Wireless Sensor Networks (WSN) based Air Conditioner Temperature Controlling System

Introduction

This Intelligent Air Conditioner Temperature Control System will be implemented by using a Wireless Sensor Network (WSN). WSN is a wireless network that has distributed autonomous devices that use sensors to cooperatively monitor physical or environmental conditions, such as temperature, humidity, sound, vibration, pressure, motion or pollutants at different locations. Those are used in gathering the information needed by smart environments, whether in buildings, utilities, industrial automation, shipboard, transportation systems automation, habitat monitoring, healthcare applications, home automation, and traffic control systems etc. Sometimes we want to change the locations of sensors time to time. In such applications, running wires or cabling is usually impractical or difficult. A sensor network is required that is fast and easy to install and maintain [1]. How a WSN differs from a typical wireless network is a WSN is distributed and the devices that form the sensor network communicate with each other collaboratively to achieve a common objective. AWSN has one or more base-stations which collect data from all sensor devices. These base stations are the interface through which the WSN interacts with the outside world.

A wireless sensor device is typically called a mote. A mote is a battery-operated device, capable of sensing physical quantities. In addition to sensing, it is capable of wireless communication, data storage, and a limited amount of computation and signal processing as well.

Some of the leading manufacturers of wireless sensor networks are Crossbow Technology, Inc and Digi International. Crossbow Technology Inc. is the leading end-to-end solutions supplier in wireless sensor networks and inertial sensor systems.

Project Objective

When air conditioning larger size office spaces which contains more than one AC machine it is difficult to maintain a constant temperature through out the building. Mostly places where the air conditioners are on operation are cooler than other places. And also it is less cool where the entrance doors are situated and on occasions where more people are getting together in small areas. As a solution for this problem we will built a wireless sensor network attached to the air conditioners by which the air conditioners will communicate with each other and maintain a constant temperature throughout the building.

Problem Areas

Power Consumption

In a wireless sensor system, each node has a short-range transmission due to low radio frequency (RF) transmit power. Short-range transmission minimizes the possibility of the transmitted signals being eavesdropped; also, it helps in prolonging the lifetime of the battery. In some sensor system applications, the nodes are hard to reach and it is impossible to replace their batteries. In other applications, the nodes must operate without battery replacement for a long time. Such conditions make the system power consumption a very crucial parameter [2].

Frequency

Selection of the operating frequency for wireless sensor systems must comply with government regulations and wireless standards. Currently, frequencies used for wireless sensor systems include 315 MHz, 433 MHz, 868 MHz (Europe), 915 MHz (North America), and the 2.45-GHz Industrial-Scientific-Medical (ISM) band. The 2.45-GHz band provides implementation flexibility due to the abundance of commercially available RF devices in that band.

Using lower frequencies would help in extending the communications range due to low path loss attenuation. If the density of deployment allows for few meters spacing between the nodes, the choice of lower frequencies would be a good choice [2]. In contrast, for future wireless sensor systems that require very small size nodes and very high density of deployment, the best suited operating frequency might be the millimeter wave bands (70 GHz or above). The advantage of these high frequencies include small size antennas, frequency reuse, and low power consumption. However, these very short-range wireless links may involve routing issues.

Security Considerations

A key requirement from both the technological and commercial point of view is to provide adequate security capabilities. Realising privacy and security requirements in an appropriate architecture for WSNs offering pervasive services is essential for user acceptance. Three key research areas for developing secure and reliable WSNs: “Security & Reliability”, “Routing & Transport” and “In-network Processing” [3].

The current wireless sensor networks suffer from one or more of the limitations below:

• Specific mission dependent- requires pre-determined locations of sensors and nodes.

• Low level programming and tasking tools

• Sensor and node level manual tasking – applicable to small scale systems only

• Nodes and sensors loss vulnerability to the loss

• Operation and inter-sensor cooperation must be defined in advance and is limited by the topology

• Not adaptable to dynamic changes in the operating environment

• Very limited capabilities for expansion and for large scale deployments

• Operation schemes are not capable to operate in a context triggered mode inter-sensor cooperation.

Why people go to WSN

Wireless sensor network applications have enormous potential benefit for scientific communities and society as a whole. There is a tremendous potential for Wireless sensor networks (WSN) to become the future most ubiquitous tool of the industry and society. The wide adoption of WSN technology depends on affordability, standardization, the development of generic building blocks and on the availability of user-friendly customization tools.

Limitation

Fundamental limitations of wireless sensor networks impose a barrier to implement it in critical mission applications as well as in harsh outdoors conditions and applications (such as the monitoring of natural resources and the environment). Presently WSN are designed and utilized for very specific applications with limited number of sensors and nodes, each of these systems is Unique and specially tailored to its application. There is no affordable and adjustable system, available today for a generic range of applications. Currently available WSNs have limited scalability, as each sensor and node should manually be programmed, located and managed. Large scale expansion in these systems would require tremendous effort in planning the deployment, in tasking and in managing.

Project implementation Plan

The following resources will be required for the implementation of this project,

Hardware

• XBEE series 2 OEM RF Modules.

• XBEE Development kit.

• Thermal Sensing Devices, Thermometers

• Air Conditioners, Their Remote Controller circuit.

• Multi-meters, Project Boards, Power supplies

Software

• nesC programming language

• TinyOS operating system

• TOSSIM wireless sensor network simulator

• IEEE 802.15.4 and Zigbee protocol stack

Other Resources

• Product Manual v1.x.1x – Zigbee protocol

• IEEE 802.15.4 Documentation

A wireless sensor network for communication among the Air Conditioners will be developed. This will be developed using the zigbee protocol stack.

Zigbee is a communication protocol that has been developed to use on low power digital radios based on the IEEE 802.15.4 standard for wireless personal area networks (WPANs). This protocol is simpler than other WPANs such as Bluetooth and it is focused at providing applications that require a low data rate, long battery life, and secure networking [5].

Zigbee Protocol stack,

There are three different types of Zigbee devices,

1. Zigbee Coordinator - This device starts and controls the network. The coordinator stores information about the network, which includes acting as the Trust Center and being the repository for security keys.

2. Zigbee Router - These devices extend network area coverage, dynamically route around obstacles, and provide backup routes in case of network congestion or device failure. They can connect to the coordinator, other routers and end devices.

3. Zigbee End Devices - These devices can transmit or receive a message, but cannot perform any routing operations. They must be connected to either the coordinator or a router but they cannot connect to other end devices. Deliverables

• Stand alone application for controlling the overall temperature of the Air Conditioners of the building.

• Motes which communicate with each other and can control a temperature of an Air Conditioner remotely.

References

[1] “Wireless sensor network”, Wikipedia, Wikimedia Foundation, Inc., 2008. http://en.wikipedia.org/wiki/Wireless_sensor_network

[2] Roshdy Hafez, Ibrahim Haroun, Ioannis Lambadaris, “Building Wireless Sensor Networks”, Microwaves & RF, Penton Media, Inc., 2005. http://www.mwrf.com/Articles/ArticleID/11071/11071.html

[3] Dirk Westhoff, Joao Girao, Amardeo Sarma, “Security Solutions for Wireless Sensor Networks”, NEC Technical Journal, NEC Corporation, 2006. http://www.nec.co.jp/techrep/en/journal/g06/n03/060322.html

[4] Anna Parnes, “Self Configurable Automatic learning Large-scale WSN and High level application tool”, 2007. http://www.kpk.gov.pl/7pr/pp/i.html?id=1048

[5] “Zigbee”, Wikipedia, Wikimedia Foundation, Inc., 2008. http://en.wikipedia.org/wiki/ZigBee