So how does a provision refrigeration plant work? With 3 "FRIDGES"

[SchoolBoy]

I am trying to make a schematic of a provision refrigeration system. Which is running 2 compressors and has 3 fridges. It has to be a simple drawing, with no refrigerant types, hi - low pressure cutouts etc..

Until now I have made a schematic like this:


6398
But it looks like it will not work this way, as we know the temperature depents on pressures. In my schematic the pressures in every fridge are the same = same temperatures in each fridge.

or there is a possibility to fit different size TX valves into each line to achieve different temperatures?

Thanks guys ;)

[SchoolBoy]

Can anyone please also comment what have to be the evaporation temperatures of the refrigerant in each evaporator to reach temperatures as stated? -20C, +2C and +10C. If we use for example R404 refrigerant.

[james10]

evaporation temp is 5 degrees lower than setpoint regardless of refrigerant type under normal circumstances you could use evaporator pressure regulators (EPR) to control your temp rather than expansion valves, you provide constant liquid refrigerant to the EPR which you pre set to your desired temp

[Brian_UK]

A sample diagram is here with all of the parts...

http://www.sporlanonline.com/5-180_072010.pdf

Also for documentation on the various components see here also...

http://www.sporlanonline.com/literature.shtml

[SchoolBoy]

Thanks guys, my system has to be with a TXV, rather than with EPR.

From which aspect does the boiling point depend on, and what does it mean "R-134 boling point -26,2C"

[james10]

water boils and begins to have a latent heat change at 100c water-steam
R134a does the same exept liquid to vapour at -26.6c

[Gingerair]

Use the EPR's with TXV's
-http://www.sporlanonline.com/90-20.htm

[Tycho]

First you need to add more valves

mark 1 on the drawing: you need evaporating pressure regulators on the suction of the two cold (3*C) and cool (10*C) rooms, because they have a higher evaporating pressure than the freezing room.
http://www.danfoss.com/Products/Categories/Drawings/RA/Pressure-and-Temperature-Regulators/Pressure-Regulators/KVP-evaporating-pressure-regulators-suction-line/430c1c43-b239-4e46-89e9-db1e502a4f50.html

mark 2 on the drawing: You need a non return valve on the suction of the freezing room, this to prevent refrigerant from migrating to the freezing room evaporator when the temperature controller to that room closes the solenoid valve.

using R-404a as a refrigerant
http://img88.imageshack.us/img88/2979/projec1.jpg
(ms paint edit :))


Bonus points: if the freezing and cool room has reached it's temperature and the solenoids are closed, but the compressor is to big to run the cold room alone and keeps pumping down. You can rig the wiring so that the freezing room solenoid is activated (as long as it is not in a defrost cycle), this should give the compressor enough capacity to keep running and be able to maintain the temp in the cold room.

[Tayters]

Can't you have one condenser with NRV in compressor discharge lines.

More bonus points for noting capacity of rooms. The lowest temp room should be about 60% of the load on the system. This way the 2 other rooms reach temp and close LLSV then the suction pressure drops and the low temp room starts to pass refrigerant through the NRV as Tycho suggests. That's the theory I've read for 2 different rooms on 1 system so I think it would follow for 3.
Take a butchers at the Danfoss website. I think it's mentioned in Fitters Notes.

Cheers,

Andy.

[Tycho]

Can't you have one condenser with NRV in compressor discharge lines.

More bonus points for noting capacity of rooms. The lowest temp room should be about 60% of the load on the system. This way the 2 other rooms reach temp and close LLSV then the suction pressure drops and the low temp room starts to pass refrigerant through the NRV as Tycho suggests. That's the theory I've read for 2 different rooms on 1 system so I think it would follow for 3.
Take a butchers at the Danfoss website. I think it's mentioned in Fitters Notes.

Cheers,

Andy.

You could do with 1 condenser as you said, but if it is for a provision plant on a ship that spends a long time at sea, they will have a "standby" compressor unit.

On supply ships for the oil industry they also charge both compressor units with enough ***** to run the system, so if a condenser starts leaking, they can seal that one out of the system and start the other one with no downtime.

On fishing vessels they have two units, but only enough ***** to run one at a time.

[helm_n]

Do anyone know how to properly to do compressor sizing? 3 rooms have different evaporating temp. Condensing temp is around 40 degC. Let say +10 room required cooling is 10000 btu/h, +2 room at 12000 btu/h and -20 room at 15000 btu/h.

[chillerman2006]

Off topic - needed removing

[750 Valve]

evaporation temp is 5 degrees lower than setpoint regardless of refrigerant type under normal circumstances you could use evaporator pressure regulators (EPR) to control your temp rather than expansion valves, you provide constant liquid refrigerant to the EPR which you pre set to your desired temp


Thanks guys, my system has to be with a TXV, rather than with EPR.

From which aspect does the boiling point depend on, and what does it mean "R-134 boling point -26,2C"



Reading this thread is like the blind leading the blind. :)

[paul_h]

Hey 750, How's it going?
I've been away for a month or two sorting out the calibre I need for the future hole in my head.
What have you been up to?
tycho was right wasn't he?

edit: duh EPRs needed of course on the med temps, nothing needed for the freezer (except a CPR)
beep boop bop, I am a robot that reads fault codes, voltages, amps, diodes, thermistors etc in sh1tty domestic a/c - refrig

[chillerman2006]

Evening Paul

or I should say Morning,

I normally find systems with multi evaps, require 'EPR's on the chilled sections to prevent them freezing the produce & 'LLS' on every circuit to shut them down on their stat's ...

R's chillerman

[paul_h]

What's a chiller?
Pretty sure I worked on one in 1993.
Yeah I figured the EPR out myself.
Sorry, normally late at night when I post here :)

[chillerman2006]

I am a robot that reads fault codes, voltages, amps, diodes, thermistors etc in sh1tty domestic a/c - refrig

Yeah ok :rolleyes:

Have seen alot of your posts, lots of common sense, educating us older folk,

R's chillerman