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Tycho
12-12-2014, 08:31 PM
Hi all

I'm looking for a list of "normal" or acceptable running pressures/temperatures for Howden XRV and WRV range compressors working on Freezing and RSW applications (NH3).

I know what is normal for both applications and I know the maximum allowable pressures and temperatures for both applications, but I have been working with a customer that has two identical XRW 204 compressor units with water cooled oil coolers, one unit has an oil temperature of 50.7 C and the other has 52.4 C, water through the oil coolers are full flowand in is 8C and water out is 9 C.

Both units are identical, and they are fitted with a danfoss ORV three way mixing valve with a thermostat set at 49C

they are saying that the oil coolers are too small and wants them replaced with bigger ones for when the sea water temperature in Norway rises to 15-17C in summer

I've been trying to tell them that the oil coolers are more than big enough, and that the 1,7 C difference in oil temperature is because of the ORV mixing valve, which has a +/- 5K operating range.

Last bit there was just a rant :)

I hope someone has a spreadsheet of normal and acceptable data for the XRW and WRV range :)

RANGER1
12-12-2014, 09:17 PM
Tyco,
Your company uses a lot of Howden screws.
I would have thought someone in your company has the HOwden selection software.
This has to have the information or each conditions you put into it to calculate oil cooler heat load & expected discharge temperature etc
I am not aware of a spreadsheet for any brand of compressor unless prior to the computer age.
If you cannot get software I or someone who has it can only put in data for each condition.

You are of course right with ORV valve as well temp sensors have different accuracy as well.
Can you also get & give design & engineering data on oil cooler to show capacity of oil cooler
under the different design water in/out conditions.
Can anything be simulated to prove acceptable.
The Trouble with these 3 way valves is that you do not know is opening position!
We have used Danfoss ICM to dial in oil temp, but of course more expensive.

Tycho
12-12-2014, 10:09 PM
We use Howden screws exclusively for medium to large applications, so we have the howden selection software, but that only gives you the size of the compressor with a given suction/discharge, the part of the calculations I have seen does not give you expected Oil temperature or discharge temperature.
I could list the expected pressures and temperatures off the top of my head :) but that would just be bragging :D

The client we are dealing with is Russian, I supervised and commissioned the plant in Croatia in November-December last year, and since the delivery was delayed, they are nearing the end of their warranty time around the 20th of this month.
Also, I have noticed that Russian clients (No offense) always feel like we are trying to trick them.

the ship has box coolers (all equipment is cooled by freshwater, the freshwater is cooled by external box coolers that work when the ship is moving) that the supplier says need 4 knots for them to work, in Croatia with a sea water temperature of 20C and the ship stationary in port we managed to keep the oil temperature
steady for 5 hours before it started rising, since the ship wasn't moving and we were warming up the stationary water around the box coolers (condensers were also a part of this heat load)

We've been using the danfoss ORV valves for 8-10 years without any problems, they are stable and work very well and keep a steady OT (there was some problems in the beginning, but danfoss sorted that out very quickly).

We use the one with the temperature at 49C, and we see that normally that will give us an OT of 49-52C depending on the compressor, with the XRV127 a 49 degree thermostat will keep the temp at 49-50, with a XRV163 it's the same, with a 204 we experience OT temperatures of 49-52...

I read up on the ORV after my original post, and it says that the valve is closed, only allowing warm oil to flow to the compressor until it is 5K below the set temperature, then the valve starts opening, and at the set temperature the valve will be half open.
if the temperature is 5K above the set temperature, the valve will be full open.

On the system I am talking about, we have a temperature difference of 1.7K wich in my mind means the valve is half way open :)

*rant rant rant*

The problem is that when talking to Russian clients, no matter if you tell them "Yes, I see that there is a temperature difference between the two compressors, but you have to consider that the second unit is farther away from the pump supplying the oil cooler, there may be differences in the ORV mixing valve, and a 1.7K difference in oil temperature as long as the temperature is within the limits of this kind of compressor at these kinds of operating pressures are perfectly normal, there is nothing we can do..."

then they will say "So, with this oil temperature now, what will happen when the temperature of the sea rises?"

And I will say: "Nothing really, that is why we have the ORV valve there, to keep a steady oil temperature no matter what the sea water temp is"

And he will say "yes, but now it is 8 degrees in the sea, what will happen when it is 15 degree in the sea?"

I say "In Croatia it was 20 degrees in the sea and we still ran the system without problems while the ship was not moving"

And here the logic sense of a Russian shipowner kicks in and he goes:

"YES! I hear you talking about Croatia, that was Croatia, we are not in Croatia anymore, we are in Norway now, it's a different place, it's not the same, the seawater temperatures of Norway is not the same as in Croatia"

I had a snappy reply to that about Norway never seeing temperatures in the sea above 15C
but I got a shoulder in the side from the project manager...

Going on board to measure the flow through the oil coolers with our Controlotron clamp on flow meter on monday..
*sigh*

RANGER1
13-12-2014, 02:01 AM
Tyco,
We recently were given a new Howden software program which I have not looked at yet but the previous program gave absorbed power, oil flow & oil heat load etc.
You could then show theoretical heatload against theoretical oil cooler design.
Ok that's theoretical, but all the same very important.
With ORV can you restrict sea water to increase fresh water temp?

I know nothing is easy especially with Russians, they like problems, excuses, reason to not pay bill.
Can you ask him what would satisfy him, probably nothing!
I did a job in Russia over 20 years ago, they are not happy unless problem, but of course this type are everywhere, but a lot in Russia.
He could accidentally disappear overboard, that could solve problem!
A gift of Vodka can sometimes help to, for him & you too.
Can you give some conditions, machine etc & I can at least look at it.

Segei
14-12-2014, 08:29 PM
I had similar issue with Amot mixing valve. Thermostatic element was gradually loosing charge and oil temperature was higher than for another compressor. Can you switch termo. elements of mixing valves for these compressors? At least this action will eliminate this issue.