Overview
A green roof is a roof that is partially or fully covered with soil and plant life. A typical green roof consists of a waterproof membrane under layers of soil and vegetation. While variations of green roofs have existed for centuries, it has only been in the past 50 years that the green roof movement has developed. European countries have spearheaded the movement back in the 1960s. Now many countries, including the United States, have recognized the beneficial impacts of green roofs, especially in urban areas.
There are numerous benefits for implementing green roofs in urban areas. The most obvious is the environmental impact. A green roof may act as a stepping stone for many bird and insect species that previously had nowhere to go. The plants and trees that may be present on the roof increase the amount of carbon dioxide that is absorbed and produce more oxygen. This can lead to a decrease in the amount of CO2 in the atmosphere and help fight global warming.
The green roof can also absorb more rainfall, which reduces stormwater runoff. This is very important as stormwater runoff has been identified as one of the leading causes of water pollution in and around urban areas. As opposed to a natural environment where upwards of 60% of rainwater is absorbed, a city offers nowhere for water to go except the sewer. During instances of particularly heavy rains, sewers may overflow causing pollution in nearby streams, ponds, rivers, and lakes.
A green roof acts as a natural insulation for the building, absorbing sunlight and keeping the building cooler in the summer. In the winter, green roofs reduce heat loss and energy consumption. Maintenance and energy costs can be significantly lower for buildings utilizing green roofs.
Common with many green roofs is a monitoring system to quantify the environmental impact of the green roof. NexSens Technology has experience in providing turnkey systems for monitoring such parameters as precipitation, solar radiation, photosynthetically active radiation (PAR), barometric pressure, wind speed & direction, relative humidity, air temperature, roof temperature, soil moisture, temperature, & salinity, stormwater runoff, and more.
Selecting Sensors
NexSens offers a wide range of instruments for a variety of parameters related to green roof monitoring. Sensors are available for weather, soil, light, and water.
For light monitoring, NexSens offers sensing solutions from LI-COR. LI-COR offers sensors for the measurement of both PAR and solar radiation. PAR, which stands for Photosynthetically Active Radiation, is measured to determine the amount of energy plants use during photosynthesis. Pyranometers measure solar radiation for agricultural, meteorological, and solar energy studies.
Precipitation may be measured with a variety of instruments. When dealing strictly with liquid precipitation, RM Young offers a high accuracy tipping bucket rain gauge, which uses a proven tipping bucket mechanism for simple and effective rainfall measurement. If the application demands the measurement of all forms of precipitation, the OTT Pluvio2 Precipitation Gauge features a highly-accurate weight-based technology to quantify rainfall, snow, and hail.
For projects requiring more than just precipitation data, the Vaisala WXT520 measures six of the most essential weather parameters. This multi-parameter weather sensor measures wind speed & direction, liquid precipitation, barometric pressure, temperature, and relative humidity. Vaisala also offers carbon dioxide sensors for ecological measurements. The GMP343 carbon dioxide sensors are excellent for monitoring soil respiration on green roofs.
Soil moisture, salinity, and temperature may be measured using the Stevens Hydra Probe II. Stevens patented Hydra Probe design measures the dielectric constant for water content and the conductivity simultaneously. A built-in thermistor determines soil temperature.
For quantifying stormwater runoff, there are two common approaches. The first approach is to direct runoff through a weir or flume structure, using a vented water level sensor and industry-standard flow calculations to output total flow. If this solution is not feasible, a tipping bucket rain gauge may also be used. With this solution, stormwater runoff is funneled through the rain gauge and measured accordingly.
Data Logging and Telemetry
All of the sensors mentioned above may be simultaneously connected to a NexSens iSIC (Intelligent Sensor Interface & Control) data logger. The iSIC data logger delivers unmatched sensor interface and data collection with options for direct connect, or landline phone, cellular, radio, Ethernet, WI-FI, and satellite telemetry.
A common solution for green roof monitoring systems includes radio telemetry data loggers mounted on the roof. Data can be wirelessly transmitted through the roof to a radio base station and Windows-based computer within the building. This eliminates the need to drill holes into the roof for cable runs.
Each iSIC data logger simultaneously supports 8 analog inputs & 4 digital inputs for multi-sensor data logging capability. Junction boxes are available to help manage sensor wiring to the data logger. The system is powered with a 12V sealed lead acid battery that receives a continuous charge from an AC float charger or a solar panel. AC power is usually available on roofs; however, a completely autonomous solar charged solution is more common, as it helps to complement the overall goals of the green roof implementation through energy savings and environmental sustainability.
Managing Data
Data from the green roof sensors is logged and transmitted at a user-defined interval (minimum 1 minute) back to the project computer running iChart Software. iChart is a user-friendly Windows-based software package that serves as the centralized interface and database for all incoming data. The software allows users to generate customized reports with company logos and relevant project information listed in the header. Reports can be converted to PDF, exported to Microsoft Excel, sent to interested parties via e-mail, uploaded to a web server, and more.
NexSens WQData is an optional web-based data management solution for green roof monitoring systems and other environmental data. The modular datacenter interface can be easily customized to include project-specific themes and information. WQData allows users to access to bridge scour data from any web browser.
On-Site Services
To ensure that customers can begin using their green roof monitoring system as quickly and efficiently as possible, our application engineers are available for training and technical support, both by phone and in person. Our company offers both extensive field experience and a wide array of deployment hardware to facilitate seamless implementation of the project. Contact our application engineering team for your next green roof monitoring project.
