Justifying the High Performance Wrap Around Modified Glycol Loop for Heat Recovery: A Case Study of a Lab Project in China

Paul Tsang, Jacobs Engineering Group
Betty Liu, Jacobs Engineering Group

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A run-around glycol loop is commonly done for laboratory ventilation systems to capture the waste heat from the exhaust air stream to preheat the incoming outside air. This energy recovery approach uses a glycol solution as a heating medium to transfer energy and allow a total separation of the exhaust and incoming air stream. It prevents cross contamination of fresh air which is an important aspect of this recovery scheme. However, the efficiency of this standard/traditional run-around glycol loop is limited to 30-40 percent. This method of heat recovery is mostly implemented in the cold climate regions, where the energy recovery is taking place for the heating mode. The payback is typically 6-7 years, depending on the operation.

A case study was done for a lab project in the Shandong Peninsula of China for an undisclosed client. The building accommodates a very high density of fume hoods for research. This results in a high demand for outside make-up air. The design requirement for ventilation is 64.4 m3/hr per m2 (3.5 CFM per sq.ft.). This is almost double a typical chemistry lab, which is about 2 cfm per square foot. Because of the high consumption of energy required to run the building, energy recovery has become an important feature of the mechanical design. The glycol loop system has been modified to serve both the preheat and reheat loop. When energy is introduced at the reheat coils, it reduces the amount of energy required during the cooling mode. The system is optimized and utilized year-round, not just the heating season. The modified loop is definitely more expansive with additional piping, coils, valves and controls. As part of the case study, several factors were considered during the decision making, such as the amount of reheat required, the operating conditions, the schedule, and the installation cost.

Learning Objectives

  • Learn about the modified high performance wrap around glycol loop;
  • Comparison of the traditional run around glycol loop to the modified system;
  • What are the factors considering the implementation of the modified system; and
  • What are the type of projects for this heat recovery application.


Paul has experience in design and construction management of mechanical systems. Paul's expertise includes HVAC systems, clean rooms, laboratories, animal facilities, process piping design, energy analysis, conservation and heat recovery. He has managed projects in life sciences and lab building construction and served as project manager and senior HVAC engineer.

Betty is a professional in HVAC and plumbing designer for labs, pharmaceuticals, manufacturing warehouses, commercial, retail, and higher education buildings with enthusiasm in both engineering and sustainability. She strives to integrate sustainability into traditional engineering design workflow into order to build a greener community.


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