Parallel Compressors operation problems

[caatc]

I’m working for a client who wants to replace a single direct expansion ac system compressor with two compressors both rated for the total system load. However, they want to operate both compressors during peak load conditions. What kind of problems, other than oil return problems, can be expected with parallel operation and how can they be avoided?

 

[pmover]

2 - 100% compressors in parallel, both operating at same time is the operator's discretion; but not prudent from an energy usage standpoint. however, if the application requires a unit immediately available in case of failure of one unit, then perhaps a more efficient setup can be investigated (i.e. 3-50% units). i would consider balancing the piping system and load to each compressor by monitoring current or compressor flow to each compressor.
hope this helps.
-pmover

 

[imok2]

Without pumpdown, for installations of the evaporator or evaporators above the condensing unit, the suction line should be trapped by running the piping upward from the coil outlet trap, and as near the coil as possible, and to the height of the coil, to prevent the condensed vapors remaining in the coil from draining directly into the compressor. If you have a pump down then you can go directly to the condenser with regards to the parellel compressors ..If they are on one evaporator and the object is to get a reduction in capacity as the load is reduced ...then you have to make sure that the compressors have a connecting oil line
and an equilization line to each compessor that is above the oil to equilize the pressures in both compressors for proper oil level