Or observe how often the AC (or heat) comes on and how long it runs each time. There's a strong correlation between that and outdoor temperature. You might eve

Or observe how often the AC (or heat) comes on and how long it runs each time. There's a strong correlation between that and outdoor temperature. You might even be able to come up with a numerical guesstimate. Theoretically, a properly designed AC system is sized to run 100% of the time during the hottest weather. And obviously 0% if it's cool enough outside. Or just look around the office and note how people are dressed, whether there are coats on people's chairs, how heavy those coats are, and whether you see any umbrellas lying around.