Greenhouse Thermal and Airflow Performance with and without Heating System

Description

Greenhouse Thermal and Airflow Performance with and without Heating System

Project Description

This project focused on simulating airflow, heat transfer, solar radiation, and humidity distribution inside a greenhouse using ANSYS software. The objective was to compare the thermal performance of greenhouses equipped with and without a heating system by analyzing the variation in internal temperature, air velocity, and humidity levels. The simulations were conducted under steady-state conditions to represent the long-term behavior of the system, incorporating solar radiation effects through ray tracing and considering the thermal characteristics of the materials used in the greenhouse structure.

Geometry and Mesh

The 3D geometry of the greenhouse was created using ANSYS design modeler software. The model consisted of a computational domain and a room region, representing the fluid domain, and a ground region modeled as a solid body. The computational domain was 30 m wide, 10 m high, and 42 m long, the greenhouse was 4 m wide, 3.5 m high, and 10 m long, and the ground region was 4 m wide, 0.2 m high, and 10 m long.

The model was then imported into ANSYS Fluent software, where a computational mesh of approximately 1,860,000 cells was generated, providing sufficient resolution to balance simulation accuracy and computational cost. The second case also had 8 heaters with a power of 2,000 watts and a width of 0.07 m, a height of 0.6 m, and a length of 1.2 m, and approximately 3,110,000 computational meshes.

Setup

The greenhouse simulation was performed in ANSYS Fluent using a pressure-based solver, which was chosen due to the steady state of the problem and its independence from transient effects. The gravitational acceleration in the Y direction was set to -9.81 m/s. The energy equation was enabled to consider heat transfer within the domain. Turbulence was modeled using a k-ε model standard.

Radiation effects were included using a discrete coordinate (DO) model with active solar ray tracing to account for solar heating. Humidity effects were simulated by enabling the species transport model, with the density set to an ideal incompressible gas mixture of air and water vapor. The side surfaces and the roof and floor of the greenhouse are walls. In the second case, the heater surfaces are considered as walls.

Also, all the walls were modeled with a no-slip condition. The pressure-velocity coupling was performed using the Coupled algorithm to ensure strong convergence, and the solution was initialized using the standard initialization method in Fluent. These settings provided a stable numerical basis for solving the governing equations for the transfer of mass, momentum, energy, radiation, and species in the greenhouse environment.

Results

Simulation results include detailed temperature distributions, velocity, radiant heat flux, and water vapor mass fraction inside the greenhouse. These results can be presented via contour plots and vector fields for visual interpretation, along with quantitative data for key locations within the structure. Output analysis allows for assessment of temperature uniformity, ventilation effectiveness, solar radiation absorption, and moisture distribution.

As you can see in the table below, the average temperature and flow velocity in the two cases are compared.

Considering the average temperature obtained and the contours, it can be seen that the temperature difference between Case 1 and Case 2 is about 16 degrees. The difference in average velocity between the two cases is approximately 0.09 m/s. Velocity contour also show the difference in flow regime in a section of the greenhouse. Also, the velocity vectors and their magnitudes indicate the direction of solar radiation. The side where the magnitude of the velocity vectors is larger has a higher temperature and indicates the direction of solar radiation to that part.

Figure 1_ Temperature contour with heaters

Figure 2_ Temperature contour without heaters

Figure 3_ Velocity contour with heaters

Figure 4_ Velocity contour without heaters

Figure 5_ Velocity vector on the walls of the greenhouse with heaters

Figure 6_ Velocity vector on the walls of the greenhouse without heaters

Figure 7_ The velocity vector of the greenhouse zone with heater

Figure 8_ The velocity vector of the greenhouse zone without heater

Figure 9_ The velocity vector of the all zone with heater

Figure 10_ The velocity vector of the all zone without heaters