ENERGY STAR Building Design Profile

This building design achieved Designed to Earn the ENERGY STAR, distinguishing it as one of the nation's best in design intent. If the office operates as planned, and continues to meet or exceed EPA criteria for energy performance, the building can earn the ENERGY STAR label.

The design of the Southface Eco Office began with an inter-disciplinary design charrette involving the full design team and the client. One of the targets established during the charrette was a 60 percent reduction in energy use below that of conventional design and construction practices, with a goal of achieving all 10 LEED Energy Optimization credits.

The process for reducing the building's energy consumption comprised three primary activities: (1) reducing loads, (2) meeting loads efficiently, and (3) greening supply.

REDUCING LOADS

The team started by analyzing the energy demand profiles for conventional commercial facilities. Artificial lighting (and the associated cooling load) typically accounts for as much as 40 percent of total energy use in a commercial facility, representing the single largest load. Consequently, providing abundant, glare-free daylighting to offset the energy demands of artificial lighting became an important focus.

The project was sited to the east of the existing Southface building, creating an elongated east-west axis. A majority (94 percent) of the building's glazing is oriented to the north and south, with only minimal-view glazing on the east façade and the west façade, which abuts the existing facility. External shading devices provide additional control of unwanted solar gain and glare. Fixed horizontal aluminum overhangs appear on the south façade. The open office area's east-facing view glazing features a fixed overhang supplemented with operable exterior venation. East-facing glazing at the corridors features electrochromic glass that allows occupants to electronically vary light. Existing and newly planted trees control the north façade's minimal sun exposure.

To further reduce load, the team selected an Insulated Concrete Form (ICF) wall system. The manufacturer's literature for Georgia indicates that its ICF wall system will outperform a stud wall insulated to R-50 due to the effect of thermal mass. An extensive green roof covers the facility, reducing the building's cooling load by significantly lowering the roof surface temperature compared to that of a conventional roof.

The building also harvests available daylight, with photo sensors and dimming ballasts that automatically reduce artificial lighting when daylight is available. Occupancy sensors turn lights off when spaces are unoccupied, further decreasing lighting energy usage.

MEETING LOADS EFFICIENTLY

Natural light will provide the majority of the Eco Office lighting. The artificial lighting was designed to complement the daylighting design—supplementing daylight levels where needed and providing nighttime illumination. Lighting is oriented parallel to the windows, and the daylighting sensors control each row individually. This allows lights to be turned on successively from the back of the space toward the windows as required to balance daylight levels.

To create a more efficient system while providing precise humidity control and copious fresh air, the design team chose a Dedicated Outdoor Air System (DOAS) in lieu of a conventional system. DOAS provides 100 percent outside air to building occupants and de-couples the latent and sensible loads, allowing each to be handled independently and more efficiently. The DOAS system comprises three pieces of equipment deployed in series. First, a dew-point evaporative cooler pre-conditions the 100 percent outside air stream using harvested rainwater. Second, an energy recovery wheel utilizes the building's exhaust air stream to remove moisture and heat from the incoming air stream. Third, a liquid desiccant system is used to remove moisture during peak summer loads.

GREENING SUPPLY

The project includes two grid-tied Building Integrated Photovoltaic (BIPV) Arrays. An array salvaged from a decommissioned BP gas station will be installed in a canopy over the rooftop observation deck with a peak capacity (inverter capacity) of 6.4 kW. A second 1kW curtain wall integrated array will be installed on the upper portion of the atrium's sloping south curtain wall. From a LEED perspective, the percentage is calculated on regulated loads, which means that the BIPV supplies around 15 percent of the building's regulated load, qualifying for two LEED Renewable Energy credits.

RATING THE DESIGN ENERGY INTENT

The energy performance of the Southface Eco Office was modeled using eQUEST (Doe 2.2); solar angles and shading design were analyzed using SketchUp, MicroStation, and Chhaya (a shading software developed by Vikram Sami and Victor Olgyay using the Eco Office as one of the development case studies); and the daylighting design was studied with LumenMicro. Energy data and characteristics of the building were input into EPA's Target Finder tool, and the resulting estimated design energy rating was 100 (out of a possible 100). Target Finder output also provided associated energy costs and greenhouse gas emissions.

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