User Notification "Concentrated CAV model must be used..."

Product(s): Hammer
Version(s): 08.11.XX.XX, 10.XX.XX.XX
Area: Modeling 


After computing a transient analysis, the following user notification is generated:

"Concentrated CAV model must be used. Note that each neighbour node of an extended CAV must be: 1) lower than the CAV, 2) a junction with no demands, 3) associated with only one CAV. The CAVs which violate the requirements include: " 


There are a couple of reasons that this user notification is occurring. This message will only occur when "Run Extended CAV" is set to True. This is done in the Transient Calculation Options. With this setting, it allows some tracking of the air pocket that forms when the pressure at the air valve drops to zero. However, there are a few limitations to how the air valve is set up in the model.

When using Extended CAV, the air valves must be set up as follows:

1) The air valve must have a higher elevation than the adjacent nodes.

2) The nodes on either side of the air valve must be junctions.

3) The junctions adjacent to the air valve cannot have a demand.

4) The air valve type must not be "slow closing" (which currently does not support Extended CAV)

If any of these qualifications are violated, the user notification above will be generated. The image below shows one setup for using Extended CAV.


Note that the nodes on either side of the air valve are junctions. In addition, the air valve is at a local high point. Lastly, J-1 and J-3 do not have any demands applied to them.

If you need to use Extended CAV, you will need to review the model to see if any of the qualifications are violated. Remove any demands on junctions adjacent to the air valve, make sure the air valves are not in series, and make sure that the air valves are at local high points in the model.

If you don't need to use Extended CAV, or if you need to model air valves in series, air valves that aren't at high points, or adjacent junctions with demands, you can also calculation option property "Use Extended CAV" to False.

For more information, on air valves and the use of the "Extended CAV" option, please refer to the Help documentation included with HAMMER, or browse the following TechNote: Modeling Reference - Air Valves.

Note that the air valve is still functioning. HAMMER is simply using the Concentrated CAV method instead of the Extended CAV method for the air valves referenced in the user notification.

See Also

Slow Closing air valves and Extended CAV