Here’s a simple-minded geophysics question, appropriate for the 95-degree heat that we’re experiencing in Boston right now: Why are underground parking garages hot?
At a friend’s house and they don’t have air conditioning? Go to the basement where it will be cool.
Have a collection of fine wine from Costco that you want to keep cool? Dig a cave and park the bottles there so that they will stay at a constant temperature somewhere near the average temperature at the surface of the Earth (pilots are taught about the standard atmosphere that is 15C at the surface, about 59 Fahrenheit).
Go into a parking garage underneath an office tower or apartment block and it will be hot and stuffy, oftentimes even hotter than the surface shade temperature. How is this possible?
Here are some possible explanations, but I can’t figure out which, if any, is correct.
- The parking garage is mostly air, which has low thermal mass, with relatively small patches of contact with the cool adjacent (high thermal mass) ground. The air-to-ground-contact ratio is much higher in a parking garage than in a natural cave or a purpose-built wine cave.
- Much of the thermal mass in the garage consists of cars, which have recently driven in from the hot surface and are therefore hot.
- The parking garage has high capacity exhaust fans so that people don’t die from CO poisoning. Therefore hot air is being sucked into the cave to replace the dirty air that is blown out.
- The parking garage has some doors that are typically open to the surface (this one does not seem significant to me since hot air rises).
- The cars generate a lot of waste heat as they drive around within the garage.
What do folks think? Why isn’t going down into an urban parking garage a pleasantly cool experience, like going into a natural cave?