Fans and EXV hunting on McQuay chiller

[nicolacozma]

Hello,

During commissioning of an ALS F SE 296.3 McQuay chiller I notice that the opening of the EXV has an important variation in a short time. The superheat also have a major variation. Also I notice that this variation is linked with fan step changes.
Commissioning was performed at 5 degree outdoor temperature, and I suppose that is the reason for this behavior.

Colud be other reasons for this phenomena?

Thanks in advance for your opinions.
Nicola

[Brian_UK]

How do your commissioning result compare with the manufacturers control logic and design operation?

[nicolacozma]

I ask for an updated settings list and I check all the manufacturer parameter. All parameters are OK.

R134
Outdoor temp 5 degree
Setpoint temp 10 degree
LP 2.5bar
HP 10.8bar
superheat 6.4 degree
subcooling 7.2 degree
EXV opening 2430pls
LWT 14 degree
RWT 16 degree
Compressor load 100%

When the fan stage-up at 11.5 bar then HP goes down to 8.2 bar and EXV opens to aproximative 3300pls. All these changes happends during 10 sec.

All 3 circuits have the same behavior more or less.
Hope this info could help to understand better this behavior.

Regards,
Nicola

[nike123]

What is used controller and EEV driver?

[HallsEngineer]

its a carel EXV driver and yes this does happen due to the fact that the duty of the valve drops when the DP drops. I would say change the superheat to 5'c to get better performance. there is not a problem with this change in duty as the valve is doing its job and keepin the superheat constant as possible. I would also change the condenser fan settings possibly a higher setting with a good differential to stop short cycling. It sounds as though you have many steps overlapping.

[nike123]

Could you post parameters or send by mail if you don't want to go public with them?

[TXiceman]

I presume the fans youa re talking about are the condneser fans.

Sounds like you have the band on the condenser fan control set too tight and have fans banging on and off too often. Every time a fan cycles, it sneds the cond pressure the other way and the EXV flow changes. The dP across the valve increases and the flow goes up, the superheat down and then back the other way. The valve never has a chance to settle down.

Increase the band on the condenser controls and let the discharger presse float up and down slowly, rather than bang off, bang on and bang off. This should settle down the system and giver the EXV a chance to control and settle down.

Ken

[nicolacozma]

I`m sorry but it`s difficult to put on this reply 63 parameters.

Yes there is a Carel EXV driver with an Danfoss EXV.

The fan steps are: 10/1.5bar , 11/2bar, 12/2.5bar, 14/3.5bar (Setpoint/Diff).

Do you have another stageup limits in order to avoid the fun hunting?

Thanks
Nicola

[nike123]

I`m sorry but it`s difficult to put on this reply 63 parameters.

Thats why I told that you could send me by mail.


Yes there is a Carel EXV driver with an Danfoss EXV.
Did you checked his parameters! Especialy "proportonal gain"

Proportional action (P), defined by parameter K = proportional gain.
The proportional action opens or closes the valve by K steps whenever the superheat increases or decreases by 1 °C.
Consequently, the higher the value of K, the faster the reaction of the valve to variations in the superheat.
The proportional action is fundamental, as it affects the speed of response of the valve in general, however it only
considers the variation in the superheat, and not the corresponding set point.
Therefore if the superheat does not vary significantly, the valve will essentially remain steady and the superheat set
point may not be reached.

The fan steps are: 10/1.5bar , 11/2bar, 12/2.5bar, 14/3.5bar (Setpoint/Diff).

Do you have another stageup limits in order to avoid the fun hunting?

Thanks
NicolaNo, I just wanted to study yours.

This is from Carel EEV controler manual:


8.3 Recommended parameters
Below are the most suitable values of the parameters for each application and specifically for CAREL valves. If
valves made by other manufacturers are used, the same recommended parameters can be used initially, modifying
the “Proportional gain” based on the maximum number of control steps for the valve installed.
Example of adapting the proportional gain for the different valves
Reference:
CAREL E2V (480 maximum control steps), proportional gain = 5
→ Sporlan SEI - 1, (1596 steps), proportional gain = 5 x 1596 / 480 = 16
→ Alco EX-5 (750 steps), proportional gain = 5 x 750 / 480 = 8
The following tables also show a specific category called perturbed system.
Perturbed system defines a refrigeration unit in which the condensing pressure and/or the refrigerant charge vary
continuously and rapidly. The superheat can also vary when the subcooling is low or null (critical refrigerant charge)
and the superheat set point is less than the value specified in the tables or low in general.
In a perturbed system, the control variables (superheat and evaporation temperature) vary significantly, however not
due to the electronic valve, which consequently must have more intense reactions to be able to keep the superheat
around the set point. Obviously, the more perturbed the system, the lower the probability of achieving a stable
superheat.
control

I uploaded manual here (http://www.mediafire.com/?4lgydjezje1).

[TXiceman]

The manufacturers settings are a starting guideline in my opinion. You really need to tweak the settings based on YOUR system and application. So, I'd start by spreading them just a bit and see it improves.

it is quiet possible you have a defective EXV though.

ken

[psycho]

lots off very technical solutions and dont want to imply that you dont know wat your doing but have you got a full refrigerent charge on each ciurciut? i know its probably the first thing that you checked,but low charge would give you them symptons and new mquay chillers ( had a similar als and found not 63 kg 134a in cuircuit but 32,or even 14! at the commissioning stage too

[psycho]

yeah new chillers leave the factory with the correct charge but develop leaks in transit , Do you have any fans on inverters? selpro's or intea's,look for correct wiring and pot settings iff so, wouldnt really expect fan steps too eratic with those in /out water temps at that ambiant with correctly operating fan inverters. you can check your 0-10vdc to inverters on the carel (y outputs) .switch off a couple off fans via o/l's and prove inverter's by looking for increase in fan amps etc

[Marc O'Brien]

You say your saturated condensing temperature is fluctuating between about 40 dC and 36 dC?

What is your saturated evaporating temperature fluctuating between and of course what is your superheat fluctuating between?

The subcooling you read, where is that taken? Immediately after the condenser before any other components?

Need to see a little more info before considering yet if there is even a problem. I've Factory Tested 16 chillers at McQuay's factory in Rome and initially what you describe doesn't immediately sound like a seriously radical problem except that improvements may be possible by adjustments to the fan settings and algorithms.

You should only consider altering the EEV parameters once you have satisfactorily stablised liquid line pressures and subcool.

Call the McQuay factory in Rome and speak to Marco or Lazio from the sales and chiller testing department - if you give them the model and serial they can help with the minimum ambient design data and make suggestions if necessary.

[Marc O'Brien]

yeah new chillers leave the factory with the correct charge but develop leaks in transit

Or the fan signal wires are crossed so that compressor 1 is driving compressor 2's fans etc. Had this once but it wasn't a lingering problem - it was immediately obvious.

[nicolacozma]

Hello,

I will try to play a little bit with all parameters that you have told me.
I will turn back on site as soon as the outdoor temperature will rise more than 10 degrees.

Thanks for all your replies.

Thanks nike123 for Carel EEV manual.

Regards,
Nicola