How you designe interHX?

[ALKUL]

Im intrested how you designe your inter HX in you cascade systems.

I have orded a two compressors of type Danfoss SC21CLX and i am going to build a two compressor cacade system. these compressors have 6mm discharge conector and 10mm suction conector. So im going to use 12mm (1/2") copper tube for evaparator and 6mm (1/4") tube inside for condens.

How would you decide the lenght of the copper tubes?

[JSU]

First off welcome :) . Second i believe that all danfoss compressor ending with clx instead of cl are 110v. People have experimented with differant sizes. Looks through the -114c thread. The beginning hxs didnt work out that well. Further on basicaly the conclusion has been drawn at 15' and 2x3/6in tubes inside 1/2in tubing. Good Luck!

btw have you built systems before?

[ALKUL]

I have the Danfoss rs+ program up here and it says its a 220-240/50Hz also we only have 230V in Iceland so they wont import 110V compressors.

I have build one system before it was only a small one it was a singel stage with a 5cc compressor. i was -35idle and -20 on load on my old P4 3,2ghz @ 4ghz Northwood

Is there any tread about deciding on the length/diameter on captube's?

[gkiing]

First off welcome :) . Second i believe that all danfoss compressor ending with clx instead of cl are 110v. People have experimented with differant sizes. Looks through the -114c thread. The beginning hxs didnt work out that well. Further on basicaly the conclusion has been drawn at 15' and 2x3/6in tubes inside 1/2in tubing. Good Luck!

btw have you built systems before?

How can you have 3/6" tubes inside a 1/2" their the same size?? Did you mean 3/16 which is really small.

For cap tubes use 0.031" (0.8mm i think), not sure of the length.

[JSU]

oops yeah 3/16 sorry ;)

[Tyrou]

on my casccade, I made an hx with 1/4" tube inside 1/2", it's quite difficult to put the little tube inthe larger one, but esay to bend in a nice spiral :)

I made two HXs, 5 meters each, connected in parrallel :)

[Tonic]

I'm suggesting to try berkut's HX. A combo of suction HX on second stage and of first
stage evaporator

There are three tubes, two of them are inside biggest tube. Smallest tube is inside
middle tube. Biggest tube is a first stage evaporator, middle tube is a condenser of
second stage and inner tube is a second stage suction side

To simplify your life, I'm posting a draw

http://img.photobucket.com/albums/v613/Cinot/autokaskada/HX.gif

Greetings
T

[Tyrou]

it's awesome for subcooling but hard to bend/fit in a reduced size :(

[hatemi]

The CLX at the end of the model number means this:
C=LPB
L=R404a/507
X= High starting torque ie. the start capasitor.

For the HX a 6mm inside a 10 or 12mm will work just nicely:) Make it about 5M long.

[Tyrou]

could you tell me how much did you pay for the SC21CLX (in PM if you prefer ;))

[Tonic]

Tyrou,

If this HX have a dimensions, which bothers you, just cut him to half and connect
parts paralelly

[Tyrou]

good idea, I planned to use that kind of HX on my forecoming autocascade :)

[ALKUL]

Tonic,
what would the temps be in an idiel 2 stage system at the 2nd stage suction? Would it be colder than -45°? Wouldn´t it be better to have two separate HX, first to condens the 2nd stage gas and then another to handel subcooling/overheat?

Tyrou,
i payed a 40.000 icelandic kronur for the compressors. Its about 650 dollars! The tax in Iceland is about 25% so every thing is expencive.

[Tyrou]

Arf, it's the same kind of prices as in France, we have 20% VAT, and everything is deadly expensive :( For my own cascade, I used old compressors, from dead air conditionners, it's way cheaper :D

[ALKUL]

So when you decide on the cap tube lenght. Do you have some rule to go with for the start and makes some changes on the lenght to finetune the system?

[Tyrou]

I highly recommend you to use CPEVs or TXVs instead of cap tube, some people here have very successful cascades with cap tube (pc ice :D), but most of us use TXV/CPEV, as they are adjustable to tune the whole rig :)

[ALKUL]

would it not be saver to use capillertube on the 2stage due to the low temp? I´m gonna use TXV on the 1stage but...

[Tyrou]

I currently use a PXV on the first stage, and a CPEV on the second one, it works all right :)

[Tonic]

Tyrou, do you have any problems with controlling CPEV, when he's frozen?

ALKUL, I'm sure that suction temperautre is lower than 1st stage evaporator.

Why? Because 1st stage evaporator evaporate at -30*C to -50*C, 2nd stage
evaporator evaporate at -60*C to -100*C. 2nd stage suction is drawing gas
from 2nd stage evaporator, so, it haves temperature closed to evaporator's
(it's higher, but not that much)

P.S. those temperatures are examples :)

[Tyrou]

controlling the CPEV when frozen is not an issue, it could still be tuned as you like. The only problem I have is my CO2 which is always clogging in the CPEV and in the evap, but the problem is due to the CO2, not to the CPEV