ystems
have been constructed. A low-cost monitoring system for use on a generic green roof
was designed and assembled to measure the flow rate of the runoff and the water table
level on the roof, and to collect samples for water quality analysis, so that the effects of a
green roof on storm water runoff can be measured.
2 Table of Contents
Abstract...........................................................................................................................2
Table of Contents ...........................................................................................................3
Introduction....................................................................................................................4
Purpose of the Project ..................................................................................................4
History of the Project...................................................................................................6
General Description of the Design...............................................................................7
Implementation of Design .............................................................................................8
Overall Mechanical Design of the System...................................................................8
Flow Rate Meter ........................................................................................................10
Capacitive Level Meter..............................................................................................12
Design of Sample Collector .......................................................................................17
Design of Data Collection by Microcontroller ..........................................................20
Printed Circuit Boards Data-Logger/Transmitter and Receiver .............................23
System Cost ..................................................................................................................25
Conclusion ....................................................................................................................25
Future Work.................................................................................................................25
References.....................................................................................................................27
Acknowledgements ......................................................................................................27
Appendix.......................................................................................................................28
Pelton Turbine Diagram.............................................................................................28
Turbine Frame Diagram.............................................................................................29
Printed Circuit Board Design.....................................................................................30
PIC Microcontroller Code..........................................................................................30
MatLab Serial Port Reader and Text File Logger......................................................33
3 Introduction
Purpose of the Project
The idea of implementing green roofs on buildings is becoming increasingly
popular. Many small-scale green roofs have been constructed worldwide. Besides
energy conservation and aesthetic satisfaction, green roofs are beneficial because they
reduce storm water runoff and alleviate non-point source pollution in highly developed
residential areas. Functioning as a reservoir, green roofs retain a certain amount of storm
water after rainfall and reduce the total amount of runoff through evapotranspiration.
Gravel, soil and vegetation on green roofs also reduce pollutants and nutrients in storm
water through filtration and biological process.
There has not been much empirical information obtained regarding the
performance of green roofs in reducing storm water runoff and pollutants. Therefore, it is
necessary to install monitoring systems on Water-&-Pollution-Level-Monitoring-System-for-a-Green-Roof/' >various types of green roofs in order to
perform experiments to determine the ability of roofs to retain water and reduce
pollutants. The results of these experiments could be further used to develop a
mathematical model to quantify the benefits of installing green roofs. Nevertheless, so
far most of these monitoring systems require the installation of expensive instruments for
measurements. Moreover, most of them were designed for very specific sites. These two
factors have prevented monitoring systems from being widely implemented on green
roofs, which has resulted in the aforementioned lack of quantitative knowledge of the
performance of green roofs.
Swarthmore College has recently constructed two green roofs on its campus. The
first green roof was installed on the shed behind Papazian Hall. Due to its success, a
4 second green roof was installed on Alice Paul Hall in 2004. The two green roofs on
campus have provided us with an opportunity to design an economical monitoring system
which will make the measuring process easy and affordable for most clients who have
installed green roofs. Moreover, the monitoring system should be able to be easily
installed on different green roofs regardless of their types and geometric characters. In
general, our monitoring system should meet the following goals:
1.

The system should be able to detect the flow rate of storm water effluent of a
green roof. By comparing the amount of storm water effluent from a green roof
and that from a conventional roof, we can determine the amount of storm water
runoff reduction the green roof can achieve.
2.

The system should be able to detect the level of the water table on a green roof.
The resulting data will help us to understand how the roof Water-&-Pollution-Level-Monitoring-System-for-a-Green-Roof/' class='doin' >functions as a water
reservoir.
3.

The system should be able to collect samples of storm water effluent for water
quality analysis. By comparing the quality of storm water runoff from a green
roof and that from a conventional roof after the same rainfall, we can determine
the ability of the green roof to remove pollutants and nutrients from storm water.
4.

The system should be affordable to general clients. The total cost of the system
should not exceed $200.
5.

The system can be installed on different types of green roofs with minor
modification.
6.

The system should be easy to operate and maintain.
5 By designing this monitoring system we hope more useful data will be accessible
for researchers to assess the performance of green roofs in alleviating environmental
issues associated with storm water runoff in highly developed area.
History of the Project
Our project is a continuation of some of the previous work done by professors and
students of the Engineering Department of Swarthmore College.
A prototype of the monitoring system was designed by Simeon Realov 06 and
Frank Kyei-Manu 06 under the guidance of Professor Carr Everbach. The system
consisted of a commercial flow rate meter, a parallel plate capacitive level meter, and a
wireless data-logging system. The commercial flow rate meter could not handle high
flow rates and failed to operate after the inside turbine was clogged by particles from the
water. The parallel plate capacitor level meter failed to change its capacitance with a
change in the water level. The wireless data transmission was noisy and had a very short
range. Despite these problems, the prototype did provide us with a foundation on which
we could develop our system. We kept the idea of using a capacitance level meter and
wireless data transmission in our project (more details in Water Table Level Meter and
Printed Circuit Boards Design Process).
After the failure of implementing the commercial flow rate meter, Professor Carr
Everbach, assisted by a high school student, designed a Pelton turbine flow rate meter.
We kept many of the ideas of this design in our project (more details in Flow Rate Meter
Design Process). The major flaw of the original design was its use of steel ball
bearings for the turbine shaft. The bearing is vulnerable to rust which causes an increase
of friction with time, and this results in inconsistent flow rate data.
6 General Description of the Design
Our system consists of a water table level meter, a flow rate meter, a sample
collector, a printed circuit board for data-logging, system control, and wireless data
transmission, a printed circuit board for wireless data reception and wired transmission of
data to a computer, and a MatLab program to record the data in a text file on the
computer (Figure 1). The brain of the system is the printed circuit board for data-
logging, system control, and data transmission. It measures the reading from level meter
and flow rate meter, controls the sample collector to operate at specific time periods, and
wirelessly transmits data to the receiving end.


Figure 1. The general components and data flow of the system.
Sample collector
Flow rate meter
Water table level meter
Green Roof
Effluent
Water Quality
Analysis
Remaining Water
on the roof
Water table level
Flow rate
Control
Microcontroller/ Data logger /
Transmitter
Wireless Data
Transmission
Receiver
Serial Port
Software for data
logging
7 Implementation of Design
Overall Mechanical Design of the System


Overflow pipe
Inlet funnel
Flow rate meter
Sample collector
Figure 2. The integrated system of an inlet funnel, a flow
rate meter, a sample collector, and an overflow pipe

As