I've been having some discussions with a fellow engineer about the use of superfeed on a screw compressor.

We have a plant with two Howden WRV 255 servicing 4 quick freezing tunnels.

refrigerant is NH3 (hence this forum )

they are fitted with a superfeed at -25C (according to the compressor supplier, these compressors should not run with a superfeed pressure above -25C, supplier is not howden)


it's an open superfeed, and the cycle goes like this:
when the pilot receiver reaches high level. the valve to the liquid separator opens and drains from the superfeed container, when the superfeed container reaches the low level it takes liquid from the pilot receiver.


The superfeed suction to the compressor has a danfoss ICS valve with a CVC, so it is keeping the pressure in the superfeed suction at a steady -25C, the pressure in the superfeed container is what it is depending on how much liquid is going through it towards the liquid separator.

Now, our discussion is weather or not the superfeed is economical, we both are "greasmonkeys" and havent done any calculations... but we both agree that a closed superfeed container would be more efficient than an open one.

the main argument is whether a closed superfeed container is efficient or not.

I say that "if it didn't give you any benefit, it wouldnt be used"

he says "is the extra effect weighing up for the extra power consumptions?"


I'm thinking along the lines that if a AC unit had a COP of 1, we could just as well have used electricity.


there has to be some savings/winnings of using a superfeed..

I have been looking around the internet for any literature on this but have turned out lot's of hit's on reciprocating compressors but nothing on screw compressors.


What are all your opinions?