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Article Excerpt
INTRODUCTION
During the past decade, utility companies and others have offered new construction programs to promote energy savings based on energy-efficient design, which maximize design flexibility as well as energy savings. For such programs, the concept of Measurement and Verification (M&V) continues to become more important because efficient design alone is often not sufficient to deliver an efficient building. The International Performance Measurement & Verification Protocol (IPMVP 2001, 2003), ASHRAE's Guideline 14-2002 (ASHRAE 2002), and the Federal Energy Management Program (FEMP 2000) contain M&V methods for existing building retrofits, but include only a general M&V framework and selected approaches for new buildings (IPMVP 2003). In 1995, the U.S. Green Building Council (USGBC) developed the Leadership in Energy & Environmental Design (LEED) program in response to the U.S. market's demand for a definition of "green buildings" (USGBC 2002). The LEED guide (e.g., Prerequisite EA-P2) requires the user to demonstrate building energy performance levels consistent with the ASHRAE Standard 90.1-1999 (ASHRAE 1999), or other equivalent local energy codes.
Several studies have reported on the effectiveness of efforts to improve energy efficiency of new buildings in terms of whole-building energy performance. Of importance to this work, the National Renewable Energy Laboratory (NREL) published reports on the energy performance evaluation of six high-performance buildings (Torcellini et al. 2004), compared to a code-compliant baseline model, using as-built simulation or measured data and utility bills. Unfortunately, the reports did not provide details about all aspect of the calibrations and did not evaluate individual measures in terms of whole-building performance. Therefore, there remains a need for a standard M&V method to measure energy savings from new construction that could have different baselines and would allow for individual measure to be evaluated separately or combined.
Simulation models that are calibrated to measured data can be used to evaluate the energy performance of a new building if it is compared to an energy baseline such as similar buildings, or the simulated use of a similar building that is code compliant (IPMVP 2003). Unfortunately, the reliability of energy simulation results is often compromised by a lack of certainty that the simulation reflects the actual conditions (Sylvester et al. 2002; Song 2006). In addition, many important questions remain, for example: How do we calibrate a simulation with measured data? How do we develop energy baselines for comparison to the new building? How do we calculate energy savings compared to the energy baselines?
Therefore, this study developed an enhanced method based on calibrated whole-building simulation (Song and Haberl 2007) for evaluating the energy performance of new commercial buildings and demonstrated its use using a case study building in Austin, Texas, including: 1) Baselines for building energy use, 2) Whole-building energy monitoring, 3) As-built simulation calibrated with measured data, and 4) An analysis of actual energy savings compared to three different energy baselines, which include an Energy Use Index (EUI) comparison with sub-metered data, a comparison against ASHRAE Standard 90.1-1989 and Standard 90.1-2001, and an evaluation of the performance of specific Energy Conservation Design Measures (ECDMs) using an ECDM subtraction method.
METHODOLOGY
Figure 1 shows the schematic M&V methods developed in this study for new buildings. For evaluating the energy performance of the case-study building, measured data from a data logger were first verified with monthly utility billing data. Measured Energy Use Indices (EUIs) with sub-metered data were then compared to those of similar buildings in a control group, in terms of whole-building energy performance. In addition, the indices were disaggregated into energy end-use such as whole-building electricity (WBE), whole-building heating (WBH), whole-building cooling (WBC), motor control center (MCC), and lighting and receptacle (L&R). Second, the as-built simulation model was calibrated with measured data and/or manufacturer's performance data until the simulated data matched with the measured data to a suitable level. Third, a code-compliant baseline with Standard 90.1-1989 and Standard 90.1-2001 was developed based on the calibrated as-built simulation to account for the actual as-built conditions. The simulation results from the as-built simulation were further compared to evaluate the whole-building and building component performance. Finally, savings from the Energy Conservation Design Measures (ECDMs) were analyzed using the calibrated as-built simulation compared to the design baseline (i.e., base-case simulation), which has the same shape and function as the case-study building (i.e., calibrated as-built simulation model), but doesn't include the ECDMs.
[FIGURE 1 OMITTED]
BASELINES FOR BUILDING ENERGY USE
The energy savings in an energy efficient new building can be calculated as the difference between the energy uses predicted by a baseline (i.e., a simulation model or a regression model) versus the measured as-built energy data. The methods of developing the energy use baselines used in this study are described in the following sections, including: Utility billing data, Energy Use Indices (EUIs), and code-baselines (i.e., simulation models) compliant with ASHRAE Standard 90.1-1989 and 90.1-2001, and design baselines (i.e., base-case simulation).
Utility Billing Analysis
Monthly electricity billing data for several years were analyzed to identify energy use trends and then compared to the measured data. Figure 2 illustrates the whole-building electricity (WBE) and energy use intensity (EUI) for the period 1999 to 2004. The case-study building started to operate normally in 2001 as shown in Figure 2. The measured data were also verified against monthly utility data for 2001 and 2004 as shown in Figure 3. Since only a small difference in electricity use could be seen from 2001 to 2004, the 2001 measured data were used in this study for the performance evaluation of the case-study building.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
Building Energy Use Indices (EUIs)
Energy use indices (EUIs) have been used as an indicator of energy efficiency for quick comparisons to other reference buildings with similar functions in similar climates. Most EUIs express annual total energy use per square foot (or square meter) of conditioned area. In this study, the indices were disaggregated into energy end use such as whole-building electricity (WBE), whole-building heating (WBH), whole-building cooling (WBC), motor control...
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