Ventilation Modelling Using CFD

Learning outcomes:

- Evaluate complex mathematical models of energy and fluid flow in buildings.
- Solve complex energy and flow problems for buildings using dynamic thermal simulation and computational fluid dynamics.

Assignment Brief:

A typed report presenting the results to the tasks specified in the attached, describing and analysing the results using the air distribution performance index criterion and drawing conclusions which address the report objectives.

Resources required...

In the School IT laboratory:

• This assignment will be carried out using PHOENICS.

In the module assessment and learning materials directories of Blackboard:

• PHOENICS practice tutorials - a set of 4 self-study tutorials for CFD modelling using PHOENICS covering wind flow around buildings; airflow in a duct fitting; non- isothermal room air distribution and convective flow over a hot water radiator.

Model-building using PHOENICS will be demonstrated in the IT laboratory during the laboratory sessions on Fridays.

Proceed as follows...

Five variants of a simple case comprising a single rectangular room with the size of 5.2m x 3.6m x 2.7m (high). Two isothermal cases A and B focusing on the air distribution in the room. Cases C, D and E concentrate on the natural and mixed convection heat transfer in the room.

In case A, B & D, a supply grille with an overall dimension of 0.4m x 0.15m is positioned at the centre of the west-facing wall at a distance of 0.2m from the ceiling to the top edge of the diffuser. The discharge angle of the diffuser is horizontal. There are two extract grilles located in the north-east and south-east corners of the ceiling, with a distance of 0.2m from the upper edge of the north-and east-facing walls or south-and east-facing walls. The dimensions of the extract grilles are 0.3m x 0.3m.

In case C & D, there is a sash window size of 3.2m x 1.5m located in the south-facing wall, at a distance of 0.8m above the floor. In case C, a single panel radiator with a dimension of 2m x 1m x 0.05m is added to the room, which is located 0.1m in front of the south-facing wall and 0.1m above the floor.

Present your results as graphic images only. For cases A and B you need only present graphics of room air velocity. For cases C, D and E you should present graphics of both room air velocity and temperature. Discuss all results in the context of satisfactory room air distribution (cases A and B) and room air distribution and thermal comfort (cases C, D and E).

The following section are provide more information and sample of model of each specific case.

The boundary conditions of the five cases are as follows:

A. Isothermal forced convection with a supply air grille and two extract grilles. Supply grille discharge velocity = 3.0ms^-1.

Figure 1: Model sample of Case A

B. As Case A but with an beam obstruction to the air flow. The beam is spans the width of the space and is located adjacent to the ceiling equidistant between the east- and west-facing walls. The dimensions of the beam are 3.6m x 0.2m x 0.4m.

Figure 2: Model sample of Case B

C. Natural convection in winter heating by means of a radiator located beneath a cold window. The surface temperature of the radiator is 70°C. Wall / ceiling / floor surface temperatures = 17°C. Window surface temperature = 5°C.

Figure 3: Model sample of Case C

D. Mixed convection in summer cooling condition with a supply grille and two extract grilles. Supply grille discharge velocity = 3.0ms-1. Supply air temperature = 12°C. Wall / ceiling / floor surface temperatures = 24°C. Window surface temperature
= 35°C.

Figure 4: Model sample of Case D

E. Single-sided window natural ventilation with room heat gains. Wall/Ceiling surface heat flux = 5W/m². Sunlight is coming in at 30 degree in the Z-X plane to the room through the window. Set up window as an opening and simulate this case in range of window opening states and set the external temperature to 10°C. Model a person standing in the centre of the room with 58W heat gain in dimension: Body width: 0.6 m, Body depth: 0.3 m, Body height: 1.76 m.

Attachment:- CFDModelling.rar