A Look Behind the Curtain of Energy Performance

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26-04-2013 | David Leipziger | United States, 美国
Categories: Assessment Systems

The glass and steel office building at 10 Exchange Square sits in the middle of bustling downtown London, halfway between St. Paul’s Cathedral and the Tower of London. As part of the UK’s mandatory energy rating policy (a directive of the European Union), 10 Exchange Square was given a low grade of “E” on the alphabetical scale (A to G) for energy efficiency. The curious part is that in terms of actual consumption, 10 Exchange Square is 66 percent more efficient in use per  square meter than a comparable B-rated office building. What gives?

The issue is that performance depends on how it is measured. A report from Jones Lang LaSalle and the Better Building Partnership cites the 10 Exchange Square example as part of a thesis that there is no correlation between the UK’s mandatory efficiency ratings (EPCs—Energy Performance Certificates) and actual building energy use. Yet it is not surprising that an EPC would differ from actual consumption; the EPC is designed to estimate consumption based on very specific assumptions. Those assumptions exclude the energy consumed by any products or appliances (known as plug loads) and determine efficiency based on emissions, not simply on consumption. In short, comparing actual usage to a performance rating is a bit of an apples-to-oranges exercise.

In the same way, comparing ratings between countries can be nearly impossible. The same discrepancies arise for all aspects of assessment. How can you compare two ratings that measure floor area differently? That use different scales? That define building types differently? Such challenges are compounded by local policy goals, cultural differences, and the priorities of building stocks.
Yet dozens of cities, states, and countries around the world are pursuing benchmarking policies to improve energy efficiency in buildings. With so much experimentation and innovation, there is much to learn about effective program design and market impact. The lack of international consistency seriously impedes best practice sharing and hamstrings the responsiveness of the global real estate market. 
Part of the solution lies in the development of a standard framework for comparing building efficiency policies around the world. IMT has produced just that in a new paper, Comparing Building Energy Performance Measurement.
While this classification does not allow building-to-building comparisons, it facilitates evaluation and analysis by making clear what assumptions and objectives underlie existing systems. It’s a peek behind the curtain of energy performance that enables stakeholders to make determinations about what is important to them. 

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The features of an energy efficiency assessment including the nature of comparison, energy use assessment method and building inputs. An energy rating’s terms of comparison can be relative to other buildings or to an absolute score (ie. technical or statistical) its energy use assessment method either based on forecasted consumption (asset/calculated/predictive) or actual consumption (operational/measured/performance-based); individualized building inputs can use either standardized or customized (standard or tailored) values. [Source: Institute for Market Transformation]

The ratio between the energy services provided and the energy consumed. Something is more energy efficient if it delivers more services for the same energy input, or the same services for less energy input. [Source: IEA Glossary]

The calculated or measured amount of energy needed to meet the energy demand associated with a typical use of the buildings, which includes inter alia, energy used for heating, cooling, ventilation, hot water and lighting (EU). [Source: EPBD recast, 2010/31/EU]