A Wireless Sensor Network based System for Reducing Home Energy Consumption

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A Wireless Sensor Network based Systemfor Reducing
Home Energy Consumption
Antimo Barbato
Politecnico di Milano
Milano,Italy
barbato@elet.polimi.it
Luca Borsani
Politecnico di Milano
Milano,Italy
borsani@elet.polimi.it
Antonio Capone
Politecnico di Milano
Milano,Italy
capone@elet.polimi.it
ABSTRACT
In this paper we present a work in progress within the Euro-
pean project AIM for the design of a system based on wire-
less sensor networks to save energy in home environments.
1.INTRODUCTION
According to recent studies [3] energy consumptions are in-
creasing year after year,and if effective energy saving poli-
cies will not be adopted,in 2030 they will rise by 28% on
2006 value.The residential sector,in particular,accounts
for an increasing percentage of the total consumption which
is now above 27.5% (source Earthtrends).These predictions
have recently drawn the attention of the research commu-
nity as well as of the industry world to a new generation of
home automation systems for energy saving ([6],[4]).
In this paper,we present an integrated systemcurrently un-
der development within the European project AIM [1],for
profiling and reducing home energy consumption.We focus,
in particular,on the key role played by wireless sensor net-
works to automatically control home appliances according
to users habits.To create a system where user doesn’t need
to waste a lot of time in complex settings of system parame-
ters,one of the challenges of AIMproject is to automate the
set up of a part of these parameters with a system able to
predict actual user preferences on the basis of previous ob-
served behavior.This is the main role of the sensor network
that senses physical parameters estimating user behavior for
future periods and adjusting prediction in real time.On the
basis of this information the AIM system is able to best
schedule tasks for every appliances,for example heating the
room at the desired temperature before the user come in.
In order to show how the proposed automation systemworks
during the demo session where the real home devices will
not be available,we also implemented an application soft-
ware that can be used to create some virtual devices (e.g.
air conditioners or lighting systems) simulating the home
environment.
2.WIRELESS SENSORS FOR SMART EN-
ERGY MANAGEMENT
In the AIMarchitecture,the wireless sensor network (WSN)
provides the basic tools for gathering information on user be-
havior and his interaction with home appliances.Moreover,
the WSN provides measurements of some physical param-
eters like temperature and light that can be used by the
system to perform some automatic adjustment of the en-
ergy management system.For this purpose we implemented
a hierarchical hybrid network architecture called MobiWSN
[5].This architecture is composed by heterogeneous islands
of sensor nodes (using IEEE 802.15.4 technology) with each
of them created defining a tree network topology.Each is-
land is managed by a Gateway and is able to communicate
with it using a stateless protocol we called Information Ex-
change Protocol (IEP).The MobiWSN Gateways are inter-
connected using a mesh configuration to ensure reliability
and resilience to failure,and can communicate with an ad-
ditional node,called Manager,that is in charge of managing
network creation and reconfiguration.The MobiWSN ar-
chitecture,besides providing measurements of physical pa-
rameters like temperature and light,is also able to detect
user presence in each room of the house.This functionality
has been achieved defining a specific protocol that we called
infrared-based Presence Detection System (i-PeDS),based
on Passive InfraRed (PIR) sensors.
3.USER PROFILING
The basic function of the user profile is the characterization
of users behavior so that some settings of the energy man-
agement system can be made automatically.For this reason
we used the MobiWSN architecture for monitoring environ-
mental parameters,such as user presence,temperature and
light.This information is aggregated and processed in or-
der to create three different types of profile (user presence
profile,temperature profile and light profile) that represent
users habits.In the user presence profiling (the same can
be said of temperature and light profiling) the sensor net-
work collects 24 hour information (here called“daily profile”)
about users presence/absence in each room of the house in
a given monitoring period (i.e.week,month).At the end
of the monitoring time the cross-correlation between each
couple of 24 hour data presence is computed for each room
of the house in order to cluster similar daily profiles.In
particular,daily profiles y(t) and x(t) are said similar if:
r(x,y) >
1 −A
2
[r(x,x) +r(y,y)]
Where r(x,y) is the mean value of the cross-correlation be-
tween signals x(t) and y(t) calculated with an accepted de-
lay of ±B (in minutes),A and B are constants (respectively
equal to 0.12 and 10 in our numerical results).
For each cluster the average of the daily profiles identifies a
final presence profile that provides the 24 hour probability
distribution of the user presence in the roomthe cluster is as-
sociated with (Figure 1).At the end of calculation a matrix
is generated where each room is associated with a column
that represents the sequence of presence profiles identified in
0
2
4
6
8
10
12
14
16
18
20
22
24
0
0.2
0.4
0.6
0.8
1
Final Presence Profile
Day Time [hours]
User Presence Probability
Figure 1:Example of final presence profile.
the monitoring period.Each matrix column is statistically
elaborated in order to predict the presence profile in a given
day,for each room,on the basis of the observed profiles
in the past days.For room i,for example,the prediction
algorithm performs:
1) for each presence profile j in the selected column,the
probability that it occurs after the sequence of pro-
files of the past M days in room i (with M = 1) is
calculated;
2) if a profile j exists with such a probability higher than
a threshold (experimentally set to 0.75),the algorithm
stops and j is the predicted profile;otherwise M is
increased by 1 and the algorithm goes back to step 1.
The prediction algorithm provides presence,temperature
and light profiles for each day of the year.Obviously users
habits are only partially predictable.For this reason the sys-
tem has to be able to detect exceptions in the user behavior
and to adjust missed predictions.For this purpose we im-
plemented a specific algorithm,called Updating Algorithm,
that uses real time data provided by the sensor network to
dynamically update the predicted profiles during the day.
4.NUMERICAL RESULTS
As previously mentioned,we implemented a prototype ver-
sion of the proposed sensor network architecture for energy
management.However,to evaluate the performance of the
user-habits prediction algorithms we have been forced to rely
on simulation mainly because of the long period of time re-
quired for testing them in a real environment.The system
has been tested referring to a five room house with a sim-
ulating period of 300 days,creating a realistic sequence of
daily presence,light and temperature profiles.The presence
prediction algorithmhas been simulated in three user behav-
ior exceptions cases:exceptions spike (there are 20 isolated
exceptions in the users behavior),exceptions burst (there
are 4 sequences of 4 contiguous exceptions) and behavior
variation (user changes his behavior two times during the
year).The results of the 300 days simulation are presented
in Table 1.
Room
1
2
3
4
5
Exceptions Spike
88.00%
90.33%
87.67%
88.67%
87.00%
Exceptions Burst
94.00%
92.00%
93.67%
91.67%
93.33%
Behavior Variation
90.00%
91.00%
90.00%
91.67%
90.67%
Table 1:Percentage of correctly predicted profiles
for each room of the house.
The presence,temperature and light profiles can be used
to optimize the using time of home appliances and to min-
imize the home energy consumption.In Figure 2 and 3 we
present an example of the automatic temperature manage-
ment benefits.The management system allows some energy
savings turning off the cooling system of the rooms that
are not required to be air conditioned because the user will
not enter those rooms with high probably and turning it off
in the whole house if the user is not present and probably
will not return for a long time.In contrast,in the “classi-
cal scenario” the cooling system is supposed to be On in all
rooms and to be preprogrammed from the user to approxi-
mately follow his daily/weekly schedules.In the simulation
performed,the home temperature management has reduced
the working time of the cooling systemby nearly 28 percent.
0
2
4
6
8
10
12
14
16
18
20
22
24
Cooling System is Off
User is Present
Cooling System is On
User is Absent/
Daily Cooling System Working Mode
Day Time [hours]


User Presence
Cooling system
working mode
253.15 minutes
Cooling system working
time = 316.17 minutes
63.02 minutes
Figure 2:Room 3 daily cooling system working
mode without home automation
0
2
4
6
8
10
12
14
16
18
20
22
24
Cooling System is Off
User is Present
Cooling System is On
User is Absent/
Daily Cooling System Workig Mode
Day Time [hours]


User Presence
Cooling system
working mode
63.15 minutes
73.13 minutes
Cooling system working
time = 199.45 minutes
63.21 minutes
Figure 3:Room 3 daily cooling system working
mode with home automation
5.DEMOAPPLICATION AND SETUP
In our implementation of the sensor networks described in
Section 2 we use Crossbow Micaz and iMote motes [2] equip-
ped with Crossbow MTS300 and IMB400 sensor boards that
provide temperature,light and motion information.One of
these sensors is connected to a PC and works as a gate-
way.We developed our network application under TinyOs,
a free and open source component-based operating system
for wireless embedded devices with reduced computation
and memory capabilities.We further implemented a Java
Application that we called Home Virtualization Application
(HVA) with a friendly graphical user interface (Figure 4).
The HVAis used to implement some virtualized devices (e.g.
air conditioners,lighting systems,TV,WiFi routers) and to
show how information provided by the MobiWSN platform
can be used to automatically and best control home appli-
ances according to users habits.
The HVA graphical interface is structured so that data can
be showed through two main panels:House panel and Room
panel.The first one represents the house map and some
house information while the second panel is composed by a
3D animated image associated with the selected room and
four java panels:
Figure 4:HVA Graphical User Interface
(a)
(b)
Figure 5:HVA Devices and Presence Panels
• Information Panel:shows information (temperature,
light,user presence and power consumption) provided
by sensors located in the selected room;
• Room Devices Panel:shows the virtualized devices
located in the selected room and their status (Figure
5(a));
• Consumption Panel:represents the consumption chart
of the selected room for the current day;this chart
is computed using the devices status information and
consumption data;
• Presence Panel:represents the predicted presence pro-
file and the daily presence profile of the selected room
for the current day (Figure 5(b)).
The demonstration will show how the AIMautomation sys-
tem uses information provided by the sensor network to au-
tomatically control home appliances.During the demon-
stration five sensors will be deployed in the demo room and
the HVA application will be launched supposing that the
monitored house is composed by one room only (the demo
room itself).The conference attendees must stand in front
of the PC where it’s possible to see how the virtualized de-
vices are controlled based upon real-time data provided by
the sensors (e.g when the sensors detect users presence the
automation system will switch on the virtual air conditioner
to bring the temperature to the desired value).
6.CONCLUSION
In this paper we presented a home energy management sys-
tem under development within the European project AIM.
We proposed a heterogeneous hierarchical sensor network
architecture to gather physical parameters and to monitor
user behavior.Data collected by the sensors are used to
create user profiles.Based on user profiles and real-time
information provided by the system,we can predict user be-
havior and optimize the energy consumption automatically
controlling home appliances.We proposed a new approach
to implement a self adaptive prediction algorithms to set sev-
eral parameters (light intensity,temperature,etc.) accord-
ing to user estimated preferences.The presented solution is
simpler than other profiling systems,mentioned in Section
1,which rely on complex learning techniques:just replicat-
ing a previously observed set up that satisfied the user in
a similar context provides good results.We implemented a
prototype version of the proposed sensor network architec-
ture and simulated our prediction algorithms over long time
periods showing their effectiveness in estimating users be-
haviors.In order to show how the system works even if the
real home devices are not available,we also implemented an
application that is used to create virtual devices.Moreover,
a prototype of the whole AIMsystemhas been realized with
the collaboration of the other partners of the project and it
is actually under test in different real use case scenarios.
7.REFERENCES
[1] Aim project.http://www.ict-aim.eu/.
[2] Crossbow.http://www.xbow.com/.
[3] U.S.Department of Energy.Buildings energy data
book,2008.
[4] H.Hagras,V.Callaghan,M.Colley,G.Clarke,
A.Pounds-Cornish,and H.Duman.Creating an
ambient-intelligence environment using embedded
agents.IEEE Intelligent Systems,pages 12–20,2004.
[5] A.Laurucci,S.Melzi,and M.Cesana.A reconfigurable
middleware for dynamic management of heterogeneous
applications in multi-gateway mobile sensor networks.
Demo presented at IEEE SECON,Rome (Italy),2009.
[6] V.Singhvi,A.Krause,C.Guestrin,J.Garrett Jr,and
H.Matthews.Intelligent light control using sensor
networks.In Proceedings of the 3rd int.conference on
Embedded networked sensor systems.ACM,2005.