ASHRAE Journal- September 2008

Method Name Criteria “This is based on a 10% dissatisfaction criteria for general (whole body) thermal comfort based on the PMVPPD index, plus an additional 10% dissatisfaction that may occur on average from local (partial body) thermal discomfort.” (Standard 55-2004, Section 5.2.1.1) Limits Typical Indoor Environments 1. Met rates between 1.0 met and 1.3 met. 2. Clothing between 0.5 clo and 1.0 clo. Naturally Conditioned Spaces “Derived from a global database of 21,000 measurements taken primarily in office buildings.” (Standard 55-2004, Section 5.3) 1. Met rates between 1.0 met and 1.3 met. 2. Occupants may freely adapt their clothing. 3. Space equipped with operable windows that open to outdoors and that can be readily opened and adjusted by occupants. 4. Opening and closing of windows must be the primary means of regulating the thermal conditions in the space. 5. Does not apply when the heating system is in operation. 6. Not applicable when mean monthly outdoor temperature is less than 50°F or higher than 92.3°F. Table 2: Summary comparison of Standard 55-2004 comfort criteria. having jurisdiction need not meet the requirements” of the prescriptive approach, but gives no indication of what an “engineered” system would consist of. The 2005 ASHRAE Handbook— Fundamentals provides only two pages (27.10 – 27.11) to explain the physics of how natural ventilation flows can be cal- www.info.hotims.com/19354-52 culated and provides qualitative guidance regarding placement of openings. In looking for further guidance, one would primarily turn to the CIBSE Applications Manual AM10, Natural Ventilation in Non-Domestic Buildings,2 which is referred to as the basic criteria used by the U.S. Green Building Council’s LEED® for New Construction, Version 2.23 to establish minimum proof that the natural ventilation system is likely to give comparable IAQ ventilation as compared to a mechanically ventilated system. Table 3 lists the documentation requirements by associated LEED credit, and it begins to point towards the level of analytical investment that is appropriate for proposing a naturally ventilated or naturally conditioned space at the construction documents phase. What designers need to know is whether they should propose a natural ventilation system in the first place. Common sense must impose itself early in the project to evaluate whether natural ventilation is feasible. As a minimum, the Natural Ventilation Top 10 Feasibility Question List (Table 4) must be reviewed as a starting point if natural ventilation is to be used as a primary cooling mechanism. This early-phase decision aid collates nominal rules of thumb regarding the limitations of natural cooling capacities, the appropriateness of the climate, the cleanliness of the ambient air, the feasibility of ensuring low-velocity air movement paths, and the ashrae.org availability of thermal mass manipulation as an auxiliary cooling technique. For reference, the right column provides a sample of the necessary data as it applied to the design of the San Francisco Federal Building project. As can be seen in the examples, all of the numerical/graphical output for this preliminary analysis can be easily generated through the use of data from the Department of Energy’s typical meteorological year files. Once the design team has successfully answered the questions sequentially to the affirmative and has chosen to pursue natural ventilation, the analytical team must select the appropriate next-step calculation tool to confirm that the proposed scheme will meet the design intent. As noted in the CIBSE Applications Manual AM10, Chapter 4.2,2 the main tools “can be summarised (sic) under the following headings: envelope flow models, computational fluid dynamics (CFD), combined thermal and ventilation models, and physical scale models.” For most natural conditioning options, the next step would be to perform multizonal dynamic heat transfer and bulk airflow simulations using one of a handful of software programs, as it is difficult to predict air change rates under a variety of wind and buoyancy conditions solely through iterative hand calculations. These programs allow the user to input outside air temperatures, building envelope geometry and materials, opening sizes and pressure coefficients, internal heat loads, September 2008 38 ASHRAE Journal http://www.seiho.com http://www.seiho.com http://www.info.hotims.com/19354-52 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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.