http://dspace.cityu.edu.hk:80/handle/2031/5667 2013-05-01T20:40:11Z 2013-05-01T20:40:11Z Kwok, Sai Kwong (郭世剛) http://dspace.cityu.edu.hk:80/handle/2031/6175 2011-05-25T01:16:28Z 2010-01-01T00:00:00Z

Title: An intelligent approach to access building occupancy for cooling load prediction Authors: Kwok, Sai Kwong (郭世剛) Abstract: Building cooling load prediction is one of the key factors in the success of energy-saving measures. Many computational models available in the industry today have been developed from either forward or inverse modeling approaches. However, most of these models require extensive computer resources and involve lengthy computation. This thesis discusses the use of the multi-layer perceptron (MLP) model - an artificial neural network (ANN) model widely adopted in engineering applications that offers unique characteristics such as adaptability, nonlinearity, and arbitrary function mapping ability - to predict the cooling load of a building. Although it is common knowledge that the presence and activity of building occupants have a significant impact on the required cooling load of buildings, practices currently adopted in modeling the presence and activity of people in buildings do not reflect the complexity of the impact occupants have on building cooling load. In contrast to previous ANN models, most of which employ a fixed schedule or historic load data to represent building occupancy in simulating building cooling load, this thesis introduces a stochastic model of occupants’ presence and activity and uses it as one of the input parameters to mimic building cooling load. The training samples used include weather data obtained from the Hong Kong Observatory and building-related data acquired from two existing grade A mega office buildings in Hong Kong with tenants including many multinational financial companies that require 24-hour air conditioning seven days a week. The dynamic changes that occur in the occupancy of these buildings therefore make it very difficult to forecast building cooling load by means of a fixed time schedule. The paper also discusses the practical difficulties and limitations encountered in obtaining building-related data, particularly those faced in acquiring dynamic data. The performance of simulation results for the two mega office buildings examined demonstrate that building occupancy data play a critical role in building cooling load prediction and that their use significantly improves the predictive accuracy of cooling load models. Keywords: Artificial Neural Network, Cooling Load, Building Occupancy. Notes: CityU Call Number: TH7687.5 .K85 2010; xvii, 219, [32] leaves : ill. 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2010.; Includes bibliographical references (leaves 191-213)

2010-01-01T00:00:00Z Chan, Ka-Lung Raymond (陳家龍) http://dspace.cityu.edu.hk:80/handle/2031/6169 2011-05-25T01:16:15Z 2010-01-01T00:00:00Z

Title: An optimal and life cycle model for design, operation and maintenance of air-cooled chiller plants for commercial buildings Authors: Chan, Ka-Lung Raymond (陳家龍) Abstract: Chiller Plants in Hong Kong consumed over one-eighth of the energy consumption. Passive designed chiller plant with excess cooling capacity or redundant chiller(s) in small to medium-sized commercial buildings has always existed because of concern of reliability and the buildings aiming for basic operating criteria only. Since air-cooled chiller plants were widely used in commercial buildings in Hong Kong in past two decades, the situation of excess cooling capacity and opportunities of energy saving at chiller plant of small to medium sized commercial buildings are worth of studying. Four small to medium-sized commercial buildings in Hong Kong were selected and operating log sheets of the air-cooled chiller plants were collected. The cooling load profiles of the four buildings were developed and compared with design data. From the results, the phenomenon and level of excess cooling capacity of air-cooled chiller plant in small to medium-sized commercial buildings in Hong Kong was demonstrated. Once the situation of excess cooling capacity or redundant chiller(s) in small to medium sized commercial buildings was identified, some questions that came in mind were how to reduce the excess cooling capacity, increase the energy conservation and then maintain the reliability of the chiller plant at the same time. It involved some changes in design, operation and maintenance. There are a lot of correlations amongst the actions taken to support the changes for achieving the objectives. Therefore, an optimal and life cycle model for design, operation and maintenance (OLDOM) of air-cooled chiller plant for small to medium-sized commercial buildings in Hong Kong - for optimization of energy saving of the chiller plant in its entire life was developed. The existence of excess cooling capacity is not because of the wrong calculation; it is mainly due to provision of too much safety margin to maintain the reliability. In this research, making use of the physical characteristics of air-cooled screw chillers to size the chiller plant is introduced and discussed. It reduces the level of excess cooling capacity and maintain reasonable safety margin in sizing of chiller plant. The saving in capital investment of redundant chiller is used to adopt integrated design and install metering and monitoring devices for energy management in operation. Developers, electrical and mechanical consultants, operation and maintenance professionals, and commissioning authority have to participated and work together at the design stage in application of the OLDOM model. The communication and commitment amongst them to enhance the operation and maintenance is important and highlighted. Integrated design is discussed and recommended to increase the energy efficiency in air-cooled chiller plant, including buying efficient and reliable chillers at the very beginning, applying unequally sized chillers in series chiller plant configuration at low flow design with variable primary flow and chiller plant control at the system level. The additional costs spent in integrated design can be offset by savings in capital investment of redundant chiller(s). It enables developers and consultants to adopt the OLDOM model to their future development without a budget concern. The change in design concept enriches the requirements in operation and maintenance. The operators focus on maintaining the chiller plant in normal operation rather than effective and efficient operation is observed during the data collection. With the availability of appropriate metering and monitoring devices, and chiller plant control or building management system, the energy efficiency of chiller plant can be continuously optimized throughout its life time with assistance of experienced operators or Energy Manager. The life cycle cost savings are significant and important in energy conservation. The approach is more effective than the ad hoc and top down energy saving projects. It also enables the systems of the buildings to be reviewed and re-commissioned from time to time. To further support the reliability of the chiller plant without redundant chiller, a risk-based preventive maintenance strategy is applied. The specific risk level of each component of the air-cooled screw chillers is evaluated and developed by conducting a survey with the local industry. The developed risk levels are compared and high risk components are highlighted for better planning of the maintenance schedule or optimal inspection period. It will reduce the frequency and possibility of failure of air-cooled chillers for maintaining adequate cooling capacity of the chiller plant, at or above the defined threshold level, without regard to the time of cooling required. With the risk-based preventive maintenance, all maintenance and services will be well scheduled and the frequency of emergency shut down of the chillers will be minimized. In the long run, the repair cost will be lowered. This optimal and life cycle model for design, operation and maintenance (OLDOM) of air-cooled chiller plant would be an integrated and cost effective approach in comparison to the current discrete practices. Notes: CityU Call Number: TH7688.C64 C45 2010; xiv, 302 leaves : ill. (some col.) 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2010.; Includes bibliographical references (leaves 218-227)

2010-01-01T00:00:00Z Kwok, Chi Ko (郭志高) http://dspace.cityu.edu.hk:80/handle/2031/5805 2010-03-19T06:27:49Z 2009-01-01T00:00:00Z

Title: Study of important factors affecting final account settlement satisfaction of Hong Kong civil engineering projects : contractor's perspective Authors: Kwok, Chi Ko (郭志高) Abstract: Construction projects generally comprise four stages, namely, design/planning stage, tender stage, construction stage and final account / defect liability stage. The role and performance of various project participants and contracting parties in a construction project can in each stage influence the project success. Whilst many research studies addressed construction projects performance by examining critical factors to the project success or failure, most of them focused on construction stage with little attention to final account stage. In fact, the backlogs in settlement of Final Account have existed for decades and the important factors significantly affecting settlement of Final Account of construction projects are, among other things, largely founded as Project-related, Contractor-related and Engineer-related. These factors usually attract less attention and priority by project participants and contracting parties in the less pressing final account stage. Undue protracted inaction makes settlement of Final Account more difficult and frequently gives rise to dispute unnecessarily. This research adopts the technique of Multivariate Discriminant Analysis (MDA) to identify the most influential factors affecting the settlement of Final Account. The factors selected for use in the MDA modelling were determined by a pilot study involving face-to-face structured interviews with fellow practitioners who commented the variables identified from rigorous literature review and verified the sustainability of the questionnaire. Independent interviews were also conducted with construction professionals from senior management level of Group C civil engineering contractors, thus bringing into the research independent valuable views. The data were collected through questionnaire survey on civil engineering projects completed by Group C contractors in past ten years, where Final Account was settled or not yet settled. Final account settlement satisfaction is considered as favourable if that final account was achieved on time, i.e. within the prescribed time frame, otherwise it is considered as adverse if it was achieved beyond the prescribed time frame. The main objectives of this research are to identify, through in-depth investigation and exploration, important attributes that can clearly distinguish between on-time settlement and delayed settlement of final account projects, and to develop a quantitative model for prediction of the same. With the use of 108 project data sets and the MDA technique, a discriminant function was derived to classify final account projects into favourable final account settlement satisfaction (on-time settlement) and adverse final account settlement satisfaction (delayed settlement). The research problems as presented corresponded to the classification and prediction ability of MDA and as a result five (5) discriminating variables were identified out of thirteen (13) selected variables. These five discriminating variables are:  Contractor’s organizational approach  Contractor’s employment of consultant  Contractor’s resources allocated to the Final Account project  Engineer’s process of assessment /agreement  Engineer’s resources allocated to the Final Account project A Relative Important Index (RII) study was conducted to further verify and compare the importance of the above critical variables. The classification result of the hold out samples was same as the classification result performed by the discriminant function, which gave an accuracy of 100 % on the hold out samples. Notes: CityU Call Number: TH438 .K84 2009; xiv, 253 leaves 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2009.; Includes bibliographical references (leaves 189-202)

2009-01-01T00:00:00Z So, Yu Shing (蘇汝成) http://dspace.cityu.edu.hk:80/handle/2031/5803 2010-03-19T06:26:38Z 2009-01-01T00:00:00Z

Title: Scaffolding systems in Hong Kong : current practice and development of MBMSS Authors: So, Yu Shing (蘇汝成) Abstract: Scaffolding is widely used in the construction industry. Traditional bamboo scaffolding has a long history and metal scaffolding has been in use for nearly 100 years. To meet safety requirements, address the problems involved in high rise building construction and take advantage of modern building technology, a new design scaffolding system has been invented. The Metal Bamboo Matrix Scaffolding System (MBMSS) takes advantage of the merits of both bamboo and metal scaffolding. Drawing support from academic research, and in conjunction with a standardised operational process and management protocol, MBMSS has been developed into a flexible scaffolding system that fulfils the requirements of various scenarios in the construction industry. The system has been patented in Europe, Hong Kong and China, and has been used in construction projects since 1998. The live load of MBMSS is less than metal scaffolding, and the new system has better safety features than bamboo scaffolding in terms of structural calculation and a standardised working environment. A new calculation approach, NAF-Nida, has been adopted, and safety has been further improved by considering the imperfection of alignment and deformation of the scaffold members; taking the nylon safety net vibration induced by wind into consideration, anchoring intervals and safety precautions during typhoons have also been reviewed. A modern operation and management scheme has also been developed to ensure the system‟s safety standards and address quality assurance and cost control. MBMSS is an integrated system and its performance has been proven by hundreds of projects implemented in actual environments and various working scenarios. Notes: CityU Call Number: TH5281 .S67 2009; 226 leaves : ill. (some col.) 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2009.; Includes bibliographical references (leaves 185-191)

2009-01-01T00:00:00Z