Subcooled R22 Temperature control

[Kevin Yeo]

Hi guys,

For 2 stage low temperature multi compressor rack system with subcooler (PHE type), is it necessary to control the leaving liquid R22 temperature?

At this moment, we place solenoid valve at inlet of warm liquid (from receiver) and a NRV at the outlet of subcooled liquid line. This solenoid valve close and open in accordance to compressor auxillary control (NO). Will this help to minimize temperature fluctuation at PHE heat exchanger

Rgds,
Kev

[taz24]

Hi guys,

For 2 stage low temperature multi compressor rack system with subcooler (PHE type), is it necessary to control the leaving liquid R22 temperature?

At this moment, we place solenoid valve at inlet of warm liquid (from receiver) and a NRV at the outlet of subcooled liquid line. This solenoid valve close and open in accordance to compressor auxillary control (NO). Will this help to minimize temperature fluctuation at PHE heat exchanger

Rgds,
Kev

I'm not sure why you would want to control the tempreture like that.
If you have the liquid passing through one side of the heat exchanger what are you using to reduce the tempreture of the refrigerant.
Do you have a TEV fitted?
If you do then the suction from this valve then returns to cool the interstage discharge gas on the two stage compressors.
The temp of the liquid is then controled by the correct sizeing and modulation of the heat exchangers TEV.

taz.

[Kevin Yeo]

Hi Taz,

Sorry for not making it clear enulf. I've attached a schematic diagram of what we use. Instead of using the original 3/8" solenoid valve from Bitzer, we use it at the inlet liquid line (from receiver). And we rely solely on the TXV (external equalized) to control subcooled liquid temp.

rgds,
Kev

[tony--1]

HI kevin

You don`t need the s/vavle in line from receiver opening and closing

[750 Valve]

Mate what you are saying is viable if there are parallel compressors - you would be matching the mechanical subcooling to the mass flow required by cycling a HX off if the comp isn't running but with a single system its not required - stick an epr on the suction line coming out of the HX and set it for a minimum temp. This works well for us both in single and multiple comp setups.

[taz24]

Hi Taz,

Sorry for not making it clear enulf. I've attached a schematic diagram of what we use. Instead of using the original 3/8" solenoid valve from Bitzer, we use it at the inlet liquid line (from receiver). And we rely solely on the TXV (external equalized) to control subcooled liquid temp.

rgds,
Kev


From the drawing, the mag valve (solenoid valve) in the liquid line will shut down liquid supplied to both the evaps and the heat exchanger.
The only time this valve would be denergised would be when the system was down to temp and the pack (rack) would be pumped down.
On a multi evap system this will never happen because the duty to the pack will be continuous, the pack will never achieve shut down.
So the mag valve fitted where it is will not normally close?.

But I'm not sure why it is an issue.

Does the system work OK? or are you experienceing problems?

Your question orriginaly was is it nessesary to regulate the flow of subcooled liquid?
In answer the liqid flow rate and the setting of the TEV valve would regulate the temp of the liquid flowing through the heat exchanger.

So the desired temp of the liquid is controlled by the flow rate of the liquid through the heat exchanger and therfor no other flow control would be required.

taz.

[Kevin Yeo]

Dear all,

Thanks for your advice. The schematic diagram is actually one part of the multi compressors PHE circuit. And its a multi compressor system.

I have a main warm liquid line (from receiver) feeding warm refrigerant into individual PHE (3 no in this case because 3 compressors). The compressor regulation is controller by Danfoss compressor managers. Bitzer supplies 1 no 3/8" Solenoid valve for the injection circuit and the 230V is from individual compressor N-O auxillary contact. I'm thinking when the compressor regulation is off, then there will be no cooling to the warm R22 flowing thru the PHE.

As such, I'm wondering if the Solenoid valve should be located at the warm liquid prior to entering PHE and using N-O auxillary contact from individual compressors.

Rgds,
Kev

[hendry]

Kevin Yeo,
i've reviewed what others have said.

1]you should run a HAZOP on your design.
2]you definitely need to control the subcooled temp b'coz any fluctuation affects your end results.
3]ctrl & instrumentation method varies from one to the other; choose wisely.

[Brian_UK]

Kevin Yeo,
i've reviewed what others have said.

1]you should run a HAZOP on your design.
2]you definitely need to control the subcooled temp b'coz any fluctuation affects your end results.
3]ctrl & instrumentation method varies from one to the other; choose wisely.
Hendry, you have the ability to state the obvious :rolleyes:

[Kevin Yeo]

Hi Hendry,

Hazop??

rgds,
Kev

[hendry]

HAZOP is an abbreviation for HAZard and OPerability analysis.

It is some what similar to HACCP conducted for food industries.

by so doing, you have eliminated many practical issues.

[750 Valve]

Kevin Yeo - yes fit a LLSV to the inlet of the PHE where the warm liquid to be subcooled enters, if a comp cycles off then as you suggested - cycle off a PHE to match your mass flow rate. I have seen this done many times and it will work, although if you have an uneven rack (different sized comps) it could get painful - I've only ever seen it with an even rack or compound 2 stage compressors where the suction from PHE dumps into 2nd stage for desuperheating

[Kevin Yeo]

hi guys,
Thanks very much for your feedback.