ASHRAE Journal- September 2008

Table 4: Natural Ventilation Top 10 Feasibility Questions (Continued) Data to Review Question to be Asked (If Answer is Yes, Move to Next Question) Does the climate have regular outside air temperatures over 80°F? If yes, review whether exposed thermal mass is possible. Sample Answers from the San Francisco Federal Ofﬁce Building Design Process 8. High Afternoon Temperatures Climate did not have usual temperatures over 80°F except in rare cases, as 1% design temperature for cooling is 78°F db/62°F wb. Night purge is possible due to low nighttime temperatures, as shown below in the frequency of occurrence plot for nighttime temperatures. Does the climate have a diurnal range that has nighttime temperatures below 65°F for at least 8 hours a night on the worstcase days? If yes, move to multizone modeling of thermal mass and consider night purge. Nighttime frequency of occurrence psychrometric chart for San Francisco. Figure © Arup Throughout the year, do you have consistent outside air dew points throughout the year of less than 64°F? If yes, move to multizone modeling and consider a radiant cooling system. 9. Diurnal Range on Hot Days 7 p.m. to 7 a.m.—98.2% of hours are below 18°C (65°F) 10. Dew-Point Temperatures Throughout Year Not applicable, as radiant cooling was not used. and artiﬁcially controlled surface temperatures for room-sized volumes of space. The analytical engines have the ability to predict bulk airﬂow quantities moving in and out of each opening and zone, as well as air and surface temperatures taking into account the time lag associated with thermal mass manipulation. Usually, the software is run in an iterative manner to test the sensitivity www.info.hotims.com/19354-65 of opening sizes and loading conditions to optimize thermal comfort under all conditions. The results of the dynamic heat transfer simulations will give the user the ability to calculate the average operative temperature within each large-scale zone for the purposes of comparing it to the applicable comfort model, and will determine whether the space can be successfully considered to be naturally conditioned. Often, results from physical wind-tunnel testing are used to establish the pressure coefﬁcients at the boundary of the modeled space. After this ﬁrst round of room-level analysis conﬁrms that natural ventilation for cooling remains feasible, most natural ventilation design teams invest in performing a series of analyses using CFD, a computer-based iterative calculation methodology that simultaneously solves the Navier-Stokes equations for a designated volume of air deﬁned by user-input boundary conditions. CFD relies on “meshing” of the room volume to create an interlinked set of cubes of air September 2008 42 ASHRAE Journal http://www.wrightsoft.com http://www.wrightsoft.com http://www.info.hotims.com/19354-65

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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