Mingsheng Liu

Is Commissioning Once Enough

ABSTRACT Over the last decade, the Energy Systems Laboratory has developed a commissioning process called Continuous Commissioning®. This process is used to resolve operating problems, improve comfort, optimize energy use, and sometimes to recommend retrofits. The process has produced average energy savings of about 20 percent without significant capital investment in over 150 large buildings in which it has been implemented. Payback has virtually always been under 3 years, with two years or less in most buildings. This article describes the process and presents a case study that explicitly shows the value of follow-up consumption tracking and commissioning. Examination of 20 building-years of heating and cooling consumption data from commissioned buildings found an overall increase in heating and cooling of 12.1 percent over two years. Almost 75 percent of this increase was caused by significant component failures and/or control changes that did not compromise comfort, but caused large changes in consump...

Single-Duct Constant Air Volume System Supply Air Temperature Reset: Using Return Air Temperature or Outside Air Temperature?

The supply air temperature set point for a singleduct constant air volume air handling unit (AHU) system is often reset based on either return air temperature or outside air temperature in order to reduce simultaneous cooling and heating energy consumption. Both reset strategies make engineering sense as long as the reset schedules are reasonable. Quite often the decision to use one over the other is made with the assumption that they will all achieve some sorts of energy savings. However, the impact of these two strategies on AHU energy consumption could be very different. A comparison of these two commonly used supply air temperature reset strategies for a single-duct constant air volume system is presented in this paper. It is shown that from either the building energy consumption or building comfort point of view, the reset strategy based on outside air temperature is inherently better than that based on return air temperature. Significant amount of heating energy savings can be achieved by switching from return air temperature based reset to outside air temperature based reset. The reset strategy can also benefit variable air volume (VAV) AHUs. An improved supply air temperature set point reset control strategy is proposed by combining and staging the outside air and return air temperature based resets.

Implementing the continuous commissioning process in retrofit projects

ABSTRACT Continuous Commissioning (CCSM) is an ongoing process to resolve operating problems, improve comfort, optimize energy use and identify retrofits for existing commercial and institutional buildings and central plant facilities. CC focuses on optimizing/improving overall building systems control and operations and on meeting existing facility needs. Implementation of the CC process has typically decreased building energy consumption by 20 percent in over 100 large buildings where it has been implemented. This article presents methods and procedures for applying CC concepts to building commissioning projects to reduce the initial cost and maximize energy savings. The process is demonstrated using case studies where the retrofit project was decreased by 25 percent while the energy savings were increased by 30 percent.

Introduction to the DOE Continuous Commissioning Guidebook-Maximizing Building Energy Performance and Efficiency

Continuous Commissioning (CC) is an ongoing process to resolve operating problems, improve comfort, optimize energy use and identify retrofits for existing commercial and institutional buildings and central plant facilities. CC focuses on optimizing/improving overall system control and operations for the building as it is currently utilized and on meeting existing facility needs. The innovative optimal engineering solutions are developed using engineering based model analysis integrated with the scientific field measurement or experiments. Integrated approaches are used to implement these optimal solutions to ensure local and global system optimization and to ensure persistence of the improved operational schedules. The implementation of CC process can typically decrease building energy consumption by 20%. Authors have completed the CC guidebook with financial support from DOE. This paper introduces the CC guidebook, which includes the CC process, the primary CC techniques and measures, and a case study.

Commissioning a Dual-Duct Constant Volume System to Operate like a VAV System

This paper describes a study that involves commissioning of a full-size dual-duct constant volume (DDCV) system, which serves a four-story office and classroom building with a gross floor area of 6,317 m 2 (68,000 ft 2 ) in a university campus. In early 90s, a variable speed drive (VSD) was installed as a retrofit process. The fan has been operated under constant low speed of 50Hz to limit airflow. The total airflow rate was 22.8 m 3 /s (48,300 ft 3 /min) after the retrofit process. During the current commissioning process, fan speed control was changed from the constant low speed to the static pressure control used in dual duct variable air volume systems. The system maintains the minimum static pressure of hot and cold ducts at a set point. Hourly data of thermal energy and fan power consumptions have been collected from the energy management and control system through the Internet to verify savings of the new control scheme. During the data collection, steam valve leakage was detected, which caused energy wastage as well as a thermal comfort problem. Analyses show that the static pressure control scheme and the steam valve shut-off during summer incur substantial energy savings as well as improve thermal comfort. Additionally, throughout the analyses, it was determined that the system operation can be optimized by resetting cold and hot deck temperature with the pressure control operation of the VSD in the DDCV system.