Sponsored by American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)

A modern chilled plant in HVAC system

A water-side economizer (WSE) is a cooling system by which the chilled water is cooled by the cooling tower directly/indirectly without the use of mechanical cooling. Employing WSEs can decrease the building energy consumption by reducing the chiller operating time or increasing the chiller efficiency. WSEs, however, may pose challenges to the operation of chiller plants. For example, using WSE may result in chiller short cycling and temporary loss of chilled water supply temperature control. Moreover, having cold condenser water may cause the chillers trip on low head pressure, i.e., a lower pressure difference between the condenser and the evaporator. The above challenges can be addressed by adopting certain control sequences and there have been several control sequences successfully demonstrated in real-world applications. However, they are not intensively evaluated against all plant configurations, under all possible weather conditions. It is necessary to consider the effects for all plant configurations and all weather conditions when developing and evaluating a near-optimal WSE control sequence for large-scale applications.

Therefore, the objectives of the proposed research is to:

  • evaluate state-of-art control sequences for water side economizer (WSE) and develop a near-optimal sequence based on the comparison;
  • develop open-source dynamic models for controls evaluation of the chilled water plants with WSEs;
  • demonstrate the value of using a multidisciplinary modeling and analysis environment for integrating and sharing research among different TCs.

To achieve the above objectives, researchers in our lab will

  • conduct a comprehensive review on the state-of-the-art control sequences for WSEs. 
  • develop Dynamic Models for Different Configurations of Chiller Plants with WSEs. 
  • evaluate Strategies for WSE Sequencing. 
  • develop a Near-Optimal Control Sequence for WSEs.