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Ventilation system modelling using Flowmaster

Opening doors during the introduction of a tanker truck


Fig. 1 – Ventilation system scheme

The number of ventilation systems in all sectors of industry is constantly increasing. Their functions are diverse:

  • To improve comfort and hygiene in work areas.
  • To protect people against the emission of pollutants.
  • To protect products and materials.

Consequently, in order to design a system, it is important to know how different components should be used (fan, dampers or others) to respect various criteria and also to predict air flow rates, pressures etc.

Flowmaster is a software tool which allows the modelling of HVAC systems using a 0D or 1D approach, with the potential for conducting steady-state or transient simulations with or without heat transfer. This permits the rapid determination of fluid pressure, flow rate and temperature across a network.

The studied system showed in figure 1 is composed of two main rooms (room 1 and room n2) with three doors: one between the two rooms, one between the room 1 and the external environment and the last between room 2 and a room with a relative pressure of -60 Pascal There are also eleven dampers. The initial relative pressures are respectively -20 Pascal for the first room and -80 Pascal for the second. The initial leak for each door is specified in figure 1.

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Fig. 2 – Flowmaster representation of the network


Table 1 – Flow balancing results

Dampers 1 to 6 represent the blowing line with a constant volumetric flow rate of 4546 m3/h and dampers n7 to 11 represent the extraction line with a constant volumetric flow rate of 4641 m3/h. There is also a constant extraction of 126 m3/h from the system.
The objective is to determine the optimal position of the dampers in order to maintain the flow rates and pressures in the rooms (see table 1), and then to run a transient simulation with the initial configuration in order to find the impact of opening doors 1 and 2 when a tanker truck enters the system.

Creation of network and implementation of data
The network is built based on the P&ID using corresponding Flowmaster components. Since Flowmaster does not allow 3D components, the rooms are each represented by a node. The volume of air in rooms is neglected in this study but it can be taken into account if necessary. The corresponding Flowmaster network can be seen on figure 2. The corresponding data has been entered in each component.

Initial configuration
The first step is to find a good opening ratio of dampers in order to meet the flow rates of initial configuration. For this, the “Flow balancing” module of Flowmaster is used. The flow rates are imposed in dampers and Flowmaster determines the corresponding opening ratios in order to meet these flow rate. Below is an example of flow balancing on the extraction line.

Table 1 shows required opening ratio obtained in order to respect flow rates demand for the different dampers.
Once these opening ratio are determined, they can be entered in the Flowmaster dampers components in order to run a steady state simulation and see if the initial configuration is well modelled.

Opening doors during the introduction of a tanker
The final step is to run a transient analysis in order to see how flow rates behave when both the door between the first room and the external environment, and the door between the two rooms are opening.

In this scenario, each door takes 3 minutes to open, dampers 4,5 and 6 are closed during the same period and consequently dampers 1 and 2 (which were initially closed) are opening in order to allow a volumetric flow rate of 1800 m3/h to pass (a flow balancing simulation allows the determination of the corresponding opening ratio). Tabular controllers are used in Flowmaster in order to control the position of doors and dampers over time. In the same time dampers 2,7,8,9,10 and 11 need to keep constant volumetric flow rates during all the process. For this, PID (proportional, integrate, derivative) controllers are used for each of these dampers. The corresponding network for this scenario can be seen on figure 4.


Figure 3 – Flow balancing on extraction line


Figure 4 – Flow balancing on extraction part

Results of the transient simulation can be seen in figures 5 to 8. From 0s to 10s the system is running with the initial configuration and the three minutes cycle begins at 10s.
Volumetric flow rates in all dampers are as expected and can be seen on figures 5 and 6. After three minutes volumetric flow rates for dampers 4,5 and 6 change from 1200 m3/h to 0 and consequently volumetric flow rates for dampers 1 and 2 change from 0 to 1800 m3/h. For the other dampers, volumetric flow rates are constant during the entire simulation.

The volumetric flow rates of the two doors which are opening are increasing over time due to opening of the doors and the variation of flow in the blowing line. An inversion can be observed on the second door due to relative pressure increase in the second room which increases from -80 Pascal to 0. The final room remains at -60 Pascal. This inversion is consistent.

The initial relative pressures for room 1 and 2 are respectively -20 Pascal and -80 Pascal and quickly increase to approximately 0 Pascal due to doors opening and the impact of the external environment (figure 8).

Results show how flow rates for the different doors and pressures behave when doors are opening during the introduction of a tanker truck.
Flowmaster can be used in ventilation systems in order to determine operating conditions with flow balancing and to predict what can happen during various scenarios in steady-state or transient simulations with or without heat transfer.
It can also be used to model the head loss created in a system and so be used to size a fan.


Figure 5 – Volumetric flow rates in dampers versus time


Figure 6 – Volumetric flow rates in dampers versus time


Figure 7 – Volumetric flow rates crossing doors versus time


Figure 8 – Pressure versus time in each room

Articolo pubblicato sulla Newsletter EnginSoft Anno 11 n°1

Philippe Gessent

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