Stumbled on a few options. First, if you want to turn fans on and off as needed:
The project helps you control two fan’s to cool whatever you need. It works by cooling with the first fan when the sensor detects a user adjustable temperature, and it turns the second fan on, when the temperature exceeds 5 degrees over the user adjusted temperature.
I agree with the author on these being the most efficient way of controlling the temperature and to preserve energy. Also each fan will turn off if temperature drops 5 degrees below the user adjusted temperature. You might ask why 5 degrees ? well to avoid the fans turning on or off too often when temperature varied with only 1 degree plus or minus.
Second option:
http://jos.vaneijndhoven.net/fancntl/index.html
* Three temperature sensors are supported, each controlling the speed of a (group of) fan(s).
* A small potmeter for each sensor allows to choose the actual temperature above which the fan starts running. Higher temperatures cause a linear increase in fan speed.
* When the measured temperature decreases, the actual fan speed is decreased only very slowly (taking several minutes), to avoid control instability.
* An additional potmeter provides a minimum fan speed, independent of temperature.
* The circuit is built with very few components, thanks to a low-cost PIC 16F676 microcontroller. This controller takes care of A/D conversion of the analog inputs, proper signal filtering, and the creation of PWM output signals to drive the fans. The PWM driving of the fans is a fast on/off switching with variable duty cycle, so the output transistors will remain cool even when driving many fans.
* A bicolor LED gives a visual temperature indication by gradually changing color from green to red.
Just a thought. I will keep looking and brainstorming before I implement the cooling design in my own build.