Outdoor Thermal Comfort under Photovoltaic Canopy Structures–A Field Study at Arizona State University

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Wednesday, 7 January 2015
Ariane Middel, arizona state university; and N. Selover, N. Chhetri, and B. Hagen

Shade is an important factor in creating comfortable, pedestrian-friendly outdoor spaces in desert urban environments during the hot summers. Shading at street level can be achieved through various design strategies, including building clustering, overhangs and awnings, tree canopy, and artificial shading structures, such as photovoltaic canopies. In December 2013, three 10 m high photovoltaic canopy structures were installed on Arizona State University's Tempe campus, covering a pedestrian mall next to the Memorial Union (MU). The structures consist of 1,380 solar panels, which generate energy in addition to providing shade to the campus community. This project uses microclimate observations and field surveys to assess the impact of these photovoltaic canopies on pre-monsoon microclimate beneath the canopies and pedestrian thermal comfort at the pedestrian mall.

We installed six shielded sensors at 2.6 m height near the MU to monitor temperature and humidity at a 5-minute frequency interval for a full year. Two of the sensors were mounted underneath the solar canopy structures; four sensors were deployed in the vicinity of the structures in both unshaded locations and under shade trees. In addition, we conducted a three day field study in mid-June 2014 under clear weather conditions. During the field study, we observed radiant heat measures, solar radiation, and surface temperatures underneath the permanent sensor installations every hour from 7:00 a.m. to 10:00 p.m., calculating Mean Radiant Temperature (MRT) and thermal comfort indices from our microclimate observations. In addition, we surveyed 304 people on-site about their thermal perception, comfort level, thermal preference, sun exposure and activity prior to the survey, and adaptation level. We linked survey responses to the meteorological observations and comfort indices to compare pedestrian comfort under the photovoltaic canopies to comfort levels under trees and in sun-exposed locations. Results from this study will give insight into the benefits of shade for thermal comfort and help design more walkable outdoor spaces to mitigate heat during summers in hot, arid environments.