very nice project, also is working on something similar with the use of sensor SENSIRION SHT21, who ordered a sample and came recently
Here is the datasheet:
http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
if you wanted to write to him, I have a library for the Arduino and an example of reading and the PCB.
greetings