Chiller with Bitzer compressor and eco

[Qball]

Hey all,

First of all i am pretty new in the Refrigeration, like 1,5 year en still learning.
Last week i visited a chiller installation and it gave me some headache.

I noticed that the pressure of the eco was constant going up and down rapidly a diff of 1,2 bar.
But also the temperature.

And at some point the compressor was taking liquid, i could hear it and see it in the sightglass of the oil.

Then i noticed something with the piping of the eco.
Normally the pipe of the eco is taken form the high pressure liquid, then a expansion valve then the subcooler, but in this situation the eco pipe taken after the subcooler.

Also when i look up in the bitzer software the expansion valve for the eco has to be like 27 kW, this installation has a valve for 45 kW they also turned the orifice way back.

What do you guys think ?

Bitzer eco.jpg

[RANGER1]

Hey all,

First of all i am pretty new in the Refrigeration, like 1,5 year en still learning.
Last week i visited a chiller installation and it gave me some headache.

I noticed that the pressure of the eco was constant going up and down rapidly a diff of 1,2 bar.
But also the temperature.

And at some point the compressor was taking liquid, i could hear it and see it in the sightglass of the oil.

Then i noticed something with the piping of the eco.
Normally the pipe of the eco is taken form the high pressure liquid, then a expansion valve then the subcooler, but in this situation the eco pipe taken after the subcooler.

Also when i look up in the bitzer software the expansion valve for the eco has to be like 27 kW, this installation has a valve for 45 kW they also turned the orifice way back.

What do you guys think ?

Bitzer eco.jpg

Qball, agree it's a bit unusual as to me does not achieve anything extra,as same load still ends up in economizer port.
Maybe you have to investigate expansion valve operation.

Ensure refrigerant charge is right, discharge pressure is stable, then check superheat's of economizer & evaporator etc.

[Balance Piston]

Another problem with that design might be the pressure drop in the liquid line as it goes through the plate / frame heat exchanger prior to entering the expansion valve. As the load on the chiller increases, the liquid line flow increases, and the pressure drop through the heat exchanger increases. This will have an affect on the operation of the economizer expansion valve. If it's piped the other way (first picture) there is minimal pressure drop in the liquid line supplying the economizer expansion valve.

How long has this system been in operation?

Does the compressor load fluctuate?

[Balance Piston]

Thinking about this a little more: I guess my comment would be assuming the heat exchanger and piping were sized according to the top picture. If they were sized for two expansion valves then you may not much of a significant pressure drop or fluctuation in pressure. Either way it's an odd design and I can't say that I've ever seen like that but then again I haven't seen an actual expansion valve in ten years, we typically use flooded economizers with Fisher level control valves.

[Qball]

The installation is running for several of years now. Although it's mine first visit.
When you compare this installation with the software from Bitzer, it should be like the first picture.
They mounted the piping like picture 2 also the expansion valve (alco) is too big.

What i have seen is that the discharge pressure and auctionaris pressure is steady, except for the eco pressure, that is the one that fluctates, also the temperature.

Today i am going back to that plant, is there something what i have to check ?

[RANGER1]

Check TX valve on economiser maybe install new kit or correct size valve.
Check TX bulb position etc as you suggest flood back to compressor.
Assume main evaporator ok & not flooding, controlling superheat.
Is there a pressure regulator in economiser suction line?
Is compressor loading or unloading causing different pressure in Eco suction line?

[Qball]

Check TX valve on economiser maybe install new kit or correct size valve.
Going to install a valve with less kW.

Check TX bulb position etc as you suggest flood back to compressor.
Position checked and pasted with thermo pasta en insulated

Assume main evaporator ok & not flooding, controlling superheat.
Superheat is between 6 and 9 K

Is there a pressure regulator in economiser suction line?
nope

Is compressor loading or unloading causing different pressure in Eco suction line?
I think the TX valve is hunting out of his range

I think they put the piping of the eco at the outside of the subcooler because they dont use a liquid vessel and u want to maintain a stable mass flow.

[RANGER1]

Thank's keep us updated on what you
find

[Magoo]

To recap., the econo TXV is oversized and fed with sub cooled liquid which will increase capacity even more. The TXV will be hunting madly as used said and saturating back to compressor.Amazing it has not killed the screw compressor already.
Do you have a lot of oil carry over in system?
I have not come across using sub cooled liquid for econo, quite a good idea though if sized correctly. Definitely needs a evap pressure reg control valve though, as per RANGER 1
magoo

[Qball]

There is no pressure regulator in the econo, althought there is one for the evap itself.
Next monday we will do 1 of the 4 systems, and i will post results.