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More Outdoor Air, Less Energy for HQ

By Steve Gross, Associate Member ASHRAE; Hormoz Janssens; Shawn MacLean, P.E., Member ASHRAE

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©2019 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 61, no. 6, June 2019.

About the Authors
Steve Gross, P.E., is an associate, senior energy analyst, Hormoz Janssens, P.E., is a managing principal, and Shawn MacLean, P.E. is a principal at Interface Engineering, San Francisco.

Marine Way, Intuit’s new 185,000 ft2 (17 187 m2) headquarters building in Mountain View, Calif., houses office and conference space for the Silicon Valley technology firm. The combination of creative low first cost and low energy mechanical systems, an intelligent façade shading system, and a solar photovoltaic system has resulted in a unique space with a small environmental footprint.

Energy Efficiency

Energy efficiency was a primary focus of the design. To that end, a rigorous conceptual design-phase efficiency charrette was held with all the project’s stakeholders, including the owner, facilities personnel, architect, engineers and future occupants. The goal of the charrette was to brainstorm how the building’s form and façade could contribute to energy efficiency and occupant satisfaction without sacrificing the desired aesthetic.

The design team chose a fritted curtainwall system that incorporates an automated shading system. The shading system controls each curtainwall bay independently, in response to real-time sky conditions, to maximize daylighting harvesting while always preventing glare and direct solar beam onto the occupants of the open office.

This automated shading system was estimated to reduce the annual utility costs of the building by approximately 2%, compared to manually operated window shades.

The building’s mechanical design incorporates an underfloor air distribution (UFAD) system. The team, having substantial experience with UFAD systems, decided to alter the traditional system design by decoupling interior loads and building ventilation from perimeter heating and cooling loads by incorporating a perimeter overhead radiant panel system (Figure 1). In the open office spaces, this allowed all the typical fan powered boxes, ductwork, and reheat to be eliminated. This approach also eliminated concerns of distribution losses that are a typical complaint of UFAD systems at the perimeter.

The UFAD system allows an elevated supply air temperature of 62°F (17°C) to be used, which in turn allows an elevated chilled water temperature of 52°F (11°C) to be used (versus the traditional 55°F and 44°F (13°C and 6.7°C), respectively). These milder temperatures result in an extremely high chiller efficiency of 0.50 kW/ton (0.14 kW/kW) at design conditions and a NPLV of 0.3 kW/ton (0.09 kW/kW). It also allows the integrated waterside economizer to function for approximately 1,500 additional hours, and the airside economizer to function for an additional 2,700 hours per year.

The mechanical design also eliminates reheat by using the perimeter radiant panel system, which is provided heating hot water from a 95% efficient condensing boiler plant.

The lighting design uses high efficacy continuously dimming fixtures that are controlled based on available daylight. The lighting design achieved a lighting power density of 0.66 W/ft2 (7.1 W/m2). The result is a 57% reduction over the ASHRAE Standard 90.1-2007 baseline building’s lighting energy consumption.

These energy conservation features combine to reduce the annual energy cost of the Marine Way building by 40% over a Standard 90.1-2007 baseline building. The final energy model predicted the building’s EUI to be 41.2 kBtu/ft2·yr (467.9 MJ/m2), before accounting for renewable energy production.

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Figure 1