car park gate modelling as a damper with HVAC

[José Felipe Pérez Segovia]

Dear all, 

I am modelling a car park gate using the HVAC module. I create two HVAC vents connected by means of a duct. In the duct I stablish that the area is the free area of the gate. In this case 0.2*14=2.8. The perimeter of the car park gate is the real perimeter of the car park gate. The loss of charge (K) is obtained from tables. I prescribe that there is not friction to include to make the K used in the expression:

lossP=kv^2/rho/2

I include an small example of the code.

I would like to confirm that I am using properly the HVAC module and the approach that I am using is acceptable.

[dr_jfloyd]

I haven't run your case but looking at the inputs, they look OK.

The VENT area is 5 m x 2.8 m. This is a fairly large area. Something to consider is that flows in an HVAC duct are unidirectional.  With a 2.8 m high opening (event though the free area is much smaller), depending on the geometry, fire location, and exhaust flow the conditions at the gate could result in bi-directional flow. If this is a possibility, you should split the area of the gate into multiple VENTs each with part of the free area.

[José Felipe Pérez Segovia]

Thanks for your reply and your advice.

I am taking a look in more detail. The variable that I am less convinced is the perimeter. As I mention I use the entire perimeter of the gate. However, I went through the technical guide. It seems to me that the perimeter is only used to calculate the hydraulic diameter. With the hidraulic diameter the f is calculated and with f, D and L the k friction. In my set'up I have prescribed K and no friction as 

&HVAC ID='Duct12', TYPE_ID='DUCT', AREA=2.8, PERIMETER=15.6, LOSS=15.0,15.0, NODE_ID='Node23','Node24', LENGTH=0.2/

Then, I think that the perimeter should not have influence on the calculation.

[dr_jfloyd]

You are correct. The flow loss through a duct is the sum of the wall fraction loss (f L/D where f is a function of the ROUGHNESS) and losses due to fittings. In this case your LOSS is for the gate as a whole and your aren't using the ROUGHNESS which means you are not computing an f and the diameter isn't being used.