A study of energy use for ventilation and air-conditioning systems in Hong Kong

Pao Yue-kong Library Electronic Theses Database

A study of energy use for ventilation and air-conditioning systems in Hong Kong

 

Author: Yu, Chung-hoi Philip
Title: A study of energy use for ventilation and air-conditioning systems in Hong Kong
Degree: Ph.D.
Year: 2001
Subject: Ventilation -- China -- Hong Kong
Air conditioning -- China -- Hong Kong
Buildings -- Energy conservation -- China -- Hong Kong
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xv, 159, [117] leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1599565
URI: http://theses.lib.polyu.edu.hk/handle/200/513
Abstract: Most of the local modern buildings are high-rise with enclosed structure. Mechanical ventilation and air conditioning (MVAC) systems are installed for thermal comfort. Various types of MVAC systems found in Hong Kong were critically reviewed with comments on their characteristics in energy efficiency as well as application. The major design considerations were also discussed. Besides MVAC, other energy-consuming components in commercial buildings were also identified, such as lighting, lifts and escalators, office equipment, information technology facilities, etc. A practical approach has been adopted throughout this study in order that the end results will have pragmatic value to the heating, ventilating and air-conditioning (HVAC) industry in Hong Kong. A survey on sizing air-conditioning plant for commercial buildings was carried out in Hong Kong to find out the industry norms and engineers' practice in the design of energy-efficient buildings. Specially prepared questionnaires were sent to 38 local firms consisted of consulting and contracting engineering firms, owners and developers, and government departments. The number of firms being invited to participate in this survey represent an average of 84.5% of the leading firms in Hong Kong that have design capability. It was followed up by interviews with selected engineers with 6 to 18 years professional experience. The computer package, TRACE 600, was selected for most of the building modelling and energy simulations in this research. It is one of the most popularly used packages in local consulting firms for estimating building thermal load and energy in large-scale projects. A validation study revealed that the cooling energy simulation by TRACE has 14.8% deviation from the measured data, which is acceptable to most local firms. The program structure, weather data of Hong Kong, calculation methodologies, systems modelling, and equipment performance simulation were investigated. A series of energy simulations were performed using TRACE based on sample buildings of volume size varying from 4,000 m3 to 40,000 m3; and the results were compared with those obtained earlier by the research software, BLAST. Indoor Air Quality (IAQ) has become a major issue in commercial buildings worldwide including Hong Kong. Ventilation rate is no doubt a critical element in the design of HVAC systems, which can be realized more obviously in railway train compartments where the carbon dioxide level will be built up quickly when the compartments are crowded during rush hours. A study was carried out based on a simplified model using a train compartment that is equipped with an MVAC system. The energy impact at different ventilation rates was evaluated and a correlation equation was derived. Also, the relationship between carbon dioxide level and ventilation rate provides clue to energy saving through ventilation control with respect to building occupancy. Overall Thermal Transfer Value (OTTV) is a single-value parameter for controlling building energy use and is relatively simple to implement legislatively. The local government has taken a first step in reacting to the worldwide concern of energy conservation and environmental protection since 1995. Different methods of OTTV calculation were studied and the computation results were compared. It gives a clear picture of the advantages and limitations for each method to the building designers. However, due to the limitations of using OTTV as the only parameter for building energy control, some new approaches to a total control of building energy use were discussed and they might be considered for future revision of the building energy codes in Hong Kong. A sample database of 20 existing commercial buildings was established for further analysis of building energy use. The Princeton Scorekeeping Method was applied to derive correlation relationships between the building envelope heat gain and the electrical energy use for MVAC system with key parameters derived. A detailed study of other building parameters impacting on the energy use with the aid of computer modelling has revealed a number of energy saving measures applicable to commercial buildings in Hong Kong. Useful reference is then provided for engineers in designing energy-efficient commercial buildings or generating better design concepts for MVAC systems. Heat gains through building envelopes were reviewed with reference to fundamental theory behind as well as the heat transfer equations presented in the literature. The prevailing methodologies of cooling load estimation and energy calculation were studied. Building energy auditing methods were discussed with reference to the local practice as well as international standards and guides. The common procedures of building energy auditing with three stages were outlined: historical data collection/analysis, preliminary site survey, and detailed energy consumption investigation. A typical commercial building was selected for detailed study of energy use by MVAC systems. Data from preliminary building energy auditing were analyzed, and the results were compared with other similar buildings. TRACE 600 was used to justify the results. 20 scenarios of energy saving measures were investigated for a realistic commercial building. Alternative forms of energy for substituting or supplementing the existing conventional energy supply to commercial building application were also discussed, including: geothermal, solar photovoltaics, and cogeneranon. As a conclusion to this study, better design concept and process were proposed for engineers; recommendations were made for consideration in the next revision of the local OTTV regulation; and some practical proposals were offered to the building owners in pursuing a sustainable energy-efficient building.

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