The optimal functioning of elevators is ubiquitous for a habitable and comfortable indoor environment in multi-story buildings. Presently, numerous issues are encountered, such as frequent and prolonged breakdowns, passenger entrapment, injuries, accidents, extended waiting times, unlevelled stopping, and high energy consumption. Thus, strategies to enhance their performance are imperative. Generally, elevators are subjected to preventive maintenance in which only visual inspection determines their overall performance. This methodology ignores the underlying conditions and is marred with the subjective opinions of inspectors. Another issue affecting their performance is that many elevators around the globe have surpassed their useful life. These elevators consume a significant amount of energy since they incorporate conventional motor drives instead of the energy-efficient AC drives with variable voltage variable frequency (ACVVVF). However, for the replacement of non-ACVVVF drives, the building owners need estimated quantitative potential savings. The reliability of elevators beyond their useful life is also a big concern. For the improvement of reliability, full-modernization is a promising option. Nevertheless, complete replacement is not feasible in many cases due to economic and environmental constraints, thus requiring alternate strategies. Moreover, the procurement of elevator maintenance services lacks any guidelines, e.g., a set of rules to select an appropriate maintenance contractor does not exist. Ineffective procurement is also a threat to the performance of elevators. Besides, there is no evidence that the contractors accurately perceive the relative significance of building owners’ expectations/duties during procurement. This ambiguity is alarming since a lack of a clear understanding of contractors leads to dissatisfaction of building owners, which may take a toll on their real-time performance. Therefore, to address the issues, this thesis aims to: 1. Improvement of performance assessment during preventive maintenance. 2. Improvement of reliability and energy consumption of elevators which have surpassed their useful life. 3. Identification of the gaps in procurement and suggesting relevant enhancements. To propose a performance measurement model, firstly, a conceptual hybrid performance measurement model of elevators (HPMME) was proposed. The model consisted of three latent constructs involving three key performance indicators (KPIs) (condition of equipment, level of service, and risks) and 34 observed variables based on a comprehensive literature review and three rounds of brainstorming sessions with elevator experts. A questionnaire survey was carried out to evaluate the relative importance of the three KPIs and their observed variables. The survey data’s exploratory factor analysis was then conducted to identify the latent constructs representing the KPIs and their associated observed variables. For the validation, modification, and improvement of the conceptual HPMME, structural equation modelling was performed. Finally, the HPMME was further validated by experts. Secondly, to promote the replacement of non-ACVVVF drives, an explicit data-driven multiple linear regression model for predicting the annual energy consumption of elevators based on the type of their motor drive was proposed. The motor drives considered in the model included: ACVVVF, AC 2 speed motor drive, DC motor drive with the solid-state controller, and AC motor drive with a variable speed controller. This model consists of the elevator and building parameters of average rated capacity, motor rating, number of elevators, domestic units in the building, and motor drive type. The model was formulated after analyzing the historical elevator energy consumption data of 196 residential buildings in Hong Kong and validated using statistical measures and through its application to 25 additional residential buildings. Third, for improving elevators’ reliability beyond their useful life, 25,548 breakdowns attributed to 5400 elevators in public rental housing (PRH) buildings in Hong Kong were analyzed. The Pareto analysis revealed four main risks causing elevator breakdowns: faults in the controller, car door mechanism, landing door mechanism, and other equipment in the car cage. A comparison of the monthly breakdown rate of these four components in elevators belonging to different age groups (especially those within and beyond their useful life) by employing ANOVA indicated that the faults in the controller are the trigger of the onset of a wear-out phase and its risk-based maintenance would improve the reliability and useful life of elevators in PRH buildings. Fourth, for improving the selection process, the prevailing best value (BV) criteria were determined. The content analysis of “Request for Proposals (RFPs)” of 57 projects indicated 9 BV criteria: experience, past performance, responsiveness to RFP, maintenance strategies, financial capability, diversity, contractor resources, and legal status. Appropriate modifications to criteria and associated indicators were suggested in the light of literature and KPIs, such as, assign greater significance to past performance and the qualifications. Furthermore, utilize references and previous records to predict safety performance, compliance with regulations, and service availability. Also, analyze the maintenance methodology to substantiate safety performance and compliance with regulations. Moreover, ask the contractor to validate their arrangements of adequate spare parts availability. Fifth, this research identified the expectations of building owners. The content analysis of RFPs revealed 40 duties, which expressed four main expectations of building owners: prompt response to call-backs, optimal equipment performance, proper execution of assigned duties and responsibilities, and attaining the performance requirements with specified thresholds. A questionnaire survey was conducted to evaluate the perceptions of contractors. Exploratory factor analysis and Structural Equation Modelling of survey data revealed that except for the callbacks, the building owners’ remaining three expectations were perceived significant by the contractors. Furthermore, the contractors do not consider the condition of controller and guide shoes, provision of adequate resources, quality of replacement parts, rigorous testing of equipment as an essential indicator of their performance, which was emphasized strongly by the building owners in the RFPs. Each of the five parts mentioned above has its associated benefits. The hybrid performance measurement model can act as a tool to quantitatively measure elevators’ performance, which would enable the relevant authorities in important decisions that include but are not limited to the prioritization of elevators for the modernization and the allocation of the workforce and other resources. Also, maintenance contractors can identify the critical areas of performance improvement, leading to end-user satisfaction. Using the explicit energy prediction model, the building owners could carry a cost-benefit analysis associated with replacing non-ACVVVF drives with ACVVVF. In lines with this research’s findings, an increase in maintenance of controller would optimize the reliability of elevators beyond their useful life and bring it at par with those within their useful life. Hence, the building owners facing financial or environmental constraints in replacing elevators beyond their useful life could sustain their use for an extended duration. In the future, building owners could formulate their future selection criteria in the light of this research leading to informed and intelligent decision making. Moreover, the duties assigned by building owners not perceived significant by the contractors could be given a higher preference in RFPs by associating a reward/penalty with them.
| Date of Award | 2021 |
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| Original language | English |
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| Awarding Institution | - The Hong Kong University of Science and Technology
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| Supervisor | Xueqing ZHANG (Supervisor) |
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