Some technical questions

[Fakhr E Alam]

Hi i have some questions related to refrigeration and compressor . i work in a company and we have sabroe 128HM compressors for cold storage.

1: whats the difference between suction temperature and suction super heat, also discharge temp and super heat.

2: there is one room which give problems , set temp is 4'C while room temp stay above 6'C. there's anothor temp mention in the PLC display "duct temp" we don't have ducts. we have liquid R22 line. what's a duct temp? duct temp always stay in between 4 and 6 degree C. Is this the temp of small duct after the expansion valve which has further parallel branches in the evaporator ?

3: Does anyone has worked with the sabroe 128HM mkIII , i have problem understanding the functions of some pipe connections to the compressor.

[The Viking]

Hi Fakhr,

1. Suction temperature is the actual measured temperature of the refrigerant returning to the compressor,
Super heat (or, in case of refrigerant in liquid state, sub cooling) is the difference between the saturated temperature of the refrigerant at a given pressure and the actual measured temperature.

2. The duct temp is most likely the temperature of the air exiting the evaporator and being supplied it to the room.

:cool:

[Fakhr E Alam]

Hi Fakhr,

1. Suction temperature is the actual measured temperature of the refrigerant returning to the compressor,
Super heat (or, in case of refrigerant in liquid state, sub cooling) is the difference between the saturated temperature of the refrigerant at a given pressure and the actual measured temperature.

2. The duct temp is most likely the temperature of the air exiting the evaporator and being supplied it to the room.

:cool:

ok . but i don't get the readings on compressors electronic display. its showing suc tem and superheat at the same time . see it for yourself.

1406914070

[Brian_UK]

ok . but i don't get the readings on compressors electronic display. its showing suc tem and superheat at the same time . see it for yourself.

1406914070Yes, that is correct, the two temperatures are distinct and separate. The Viking explained them above. M

[Lundh]

So the 27,5 is the suction temperature and the 58 is the discharge temperature leaving the compressor

[Lundh]

Regarding the cold room temperature issue. Does the compressor runs continually? I think you should check a number of things to troubleshoot why the cooling is insufficient:

Suction pressure
Thermostat
If the compressor runs continually
Filter
Blocked condenser --> condensing pressure
Shortage of refrigerant

[Josip]

Hi, Fakhr E Alam :)


ok . but i don't get the readings on compressors electronic display. its showing suc tem and superheat at the same time . see it for yourself.

1406914070

Your suction pressure of 1,9 bar corespond to saturated temperature of ST -15,6*C (257,55K) from tables for R22 ... for other refrigerants is different ... UNISAB II can be set up in that way too .. to read *C/R or *F/R or bar/psi ... you need to read your Unisab manual how to set up start screen and which units you want to use .. pressure or temperature

you can download app for your computer or for your phone ... just google for ... refrigerant slider ... or click on link ... to se tables for refrigerants ...

http://refrigerationandairconditioning.danfoss.com/support-center/apps-and-software/coolapps/

https://play.google.com/store/apps/details?id=com.danfoss.koolapp

http://windowsphoneapk.com/APK_KoolApp-Ref-slider_Windows-Phone.html


.... your actual suction temperature is 8,8*C (281,95K) ... ((8,8 - (-15,6))= 8,8+15,6 = 24,4 *C,
but the right way is to say 24,4K without "degree" just Kelvin ... (281,95 - 257,55) = 24,4K

the difference between suction saturated temperature and actual temperature we call suction superheat (SSH), but should be expressed in K ... thus, always positive value even if we are completely in negative temperature expressed in *C ...


for exmaple ST=-42,5*C (230,65K) and actual temperature at compressor suction is -21,8*C (251,35K) we cannot say that SSH is ... (minus) -20,7*C ... can be only 20,7*C or simply 20,7K ... there is no negative SSH ...(SuctionSuperHeat)

all is much easier when we use absolute temperature scale .... because there is no negative temperature expressed in absolute scale i.e. K (Kelvin) ... the lowest temperature in the universum is 0K ...

... your actual discharge pressure is 11,3 bar and correspond (again to saturated temperature from tables) to 31,4*C (304,55K) and your actual discharge temperature is 58,3 *C (331,45K) .... the difference between discharge actual temperature and saturated temperature we call discharge superheat (DSH) and should be expressed in K too .... i.e. (331,45 - 304,55) = 26,9K

For problems regarding function/s of compressor piping .... please .... upload a scheme of your compressor (can be hand made drawing) and mark pipes which function you do not understand ...


Hope this will be of some help to you.

Best regards, Josip :)

[Lundh]

Hi Joseph,

That was a very good explanation,you made it very clear how to read and understand the data :)
So there is nothing wrong with he's suction and discharge pressure. Do you have any qualified advisces for what he should check to figure out the problem? I think troubleshooting in refrigerant systems is very interesting

[Josip]

Hi, dear Lundg :)


Hi Joseph,

That was a very good explanation,you made it very clear how to read and understand the data :)
So there is nothing wrong with he's suction and discharge pressure. Do you have any qualified advisces for what he should check to figure out the problem? I think troubleshooting in refrigerant systems is very interesting

thanks ....

... probably there is nothing wrong with both pressures - if system required to be set in that way (that we do not know - together with some other important data) but for sure suction superheat (SSH) is too big ... but ... again big ... BUT....

.... if the temperature within cold room must be 4*C (277,15K) and suction pressure/temperature is at -15,6*C (257,55K) ... something is not good

... to run a cold room at 4*C ... suction temperature can be at -5*C or even at 0*C (268,15K - 273,15K) ... there can be a lot of causes to have that discrepancy ...

OP wrote:

2:there is one room which give problems , set temp is 4'C while room temp stay above 6'C. there's anothor temp mention in the PLC display "duct temp" we don't have ducts. we have liquid R22 line. what's a duct temp? duct temp always stay in between 4 and 6 degree C. Is this the temp of small duct after the expansion valve which has further parallel branches in the evaporator ?


Probably ... HE in that cold room is starving or without heat echange, because, it is blocked by ice due to too low suction temperature ... or not enough refrigerant - again low evaporation temperature .... maybe blocked filter on the liquid line to HE - because another rooms are working OK -what we do not know !?! ... but if true that means system is not empty ... maybe some valves are closed ... maybe HE is blocked with oil .... we miss a lot of data needed to give some good suggestion ... all this above is guessing and sometimes lead in wrong direction .... we are waiting for OP to give us more relevant data ... if ;)


Best regards, Josip :)

[Lundh]

Dear Josip,
Yes i can see the issue with the very low suction pressure and temperature, and the SSH in this running condition is (24,7-(-15,6)) = 40,3 K which sounds crazy. The system must be running at a very low COP atm. Could this very high SSH be caused by poor or non isolated suction line? But yes alot of data is needed, i hope our Saudi friend will provide us with more useful information :)

By the way do you work with installation/service and troubleshooting in refrigeration systems?

[Josip]

Hi, Lundh :)


Dear Josip,
Yes i can see the issue with the very low suction pressure and temperature, and the SSH in this running condition is (24,7-(-15,6)) = 40,3 K which sounds crazy. The system must be running at a very low COP atm. Could this very high SSH be caused by poor or non isolated suction line? But yes alot of data is needed, i hope our Saudi friend will provide us with more useful information :)

By the way do you work with installation/service and troubleshooting in refrigeration systems?

SSH is 24,4K ... real suction temp=281,95K - saturation temp=257,55K = 24,4K ...

even without insulation (the other part of the system is running well), we'll get some ice formation on the suction pipe what will be quite good insulation and suction superheat will not be so big if system is working well ... compressor will run longer time and that is all ... I believe there is some other problem ....

Yes, about 37 years ... but still learning;)


Best regards, Josip :)

[RANGER1]

Agree with Josip,
Also compressor suction pressure control point should be checked in Unisab, as could be set to low.
Depends what else is on suction of this machine, rooms etc, if anything.
From picture machine is fully loaded 100%

Are there any back pressure regulators on 4deg C room as well?

[kingJ]

hi! can someone give an advice about suction temperature too high? and what was the cause of this alarm?

[Magoo]

High suction superheat reflects as a high discharge super heat, actual gas temperature leaving compressors versus the Saturated discharge temperature.

[kingJ]

We recently experienced this issue on "suction temperature too high" alarm in circuit 2 of our 40 tonners Trane CGAM Chiller. We have noticed that during standby mode the suction temp display in ckt 2 is higher by 20 degree fahrenhiet compared to ckt 1 (which is in healthy condition). After the chiller set in operation mode & both circuit are running, the suction temp of ckt 2 increases up to 160 deg.fah. while the circuit 1 remain close to entering/leaving water temp. The discharge pressure in ckt.2 is somewhat a half value of discharge pressure in ckt.1. And by the time the EXV in ckt 2 gradually increases up to 100% opening such time the ckt.2 stopped with an alarm suction temperature too high. We suspected that the problem is within the sensor, but we are not sure if this is the cause of alarm. Is there anyone can give as light regarding with our problem. thank you

[sterl]

If I read correctly: Circuit 1 is working near expectation but circuit 2 makes a low discharge pressure, does not pull down its suction pressure, and cuts out on high suction temperature after fairly short running interval.

My first guess would be the refrigerant is short charged; and with scroll compressors, the oil in that circuit is either 1) not returning or 2) all going to one machine, the other one is more or less oil dry. Nominally, if the refrigerant has been leaking, the oil charge will be low and in the wrong place as well.