Predictive Maintenance of HVAC Systems using Machine Learning Nitin Goyala*, Naman Guptab*, Palak Bhatnagarc, Poorva Jaind, Priya Raie, Mukul Malikf nitin.goyal@imsec.ac.in, Computer Science and Engineering, IMS Engineering College, Ghaziabad, Uttar Pradesh, India 153namangupta@gmail.com, Computer Science and Engineering, IMS Engineering College, Ghaziabad, Uttar Pradesh, India c A2019CSE6548@student.imsec.ac.in, Computer Science and Engineering, IMS Engineering College, Ghaziabad, Uttar Pradesh, India d A2019CSE6671@student.imsec.ac.in, Computer Science and Engineering, IMS Engineering College, Ghaziabad, Uttar Pradesh, India e A2019CSE6675@student.imsec.ac.in, Computer Science and Engineering, IMS Engineering College, Ghaziabad, Uttar Pradesh, India f A2019CSE6785@student.imsec.ac.in, Computer Science and Engineering, IMS Engineering College, Ghaziabad, Uttar Pradesh, India a b Abstract: Industry has decreased losses mostly due to motor failure and considerably improved system dependability by continuously monitoring the status of electric motors and other equipment used in HVAC systems. Predictive maintenance is the process of predicting the actual faults that may occur and preventing them to avoid system failure or component loss. Predictive maintenance, combined with intelligent sensors, artificial intelligence, and machine learning algorithms, makes the automated industries work more efficiently. Industry 4.0 is the new trend throughout the internet, which can be seen in newspapers, technical articles, or company websites. Predictive maintenance is the key concept for Industry 4.0, which helps the industry manage their machines more efficiently and effectively with the help of intelligent sensors put together with the machines in the industry. Although many advancements have been proposed till now in the process of predictive maintenance, it is also important for the process to be cost-efficient and efficient for small-scale industries too, with which they can also evolve themselves with the concept of Industry 4.0. We studied the publications that were published in the recent 20 years using a systematic review of the literature (SLR). In the predictive maintenance process, the application is composed of many IoT devices, such as Node-MCUs and RS-485 sensors, which are all connected to the HVAC systems and will collect data on a regular basis and push it over the databases with which it is integrated. The data thus obtained is first filtered for further processing. With this filtered data, the analysis is performed, and finally, the user is prompted if the system needs maintenance to avoid a complete failure. As of now, we are working on two fields, i.e., temperature and energy consumption, but in the future, we can extend it to detect more failures in HVAC systems, such as gas leakage, etc. 1. Introduction It is no secret that HVAC systems [1] can be expensive to operate and maintain. Maintenance is a very crucial aspect in the industry to take care of, with its effect on cost and reliability being significant. In fact, National Institute of Standards and Technology (NIST) [2] claims, HVAC systems are one of the single largest energy consumers in buildings, accounting for approximately 35% of total energy use in large commercial buildings and about 55% of total energy consumed in residential buildings. This is especially problematic for large multi-facility organizations that have expansive heating and cooling systems to manage across their portfolio. For many of these organizations, improving the efficiency of their HVAC systems has been a top priority for several years now, as anything they can do to reduce their energy consumption and operational costs will have a major impact on their bottom line [3]. Predictive maintenance solutions are one method of doing this. An asset's system's key performance indicators are monitored and analyzed using predictive maintenance [4], a technology that employs artificial intelligence and machine learning to spot possible issues before they arise and result in expensive operational interruptions. The term "predictive" [5] refers to the capability to predict when a critical fault might occur so that the problem can be addressed before it causes serious damage to the asset or disrupts business operations. When implemented properly, it can help reduce equipment downtime by as much as 70% and increase operating efficiency by up to 10%, leading to significant cost savings for your organization [6]. There are several benefits to implementing predictive maintenance in your facility. These include: Reduced Equipment Downtime [7] because predictive maintenance systems are capable of detecting potential faults before they cause a problem, they can help minimize the impact of an unplanned outage and help the consumer get the most out of the product through proper maintenance. The amount of downtime needed for maintenance is decreased with the use of a well-defined predictive maintenance algorithm. The predictive maintenance research in the current study [8] is concentrated on internal components, such as gas leakage and motor rotation analysis. Data is collected by sensors, and after additional processing, it becomes a filtered dataset. With supervised learning algorithms [9] applied to this dataset, an alert is generated if it is needed. Although advancements to the process are continuously being made with more efficient algorithms and more advanced sensors, Intelligent sensors [10] came into existence in the process in the last 10 years, and with them, the process becomes more effective as compared to traditional ones. Intelligent sensors aid in the storage of everlasting data generated by sensors connected to devices. Furthermore, the current studies [8] focus more on the working of internal components such as gas leakage, motor rotation, capacitor faults, etc. The majority of previous research has concentrated on the traditional method of predicting failure in internal components. Some progress has been made in recent years, with increased efficiency but less cost-effective models. The models proposed [11] must be cost-effective to support small-scale industries and allow solo entrepreneurs to scale their businesses with lower maintenance costs. Predictive maintenance is the main pillar of Industry 4.0 [12]; it allows industries or factories to run more efficiently while limiting the costs associated with faulty machines. Effective maintenance techniques may cut down on building upkeep expenses and potentially prolong the life of building parts. In order to avoid replacing equipment before it has reached the end of its useful life, it is essential to create a maintenance plan when a machine or piece of equipment begins to exhibit warning signs of potential failure in the future [13]. This is significant because, throughout the course of the system's lifespan, maintenance expenses might account for up to 75% of all maintenance expenses worldwide. Performance monitoring, which passively assesses the system and notifies the user (technician, application engineer, facility manager) about potential concerns, is a crucial step toward better HVAC control (hardware defects, poor control, etc.). Some of problems include using the wrong amount of outside air, which causes unnecessary mechanical Electronic copy available at: https://ssrn.com/abstract=4366923 cooling, oscillating control signals [14] caused by improper PI constants, a permanent setpoint offset, and more. There are currently a number of HVAC monitoring dashboards on the market, but they are often just used In [18] Trivedi et.al. presents a study on air-conditioning systems are widely used appliances in industries and homes worldwide. Productivity is also increased with the comfort provided by air conditioning systems in industrial and commercial settings. Using distributed sensing and supervised machine learning, a model for predictive AC maintenance is put out in this research. In order to identify the location and defect in the ACs, it uses a decision tree method and SVM. In [19], Dalzochio et.al. presents a study on the advances in the predictive failures of Industry 4.0. The major objective of this study is to analyze the logic behind predictive maintenance in the context of Industry 4.0. Predictive maintenance is a new, hot issue, however there are difficulties in the field of machine learning. The review's main objective was to find frameworks that implement ontology-based or ML-based reasoning. for simple trends. Boilers are one piece of equipment that has an on-board diagnostics and monitoring system. The remaining of the paper has been organized as follows depicted in Figure 1: Section II of this paper illustrates the literature survey on predictive maintenance on HVAC systems proposed in the last 20 years of research papers. A literature review [15] is being presented to have a clear understanding of the current literature on predictive maintenance. In Section III, the different algorithms used so far in predictive maintenance are described, along with their features, advantages, and disadvantages. Section IV explains the conclusion and future scope of the research work conducted. Figure 1: Organization of the paper 2. Literature Survey The initial approaches discuss fault detection in the motors or other internal components of HVAC systems. The major problems they focus on are gas leakage and motor rotation. The methodologies, which first launched the residual generation and analysis approach, employ diagnosis algorithms for HVAC systems. A comprehensive difference between all the paper is being depicted in Table 1. In [16] Sakali et.al. presents a study on the building sector, or corporate sector, is found to be the largest energy consumers and greenhouse gas emitters, ranging from 30% to 40% of the total energy consumption. The majority of predictive models are used in HVAC systems with sensors for preventive maintenance. Different types of use cases need to be handled with different algorithms, such as rule-based models, fuzzy logic models, case-based models, ANN, SVM, PCA, KNN, and some supervised learning algorithms. Predictive maintenance has become more efficient as a result of IoT and artificial intelligence. It is observed here that the DBN is less considered in predictive maintenance, and SVM and ANN are the most widely used techniques in the process. In [17] Paolanti et.al. presents study on the cutting machine and tries to find a new predictive maintenance technique that gives more accurate results. Its contributions mainly focus on the area of cloud architecture in Industry 4.0 and the machine learning approach to the real datasets from the machines working in the field. It enables the adoption of dynamic rules for maintenance management, which may be accomplished by training the Random Forest technique. In [20] Marik et.al. presents a study on energy efficiency can be increased with the help of intelligent control on HVAC equipment. MPC is a strong, industry-proven technology for improved control of complex systems, but for the time being, its use in buildings seems to be a long way off. Low-cost sensing devices or equipment have already made significant progress in the field of predictive maintenance with traditional push. The goal in this field is to create non-intrusive, inexpensive sensors that are simple to instal and can wirelessly connect with building management systems. With these many advancements, further processing can be done that generally requires real-time data that is not present. In [21] Singh et.al. presents a study on induction motors consume the majority of energy in industries. Induction motors consume a lot of energy, hence many efforts have been made to decrease their energy consumption by improving the motor's efficiency and lowering its fault ratio. The paper proposed a methodology that can be found effective for motor maintenance decision-making, which at first focuses on efficiency and then on the costeffective solution, if one can be derived. In [22] Pech et.al. presents a study on new technologies become available in modern smart factories, production automation can be linked to automated predictive maintenance. Intelligent sensors enable the storage of everlasting data processed by system-integrated sensors. The approach has the benefit that it may be employed in real-time, lowering the financial expenses associated with production failure or downtime. The outdated notion of software as a service is being replaced by the new idea of machine as a service. In [23] Ran et.al. presents a study on examination of the architecture, purposes, and approaches to predictive maintenance systems has been completed. Cost minimization, availability and reliability maximization, and multiple objectives are the main objectives for performing predictive performance, with the result that these can be achieved. Deep learning approaches are found to be more efficient and cost-saving in the case of predictive maintenance machines in Industry 4.0. In [24] Halm-Owoo et.al. presents a study on fault detection and diagnostic techniques in HVAC systems are the main issue, and this paper proposes a clear understanding of all the Fault Detection and Diagnostic (FDD) concepts. In the process of locating system flaws, a single system is inefficient. The model thus far proposed will not be accurate due to the less diverse dataset of the sensors applied to the RAC system. Electronic copy available at: https://ssrn.com/abstract=4366923 In [25] Osterrieder et.al. presents a study on industry 4.0 being the new emerging concept in all the newspapers, scientific journals, company websites, etc. The main constructs of it are smart factories that can be operated without the intervention of human beings by collecting, processing, transferring, and generating data. AI and ML are being used in Industry 4.0 to make factories smarter in their functions by applying more relevant models or algorithms. Table 1: Literature Survey Electronic copy available at: https://ssrn.com/abstract=4366923 NAME OF PAPER OBJECTIVE ALGORITHMS USED FOCUS ON CONCLUSIONS Review of predictive maintenance algorithms applied to HVAC systems. [16] To explain and draft difference between existing algorithms being used for Predictive Maintenance. ANN [27], SVM [28], KNN [29], CNN [30], RNN [31], fuzzy-logic based model [32], supervised model [33] Differentiation between the algorithms and to predict their accuracy. SVM, ANN are most widely used algorithms whereas DBN [39] is less considered. Machine Learning approach for Predictive Maintenance in Industry 4.0. [17] Testing conditioning monitoring with predictive maintenance on real-time machines in Industry 4.0. Decision Forest Machine Learning Algorithm [34] Motors used in different devices in Industry 4.0. Shows 95% accuracy in the preliminary results, observed thus far. Predictive Maintenance of Air Conditioning Systems Using Supervised Machine Learning. [18] Machine learning and reasoning for predictive maintenance in Industry 4.0: Current status and challenges. [19] Identifying gas leakage and capacitor malfunction in Air Conditioners. Decision Tree Machine Learning Algorithm [35] and SVM algorithms Gas Leakage and capacitors malfunction 93.5 accuracy had been identified with decision tree algorithm. Uses several models to boost efficiency as it looks at scholarly advancements in failure prediction. SLR methodologies [36] Importance of Predictive Maintenance in Industry 4.0 with AI and ML algorithms. Predictive maintenance's primary challenges with machine learning and reasoning are discussed and demonstrated. Advanced HVAC Control: Theory vs. Reality. [20] Aims to list the causes of poor HVAC and suggest potential solutions for more effective control methods. . Model Predictive Control (MPC) [37] To minimize the cost involved in predictive maintenance techniques. Smart Integration, interoperability, standardization has been developed to achieve the desired goals. Efficiency monitoring as a strategy for cost effective maintenance of induction motors for minimizing carbon emission and energy consumption. [21] Predictive Maintenance and Intelligent Sensors in Smart Factory: Review. [22] Industry 4.0 aims to lower the power consumption of motors. Supervised learning algorithms To minimize the energy consumption by faulty motors and C02 emission by the same. Combined the methodologies for motor maintenance with the cost-effective methods. Review the most recent research on intelligent sensors and predictive maintenance in smart industries. Comprehensive analysis of the literature on predictive maintenance with a focus on the goals, methods, and designs of the systems. Classification [38] Internal components of HVAC systems and sensors being used in the process. Methods for Smart and Intelligent Predictive Maintenance. Advanced Deep Learning Techniques. Focused on system architecture and its process to evolve a low-cost approach for the process. Concluded a comprehensive survey of system architecture used in predictive maintenance. Understanding of fundamental principles correlated with RAC systems.[26] ANN Applications used in RAC systems to reduce the faults. A general understanding of the state of currently operational commercial RAC systems. A Survey of Predictive Maintenance: Systems, Purposes and Approaches. [23] Applications of fault detection and diagnostic techniques for refrigeration and air conditioning: a review of basic principles. [24] AUTHOR 4 Electronic copy available at: https://ssrn.com/abstract=4366923 The smart factory as a key construct of industry 4.0: A systematic literature review. [25] Grouping of the selected publications into eight different viewpoints on the smart factory. Supervised learning algorithms Classification of literature with respect to eight different parameters. Clear understanding of previous literatures w.r.t the new trends in the Industry4.0. Figure 2: Predictive Maintenance Algorithms 3. Related Work A predictive maintenance software analyses data collected from the operating system using condition monitoring and prognostics algorithms. Data from a machine is used in condition monitoring to evaluate the machine's present state and to find and fix machine defects. Machine data is information gathered using specialised sensors, such as measures of temperature, pressure, voltage, noise, or vibration. The measurements, known as condition indicators, are derived from the data by a condition monitoring algorithm. Any aspect of system data with predictable behaviour changes as the system deteriorates is a condition indicator. Any number obtained from the data that groups system statuses with the same characteristics together and differentiates between them is a condition indicator. So, by comparing fresh data, a conditionmonitoring algorithm may carry out defect identification or diagnosis. A concise definition of the algorithms had been depicted in Table 2. 3.1.1. 3.1.2. Types of Knowledge based models These are mainly divided into three sub-categories as depicted in Figure 2, i.e., • Knowledge-based models [40] 3.1.2.1. Case-based model [43] • Models-based models [41] • Data-driven based models [42] A knowledge base and an inference engine are the two components of a knowledge-based system. Instead of being implicitly incorporated in procedural code, the knowledge base explicitly specifies the facts about the world. Other common approaches, rather than the subsumption ology, have frames, conceptual graphs, and logical assertions. New knowledge may be inferred thanks to the second component, also referred to as the inference engine. It can take the most typical form of IF-THEN rules using forward and backward chaining techniques. Other strategies employ logic programming, blackboard systems, and automated theorem provers. Case-based reasoning is used in the knowledge-based reasoning system. It involves the review of past knowledge of similar situations. And on the basis of what it finds, the knowledge-based system provides solutions that were effective in those given situations. 3.1.2.2. 3.1. Knowledge Based Models A computer software known as a knowledge-based system (KBS) employs a knowledge base to resolve extremely complicated issues. This phrase covers a wide range of system kinds and is quite general. The most common kind that unifies all knowledge-based systems is the endeavour to represent knowledge explicitly and a reasoning mechanism that will allow it to derive new knowledge for the system. Features Rule-based model [44] The rule-based systems depend on human-made, hard-coded rules. It uses these hard-coded rules to analyse and manipulate the data to achieve specific outputs. This may involve using IF-THEN rules that establish that if a user makes a certain request, then the system can deliver a certain outcome. 3.1.2.3. Fuzzy Logic based model [45] The Fuzzy logic-based model is a logical mathematical procedure which is totally based on IF-THEN rules system. It allows the human thought process to be produced in a mathematical form. It is a method of processing variables that enables the processing of several potential truth values through a single variable. Advantages: • Any choice can be accepted by the knowledge-based system as long as it is solely based on the manager's prior knowledge or expertise. • It makes it possible to quickly analyse a lot of data. • It always takes current data into account. • Previous experience is unimportant in this case. • Different persons might make the decisions without the outcome altering. • A knowledge-based model is extremely dependable. Electronic copy available at: https://ssrn.com/abstract=4366923 Disadvantages: • There is no pattern-specific result. • People are likely susceptible to the errors. • Previous experiences were not always positive. • The manager needs to devote a lot of time to data analysis. • It does not accept judgements that depart from the law. stakeholders understand the system. • Information coherence: The complexity challenge has existed since the beginning of Systems Engineering. It addresses the issue by enabling the system engineer to create a much more comprehensive vision of the system. This simple model allows for much greater consistency in information. 3.2. Model based Models Making unique models for each new application is possible with the model-based approach to machine learning as depicted in Figure 3. Although, it frequently does not, this model could occasionally match a conventional machine learning method. In order to specify the model, a model specification language is typically used, allowing for succinct code definition. This code allows for the automated generation of the program that will use that model. Disadvantages • Functionality: One of its major issues is usability; the approach requires more effort to use, and simple characteristics are complicated. If it is superior to existing systems engineering and project management approaches, it will be easy to navigate and use. • Static overtime: The model becomes static over time as it is built on a static framework. This can result in a lack of agility and an inability to respond to environmental changes. A model change will necessitate a rethinking of everything that has come before, which can be a timeconsuming and difficult process. • Effort to use: The approach necessitates more effort, and simple characteristics may be overly complex. This can lead to frustration and the impression that the strategy isn't working. The extra effort may also be ineffective, especially when traditional methods are adequate. 3.3. Data Driven Models Figure 3: Model Based Models Architecture 3.2.1. Features: • The capacity to build an extremely wide range of models, together with appropriate inference or learning algorithms, in which many conventional machine learning approaches emerge as special instances. • Separation between the model and the inference algorithm ensures that, in the event that the model is amended, the correspondingly adjusted inference method is automatically constructed. Advantages • Integration of time and effort: A model-based system is an interconnected system. When you make changes to a model, all of its dependents are automatically updated. In a DBMS [46], any change to a document necessitates editing the document and updating all related documents. • Interaction: The use of models as the primary mode of communication among team members improves understanding and allows for more detailed communication. Diagrams and pictures help all Data-driven models describe how a site's overall structure is described. Relationships and regulations that restrict how data can be stored and used are also incorporated into a database model. Models for data management and storage were developed decades ago. Data has always been essential to businesses and institutions. Data-driven models are becoming the focus of much more investment due to their limitless applicability. A data-driven model is built on an analysis of data regarding a particular system. The fundamental idea underlying datadriven models is to identify correlations between system state variables (input and output) without taking into account the system's physical phenomena. This model primarily shows how the logical structure of a database is modelled. It includes all the relationships and constraints that determine the data. Data is a fundamental part of all companies, and due to the infinite number of applications available. Data-driven models have become important for structuring. 3.3.1 Features: The generation, evaluation, and updating of data is continuous. Additionally, it is crucial to software engineers' job since it offers precise, useful feedback that enables them to determine where and how to make changes to a product or procedure. Data is an integral part of any digital transformation. The four pillars of data-driven models are: • Company Vision— Although technically not one of the pillars, it is a crucial component. Each pillar is influenced by the vision and is defined by it. • KPIs are used to track continuous business performance, which includes profitability and progress toward a goal. • OKRs: It measures what is happening now to achieve and improve the company's results. Strong OKRs result in improved KPIs. • Engineering metrics typically reveal what constitutes a good measure for software development or a great developer. Electronic copy available at: https://ssrn.com/abstract=4366923 • Good engineering metrics should lead to consensus on software engineering standards, a high standard for work quality, and the development of more and better features to support more value work. Table 2: Description of the Algorithms S. No. 1. Name of Algorithm Knowledge Based Model 2. Model Based Model 3. Data-driven Based Model Principle It is a computer software that employs established information to unravel complicated issues. It is a computer program that divides the complex problems to the small models. Models are described on the basis of previous old data stored. 3.3.2 Types of data driven models: The different types of data-driven models are: • Hierarchical Model: data is organized hierarchically. • Network Model—improvement to the hierarchical model for reducing data redundancy. • The Relational Model, which is the most common of all. • Object-Oriented Database Model—it defines a database as a collection of reusable objects associated with its features and methods. It also includes the multimedia and hypertext databases. Advantages • Knowledge about the underlying process is not required. • Applicable to problems that cannot be physically analysed. • A random source for datasets. Disadvantages • Ignore the physics of the underlying system. • Correlations are only valid within the range of the dataset. • Prediction accuracy is determined by the quality of the data. Advantages Accept any decision based on previous knowledge. Disadvantages No pattern specific result, Integration of time and effort, Information coherence. Static overtime, Complex to use. Random dataset. Accuracy is determined on the basis of quality of data. are used to implement deep learning, and the biological neuron—a.k.a. brain cell—serves as the inspiration for these networks. 4. Conclusion and Future Work As a result, using additional techniques to apply a hybrid multi-based model will produce complete findings. It might thus be advised, based on the results of the survey, to combine many ML or DL models in order to get better predictions than when using a single model. It is thus also suggested to mix classification and anomaly detection methods in order to preserve the accuracy of classification models without sacrificing the advantages of anomaly detection methodologies. A hybrid multi-based model will therefore yield comprehensive results when used with additional methodologies. In order to obtain better forecasts than when using a single model, it may thus be suggested, depending on the survey's findings. The accuracy of classification models may be maintained without compromising the benefits of anomaly detection approaches by combining classification and anomaly detection algorithms, it is claimed. 3.4. Examples of Data Driven Models 3.4.1. Supervised Learning A model is created by the supervised learning algorithm using a collection of labelled data. Once the correctness of the model has been verified, you may utilise it in production with actual data. The desired result serves as the supervision, allowing you to modify the function based on the actual output it generates. 3.4.2. Unsupervised Learning Unsupervised learning analyses and groups unlabelled datasets using machine learning methods. The models themselves glean insights and patterns from the data. It is comparable to the learning that occurs in the brain when a person learns something new. Unsupervised learning aims to discover the underlying structure of a dataset, categorise the data based on similarities, and describe the dataset in a compact form. 3.4.3. Deep Learning In artificial intelligence, deep learning is a subset of machine learning. By using different types of data and using different learning strategies, deep learning differs from traditional machine learning. Neural networks REFERENCES [1] MarijaTrčka, Jan L.M.Hensen, Overview of HVAC system simulation, 2010. [2] Peter Mell, Timothy Grance, The Nist Definition of Cloud Computing, 2011. [3] Cristina Gimenez, Vicenta Sierra, Juan Rodon, Sustainable operations: Their impact on the triple bottom line, 2012. [4] Sule Selcuk, Predictive maintenance, its implementation and latest trends, 2017. [5] Waljee AK, Higgins PD, Singal AG. 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