This is a couple of useful screens for installing weather sensors, especially temperature/humidity/barometer, in outdoor or totally remote systems. Screens like this are known as a Stevenson Screen, or a "Meteo Pagoda", in our own parlance at Valarm. The screen is obviously designed to allow the ambient atmosphere to contact the sensors, without exposing the sensors directly to rain or snow.
Two versions are presented here: a simple "passive" version and another with provision to add a 40mm fan or 40mm blower to force ambient air to circulate past the sensor. Adding a fan to such a system creates a significant extra power drain, a concern since many such systems are solar or battery powered. But forced airflow definitely creates a more accurate recording of ambient temperatures, especially in sunny environments. Note though you should still always attempt to keep such sensors/systems well shaded, and/or at least work to install the sensor on the North side of the installation, if you are in the northern hemisphere, and vice-versa for the the southern hemisphere. Unless of course you are trying to record the temperature "in the sun" - though this is not the normal meteorological practice, nor the public expectation. (That's what the UV or Heat Index is for). You can use the "fan-forced" version without a fan, of course. It just takes quite a bit longer to print and uses more material.
The fan required is a 40mm fan (attaches to the front of the screen) or a 40mm blower (attaches against the back wall). We use #6 stainless hardware (machine screws/washers/nuts) for the front fan, or the self-tapping screws that ship with most fans/blowers to attach a blower to the rear wall.
O-ring: In case you will be placing your sensor INSIDE a larger enclosure, to which this screen is mounted, a provision for a rubber o-ring makes it easy to seal this against the main box to reduce the amount of water that might seep into the main enclosure. A printable cutting template makes it easy to cut the screw holes for mounting the screen, and for cutting the slot to expose the sensor to the elements. The O-ring is a Sur-Seal ORBN019x250, buna nitrile rubber, 70 durometer, 13/16" ID, 15/16" OD. Also available in smaller packages.
For remote monitoring installations we build at Valarm, we have printed this in PLA for a few years, and they really do last a very long time out in the elements. Yes, PLA does lose color under UV exposure, but we're typically starting with white anyway, and always trying to keep the part in the shade. Yes, PLA does eventually become more brittle under UV, cold/heat and general exposure. But this part is not expected to be strong or particularly load bearing. If you want extended life from this part, there are certainly better materials (ABS is NOT one of them). Or you can simply give it a nice coating of a UV-filtering poly/urethane clearcoat from a spraycan. Note that these are never completely "clear" and your part will be visibly yellowed by the coating.
This design is part of a "commercial" system that is available for purchase as a complete kit on our website, where you can also purchase the specific "Meteo" sensor around which this design was built. But we encourage you to print it yourself, use other sensors, or whatever else you might come up with, and we would of course love to hear about the results!
4 or 5 bottom layers (since printed upside down) will create a nice sturdy top. 3 outline layers, and 3 top layers with 30% infill and hopefully a cooling fan to handle the bridging, will complete the picture.
Easily obtained at your local hardware or home improvement store, #6 stainless steel screws (1-1/8" to 1-1/2" in length) with nylon-lock nuts and washers can be used to secure the optional fan. There's certainly metric equivalent hardware that will work fine too.
The full version (fan-forced) takes a good 6-7 hours to print on our MakerGear M2 in PLA-Plus, and the compact/fanless version prints in under 4 hours.