Heat in Crowded Places: Origin and Explanation

[Likith D]

So, I have noticed that when people are crowded in small rooms, it feels hot. In fact, everyone in the crowd feels hot and starts sweating. I am wondering about the origin of all this heat.

I do know that by first law of thermodynamics, if two people touch each other and if one of them feels the other is hot, the other person has to feel that that person is cold.
The problem is if all the people in crowded places feel hot, then heat must be generated by themselves or the air (with respired CO2) around them must be hot (in which case, crowded open places should not feel hot, which I'm not sure about).
It cannot be the feeling of heat by some other person, because if that is so, the other person should feel cold by that person.

 

[Chestermiller]

So, I have noticed that when people are crowded in small rooms, it feels hot. In fact, everyone in the crowd feels hot and starts sweating. I am wondering about the origin of all this heat.

I do know that by first law of thermodynamics, if two people touch each other and if one of them feels the other is hot, the other person has to feel that that person is cold.

The first law of thermodynamics does not say anything like this. Where did you get this unusual idea? Please provide a reference.

 

[Likith D]

The first law of thermodynamics does not say anything like this. Where did you get this unusual idea? Please provide a reference.

Heat is transferred from one body to the other and in case there is no generation of heat energy by chemical/physical means (which is how out body tries to regulate internal body temperature) or heat provided from the external environment (our body is not a conformer of external heat, it tries to maintain a temperature but it takes time to do it, in which case we can ignore the fact that the body is indeed a regulator).
In this particular problem, if we ignore the above two causes, we obtain that

if two people touch each other and if one of them feels the other is hot, the other person has to feel that that person is cold.

Which doesn't make sense in the above case because every single member feels hot, and nobody feels "cold". Therefore, I conclude that heat in this case is either heat being generated by our bodies or the external environment (with respired CO2) is heat source. Also, it could be that heat is generated naturally by the body is not expelled as it used to in uncrowded places and we are left with that excess heat.

 

[russ_watters]

In order to feel comfortable, humans have to be continuously losing heat to a cooler environment. Put too may people in a room with inadequate HVAC and the room starts getting warmer, making it harder for people to lose heat.

 

[kuruman]

So, I have noticed that when people are crowded in small rooms, it feels hot. In fact, everyone in the crowd feels hot and starts sweating. I am wondering about the origin of all this heat.

The average basal metabolism of a human is close to 100 W (assumed 2000 kcal/day). That means that each person puts out approximately the heat of an incandescent 100 W bulb, just sitting there. That can add up quickly in a small crowded room and raise the temperature appreciably.

 

[Likith D]

In order to feel comfortable, humans have to be continuously losing heat to a cooler environment. Put too may people in a room with inadequate HVAC and the room starts getting warmer, making it harder for people to lose heat.

So, that would mean humans are less (thermally) conductive than air?

 

[russ_watters]

So, that would mean humans are less (thermally) conductive than air?

What? I have no idea how you got that from my post and it makes no sense. Please explain what you are thinking.

 

[Drakkith]

So, that would mean humans are less (thermally) conductive than air?

No, that's not what that means. People are constantly generating heat inside themselves via chemical reactions. These reactions would eventually heat the person up to the point where they die unless that heat is transferred out to the environment. If the air gets too hot, heat transfer to the environment is impaired, or even reversed if the air is hotter than a person's body temperature. Luckily we have evolved to sweat, which allows us to lose heat by evaporation of water and survive even when the air is much warmer than body temperature.

 

[kuruman]

So, that would mean humans are less (thermally) conductive than air?

Humans cannot be viewed as a hunk of conducting material. As you very well know we regulate our body temperature through the circulatory system. When we fell hot, more blood is pumped to the skin which is air cooled and, if that's not enough, we sweat and lose heat by vaporization.

 

[Likith D]

What? I have no idea how you got that from my post and it makes no sense. Please explain what you are thinking.

If humans are able to loose heat quicker in normal open air than crowded rooms, then their thermal conductivity of open air and crowded room for a human have to be different because it deals with the rate of loss of heat facilitated by air/human in this case.

 

[russ_watters]

If humans are able to loose heat quicker in normal open air than crowded rooms, then their thermal conductivity of open air and crowded room for a human have to be different because it deals with the rate of loss of heat facilitated by air/human in this case.

No, as I said it is primarily because the air gets warmer in a room with more people. The people themselves are not conducting heat or directly inhibiting conduction of heat unless you are very near or touching each other.

"Thermal conductivity" is not, on the first order, temperature dependent.

 

[Likith D]

So humans keep generating heat, which is okay in an open system, but in a closed system we end up leaving that extra heat hanging in the air or even in our bodies. That explains it, but can we extend it to an open system. Maybe, like what happens when people gather up in an open field. Probably it would still be hot for every person?

 

[Chestermiller]

So humans keep generating heat, which is okay in an open system, but in a closed system we end up leaving that extra heat hanging in the air or even in our bodies. That explains it, but can we extend it to an open system. Maybe, like what happens when people gather up in an open field. Probably it would still be hot for every person?

If the people are in an open field, cooling air can flow through from the surroundings to remove the heat. This is not the case in a closed room without circulation.

 

[Dale]

Therefore, I conclude that heat in this case is either heat being generated by our bodies

Yes, this is what it means for humans to be warm blooded.

 

[anorlunda]

An old rule-of-thumb I remember is 200 watts per person heat generation.