Another facility is also running R-22 but employs 2 stage open drive 5h120 carlysle (one for booster, one for high stage).The advantage of the semi hermetic rack system in the first example is that if a compressor goes down it may or may not be an emergency.My instructor told us that open drive systems ALWAYS leak around the shaft seal and that is why hermetic and semi hermetic are better.
If the other compressors in the rack can handle the load, the customer can plan for the changeout; whereas in the 2-stage example the whole system of 8-10 dock/freezer coils would be offline until that compressor is fixed.The advantage of the open drives is that the compressors generally use better components and if serviced at proper intervals the individual internal parts can be changed, bringing the compressor back to full capacity.Also, fewer moving parts than the vilter 440/450 compressors. Been taught how to replace shaft seal and did 1 alignment.Sorry for the long post, but it really boils down to knowing what you need for your refrigeration and then backing into the strategy that is going to be the best. A friend who works for a competitor just installed a bunch in a meat plant running 407a..the motors were run off yaskawa vfds.If you don't get it correct it'll take out your shaft seal shortly. If you're handy, work in house and have the time then I say yes definitely as if they're installed and set up properly they'll run for years.
The reason that there's not a lot of them around anymore except in ammonia is that we're a throwaway society now.By eliminating the separate motor and all the associated drive pieces, a much cheaper alternative became available.It is true that you now risked the contamination of the system with a motor burnout, but the cost savings was large enough to offset the increased clean up costs.Just keep your drip buckets emptied and life is good.I've been in the compressor remanufacturing business since 1972 and have some experience with both open and semi hermetic compressors.This is usually remedied by running the compressor, but can require replacement if problem persists.