Green Roof Performance to be Tracked with Weather Stations
Allegheny County officials are facing an expensive wastewater system upgrade, and they hope reducing stormwater will help reduce the severity of Combined Sewage Overflows (CSOs). A few months ago, they settled on a green roof solution; a plan to cover one half of the building’s roof with boxes of plants settled in a growing medium. The area is as wide as a basketball court and twice as long.
In April, 2010, they began to build the green roof, and chose to equip the new roof with web-based weather stations from Massachusetts-based Onset to monitor its performance.
Monitoring the green roof’s success in reducing runoff is critical to the project, according to Darla Cravotta, the special projects coordinator with Allegheny County.
“We can’t talk about the benefits of a green roof without monitoring it,” said Cravotta. “But when we have data, we can encourage other people to build green roofs,” she said.
Allegheny County has a team of four companies working on the project, which is being funded through the Department of Energy’s American Recovery and Reinvestment Act (ARRA). The project team includes Cuddy Roofing, Eisler Landscapes, IDC Architects, and Civil & Environmental Consultants, Inc. (CEC). The first three companies are working on designing and building the green roof, while it will be up to Pittsburgh-based CEC to monitor a multitude of data points over the next six years.
John Buck of CEC will use eight Onset HOBO® U3O weather stations with approximately 90 sensors to track soil temperature, soil moisture, runoff duration, wind speed, wind direction, air temperature, relative humidity, and solar radiation.
It’s not the first time Buck has used Onset devices in a project. In a 2005 job, for example, he used Onset data loggers to track data for an alternative soil cap study at a solid waste disposal site. “We had a pretty hot setup for the time,” Buck said.
“We created a 900 MHz network that relayed data and emailed me three times a day.” But that system had weaknesses that the U30 devices have overcome, he said. “When you considered the dependence of that system on the computer at the site, and the power outages, Windows® updates, and the fact that the computer hated zero degree weather,” he said, “you’ve got a lot of variables. The U30 cut out the intermediate computer and 900 MHz radios and simplified the system.”
For example, the U30s are weatherproof and transmit the data via Wi-Fi to Onset’s web server, a major advantage, he said.
Originally, Buck wanted to use Wi-Fi communications for all eight weather stations. “But it turns out that Wi-Fi did not transmit through the roof,” he said. Instead, he put two Ethernet-enabled U30s inside the government building and placed an access point on the roof so that the other six Wi-Fi devices on the roof could communicate. Buck is using Onset’s HOBOlink® web server as a data repository and a way to monitor the system remotely, sensor-by-sensor, he said.
The stations will also be used to detect humidity spikes in several roof areas. The county administrators acknowledged that the 1923 building already had a history of roof leaks, a problem that could be made worse by putting structures up there. “There are people who are understandably nervous about more roof leaks,” Buck said.
If pre-set humidity limits are reached – which could suggest a possible roof leak – the station will automatically send Buck a text message alert. “We’ll get a message before the water starts dripping,” he said. “That wasn’t a primary objective of the project, but it is a benefit.”