Evaporator condenser winter issue

[hladotech]

Dear speculators,

I've faced some strange evaporative condenser behaviour at cold ambient conditions - sudden head pressure growing and falling.
Look at diagramm: compressor power goes down but pressure is still.
Have any ideas?
15086

(it is the only condenser in ref. circuit)

[redroge]

Fan(s) cycling?

[Segei]

Pressure increase can happen because of wind force and direction change. Significant pressure drop is water pump cycling. This is another prove that wet operation of the evaporating condenser much more efficient than dry operation.

[RANGER1]

hladotech,
On trend page it is showing discharge pressure & % loading of compressor.
Discharge pressure ranging from 19.1 bar to low of 5.6 bar when unloaded.

Could be a number of issues

1/condenser fan/pump control
2/control overshooting
3/evaporator starving of refrigerant
4/system low on refrigerant
5/condenser filling up with refrigerant
6/when compressor unloaded it may not pumping

The list goes on.

What refrigerant is being used?
How does this system work, give us a description.

[hladotech]

Dear replyers,

Thanks for reaction!

About system:

15087
- compressor is slide loading
- water pump cycling strictly avoided
- cond. fan is VFD driven
- piping is done in accordance to B.A.C. manual except receiver gas equalaizing (cond. pressure always above temp. in machine room)
- refrigerant is 507a
- 5.6b at trend is OFF
- slider unloading is set for 18.8b (once I've changed it to 20b it reaches very quick)

Refrigerant charge starving can't affect high pressure. Evaporation is in range and superheat is good too.

Wind can't affect:

15090

*- two cond.=two chillers

Once again: it starts to trip in cold ambient (close to 0*C), also it could be just coincedence...

[RANGER1]

Dear replyers,

Thanks for reaction!

About system:

15087
- compressor is slide loading
- water pump cycling strictly avoided
- cond. fan is VFD drivenhat what is vsd setpoint? would expect discharge pressure a lot smoother
- piping is done in accordance to B.A.C. manual except receiver gas equalaizing (cond. pressure always above temp. in machine room) can you always see a level in it?
- refrigerant is 507a
- 5.6b at trend is OFF what do you mean by this?
- slider unloading is set for 18.8b (once I've changed it to 20b it reaches very quick)Is this for high amps (current limiter) or what causes slide to unload.
Refrigerant charge starving can't affect high pressure. Evaporation is in range and superheat is good too. without knowing anything about your system, thought refrigerant could bank up into condenser causing high pressure.

Wind can't affect:

15090

*- two cond.=two chillers

Once again: it starts to trip in cold ambient (close to 0*C), also it could be just coincedence...

What do you think is wrong with system as we can only speculate!

[hladotech]

Ranger1,

- VFD to 15b
- I can't say about level at that moment
- 5.6b is stand-by pressure (cmp. is off, pressure measured at cmp.)
- slide unloaded by high pressure limitation
- what should I observe at evaporation in case of refrigerant banks up?

thanks

[RANGER1]

Ranger1,

- VFD to 15b
- I can't say about level at that moment
- 5.6b is stand-by pressure (cmp. is off, pressure measured at cmp.)
- slide unloaded by high pressure limitation
- what should I observe at evaporation in case of refrigerant banks up?

thanks

I wa suggesting check refrigerant level in liquid receiver, as level
should alway be visible in sight glasses.
Makes me wonder if air in system, has any maintenance been carried out recently?

[Segei]

I agree with Ranger1. Most likely air in the system prevent free draining of liquid refrigerant from evap. condenser. Monitor liquid level in HPR.

[hladotech]

Dear colleaques,

Thank you for an answers. I'll try to check SG issue next time it appear.
But it is hard for me to understand:
- this issue happened at cold ambient conditions, air affecting strictly at cold?
- how air could enter in pressurized circuit, also suffient vacuuming was performed at start-up
- I'm new to E-Condenser, I used to deal with air condensers and HFC, not ammonia. So we perform system as we do it usually with A-cond. and HFC. Are they really so different to drain, air entrance, liquid bank up?

[hladotech]

Another one: how will evaporator reacts on low refrigerant (I could try to check low level indirectly by evaporator's behaviour log)?

[mbc]

Hi
it happen when in our discharge pipe from compressor to collector of condenser we have liquid our oil and it blocks our pipes .

why it’s happen?

if our slope pipe from compressor to condenser is wrong or we had loop in our piping
I saw your piping looks like me you have loop on your system
you have horizontal pipe (No.1) inlet then vertical goes up(No.2) then horizontal pipe to condenser (No. 3)
to solve that put check valve near condenser inlet((between 2&3)) ( angle SCA 40 our in horizontal pipe in inlet of condenser in 3 )

[RANGER1]

hladotech,
If you are sure no air in system then try to stabilize system by holding compressor at example 25%.
Also hold condenser fan at a speed to control discharge pressure at suitable pressure.
Observe operation, is it stable, if no maybe air or refrigerant levels not correct.
If stable, maybe controls to load compressor to fast &/or condenser fan to slow to control pressure, overshooting set point.
If you can manually stabilize system, then you should be able to make adjustments to controls to do the same.
Plant pull down load could also be a factor if load very high.
Slowly load compressor to allow for pull down of product cooling.

[Segei]

Significant difference between performance of air condenser and evaporative condenser is subcooling. Properly designed and operated evap. condenser doesn't subcool liquid refrigerant. Liquid refrigerant should freely drain from condenser to HPR. In your case saturated refrigerant temperature should be 35-40C. If condenser hold liquid refrigerant, temperature will be significantly lower.

[hladotech]

Dear colleqaues,

It's happened again and I check ref. level at HPR SG - it is OK (full with ref.).
And one more point: we have two simillar units at one plant and they are acting same with that issue...
So it can't be air and can't be ref. charge.
Also we have precies capacities PID control for all driven equipment.
It is very strange creation that E-Cond....
We are not newbie in refrigeration except of E-Cond...

There is my piping (vertical leg is about 5m):

15093

New issue trend at second unit:

15094

It looks like Ranger's point about fast loading...but it is not so fast as for me...anyway...

[mbc]

Hi
as I wrote before you have lope on your discharge pipe and also you have to put equalizing pipe between condenser and receiver tank to help draining refrigerant to receiver in off time and running time
also it help you when your receiver stay in warm area ( warmer than condenser )

check slope of pipe on discharge line

Could you put photo of pipe between compressor and condenser Please

[RANGER1]

hladotech,
As MBC says equalizing line from liquid receiver to discharge line required usually if more than one condenser.
Alsp P or S trap on liquid drain of each condenser which has to be installed correctly as well.
Example in link is for ammonia, your refrigerant distance between outlet of condenser & P or S trap height will have to be calculated, or will not work.
Equalizing line also correct size important, can't be to big, but can be to small.

https://www.evapco.com/sites/evapco.com/files/2017-05/131A.condensers_piping.pdf

[hladotech]

As I said before there is only condenser in one circuit. These two units are separated.

As I said before cond. temp. is higher then machine room so there can't be evaporation in receiver and no need to equalization.

As I said before I did all in accordance to Evapco's and BAC's manuals.

Using numbers of air condenser over 1MW each we have never faced such problems and nobody ever performs 0.5 m/s drain line as well as a kind of some equalization for the air condenser.

[hladotech]

mbc,

E-C is self-drained as it has sloped pipes in exchanger's bundle. Draining at OFF is not a problem at all.

There is no traps in my piping and no blockages:

15095
the rest of layout you can see praviously attached.

[mbc]

Hi hladotech

in your photo
you have horizontal pipe (No.1) inlet then vertical goes up(No.2) then horizontal pipe to condenser (No. 3)
and your check valve lower than in let to condenser inlet pipe
so oil and liquid ( gas become liquid at around pipe when it goes to condenser ) block the discharge pipe

To solve that you have 2 option
1 ) put check valve (angle type) between 2 and 3
2 ) put 2 pipe in discharge ( S=S1+S2) S1= 1/3S & S2=2/3 S
15097

[RANGER1]

Maybe you need to install a few pressure gauges if you have access points to see any pressure differences in discharge side of system.
You could also temporarily vent off top of liquid receiver to suction of side of plant to simulate balance line.
If it helps, then consider balance line, as MBC say's liquid receiver may reject incoming refrigerant due to it being warmer.
Also a temperature trend on liquid drain of condenser to see if temperature change coincides with high discharge pressure.

[hladotech]

Thank you all,

I have service point access after check valve at vertical leg. So next time it'll appear I connect gauge to see what happens and thus I could check MBC's supposing about blockage at N-R valve.