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The Real Energy Efficiency Numbers
February 13, 2008 - Contact FacilitiesNet Editorial Staff »
Hello. This is Greg Zimmerman, executive editor of Building Operating Management magazine.
Today’s tip involves energy claims of LEED-certified buildings and other new facilities purported to be energy efficient.
Most of you are probably familiar with claims such as this: “Our new LEED-certified building is expected to save more than 35 percent on energy compared to similar buildings.” It’s certainly possible that this claim may be true, eventually. It’s just as likely that it’s not.
The thing is, those numbers are based on pre-construction energy models. And while most are fairly accurate at the time they’re run, dozens of things change over the period between when the energy calculations are done and the building is actually completed and occupied. Most experts recommend using pre-construction energy efficiency numbers only as a guide, not a set-in-stone figure.
Most experts also say it takes three years of a building being in service before an accurate and consistent energy claim can be made. During the first year, when equipment is new, there are usually problems that need to be ironed out and tweaks made, even for commissioned building. The second year is when the operations staff finally begins to get the hang of how to run the building at peak efficiency, and the third year is when it finally all comes together to establish a fairly accurate number that will be serve as a solid baseline going forward.
Of course, benchmarking and metering is as critical in the first few years – mainly to discover and diagnose problems – as it is in subsequent years to make sure your building is consistently energy efficient.