A Remote Monitoring and Control System for Cultural Heritage Buildings Utilizing Wireless Sensor Networks

Abstract: This dissertation presents the study of a wireless remote monitoring and control system utilized for cultural heritage preservation purpose. The system uses wireless sensor networks to remotely monitor and control the indoor climate, i.e., temperature and relative humidity of the cultural buildings.The system mainly consists of three parts, i.e., the wireless sensor network part, the gateway part and the web service part. Wireless sensor networks are deployed in different cultural buildings. The ZigBee protocol is utilized for the wireless sensor network communication. Sensor nodes report the indoor climate periodically. By connecting with radiators and/or dehumidifiers, the wireless control nodes can control the indoor climate according to the remote configuration. A gateway maintains the communication between a wireless sensor network and the web service. In monitoring function, the gateway forwards sensor messages from the wireless sensor network to the web service. In control function, the gateway synchronizes the climate settings from the web service to the wireless sensor network. The gateway also sends control commands to the wireless control nodes in the wireless sensor network. The web service provides a web-based user interface for the system.Different from ordinary cable-connected sensor networks, a wireless sensor network that works for cultural heritage preservation should be a system with a large number of sensor nodes covering a large area in a building, high reliability in message transmission, low power consumption and low cost. In this study, the performance of the ZigBee wireless network is improved to meet such requirements base on the investigation of the ZigBee protocol limitation. Firstly, a method for enhancing the wireless sensor network communication reliability is developed. The reactive routing protocol defined by the ZigBee standard is improved so that the wireless nodes automatically detect and repair network communication problems. This method minimizes the message lost within the wireless sensor network by always reserving a route from the source node to the destination node. Secondly, a generic low power working method is developed for sensor devices. This method defines the general sensor module behavior which includes sensor data collecting, sensor message forwardingand wireless network rejoining upon communication failure. It allows sensor devices to maintain high message reliability with low power consumption. Especially, these methods are developed as a complementary infrastructure of the ZigBee wireless sensor network in order to increase the transmission reliability with low power consumption. Finally, methods and algorithms are developed to make it possible to power the ZigBee message relays (i.e., routers) with small batteries. In this system, the whole ZigBee network is synchronized. Wireless communications within the ZigBee network are scheduled so that every wireless transmission is collision-free. During the period when no communication is scheduled, the router can go into low power mode. This design improvement removes the original requirement of using mains power for ZigBee message relays. A truly battery-driven and low power consumption wireless sensor network is developed for monitoring cultural heritage buildings without (or with limited) mains power.The remote control function is developed to mainly prevent biological degradation by controlling indoor climate, i.e., temperature and relative humidity. After studying the requirements for heritage preservation, a high flexibility, high reliability and low cost wireless indoor climate control system is developed. Different control algorithms are implemented to achieve different control results.Till today, the remote monitoring and control system presented in this dissertation has been installed in 31 cultural heritage buildings both in Sweden and Norway.