Modeling Air Handling Units to Create a Diverse Fault Dataset for FDD Innovation: Lessons Learned and Recommendations

As energy management and information systems (e.g., automated fault detection and diagnostics [AFDD] tools) become more prevalent in the commercial building stock, it is important to determine the effectiveness of these technologies by benchmarking their performance. The authors have been working to develop the largest publicly available dataset of HVAC fault datasets for performance benchmarking applications, covering the most common HVAC systems and designs including chiller plants, rooftop packaged units, dual duct air handling unit and single duct air handling units. This study covers the development, modeling, and validation of a synthetic fault dataset for the air handling unit (AHU), one of the most common HVAC configurations found in the commercial building stock. Despite this being a common system, real-world time series data are scarce and usually do not span a wide range of weather conditions. Due to this limitation, two detailed AHU models, which included the single duct AHU and dual duct AHU developed in the Modelica language and HVACSIM+ were employed to carry out annual simulations of numerous common sensor faults, mechanical faults, and control sequence faults. The fault inclusive data were then validated by comparing fault effects on system performance to expected symptoms. We summarize the nature of each fault and their impacts under different weather and operation conditions. We report some lessons learnt during the efforts of validating the high volumes of the FDD data sets. Finally, we highlight considerations for FDD developers that may want to use this dataset to assess their algorithms’ performance and their improvement over time

Advanced Solver Development for Large-Scale Dynamic Building System Simulation

Efficiently, robustly and accurately solving large and sparse nonlinear algebraic and differential equation system for dynamic building simulation is becoming more and more essential due to increasing demands to simulate large-scale problems for multiple buildings coupled with various levels of strength either through the smart grid or other means, such as district heating/cooling and shared distributed energy resources. This study is interested in advancing solving techniques that either improve the quality and efficiency of a dynamic building simulation model generically or improve the performance of the underlying equation solver. Nowadays, many commonly used tools for dynamic building system simulation still employ direct Newton methods. These methods are not only lack of convergence for stiff problems or cold starts, but also fail to meet the increased memory requirements associated with large-scale problems or more specific issues that arise in problems where the nonlinear equations resulted from the discretization of an underlying engineering differential equation. Therefore, a Newton-Krylov method that satisfies the computational need for large-scale dynamic building system simulation is investigated. An ideal preconditioner and an automatic update scheme are employed to ensure fast and robust simulation by way of the Newton-Krylov method. In addition to the comparison study focuses on the numerical solution methods, a generic function smoothing technique for the rare occasion that discontinuous functions are encountered is also investigated. Four testbeds, namely, 4Z5B, 4Z1B, 12Z5B, and 40Z5B, are developed in an HVACSIM+ environment to evaluate the advancement techniques. All testbeds simulate the airflow and thermal behaviour of building zones (from four zones, 4Z, to forty zones, 40Z) that are served by air handling unit (AHU) and variable air volume (VAV) systems. 4Z5B and 4Z1B testbeds simulate the same building system with the same number of equations but with different equation groupings while 4Z5B. 12Z5B and 40Z5B testbeds have the same equation grouping but are corresponding to very different building system sizes (four, twelve, and forty zones, respectively) and therefore different numbers of equations to be solved. The following tasks are completed and summarized in this report: (1) Develop numerical testbeds to evaluate solution methods and techniques. (2) Investigate potential numerical issues in a typical dynamic building system simulation model and seek generic techniques to improve the quality of the model. (3) Examine the performance of a Newton-Krylov method on solving dynamic building system simulation equations. (4) Improve the performance of the Newton-Krylov method by developing and employing proper preconditioning techniques. (5) Investigate potential strategies to construct physics-based preconditioners. (6) Investigate the impact of finite difference step size in Jacobian approximation on the performance of dynamic building system simulation. The major numerical issue found in the testbeds mentioned above is the discontinuity of the simple coil component model. A generic smoothing technique is employed to improve the performance of the discontinuous simple coil component model, and the smoothed model results in a more stable and more accurate solution. A Newton-Krylov method is employed to increase the computational speed of a large-scale simulation. However, the direct implementation of the Newton-Krylov method results in stability issues. Therefore, a preconditioned Newton-Krylov method that employs the ideal preconditioner and an automatic update scheme is developed in this study, referred to as INB-PSGMRES(m). This method performs as robust as the default Powell's Hybrid (PH) method in HVACSIM+ while saving a significant amount of computational time. Its computational time saving against the PH method is at least 49.7%, 91.8%, 88.7%, and 97.1% for 4Z5B, 4Z1B, 12Z5B, and 40Z5B testbeds, respectively. It is found that because of the employment of preconditioning, two important parameters of the INB-PSGMRES(m) method, i.e., the forcing term and the restarting parameter, have little impact on the simulation performance. A few potential partitioning strategies for developing a physics-based preconditioner are investigated. Due to the strong coupling of mass flow rates and pressures between each nodal point of the airflow network system, it is difficult to construct an effective physics-based preconditioner for the airflow network of an AHU-VAV system. On the other hand, the thermal network can be effectively exploited. A preconditioner that targets the coil related equations is found effective at reducing the condition number of the Jacobian (which typically leads to fast linear convergence in a Krylov method) due to the high nonlinearity of the coil component model and its strong impact on the temperature and humidity in the HVAC system. Four finite difference step sizes for the Jacobian approximation and four finite difference step sizes for the Jacobian-vector approximation are investigated. For the Jacobian approximation, the current finite difference step size employed by HVACSIM+ is effective for the operating period. Its performance can be improved for the nonoperating period by adding a lower bound to the finite difference step size.Ph.D., Architectural Engineering -- Drexel University, 201

The Sensor Roller: A Piezoelectric Energy Harvesting Roller in a Bearing for Self-Sustained IoT Sensors

With the high-speed development of the Internet of Things (IoT), powering such a massive number of wireless IoT sensors with chemical batteries become more and more unpractical. To make the IoT sensors self-sustained, Piezoelectric Energy Harvesting (PEH) technology provides an excellent solution to power the devices with a relatively long service time. By harvesting the ambient mechanical vibrations, PEH could generate a stable power source without wind or light.Currently, the famous bearing manufacturer, SKF, collaborates with TU Delft to design a self-sustained smart IoT roller with PEH technology, which will be implanted in huge bearings, such as the bearing in the wind turbines. This thesis project is a feasibility study investigating the possibility of replacing the chemical battery with the Piezoelectric Energy Harvester in SKF's smart IoT roller, called Sensor Roller. The objective of this project includes the system design of two generations of the prototype harvester. The first prototype concentrates on the properties of the piezoelectric material, while the second prototype focuses on the structure of the harvester. The design work consists of the raw data analysis of the target roller from SKF and the prototype construction and simulation in COMSOL Multiphysics. Besides, to make the results more reliable, two stages of the test with the practical components are made to study the harvester's performance under the actual working condition of the roller in the bearing. As a result, a tube shape Piezoelectric Energy Harvester with suitable materials and parameters is built. According to the simulation results, under a safe pressure level of the piezoelectric material, the proposed harvester achieves 8.1mW output power, which is enough for the loading sensors. The designed Piezoelectric Energy Harvester is being manufactured at present, and it is planned to be installed in the target roller to get the system-level test in the future.In addition to the harvester, some rectifiers are designed and taped out to improve the performance of the proposed Piezoelectric Energy Harvesting system. Three rectifiers are made with the Silicon Carbide (SiC) process to obtain a high voltage and temperature tolerance: a Full Bridge Rectifier (FBR), a Passive Rectifier, and a Synchronized Switch Harvesting on Inductor (SSHI) rectifier. Meanwhile, another SSHI rectifier is made with the 0.18um Silicon BCD process that focuses on solving the cold-startup problem. Consequently, simulated with the real transducer of the proposed harvester, both the FBR circuit and the Passive Rectifier circuit with the SiC process achieve over 10mW output power, and the SiC SSHI circuit achieves 37.1mW output power. As for the cold-startup SSHI rectifier circuit, it successfully reduces the required open circuit voltage by 4x to start up the SSHI system from the cold state.The results of this project show the great potential for applying the Piezoelectric Energy Harvesting technology to power the IoT sensors in the roller of bearing. Although some future works should be finished to build the commercial version of the energy harvesting roller, we are convinced that the fully self-sustained Sensor Roller with Piezoelectric Energy Harvesting technology will possibly show up in the near future.Electrical Enginee

A Highly Efficient Fully Integrated Active Rectifier for Ultrasonic Wireless Power Transfer

Ultrasonic wireless power transfer (WPT) has been proved to be a promising approach to power biomedical implants. To extract the energy generated from the transducer, a rectifier is typically required. Previous inductor-based rectifiers (SSHI and SECE) require a large off-chip inductor to achieve good performance, which is not desired for miniaturization and safety reasons. Synchronized switch harvesting on capacitors (SSHC) rectifiers have been proved to achieve high performance without inductors; however, they are mainly designed for low-frequency kinetic energy harvesting. In this paper, an improved SSHC rectifier is designed to achieve a fully integrated design with all flying capacitors implemented on-chip. The proposed SSHC rectifier can properly operate at ultrasonic excitation frequency (100 KHz) with precise switching time control and ultrafast voltage flipping techniques. In addition, an on-chip ultralow-power LDO allows the system to be self-sustained. The system is designed in a TSMC 180nm BCD technology and post-layout simulation results are presented.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Instrumentatio

Process parameter analysis of ultrasonic vibration-assisted polishing of SiCp/Al ceramics based on optimized Hilbert trajectories

As an important ceramic matrix composite material, SiCp/Al ceramics have found extensive applications across several domains. However, the intricate nature of their material properties has resulted in a scarcity of scholarly investigations pertaining to the topic of ultrasonic vibration-assisted polishing (UVAP) of SiCp/Al ceramics. To solve this problem, a theoretical derivation of the material removal model (MRM) for UVAP SiCp/Al ceramics is presented in this paper. The selection of UVAP feeding speed is analyzed and discussed. The process parameters of UVAP of SiCp/Al ceramics are optimized based on the improved Hilbert's trajectory characteristics. According to the experimental results, high-quality machined surfaces can be obtained and the “fish scale” phenomenon can be avoided when the feeding speed is 0.015 m/s. Compared with the traditional trajectory, the improved Hilbert trajectory is easier to achieve uniform surface polishing. The introduction of ultrasonic amplitude (UA) can increase the material removal rate (MRR) by more than 21.6 % compared with the conventional polishing method. The maximum removal depth (MRD) increased by more than 27.76 % and the surface roughness (SR) is reduced by more than 76.45 %. The research results have an important application value for realizing efficient and high-quality polishing of SiCp/Al ceramics

A labeled dataset for building HVAC systems operating in faulted and fault-free states

Abstract Open data is fueling innovation across many fields. In the domain of building science, datasets that can be used to inform the development of operational applications - for example new control algorithms and performance analysis methods - are extremely difficult to come by. This article summarizes the development and content of the largest known public dataset of building system operations in faulted and fault free states. It covers the most common HVAC systems and configurations in commercial buildings, across a range of climates, fault types, and fault severities. The time series points that are contained in the dataset include measurements that are commonly encountered in existing buildings as well as some that are less typical. Simulation tools, experimental test facilities, and in-situ field operation were used to generate the data. To inform more data-hungry algorithms, most of the simulated data cover a year of operation for each fault-severity combination. The data set is a significant expansion of that first published by the lead authors in 2020

A labeled dataset for building HVAC systems operating in faulted and fault-free states.

Open data is fueling innovation across many fields. In the domain of building science, datasets that can be used to inform the development of operational applications - for example new control algorithms and performance analysis methods - are extremely difficult to come by. This article summarizes the development and content of the largest known public dataset of building system operations in faulted and fault free states. It covers the most common HVAC systems and configurations in commercial buildings, across a range of climates, fault types, and fault severities. The time series points that are contained in the dataset include measurements that are commonly encountered in existing buildings as well as some that are less typical. Simulation tools, experimental test facilities, and in-situ field operation were used to generate the data. To inform more data-hungry algorithms, most of the simulated data cover a year of operation for each fault-severity combination. The data set is a significant expansion of that first published by the lead authors in 2020

A Reconfigurable Cold-Startup SSHI Rectifier with 4X Lower Input Amplitude Requirement for Piezoelectric Energy Harvesting

Synchronized switch harvesting on inductor (SSHI) is an efficient active rectifier to extract energy generated from piezoelectric transducer in piezoelectric energy harvesting system. Unlike passive rectifiers, SSHI rectifiers require a power supply to drive synchronized switches. Unfortunately, there is no stable supply when the system starts from the cold state. Most designs let the system work as a passive full bridge rectifier (FBR) to charge power capacitor until a supply is available. However, a FBR requires high open-circuit voltage (VOC) and the FBR’s output voltage cannot go over VOC. This prevents the system from starting the SSHI rectifier if VOC is low. This paper proposes a new transducer reconfiguration design to lower the required VOC by 4 $\times$ to start up the SSHI system from the cold state. The proposed system is designed in a 0.18$-\mu$m BCD process and post-layout simulations show that the successful cold-startup under low VOC voltage.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Instrumentatio