Durham School of Architectural Engineering and Construction


Two-Pump Systems for Central Plant

Zhan Wang

Document Type Article

A DISSERTATION Presented to the Faculty of The Graduate College of the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctoral of Philosophy, Major: Engineering, Under the Supervision of Professor Mingsheng Liu. Lincoln, Nebraska: 2010
Copyright 2010 Zhan Wang


In a conventional central plant design, it is common to maintain a one-to-one correspondence between the pumps and the individual primary users such as the central plant chillers, the cooling towers, and the boilers. Generally, an additional pump is installed as a backup. However, sometimes problems arise when conventional pump system design and control methods are utilized. Many systems have high capital costs, and high operation and maintenance costs. Other issues include motor overload from mismatch of the single pump performance and the system performance when more than one pump is designed. Finally, energy costs are still high due to issues caused by the conventional control logic for pump activation and deactivation even with the application of variable frequency drives.

This research proposes an innovative pump system configuration as a solution to the previously stated problems. The new pump system is configured to support a minimal number of pumps. It is named the Two-Pump (T-P) system because two is generally the number of pumps needed to satisfy the water loops for many chiller plants. The pump system introduces a pump selection method to ensure that the system characteristics optimally fit into the pump best efficiency zone, and a motor sizing method to prevent motor overload. In addition, a capital cost analysis conducted on the central chiller plant supports the implementation of the proposed system design. Finally, the system includes a new set of control algorithms that can activate an optimal pump number to enable it to operate at its highest efficiency. The simulation and experimental results from the implementation of the system in the chilled water loop further prove that the proposed T-P water distribution system is simpler, has a lower capital cost, and is more energy efficient than the prior art.