Generic wireless sensor network for dynamic monitoring of a new generation of building material

Abstract

Existing testing methods for building materials before deployment include a series of procedures as stipulated in British Standards, and most tests are performed in a controlled laboratory environment. Types of equipment used for measurements, data logging, and visualisation are commonly bulky, hard-wired, and consume a significant amount of power. Most of the off-the-shelf sensing nodes have been designed for a few specific applications and cannot be used for general purpose applications. This makes it difficult to modify or extend the sensing features when needed. This thesis takes the initiative of designing and implementing a low-powered, open-source, flexible, and small-sized Generic wireless sensor network (GWSN) that can continuously monitor the building materials and building environment, to address the limitations of the conventional measurement methods and the technological gap. The designed system is comprised of two custom-made sensor nodes and a gateway, as well as purpose designed firmware for data collection and processing. For the proof of concept and experimental studies, several measurement strategies were designed, to demonstrate, evaluate, and validate the effectiveness of the system. The data was collected from selected case study areas in the School of Energy, Geoscience, Infrastructure and Society (EGIS) laboratories by measuring and monitoring building structures and indoor environment quality parameters using the designed GWSN. The measured data includes heat flux through the material, surface and air temperatures on both sides of the material/structure, moisture variation, ambient temperature, relative humidity, carbon dioxide, volatile organic compounds, particulate matter, and sound/acoustic levels. The initial results show the potential of the designed system to become the new benchmark for tracking the variation of building materials with the environment and investigating the impact of variation of building materials on indoor environment quality. Based on the estimates of the thermal performance data, the sample used in the experiment had a typical U-value between 4.8 and 5.8 W/m2K and a thermal resistance value of 0.025m2 ·K/W[1][2]. Thermal resistance values from the GWSN real-time measurement were between 0.025 and 0.03 m2K/W, with an average of 0.025 m2K/W, and thermal transmission values varied between 4.55 and 5.11 W/m2K. Based on the data obtained, the results are within the range of typical values[3]. For thermal comfort measurements, the results of humidity and temperature from GWSN were compared to values in the Kambic climatic chamber in the EGIS laboratory, and the accuracies were 99 % and 98 % respectively. For the IAQ measurements, the values of CO2 and TVOCs were compared to the commercial off-the-shelf measuring system, and the accuracies were 98 %, and 97 %. Finally, the GWSN was tested for acoustic measurements in the range of 55 dB to 106 dB. The results were compared to class one Bruel & Kjaer SLM. The accuracy of GWSN was 97 %. The GWSN can be used for in lab and in-situ applications, to measure and analyse the thermal physical properties of building materials/building structures (thermal transmittance, thermal conductivity, and thermal resistance). The system can also measure indoor air quality, thermal comfort, and airborne sound insulation of the building envelope. The key point here is to establish a direct link between how building materials vary with the environment and how this impacts indoor environment quality. Such a link is essential for long-term analysis of building materials, which cannot be achieved using current methods. Regarding increasing the power efficient of the implemented GWSN as well as its performance and functionality, a new sensing platforms using backscatter technology have been introduced. The theory of modulation and spread spectrum technique used in backscattering has been explored. The trade-off between hardware complexity/power consumption and link performance has been investigated. Theoretical analysis and simulation validation of the new sensing technique, using backscatter communication, has been performed. A novel multicarrier backscatter tag compatible with Wireless Fidelity has been implemented and an IEEE 802.11g OFDM preamble was synthesized by simulation. The tag consists of only two transistors with current consumption no larger than 0.2 μA at voltage of less than 0.6 V. Novel harmonic suppression approaches for frequency-shifted backscatter communication has been proposed and demonstrated. The proposed approaches independently manipulate mirror harmonics and higher order harmonics whereby; specified higher order harmonics can be removed by carefully designing the real-valued (continuous and discrete) reflection coefficients-based backscatter tags. When successfully implemented, the backscatter system will reduce sensor node power consumption by shifting the power-consuming radio frequency carrier synthesis functions to carrier emitters.