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3rd comment on the original post explains with physics, "J G July 5, 2013 @ 10:10 pm 3 It’s very definitely waste heat from the cars. Typical car engine run

3rd comment on the original post explains with physics, "J G July 5, 2013 @ 10:10 pm 3 It’s very definitely waste heat from the cars. Typical car engine runs just under boiling – 80 C differential from ‘room temperature’. The hot sections of most cars will weigh about 250kg, specific heat of steel is 0.49 j/g per degree K Meaning each car brings about 6000kj of waste heat into the garage, plus another 100kj+ for each second they run in the confines of the garage. Air has a specific heat of roughly 1 j/g per degree K, and a kilogram of air takes up nearly a cubic meter. So a car can heat 200 cubic meters (a cube roughly 6m) of air quite uncomfortably warm, which is much larger than the area the car occupies. This is just back-of-the-envelope math, but air has extremely low specific heat by volume, so it’s very easy for a hot engine to heat up a nonsensically large space."

brudgers 13y ago
If it is using 1j/g/degree K, then it is doing it wrong. It's a question of Psychrometrics http://en.wikipedia.org/wiki/Psychrometrics http://en.wikipedia.org/wiki/Psychrometrics Air is humid, the Enthalpy is significantly higher than the specific heat of dry air. Latent heat is the major factor in the real world. And car exhaust is loaded with water vapor (and CO2). See examples here: http://www.engineeringtoolbox.com/enthalpy-moist-air-d_683.html http://www.engineeringtoolbox.com/enthalpy-moist-air-d_683.h... Latent heat is why auditoriums get hot, when filled with people.
- Tloewald 13y ago
  The linked document shows humid air having an enthalpy of 75kJ/kg at 25C, so that explains why humidity increases perceived heat and increases the energy needed to heat up humid air, but the heat itself is coming from car engines, and the humidity from tailpipes. On the whole, i don't find underground carparks notably humid, but they are warm.

brudgers 13y ago

If it is using 1j/g/degree K, then it is doing it wrong. It's a question of Psychrometrics http://en.wikipedia.org/wiki/Psychrometrics http://en.wikipedia.org/wiki/Psychrometrics Air is humid, the Enthalpy is significantly higher than the specific heat of dry air. Latent heat is the major factor in the real world. And car exhaust is loaded with water vapor (and CO2). See examples here: http://www.engineeringtoolbox.com/enthalpy-moist-air-d_683.html http://www.engineeringtoolbox.com/enthalpy-moist-air-d_683.h... Latent heat is why auditoriums get hot, when filled with people.

Tloewald 13y ago
The linked document shows humid air having an enthalpy of 75kJ/kg at 25C, so that explains why humidity increases perceived heat and increases the energy needed to heat up humid air, but the heat itself is coming from car engines, and the humidity from tailpipes. On the whole, i don't find underground carparks notably humid, but they are warm.