ASHRAE Journal- September 2008

Keyword Ventilation Natural Ventilation Deﬁnition “The process of supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity or temperature within the space.” “ ventilation provided by thermal, wind, or diffusion effects through doors, windows, or other intentional openings in the building.” “ refers to a hybrid approach to space conditioning that uses a combination of natural ventilation from operable windows (either manually or automatically controlled), and mechanical systems that include air-distribution equipment and refrigeration equipment for cooling.” “ shall be permanently open to and within 8 m (25 ft) of operable wall or roof openings to the outdoors, the openable area of which is a minimum of 4% of the net occupiable ﬂoor area. ” “The means to open required operable openings shall be readily accessible to the building occupants whenever the space is occupied.” “ are those spaces where the thermal conditions of the space are regulated primarily by the occupants through opening and closing of windows.” “ a simpliﬁed graphical method for determining the comfort zone that may be used for many typical applications “The range of operative temperatures presented in Figure 5.2.1.1 [from Standard 552004] are for 80% occupant acceptability.” “ Field experiments have shown that occupants’ thermal responses in [occupant controlled naturally conditioned spaces] depend in part on outdoor climate and may differ from thermal responses in buildings with centralized HVAC systems primarily because of the different thermal experiences, changes in clothing, availability of control, and shifts in occupant expectations. “ Allowable indoor operative temperatures for spaces that meet these criteria may be determined from Figure 5.3 [from Standard 55-2004].” Source Standard 62.1-2007, Section 3 Standard 62.1-2007, Section 3 Mixed Mode Web Site of the Center for the Built Environment at the University of California, Berkeley1 Mixed Mode Systems Naturally Ventilated Spaces Naturally Conditioned Spaces Typical Indoor Environment Method for Thermal Comfort Standard 62.1-2007, Sections 5.1.1, 5.1.2 Standard 55-2004, Section 5.3 Standard 55-2004, Section 5.2 Adaptive Model of Thermal Comfort Standard 55-2004, Section 5.3 Table 1: Deﬁnitions related to natural ventilation. The potential for natural ventilation as a viable means of comfort conditioning often relies on mixed mode approaches that use natural ventilation for most of the year, but rely on mechanical cooling for peak loading conditions. Commonly mixed mode systems are categorized as one of the following:1 Concurrent (same space, same time); Changeover (same space, different times); or Zoned (different spaces, same time). Additionally, it is necessary to deﬁne exactly how natural ventilation is used. Windows often are provided as a user amenity within fully air-conditioned spaces to give the occupants a connection to the outdoors and some level of control over increased localized ventilation. This case is not covered by any code or standard, as the natural ventilation is not necessary for human health or comfort. In the case where natural ventilation is used as a primary ventilation or cooling mechanism, it is necessary to differentiate between natural ventilation for indoor air quality (IAQ) or natural ventilation for controlling humidity or temperature, as Standard 62.1-2007 governs the former, while Standard 55-2004 addresses the latter. As the focus of Standard 62.1-2007 is indoor air quality, “naturally ventilated space” per the standard’s Section 5.1.1 is primarily meant to fulﬁll the IAQ purpose alone. Therefore, the use of natural airﬂows to condition spaces September 2008 falls under the deﬁnition of “naturally conditioned spaces” per Standard 55-2004. This document deﬁnes two sets of criteria for acceptable thermal conditions, one for typical indoor environments (using the laboratory-based PMV-PPD model) and another optional method for naturally conditioned spaces (using the ﬁeld-based adaptive thermal comfort model). A comparison of Figures 5.2.1.1 and 5.3 in Standard 55-2004 show that: “in naturally conditioned spaces, occupants will tend to accept a wider range of indoor comfort temperatures as compared to those limits established as acceptable for typical indoor environments.” A number of explicit limitations in Standard 55-2004 reduce the applicability of the extended comfort range to only those periods of time when no mechanical conditioning is provided (Table 2). Therefore, concurrent mixed mode systems should meet the PMVPPD based typical indoor environment comfort criteria throughout the year. Zoned and changeover systems should do so wherever and whenever mechanical conditioning is provided. Design Guidance, or Lack Thereof Standard 55-2004 states that “no speciﬁc guidance for naturally conditioned spaces is included in this standard.” Standard 62.1-2007, Section 5.1, explicitly states that “an engineered natural ventilation system when approved by the authority ASHRAE Journal 37

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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