, this because of the factors I just explained. The mean temperature overall was nearly identical to the Stevenson screen.

Ook mijn vriendelijke groeten, leuk om eens met een Nederlands sprekende weerfreak te kunnen praten! 

I want to add even more than what you wrote.
The distance between the upper cone and the solar shield is very small and in no wind conditions, the heat remains between the shield and the aerocone without being able to escape.
The space is often occupied by the wires of the various sensors arriving at the ISS

The color of the aerocone does not affect. I also colored it white to try but the problem remains.

I also tried to see the screen with more than forty degrees and a thermal camera. The problem remains the lack of ventilation.

The solar panel helps to keep the screen in the shade but being only on one side, it works only on certain days of the year and for certain latitudes.

The only way to make a Davis solar shield work well, is to remove it from the Aerocone and add plates.

I have this screen among mine that I compare every day.

http://www.kwos.org/comparison/

[Jorginho]

Can you post a screenshot of the screen instead? The link isn’t safe according to my pc.

No, because it is in a pdf file. It is the KNMI...it is site entered by 10000s every day. It is very safe. But it is up to you. Just look up Vaisala DTR-513 (I think) and you'll probably find a pic of a crosssection somewhere (well to be honest I did once so it seems to be very dependent on the exact wording of your search).

[Jasper3012]

The VP2 cools down too slow at night due to the large rain gauge right above the shield blocking outgoing long wave radiation (heat). By day, because the rain gauge is directly above the radiation shield, it shades the shield substantially so it keeps the error lower. Removing the rain gauge would expose the shield to direct sunlight, which would create a much higher error. So pretty much, if you removed the rain gauge you'd get a cooler min temp but a much higher max temp, if you get what I mean.

The study, where they compare the Stevenson screen vs VP2, came to the same conclusion. Over a yearly period, the VP2 recorded a slightly higher avg min temp than the Stevenson screen and a slightly cooler avg max temp, this because of the factors I just explained. The mean temperature overall was nearly identical to the Stevenson screen.

Ook mijn vriendelijke groeten, leuk om eens met een Nederlands sprekende weerfreak te kunnen praten! 

I want to add even more than what you wrote.
The distance between the upper cone and the solar shield is very small and in no wind conditions, the heat remains between the shield and the aerocone without being able to escape.
The space is often occupied by the wires of the various sensors arriving at the ISS

The color of the aerocone does not affect. I also colored it white to try but the problem remains.

I also tried to see the screen with more than forty degrees and a thermal camera. The problem remains the lack of ventilation.

The solar panel helps to keep the screen in the shade but being only on one side, it works only on certain days of the year and for certain latitudes.

The only way to make a Davis solar shield work well, is to remove it from the Aerocone and add plates.

I have this screen among mine that I compare every day.

http://www.kwos.org/comparison/

Interesting, thanks for the comment. Think we can all agree there's a flaw in the VP2 design. I've solved it by geting a MeteoShield Pro, but there's probably cheaper options aswell.

[Jarle]

Been running the Barani Pro shield for a couple of weeks now, alongside the Campbell Scientific Met21 shield, Davis Vantage Vue and Davis VP2+ w/24 hr fan. All equipped with calibrated Davis sensors.

Have to say it’s been a disappointment so far. Running 0,5-0,8c higher than the fan aspirated shield on calm, sunny days. So far it is no better than the MET21 (which is also black inside). In fact it’s giving me  quite the same readings as the Vantage Vue. As of now the Barani shield is unfortunately nowhere close to being an alternative to the fan aspirated shield for me.

I live on 59 degrees north and the sun angle is starting to get low these days. I guess that can influence on the accuracy of the shields. Anyway, I will compare all four of them during all of next year so the jury is still out 

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[raffaello.dimartino]

Do you have any graphs where you compare shields?
I see the photo, how are the solar screens oriented? The Vue looks opposite to the others, I see shadow on it while the others are hit by the sun.

I compare many solar shields every day. Two of them are Barani, so I'm curious to understand why it goes like this with you.
http://www.kwos.org/comparison

Thank you
Raf

[johnd]

I see the photo, how are the solar screens oriented? The Vue looks opposite to the others, I see shadow on it while the others are hit by the sun.

Specifically on the Vue: If you think about the design (ie with the solar panel facing south) then its small shield will be at least partially in the shade of its ISS body relative to the midday sun. Of course this is less true 2-3 hours either side of midday, but it still helps to give the inexpensive Vue an adequate temperature performance (though I wouldn't expect it to be fully on a par with the VP2, let alone other substantially more expensive shields such as the Barani one.

But, just to reiterate, Jarle's results do mirror what I've seen reported in another recent trial for the Barani Pro, ie approaching the Campbell Met21 in performance.

[raffaello.dimartino]

But, just to reiterate, Jarle's results do mirror what I've seen reported in another recent trial for the Barani Pro, ie approaching the Campbell Met21 in performance.

So, without thinking about the Vue, I will be able to agree with you about the MET21 when, next summer (now it is no longer time to test solar shields) I will finish testing the MetSpec shields that are nothing but the campbell
You can see two of them on my comparison page, called RAD02 and RAD14.

[raffaello.dimartino]

As of now the Barani shield is unfortunately nowhere close to being an alternative to the fan aspirated shield for me.

I forgot to mention that no passive can be a substitute for a forced ventilation one. Especially if the area is often windless and strong sunshine.

However, the forced ventilation shield must have the fan controlled by software. It cannot be left on all the time.

Raf

[Jarle]

Do you have any graphs where you compare shields?
I see the photo, how are the solar screens oriented? The Vue looks opposite to the others, I see shadow on it while the others are hit by the sun.

I compare many solar shields every day. Two of them are Barani, so I'm curious to understand why it goes like this with you.
http://www.kwos.org/comparison

Thank you
Raf

Raf,
The MET21, Barani and VP2+ are all facing south. I have lined them up very carefully so they get equally exposed for sun.

Not the best of graphs, but as you can see of the comparison charts from the VP2+ (orange color) and the Barani shield on this clear and mostly calm afternoon, the difference appears after 4 pm. At the same time the sun angle is getting very low at this time of year. I believe the low sun angle to some extent gives the same effect on radiation shields as radiation from snow.

Due to the low sun angle during winter months, the Norwegian Met Office have designed their very own radiation shield that is being used with all official weather stations in Norway. For instance I also own a MA11 shield used by KNMI in The Netherlands, and that is completely useless during winter where I live as the low sun shines directly on the sensor inside the shield (the angle on plates is too poor).

The Vue is btw not a part of the original setup. It was originally planned for another location. As you have noticed the temperature sensor is partly in shadow during the day so it will not get a fair comparison with the other three.

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[raffaello.dimartino]

Raf,
The MET21, Barani and VP2+ are all facing south. I have lined them up very carefully so they get equally exposed for sun.

Not the best of graphs, but as you can see of the comparison charts from the VP2+ (orange color) and the Barani shield on this clear and mostly calm afternoon, the difference appears after 4 pm. At the same time the sun angle is getting very low at this time of year. I believe the low sun angle to some extent gives the same effect on radiation shields as radiation from snow.

Really perfect Jarle,
the behavior of the two shields is perfectly in line with expectations.
My tests also report similar results compared to an artificially ventilated solar shield.
And my Apogee does not have the fan always on at maximum speed, otherwise you would notice even more difference.

http://www.kwos.it/joomla/it/articoli/144-meteoshield-professional-new

But let's remember that we are comparing two different types of shields.

Ventilated screens also have their strengths and weaknesses.

[mauro63]

Raf,
The MET21, Barani and VP2+ are all facing south. I have lined them up very carefully so they get equally exposed for sun.

Not the best of graphs, but as you can see of the comparison charts from the VP2+ (orange color) and the Barani shield on this clear and mostly calm afternoon, the difference appears after 4 pm. At the same time the sun angle is getting very low at this time of year. I believe the low sun angle to some extent gives the same effect on radiation shields as radiation from snow.

Really perfect Jarle,
the behavior of the two shields is perfectly in line with expectations.
My tests also report similar results compared to an artificially ventilated solar shield.
And my Apogee does not have the fan always on at maximum speed, otherwise you would notice even more difference.

http://www.kwos.it/joomla/it/articoli/144-meteoshield-professional-new

But let's remember that we are comparing two different types of shields.

Ventilated screens also have their strengths and weaknesses.

I agree, and I would like to add that could be useful to have a comparison of Met21 vs Meteoshield Pro, not necessary with graphs, could be enough csv files, complete with wind and solar radiation data

Mauro

[Jarle]

Really perfect Jarle,
the behavior of the two shields is perfectly in line with expectations.
My tests also report similar results compared to an artificially ventilated solar shield.
And my Apogee does not have the fan always on at maximum speed, otherwise you would notice even more difference.

http://www.kwos.it/joomla/it/articoli/144-meteoshield-professional-new

But let's remember that we are comparing two different types of shields.

Ventilated screens also have their strengths and weaknesses.

Raf,
I went through your webpage and you are playing in another league than me when it comes to radiation shield comparison. Very nice and very helpful!

I agree with your conclusion regarding passive vs. fan aspirated shield. Interesting enough, though, my observation is that those late afternoon errors doesn't seem to apply to the same degree on the MI-74 radiation shield designed and used by the Norwegian Met Office (all passive). Picture below.

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The most interesting part for me personally will be whether the Barani shield will better the readings from those of the MET21. Next summer I'll hopefully find out.

[CW2274]

However, the forced ventilation shield must have the fan controlled by software. It cannot be left on all the time.

I must have missed that note. My 24hr aspirated VP2 with a 60CFM case fan has been running full power 24/7/365 for over five years. Also, practically all of our "official" measurements in the US come from airport aspirated ASOS's. Their fans run 24/7/365 as well.

[Daniel785]

What is the price of the MET21 also will it fit the WH32-EP? I've got the MeteoHelix just looking to compare other radiation shields😁

[raffaello.dimartino]

However, the forced ventilation shield must have the fan controlled by software. It cannot be left on all the time.

I must have missed that note. My 24hr aspirated VP2 with a 60CFM case fan has been running full power 24/7/365 for over five years. Also, practically all of our "official" measurements in the US come from airport aspirated ASOS's. Their fans run 24/7/365 as well.

Yes I know this. The reason why I wrote it, is not because they break easily, but because there are studies that confirm some situations of overcooling the sensor inside due to the use of the fan in conditions of rain, freezing rain, etc.

I preferred to use the pwm function that all professional screens have to adjust the fan according to the weather conditions.

Read my review on the Apogee: http://www.kwos.it/joomla/it/articoli/145-schermo-solare-aspirato-apogee-ts-100

Of course, even in this case, mistakes can be made ...

[raffaello.dimartino]

I agree with your conclusion regarding passive vs. fan aspirated shield. Interesting enough, though, my observation is that those late afternoon errors doesn't seem to apply to the same degree on the MI-74 radiation shield designed and used by the Norwegian Met Office (all passive).

Yes, indeed it is interesting. I have never tested an MI-74.
It is also likely to perform well or perform better only in certain situations.
Do you have it in the same location? Or are you comparing it to another similar weather station?
I will find out more about the MI-74.

[CW2274]

However, the forced ventilation shield must have the fan controlled by software. It cannot be left on all the time.

I must have missed that note. My 24hr aspirated VP2 with a 60CFM case fan has been running full power 24/7/365 for over five years. Also, practically all of our "official" measurements in the US come from airport aspirated ASOS's. Their fans run 24/7/365 as well.

there are studies that confirm some situations of overcooling the sensor inside due to the use of the fan in conditions of rain, freezing rain, etc.

How does a fan "over-cool" ambient air temperature? Wind chill factor is irrelevant to a sensor.

[raffaello.dimartino]

How does a fan "over-cool" ambient air temperature? Wind chill factor is irrelevant to a sensor.

it is not a question of wind chill but of contact of suspended particles colder than the normal temperature of the surrounding air, which are carried by the fan itself on the surface of the thermometer.

http://www.kwos.it/joomla/it/articoli/151-overheating-e-overcooling-degli-schermi-solari

[CW2274]

How does a fan "over-cool" ambient air temperature? Wind chill factor is irrelevant to a sensor.

it is not a question of wind chill but of contact of suspended particles colder than the normal temperature of the surrounding air, which are

Nope, don't see it. What happens to a passive shield during moderate or greater winds in high RH's? Let's say a simple tropical storm, if even that. I guess that would be a skewed temp as well? Unless you group all wind flow, not just aspirated but passive into your reasoning, nope, don't see it.
 
The only time I will agree to a fan being somewhat influential, in the negative, is if the sensor is directly measuring only the dew point.

[raffaello.dimartino]

Nope, don't see it. What happens to a passive shield during moderate or greater winds in high RH's? Let's say a simple tropical storm, if even that. I guess that would be a skewed temp as well? Unless you group all wind flow, not just aspirated but passive into your reasoning, nope, don't see it.
 
The only time I will agree to a fan being somewhat influential, in the negative, is if the sensor is directly measuring only the dew point.

Well, of course, everyone can have their own ideas.

It is possible that with a tropical storm could also happen for passive screens, but in that case, it is an atmospheric condition and not a "human mechanical" element that causes.
In fact, even single-chamber passive solar shields (those of old conception) can suffer from a similar phenomenon.
For double chamber screens, it is necessary to have even stronger winds during "cold" rainy phenomena.

I speak on the basis of direct experiences and on experiments carried out ad hoc to study this phenomenon.
Studies carried out by research centers.

However, this is not the thread to discuss these things. I guess.