How to determine energy savings from weather and usage data

[Raddy13]

I bought a Nest thermostat a few months ago and I wanted to figure out how much energy it has statistically saved me. I have my usage data going back four years (I track the utilities to split with roommates) and I can find the historical weather data for my area for each day of the month. One of the complicating factors is that I've had two roommates, and my most recent one is a big gamer so electricity consumption has gone up since he moved in.

So the two parts are: How do I estimate how much excess power usage is from the new roommate and then, comparing the historical weather data, how do I estimate how much energy (if any) the thermostat has saved me?

 

[scottdave]

This is just an idea. Do you know how many watts his gaming computer uses? If it is in a season which you would be running the AC, I guess you could approximately double that, as a computer is basically a heat generator (there is no physical work performed, just exhausting hot air). So for example if the computer used 300 W and you are in the summer, the AC has to do (roughly) 300 W worth of cooling just to cancel out the computer running, so roughly 600 watts are being used. If you are in the winter, and would be running the heater, then your computer is helping to heat the room. I hope that made sense. You won't be able to just look at the label on the back of the computer and say "it uses X watts" Computer processors have more than one mode of operation, so sometimes it will be using more than other times.