intelligent venting fan

With the success with the prototyping of a low power circulation fan for Tatyanna I want to proceed to build a more refined assembly.

prototype of a 320mA 4.5" dia computer fan used as circulation fan

My intended goal of this fan is to mitigate cabin temperature rise due to solar gain in the summer. It is used in conjunction to many other measures I devised.
The most frequent use of it would be when the vehicle is parked at home. There are a few problems with high cabin temperature during storage and to list a few:

• deterioration of cabinet edge trims. the plastic edge trims tends to shrink when subjected to direct sunlight or high temperature. I know this from observation in both Westfalia Vanagon Campers and James Cooks.
• spoilage of food condiments in the kitchen cupboards. I leave them in the vehicle during the season of high camping activities.
• general deterioration of the interior material. you can smell out-gassing of plastics and foam etc

So for the final rendition the changes I would like to make are:

• replace the cardboard with sandwiched foam board (often use in exhibit billboards)
• move the fan grill to the inside (the fan it is set up to suck air from outside)
• make the power cord detachable at the fan/frame assembly for ease of deployment and compact storage
• devise a better way to insert and keep in place the assembly in the upper wing window; this may just entail filling the bottom gap of the window where things can fall into the abyss between the two layers of the high top roof

prototype venting fan assembly

 
powered by 12vdc

320ma computer fan - fan blade diameter 4.5 inch

sandwiched foam board

 
The most significant enhancement I would like to make it adding a microcontroller. In the current rendition I have to manually turn on and off each day. I don't mind the work but I just don't like the wear and tear of frequent opening and closing of the sliding door. Also circulating unfiltered air through the cabin induce a lot of dust and dirt, especially pollens during spring in Oregon.

The microcontroller program function is very simple so an 8-bit one from Microchip PIC family with built in temperature sensor would be ideal. I just want it to detect the ambient temperature and turn on the fan when a threshold is exceeded. I would use a rather wide hysteresis to prevent it from annoying cycling.