One thing about the Cotton Region Shelter design is that it’s made of wood. Even though it is painted white, it still has a lot of thermal mass on the outside and it tends to unevenly heat the interior, especially on very hot and still days. I built a solar powered fan aspirator to hopefully even out the temperature spikes seen on the daily graphs during the hottest part of the day. Here is how I constructed it.
I purchased a simple 5V DC powered computer fan and a 10W solar panel. The panel has a USB cord and so does the fan unit. Plug both pieces together together and place the panel in direct sunlight and the fan runs continuously. While I do have external 5VDC power at the shelter that powers the sensor circuit boards, I chose to opt for a separate solar powered setup. No batteries are needed and the fan only runs when the sunshine is shining on the outside of the instrument shelter, exactly when it is needed. I chose a squirrel cage fan design as it seemed to fit my design better and it also moves more air volume.
Next I built a simple fan bracket using 3/16″ plywood and hot melt glue.
I designed the bracket and fan assembly to pull ambient air from the bottom of the instrument shelter via the 1/2″ slats in the floor of the shelter. To achieve this I built a small three sided box of plywood and the hot glued it onto the fan intake as shown here.
Next, I mounted the completed fan housing inside the instrument shelter so that the fan exhaust blows directly up about 10 inches onto the Davis temp/humidity sensor as shown. The movement of air across the sensor is gentle and quiet, without undue turbulence.
I mounted the small 10W solar panel outside of the instrument shelter on the roof at a 45 degree angle facing South. Now the fan runs anytime that the sun is shining directly on the shelter box. This eliminates unnecessary running at night or cloudy days and saves wear and tear on the fan hopefully.
I don’t have any solid data for a comparison yet as it is the Fall season here and the temperatures are cool and dry at the moment. Next summer when we have consistent +100 degree days, the fan will be an improvement for accurate data.