Temperature

I mean the effect from sensing the return temperature.Each unit has its own set point because of different locations it served.But their returna air temperature is mixed inside the above false ceiling.Will this affect my thermostat sensing?

It will have the immediate effect of baffling a good engineer from a lack of definition. But now that the baffles are installed the operation becomes clearly obvious and requires no further discussion.

It all depends upon how your duct distribution system is designed. IF each unit has separate supply and return duct system I do not anticipate any mixing of air. As three units work at the same location nose level may be a problem . For that roper acoustic treatment can be carried out. You may have look the condensate drain also. If it is not properly installed it will spoil the ceiling.

mr.swamy.what if the return air for each indoor unit is not ducted, there will be mixing of air right?Then it follows that a mixed temperature will create, therefore there will be effect on the sensing of thermostat for each different area being conditioned?

Yes

the 3 thermostats will sense the same temperature as the 3 units are sucking the same air...

result: your 3 units will start and stop at the same time if you have same settings,

and , as they are serving different location, temperature regulation will not be accurate

I suggest to set the a little difference in thermostat setting not to have a big rush current on your electrical grid

for the noise, I will not elaborate it as it is not your concern

Greetings

I think we need a more complete description of what ducting is shared versus separated. And maybe an assessment of how much heat is rejected into the above-ceiling space. For this we need to know the details of each of the three units.

1. NOSIE, NOISE, NOISE, NOISE Last year, one smart engineer in my office decided to put (4) 5-ton units close to each other and I can tell you, the combination of the noise factors is not a linear..

True enough; it would be about √n, which is not linear.

I sincerely suggest you read up on octave bands before you put your self out in the open like this...

It is linear on a logarithmic scale. Double the noise is 3dBA plus.

position (and calibration) of the T-stats in each area is critical for temp. control.

H T H cheers