CDF, Application to HVAC Systems

Computational fluid dynamics (CFD) is the area of ​​knowledge that deals with the numerical simulation of fluid flows, heat transfer, and chemical reactions (ESSS, 2016). This area starts from the combination of fluid mechanics and numerical calculation, implemented using computational capacity to solve continuity equations throughout the analyzed volume. Its application allows the possibility of analyzing, planning, and managing the necessary resources to develop a new product or determine the characteristics of a new one with complex geometric or flow conditions that could not be solved analytically.

Illustration L-AV Difusser CFD Analysis, Laminaire (2021)
Illustration L-AV Difusser CFD Analysis, Laminaire (2021)

The application of CFD in HVAC systems is relevant given the ability to analyze the performance of the products and determine the behavior of the fluid that interacts with the HVAC element. On many occasions, the measurement of variables to determine the performance of a product requires specialized and conditioned test benches that have a high value that many companies cannot afford. In response to this problem, CFD analysis can be used to obtain a result that must be analyzed carefully from the theoretical point of fluid mechanics to determine if the results are correct and correspond to the phenomenon that occurs.

CFD ANALYSIS STRUCTURE

3 basic steps are followed to do a CFD analysis of a product:

  1. Pre-Processing: defining the simulation objectives, making possible simplifications, evaluating the boundary conditions, generating the CAD model, meshing, and setting up the simulation.
  2. Processing: evaluating the convergence of the solution.
  3. Post-processing: obtaining the calculations of the variables, graphs, animations, videos, and all necessary resources. The model must also be validated with experimental/analytical data.

Then, why don’t all companies use fluid simulation in product design?

A series of tools and specific knowledge must be present to carry out a good flow simulation so that the results obtained are related to reality. Among the difficulties to performing a good CFD analysis are (SimScale, 2021):

  • Accessibility and Operational Costs: the tools to perform CFD analysis are simulation software and computer equipment. On one hand, most software must be installed locally and have a high cost due to their development; on the other hand, the computer equipment must have a great processing capacity to reduce simulation time and obtain more refined results.
  • Technical Knowledge: the computational tools require simulation experts with knowledge in matters such as heat transfer, materials, fluid mechanics, physics, and in general in all areas of engineering. These experts apply the simplifications and considerations according to their knowledge.

Advantages of implementing computational simulations:

  • Precise and individual designing of an HVAC system performance.
  • Cost reduction by knowing and improving the design.
  • Efficiency improvement of equipment/products.
  • Determining failures and redesigning of substandard installations.
  • Proposing of different operating scenarios without a physical test bench.
  • Measuring the equipment operation under different initial conditions.

Committed to the continuous improvement of our products, Laminaire has implemented CFD analysis simulations on diffusers, grilles, and metal facades to determine their behavior and performance, as well as to identify and report on their capacity and their continuous improvement to provide a better product to our customers.

Example: Dynamic and Thermal Fluid Analysis, L-AV-4W diffuser

In the Pre-processing stage, we used a simplified CAD model of the L-AV square ceiling diffuser with 4 diffusion ways. The nominal dimensions of the model to be simulated are 12 inches x 12 inches.

Illustration 2. CAD MODEL L-AV DIFUSSER
Illustration 2. CAD MODEL L-AV DIFUSSER

For simulation purposes, we prepared a room measuring 5x5x3 m in height, and we created internal plans to evaluate air diffusion in the operating area. We located the diffuser in the upper part, and we added a grille to the wall.

Illustration 3. IN-ROOM CUTTING PLANS
Illustration 3. IN-ROOM CUTTING PLANS

The boundary and flow conditions that were evaluated are the following:

  • Fluid: AMBIENTE AIR.
  • Flow: 550 CFM.
  • Inlet Temperature: 14 °C
  • Outlet Temperature: 20.8 °C.
  • Wall Temperature: 28 °C.

Finally, after verifying the convergence of the results obtained, we proceed to obtain the results of the simulation, in this case, it was possible to obtain, among others, details about:

  • Speeds developed in the operating area.
  • Temperature profile throughout the room.
  • Flow lines developed in the room (2D-3D).
  • ISO-Temperature Surfaces.
  • Particle trajectories videos.
  • In-room temperature plan videos.
  • Coanda Effect evidence.
  • Diffuser cooling ability.
  • Diffuser shot details.

 

Illustration 4. Speed, axis XZ, Streamlines (3D) and ISO-temperature surfaces 16 °C, 18 °C and 20 °C, Laminaire (2021)
Illustration 4. Speed, axis XZ, Streamlines (3D) and ISO-temperature surfaces 16 °C, 18 °C and 20 °C, Laminaire (2021)

BIBLIOGRAPHY 

ESSS. (2016). Dinámica de Fluidos computacional: ¿qué es? Retrieved from https://www.esss.co/es/blog/dinamica-de-fluidos-computacional-que-es/

SimScale. (2021). Validación de la ventilación pasiva en el diseño de edificios. Retrieved from https://www.simscale.com/blog/2018/06/passive-ventilation-building-cfd/?utm_source=hpac&utm_medium=referral&utm_campaign=hpac

 

Article:

Ing. Luis Felipe Trejos T. – Director of operations

Laminaire S.A.S

 

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