Coupling Computational Fluid Dynamics and Finite Element Analysis to Optimize Heat Transfer in Buildings

Vincent Y. Blouin, PhD

Assistant Professor

School of Architecture

School of Materials Science and Engineering

Outline

• Research goals

• Thermal behavior of buildings

• Method– Finite Element Analysis (FEA)– Computational Fluid Dynamics (CFD)– Coupling FEA and CFD

• Numerical difficulties

• Results

• Conclusion

Research Goals

• Develop numerical simulation of thermal behavior of buildings by combining CFD and FEA in an iterative transient model.

• Use model in architectural building design and optimization to maximize building performance and minimize energy consumption by integrating advanced materials (e.g. Phase Change Materials).

Rationale for the Research

• Emergence of new advanced materials in architectural design justifies the need for advanced design methodologies.

• Phase Change Materials (PCMs) have the potential to reduce energy costs by up to 40% if properly designed. Design rules based on numerical simulation must be developed.

Thermal Behavior of Buildings

• Excessive heat gains/losses in buildings are due to:– solar radiation– thermal radiation– indoor and outdoor natural and forced convection– heat generation from lighting, appliances, electronics and users

• To mitigate these effects and maintain a comfortable temperature large amounts of energy are required.

• These effects are time-dependent and control the daily and yearly thermal balance and fluctuations.

Method

• The transient heat transfer problem of the building is solved by Finite Element Analysis (FEA) using ABAQUS.

• The steady-state fluid flow problem of indoor and outdoor fluids is solved by Computational Fluid Dynamics (CFD) using FLUENT.

• These two interrelated problems are coupled in an automated iterative procedure using MATLAB.

Method

FEATransient thermal analysisInput: Heat fluxesOutput: Wall temperatures

CFDSteady state fluid flow analysisInput: Wall temperaturesOutput: Heat fluxes

• The heat fluxes due to convection are computed by CFD based on the wall temperatures, which are computed by FEA based on the heat fluxes.

Method

• The transient heat transfer analysis is controlled by the FEA.• The time duration is discretized into time increments Dt.• A steady state CFD analysis is performed at each increment.

Transient FEA Time (hours)

0 1 2 24 …… …

Steady-state CFD

Steady-state CFD

Steady-state CFD

Steady-state CFD

t

CFD Results

• Air flow by natural ventilation through open windows

CFD Results

• Outdoor air velocity field due to a 3-mph transversal wind (from left to right)

CFD Results

• Indoor surface heat fluxes due to forced and natural convection

FEA Results

• Temperature distribution through walls (exterior façade and roof are heated in part by solar radiation)

FEA Results

• Outdoor air velocity field due to a 3-mph transversal wind (from left to right)

04/20/23 Vincent Blouin, vblouin@clemson.edu 14

Results

• Temperature fluctuations through building envelope during a 4-day period

Results

• Comparison of indoor wall temperatures during a 4-day period without and with Phase Change Materials (PCM’s)

No PCM’sT= 5.0oC

With PCM’sT= 3.5oC

Latent heat = 10 KJ/kg

Results

• Comparison of indoor wall temperatures during a 4-day period for two amounts of Phase Change Materials (PCM’s)

Latent heat = 10 KJ/kgT= 3.5oC

Latent heat = 20 KJ/kgT= 2.5oC

Computational Issues

• Design and optimization requires hundreds of simulations.

• Each simulation is an incremental FEA process that may require hundreds of CFD analyses.

• Both FEA and CFD are computationally intense. To achieve the desired accuracy, both models require millions of degrees of freedom.

Conclusion

• Method is computationally challenging• However, it provides versatility and

freedom in terms of geometry and material properties

• Provides a way to simulate thermal behavior of buildings for design and optimization

Future Work

• Validate method with established methods (e.g. enthalpy method)

• Compare with Fluent’s conjugate heat transfer method and other multi-physics software

• Study scalability of the method

Thank you!