Refnets

[Rfcont]

Hello to all

At installation VRF systems are the requirement to establish refnets in a horizontal plane with a deviation no more than 30 degrees.
For what it is necessary?

THANKS

[The Viking]

First off all,
I assume we are talking Daikin VRVs now, as we are talking about refnet joints?

The point of using refnet joints is to ensure equal distribution of liquid and oil, if the joint has one leg "pointing" lower than the other then this distribution will be affected.

BTW, they can be installed vertically as well, as long as the refrigerant flow is vertical (there are limitations, check the leaflet in the box they comes in), like for example in a riser.

[techguy]

Hi

I have a video file which shows the necessity for this its been around for a long time . Can't add it as an attachment its to big. Drop me a line i'll mail it to you

Basically the further you go off the horizontal plane the less liquid refrigerant you get flowing into the branch .


T

[Pol]

Techguy,

I`m highly interested in that video! What size is it? Could you please post it somewhere for download?

Thx,

Pol

[Peter_1]

I will post it on an external server.
As soon running download is finished, I'll post the link.
I allways show the students this video to understand better what's happening.

On the other hand, Mitsubshi has Y joints which can be mounted almost in any position and the design is very
simple but works anyhow perfect.
They accomplish it via capillary tubes.

[Peter_1]

This link last +/- 14 days after last download:
http://www.megaupload.com/nl/?d=3W0X4RZ0

[The MG Pony]

Thanking you greatly for the video, I'll try and figure out how to make a direct URL to my FTP server and load it there.

[Pol]

Thank you very much, Peter!

[Peter_1]

Figured out how Mitsubishi is doing this?
I like much more the Mitsubishi way.
Viking, are you sure about mounting these vertically?

Graag gedaan Pol.

[Thermatech]

After you have seen the Daikin vidio you will understand that if the liquid line has liquid & bubbles then the orientation the refnet is important for correct distribution of liquid.
Mitsubishi from the very first City Multi had large subcooler with very exact LEV subcooler control.
Mitsubishi City Multi could always ensure that liquid supply to indoor units has no bubbles & so no need for refnet kits.
Also subcooling provides slight extra performance & COP.Also helps reduce refrigerant noise at indoor units.
In time other manufacturers are gradually introducing subcoolers also but suspect this is more for performance advantage.

[Rfcont]

Awesome video
Interesting, though, I think, VRF the system is the closed hydraulic system and theoretically gravitation should make smaller influence that is shown.

[Rfcont]

In many manuales to AHU systems (http://www.docs.hvacpartners.com/idc...it/39m-1si.pdf)considered the way of connection of evaporators located one above another.
If to look pages 55 and 56 that it is visible that the liquid line is connected to evaporators through the usual T-junction located in a vertical plane.

Why same reasons as in a case with VRF here are not taken into consideration?

[Peter_1]

What also is important is that for liquid lines you make the T connection as much as possible downwards and all suction upwards.

Even with no subcooling and/or with 30% flashgas in the lines (expansion in the outside unit as with multisplits), then the Mitsubishi still keeps working with their capillary solution.
Each liquid branch gets the same rate of pure fla****as, a mix of flashgas/liquid and pure liquid.
The mix is re-disitributed and mixed equal via the cap tubes, whatever this header is installed.
1-0 for Mitsu on this one

[The Viking]

Figured out how Mitsubishi is doing this?
I like much more the Mitsubishi way.
Viking, are you sure about mounting these vertically?

Graag gedaan Pol.

- In short, Mitsu has a receiver in their BC box and keep the liquid level in it half way up, the units that ask for cooling takes liquid from the bottom and the units that wants heating gas from the top.
- As I stated in another tread, each system has it's benefits. Personally, I fully agree with you but this is purely because I worked more on them and therefore knows better what to look for when things goes wrong.
- You can download the manual yourself from www.daikin.co.uk (then click on "aftersales service" > "technical downloads" and search for "ref", you will then find a file called "IM-Refnet Joints" this is the one you want to look at, especially the top RH corner of the last page) NOTE: Vertically as in Inlet/Outlet above/below each other, outlet/outlet is still horizontal.

RFcont:
I believe that what upset things is that VRV/VRFs doesn't run fully charged (as "proper" refrigeration system would, with sub cooled liquid at all times), in a properly designed VRV/VRF system the outdoor unit could even be seen as being too small (from a "proper" system point of view).

[Thermatech]

To prevent any confusion ,,,,,,,,,, the pictures of Mitsubishi distribution pipes are for use on Mr Slim split systems only. Need when connecting 1,2,3 or 4 indoor units to one outdoor unit.
These special distribuution pipes are needed because Mr Slim split systems have liquid expansion device at the outdoor unit.

This thread is specifically about VRF systems & use of refnet's.

Mitsubishi Electric City Multi VRF systems never have any flash gas or bubbles in the liquid line because system has very exact subcool control.
The only time you will see bubbles in liquid line on this type VRF system is when the system has low refrigerant charge or when subcooler control LEV valve has failed in closed possition.

Indoor unit LEV valve is small needle valve & needs pure liquid to control refrigerant volume flow through the indoor coil & get good control on indoor unit super heat in cooling mode.
If liquid line suddenly gets bubbles then refrigerant volume through the LEV valve into coil is reduced & super heat control lost. The indoor unit will then see SH target not maintained & will start ramping open the LEV valve more & more to try & get target SH.
Then if bubbles stop & liquid line has liquid only the LEV valve is much to much open & liquid floods through the indoor coil. The indoor unit sees SH target overshoot & starts ramping down LEV valve.

Mitsubishi Electric City Multi VRF systems never have this poor indoor control because the liquid line is always pure subcooled liquid.,,,,no flash gas,,,no bubbles,,,,, no poor performance,,,, no need for any special refnet.

[Peter_1]

Thermaetch, this is the first time that someone explained this so clear to me.
Good job and thanks.

[vac-man]

hello all..have started installing daikin vrv recently and was a little unsure of positioning of refs`found your information on the forum very helpful as no-one i work with could explain the proper reason behind this..