Yes, No or maybe??

[joken]

Opinions please. M.E. is proposing installing two 4.5 ton split systems to cool electrical rooms. There is no way to get OSA to these rooms and I do not have chilled water below 47 degrees OSA. My concern is that the condensing units will be on the roof and be aprox 100' above the fan coils. Am I looking at potential oil return or other problems even with increased line sizes and traps. Any advise here is much appreciated.

[Pneuma]

If it goes that way make sure you get the split system manufacturer to approve the piping before you do the job. The best other option, not having seen the site, would be a dry cooler system.

Good luck!

[Coolmaniac]

What he said^^^^^^ or run water cooled units off the chilled with head press controlled water valves.

[mech_head]

can you put the condensor coils remote and keep the compressors inside?
More piping but if is done properly and you talk to the manufacturer it shouldn't be a problem.
I know Mitsubishi city multi's can go a long way with no traps. That may be an option.
Just thinking out loud - so to speak

[drivewizard]

If you put the compressors on the roof, make sure you put a liquid stop solenoid in the liquid line at the AHU. Not for a pumpdown, but just to stop the liquid from draining into evap on the off cycle. So when t-stat opens it breaks contactor and solenoid power. Will need a man reset LPC set at about 5#-10# in case solenoid doesn't open for some reason.
Doing this will save you some compressor replacements.
Most system piping designs do not utilize traps any more. I will try to attach attach a service bulletin with the new guidelines.
It is for larger units but the same guidlelines should apply. Good Luck

[roadking99]

I would install splits with 410A then you wouldnt have to worry about oil return.