Understanding and tightening the gap between simulated and actual energy use.
Status: Completed
Funding Sources: CBE Industry Consortium
Project Objective
This project explores the gap between simulated and actual energy use in buildings. The objectives of this study are to: (1) identify the range of assumptions made by energy modelers regarding the energy use of plug loads in buildings; (2) explore the accuracy of simulated plug loads end-use component; and (3) analyze the taxonomy of plug/receptacle loads, process loads, and unregulated loads as treated by codes and standards, energy simulation programs, and building operators.
Significance to Industry
Plug load energy use is emerging as an increasingly important factor in commercial buildings. While codes and standards have steadily mandated increased efficiency of heating, cooling and lighting in buildings, criteria for plug loads (e.g., unregulated loads) are missing, due to the lack of control design teams have over specifying and installing equipment in this category. As regulated loads are reduced, unregulated energy use will claim a larger proportion of total energy use in buildings. Relatively little is known about plug load energy use trends across different sectors due to difficulty in obtaining submetered energy use data.
Understanding the gap between estimated and measured energy use of plug loads can help inform simulation experts, owners, practitioners and occupants, by not only increasing awareness of the variation between simulated and actual plug load energy, but also to create an impetus to increase the efficiency of this end use, and increasing the likelihood that aggressive goals such as net-zero may be reached.
Research Approach
The project was organized into the following major tasks:
Background Research: The first phase of this project was to review research and design literature to synthesize existing information on plug load energy simulations and use. This literature review provides a taxonomy and terminology of “plug loads,” “receptacle loads,” “process loads” and “unregulated loads” from various standards and guidelines, to understand the variety in scale and character of this nebulous energy category.
Data Collection and Analysis: Energy modeling inputs from LEED-NC and LEED-CI projects were collected, organized, and statistically analyzed with a focus on plug/process load assumptions, building use, square footage, and occupancy. We also sought information from energy modelers regarding their assumptions for plug load energy use.
Comparison of Simulated to Actual Energy Use: A subset of projects within the LEED-certified set of projects that have submetered plug load data were identified and selected for analysis. The analysis includes review of submetered energy data, conducting site visits, interviews with building managers, and review of electrical drawings and/or BMS data to identify the equipment contributing to the plug load energy use and their operating characteristics. The actual measured plug load data was compared to the original energy model’s plug load input assumptions.
Publications and Reports
Fuertes, G. and S. Schiavon. 2013. Plug load energy analysis: The role of plug load in LEED certification and energy modeling. Energy and Building,Volume 76, 328-335.