Old Made New: Rethinking Run Around Loop Energy Recovery to Make it Cool in the Desert

Paul Erickson, Affiliated Engineers, Inc (AEI)

The recently completed Arizona State University Biodesign Institute Building C project had three major goals for the design team: generic and flexible workhorse lab facility, high level of sustainability, and a cost target less than recent lab facilities throughout Arizona. All of these demanded an integrated design approach, which resulted in our team devising a way to enhance the traditional run around loop (RAL) energy recovery system in such a way that it could be leveraged to alleviate space and flexibility challenges, while significantly boosting energy performance on the airside and for the chilled beam hydronic cooling system.

RAL energy recovery is not new, and though it's been around for decades and is tried and true for labs, it's historically been an unintelligent system and its energy performance toward the bottom of airside energy recovery systems. The project needed something on par with a total energy wheel, given the intense heat of Tempe and the additional challenge of latent heat in the monsoon season. Roof space was a constraint on the narrow footprint of the building, penthouse space limited due to costs, and penthouse height was capped due to a line of sight requirement. This translated to a need for shorter air handling units and an energy recovery approach other than a bulky energy wheel.

A fresh look at RAL, in considering the mainly very dry climate, revealed that indirect evaporative cooling would be extremely effective at providing improved precooling, thud eliminating the need for campus chilled water for a significant number of hours annually. The intended supply air strategy also led to improved performance of the chilled beam zone-level cooling system, when paired together. The pendulum was swinging back in favor of a RAL system, because it saved on space, enhancements raised its energy performance, and from cost and flexibility perspectives, the exhaust system for general and lab could be combined within the building, making it overall much simpler.

The last step was determining how to design and control the system. The outcome is a single-coil AHU design. The coil serves as energy recovery, preheat, and cooling coil. The loop is supplemented by heating and cooling heat exchangers served by campus utilities. It was decided that an engineered, custom packaged solution was the most advantageous path for numerous reasons including complexity of control and controls integration, challenges of procurement and construction in a field-built approach, and for long-term maintainability. The engineered system also brought a higher level of system energy performance and optimization capability.

Learning Objectives

  • Develop an understanding of performance differences between energy recovery system types
  • Gain an appreciation for the potential interactions and benefits of a run around loop system with other high performance design strategies
  • Be able to apply lessons from this Southwest climate to other areas of the country
  • A basic understanding of energy code requirements for energy recovery in lab buildings


As AEI's Building Performance Practice Leader, Paul Erickson, LEED AP BD+C, manages the firm's sustainable design services and champions high performance design on projects around the country. As a principal and project manager on laboratories and other project types, he is dedicated to integrated design, driving innovation, utilizing a host of performance simulation tools, and ensuring that design solutions can be operated and maintained in the long term.


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