# The State-of-the-Art of Sensors and Environmental Monitoring Technologies in Buildings
## 2 Sensors and Monitoring Technologies  
Modern-day buildings can be highly adaptable to frequent changes in environmental conditions owing to a broad spectrum of semi-automated and manual systems consisting of various mechanical, electrical and electronic, thermal, and software sub-systems. Recent research studies have proposed the development and application of control algorithms [20], feedback mechanisms [21] and heating, ventilating and air conditioning (HVAC) systems [22] for building applications, and at the core of these systems and approaches are sensors and monitoring devices which feed information to control algorithms and models regarding various building parameters and its occupants. Most sensor devices available today can be used in conjunction with widely adopted controllers (e.g., PID (programmable-integrative-derivative), ON/OFF, and Fuzzy Logic controllers) and can generally be classified into two main types based on their operating principles, i.e., mechanical and electronic. Mechanical sensors are typically employed for direct control/visualization purposes and tend to be low cost, whereas electronic sensors have the added capability to convert a detected parameter into a digital value that can be used for monitoring and control, and generally tend to be more robust and scalable. In terms of communication and storage, most sensors available today can be classified into three main types, i.e., wired, wireless and portable, and in terms of applications, they are typically acquired for direct visualization, and in Building Management Systems (BMS) and HVAC systems within buildings. The following sub-sections provide a more detailed insight into various essential sensing and monitoring technologies commercially available today for use in buildings (see Figure 2) with their key characteristics summarized in Tables 1 and 2. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter.** & **Sensor** & **Measurement Range** & **Accuracy** & **Response Time** & **Power Consumption** & **Applications/Technology** & **Cost** \\ \hline \multirow{8}{*}{Temperature} & Thermocouples & \(-\)100-500 °C & \(\pm\)1-4 °C & 5-80 s & Low-High (0.5 u/A-30 mA) & BMS, HVAC/Wind, Verticle & 56-50 \\ \cline{2-8}  & RTDs & \(-\)50-250 °C & \(\pm\)0.2–1 °C & 1-8 min & High during measurement (1-5-100 mA) & BMS, HVAC and Visualisation/Wind, Wireless & 830-100 \\ \cline{2-8}  & Thermistors & \(-\)50-130 °C & \(\pm\)0.05-05 °C & 0-210 s & High during measurement (1-80 mA) & BMS, HVAC and Visualisation/Wind, Wireless & 820-70 \\ \cline{2-8}  & IC sensors & \(-\)40-150 °C & \(\pm\)0.5–1 °C & 0.5-100 s & Low (0.5-100 mA) & BMS, HVAC and Visualisation/Wind, Wireless & 81-15 \\ \hline \multirow{8}{*}{Carbon emissions} & NDIR (CO\({}_{2}\)) & 0-10,000 ppm & \(\pm\)30-200 ppm & 30-100 s & Low-High (20-200 mA) & Airflow Control, Monitoring/Wind, Wireless & 5100-600 \\ \cline{2-8}  & MOSFET (CO and VOC) & 400-20,000 ppm & \(\pm\)30-100 ppm & 50-60 s & High (by. -50 mA) & Airflow Control, Monitoring/Wind, Wireless & 525-250 \\ \cline{2-8}  & Electrochrom. (CO and VOC) & 0-1000 ppm & \(\pm\)0-30 ppm & 10-60 s & Low (00 u/A-10 mA) & Airflow Control, Monitoring/Wind, Wireless & 5100-650 \\ \hline \multirow{8}{*}{Humidity} & Capacitive sensors & 0\%–100\% RH & \(\pm\)0.0\%–5\% & 15-90 s & Low (2 u/A– mA) & RMS, HVAC and Visualisation/Wind, Wireless & 840-200 \\ \cline{2-8}  & Reistive sensors & 5\%–900\% RH & \(\pm\)15\%–10\% & 10-60 s & Low (0.5-5 mA) & BMS, HVAC and Visualisation/Wind, Wireless & 825-170 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the key characteristics of temperature, carbon emission, and humidity sensors used in buildings. Data has been deduced or calculated from published literature, and various manufacturer datasheets and user manuals available online at the time of publication.