Desuperheating by liquid injection

[RANGER1]

First: if you want LRi on the LRI port of the compressor, wich is at the end of the compression, you NEED TO HAVE A PUMP, to supply the refrigerant to the TEAT valve, because the pressure at the end of the compressor compression is higher than the condenser pressure if you have a "normal system with a PM valve between the compressor and the condenser... you can have a discharge pressure of 30C, and a condensing pressure of 20C on a system with a VFD controlled condenser pump...
Second: I don't get this... if I am supplying "evaporated liquid" from the condenser as compared to gas from the economizer tank, what is the difference? there will be extra work on the compressor no matter what... So normally the economizer supplies the economizer port with gas at around -10C... There is extra load on the compressor in either case, how is the load from the LRI introduced in the economizer port different from the gas introduced to the LRI port?
I have seen a howden 255 with an economizer fitted, where the economizer valve opened when the compressor was at 100% and it was injected with -10C gas where the compressor almost took a bow and called it a night... so we had to introduce the economizer at -25 and slowly raise it to -10.
Third: The LRI port only works if you have a pump feeding refrigerant to the TEAT
if you want an economically working LRI, you have to use the economizer port... because the condensing pressure is lower than the pressure at the compressors "LRI stage"

Tyco can you remind me of what LRi & LRI is?

I feel a lot of your statements are a bit of a set up but here goes.

Liquid refrigerant injection into liquid injection port does not need a pump, it goes inbecause pressure is lower.
To the best of my knowledge economizer port is positioned to open to rotor thread almost immeidiately
after male rotor closes of female rotor vane. At this point as rotor continues to rotate it starts to reduce volume in female rotor thread(compress).
At this point economizer port is open to this vane in female rotor, which is slightly higher than suction pressure(asssuming compressor is over80% loaded).So this allows economizer suction to flow into rotor vane.
After it passes that port, then liquid injection port is open to metered liquid refrigerant to control discharge/oil temp.
So not sure why you need a pump.
If wrong selection of Vi is selected maybe, but over compression is possibly the last thing you want(draws more power consumption.
You also mention "normal system" having PM valve in discharge line raising pressure upstream of valve.
Why?
To me its another waste of power. Everything points to having as lower condensing pressure as possible.

If you inject gas from economizer you are increasing nett refigerant effect byu subcooling liquid refrigerant feeding evaporator. Your compressor basically increase in capacity, using a bit more power though.

If you inject liquid from condenser you get cooler discharge temp but thats all, not increased refrigeration effect.
I however agree that injecting liquid for oil cooling & economizer will still work but possibly a little shy of using correct ports.
Only Howden could tell us that!

[Tycho]

Tyco can you remind me of what LRi & LRI is?

I feel a lot of your statements are a bit of a set up but here goes.

Liquid refrigerant injection into liquid injection port does not need a pump, it goes inbecause pressure is lower.
To the best of my knowledge economizer port is positioned to open to rotor thread almost immeidiately
after male rotor closes of female rotor vane. At this point as rotor continues to rotate it starts to reduce volume in female rotor thread(compress).
At this point economizer port is open to this vane in female rotor, which is slightly higher than suction pressure(asssuming compressor is over80% loaded).So this allows economizer suction to flow into rotor vane.
After it passes that port, then liquid injection port is open to metered liquid refrigerant to control discharge/oil temp.
So not sure why you need a pump.
If wrong selection of Vi is selected maybe, but over compression is possibly the last thing you want(draws more power consumption.
You also mention "normal system" having PM valve in discharge line raising pressure upstream of valve.
Why?
To me its another waste of power. Everything points to having as lower condensing pressure as possible.

If you inject gas from economizer you are increasing nett refigerant effect byu subcooling liquid refrigerant feeding evaporator. Your compressor basically increase in capacity, using a bit more power though.

If you inject liquid from condenser you get cooler discharge temp but thats all, not increased refrigeration effect.
I however agree that injecting liquid for oil cooling & economizer will still work but possibly a little shy of using correct ports.
Only Howden could tell us that!

Finally, there it is

With LRI from the condenser, you take liquid directly from the condenser without any sub cooling effect.
You add load to the compressor and condenser without any gain other than cooling the discharge and oil in the compressor system

The PM valve is between the compressor and condenser to keep a stable discharge pressure of 30C and prevent oil carryover, so with 30C in the discharge you may end up with 10-20C in the condenser, depending on seawater temp.

When I talk about needing a pump to feed it into the LRI port, I see that I have forgotten to mention that it is a cooling system, not a freezing system. suction of -8C.
I am speaking from experience, that when the system starts with a suction pressure of around 5-6C you will need a condenser pressure of minimum 17-19C before it starts to feed into the economizer port.

on the Howden XRV's we use, I have never been able to feed the LRI into the LRI port, the LRI port is all the way at the end of the compression, right before the rotors opens to the discharge.

Was fun playing a little devils advocate here