High efficient Shell and tube heat exchanger

[henj]

I need a heat exchanger for air to air at atmospheric condition with a thermal efficiency of 90%. My problem is that when I increase the area of the tubes by tube numbers/sizes or length the velocity of air drop and thereby decrease the h and U values too. Is this efficiency simply above the limitation for a shell and tube type of exchanger?

The design values are:
0.718 kg/s air on both side
Temperatures: Shell side in: 150 C out: 42 C, tube side in: 30 C out: 138 C.
We want to keep the total pressure drop of both sides below say 2 kPa as fan operating.

One solution is a heat exchanger with a U at 10 W/m2-K and a area around 740 m2 which would be to costly. (BEM shell Ø1000 4000 tubes Ø10 6 m long in AISI 316)

Any ideas to solve this this velocity /area problem in this case?

[henj]

(BEM shell Ø1000 4000 tubes Ø10 6 m long in AISI 316)

Understood as BEM shell ID 1000 mm and 4000 tubes OD 10 mm 6 m long