I used an LCD shield to display the current temperature and speed of the fan, but you can use the circuit without the LCD display. You also need to select the transistor by the type of fan that you ...

To address this issue, he put together a simple but very elegant temperature controlled fan to vent the enclosure when the internal conditions go above the optimal temperature.

This custom fan controller, on the other hand, eschews the operating system almost entirely in favor of an open source fan controller board that can be reached over a network instead.

Alternatively, if the outside temperature is < desired temp, just blow air in regardless of the inside temp. All you need then is a temperature controlled fan.