Optimizing Complex HVAC Systems With CFD

Anil Kapahi, Jensen Hughes
Fengchang Yang, Jensen Hughes

Designing energy efficient buildings can have an enormous impact on reducing carbon emissions; effectiveness of the Heating, Ventilation and Air Conditioning (HVAC) systems is critical to building energy efficiency. Maintaining thermal comfort while satisfying building performance requirements in demanding environments such as clean rooms and laboratories can be challenging to implement efficiently.

HVAC system optimization has traditionally used simple energy calculations which treat the building area as one single control volume; this approach can oversimplify buildings with critical operating parameters. As a result, performance-based design using computational fluid dynamics (CFD) simulations has gained significant traction in the planning and construction of modern HVAC systems.

This presentation reviews projects that employed CFD simulations to optimize energy use considering temperature, humidity, and thermal comfort requirements. The projects considered external solar radiation and heat sources within the building (personnel, equipment, lighting) with a 3D CFD model. The building model was analyzed with ANSYS Fluent to simulate the HVAC system's effectiveness at managing the temperature, relative humidity, and air flow within the building. The results of the simulation were then used to quantify the thermal comfort using industry standard parameters such as predicted mean vote (PMV) and predicted percentage of dissatisfied occupants (PPD) to ensure the desired comfort level for building occupants. This performance-based design approach helped the owner and designers to make rational and timely decisions on choosing/designing the HVAC system, which significantly reduced the building construction cost.

Learning Objectives

  • Recognize key thermal comfort measures;
  • Identify methods for evaluating building HVAC performance;
  • Understand internal and external heat sources and associated impact on HVAC thermal performance; and
  • Explain key outputs from CFD modeling of HVAC performance.


Dr. Kapahi is a Computational Engineer with 14 years of experience in designing and developing multi-physics algorithms in academia and industry, focusing on Computational Fluid Dynamics and Finite Element Analysis applications. He has consulted for the DoD and DoE, has a strong scholarly contributions to both computational and physical sciences, and supports projects involving thermal and structural analysis. He graduated with his PhD in Mechanical Engineering from the University of Iowa.

Dr. Yang's experience relates to multiphysics modeling and research, including solid material burning, micro/nanofluidics, advanced battery modeling and particulate flow. He has authored more than 10 technical publications and supports Oak Ridge National Lab. His expertise focuses on the multiphysics modeling of coupled fluid, heat, chemical species, particulate transport and chemical reactions in complex systems. He graduated with his PhD in Mechanical Engineering from Virginia Tech.


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