[gregmac]

Do the huge corresponding drops in CO2 and temperature at 11pm and 9am mean that the "solution" was to open a window or door for ~15 minutes a couple times a day?

Seems like a simple solution, other than there's a good half-hour of sub-17 degree temperatures right at the start of the workday, which isn't exactly a great motivator to start working. Unless you are skilled at typing with winter gloves on, I guess.