The quickest route is to take the airport-tianjin railway station back square special line from the airport exit, get off at tianjin railway station back square, get off at the front square through the entrance, take bus No.645 to platform A of the front square, and you can go straight to Zhongbei Town.
The advantage of this line is that the density of cars is high, and there are seats at the starting station. The only drawback is that it is a little troublesome to walk from the back square to the front square.
But it's worth it compared with taking the bus more than twice.