Room ventilation systems are essential components of modern building design, providing crucial indoor air quality and thermal comfort for occupants. The strategic placement of cooling ducts within an enclosed space facilitates efficient temperature distribution and plays a vital role in maintaining comfortable living and working environments. In this tutorial, we examine how HVAC systems utilize ceiling-mounted ducts to create effective cooling through natural convection rather than high-velocity forced air. Understanding these airflow dynamics is crucial for optimizing ventilation performance in residential and commercial spaces, particularly when dealing with external heat sources like windows that can significantly impact the thermal balance within a room. A room ventilation system benefits from a cooling duct is numerically investigated in this independent study.

Figure 1: Room schematic equipped by cooling duct

Simulation Process

The room model is primarily created using Design Modeler. As portrayed above, a door, a window and HVAC ducts are installed. The domain is then discretized into hexagonal cells using ANSYS ICEM software. This structured mesh was established from 1078800 number of cells.

The ultimate goal of the present study is to get acquainted with the power of CFD simulations. Thus, the simplest assumptions are taken. While the window`s temperature is 37.1°C, the 9-degree ducts are expected to cool down the room.

Figure 2: Grid generation by ANSYS ICEM

Post-processing

The simulation results reveal how air moves inside the room when cooled by ceiling-mounted ducts. Looking at the flow patterns, we can see several circular motions (called vortices) forming throughout the room, where air spins in different areas rather than flowing straight. The cooling happens mainly through natural convection – cold air from the ducts naturally falls downward while warm air rises. This creates a gentle circulation that helps cool the room without needing high-speed air blasts. The blue areas in the images show slower moving air (close to 0 m/s), while the green-yellow areas show faster movement (around 0.17-0.26 m/s).

The 3D view shows how temperature differences between the hot window (37.1°C) and cool ducts (9°C) drive this air movement. The system managed to bring the overall room temperature down to about 28.5°C despite the heat coming from the window. We can see that air velocity is higher near the walls and cooling ducts (shown in green) and slower in the center of the room (shown in blue). This pattern confirms that placing ducts near the ceiling works well for cooling since it takes advantage of natural air movement – cold air falls down while warm air rises, creating natural circulation throughout the space without needing powerful fans.

Figure 3: Natural-driven cooling system in a room