Quote Originally Posted by Segei View Post
In North America typical ammonia refrigeration plant has minimum condensing temperature is 20C or 110 -115 psig. This is just typical plant operation. I know a few plants that have condensing temperature of 10C. Suction pressure of these plants around 0 bars. For higher suction pressure we need oversized oil separator. Cost of the compressor with this oil separator will increase by 5%. I talked to several compressor manufacturers and everybody claim that their compressors can operate at condensing pressure 15C even with 2 bars suction pressure, but oil separator should have right size.
On freezing plants with -0.3 bar in suction, we still run with a PM valve on the discharge to keep the discharge at 30C, if we do this, we can use the same oil separators on -0.3 bar suction, or at 3.5 bar suction to prevent any accidental oil loss in case of a "alarm stop" on the compressor... we have a "fineoil separator" incorporated in our design, so we can run on any pressures you say and still get 99% of the oil loss back into the compressor suction... we design our freezing systems with two PM valves, so when you need a defrost, we shut of all hotgas to the condenser because the condenser PM is on 0.1 bar higher pressure. and lead it all to the plate freezer or evaporator that needs the hotgas... sure we are like the most expensive air--air-split unit
but after awhile, we will give you more back for your buck...


Of course you could add a full speed condenser pump, but with a regulating valve at the outlet of the condenser... where is the gain, with the full speed pump with the trothling valve, or with the VFD pump with a full open outlet?