MIN() results are not correct
Since you are using 2012, you can use TRY_CONVERT as Lamak alluded to if you can't change the street number data type. Note, if you have something other an an INT in this column, then your results will not contain these rows

SELECT 
   zone_number,
   min(try_convert(int,street_number)) as street_number
FROM
   A
GROUP by ZONE_NUMBER