If we use in room space split ac & fresh air fan in this situation how to balance outside air temp. 50 c and inside we need temp. 25 c at pick time?

Basically it's not about balance you can not start from that point, do as following steps:

- Identify how many people in this room according to interior design.

- Identify the activity of people.

- Pick Up the amount of fresh air needed from ASHRAE

- Calculate the amount of fresh air needed for the room

- Take into your consideration the diversity needed

- Volume damper should be fully opened

- Measure the CFM of fresh air outlet

- Start to modulate the volume damper to maintain the calculated CFM

* for the effect of fresh air load:

it should be calculated in HAP previously, if it is not you have to check the load needed by HAP and insert the amount of fresh air to fined out the capacity of SU.