Matching evaporator to a compressor capacity

Set up:

Refrigerant.- R-22
Condenser unit: Maneurop 4.4Kw
Evaporator unit: Bohn ADT 208 Low profile 4 fans
Walk in freezer: product raw meat, and suff :rolleyes:

Hi, recently I was called to a new customer "Walk in freezer".
We showed up, the owner descrives is problem as the meat sweating, and floffy
Needles to say evaporator has one or two degree under the ambient temperature.:confused:


We chek up for compressor and evaporator, turn to be, it was almost with out gas...
retrive the gas in the system, charge with argon, chek for leaks, two locknuts were lossen, tigth them down. Re-chek for leaks. Done. We make the vaccum and start to chargue the system with brand new refrigerant... The pressures were extranges.... 35psi Down Side. 325 High Side problem were the low side start to drop 34-33-32-30- low pressure control disangage the compressor.

At this point the owner of the place tell us... thath is the second compressor, becouse the previous one was burned down... I suspect from dirty on the system, however the system were working during a nice perid of time so, we did the next:

Retrive the refrigerant, changue the liquid filter, and sigth glass, change compressor oil, add a suction line filter, changue the txv valve, add a liquid tramp. Chek for leaks, make the vaccum, charge the refrigerant... we get better response, still the pressures were unadequate.

Problem: The compressor is too big for the evaporator and this causes overfill of the TXV, with the liquid retur to the conderser, or if this get closed by TXV normal action, the succion pressure drops and disangage the compressor.

Probables solutions:
1.- Changue the entire condenser unit, for the adecuated size. :YouNoSay:

2.- Changue the evaporator. (A litte bit more difficult, the one installed has the size of the room)

3.- Add a second evaporator. (How this would be perfomerd?)

4.- Add a hot gas bypass http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/rd4ec405.pdf,
or a capacity regulator (http://www.ra.danfoss.com/TechnicalI...1/rd4ec405.pdf)
In wich I have zero experience.


5.-Add a inverter to compressor to match the capacity of the evaporator.
This one is my favorite, it makes the compressor, to be relaxed, and we get
soft starts, and as all you know... compressors love soft starts, so give thath compressor a soft start. :D

I hope have give the rigth idea of the problem, the setings and the information required for you to help me a litte bit.

Kind regards.

Alejandro.

Sweating meat in chiller equals high relative humidity in chiller, slime on meat and bacteria, equals mis match between evaporator capacity and compressor capacity. Too much sensibe cooling and little latent cooling.

Thank you, you an idea were I can find, more information about meat conservation.... I have read the Bohn and Danfoss engenieering manuals, still, I like to know more.

Kind Regards.

Hi Alejandro. Is this a chiller or freezer? Below is assuming a chiller as the ADT208 is a med temp evap. Not suitable for low temp. R22 not so good for low temp, R404 would be better if a new compressor was bought. Assuming to room is relatively air tight.......

Whats the model number of the Maneurope? at 4.4kw cooling its either a MTZ28xxxx (4.4kw@-5'C/45'C) or MTZ32xxx (4.4kw@-5'C/55'C?). If your compressor is a MTZ36/40 or bigger then yes, compressor is too big. What size is the suction pipework? 1/2" or 5/8"?

The ADT208 is rated at 6kw @10'K but for a chiller you only want 6-8'K. so about 3.6-4.8Kw. If this is so and your compressor is 4.4kw then your machinery is right. Low superheat will get you ice strips on the evap fins and high humidity, low suction and low hp pressures. Also low superheat wont give the compressor the low suction temp required to keep it cool, this could have caused the last one to burn out if the maneurope ran hot all the time.

Low suction and high Hp sounds like too small TXV or superheat, with overcharging or undercondening (too hot condensor). Wash the condensor fins with water to ensure its completely clean if you can. Is it fitted with a reciever tank?

Check your LP/HP settings. HP can be upto 350 psi max as long as your HP relief valve is higher. I wouldnt go any higher.

Whats the ambient temp where its located as it could be under condensing if your ambient is too high? (check liquid temp at the drier or sightglass < 55'C), Is the sightglass full when it running?

also whats TXV are your using and orifice (insert) size (My pref is Danfoss if flare)?

Have you set the superheat? if you cant because of LP and hot room then open the TXV all the way and monitor the suction for frost or high pressure HP side. When frost appears start checking your superheat (set between 6-8'K) if superheat/orrifice is too small you will get low suction pressure, also make sure when it is running you have a full sightglass, even when high temp inside.

Sounds like you have done all the other stuff right though. Not sure a VSD on a Maneurope is a good idea. Another soultion for an oversized compressor can be a EPR valve and a small TXV (or capiliary) feeding directly into a suction accumulator for the suction cooling. Not ideal.

Hot gas bypass can be difficult too with high suction temps / hot compressors.

If compressor too big, A second evap is a easy, simply T the suction and liquid pipeworks together but ensure the suction and liquid pipework from the "T" to the condensing set is bigger too. Can make TXV superheats tricky to setup.

Hope this helps.
I have been out of the game for a while so anyone can feel free to correct something if it looks wrong.

Keen to hear your thoughts and the info on the compressor model etc.

Your compressor is from 2007 so I guess the freezer was fine for a few years. Your pressure readings indicates of a restriction some where on the high side, R-22 is fine for 18-C.

Quote:

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Originally Posted by chemi-cool

Your compressor is from 2007 so I guess the freezer was fine for a few years. Your pressure readings indicates of a restriction some where on the high side, R-22 is fine for 18-C.

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Hi, yes yes in deed all the piping was fitting into a pvc and all the conexions and joint were invisibles, so we must think some like this, when we remove the pvc... oo the horror... the already small tubes were bending witout even a spring bender (both lines are soft copper) and both of theme were strangulated... so we will changue the lines... and we still have a very different capacity in the condensor, and in the evaporator. =Z

And for the "working rigth" this set-up has already a burn out compressor and always was problematic, higth temp, no cold in the chiller, etc etc... Its very relative the therm refrigeration on some places over here...

Thak you.
Alejandro

Hi Tgaguy...
Yes in deed I use the therm freezer never the least is a chiller. A walk in chiller, for meat conservation (Carcass, pieces, etc, etc)

The room temperature will be between 0-4°
And the relative humidity will be 85-90%
This is fresh learned from Grantt Macool =)

A new compressor was bougth but, were the same refrigerant R-22 and still is operating
(is the one Im servicing)


"Whats the model number of the Maneurope"
The maneurop model number is ... MTZ 64... way too big rigth?

"What size is the suction pipework? 1/2"
Another gem in the crown... the liquid line is a 1/4" and the suction line is 1/2" both in soft copper. And the bendings... I put a picture of it soon.


"Also low superheat wont give the compressor the low suction temp required to keep it cool, this could have caused the last one to burn out"

Well Im not very sure the dudes install this set up were worried by the superheat, the pipings, the electrics, or even the rigth amount of gas =), when we servicing this unit we retrive about 3kg of R22... the catalogue marks 10KG at least for two piston compressor like this. =)
For flood the condensor we chargue the 3Kg plus more 13Kg


"Low suction and high Hp sounds like too small TXV or superheat, with overcharging or undercondening (too hot condensor). Wash the condensor fins with water to ensure its completely clean if you can"

Yes, sir. At the beginign we clean up the condenser the evaporator, and the stuff... you will be surprised how much grease can you remove from this condenser... =)


"Whats the ambient temp where its located"
Well the condenser is prepared for 55°C and in here the heat just its about 30°C


" whats TXV are your using"
Yes in deed very reliable TXV from Danfoos, and is flare!...
Number 5 orifice, the catalogue demand Number 3 for this evaporator
but, the suction when down and the machine stops and re-start in a very caothic way
(1min run... 5 min stops and re do again... letal =Z )

Have you set the superheat?
Yes we tried... but the compressor were stop and stop...(LP drops) so we open a litte bit the valve just for flood the evap... and it works... we are having a nice cold... still we are not efficients)

VSD on a Maneurope is a good idea.
Why? there are not strong windings?

"Another soultion for an oversized compressor can be a EPR valve and a small TXV (or capiliary) feeding directly into a suction accumulator for the suction cooling. Not ideal."

Never instaled a EPR valve... but a small capilary sounds interesting... you have done some like this?


Hope this helps.

It does =D Thank you so much... if you need more info, please let me know =D

Some photos of the interior of the chiller. =)
I will look for the ones with the bendings on int.

Cheer it up!

AlexLPD, Your info is helpful.

The main problem is that your compressor is rated at 19Kw, and your evaporator is only 6kw. Your evaporator just cant feed the compressor fast enough with gas and causes your compressor to cut out on LP when trying to cool the room.

Your compressor wants 22.6 m3/h but the evaporator only supplies about 7-8m3/h. The compressor is 3 times too big. Its like trying to water your garden with a drinking straw instead of a hose.

The MT22 has 1/2in suction which matches your pipeing, whereas the MT64 wants 7/8" suction

You have a few Options, none of them cheap.
1- Add more evaporators to bring the total evap capacity upto 19kW ( Add ~13kW), bigger main pipework/drier etc

2- Replace the compressor for a MT22. easiest solution.

Using an EPR and capilary just wont work as your compressor is just far too big.

Hope this helps explain.

Also not sure about running it with a VSD. It may run too slow and you could have oil pressure problems internally. you could be down to about 20-25hz.

Better to check with Maneurope supplier. I dont seem to see and info on VSD use.

Quote:

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Originally Posted by Tgaguy

AlexLPD, Your info is helpful.

The main problem is that your compressor is rated at 19Kw, and your evaporator is only 6kw. Your evaporator just cant feed the compressor fast enough with gas and causes your compressor to cut out on LP when trying to cool the room.

Your compressor wants 22.6 m3/h but the evaporator only supplies about 7-8m3/h. The compressor is 3 times too big. Its like trying to water your garden with a drinking straw instead of a hose.

The MT22 has 1/2in suction which matches your pipeing, whereas the MT64 wants 7/8" suction

You have a few Options, none of them cheap.
1- Add more evaporators to bring the total evap capacity upto 19kW ( Add ~13kW), bigger main pipework/drier etc

2- Replace the compressor for a MT22. easiest solution.

Using an EPR and capilary just wont work as your compressor is just far too big.

Hope this helps explain.

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Yes in deed. All this was very helpfull, the room size dont let me put the Medium profile bohn evaporator thath I would like to this. So... I would look for someone in here to make a custom made evaporator, I hope this will be no so much expensive.

Thanks a lot for the reply. =)