18 traffic or industrial activities. Third, if the outside air is of sufficient quality, it also has to be of adequate temperature and relative humidity to maintain indoor comfort. Several early stage design tools have been proposed to help design teams with the final task, i.e. to decide whether natural ventilation is an option in terms of indoor temperature and relative humidity for a given climate, program and façade orientation. Fig 1.7 shows an example output from the ECOmpass tool for an sidelit office in Boston (CDDI-4).8 Each pie slice indicates for a given cardinal direction (north, south, east, west) whether an office can (green) or cannot (gray) be naturally ventilated assuming that occupants may dress lightly (knee length trousers/ short sleeved shirt) to avoid overheating. Yellow indicates a borderline situation. Columns correspond to varying window-to-wall ratios (WWR). Rows represent the combined use of increasingly more passive design strategies from bottom to top starting with daytime natural ventilation and adding external shading, nighttime ventilation and thermal mass construction. The figure demonstrates that a naturally ventilated building in Boston requires careful deployment of shading controls, nighttime flushing and ideally some active thermal mass (CDDI-8). Apart from Boston being a borderline climate for natural ventilation in offices, Fig 1.5 also shows that the Medium Office Boston is significantly deeper than five times its floor to ceiling height 40% 50% 60% 70% 80% 20% 30% XX% N W E S Daytime ventilation Shading Night ventilation Thermal mass No AC required (< 20kh) Might require AC (<1200kh) Requires AC Window-to-wall ratio Fig 1.7 Passive conditioning study for an office in Boston using ECOmpass (Visualization and simulation: Svenja Herb)
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