how does 35 Billion translate to 90 years ? China is using 8Milion/day 8 * 365 = 2920 Million/year (2.9 Billion) (10 to the power of 9 or a thoutand million) so 35 Billion should last for for 12 years at the current consumption. 2.9 Billion + 35 years = 261 Billion dosent come close if you use 10 to the power of 12 for the definition of a billion.

You can run a one wire network which uses 2 wires. There is a range of devices you can read information from, http://owfs.org/. For example you could run a temperature sensors in each room. Combined with a tool like http://www.cacti.net/ you can log an ongoing temperature graph. Combined with X10 http://www.linuxha.com/ you now could act on the information you receive. for example if the room reaches a certain temperature you switch on the fan. racker79