Hi jaganathan,
For FDD , If the TTI bundle size is 4 then same HARQ process is used for the all 4 transmission. then max of 4 harq process is enough for the 16 ms RTT.
For TDD, there are 3 HARQ processes for UL/DL Configuration 0 and 6 whereas 2 HARQ processes used in case of UL/DL Configuration 1