ASHRAE Journal- September 2008

(called cells), with each undergoing the calculation procedure. As thousands of cells are typically created, CFD software packages tend to display the multitude of results in graphics that superimpose the data from each cell. These graphics show airﬂow patterns and temperature distribution in an easily read, intuitive manner so that the engineer can identify any bottlenecks, drafts, or stagnation points that may lead to uncomfortable air speed or air quality conditions. CFD results veriﬁed and reviewed by local building authorities are often accepted as proof of concept to meet the deﬁnition of “an engineered natural ventilation system” under Standard 62.1-2007, Section 5.1. Passive Operation on Warm Day In September (West Wing) Roof-mounted PVs. R-30 roof insulation located on the outside of the slab minimizes heat loss. On extreme days slab is kept at 68°F using return water from chiller. Air movement from ceiling fans improves comfort. Windows in multiuser classrooms have automatic operators. Large opening windows in the south corridor keep space at outdoor conditions in the summer. High performance glass reduces heat gain into space. Cooler air enters via low level windows. Heat absorbed into the thermal mass, slab. Figure © Arup Figure 1: Operating principles for the Kirsch Center for Environmental Studies building. Mixed Mode Projects in the San Francisco Bay Area The ﬁnal portion of this article incorporates a comparison of four buildings designed within the last decade, with the goal of reviewing developments in technologies and approaches. Although an overview comparison is provided in Table 5, the following sections provide an introduction to the mixed mode approaches in each building. The Kirsch Center for Environmental Studies is a small classroom building located in the South Bay in the warm environment of Cupertino, Calif. Natural ventilation alone is a viable cooling mechanism for much of the year in the perimeter zones, but there are times when additional cooling is required from a radiant slab served from the chilled water return piping. To further ensure comfort, ceiling fans are provided in all classrooms to increase air-on-skin velocity for the occupants, which boosts both convective heat transfer and sweat evaporation rates. The San Francisco Federal Ofﬁce Building has 13 ﬂoors of naturally ventilated and naturally conditioned perimeter open plan ofﬁce space. A sealed interior line of supervisor ofﬁces and conference rooms is provided with air-conditioning, as these areas are more than 20 ft (6 m) from the façade. In perimeter zones, cooling air is provided only through the windows (both manual and motorized). In advance of hot days, an exposed concrete ceiling slab is precooled through nighttime ventilation to provide heat absorption capacity on the following afternoon. The window wall incorporates mullion-integrated heating elements and trickle ventilators to ensure minimum outside air quantities under cool weather conditions when the larger windows would be closed. The Yang and Yamazaki Environment and Energy building at Stanford University, again in a warmer climate, encourages occupants to open and close windows within private northern and eastern ofﬁces for natural ventilation and natural conditioning, augmented only by ceiling fans. The atrium and ofﬁces facing south and west incorporate auxiliary chilled beams for cooling in addition to the natural ventilation. There 44 ASHRAE Journal Exposed Thermal Mass Fixed Window Automatic Window Manual Window Photo © Arup Fixed Window Finned Tube Radiator Trickle Vent Figure 2: Natural ventilation components at the San Francisco Federal Ofﬁce Building. are a number of so-called low impact spaces, which are provided with ceiling fans, natural ventilation through windows, and a radiant cooling/heating slab system. The California Academy of Sciences building incorporates a concurrent BMS-controlled natural ventilation/radiant slab cooling approach for the exhibition hall to accommodate the high occupancy density during museum special events. Ventilation openings are the main entry doors, trickle vents above the doors, and the circular windows at the roof. Within the north-facing perimeter research ofﬁce spaces, a zoned approach is pursued. The perimeter ofﬁces are in the natural ventilation mode throughout the year in which occupants have local manual control of a desk-height window and the BMS controls trickle vents and the radiators for heat. The interior zones operate simultaneously in the airconditioned mode with a VAV box system providing cooling and heating. As can be seen from the comparison chart, mixed mode approaches can work: In dry, temperate-to-warm climates; ashrae.org September 2008 http://ashrae.org

Table of Contents Feed for the Digital Edition of ASHRAE Journal- September 2008

ASHRAE Journal- September 2008 Section: Contents Contents Section: Commentary Options for Sustainability Section: Industry News The Silk Route for Energy Solar Thermal Is Unrealized Opportunity Industry Groups Sue City of Albuquerque Section: Letters Letters Section: Meetings and Shows Meetings and Shows Section: Feature Articles Article-Radiant Floor Cooling Systems Article-HVAC Design for Sustainable Lab Article-Mixed Mode Ventilation Article-Single- Design Considerations For Active Chilled Beams Article-Acoustic Design In Green Buildings Article-Teams, Contracts & BIM Section: Building Sciences Some Old Lessons Distilled Section: Washington Report Energy in Federal Buildings Section: Products HVAC&R Product Showplace Section: Emerging Technologies Toplighting & Lighting Controls For Commercial Buildings Section: Special Products Fans & Blowers Section: Classified Ads Classified Ads Section: Advertising Index Advertising Index

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