Durham School of Architectural Engineering and Construction


Date of this Version

Summer 7-26-2011

Document Type



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Architectural Engineering, Under the Supervision of Professor Mingsheng Liu. Lincoln, Nebraska: July, 2011

Copyright 2011 Xu Lian


Water Loop Heat Pump (WLHP) System has been widely utilized in the Heating, Ventilating and Air Conditioning (HVAC) industry for several decades. There is no doubt about the energy saving potential of this type of system from the design and construction perspective. However, there are still many unsolved problems, such as high loop pump energy consumption, low heat pump efficiency and high electricity cost due to improper operation, although the system design intension was to save energy. Thus, how to control the WSHP to realize its energy-efficient value is an innovative but practical topic on which this thesis will focus.

To achieve this goal, three optimal WLHP control strategies will be discussed in this thesis:

(1) Improve the water loop circulation pump control by using a differential pressure reset method;

(2) Optimize the water loop temperature control by resetting the fluid cooler supply temperature;

(3) Modify the building schedule and heat pump fan operation mode to save energy without sacrificing occupant comfort.

These new control strategies were implemented on a middle school building equipped with a very typical WLHP system in a building mechanical system commissioning project. Several experiments were conducted in order to demonstrate the energy savings and other benefits compared with the existing control and operation.

It is concluded from the results of the experiments that the new loop pump control reduced the pump speed by 16.3% on average and has the potential to save 40% to 70% pumping energy; the improved water loop temperature control saved 12.8% of heat pump electricity consumption; and the new HVAC operating schedule and heat pump fan mode are able to achieve 20% to 30% of total electricity savings annually.

Advisor: Mingsheng Liu