I am trying to find out what the purpose of this venting is? Is this for more combustion air? Not sure why else it would be needed.
The venting goes from the ductwork (Supply) to the outside. There is a second vent attached to the outside, but just hanging loose.
Never seen anything like it.
I thought it was one of those new stainless steel looking dryers. 
Mic
They’re obviously heating the outside.
With the heat in that plenum, I’m surprised to see that the vinyl hose isn’t melted. Lack of brains?
I think you’ll find that the duct from the outdoors is connected to the return plenum. This is for fresh air supply to the home when the fan is operating. The other duct just hanging is most likely intended to supply combustion air…although it may not be needed unless the home has been recently energy retrofitted and airsealed.
Was there any evidence of a doghouse outside??