Frascold Screws...Klixxon faults...

[Scooter29]

I am having grief with a system at an apple coolstore I look after. It comprises of a set of four Frascold C-TSHB 100 300 Y screw compressors with oil reservoirs incorporated to them.

The rack is being controlled with a Carel Pco controller. The two rooms are zoned and being controlled with IR33 Carels.

Room temps are great and the system seems to have heaps of capacity and works great...when it is not faulting.

The problem I am getting is random klixxon faults on the Pco from all four compressors at different times on start up.

The rooms have worked well for the last four weeks under low loadings but now with the rooms being more heavily loaded I am having the faults. During the day when the rooms are being loaded and unloaded and the comps are working hard I don't get any faults. The faults seem to appear after the days work in the coolstore has finished and the rooms have been closed up for the night. It is then that the compressors unload and drop off as the demand in the rooms drops.

I have the Pco set with a 10 second delay before registering the 'klixxon' fault and also have it set for automatic reset of the 'klixxon' faults when they occur. Sometimes the fault can be cleared on the Pco and the comp will then start up. But sometimes I can only clear the fault if I turn the control circuit off to the comp displaying the fault and then turning it back on.

The faults are random and will occur on any of the four comps. The system is running on 404a and set at a suction control pressure of 3.3bar or -10.9 degrees.

The only thing that is not quite correct with the comps is that the oil levels in all four is slightly high but that is in the built in oil reservoirs after the discharge side in the comps.

Anyone got any ideas......this is beginning to do my head in......

The apples arriving in the store have come from the packhouse in cartons chilled from another coolstore...so there is not a hell of a lot of load there.....

Thanks Scooter

[RANGER1]

Scooter29,
What type of unloading do these screws have eg steps on solonoids.
What is minimum step ie from 100 to 75 to 50% ?
Do they have a pump down that may be to long causing over heating during cycling off period?

[NoNickName]

It seems they trip on high discharge temperature or high winding temperature at low load, and this is consistent with a lower cooling of the windings at low refrigerant flow rate.
I would suggest to modify the software algorythm and use the 25% capacity only for starting, but not for cooling, or otherwise use liquid injection at low loads.
Additionally, it looks strange to me that CTSH8 are used in place of RTSH1, because CTSH are not able to equalise oil level when mounted in a pack. The C in CTSH is "conditioning", while the "R" in RTSH is for Refrigeration.

[Scooter29]

Hey thanks for the input.

The comps load in three stages. On start up capacity is at 50% with no loaders energised. Then one loader steps in to get to 75% then the second loader to achieve 100% capacity.

If all the six zones reach setpoint then pumpdown will occur. I have not seen the rooms at setpoint yet with the loads in the rooms. I checked the system last night and found two comps out on the klixxon fault...at that stage the rooms were still 2-3 degrees above setpoint. I have seen the system cycled off and all comps resting when I had only one room connected to the rack and very low loads in the room. This was achieved with only two comps running. No 'klixxon' faults appeared at that stage.

Regarding the use of the C-TSHB comps and oil balance, an oil balance balance system has been installed to the system after installation to alleviate this problem.

This is a site my company has inherited from the original company that installed it and we are finding many problems with it.

Are you saying that the C-TSHB comp is not suitable for the application it has been tasked to do...??????

Would the extra oil in the reservoirs be causing problems. I know the extra oil will hold more heat and maybe causing higher than normal discharge temps at the comps.....???????

[RANGER1]

I think you should get your hands on a data logger with continuous monitoring of
suction,discharge,oil, winding temps to narrow times etc down.

Of course pressures would be good to.

Either buy or hire one as they are a good investment.

You could also lock a compressor on 50% load & monitor it to see what happens or simulate
a few pump downs while you are on site to witness it.

Where are the klixons mounted exactly?

[NoNickName]

First of all, they are not klixons. They are kriwan INT69 motor protections, connected to three thermistors in the winding and one in the discharge.
Secondly, pump down is useless for a compressor with a built in oil separator, because the NRV is after the oil reservoir, and the oil reservoir is at discharge pressure. When pumping down, there is more difference between discharge and suction, and the screws will counterrotate much longer than with no pump down.
Counterrotation may also cause false readings in the phase sequence control of the INT69.
Finally, I can't see how oil is balanced between CTSH8 compressors, unless it is returned to the suction, which is a very bad idea (hot oil in the windings).
Definitely CTSH8 are not the most suitable compressor from Frascold for the application.

[monkey spanners]

Those Kirwan things seem to go wrong for fun, have seen lots go odd or fail completely on Copelands when they are three or four years old. If you think how many hours they have done in this time its not surprising. Might be worth trying a new one to see. NNN knows his stuff with Frascolds.

[Scooter29]

This is great info guys.

It appears that the comps are the wrong tool for the job then.......Am I on a hiding to nothing trying to get rid of these faults or is there a possible solution without breaking the bad news to the client about his incompatible compressors.....

Thanks Scooter

[NoNickName]

The compressor pack can be rectified, but it will take some tooling, money and time.
If your customer is happy with that, it can keep you busy for some time.
For sake of curiosity, where are you based? Who is the dealer that sold those compressors?
I've been with Frascold's for over two years in the after sales service, and still have some contacts, just in case.

EDIT: it's true that those kriwan things go wrong for nothing, especially now that they are being copied and sold under a similar trade name by a turkish company, selling the devices by the weight.

[Magoo]

Hi Scooter.
If all 4 machines have same fault under load, seems they are trying to tell you something is inherently wrong. Follow NNN's advise.
Do they have oil coolers? High oil temps under high load will raise the discharge and winding temps.

[Scooter29]

NNN I am in the north island of New Zealand. I don't know who supplied the system but could probably find out.

What are your thoughts regarding the mods needed to get this up and running reliably...????

I am about to go and put a set of data logging gauges on the system and try and simulate the conditions to get it to fault.

Thanks for your interest in this I appreciate it.

Cheers Scooter

[Magoo]

Hi Scooter,
the set/rack would have been built by Realcold Auckland. They would not not have fitted oil coolers is my bet. Try their applications Engineer for more info.

[NoNickName]

Yeah, Realcold is the one. I've visited them once, some time ago in 2009.

[mad fridgie]

Contact Craig Bell at Realcold (maybe one of his designs)
I think from your description you may have different kilxons faulting sometimes discharge (easily resets, short time) and motor protection (residual heat) greater time for reset.
I presume you do have defrost on these system, "electric?" this would shut down the liquid flow, maybe causing the system to pump down, even when temp is not at set point. Remove pump down control
What are your anti cycle set point limits (number of starts per hour).
Add a simple liquid injection valve, I would look at in jection into main suction to ensure correct moter cooling (unless there is a dedicated port "NNN" to confirm best option)

[NoNickName]

Liquid injection in the suction would cool the motor better. There is an eco port, but it only injects midway between the suction and the discharge, to cool the screws and reduce the discharge temperature.
Here, one would firstly need to identify what is the offending thermistor and act accordingly. Please note that thermistors repeatedly subject to high temperatures tend to deviate from their setpoint, and may trip untimely.