Author Topic: Barani pro passive shield  (Read 21117 times)

0 Members and 1 Guest are viewing this topic.

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5520
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: Barani pro passive shield
« Reply #500 on: October 12, 2020, 03:22:21 AM »
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.
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.

However, this is not the thread to discuss these things. I guess.
Well, if that's the case, then I much rather have a constant, a fan, that is just that, a constant, consistent flow, not one dictated by the "weather". Kinda the whole idea of a well aspirated shield, you never care about the wind..ever.

As far as "this isn't the thread", sure seems relevant to me.




Offline raffaello.dimartino

  • Raffaello - IZ0QWM
  • Member
  • *
  • Posts: 34
    • a Kind of Weather Observing Station
Re: Barani pro passive shield
« Reply #501 on: October 12, 2020, 03:55:13 AM »
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.

However, this is not the thread to discuss these things. I guess.
Well, if that's the case, then I much rather have a constant, a fan, that is just that, a constant, consistent flow, not one dictated by the "weather". Kinda the whole idea of a well aspirated shield, you never care about the wind..ever.

As far as "this isn't the thread", sure seems relevant to me.

In a thermodynamic system such as that of the very first PBL layer, it is not enough to have the fan always on to say that I have a constant and I am no longer interested in the wind.
I wish it were that simple. The wind carries particles in the air which still affect the temperature.

In my opinion and I repeat, it is just my opinion, we should use the technology to the fullest and since many fans now have PWM that allows you to adjust the speed. I speak for professional sunscreens. The amateur ones do not have this possibility and therefore we will always keep them on, even if we know their characteristics.

We have to "help" the thermometer to better follow the real air temperature.

As a reference we can try to have a thermometer in free air and use the energy balance formula to correct the radiative error. Or, as is done with radiosondes, use two different colored thermometers and calculate the radiative error.

Obviously, never really knowing what the true air temperature is in a complex thermodynamic system, we can never think of having a certain reference even if calculated with physical formulas.
« Last Edit: October 12, 2020, 05:19:40 AM by raffaello.dimartino »

Offline AWL

  • Forecaster
  • *****
  • Posts: 701
    • Ardmore Weather Live
Re: Barani pro passive shield
« Reply #502 on: October 12, 2020, 04:08:30 AM »

Quote
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.

Never read of this phenomenon and not going to argue the possibility of this happening under certain rare circumstances. Can't see where this would happen even a couple times a year, if that, where I live. Will stick with the fan running 24/7 at my place.

Doug

Offline raffaello.dimartino

  • Raffaello - IZ0QWM
  • Member
  • *
  • Posts: 34
    • a Kind of Weather Observing Station
Re: Barani pro passive shield
« Reply #503 on: October 12, 2020, 04:39:48 AM »

Never read of this phenomenon and not going to argue the possibility of this happening under certain rare circumstances. Can't see where this would happen even a couple times a year, if that, where I live. Will stick with the fan running 24/7 at my place.

Doug

I agree with your decision. Only those who are local or know their area well from a meteorological point of view can decide what to do.
Although it is advisable to have both a ventilated and a passive solar screen to be able to notice this type of phenomena.

Raf

Offline Jorginho

  • Member
  • *
  • Posts: 40
I don't like fans too much.
« Reply #504 on: October 12, 2020, 03:15:32 PM »
There are two reasons I don't like fans:
1) What if it stalls? Some  screens like the Davis 24H will get you very high temperatures. I have one of those Davis screens....with a broken fan.
2) Drawing air over the sensor often  means drawing moist over the sensor. More than otherwise would be the case. This means you  are measuring the wetbulb and no  longer the dry (or drier) bulb.

For us it will be difficult to tell what causes what exactly. In order to assess you are not measuring a wetbulb you need to have a drybulb. That will note higher temperature but how can you tell for sure when  the dry bulb  of course cannot be housed in a screen with a fan since you would measure the same. But if you measure in a less ventilated screen, may be you are measuring a higher temp due to radiation error. Let alone getting a calibrated sensor with  certificate (two at least)...

Suffice to say i don't like artificially ventilated screens in MY case since my  weatherstation is 3 miles away in the open and flat countryside northeast of my city. I can't go and check the screen very often  to check if the fan is still working.

So I prefer naturally ventilated screens. As far as I can tell it seems that throrough tests show that the Barani does perform better than other screens. What those thorough tests do lack, as far as I know, is being extensive. I have only  come across comparisons with 2-3 screens. I would love to see how it performs among a group like the famous test done in  Algeria.

Still: the Barani seems to have a lot going for it.

@ Jarle: a few notions.

1) KNMI uses the same screens as the SMHI does. I have one. There are no problems with low angles with or without snow. In a direct comparison with lots of snow and sun for a few weeks in januari (and end of march) 2013 I had the Vaisala and the Davis simultaneously. The Davis went berzerk going to +3,6 C whereas the Vaisala remained at 0 C. Indeed it was a very sunny, bright day aftr -10 C in the morning and -11 C the next morning.

I made this movie (below), which is nice and all but just to give you an indication of the sunny and bright weather and the amount of snow since most pics were in  the fields right next to my weatherstation. The frozen  fog in the movie with the -13,3 C are the wires that protect my station from horses...So the snowcover was always between 10-20 cm from 13-27 january. The max over that period is 0,8 C on one day, another day had 0,4 C and all others remained well below freezing which is important because dry snow is more reflective than wet snow. Also because we had some cms of snow on  every other day the cover was fresh and white for that reason too. A long winded way to tell you that this was a situation with low angles and lots of reflections. But  the Vaisala screen did fine as we would expect from a screen used in  Sweden too.



2) Your notion that the Barani (and the Met21?) are getting youhigher temperatures at low solar angles these days...You live at 59 N so that has to be pretty close to the Northsea. Where I live at 52 degrees. It is wet here with 200+ mm or more in the past mpnth or so. So a bright sunny day with you is probably very similar to one such day here. And such days become moist and foggy once the sun goes down. So it might be that your Davis is indeed measuring the wetbulb and no longer a drybulb. So it will get you lower temperatures but the screen in error could be the artificially  aspirated Davis with the fan drawing moist air over the sensor.

Nothing definitive, just some notions and an interesting discussion I think!

« Last Edit: October 12, 2020, 04:37:14 PM by Jorginho »

Offline raffaello.dimartino

  • Raffaello - IZ0QWM
  • Member
  • *
  • Posts: 34
    • a Kind of Weather Observing Station
Re: Barani pro passive shield
« Reply #505 on: October 12, 2020, 03:45:46 PM »
I saw it with great pleasure.
I agree with everything you said about artificially ventilated solar shields. It would also be necessary to have an alarm for a broken fan, to be able to replace it immediately.
Even the Apogee, with the fan stopped, has a big mistake if the wind is not sustained.
You can find a graph of this test in my review.

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5520
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: I don't like fans too much.
« Reply #506 on: October 12, 2020, 05:17:05 PM »
There are two reasons I don't like fans:
1) What if it stalls? Some  screens like the Davis 24H will get you very high temperatures. I have one of those Davis screens....with a broken fan.


2) Drawing air over the sensor often  means drawing moist over the sensor. More than otherwise would be the case. This means you  are measuring the wetbulb and no  longer the dry (or drier) bulb.
1) Hence why those of us that are able and willing use a computer case fan. Mine is rated at 70,000 hours of use. I also have a red LED on the 120vac to 12vdc transformer that sits on top of the shield that tells me it's getting power. I can also simply go outside and hear it sucking air from 40' away.

2) How does a fan cause the air to be more "wet"?? Do you not think that a a passive shield sensor doesn't get "wet" as well? Just because the fan is drawing ambient air across the sensor doesn't make the air more concentrated with water vapor. Nothing a fan does makes the wet vs dry bulb one bit different...certainly not of consequence in PWS land. Fourteen years of aspirated PWS ownership and relentless comparisons make my case as well.

Offline Jorginho

  • Member
  • *
  • Posts: 40
Re: Barani pro passive shield
« Reply #507 on: October 12, 2020, 05:50:21 PM »
Hi,

Thanks for your thoughts.

1) Drawing more air over the sensor, according to research, causes the sensor to become wetter. Just what research says.
2) There is more to it: the stronger the fan the more it influences the environment outside your screen, again according  to research. So on still calm days and nights (I think especially nights) it is like you have some local wind blowing  around your station. So a cold night will get less cold and a warm day less warm due to mixing of air, like wind.
3) I swear I tried, but I could not hear the Davis fan in my station 3 miles away. I thought it was my ears but I got in the car and pfoooh: it was broken...Nothing wrong with my ears it seems
4) I know you Americans have  3 holidays ever decade, but we Europeans have 30-40 such days per year (payed by our boss). So we go to places where the fan is not 40 feet away....In other words: how are you going to take care of your fan, in the summer (when  people tend to enjoy a nice trip to sunny beaches etc) when it is most needed.

Now this seems far fetched, but at least I am pretty anal about trying to measure as carefree and accurate as possible. A fan that breaks down a fan that breaks down a calm atmosphere around the screen and/or a fan  that creates a wetbulb is not helping me. But to each their own!

I can tell you that on cold bright nigts the Davis VP2 in my  neighborhood measures higher temperatures than  I do. Now he is 12 km away....But in the same very open  flat countryside. And 2 km to his east is a KNMI Vaisala station and it also gets lower temperatures during the night than he does. In fact that very user is looking into the Barani, I think for that reason.

It might be better to have a screen with solar aspiration. No sun? No aspiration. But the construction of the Davis would block wind big time. So for a VP2 24h aspirated screen it is probably still not an option.

There is no ideal which is nice for curious people like me, who want to see if there is some ideal that is yet to be discovered. The Barani seems like an excellent  effort and it is very  interesting if indeed radiation errors are the cause of Jarle's disappointing results.

Edit: here is the research. Sadly this research was done in the most snowpoor period ever in The Netherlands still some interesting results that to some extend coroborate Jarles findings I just read! After 1995 until 2013 the snowcover was still below the average from 1901-1988, but a lot better than 1991-1995. But still some remarkable differences are noted during those days.

https://projects.knmi.nl/klimatologie/onderzoeksgegevens/homogeen_260/meulenbrandsma2007b.pdf




« Last Edit: October 12, 2020, 06:15:43 PM by Jorginho »

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5520
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: Barani pro passive shield
« Reply #508 on: October 12, 2020, 06:05:13 PM »
1) Drawing more air over the sensor, according to research, causes the sensor to become wetter. Just what research says.
2) There is more to it: the stronger the fan the more it influences the environment outside your screen, again according  to research.

3) I swear I tried, but I could not here the Davis fan in my station 3 miles away. I thought it was my ears but I got in the car and pfoooh: it was broken...Nothing wrong with ears it seems
4)  So we go to places where the fan is not 40 feet away....In other words: how are you going to take care of your fan, in the summer (when  people tend to enjoy a nice trip to sunny beaches etc) when it is most needed.

1/2) Well, I can "research" as well...and have for a looong time.

3/4)  :roll: Sarcasm will get you nowhere.

Tell ya what...you stay passive and I won't.  ;)



Offline Jorginho

  • Member
  • *
  • Posts: 40
Re: Barani pro passive shield
« Reply #509 on: October 12, 2020, 06:10:23 PM »
Man don't take it so serious. I was just joking! I really appreciated your input and understand your position very well, but I don't like to use the smileys etcetc. I should not need them when I am (I thought) obviously joking. Sorry that it came across in a wrong way!
It was may way of saying: for me it doesn't work and I understand that for you it does, since i clearly wrote "in MY case". Because I do go on holidays and what happens then? And I already noted I live 3 miles from my station, so what than? Not a problem for you, but a serious problem for me.

I  love to research and read research  and learn, which is why i also visit these fora. Again: sorry I wasn't clear I for not being serious and teasing you a bit.

Offline CW2274

  • Forecaster
  • *****
  • Posts: 5520
    • Conditions @ CW2274 West Tucson-Painted Hills Ranch
Re: Barani pro passive shield
« Reply #510 on: October 12, 2020, 06:20:44 PM »
Again: sorry I wasn't clear I for not being serious and teasing you a bit.
No worries. I DO take my PWS seriously, probably more so than most. I don't think of it as a mere hobby. I was blessed/cursed with being a perfectionist, and my PWS is just one my foibles.

Besides, the wink was just that... I see your way, I see mine.  ;)

Offline Jorginho

  • Member
  • *
  • Posts: 40
Re: Barani pro passive shield
« Reply #511 on: October 12, 2020, 06:27:06 PM »
Fine. I am not a perfectionist per se, only when it comes to astronomy and meteorology and apparantly renovating a house...I also want to test and try myself and see what I can do. Also when it comes to these screens I always think: we should do better? I think and think and think that I could do better! But that is not very realistic but it IS worth a try. With 3D printing making your imaginary designs a reality has become a whole lot easier. etc.

I provided a link in my previous messages. May  be it is interesting for you too? Have a good day.

 

anything