Low Discharge Superheat Alarm in McQuay McEnergy 143.2 Chiller

[ishtiaq ahmad]

At 100% load the operating parameters of both circuits of McQuay McEnergy 143.2 Chiller is as under

Discharge temperature 46.8 deg.cent
Discharge superheat 1.2 deg.cent
Evaporator pressure 1.7 bar
Evaporator temperature -1.5 deg.cent
Condensing pressure 10.8 bar
Condensing temperature 45.3 deg.cent
Pressure drop across filter dryer core = 5 PSI which is within the range of 50 KPA as per manual l

It is observed that after sometime the discharge temperature and discharge super heat decrease gradually at 100% load. The discharge temperature decreases to 41.7 deg.cent when the condensing temperature is 43.6 deg.cent and the discharge superheat becomes 0 deg.cent. The chiller trips showing low discharge superheat alarm.

Some bubbles are seen in the liquid line sight glass and sweating is also observed on the compressor side.

Kindly advice about the remedy of above fault.

[nuwanchamara]

Check The DH TEMP Sensor Calibrated it ..... & Check may be Liquid coming to compressor ...

[goshen]

Hi
i would assume you are using R134a , at 100% load you are running low ! 2.2 bar is more like it .
check your txv or exv , and messure with a external thermometer to verify your temp sensors are ok .
good luck

[ishtiaq ahmad]

Hi
i would assume you are using R134a , at 100% load you are running low ! 2.2 bar is more like it .
check your txv or exv , and messure with a external thermometer to verify your temp sensors are ok .
good luck

We are using R134a. Discharge temperature sensor of both circuit shows temperature of 54.2 deg.cent with the heaters in ON condition. When sensors were taken out and kept in ambient temperature they were showing identical reading of 36 deg.cent. Pressure at the outlet of thermostatic expansion valve was checked and found to be 67 PSI which corresponds to refrigerant temperature of 19.76 deg.cent. with reference to pressure/temperature chart of R134a.

Kindly advice in the light of above as to which component of refrigerant circuit is faulty.

[goshen]

Hi
again check your ref charge!
a warning like the one you get is ment to prevent liquid carry over !
what is the ambient temp?
if this unit is a screw and you have a liquid injection system check the settings and make sure your not pumping liquid into the compressor to early !
these air cooled units usually run discharge at 60-70 degc
www.aircool-de.com/downloads/US_McEnergy.pdf
good luck !

[ishtiaq ahmad]

Hi
again check your ref charge!
a warning like the one you get is ment to prevent liquid carry over !
what is the ambient temp?
if this unit is a screw and you have a liquid injection system check the settings and make sure your not pumping liquid into the compressor to early !
these air cooled units usually run discharge at 60-70 degc
www.aircool-de.com/downloads/US_McEnergy.pdf
good luck !

Thanks for your prompt advice. The ambient temperature is 30.2 deg.cent. and the chiller is screw type. The liquid injection system is provided in the chiller. It is set to operate at the discharge temperature exceeding 85 deg.cent. We have checked that the liquid line solenoid valve is not energized as the discharge temperature is 46.8 deg.cent.
In the defective chiller the discharge temperature at 100% load = 46.8 deg.cent. and the discharge superheat is 1.2 deg.cent. The condensing temperature is 45.3 deg.cent. However, in this chiller the discharge superheat gradually decreases to 0 deg.cent. at 100% load after some time. The evaporator pressure = 1.7 bar and evaporator temperature = -1.5 deg.cent.at 100% load after run of chiller for some time.
In OK chiller the discharge temperature at 100% load = 80-85 deg.cent. and the discharge superheat = 35-40 deg.cent. Condensing temperature is 46.6 deg.cent. The evaporator pressure = 2.4 bar and the evaporator temperature = 4.8 deg.cent.
The refrigerant charge in defective chiller and OK chiller is same. The compressors of both the chillers are drawing current of 145 amps.
The liquid line sight glass of defective chiller has some bubbles. The pressure drop in the filter dryer core of this chiller at 100% load = 5 PSI (within the limits of 50 KPA as given in the manual). There is sweating on the compressor side.
The liquid line sight glass of OK chiller is clear and has no bubbles. The pressure drop in the filter dryer core of this chiller at 100% load = 3 PSI. There is no sweating on the compressor side.
Kindly advise as to which component of the refrigeration circuit is faulty.

[goshen]

Hi
the more you discribe it, it would seem your txv is defective!
your pressure and temp is to low!
good luck

[gipair]

1 . May your suction temp sensor have damage and the exv calculate wrong suction superheat ... so the exv opens too much and you have liquid at the compressor .
2. Poor water flow at the evaporator or the system have too much oil - check the oil level - may you have oil in the evaporator .
3. Too much refrigerant ...check subcooling

[moideen]

Discharge temperature depends on suction line temperature. When suction line temperature is down discharge temperature also going down. Look your evaporator temperature is -1.5c. Tell me what your chiller in/out temperature is, suction line temperature, and check the water flow also.:cool:

[jason09]

check ur chilled water flow,pressure drop

[ishtiaq ahmad]

Mr.moideen mail dated 1/9/13 refers
chiller IN Temp = 11.7 degc
chiller OUT Temp= 8.1 degc
water flow thr Evaporator= 250 Gpm after water balancing
Delta p across Evaporator= 4-5psi
suction line Temp not shown on Display
kindly advise Remedy of Low Discharge super heat alarm

[moideen]

Mr.moideen mail dated 1/9/13 refers
chiller IN Temp = 11.7 degc
chiller OUT Temp= 8.1 degc
water flow thr Evaporator= 250 Gpm after water balancing
Delta p across Evaporator= 4-5psi
suction line Temp not shown on Display
kindly advise Remedy of Low Discharge super heat alarm

Recheck your water flow rate. By considering your chiller model,McQuay 143.2 ,it is around 142 ton capacity at ARI condition. Then it is required water flow rate is 340 gpm. your current flow is 250 gpm. Increase the water flow rate after checking with your design data and manufacture.

[ishtiaq ahmad]

As per Mcquay operation Manual,water Flow Rate for Mc Energy 143.2 chiller for 5psi pressure drop is 17litre/sec which comes to about 250 GPM.Further primary pump is of 240 GPM.Also 3Nos other chillers of above Model have the same Flow Rate without Low Discharge super heat alarm.Discharge /oilTemp of circuit#2 of the chiller in OFF condition is 44 degc,same as in o.k chiller.Filter Drier core also changed.Display shows that there is no signal on the Liquid injection solenoid valve(set to open at 85 deg c) for opening it.pls advise Remedy of above Fault and the Method of checking TXV Y943 OJE-CP60

[ishtiaq ahmad]

Do you mean by Suction Temp sensor the sensor of TXV connected to compressor suction.How to check that sensor of TXV is o.k water flow at Evaporator is 250GPM and pressure Drop across Evaporator is 4-5 psi.oil level is in the Middle of compressor sight glass.What do you mean by Sub-cooling and how to check it

[moideen]

Mr Moideen mail dated 12oct13 11.01AM in Reply to my mail dt 1 Sep13 Refers

As per Mcquay operation Manual,water Flow Rate for Mc Energy 143.2 chiller for 5psi pressure drop is 17litre/sec which comes to about 250 GPM.Further primary pump is of 240 GPM.Also 3Nos other chillers of above Model have the same Flow Rate without Low Discharge super heat alarm.Discharge /oilTemp of circuit#2 of the chiller in OFF condition is 44 degc,same as in o.k chiller.Filter Drier core also changed.Display shows that there is no signal on the Liquid injection solenoid valve(set to open at 85 deg c) for opening it.pls advise Remedy of above Fault and the Method of checking TXV Y943 OJE-CP60

dear isthiaq,
Could you send me the selection data of your chiller? I have a question that the chiller flow rate calculation is tons*24/delta T. then you required 142*24/10f=340gpm.whatever your pressure drop it depend on the capacity of primary pump. If the water flow rate is increasing or decreasing from the limit, it may reduce the evaporator temperature. As you write your evaporator temperature is low (-1.5c) considering the chiller entering and leaving temperature.

[MayankBhatia]

you should Check your refirgerant charge.As your Evap pressure is very less.Also Check for EXV/TXV defective?

Do let us know the result

[mark957]

Low superheat, check the transducer and temperature sensor driver you
of the expansion valve, and verivicare the proper operation of the driver and the valve

[RusBuka]

Lol.
Don't confuse low superheat and low discharge superheat. Often that error say, "Damn, I feel sick, at low load liquid ***** come back to compressor from evaporator"

[mark957]

The low suction superheat with return of liquid gas to the compressor determines in 90% of cases a low superheat discharge, please

[RusBuka]

Dont forget eco and liquid injection. ..

[nike123]

If there is not enough heat load at evaporator, there cannot be enough suction superheat, and consequently, enough discharge superheat.


chiller IN Temp = 11.7 degc
chiller OUT Temp= 8.1 degc
water flow thr Evaporator= 250 Gpm after water balancing

By my fast calculation
11.7-8.1=3.6K
250GPM=cca 20l/s=68.2m3/h = cca 68200kg/h
68200*1,16*3.6=284803Wh of cooling cappacity wich is 2/3 of nominal 500kWh capacity.

Therefore, you are not having enough load to boil all of refrigerant at full compressor capacity.



Check again calculation of required water flow at evaporator for 100% capacity. Also, evaporator could be fouled with limestone. Therefore, it should be measured all required system temperatures and temperature differences, to make correct diagnosis.

Check evaporator approach temperature difference which should be around 5K (1 pass evaporator) at correct flow and 100% step of capacity of chiller.

In a 1 pass evaporator, approach should be 5K to 7K.
In a 2 pass evaporator, approach should be 3K to 5K.
In a 3 pass evaporator, approach should be 1.5K to 3K.

Evaporator approach is the difference between evaporating temperature measured at the well in the evaporator, and leaving chilled water temperature.

11064

[sachinp747]

hi i have mcquay chiller MNG105.2 HA ST model im facing problem for both Circuit A & B, Circuit A showing Alarm AL:E01 Exp A not recognized & Circuit B is Low Ambient tepm start up failure & with AL:206 Low Pressure Alarm #2 what the reason and how to remove this alarm