Consulting Specifying Engineer Jan/Feb 2015-CSE : Page-25

Lighting One of the most notable changes to the lighting chapter of the 2013 version is the addition of control requirements for each of the space types. There also continues to be a systematic decrease in the allowable power density used by lighting. The data in ASHRAE Standard 90.1 Table 9.5.1 reveals that the allow-able power density for a school/university has decreased by 32% since the 2007 ver-sion of this standard. Table 2 provides a summary of the data taken from various versions of ASHRAE 90.1. The theme of natural daylighting and artificial lighting control is woven through most of the significant changes in Standard 90.1-2013. Many of the pro-visions of this standard tend to primarily affect one discipline and create a ripple through other disciplines on the way to optimizing the total energy efficiency of a facility. For instance, changes in chiller efficiency largely impact the work of the mechanical engineer, but a more efficient chiller also affects the design prepared by the electrical engineer. Similarly, allowable power densities largely impact the work of the electrical engineer, but also affect the cooling design prepared by the mechanical engineer. These examples create a cause-and-effect relationship between designers and contractors. Solutions that optimize natural day-lighting and artificial lighting control require a multidisciplinary approach. The most efficient approach still requires some iteration to formulate a solution. The team of designer, contractor, and owner must collaborate during this pro-cess. The role of the designer, architect, and engineer is to assess energy efficien-cy and balance performance, aesthetics, and functionality of the lighting system. The contractor’s role is to evaluate cost and constructability. The owner’s role is to determine if the solution is useful and meets the needs of the end user. An integrated design process when all stake-holders are involved from the beginning provides a platform for shared educa-tion, understanding of requirements and desires, and fluid testing of options until Figure 3: Fayetteville (Ark.) High School earned U.S. Green Building Council LEED for Schools Silver Certification applying design techniques prescribed in ASHRAE Standard 90.1. the design solution is optimized. When these parties operate in a vacuum, the final result is often frustration, uncoor-dinated design, and energy performance that does not meet expectations. Documentation the prescriptive approach to compliance. The difference is that the words used to describe the performance approach allow for trade-off, compromise, and flexibility. This is the foundation of an integrated design process. The future ASHRAE 90.1 can be used in two ways, prescriptive or performance, to document compliance. The prescriptive method is largely an effort in applying the information provided in the tables and graphs of the main body of the document. Because it’s often deemed the easiest approach for the design phase of a project, the pre-scriptive method is the most common path for achieving compliance with ASHRAE Standard 90.1. The performance approach to this stan-dard applies rules to the desired unique-ness that provides some flexibility based on the climate of the project location. The performance approach generally requires the use of a computer-simulation tool to evaluate the impact of design strategies for the major building features that form the path of overall compliance. It also can be argued that building designs derived strictly through implementation of the prescriptive approach may not result in the most cost-efficient solutions on bid day. The performance approach to the 2013 version provides even more rules and implementation procedures than previ-ous versions. This is easily seen during a quick review of the current edition of the standard. The pages defining the rules of engagement for the performance approach are much thicker than those for ASHRAE will publish the next ver-sion of Standard 90.1 in 2016. Between now and then, there will be addendums to clarify important content and address comments from users. The natural dura-tion before Standard 90.1 is applied to actual design situation seems to be about 4 years. It takes that long for the data in 90.1 to find its way into the building codes, for the building codes to be adopted, and for general accep-tance of the material throughout the design community. In 2020, the matrix for the Architec-ture 2030 Challenge will be a building energy performance target 80% better than the 2003 benchmark for consump-tion. ASHRAE Standard 90.1 has shown leadership in energy efficiency by defin-ing the minimum criteria and processes for the built environment to be judged. ASHRAE Standard 189.1: Standard for the Design of High-Performance Green Buildings takes building design to the next level for projects that are on the path to achieve the goals of Architecture 2030. Facilities that achieve lofty energy per-formance as prescribed by Architecture 2030 typically include passive features and provisions that rely on the natural environment in the strategy for energy reduction. 25 Consulting-Specifying Engineer • JANUARY/FEBRUARY 2015

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