Low Pressure Reciever Issue?

[gproud]

Hi There:

I am operating an ammonia system with 2 x 100 HP, 2 x 350 HP and 1x 200 HP compressors. We have a freezer tunnel that is used for IQF Blueberries, 275 to 310 thousand pounds a day.

When the LPR starts filling, the discharge pressure in the system goes up by about 5 lbs, the suction pressure usually goes up by 3" and the tunnel temperature can go up by anywhere from 2 to 4 degrees celsius.



My question is, is this relatively normal and if not, has anyone any suggestions how to fix.

Appreciate any comments.

Thanks,
Gordie

[NH3LVR]

Flash gas from the liquid causes a temporary rise in Suction Pressure.This is not abnormal, although improvements might be made.
Is this tunnel the only load on the system?
Is there more than one feed Solenoid for the LPR?
What percentage of the time is the LPR feeding?
Is the LPR fed Subcooled Liquid?
The key here is to have the LPR feed most of the time, rather than large amounts for a short time.

[US Iceman]

Hi Gordie,

Welcome to the RE forums.

I'm NH3LVR on this one. The problem you are describing is due to the liquid feed to the LPR. My guess is you are using a solenoid controlled by a mechanical float switch.

When the liquid level decreases, the solenoid valve is energized to allow liquid to flow into the LPR thus maintaining the liquid level.

If this problem as you describe it is occurring all of the time, then the hand expansion valve is too far open. This increases the amount of liquid flow that can be admitted into the LPR at any given time.

During this time of high liquid flow, the flash gas volume also increases. This can cause the suction and discharge pressure to rise (or other compressors to start for a short period of time).

A very good way of reducing this problem is to replace the hand expansion valve with an electronic motorized valve from either Hansen or Danfoss.

This valve is controlled by an electronic level controller, which would also have to be installed on the LPR.

With this arrangement, the liquid feed is ON all of the time when the system is operating. This reduces the large volume of flash gas and tends to minimize the suction pressure spikes.

If the pressure spikes are occurring after defrost when you are trying to re-fill the evaporator coils, then you need to slow down this process by adjusting the controls.

LPR's do NOT like large sudden load changes as this can lead to flooding of the compressors with large suction pressure reductions.

[gproud]

NH3LVR and US Iceman:

Sorry I was so long posting a reply, 12 hours a day 7 days a week night shift will do that. I managed to find a bit of time tonight.

We did as suggested by US Iceman and closed up the hand expansion valve to the LPR until it was feeding most of the time, 75-85%. Under load the LPR stays filling and runs about 16-18%. As NH3LVR said, "This is the key," and it has worked wonders. We now have very minimal loss, if any, of temperature and pressure.

I do appreciate the time both of you took to post on this, thanks. It's great to have a way to bounce some of these things off people who have had more experience

Gordie

[NH3LVR]

Glad we could be of help.
It is nice to be able to remedy a problem in such a timely fashion.

[US Iceman]

That was an easy one Gordie.

Glad to be of service!

[smpsmp45]

It is interesting to see that some typical problems can be solved by this forum by just posting the issues. US Iceman & NH3LVR could pin point the issue in no time. Great