Ventilation System Modeling 2-Part B

2.2. Modelling a Leak:

Once the initial network has been input it is easy to perform many calculations to study the various types of failure which can occur in the system. One of them might be to predict what would happen if there was air in-leak due to a perforation.

Let us suppose there was a small perforation 10 mm diameter exactly half way along duct 20. Let us also suppose that the wall thickness of the duct material is 2 mm. PIPENET can be used to model this by using the following steps:

Create an additional node half way along duct 20

Attach a pipe 10 mm diameter, 2 mm (0.002 m) long to this node

Set the pressure at the free end of the new pipe to 0 in. H2O g.

Then a calculation can be performed.

It can be seen that this only makes a minor difference to the extract flow rates.

Now increase the perforation size to 100 mm diameter and see what happens.

3. EXAMPLE 2:

3.1. Balancing a Ventilation System

· The first objective is to select a suitable fan to drive the system.

· The second objective of this problem is to find ways of ensuring that the pressure remains negative within the compartments and the direction of flow is from less contaminated areas to more contaminated areas.

· We also consider what happens if there are doors in between the compartments, which could potentially, leak.

· Finally we consider the case in which one or more doors are left open.

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Extract fan

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Inlet fan

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Ancillary Data:

The medium is air at 20 deg C (use ideal gas).

The units to be used are Pa (g), m3/s, m (diameter), m (length). The other units can be chosen as desired.

The Network:

The schematic of the network as input to PIPENET is shown below:

The compartments are divided into two because we will introduce interconnecting doors between the nodes in other simulations later.

For the sake of simplicity no fittings are considered. The network data also has a high degree of symmetry so that copy and paste of attribute data can be used to the full.

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