It’s too hot to do anything but lie around pondering who I might be willing to smother if it would lower the temperature in here a few degrees, so I thought I’d kick this question to the board. Assuming you have a 12’12’ room with either no AC, or a unit that’s already maxed out and can’t get the room below 80F when empty, how much does each additional person in the room raise the temperature? Does the size or activity level of the person in question make a measurable difference?
Well, a Kilocalorie is about 4 BTU.
The average person needs 2000kcal/day to maintain their weight, so if that is all turned into heat, that’s about 8,000 BTU per day or 333 BTU/hr. A very small room A/C might be 5,400 BTU/hour, so it would have to run 4 minutes to remove the heat generated every hour.
A similar subject came up in a different thread some time ago. That time people seemed to agree you could consider an average human being to put out heat to the equivalent of burning a 100 watt light bulb. The old, incandescent kind.
There was some dispute on that question, many thought the average human wasn’t that bright.
It’s heat equivalent to any 100 watt light bulb. It’s just that it’d be very rare to find a 100 watt light bulb of any non-incandescent type in an inhabited room, since a 100 watt LED would be far too bright for room illumination.
To convert that into temperature, we’d need to know more than just the temperature the AC reaches unoccupied. We’d also need to know how well-insulated the room is and how hot it is outside. For instance, “the AC only gets the room down to 80” could mean that it’s 80 outside, the room is horribly drafty, and the AC is crap, in other words, the inside is always going to be the same temperature as the outside. Or it could mean that you’re on the surface of the Sun, and it’s a testament to the formidable engineering of your insulation and air conditioner that it’s able to keep the temperature at livable levels at all.
I think it’s equivalent to 100 W light bulbs. We may have to stipulate they be incandescent light bulbs, because more efficient light bulbs are often labeled prominently with the incandescent wattage they match for illumination – I recently bought “100 W replacement” LED bulbs that actually consume 15 W, but this information took a bit of searching to find. So it depends on what somebody understands a “100 watt light bulb” to actually be.
That said, I have a nice portable electric heater with a switch for 1300 or 1600 watts. Imagine putting that in a room in place of 13 or 16 people.
You need the ASHRAE Handbook of calculating loads. They have a chart of activities and the heat load from each person. Including my all time favorite engineering spec, the second highest listed activity - “moderate dancing”. Heat ranges from 400 to 2000 btu/hr for each person.
See page 25:
Aside from the heat, they would also raise the humidity, increasing the discomfort.
500 BTU/hr is a good rule of thumb for calculating heat load per person. While the average may be closer to the 333 BTU number over a 24-hour period, that includes the lower heat output during sleeping, which isn’t generally done in auditoriums, gyms, or conference rooms. Plus, while athletes performing significant exertion may put out as much heat as several people at once, there’s usually not many of them in a small space. Still, that small room A/C can quickly be overwhelmed if you have just a half-dozen people over, especially if it’s already struggling to keep up on a hot day.
So interesting to see this figure confirmed here. I made this very same calculation in about 1989 as a curious engineering student. My estimate was between 75 and 100 W, which meant “light bulb” to me.
When I tried to argue my case with a medical student who was not from a physics or engineering background, she was not having any of it. “You just can’t do that!” referring to this energy balance type thinking.
However, it sounds like 100 W (on average) is indeed the consensus by the posters on this thread. And this value (actually higher according to jjakucyk), along with the humidity increase mentioned by CookingWithGas, would be very helpful to HVAC planners, I’d say.
An interesting fact: per cubic inch, a person generates vastly more energy than the Sun does!
Does your engineering specs show whether that is horizonal or vertical?
And since someone has to ask, what was the highest listed?
It says “Athletics”.
Not sure where they copied that table from, but they clearly fucked up the cut-and-paste job. For instance, it looks like “moderate dancing” is listed as 1600, when that value is actually for “heavy work; lifting”, the real second-highest activity listed on that chart. Interesting how they list one value for “Adult, male”, but females are merely “Adjusted”. And, most of all, what the hell is a “Btu/h”? 
Btu per hour, a measure of power?
I’d prefer to see it expressed in Watts.
https://www.rapidtables.com/convert/power/BTU_to_Watt.html