View Full Version : Economiser

18-10-2007, 02:01 PM
Hi to all,

Now a days the refrigeration compressor is designed with economiser.Can i know the fundamendal details of economiser. Especially the functions & applications.

And also the fundamentals of Pump Vessel.

Awaiting for your replies.



21-10-2007, 01:26 AM
An economizer is a pre-cooler used on screw compressors to chill the liquid refrigerant before the expansion device.

The ones I've seen are a brazed plate type heat exchanger with it's own expansion valve.

Comparing compressor capacities with and without an economizer is eye opening. I've a small Frascold screw that is rated at 175K Btu/h without an economizer, and 225K Btu/h with one, truly a huge increase in capacity that's basically free.

I've got to admit, seeing a liquid line frost up on a brine chiller is pretty odd looking! Out of my condenser I get 77C refrigerant, coming out the economizer the refrigerant is down to -2C, a 79K drop. Yes, the system looses a few K Btu/h to cool it's own refrigerant but the capacity gains are well worth both the initial cost to include an economizer and employ it.

I've never run across a pump vessel, will be interested to read others input on those.

US Iceman
21-10-2007, 02:21 AM
...truly a huge increase in capacity that's basically free.

Not quite, but close. You still have to pay for compressing the flash gas created in the economizer.

On the other subject. I'm assuming he means a liquid overfeed system. A pressure vessel is used as a low-pressure receiver to store cold liquid refrigerant. The refrigerant pump pumps the cold liquid out to the various evaporators.

This is also known as a liquid recirculation system by some.

21-10-2007, 09:52 AM
Another means of employing a vessel as an economiser is known as a 'Flash Tank'.the system controls flow of liquid in/out of the vessel and the vapour above the liquid goes to the compressor at its indermediate port.This pressure is lower than that of condensing pressure and hence subcools the liquid in the vessel.

US Iceman
21-10-2007, 08:10 PM
This pressure is lower than that of condensing pressure and hence subcools the liquid in the vessel.

The liquid is not really subcooled, it's just cold. By definition a subcooled liquid exists at a temperature lower than the saturation temperature of the existing pressure.

I think it's important to distinguish between subcooling and cold liquid since this leads to a conflict of system analysis.;)

22-10-2007, 07:53 AM
Morning to all,

The suggetions are quite interesting.Can anybody give me the details for Pump Vessel.

Thank you,

Have a nice day.


22-10-2007, 02:13 PM
Hi tjk2007
Go to the first page of this site where all the different sections are listed go to Industrial and click on NH3 there are some good explainations of economisers in the thread titled economisers.