The U.S. Department of Energy (DOE) and its National Renewable Energy Laboratory (NREL) have released two technical reports that provide recommendations on how to achieve 50 percent energy savings in new and existing large office buildings and large hospitals. The studies were conducted by NREL’s Commercial Buildings Group, under the direction of DOE’s Building Technologies Program.
The report, “Technical Support Document: Strategies for 50% Energy Savings in Large Office Buildings” (PDF), evaluates the potential for large office buildings to achieve a 50 percent net onsite energy savings compared to a baseline standard (as defined by ANSI/ASHRAE/IESNA Standard 90.1-2004), across a broad range of U.S. climates. The analysis was conducted in 16 cities that represent different climate zones, such as hot and humid, hot and dry, marine, cold and humid, and cold and dry.
Researchers used several energy-efficiency measures to meet the 50 percent energy-savings target. As examples, lighting power density was reduced to 0.63 W/ft2 in office spaces, occupancy sensors were used in less frequently occupied spaces, and plug loads were reduced by 23 percent to 0.68 W/ft2 (7.3 W/m2) by purchasing high-efficiency electronic equipment and using special controls that shut off equipment when not in use.
Other installations include high-efficiency boilers (condensing, nominally 98% efficient), chillers (COP of 7), air distribution units (69% total fan efficiency), and service water heating equipment (90% thermal efficiency).
Different strategies also were implemented based on low- and high-rise building types. As an example, double pane windows with low-emissivity film and argon fill (U-0.235, SHGC-0.416, VLT-0.750) were installed in low-rise buildings, while double pane windows with low-emissivity film and tinted glass constructions (U-0.288, SHGC-0.282, VLT- 0.55) were used in high-rise buildings.
Energy-savings measures were also added based on climate. For example, exterior wall insulation was added in cold climates (up to R-19.5 continuous insulation (c.i.) for the low-rise case and R-22.5 c.i. for the high-rise case).
Similarly, the report, “Large Hospital 50% Energy Savings: Technical Support Document” (PDF) provides design recommendations to help large hospitals achieve whole-building energy savings of at least 50 percent across all eight U.S. climate zones.
The report finds that energy savings range from 50.6 percent to 61.3 percent, with the smallest savings in humid climates and extremely cold climates. The highest energy savings were achieved in marine climates, with relatively high energy savings achieved in dry climates. In general, for each climate type (humid, marine, and arid), savings were seen to decrease as the climate became progressively colder.
Energy-saving design measures used include reduced lighting power densities, daylighting sensors in applicable perimeter zones, occupancy sensors in applicable zones, demand controlled ventilation, more efficient pumps, reduced infiltration through tighter envelope construction, and integration of subsystems to achieve whole-building performance.
The DOE offers several technical support documents that provides recommendations on how to reduce energy in various applications, including a 50-percent energy savings in general merchandise, grocery store, lodging and medium office buildings and a 30-percent energy savings for highway lodging, K-12 schools, small hospitals as well as small office, retail and warehouse facilities. The technical support documents are available on the NREL Web site.