Re-orientation of AHU

as long as the cfm is there, no blockage mannage to, its will be ok then on my suggestion. the important part of the ahu is the cold exchanger via coil cooling itself and monitoring compulsory on the cfm value, must not droped between 10 to 15% the design of occupants of AHU.

I agree with the previous poster, as long as the CFM does not change. However, you do run the risk that the CFM will change, depending on the geometry of your layout after turning the AHU. If the inlet of the AHU is so close to the wall of the enclosure that the effective cross-sectional area is greatly reduced, you may have a constriction of your flow and this drag may decrease your CFM for the current fan which would normally be on the output of the AHU. You may want to mount an additional fan either outside or inside the enclosure at the vent, giving a positive pressure in the room that will assist the AHU air intake. You might also choose to mount a smaller fan with peripheral/side intakes (squirrel cage design?) directly onto the AHU at the filter, if you have the clearance. This will insure you are not reducing the available CFM.

In general, the "side" from which an AHU gets its return air is irrelevant, as long as you do not have a restriction that is smaller than the cross-sectional area of the intake itself.

Each manufacturer provides a cfm output rating for that unit based on a measured static air pressure, which is usually calculated by the size of the supply duct and a constant value for the unit coils. If the new unit was selected correctly for both the supply volume rating and the External Static Pressure actually present, and you have not restricted the return air path, you'll be just fine.

IF you find your outlets are not providing the same airflow, have a certified Test & Balance contractor come out and commission the unit and the system, adjusting all the volume dampers appropriately to maximize what your machine will provide, as close to the original design as possible (evenly).

What is AHU anyway

AHU = Air Handling Unit, can be a fan, heater, air conditioner, or a combination. Usually includes some type of filtration system, controls and control panel, sometimes even primary ducting.