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ASHRAE Journal A Standard for Natural Ventilation
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Architecture and engineering journals have been increasingly attentive to innovative non-residential buildings designed with operable windows. Such buildings may rely exclusively on natural ventilation for cooling, or may operate as mixed-mode, or hybrid buildings that integrate both natural and mechanical cooling. Architects who want to incorporate natural ventilation as an energy-efficient feature need to collaborate closely with mechanical engineers. Unfortunately, engineers often need to veto such natural approaches, citing their professional obligation to ad-here to thermal comfort standards such as ASHRAE Standard 55 or ISO7730. In their current form, these standards establish relatively tight limits on recommended indoor thermal environments, and do not distinguish between what would be considered thermally acceptable in buildings conditioned with natural ventilation vs. air conditioning. In other words, engineers have not had a suitable tool to help decide when and where full HVAC is required in a building, and under what circumstances they can incorporate more energy-conserving strategies without sacrificing comfort.5064
ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, was initially released in 1966. Since then, it has been revised once a decade, incorporating the latest technical advances in our understanding of thermal comfort. Derived from laboratory experiments using a thermal-balance model of the human body, this standard as attempted to provide an objective criterion for thermal comfort in particular, specifying combinations of personal and environmental factors that will produce interior thermal environments acceptable to at least 80% of a building’s occupants. While ASHRAE Standard 55 was originally intended to provide guide-lines for centrally controlled HVAC, its broad application in practice is hindering innovative efforts to develop more per-son-centered strategies for climate control in naturally ventilated or mixed-mode buildings. Such strategies may hold great social and environmental benefits, reducing energy consumption and increasing occupant satisfaction, especially in office buildings.
Based on ASHRAE-funded research, this article argues that adequate scientific basis now exists to amend Standard55 to include a more adaptive field-based alternative for application to naturally ventilated buildings. Such a proposal reflects findings that thermal preference in such buildings varies widely from predictions made by the present laboratory-based standard. The article suggests that one possible reason for this discrepancy may be that the heat-balance model of thermal comfort underlying the present standard cannot account for the complex ways people interact with their environments, modify their behaviors, or gradually adapt their expectations to match their surroundings.
Adaptation in Buildings
Advocates for a more flexible thermal comfort standard have long argued that the primary limitation of Standard 55 is its “one-size-fits-all” approach, where clothing and activity are the only modifications one can make to reflect seasonal differences in occupant requirements. The standard was originally developed through laboratory tests of perceived thermal comfort, with the limited intent to establish optimum HVAC levels for fully climate-controlled buildings. However, in the absence of any credible alternative, Standard 55 is applied universally across all building types, climates and populations.
As a consequence, even in relatively mild climatic zones, it is hard to meet the standard was narrow definition of thermal comfort without mechanical systems. Many researchers and designers have argued, for example, that reliance on Standard 55has allowed important cultural, social and contextual factors to be ignored, leading to an exaggeration of the ”need” for air-conditioning. Others have argued that allowing people greater control of indoor environments, and allowing temperatures to more closely track patterns in the outdoor climate, could improve levels of occupant satisfaction with indoor environments, and reduce energy consumption.