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Article-darwich.jpg

©2016 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 58, no. 9, September 2016

Abdel K. Darwich, P.E., C.Eng., HFDP, Member ASHRAE

About the Author
Abdel K. Darwich is an Associate Principal with Guttmann and Blaevoet Consulting Engineers in Sacramento, Calif.

The Jess Jackson Sustainable Building (JJSB) is an 8,500 ft2 (790 m2) research facility housing process equipment designed to serve the adjacent teaching building of the Department of Viticulture and Enology at the University of California, Davis.

The project came with a very clear goal: a passive net zero energy building able to maintain 50°F to 80°F (10°C to 27°C) internal temperatures with no added heating or cooling in Davis, Calif., where ambient temperature can exceed 105°F (41°C). JJSB is an example of highly cost-effective construction, using a pre-engineered building, extremely simple ventilation systems, and good daylighting to obtain extremely low energy use.

Nine of the building’s ten 20 ft × 30 ft (6 m × 9 m) structural bays are “plug-and-play” spaces to house experimental equipment and systems that will reduce energy and water use, such as hydrogen fuel cells and reverse osmosis water treatment.

 

Energy Efficiency

The building’s loads were analyzed in detail to determine which components contribute the most to the building heat gain/loss. These components were found to be the envelope and infiltration. To minimize envelope loads, the project used a Passivhaus approach by using a super-insulated envelope consisting of R-59.5 walls and an R-76 roof. Also, the windows selected were high performance, having a total unit performance U-factor of 0.17 and a solar heat gain coefficient (SHGC) of 0.24 with visible light transmittance of 43% for fixed glazing, and U-factor of 0.21 and a SHGC of 0.21 with visible light transmittance of 37% for operable awning windows.

The building orientation was required to follow the campus grid, but it ended up oriented to take best advantage of its southern exposure. Large overhangs shade the east and west exposures, and exterior shading fins keep mid-summer sun off the north side of the building, while south overhangs are sized to control summer sun and admit winter sun.

Infiltration rates were reduced by ensuring a tight envelope and extremely tight roll-up doors so the building would be considered tight as designated by ASHRAE (leakage rates less than 0.1 cfm/ft2 (0.5 L/s·m2) of building surface area). A blower door test was performed at the end of construction as part of the commissioning process to validate the actual infiltration rate, which turned out to be 0.08 cfm/ft2 (0.41 L/s·m2).

Daylighting helps keep the lighting loads reduced to a lighting power density (LPD) of 0.421 W/ft2 (4.53 W/m2), which is approximately 53.2% less than the allowed LPD as defined by the current California Energy Code.

The building has been designed to passively cool and heat itself as needed by taking advantage of the cool night breeze in the area (night temperature drops to about 60°F [16°C]) and thermal mass. A slab-on-grade floor and an 8 ft (2.4 m) high concrete masonry unit (CMU) wall, constructed within the thermal envelope, provide thermal mass throughout the building. Insulation was provided under the slab-on-grade, and the thickness of the insulation was optimized using advanced building modeling to balance the benefits of thermal energy storage in the slab and free heat exchange with the ground. Two 3,000 cfm (1416 L/s) fans turn on at night (when conditions are appropriate) to charge the concrete slab and CMU walls.

 

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