REVIT MEP Daikin VRV System (Flow Direction mismatch)

[mmontejo26N2G]

Hi All,

New user for Revit 2022 MEP and been starting some VRV design using Daikin Heat Pump series, already done with the piping system (LQ & Gas lines) using Daikin Refnet piping accessory. Problem is, when doing "Check Pipe System" an error/warning shows: "It is not possible to calculate the flow since the flow direction mismatch".

Checked the entire system equipment (pipe is bidirectional) and all piping is connected (tripled check each) yet the error still persists.

At this point I'm already drained and frustrated. Will be very grateful if Forum can help.

[iainsavage]

You can model refrigerant systems in Revit but I doubt if you can analyse refrigerant flow unless you’ve got some sort of add in which can do the calculations.

Native Revit can maybe calculate the liquid phase flow but I don’t think it can do the gas line.
I notice you’ve modelled it as Sanitary - is it your intention to use fixture units to represent diversity in the VRF system?

Anyway:

1. Connectors on indoor units would need to be Preset (or Fixture Unit if that’s your intention) and single direction. They need to have a flow (or fixture unit) parameter associated with them so that you can set the value for each instance or type of unit.
2. Connectors on outdoor units would need to be Calculated or System and again need to be single direction.
3. Inline components would usually have connectors set to Fitting or Global and can be bidirectional.

[dyp4f]

The warning refers to a "Sanitary 1" system. Is this your VRF piping system, classified as sanitary ?

In that case, your System Classification should be changed to "Hydronic", instead of Sanitary.

Having said that, I have to add that VRV/VRF piping cannot be calculated inside Revit.

Pipes sizing and refrigerant flows are calculated using their specific Manufacturer's software.

[mmontejo26N2G]

Thanks, man that was quick! (I thought was gonna wait for days to be notice) 🙂

Not intentional but will change from "Sanitary" to "Hydronic"

In response;

All equipment (indoor and outdoor units) connectors, and its inline components were set at "Global:Calculated:Bidirectional" for the base assumption of cooling & heating modes for the system, OR am I wrong?

Again, thanks for the quick reply.

[HVAC-Novice · Accepted solution]

Just to clarify: are you talking about water-cooled VRF (geo-exchange), or regular air-cooled? If water-cooled, those should be treated like any hydronic equipment with water return and supply. You basically have a water to refrigerant HX and the water side can be dealt with in Revit. That would be the "outdoor" unit. the actual indoor unit (in a space) would be refrigerant only in both cases. 

If air-cooled (purely refrigeration only), I wouldn't really bother with any calcs. The manufacturers have their proprietary software to lay out the system and size pipes etc. In general refrigeration systems in Revit are just dumb pipes since the refrigerant flow is, 2-phase, and has to deal with oil-return, and many other very specific requirements. 

[iainsavage · Accepted solution]

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@mmontejo26N2G wrote:

All equipment (indoor and outdoor units) connectors, and its inline components were set at "Global:Calculated:Bidirectional" for the base assumption of cooling & heating modes for the system.

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Terminal equipment connectors (in this case indoor units) should be Preset and need to be single direction In or Out.

Source equipment (outdoor units) need to be Calculated, or if there are multiple units on the same system they need to be System and have a flow factor applied to apportion the flow to each unit. They also need to be single direction In or Out.

You’ll need to decide whether to use the heating or cooling phase for sizing, or run the calculation twice. 
Bidirectional wont work because Revit will have no idea how to decide which direction flow goes at branches and if you manage to get the System Inspector to work you’ll see negative flows occurring in some pipes.