Ammonia refrigeration - economiser

[g.karsandas]

How economizer is connected in ammonia screw compressor and it function and advantages in system.
Thanks,
g.karsandas

[Magoo]

An economizer is a liquid subcooler, and vapour from economizer enters the compressor at the partial port, two options open flash or closed flash economizers. Not all screw compressors are applicable to economizer applications.
The advantage of economizer /subcooler is the the cooled liquid increase the evaporator capacity

[mbc]

in low temp evaporator temperature mainly all compressor has this system if they want to use one compressor it works as same as two stage system and also economizer reduce our out let temperature from compressor

[Josip]

Hi, g.karsandas

How economizer is connected in ammonia screw compressor and it function and advantages in system.
Thanks,
g.karsandas

Agree with the answers given by mbc and Magoo, but

the best suggestion is to search RE forums .... top right ... economiser .... it will open you many pages where you can read a lot about ....

... if there is something missing or not clear, you can always come back here and ask additional question


Best regards, Josip

[Sandro Baptista]

An economizer is a liquid subcooler, and vapour from economizer enters the compressor at the partial port, two options open flash or closed flash economizers. Not all screw compressors are applicable to economizer applications.
The advantage of economizer /subcooler is the the cooled liquid increase the evaporator capacity

Magoo, if it is open flash the liquid is not subcooling since it is at saturation temperature of the intermediate pressure

g.karsandas, as the ECO allows you to increase the capacity you can select an smaller compressor compared with one w/o ECO.

Also the ECO allows you a bigger COP so less power consumption for the same refrigeration capacity.

[Josip]

Hi

An economizer is a liquid subcooler, and vapour from economizer enters the compressor at the partial port, two options open flash or closed flash economizers. Not all screw compressors are applicable to economizer applications.
The advantage of economizer /subcooler is the the cooled liquid increase the evaporator capacity

Magoo, if it is open flash the liquid is not subcooling since it is at saturation temperature of the intermediate pressure

g.karsandas, as the ECO allows you to increase the capacity you can select an smaller compressor compared with one w/o ECO.

Also the ECO allows you a bigger COP so less power consumption for the same refrigeration capacity.

Why do you think that liquid is not sub cooled within open flash economizers? Maybe I lost a meaning due to translation!?!
If you are right, then, why do we use that type of economizers if we do not gain anything?


Economizers are working at intermediate pressure. This port at screw compressor's housing is located at place we call "suction cut-off" and compression process is starting, if gas is available at this port at a pressure above compressor suction pressure some amount will flow into the compressor. This gas will be additional to normal suction charge.

Intermediate pressure is far bellow condensing pressure and temperature and still above suction pressure and temperature within evaporator where we want to evaporate this sub cooled liquid from economizer.

Moreover refrigeration capacity factor is bigger if we use open flash instead closed system. Of course open flash is better with refrigerants like R22 and similar with higher intermediate pressure what is excluding ammonia where are better closed systems like shell&tube or shell&coil.

Best regards, Josip

[aramis]

Magoo, if it is open flash the liquid is not subcooling since it is at saturation temperature of the intermediate pressure

This would be true if the system was at thermodynamic equilibrium.

If the system stops the flash economizer would reach thermodynamic equilibrium and all subcooling would be lost … at the intermediate pressure, as you say.

But the liquid would still be much colder than the saturation temperature at the pressure you feed your expansion device.

This happens to be so even if you are not at equilibrium. So you do have subcooling at the expansion device where it matters.

[Sandro Baptista]

Hi

Why do you think that liquid is not sub cooled within open flash economizers? Maybe I lost a meaning due to translation!?!
If you are right, then, why do we use that type of economizers if we do not gain anything?

Josip,

I'm not saying that we don't gain. I even prefer the open flash eco than closed flash eco.

On the thermodinamyc view it's just not right to say the open flash have liquid subcooled but rather it just have liquid cooled because the liquid it's not at the condensing pressure (Liquid temperature is equal to the saturated temperature). On a closed flash eco you have for instead liquid -15ºC at a corresponding pressure +35ºC.

So on the situation where you don't have liquid subcooling a small pressure loss or heat gain can promote flash gas one part of the liquid fluid.

Hope you understand now what I just say.

Regards

[Magoo]

So what do you call sub-cooling through an economizer vessel, the advantage of closed flash economizers is that the liquid pressure can be kept an HP pressure. Open flash econs have to be kept at or above evap pressure to ensure flow rate, only practical on close coupled flooded recirc accumulators. and gain head from say R22 and pressure differential added. With specific weight of liquid ammonia- sub cooled it doen't move fast enough.
Unless I have got something wrong in last 40+ years.
I have a preference for closed flash econos for stable load on partial port. As opposed to fluctuating pressures from pressure regulation and bouncing motor amps to load variations. Add as well, if pessure reg has a hissy fit the oil in separator disappaerars real quick.

[Sandro Baptista]

With open eco you can get a diff pressure of about 1,0 bar...1,5 bar...it depends on the regimen but is enough to feed the pumped liquid separator. With an ICS+CVPP we can guarantee a sufficient pressure difference even at part load.
The ECO is applied just next to the liquid separator and at the same top level of liquid separator to avoid hydrostatic head loss on the refrigerant.

[aramis]

Open Flash has one clear advantage: more subcooling, at the cost of delivering the refrigerant at a lower pressure. This is why it is mostly used in liquid overfeed systems.

[Josip]

Hi, Sandro

Josip,

I'm not saying that we don't gain. I even prefer the open flash eco than closed flash eco.

On the thermodinamyc view it's just not right to say the open flash have liquid subcooled but rather it just have liquid cooled because the liquid it's not at the condensing pressure (Liquid temperature is equal to the saturated temperature). On a closed flash eco you have for instead liquid -15ºC at a corresponding pressure +35ºC.

So on the situation where you don't have liquid subcooling a small pressure loss or heat gain can promote flash gas one part of the liquid fluid.

Hope you understand now what I just say.

Regards

All, clear now. Thanks, sorry!

Best regards, Josip

[chillerman2006]

How economizer is connected in ammonia screw compressor and it function and advantages in system.
Thanks,
g.karsandas

Courtesy of US Iceman

http://www.refrigeration-engineer.co...sors&highlight=

R's chillerman

[g.karsandas]

Hi,
Thanks,
g.karsandas

[Sandro Baptista]

Courtesy of US Iceman

http://www.refrigeration-engineer.co...sors&highlight=

R's chillerman

About at US Iceman said on his thread: "I was recently asked via a PM from a RE member to discuss this topic. As there is a lot of information that could be covered in this discussion I'll start with some basics and we can proceed from there.

There are two basic types of economizers for screw compressors:

1. Flash type
2. Subcooling type

The flash type is relatively simple. High pressure liquid from the receiver is fed into a vessel through an expansion device. The liquid flashes off from receiver pressure down to the pressure in the vessel. The flash gas flows out of the vessel and back to the screw compressor side port. The cold liquid is at an intermediate pressure (between suction and discharge pressure). And, the liquid is saturated at this intermediate pressure. It is not subcooled, but rather a cold saturated liquid."

THAT'S MY MAN...It seems we are from the same school...

[Magoo]

Hi.
I do not dispute US Iceman's posting the Frick explanation of variations of sub-coolers. absolutely correct. The application will dictate the type of subcooler applicable. As yet have not seen a open flash applied to a multi- DX system, but are good for pumped overfeed systems close coupled. hence my personel preference for shell and coils type system sub-coolers.
Dependent on refrigerant applied, every 2 degrees of sub-cooling below natural condenser sub-cooling will on average increase the evaporator performance by 1 % , don't quote me on it. It is all to do with elliminating the flash gas after the expansion device at evaporator.

[Sandro Baptista]

Hi.
As yet have not seen a open flash applied to a multi- DX system...

Open flash applied to DX system I never see either. The diff pressure is very low for it.

BR