A Pilot for Measuring Energy Retrofits
Original research by Richard Sweester, President at Exergy
Introduction
Building owners and managers rely on standardized energy audits and building modeling tools to inform their investments in energy efficiency. These audits and modeling tools, however, have limitations, and often fail to accurately represent the complex dynamics of energy flows within and around buildings. Adequately characterizing and modeling existing buildings for retrofit designs (as compared to modeling new building designs) has been especially difficult. In fact, an empirical test of the quality of auditing practices, which rely on simple building models, in the Philadelphia region found three very different sets of recommended energy conservation measures (ECMs) three consultants contracted by the EEB Hub to audit Navy Yard Building 661.
One of the EEB Hub’s core goals is to improve building modeling and auditing tools and it is using Philadelphia Navy Yard Building 101, the temporary headquarters for the EEB Hub, as a test bed for this work. Instrumenting Building 101 – fitting it with sensors to measure its operational characteristics – will make it useful as a living laboratory to calibrate existing energy models; develop new, more accurate models; test actual impacts of ECMs by providing a plug-and-play environment for technologies; as well as serve as a training facility for energy efficiency building trades.
Prior to undertaking this intensive instrumentation, project leaders searched for buildings analyzed to the degree needed to fully understand building performance but found none in the EEB Hub’s ten-county region or in this climate. This makes Building 101 the first of its kind in the area.
Instrumentation and Measurement
EEB Hub researchers outfitted Building 101 with sensors and a data acquisition system to determine detailed system performance, building energy loads, indoor environmental quality (IEQ), and a detailed operation of the building control system. Accurate building and subsystem performance data is critical to improving existing building models and energy auditing; advancing building-level controls and fault diagnostics; and educating designers, contractors, and building operators.
The sensors read data from 509 sensing points, collecting 1,048 pieces of data at one-minute intervals. These data points track indoor air quality, occupant comfort, and building energy use. Specifically, air quality parameters include CO2, CO, Total Volatile Organic Compounds, small particles, indoor temperature, and relative humidity. Occupant comfort is measured by workstation-level indicators of air quality, thermal quality, visual/lighting quality, acoustics, and surveys of occupant satisfaction with each IEQ factor. In order to gain an accurate understanding of energy flows in a building, discreet measures of energy inputs and energy losses are necessary. The whole building energy balance is calculated by measuring actual occupancy rates, building energy input of electricity and natural gas, air flow into the building through the outside air dampers, air leakage through the building envelope, and the air exhausted to the atmosphere through the exhaust fans. Some spaces are also instrumented to determine energy put into and exhausted from the space (supply air, return air, hot water heating, and electricity) [1].
The Department of Energy’s Lawrence Livermore National Laboratory in Livermore, CA, will analyze the data points from Building 101 to create a graphic representation of energy within the building. This visual tool, called a Sankey diagram, will enable researchers to identify discrepancies in the predicted versus actual energy balance.
A Test Bed to Improve Reliability of Models and Audits
For the EEB Hub to achieve its overarching goal of improving regional energy efficiency, decision-makers must have access to reliable information to reduce the perceived risk that often accompanies investments in ECMs. Building 101 is one of only about a half-dozen instrumented buildings in the United States that seek to establish data for better building simulation models and controls. Existing models often perform only moderately well at predicting the energy performance of a building as a whole, and they are worse at explaining performance as a measure of discreet elements such as HVAC, lighting, and outlet or plug loads, as verified by comparison of the measured performance at Building 101 and several medium-sized office buildings in the Philadelphia region with detailed simulation models of the same buildings. Unsurprisingly, predictions of actual energy savings from energy control measures targeted at discreet components often prove inaccurate.
The data collected in Building 101 and other commercial buildings in the region is being used to calibrate models, validate model predictions, and develop new models to provide more accurate results. EEB Hub researchers have had initial success using a unique modeling approach, known as inverse modeling, to establish models of buildings that could tune a conventional forward model. In doing so, designers are able to confidently use the forward models to investigate effects of retrofits on energy efficiency [2]. In other words, researchers are better able to model how retrofitted buildings will perform by observing actual buildings under real-world conditions.
A Living Laboratory for Energy Conservation Measures
Building 101 will operate as a living laboratory with the objective of reducing uncertainty, used to test actual energy impacts of ECMs. This effort is already under way with a planned upgrade of the building’s energy management system. The new energy management system will work in concert with the intensive instrumentation and enable researchers to optimize control protocols for the building and, in turn, learn how the controls are affected by future building system upgrades.
Since Building 101 is very similar to the rest of the Navy Yard’s historic building stock, with over sixty of these buildings still requiring retrofit for reuse, many of the lessons learned from Building 101 will be directly applied to these future retrofits. The insights into building performance strategies and improvements of building models, validation of energy efficiency benefits of ECMs, and improved certainty of return-on-investment for building owners and investors will add value to projects beyond the Navy Yard, to the Greater Philadelphia Region and the nation. The EEB Hub intends to build upon the knowledge gained from Building 101 to guide other building level research in the region.
References
[1] Energy Efficient Buildings Hub. (2012). Navy Yard Building 101 Test Bed for Assessing Technologies and Tools. Retrieved from {filedir_8}Navy_Yard_Building_101_Test_Bed_for_Assessing_Technologies_and_Tools.pdf
[2] Braun, J. E. (2002). An Inverse Gray-Box Model for Transient Building Load Prediction. HVAC&R Research, 8(1), from http://www.tandfonline.com/doi/abs/10.1080/10789669.2002.10391290#preview