From: mung_me@att.net   
      
     I have a prototype central solar heater which I have been tweaking and   
   am interested in calculating heat loss in the ducts.   
      
      Here is the way I think this would work.   
      
      Insulated ducts have an R value. I think this R value relates to the   
   total inside area. So, Inside Diameter * pi * length. So the heat loss   
   is proportional to:   
      
   ti = temperature inside duct   
   to = temperature outside duct   
      
   (ID * pi * l) * (ti - to) / R   
      
   units in feet.   
      
   Is that about right?   
      
   Obviously if there is no flow through the duct, there is no heat loss.   
   So the heat loss in BTUs must be proportional to the mass of air flowing   
   through the duct.   
      
   Now, I'm getting confused (at least more confused). That should be the   
   mass of air per hour * the specific heat of air.   
      
   The mass of air/hour = the density of ~ .075 * CFM * 60 minutes   
      
   or:   
   CFM * 4.5   
      
   specific heat (dry air) = .24   
      
   what the actual specific heat of 50% RH air is beyond me, but I think it   
   is 5 or 10% higher.   
      
   So loss in BTU/hr:   
      
   (ID * pi * l) * (ti - to) * (CFM * 4.5) * .24  * 1.1 / R   
      
   with ID and l in feet   
      
   Is that about right? It seems like I missed something, somewhere...   
      
   Jeff   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)