A Simple Energy Recovery Retrofit to Achieve a 76% Annual Net Effectiveness

Mark Labac, Edge Mechanical Systems, Inc.
Rudolf Zaengerle, Konvekta USA, Inc.

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 can be accomplished quite easily with low installation cost and little to no down time for the building. Since the high efficiency system has a much larger fluid temperature difference across the coils, the flow rate of the system is much lower than the conventional system. Thus, the existing piping can be reused, which is a major capital cost savings. 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. Other components in the existing system that can be reused are the air separator, temperature sensors, glycol feeder and expansion tank.

By implementing the high efficiency system, the project for USU in this example can expect a 76% annual net effectiveness in lieu of 12%. Peak loads are expected to drop 53.6% for heating and 34.2% for 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.
  • 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 and little to no interruption in the existing building airflow.
  • The impact of energy savings, peak load reductions, emission and carbon footprint reductions from achieving a net 76% annual net effectiveness with an Intelligent High Efficiency Heat Recovery System.


Mark E. Labac, P.E., LEED AP is President of Edge Mechanical Systems, Inc., a specialty HVAC Manufacturer's Representative in Colorado. The firm specializes in energy efficient equipment, such as Konvekta, MeeFog, and MK Plastics, with a strong focus on laboratory and LEED projects. Mr. Labac has a Bachelor of Science in Mechanical Engineering from Texas Tech University, a Professional Engineer License from Texas, and a LEED AP Accreditation. Mr. Labac is an active member of ASHRAE, I2SL, and ISPE.

Rudolf Zaengerle, PhD is President of Konvekta USA, Inc., a subsidiary of Swiss based Konvekta AG, a manufacturer of high performance energy recovery systems. He holds a Master of Mechanical Engineering and a PhD in Business Administration, both from the Swiss Federal Institute of Technology, Zurich. He was an Assistant Professor at the Swiss Federal Institute of Technology's Energy Sustainability & Urban Planning Institute prior to managing Swiss technology in North America, over 20 years ago.


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