hunting expansion valve on airedale c/control

looking for some advise on an airedale close control (df65adat) ahu with 2 dx condenser (cus10ehi) serving a computer room

i just cant get the superheat to settle , the problem with hunting valve is on both circuits , i have listed operation details below,

air on condenser = 22c
air off condenser = 35c
compressor amps = 16 amps per phase
disharge pressure =18 (head pressure control fitted)
discharge pipe temp = 78c
suction pressure 3.2 bars to 6 bars
subcooling out off condenser 2 to 11c (no liquid reciever fitted)
subcooling before expansion valve
air on ahu = 25c
air off ahu = 13c (2 condensers running)
60 metre pipe run from condenser to ahu
filter all clean,belts checked , good air flow


superheat at the ahu 0 to 24 c, running within this range every 2 to 4 minutes

this systems has carel electronic expansion valve and is controlled via the airedale main controller
according to the main control the correct valve to set up and superheat is set to 6c

any help or advise on this would welcommed

thank you

Where is EEV temperature probe placed?

hi nike123
the suction transducer and pipe tempeture sensor are fitted on the suction line coming out off the evap ,
transducer is reading correct and
the pipe tempeture is also reading correct and is tightly fixed

thanks

Quote:

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Originally Posted by knight rider

hi nike123
the suction transducer and pipe tempeture sensor are fitted on the suction line coming out off the evap ,
transducer is reading correct and
the pipe tempeture is also reading correct and is tightly fixed

thanks

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On what hour of pipe is sensor? What is pipe diameter. Is it placed near object of large mass (4-way valve or simmilar)? Is it placed at horizontal portion of pipe?
Where and how is pressure transducer placed?
Does this problem is from day one or something which occurred after unit is normally worked?

unit has been installed 4 years , picked up this hunting valve on a maintence check
cooling only unit transducers is fiited horizontal ,the sensor is clampped on top off the pipe , the sizie off suction pipe is 1 and 3/8 inch
compressors have ran 18,000 hours each

Quote:

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Originally Posted by knight rider

unit has been installed 4 years , picked up this hunting valve on a maintence check
cooling only unit transducers is fiited horizontal ,the sensor is clampped on top off the pipe , the sizie off suction pipe is 1 and 3/8 inch
compressors have ran 18,000 hours each

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For that pipe size ensor should be fitted at 4Hr 30 min or 7Hr 30 min.

http://farm4.static.flickr.com/3603/...784fe4_b_d.jpg

If you want faster response sensor should be instaled in socket.

http://farm4.static.flickr.com/3579/...85d087_o_d.png


Do you have enough load!

Quote:

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Originally Posted by knight rider

subcooling out off condenser 2 to 11c (no liquid reciever fitted)
subcooling before expansion valve

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What does this mean? Is the subcooling 2C or 11C? Measured at the condenser or the expansion valve?

Quote:

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Originally Posted by knight rider

disharge pressure =18 (head pressure control fitted)
suction pressure 3.2 bars to 6 bars

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Pressures are meaningless if you don't tell us what refrigerant is in the system.

Hi mo

On Airedales the main reason for hunting on the EEV is flash gas at the valve:

Is the sight glass full ?

Does the unit have a pressure transducer to operate the condenser fans?
if it has, It is normally set for 14Bars this would be for R407c refrigerant.

With 60m seperation you may have to look at the discharge and liquid pipe sizes ?

Regards Bob

Quote:

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Originally Posted by Gary

What does this mean? Is the subcooling 2C or 11C? Measured at the condenser or the expansion valve?

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I would say that as valve hunt that in condenser liquid level is changing and therefore subcooling also hunt! Or I am wrong?
Or he has fan on-off control and that is cause of subcooling change and valve hunting.
Yep, I checked:

Quote:

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disharge pressure =18 (head pressure control fitted)

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Could be because of way on which head pressure is controlled.

hi guys

nike123 you are correct in saying the hunting valve does cause the subcoling at the condenser to go from 2 to 11c , due to the expansion valve closing down the liquid refrigerant back up the liquid line , the condenser fan moter is control via a condenser fan speed controller which is set to 17bars ,

sorry gary the gas is r407c

bob , the system does have a pressure transducer in the ahu which in turn controls the condenser fan moter at the condenser , this is set to 17 bars
the sight glass is clear ,but will flash for around a minute while the valve fully open ,liquid line is 7/8" pipe run is 50 metres


does any one have a service manual for the airetronic controler , give parameter settings

thanks

Is your electronic valve driver controlled by unit controller or is independent?
You should check parameters of valve driver!
You cannot do that without Carel software (which is downloadable) and interface.

Check this guide:
http://www.mediafire.com/?4lgydjezje1

Quote:

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Originally Posted by knight rider

looking for some advise on an airedale close control (df65adat) ahu with 2 dx condenser (cus10ehi) serving a computer room

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If I understand this correctly, there are two complete systems with the two coils serving a single AHU. Is this correct? What happens to the superheat if one of the condensing units is shut off?

In general, hunting indicates that the orifice is too large for the load or that the load is too small for the orifice. The evap dT is 12K/21.6F which indicates a fairly normal load and certainly not a high enough dT to make the valve hunt. But then, one would think that an EEV could compensate (unless it is grossly oversized). So that probably leaves us with control/sensor problems.

Quote:

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Originally Posted by knight rider

60 metre pipe run from condenser to ahu

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Is there a difference in elevation?

hi gary

1) there is 2 metre height diffence between ahu and condenser
2) you are correct in saying there are 2 circuits serving 1 ahu
3) i will switch off one circuit and monitor the running condition later on today
4 ) the tempeture sensors and transducers are reading correctly , i have checked these against calibrated instruments


nike :the main air conditioning controller (Airedale airetronix) controls a driver which in turn controls the eev


thanks

Quote:

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Originally Posted by knight rider

2) you are correct in saying there are 2 circuits serving 1 ahu

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Now, with this information, we have something else to consider. That is interaction between those two circuits. Do you have refrigerant diagram of that unit to post here?

Is this correct diagram for your system?
http://farm4.static.flickr.com/3645/...be7350_o_d.png

Also, you said that head pressure is controlled at 17 bar and here it is stated different (as Pingo pointed):

Quote:

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Head Pressure Control - Intelligent
As an alternative to the stand alone head pressure control fitted to the Condensing Units or condensers, the system can be fitted with a voltage regulating fan speed controller which allows set point adjustment and system monitoring via the indoor unit microprocessor controller.
Units fitted with optional electronic expansion valves have the head pressure factory set to 14 Barg (203 psig).
For further details please refer to the Indoor Section, General Description

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Quote:

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Originally Posted by knight rider

nike :the main air conditioning controller (Airedale airetronix) controls a driver which in turn controls the eev


thanks

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If evaporator pressure transducer is connected to Airedale controller and than control signal is sent to EEV driver than it could be problem with signal sent from main controler to EEV driver.

Note in Nike's diagram that the suction line leaving the evap goes down into a trap and then up into a reverse trap. This arrangement traps liquid refrigerant in the coil during the off cycle thus preventing floodback on startup. This is especially important where the compressor is lower than the evap.

Also note that the sensors are mounted after the reverse trap, so that they cannot sense trapped liquid.

hi nike
the diagram posted is correct and is the same manhine i'm working on
i will drop the gead pressure from17 to 14 bars and monitor

hi gary
i switched off one condenser let it run for an hour and found
air on 26c
air off18c
superheat controlling 10c to 11c

as pingo advised , these systems need the refrigerant charge to have been calculated , taking into account the pipe size and run , condenser size and ahu size ,
i have calculated,and the charge should be 27.5kg , i may need to recliam gas charge and confirm if the charge is correct



thanks


thanks

after dropping the head pressure from 17 to 14 bars here are the readings taken aftern an hours run ( i am on site with my laptop connected on the internet , what technology)

readings from airetronix controller
air on 25c
air off 14c
superheat set point at 6k
superheat ranging from 2 k to 10k within 2 minutes
driver at 470
suction 5.8 bars / 11.6
liquid line 14.1 bars / 39.3
sight glass clear

readings at condenser
14.5 bars
5.3 bars
2 / k subcooling
9 / 10k suction superheat at condenser
14 amps per phase

thanks

Hi Knight Rider

Dont rule out an air flow issue, I work on a lot of these units and have seen short circulation or blockage of air causing problems like this, with the size of the units i have seen many with air return at 25c on one side of the unit and as low as 16c on the other, especially with these new blade servers that keep being installed in the rooms, so depending which side of the unit has the sensor dictates how it reacts.
sensor located on the low return temp air side unit cuts in and out on stat frequentley and room generally overheats, the other way round and it holds the unit in cooling but half the coil is to cold causing frosting or hunting.

The units DF right. so its a pressurised floor.

Most problem call outs i get with these units end up being air flow related.

1. are there floor grilles near the unit.
2. are cables under the floor blocking air flow.
3. are there enough grilles in the room to actually allow enough air flow for the unit to function, if your not sure take a few out at the back of the room and see how the unit behaves.

Just a thought, or something else to look at.

Quote:

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Originally Posted by knight rider

as pingo advised , these systems need the refrigerant charge to have been calculated , taking into account the pipe size and run , condenser size and ahu size ,
i have calculated,and the charge should be 27.5kg , i may need to recliam gas charge and confirm if the charge is correct

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If both refrigerant circuit are hunting and if they are separated, I pretty much doubt that refrigerant is leaked in both circuit same.
Nevertheless, it could be that, from day one, both are not filled with correct amount of refrigerant.
Therefore, reclaiming, weighing and calculation of required amount is good thing to do, just to be sure that refrigerant amount is not problem.

Quote:

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Originally Posted by knight rider

hi gary
i switched off one condenser let it run for an hour and found
air on 26c
air off18c
superheat controlling 10c to 11c

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The superheat stabilized with one system running?

How about the subcooling?

Quote:

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Originally Posted by knight rider

superheat ranging from 2 k to 10k within 2 minutes

2 / k subcooling

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Subcooling stable or hunting?

hi gary ,
after switching off one condenser , the superheat did seemed to be stable around 10k , with a 6k setpoint , i did not check the subcooling at that time , due to a service call on another plant , sorry

i have left the sysyem set to 14 bar head pressure ,which seems to control better on the superhet and subcooling ,sight glass clear. i will return and check over on tuesday and post an up date

thanks

posting an update

after adjusting the head pressure down from 17 to 14 bars leaving the system to run for a few days the superheat is now controlling very well at a constant 10k

one circuit was short off gas by 3kg ( total charge should be 28kg ) , small leak found on lp connection on compressor ,

air on 24c
air off 13c
both sight glass near eev clear


job done

thanks for everyone help

Thanks for update!
I am glad that you sorted it.

head pressure on airedale units with eev should be 14bar and 8 diff on close control this should make superheat more stable and check the maximum piperun is not exceeded 60m seems a lot!