(Undated)  --  A new survey from Zillow shows Portland has among the fastest-rising rents in the nation.  The survey places Portland at Number five, with the average rent increase at seven-point-two percent from January 2014 to January of this year.  The median amount renters are paying is more than 15-hundred dollars a month.  In the top spot is San Francisco, with an increase of nearly 15 percent and a median rent of more than three-thousand dollars.