Rating Systems and the Design Process

Most building environmental rating systems and building energy-efficiency incentive programs encourage the use of integrated design, which typically involves building-energy simulation.

To maximize incentives, energy modelers tend to reference all efficiency measures against the baseline design model they use to document building energy performance. For example, for LEED EAc1, design decisions typically are based on energy and cost savings between Standard 90.1 Appendix G baseline and proposed-case models. Thus, project teams are more likely to choose measures that reflect savings
in the selected rating system over measures for which the rating system does not award credit. For instance, project teams using Standard 90.1 Appendix G generally opt for DCV, for which Appendix G allows full credit, over a hybrid ventilation system, for which Appendix G does not. Therefore, performance-rating methods play a major role in determining the types of efficiency measures that become common in the marketplace.

Missing links

An effective energy code or standard:

• Raises the baseline of building efficiency, ensuring that the least-efficient newly constructed and substantially remodeled buildings improve upon the average efficiency of older buildings.
• Fosters widespread adoption of building energy-efficiency measures.
• Mandates measures to prevent unnecessary energy use during unoccupied hours.
• Helps to ensure the persistence of energy savings.
• Adapts energy-efficiency requirements based on climate and building function and is widely applicable.

A good performance-rating method also:

• Provides a method of documenting energy performance vs. standard practice.
• Allows documentation of savings associated with efficiency measures that have little acceptance within the marketplace.
• Is free of loopholes that would allow measures with limited energy and cost benefits to receive credit.
• Provides opportunities to demonstrate energy-performance improvement across all climate zones.

Standard 90.1, IECC, and California Title 24 requirements have made tremendous strides in meeting objectives for energy codes and standards, while Standard 90.1 Appendix G and methodologies included in the Savings by Design incentive program (based on Title 24) have provided an excellent basis for performance ratings. However, as the United States faces increasing concerns about dependence on foreign oil, rising global energy costs, decreasing availability of energy, and rising anxieties about climate change, significant room for improvement remains. Specifically, building operation during unoccupied periods and the persistence of energy savings over time require further attention.

Building operation during unoccupied periods. Most standards mandate controls, but not alerts when the controls are not performing as intended. Crediting or mandating such alerts could lead to substantial savings. For example, building operators could restore the functionality of a lighting-shutoff control compromised by an inadvertent change to a lighting-shutoff schedule quickly, if they received an alert stating nightly lighting energy consumption had tripled from the previous week. This sort of monitoring function would have to be widely available to be mandated.

Current energy codes and standards give inadequate attention to unoccupied-period part-load operation of chilled-water systems. Even variable-speed chillers perform inefficiently when their load falls beyond a given level. Add pump and heat-rejection energy, and nightly light loading of chiller plants can noticeably impair the overall energy performance of a building. Consider a building with an efficient chilled-water-plant design occupied from 8 a.m. to 5 p.m. daily. If the chilled-water plant served only telecommunication and small data-center loads during unoccupied hours, energy consumption would far exceed that of air-cooled DX units.

Persistence of energy savings. Many energy-efficiency measures that meet minimum code requirements at the time of installation fail shortly after a building is occupied. Most notably, air-side economizers, particularly in coastal climates, become stuck, which leads to increased heating and cooling loads. Title 24 provides a credit for automated fault-detection diagnostics for air-side economizers, packaged DX units, and zone terminals. Such a credit should be incorporated into other energy codes and rating systems and offered for other equipment.

Conclusion

Recent developments regarding codes, standards, and performance-rating methods have led to the improved energy performance of buildings. Given the energy crisis it faces, however, the United States needs to continue to increase the stringency of energy codes and standards and establish performance-rating methods that advance market development and acceptance of energy-efficient building systems and controls. A focused effort to develop mandatory, prescriptive, and performance controls requirements for the next releases of the nation's building energy codes, standards, and performance-rating methods would help to move the buildings market toward the transformation needed to reverse the upward trend in national energy consumption.

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As director of energy services for CTG Energetics Inc., Gail Stranske, PE, is responsible for energy-engineering and sustainability-consulting activities, including building-energy simulation and analysis, energy auditing, commissioning, and Leadership in Energy and Environmental Design (LEED) Green Building Rating System documentation support. She is competent with DOE-2.1E, DOE-2.2, VisualDOE, eQUEST, and EnergyPro software and well-versed in ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings; International Energy Conservation Code; and California Title 24 compliance. She has completed LEED Energy & Atmospheric Credit 1 analysis and documentation for numerous projects and participated in energy audits and commissioning of commercial and institutional buildings totaling more than 6 million sq ft.

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