A Holistic Approach for VAV Versus Chilled Beams Design Decision

Rushil Desai, Atelier Ten
Jagan Pillai, Atelier Ten

Laboratories are some of the most energy intensive building type. A large portion of this energy is used for space conditioning, and ventilation air conditioning and distribution. In recent years decoupled system configuration with dedicated outside air units and chilled beams (referred as Decoupled System) are being implemented more widely to save energy in labs. Most design decisions to implement all air variable air volume (VAV) system vs. Decoupled System are taken based on the annual energy cost savings and initial cost of the systems.

The authors have worked on several laboratory projects where system selection was made based on annual energy cost savings and life cycle cost assessment. In many cases the Decoupled Systems have shown high initial cost and therefore a longer payback period. Because of this Decoupled System was not selected as a design strategy in spite of the annual energy savings. The authors will share their experience about how additional benefits from implementation of Decoupled System can help make a better decision. Some of the additional benefits that Decoupled Systems provide are reduced ductwork, smaller system size, reduced floor to floor height requirement, flexibility for later program changes etc. The presentation will discuss these benefits in detail and how they were incorporated in the life cycle cost analysis to make design decisions. After taking these into account, the Decoupled System were a more attractive system option even with the high initial cost.

What is very often overlooked in a comparison of these system types is the variability in operation. Both system types, as modeled in an energy simulation software to estimate annual cost savings, are operationally optimized. Therefore, the savings observed are under the best-case scenario. The authors have worked on projects where VAV systems have proven to be deteriorate in operation much faster than Decoupled System. And additional maintenance is required to have them working at their optimum operating range. The authors with the help of existing projects and energy modeling results will show the range in which the energy consumption by a Decoupled System and VAV can vary over the life of the system. Authors believe this should also be an important consideration while making the design decision.

Learning Objectives

  • know the benefits and limitations of VAV and chilled beams
  • know how life cycle cost can be used as an effective tool to make design decision
  • know about the operational deviations over time between VAV and chilled beams and its energy implication range
  • know about additional benefits beyond energy for utilization of chilled beams compared to VAV


As an Environmental Designer at Atelier Ten, Rushil is interested in net-zero energy, building to grid interoperability, and measurement and verification. He brings expertise resulting from a diverse set of experiences in energy engineering, net-zero energy and sustainability. Rushil holds a B.Tech. and M.Tech. in Energy Engg. from the Indian Institute of Technology Bombay, and a M.S. in Energy Science, Technology and Policy with a concentration in Civil and Environmental Engg. from Carnegie Mellon.

As an Associate at Atelier Ten, Jagan is an expert in the application of building energy analysis, including optimization of mechanical, and electrical system design for high-performance laboratory buildings. Jagan holds a M.S. in Mech Engg from the University of Colorado, Boulder and a B.S. in Mech Engg from the University of Mumbai,India. He is a registered Professional Engineer in the State of Colorado, LEED Accredited Professional and a Certified Energy Manager.


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