Daikin VRV piping restriction

[sumsor]

Hi all,

one of the piping restrictions on a VRV install is the maximum distance of 40m from the first refnet to the last indoor unit. I assume that has to do with the pressuredrop.
The distance between the ou and the first refnet could vary greatly(within other restrictions), but there is still the same 40m max length.
Does anybody know why?

Cheers

sumsor

[Crash Pilot]

I would say Pressure Drop and Oil Return.

This could have a bearing on system operation and compressor life.

[Crash Pilot]

Indoor units try to maintain target superheat through exp valve to control discharge superheat. If you have pressure drop then the pipe length judgement that is carried out during test operation could calculate wrong target settings and set wrong operating parameters. This can srew up a number of things.

[Crash Pilot]

Sumsor

Sent you a PM about the stages of test operation and what it looks for and how it calculates.

[Mentallist]

The reason for the 4om rule is to maintain equal and balanced pressure within the field piping and to ensure pressure drop is kept at a minimum. The greater the length of field piping, the more pressure drop, the technical data book will have a chart inside showing the drop dependant on length and height difference between indoor and outdoor units (The inverter compressor can compensate for this drop). There is a possible extension to this rule, up to 90m can be achieved, as long as the equivalent length between furthest unit to the first refnet and closest unit to the first refnet is no more than 40m (Equivalent Length). In this instance, an increase in size of main piping between refnets will be required to be done x 1 size up, and of course, only if Daikin give it the go ahead.

The pressure drop is calculated during the test operation, where it also calculates length of run (Short/Medium/Long), and is calculated as follows:

Evaporating target set to -15.

During test operation the units will attempt to reach this target, if say you have 4 x indoor units and they all achieve -10. The system adds all these figures together = -40. It then divides this total by the number of indoor units -40 divided by 4 = -10. It subtracts this -10 from the target of -15 which equals +5.

If this final figure is < 3, this would be considered a short piping run
If this final figure is < 6, this would be considered a medium piping run
If this final figure is > 6, this would be considered a long pipe run

(On an old G series VRV system, there was a switch on the PCB which should have been set)

The example above would mean the system would be considered a medium pipe run. Pressure drop is calculated during this operation.

I hope the above above helps

[sumsor]

Hi Crash Pilot and Mentallist,

thanks very much for the quick replies. Exactly what I was looking for, very much appreciated.

Sumsor

[Mentallist]

I hear that Daikin VRV piping limits will be longer come end of this year/early next year. No details as of yet, but 1 thing I did hear is the level difference between indoor units will be extended to 30m as opposed to the current 15m, may also be further extensions to current total piping length. We shall see

[Crash Pilot]

Been out of the VRV circle for a while but have heard from a friend that units are already available and being installed in Aust.