What is the purpose of the LOSS at the HVAC-node?

[mst-parkhachev]

Dear colleagues!

I can't quite understand the impact of the LOSS parameter in the terminal nodes.
The User Guide says:

For a terminal node (e.g., a node connected to the ambient or to a VENT) the LOSS is entered as a pair of numbers representing loss coefficient for flow entering the HVAC system and for flow exiting the HVAC system.

The Technical Ref Guide states that only duct losses are included in the governing equation. I didn't quite understand whether the losses specified for the nodes are automatically added to the duct losses?

When simulating ventilation, will the terminal node losses simply be added to the duct losses?

I looked at a simple project of two sealed rooms connected by ventilation.
node_loss_100.txt
This is an implementation of a fan:

&VENT ID = 'OUTLET' XB=0,0,4.75,5.25,1,2 IOR=-1 SURF_ID='HVAC' COLOR='BLUE' /
&VENT ID = 'INLET' XB=0.25,0.25,4.75,5.25,1,2 IOR=1 SURF_ID='HVAC' COLOR='RED' /
&HVAC TYPE_ID='NODE', ID='connection 1', DUCT_ID='duct 1', LOSS=1,1, VENT_ID='OUTLET' /
&HVAC TYPE_ID='NODE', ID='connection 2', DUCT_ID='duct 1', LOSS=100,100, VENT_ID='INLET' /
&HVAC TYPE_ID='FAN', ID='fan 1', MAX_FLOW=1, MAX_PRESSURE=300. , LOSS=1 /
&HVAC TYPE_ID='DUCT', ID='duct 1', NODE_ID='connection 1','connection 2', AREA=0.1, LOSS=2,2, LENGTH=5, FAN_ID='fan 1' /

The loss value of 100 is considered simply as an example. The pressure difference between the rooms increases very quickly, and when looking at the simulation results, I was unable to understand what quantitative influence the parameter in question has.

[drjfloyd]

Node losses are added to the connected ducts. For a terminal node, it is just added to the single connected duct. For multiple duct nodes (e.g. a tee), losses are added to the outflowing duct(s).

With two sealed rooms and a maximum fan pressure of 300 Pa, you will quickly move enough mass (~0.2 %) from one room to the other to stall the fan. This may make it challenging to see the effect of the loss parameters. You may want to take a look at the fan_test verification case (14.7 in the Verification Guide with input in the Examples\HVAC folder) and vary the LOSS and FAN parameters in that example.

[mst-parkhachev]

Thank You, Dr. Floyd!