From: dlzc1@cox.net   
      
   Dear RichD:   
      
   On Wednesday, November 18, 2020 at 1:35:07 PM UTC-8, RichD wrote:   
   > A nearby college includes a building, surrounded by an   
   > outdoor arcade, at street level. At one point, the warm   
   > internal air is expelled, which is natural, they perform   
   > continuous circulation. A nice spot, on a cold night!   
      
   OK.  I'd wonder why warm air was being expelled, unless fresh air was being   
   blown in an an inversion trapped the warm air below cold.   
      
   > However, I wonder, is there any hazard in breathing that air?   
   > Is it chemically processed somehow, contaminated?   
      
   Students and teachers have been breathing it.  Otherwise, it is just air.   
      
   > And, isn't it inefficient? The outgoing air ought to   
   > pass through a heat exchanger, to warm the incoming air.   
   > Isn't that wasted energy?   
      
   Sure, but any heat exchanger would be large and require cleaning.  Really   
   depends on how (and why) the warm air was being expelled.   
      
   David A. Smith   
      
   --- SoupGate-Win32 v1.05   
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