ETC Group’s energy efficiency engineers, Chris Jackson, PE, and Bryan Lang, PE, are invited to speak at the 2021 ASHRAE Virtual Winter Conference, February 9-11, 2021. The virtual on-demand presentation is titled “Easing Transitions between Flat Plate and Chiller: Strategies to Reduce Chiller Surge and Maintain Building Load Efficiently.”

energy efficiency engineers

Chris Jackson, PE, and Bryan Lang, PE

This presentation provides a review of the operational strategy to reduce the stress and impact of mode transitions in chillers and improve winter and shoulder season operation. The  content will be beneficial to facility managers, building owners, mechanical designers, controls contractors, energy efficiency engineers, and anyone who are seeking to improve building performance and to lower energy costs.

A live speaker Q&A session is on February 12th, 10:20-10:40 am (EST). See below for the abstract, and visit here to register for the 2021 ASHRAE Winter Conference.


Transitions between waterside economizer mode (flat plate heat exchanger) and mechanical cooling mode (chiller) in a chilled water plant are a common challenge facing facility teams, controls contractors, and mechanical designers. Due to these difficulties, many economizers are underutilized or abandoned entirely.

We will review operational strategies to reduce the stress and impact of mode transitions and improve winter and shoulder season operation for energy-efficient buildings.

Our focus is a plant piping configuration with the heat exchanger and chillers sharing a condenser water sump and the heat exchanger is piped to pre-cool the chilled water return prior to the chillers or carry the entire (seasonal) building load by itself.

In this session, attendees will learn strategies to:

  • reduce chiller surge at low load and low ambient temperature.
  • place demand limits preventing unnecessary stage-up.
  • optimize and maximize waterside economizer operation.

Chillers often surge at low load and low ambient temperature when compressor guide vanes close down in an attempt to increase lift. Common practice to increase lift and prevent this surge is to increase the condenser water temperature entering the chiller, effectively disabling the waterside economizer.

A lift control strategy will reduce surge while allowing for condenser water cold enough for economizing.  Such a strategy reduces the chilled water temperature setpoint while maintaining the leaving condenser water temperature. Thus, gaining the pressure difference required to keep the chiller operating smoothly.

Additional staging control is useful for demand limiting. Such a strategy will regulate temperature setpoint changes to prevent unnecessary staging.

Lastly, the chilled water temperature reset sequence is utilized to optimize energy efficiency. The highest-practical chilled water temperature will increase run hours on the economizer and decrease average chiller power.

In this session, we will discuss first-hand experience and lessons-learned for low load operation in existing chilled water plants, including:

  • developing sequences of operation
  • commissioning, troubleshooting, and fine-tuning
  • navigating various piping and equipment configurations

To learn more about ETC Group’s Energy Efficiency Engineering services, visit here or contact our energy efficiency team today!