RE: NH3 Refrigeration System Piping

From: <Steve>
Date: Fri Aug 13 2004 - 07:29:00 EDT

Hi Gerardo
I have looked at the sketches you sent Paul where is the pump?
Are you hoping it will work through natural convection? Have you worked through this?
If so, you will need to ensure the PHE discharge line is close to below the accumulator.liquid level.
As drawn, it is no surprise you have problems. Can you raise the accumutator or lower the PHE? For a wet evaporator, it doesn't stand much chance of working as drawn.

Cheers

Steve

-----Original Message-----
From: Paul Bowers [mailto:pbowers@pipingdesign.com] Sent: Friday, August 13, 2004 2:38 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] NH3 Refrigeration System Piping

Gerardo sent some drawings of his system and I've uploaded them to the website. I don't know if this will explain the situation any better or help to find a solution:

http://www.pipingdesign.com/drawings/Ortogonalviews.JPG http://www.pipingdesign.com/drawings/isometrico.JPG

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Paul: I am sending you the drawings of the unit that I am having problems with. This unit doesnt have the same performance (it is like 30% less
performance) than others who are practically the same (same compressor, same acumulator, same condenser and same evaporator). The 02 diferences that this package refrigeration system (PRS) has are: The piping arrangement from the heat exchanger to the acumulator (return line)
The height of the heat exchanger, the evaporator is 4" higher.

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Gerardo sent:

People of Piping design: I am writing to you because I have some doubts about an instalation of a flooded refrigeration system with ammonia. The main problem seems to be in the pipe arrangement of a flooded evaporator
(plate evaporator). It is a package for cooling Glycol. This client of
mine has a lot of this package refrigeration systems and one of them does not have the same performance than the others who are practically the same design. One of the diferences is on the return line of the evaporator to the suction acumulator. This reurtn line goes above the control level of liquid like about 5". The plate heat exchanger is about 10 feet away form the acumulator, and the return line from this heat exchanger to the accumulator goes up from the heat exchanger to obtain a 2% inclination to the acumulator. Which means that when the equipoment is off, the liquid entraped in this line will go to the accumulator. Since the equipment doesnt have the same performance as the other package inastalled in my client plant. We think that the fact that this line has to go up in order to achieve the 2% inclination has something to do with the performance. What are your thought regarding this matter.

Steve answered:

have you checked to see that the plate evaporator is not filled up with oil? This is more common with CFC type refrigerants but can happen occasionally with ammonia., especially if the vertical pipe is oversized
(the oil runs back down the pipe). Have you checked that your
circulation pump is working properly? It may not be producing enough head to overcome the evaporator resistance and push the gas/refrig/oil mixture back into the accumulator. I am not convinced you need 2% fall on the return line; the gas/ refrigerant mixture should sweep it clean.

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