Liquid pressure amplification (LPA)

[RONB]

I have fitted quite a lot of the Hysave LPA pumps here in thr UK. They have been fitted in tandem with inverter head pressure control systems. We generally get the head pressure running around 150 psi and the pump outlet runs between 12 to 14 psi higher than the head pressure. You have to be careful with the piping arrangement on the pump inlet side (bends etc). And you also need a constant liquid feed to the pump ,so we draw the refrigerant directly from the bottom of the receiver. There is also a recirc line for low load conditions. They also help if you have a large store that has cases a long way away from the pack that may suffer from liquid starvation. I have tried this out by putting a sightglass at a case that struggled to get to temp,and found the glass bubbling when the plant is running on high demand. Once the LPA was up and running we never had any temperature problems with the case again due to starvation. The only major problems we have had is the pump controller. They operate off two transducers one on the pump inlet and one on the pump outlet by differential pressure. The controllers kept locking up due to electrical interference. Overall they seem to do what it says on the tin as they say.

[Gary]

Wouldn't mechanical subcooling near the pump inlet be a viable means of preventing cavitation?

[joe magee]

Wouldn't mechanical subcooling near the pump inlet be a viable means of preventing cavitation?

Why? The purpose of the hysave is to raise liquid line pressure without raising discharge pressure. Balance port valves will work with very low liquid line pressures.
By using a mechanical subcooler you would need additional compressor capacity.
Free subcooling is fine with a hysave. Most of the racks I work on have mechanical subcoolers. We used to have a 70 degree min drain leg temp. We can now drop it down to 55 degrees going into the subcoloer and drop it down another 10 degrees. the capacity we get out of our txv's is great. The only downside would be the added refrigerant due to the flooded condenser.

[Gary]

Would subcooling prevent cavitation?

[nhuzain]

what is the super heat

[Josip]

Hi, nhuzain

what is the super heat

What do you think it is?

Best regards, Josip

[joe magee]

Nhuzain. Good one. Remember, Every refrigeration issue can be traced back to superheat and subcooling.

[botrous]

Hi US Iceman,
How are you doing ,

I think that Marc Obrian have these pumps in the UK.

http://fridgetech.com/hysave_lds/


Regards

[jragosta]

I have fitted quite a lot of the Hysave LPA pumps here in thr UK. They have been fitted in tandem with inverter head pressure control systems. We generally get the head pressure running around 150 psi and the pump outlet runs between 12 to 14 psi higher than the head pressure. You have to be careful with the piping arrangement on the pump inlet side (bends etc). And you also need a constant liquid feed to the pump ,so we draw the refrigerant directly from the bottom of the receiver. There is also a recirc line for low load conditions. They also help if you have a large store that has cases a long way away from the pack that may suffer from liquid starvation. I have tried this out by putting a sightglass at a case that struggled to get to temp,and found the glass bubbling when the plant is running on high demand. Once the LPA was up and running we never had any temperature problems with the case again due to starvation. The only major problems we have had is the pump controller. They operate off two transducers one on the pump inlet and one on the pump outlet by differential pressure. The controllers kept locking up due to electrical interference. Overall they seem to do what it says on the tin as they say.

Does anyone know if there is an LPA system available that works on ammonia systems? I know of one company that is working on it, but nothing available at this time. I would appreciate any info. Thanks.

[TXiceman]

When they first came out with the LPA system, I coud not justify how it would work in my mind. I still do not see how this works. it seems to defy the laws of thermodynmaics.

Anyone have any ideas on how you can explain it with thermodynamics.

Ken

[mad fridgie]

When they first came out with the LPA system, I coud not justify how it would work in my mind. I still do not see how this works. it seems to defy the laws of thermodynmaics.

Anyone have any ideas on how you can explain it with thermodynamics.

Ken

It more practical , which give theoretical performance.
basically it all about the expansion device, you need a certain pressure difference to drive the correct amount of liquid througn a valve, You could just size your valve for a very small pressure differnce (like you would have in winter) but come summer the pressure difference would be much higher, the selected valve would be effectively to big, would hunt and could cause flood back. So you size your valve around max conditions normally, so in winter your control your liquid pressure by controlling fans or water flow. Basically falsly increasing the head pressure, which uses more power. By letting the head pressure drop (less power draw) then elevating the liquid pressure to meet the expansion valve design.
You use less power to elevate a mass of liquid than you do to elevate the same mass of vapor by the same pressure increase.
The other benefit is that by elevating the liquid pressure, you have effectivly sub cooled the liquid, so reducing the chance of flash gas being formed. (again bad for the expansion device)
In many cases the system have been failures due to cavitation on the pump, would easily be fixed with a dedicated sub cooler prior to pump entry (as gary as indicated) just like pumped overfeed systems care must be taken when sizing suction head and pressure drop

[Steve Wright]

We have installed some years ago in supermarket applications. They seemed to be most effective when the condenser was on the roof probably because of the issues Gary spoke of.

It did allow us to float the head down, this was before balanced port TXV were readily available for supermarket applications.

US Iceman we just installed our first Magna-Tex pump have you used any?