It does not do any good to have the oil drain connections on the bottom of vessels for R-22. The oil floats on top of the liquid R-22. If the vessel and coil are pumped down, you might get some oil out that way, but this has to be slightly irregular way of doing things.

I would look at using R-507 instead of R-134a.

What are you using flooded evaporators on with R-22 at 45°F? That's kind of high for anything short of air conditioning. Are these coils used on a penthouse unit for cooling a process area?

By the way...welcome!