by Brianna Crandall — June 1, 2011—A new, free software tool from the National Institute of Standards and Technology (NIST) was created to help architects and designers of ventilation systems for “green” commercial buildings. With the Climate Suitability Tool, building design teams can evaluate whether the local climate is suitable for cooling a prospective building with natural ventilation or whether it requires a hybrid system that supplies supplemental cooling capacity.
The tool is based on a model of the heat-related characteristics of a building configured to take full advantage of ambient climate conditions and natural air movement. It crunches hourly weather data (downloaded from annual datasets for U.S. localities) and uses standardized criteria for rating the comfort of building occupants.
“We think this tool will be useful during the early stages of design, when decisions on the form of a building and its components are being made,” explains NIST mechanical engineer Steven Emmerich. “It provides estimates of ventilation rates for preliminary design calculations. You can approximate how many air changes per hour will be necessary to offset heat gains due to the occupants, equipment and lighting so that comfortable conditions are maintained.”
Results of the tool’s assessment procedure include an estimate of the total number and percentage of hours that direct ventilation would be effective over the total for the year; the percentage of hours for which ambient conditions would be too cold, hot, or humid for direct ventilation; the total number of days warranting nighttime cooling; and the estimated percentage of days for which nighttime cooling would be effective.
Studies of the use of the tool in the varied climates of Kansas City, Los Angeles, Miami and Phoenix have found that occupants of naturally ventilated buildings tolerate a wider range of temperature than do people in air-conditioned structures. The researchers concluded that in cities with dry climates, such as Phoenix and Los Angeles, the adaptive thermal comfort option increases the effectiveness of natural cooling.
