"Unlike lighting, people generate a lot of latent heat, and unlike office workers they are moving. Also unlike office workers, feeling a little hot means they will take their business elsewhere."

Excellent point. I remember when I put an HVAC system in many years ago (in a plant) the calculation was something like 2000btu per person in heat generated in terms of sizing.

I was curious so I just checked (couldn't back then) to see if that figure is anywhere near correct but can't seem to find the answer.

This seems to indicate that 600 watts is about 2k btu per hour it wouldn't surprise me if a human gave off 600 watts of heat:

http://www.rapidtables.com/convert/power/Watt_to_BTU.htm

Actually this more or less shows it is ballpark:

http://answers.yahoo.com/question/index?qid=20081206141450AA...