Topic: Will the SRS100 radiation shield help with radiant heating?

[Likesspace]

Hey guys,
I'm having a problem with my temperature sensor reading about 4 - 5 degrees too high.
I'm sure that this is due to radiant heat off of the garage that the sensor is attached to.
I have the sensor mounted about 6 feet up and about two and a half feet away from the wall itself.
The wall faces to the west so it does get plenty of sunshine during the day.
The temp sensor came with a very small (about 1-1/2" diameter) radiation shield that I'm sure is inadequate.
Because of that, I did purchase the SRS100 shield which came in on UPS this morning.
My question is this:
Do you think the SRS100 will help with my radiant heating problems, if mounted the same, or do you think I will have to move the sensor away from the garage to take care of this problem?
I'm trying to keep from setting a pole in my yard since it will be unsightly and a pain to mow around.
Thanks for any advice you can give me.

Dave

[SlowModem]

My question is this:
Do you think the SRS100 will help with my radiant heating problems, if mounted the same, or do you think I will have to move the sensor away from the garage to take care of this problem?
I'm trying to keep from setting a pole in my yard since it will be unsightly and a pain to mow around.
Thanks for any advice you can give me.

Dave

Hi Dave 

I think the 100 will help with direct sunlight on the sensor, but I believe the radiant heat from the building will still be a factor.

You didn't say what type of station you have, so I don't know the portability of the sensors.  I would suggest trying to move the sensors to a different side of the building (north side would be best I think) to keep it from being out in the yard.  That would minimize the radiant heat, I believe.  Otherwise, a fan aspirated shield might help, too.

That's the extent of my knowledge!   

Good luck!

Greg

[wxtech]

In my opinion, it's the radiant heat that the shield attenuates.  The sensor that you placed inside the shield should not be able to 'see' the heat source.  Your heat source is the garage wall.  A white or light color wall will radiate less.  The sensor inside the shield should not be able to 'see' anything black.  The shield should have plenty of air circulation.  The objective is to measure the air temperature.

[Likesspace]

Thanks for the replies.
I guess there's really no way of knowing for sure without giving it a try and taking a look at the results.
I'd like to leave the station where it's now mounted but I'm sick of these false readings I've been getting.
Although the north end of the garage is out of the question, (lots of trees), the east end of the garage should be a close second as the best placement option.
I'm still up in the air as to what to do, but I might just leave it as it is and see how well it does.
If that doesn't work out, I can always give the station yet another move over the weekend.
Thanks again for taking the time to offer your opinions and expertise.
As a newbie I really do appreciate the advice.

Dave

[d_l]

What is under the sensor?  Heat rising from the ground will also affect it.  That's why it is recommended to place the sensor over grass which is presumeably the normal ground cover in open areas in most parts of the country.

[wxtech]

Hey guys,
I'm having a problem with my temperature sensor reading about 4 - 5 degrees too high.
I'm sure that this is due to radiant heat off of the garage that the sensor is attached to.
I have the sensor mounted about 6 feet up and about two and a half feet away from the wall itself.
The wall faces to the west so it does get plenty of sunshine during the day.
The temp sensor came with a very small (about 1-1/2" diameter) radiation shield that I'm sure is inadequate.
Because of that, I did purchase the SRS100 shield which came in on UPS this morning.
My question is this:
Do you think the SRS100 will help with my radiant heating problems, if mounted the same, or do you think I will have to move the sensor away from the garage to take care of this problem?
I'm trying to keep from setting a pole in my yard since it will be unsightly and a pain to mow around.
Thanks for any advice you can give me.  A pole in your lawn will fix it.

Dave

Your sensor is giving you an accurate measurement of the micro climate that it is installed in.  If it's 4 - 5 degrees too high; compared to what?  If you're expecting it to be the same temperature as at your nearest airport, then you'll have to install your sensor at the airport.  Just assume that you are measuring the temperature in your garage area.

[Likesspace]

Guys,
First of all, the temp/humidity sensor has been mounted on the northwest corner, southwest corner and west side of the garage. In each of these situations the sensor was over grass except when it was on the northwest corner which was then over concrete.
I've been comparing my temp readings to a LaCrosse indoor/outdoor thermometer, which I have well shielded from the sun and which sets about 50 feet away from this new sensor.
I've also been watching the readings of other stations in my area and I am always within a degree or two of their readings until the sun starts heating the side of my garage.
I have no doubt that I am getting very inflated readings since I am ALWAYS much higher than the other stations and my own outdoor sensor, (at least when the sun gets into the game). This has been driving me nuts since I have this little problem about everything being right.
As for tomorrow and the weekend it's supposed to be mostly cloudy to partly sunny so I won't have any firm data until probably early next week.
If my new setup doesn't work (west side, over grass, inside the SR100), then I'll move it to the east side of the garage and as a last resort on a pole in the middle of the yard.
If anyone else has any ideas or suggestions, I'd love to hear them.
Thanks again,
Dave

[port1]

Everyone's replies are correct.  The shield provides protection from "solar gain"...something akin to shade.
It should be installed so you have air movement, as previously described.
P.S.  There is no "perfect installation".

If you installed the sensor in a radiation shield above a bonfire, it would accurately report that temperature.
Siting the sensor at your location simply measures the temperature at your location.
Best to use your own common sense and be happy with your installation.
That's all that matters. Oh yes, and to have fun, too!
 

Henry

[wxtech]

Dave,
Welcome to the woes of siting your wx station.  Have fun with it.  Plant the pole with some flowers around it then brag about your wx station to visitors.  It's a good conversation topic.
After you get the temperature figured out, next you'll be worrying about rain calibration & how high your anemometer should be, and the list never ends.  It's fun and beneficial to the community.
Al
P.S. Sorry that I was critical in the earlier post.

[d_l]

I think the radiation shield will protect the sensor from both solar heating and re-radiated heat from the nearby wall to some degree.  It will need air movement to be totally effective.  The wind speeds it would see would be reduced by being mounted that close to a wall so that is a factor.

Not everyone has grass growing that close to their walls.  Around here people often put crushed rock up against their foundations and the grass grows farther out from the house. In that situation the heat from the sun baked rocks would rise up to the sensor.

You didn't say what model of sensor is to be in the SR100.  Around here there are some LaCrosse sensors that could benefit from better shielding.  I can always pickout that brand of stations on the local Wunderground maps as they are 5-10 degrees hotter than the rest of the stations on sunny mornings.  On cloudy mornings or in the evenings, their temperatures aren't that unusual.

[sam2004gp]

Dave,
Welcome to the woes of siting your wx station.  Have fun with it.  Plant the pole with some flowers around it then brag about your wx station to visitors.  It's a good conversation topic.
After you get the temperature figured out, next you'll be worrying about rain calibration & how high your anemometer should be, and the list never ends.  It's fun and beneficial to the community.
Al

^^^---Ah yes, the never ending cycle.

You could also think about modifying the shield to include a Fan, to keep the air moving across the sensor.  This will prevent "warm air pockets" from forming inside your sheild.

I also have the higher temp issue.  But my only North facing location is over my concrete driveway.  So I mounted mine on the vinyl fence (White).  It shields the summer sun from the shield itself and still allows a decent airflow around the setup.

[SlowModem]

This is a good read for sensor placement/operation:

http://home.comcast.net/~dshelms/CWOP_Guide.pdf

[Likesspace]

Okay,
I've now moved my weather station for the 7,349th time and this time I'm feeling somewhat confident that the new location will work.
The temp sensor is now mounted on the east side of my garage, 5 feet up and over a grassy surface.
There will be no sunlight hitting the sensor except possibly for an hour in the very early morning.
The sensor is in a shaded area from the east, south and west so radiant heating is the only issue I have to worry about.
I'm still somewhat concerned that the interior temperature of the garage will be reflected onto the temp. sensor but if that happens then I'll have to accept the fact that a pole mount is the only logical solution. Of course I could try to insulate the interior of the garage (directly opposite of the temp sensor mounting), but I'm not sure it would be worth the effort if this does turn out to be a problem.
Saturday's forecast is for partly sunny skies so I should at least get an idea of how the new mounting position will work. Sunday's forcast is for clear skies so that will be an even better indicator.
Although today was mostly overcast, the times that the sun did come out gave me the same inflated readings that I've been used to. Not quite as drastic but still 2 - 4 degrees too high.
Anyway, I'm happy with the SR100 in that it did lower my high readings somewhat and no doubt provides better air flow to the sensor. i would recommend this shield to anyone that has need of one.
I really do appreciate the advice I've been given concerning this problem. I'll give another update by early next week once I have reliable data to report.
If all else fails I might try turning the SR100 into a FARS before resorting to the pole method. I've already had to do some "adjustments" with a spiral saw just to get my temp humidity sensor to fit inside.
BTW, for whoever asked.....
The temp/humidity sensor that I'm using is a Zephyr brand (also known as a Watson, Fine Offset, WH1081, etc.).
It's a cheap setup but all in all I'm pretty happy with the results it's given, especially as compared to my dad's Davis VP2.
My readings run pretty much neck in neck with my dad's readings (except the temp) and as he said.....he spent considerably more on his station.
I had initally planned on using this station for a year or so and then upgrading to a Davis.
After having used this one for a month, I've decided that I will probably buy another one of these $120.00 specials simply so that I will have spare parts on hand when something does fail on it.
Okay, now I'm rambling. I have this problem with literarry diareahh, so please excuse me when it happens.
Thanks again for all of your help and I'll be sure to provide an update.

Dave

[d_l]

If you are seriously considering turning your SRS100 into a FARS unit, maybe you could put an electric fan nearby blowing on it during a sunny day as a test to give you an idea of how much adding a fan to it would cool the shield. Just a thought.

[Likesspace]

Okay, so I turned my SR100 into a FARS and I still got some significant spikes when the sun was directly on it. For some reason this particular radiation shield just does not work that well when the station is mounted close to a building (unlike the standard Davis shield).
Well what I did was to make an aspirated shield out of PVC pipe and fittings an old computer fan which draws the air across the temp sensor and today I was FINALLY happy with the results.
Today we had pretty much clear skies and I was consistantly the lowest temperature reading of all of the local personal weather stations.
Also, I was always within a degree or two of the closest airport reading which is about 10 miles away from me.
My temperature curve was nice and smooth, without any spikes or lows which I have to say made me pretty darn happy.
Right now I have the computer fan powered with a 120 volt to 12 volt DC converter that I had laying around. Eventually I'd like to switch this to a 12 volt solar panel with rechargeable batteries.
If anyone has a link to the panel and battery setup, that I will need, I would really appreciate the help. I will need something that is plug and play since I know nothing about any type of electrical wiring.
The great thing about this setup is that when the fan wears out I already have 3 spares that I have robbed from old computers. Even if I eventually have to start buying the fans the price is pretty much minimal for a replacement power supply fan.
I am a little concerned about how much power I am using to run the fan. I would think that since it's only a 12 volt fan it shouldn't be much but if anyone has any insight I'd like to hear it.
Anway, I just thought I'd let everyone know of the solution that I came up with.
The shield definatly looks like a "homemade" solution but as long as it works, I'm happy.
Thanks for all of the advice I've gotten concerning this problem.

Dave

[sam2004gp]

Let's see a pic of your new shield. 

[Likesspace]

Ask and you shall receive....
As you can see, I haven't yet taken down the SR100 and this is definately temporary mounting on the new shield (zip ties).
This weekend I plan on welding up a more cosmetically appealing mounting system and then will apply a double coat of white paint to everything.
Like I said before, it's not a pretty solution, but it really does work perfectly. The air is drawn into the 3" PVC pipe (where the sensor is mounted) and is discharged out the other side.

Materials:
1 foot of 3" cellular core PVC pipe
1 - 3" x 1-1/2" DWV coupling
2 - 1-1/2" DWV 90 degree street elbows
1 - 3" x 1-1/2" DWV flush bushing
1 - 3" DWV coupling
1 - 4" x 3" thin wall (SDR35) pvc reduced coupling

I had to trim the edges of the PC power supply fan a bit (on a grinder) to make it fit inside the 4 x 3 coupling.
I kept checking the fit while grinding and finally came up with a fit where the fan "snaps" inside with no screws needed.
I also used a piece of 1/8" plywood as a spacer between the fan and the inside of the coupling. I cut a 2" hole in the center of this spacer and put it into the coupling before the fan.
This helps to seal the junction between the fan and the 1-1/2" opening above the coupling. The result is that I have a very good amount of airflow through the shield.
Anyway, here's the working product. As I said, it's not exactly finished but it is functional.
Thanks again to everyone for their help on this problem. I really do appreciate it.

Dave

[Likesspace]

Oh, one more thing.....
EVERY nearby personal weather station is a $500.00 Davis VantagePro 2.
For the past two days, I've been logging temperature curves that are just as smooth (and in a couple of cases even more smooth) as every other station.
Also, my humidity readings are within a tenth of a point of my nearby airport readings and the pressure, wind speed/direction and dew point readings are always very close to all of the others. I spent $120.00 for my station so I am really happy with the results.
Of course I've fought this problem for the past month to get these results while I'm sure the Davis owners simply mounted their stations and forgot about it.
Also, I'm paying (no matter how small of an amount it might be) to run the electric fan 24 hours a day.
Also, Also I'm sure that there is no way that my little cheap station is going to have the longevity of the Davis.
I simply make this statement to show that even a cheap station CAN perform as good as the more expensive ones if enough attention is paid to getting the right results.
I hope this post helps someone out that might be battling the same type of problem.

Dave