February 22, 2007

How much energy are you really saving?

  • Post-occupancy evaluations show green projects save energy, but there’s more to learn



    When you buy a car, you have the right to expect that it will not only carry you from place to place but that it will also live up to its performance promises. The purchase entitles you to the full value of the gas mileage, safety, comfort and convenience that you paid for.

    Though you must rely on experts to design, fabricate and construct the auto, and an extensive network of service providers to maintain it, each machine comes with a user manual and a suggested program of routine maintenance. Few would question whether a car owner should seek routine inspections and diagnostics to ensure the car continues to operate as intended.

    But what of a building? What could be more complex in design and construction? Buildings are conceived and executed in units of one and are built entirely to order. But once the keys change hands expectations begin to diverge.

    Buildings are so complex that the systems that comprise them — energy, heating and cooling, plumbing, lighting, etc. — tend to be considered and addressed separately. An owner may receive an operations and maintenance manual, but it reflects the functioning of the specific components, not the structure as a whole. So how does this owner measure the effective performance of his building?

    A typical design and construction process warrants that the project is without defect and meets the standards laid out in the construction documents for a year. But basic functionality is a far cry from efficient long-term operation, let alone high performance.

    Source: GGLO
    The chart shows how energy use in five multifamily buildings compares with Seattle City Light’s average energy use in all multifamily buildings. Both green buildings (3 and 5) showed below-average energy use. The information is part of a GGLO study to identify which sustainable features offer the best value.

    Most owners and users are only aware of poor performance when something breaks or goes wrong, and the same is true for designers and contractors.

    This lack of discrimination in the quality of performance robs owners, users and everyone else involved in the design and construction process of useful feedback that could improve the operation of existing buildings and the design of future buildings.

    One way to close this feedback loop is post-occupancy evaluation. Though a substantial body of performance information exists for commercial and institutional buildings, little post-occupancy research has been done on multifamily projects.

    GGLO partnered with three long-term property holders to analyze utility cost and usage information for five urban multifamily projects to compare the performance of green buildings with conventional buildings. In so doing, we sought to identify which sustainable features offer the best value and benefit.

    We chose to focus our initial analysis on electricity and water because utility usage is measurable, obtainable and has a direct cost impact. We hoped our results would be easy to quantify. Since reducing water and power use are often primary sustainable goals, these statistics could be a useful tool in early design discussions.

    Here are some of our preliminary observations and recommendations:

    Built Smart

    Whether you explicitly pursue sustainable design or not, Seattle City Light’s Built Smart program is worthwhile. All of the projects we studied employed Built Smart, and all but one consumed less electricity than average utility agency predictions.

    Observing Built Smart requirements for windows, insulation, thermostats and lighting does reduce electrical demand, resulting in reduced utility costs. In addition to tenant-oriented benefits, the Built Smart program also offers incentives to developers that can defray initial costs.

    Common areas

    Common-area energy usage varied from less than 30 percent of total usage to more than 60 percent. Florescent fixtures or occupancy sensors in these areas can have a significant positive impact on building performance.

    Energy modeling

    These services, needed to satisfy LEED requirements, typically require additional consultants and can add costs, but they can also add tremendous value both before and after the building is constructed. The LEED certified market rate building in our study consumed only 5.4 kilowatt hours per square foot versus Seattle City Light’s average of 10 kwh/sf and the 11.47 kwh/sf consumed by a comparable non-green market rate building.

    For the LEED certified building, this reduction in energy use equated to an annual savings of over $40,000. Such a savings, which was closely predicted by our energy model at 5.88 kwh/sf, could also prove useful when securing financing.


    Smoking in buildings is another issue brought to a head for multifamily projects by LEED requirements.

    Enforcement in residential settings can be a thorny issue. But with the increasing numbers of nonsmokers and the ventilation technologies available, multifamily project owners can now begin to realize the savings of reduced unit-turnover costs. Savings in carpet replacement and repainting alone are substantial.


    Water usage results varied considerably among the projects.

    Our LEED certified building, with its low-flow shower heads, lavatories and kitchen sinks, came in slightly under code estimates, with an overall savings of $3,200 annually.

    The variations in usage hint at a behavioral component that is difficult to evaluate. The projects with centralized laundry facilities consumed substantially less water than those with in-unit washer/dryers.

    If you have to haul your laundry somewhere and plunk quarters in a machine, aren’t you more likely to wait until you have a full load?

    Our preliminary research effort has proven worthwhile, but we need more information on more projects before we can draw definitive conclusions. We also need to bridge the gap between objective measurement and subjective behavior.

    Utility metrics provide only one part of the usage picture. To establish a more comprehensive context for analysis and interpretation, we need behavioral information from the users themselves. What good is a low-flow fixture if you leave the faucet running twice as long?

    Post-occupancy evaluation is a valuable and underused tool for establishing the measurable benefits of high-performance design.

    For green building to continue to grow and take hold among all project types, sustainable design approaches must offer appropriate, quantifiable cost benefits to owners and developers, as well as tenants and users. For sustainable design to evolve within the industry, designers and contractors need to be able to incorporate what works and improve on what doesn’t.

    Our ongoing evaluation of completed projects represents our continuing commitment to sustainable design intrinsic in all our projects.

    Michelle Rosenberger serves as co-chair of GGLO’s Sustainable Design Group and is a LEED-accredited professional. Jon Hall, AIA, also a member of GGLO’s sustainable design group, is a sustainable building advisor.

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