A Simple Energy Recovery Retrofit to Exceed Current Energy Codes

Brad Carpenter, DAC Sales
Jonathan Chan, Bard, Rao + Athanas Consulting Engineers

Traditional run-around coil systems offer many advantages such as installation flexibility and zero cross contamination; however, they have a very low energy saving effectiveness along with operational issues. The net annual effectiveness of traditional systems tends to be around 15-25%.

A high efficiency system is a run-around coil system; however, it uses strategies that are more efficient than other systems. This system uses special coils with a very close air to fluid temperature approach. The coils maintain turbulent flow through a wide range of flow rates, allowing a variable flow system. By varying the flow in the system, the effectiveness can be optimized at all operation conditions since temperatures and airflows are always changing. An industrial and reliable control system is needed to perform the calculations to always optimize the system with the changing variables. The control system monitors the entering and leaving coil air and water temperatures, the air volumes, and fan status for both the supply and exhaust units. Based on this information along with the supply temperature set point, the controller optimizes the energy recovery by varying the pump speed and control valve positions. To accomplish this task, the control system performs a numerical simulation once per second using 3D performance maps of the coils, pumps and valves. To enhance the summer effectiveness, the use of adiabatic cooling in the exhaust is used to increase the effectiveness in arid climates by another 50%. Some manufacturers can offer a financial guarantee on the annual net effectiveness of the system.

Retrofitting an existing conventional run-around coil system and adding additional energy saving equipment can typically be an engineering challenge. With high efficiency systems that are now available this can be accomplished quite easily with lower than expected installation cost.

Laboratories typically have multiple supply and exhaust units, so the supply and exhaust units can be staged on/off to replace the existing heat recovery coils with the special high efficiency coils. While the coils are being replaced in the exhaust units, a high-pressure adiabatic cooling system can be added to increase the summer effectiveness.

By implementing the high efficiency system, the project for Whitehead Institute in this example can expect in excess of a 76% annual net effectiveness in lieu of significantly less than 20%. Peak loads are expected to drop significantly for both heating and cooling.

Learning Objectives

  • Discussing the low annual net efficiencies and operational short falls with conventional run-around coil heat recovery systems commonly used in laboratories. Discussing specific deficiencies in the existing building and challenges presented.
  • Understanding the control and optimization of an Intelligent High Efficiency Energy Recovery System and its components.
  • How to implement an Intelligent High Efficiency Energy Recovery System into an existing conventional run-around coil system with minimal installation cost. Discussion on how to value the first costs of the system and how to save money on items that would not typically be evaluated with a run around glycol system.
  • The impact of energy savings, peak load reductions, emission and carbon footprint reductions from achieving in excess of 75% annual net effectiveness with an Intelligent High Efficiency Heat Recovery System.


Brad is a Sales Engineer with DAC Sales. The firm specializes in energy efficient equipment, such as Konvekta, with a strong focus on laboratory and LEED projects. Brad has spent eight years as a manufacturer's representative for custom air handling equipment, energy recovery units, fans, variable speed drives and lab controls in the New England region. Brad also worked as a mechanical Engineer for three years with TRO Jung|Brannen in Boston. Brad is a member of Boston ASHRAE.

Jonathan Chan - Biography coming soon.


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