Solar Chimney for a Room HVAC, CFD Simulation

Description

Project Description

The problem is simulating the HVAC inside the room considering a solar chimney. The present model consists of two main parts, including the interior of the room and a sloping solar chimney on the ceiling of the room. The solar chimney consists of glass plates on its side surfaces that are in contact with the environment and, as a transparent medium, receive the solar energy and also have a plate on its back as a heat-absorbing surface. It is assumed that the adsorbent surface behind the chimney has a constant temperature of 335.15 K, while the glass surface in contact with the external environment has heat transfer with its surroundings.

The ambient air temperature is 308.15 K and the convection heat transfer coefficient is 8 Wm-2.K-1. It is also assumed that the heat received from sunlight inside the chimney creates a constant heat source inside the chimney, equivalent to 15000 W.m-3. The airflow from the inlet section at the bottom of the room has a pressure-inlet boundary condition; In this way, this incoming airflow at a temperature of 308.15 K is sucked into the room by the heat of the solar chimney and is transferred to the environment outside the room.

Geometry & Mesh

The 2-ِD geometry of the present model is carried out using Design Modeler software. The geometry of the model consists of two parts, including a room measuring 2 m⨯3 m and a solar chimney with a length of 2 m, with a slope of 45 degrees to the ceiling of the room and with a width of 0.15 m. The figure below shows an overview of the model’s geometry.

The meshing of the present model has been done using ANSYS Meshing software. The mesh type is structured and the element number is 42846. The figure below shows a view of the mesh.

CFD Simulation

To simulate the present model, several assumptions are considered, which are:

• The solver is based on a pressure-based perspective.
• The simulation examines both the fluid behavior and the thermal (heat transfer) behavior of the model.
• The present model is steady-state.
• The effect of gravity on the fluid is considered to be 9.81 m.s-2.

The following is a summary of the steps for defining a problem and its solution:

Models
k-epsilon		Viscous model
standard		k-epsilon model
standard wall function		near-wall treatment
on			Energy
Boundary conditions (Solar Chimney)
pressure-inlet			Inlet
00 pa		gage pressure
308.15 K		temperature
Pressure outlet			Outlet
0 pascal		gauge pressure
wall			wall absorbing
335.15 K		temperature
wall			wall room and wall glass
308.15 K	free stream temperature	convection
8 W.m-2.K-1	heat transfer coefficient
Solution Methods (Solar Chimney)
SIMPLE			Pressure-velocity coupling
Second-order		pressure	Spatial discretization
second-order upwind		momentum
first-order upwind		turbulent dissipation rate
first-order upwind		turbulent kinetic energy
Initialization (Solar Chimney)
Standard		Initialization method
-0.15 m.s-1		x-velocity
0 m.s-1		y-velocity
0 pascal		gauge pressure

Solar Chimney Results

After the solution process is completed, two-dimensional contours of pressure, temperature, and velocity, as well as pathlines and velocity vectors, are obtained. Also, the diagram of temperature distribution in the transverse direction at a point in the middle of the solar chimney (at a distance of one meter from the inlet and outlet of the chimney) and the graph of velocity changes in the transverse direction in the chimney outlet section is obtained.

Solar Chimney Validation

The temperature profile at a point in the solar chimney at a distance of 1 m from the chimney inlet in the chimney with a thickness of 0.15 m has been obtained and compared with the temperature profile of the same case in the article.

 

There is a mesh file in this product. By the way, the Training File presents how to solve the problem and extract all desired results.