Evaluation on economical benefits of economizer control in Hong Kong buildings

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Evaluation on economical benefits of economizer control in Hong Kong buildings


Author: Lui, Ka-wai
Title: Evaluation on economical benefits of economizer control in Hong Kong buildings
Degree: M.Sc.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Buildings -- Energy conservation -- China -- Hong Kong
Buildings -- Automatic control -- Evaluation
Ventilation -- China -- Hong Kong
Department: Multi-disciplinary Studies
Dept. of Building Services Engineering
Pages: x, 140 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1661023
URI: http://theses.lib.polyu.edu.hk/handle/200/2067
Abstract: Previous researches found that the application of economizer control to ventilation system in building could save more than 10% of the total cooling energy. However, economizer control is rarely applied in practical situation. This study aims at evaluating the economical benefits of such kind of application. In the very beginning, questionnaires are sent to local HVAC designers to collect their views on building ventilation designs, followed by a general review of the most commonly adopted design standards, guidelines and code of practices for building ventilation designs. Arrangements of economizer control on various types of building ventilation systems are also introduced. Four existing commercial centers with central air-conditioning and mechanical ventilation systems installed are taken for detailed analysis, including building layouts, functions and the associated ventilation system. It mainly aims at finding out the space constraints in the application of economizer. A term "Potential areas for economizer" is introduced to identify areas where economizer control can be adopted without making major modifications of the building layout. Two most commonly adopted ventilation systems, PAFCU system and AHU system, are studied in details. To incorporate economizer control, the initial cost of the system may be higher. Therefore, cost analyses are conducted for conventional control and economizer control when applying PAFCU and AHU systems in order to obtain the cost implication and whether there are any favorable paybacks. The payback period is more than 50 years for small PAFCU system, assuming a 10% annual cooling energy saving. For large PAFCU system, over a 20-year payback period is found. In an AHU system, the same assumptions are applied with no additional space requirement. The payback period varies from about 4 years for small AHU system to less than 1-1/2 years for large AHU system. However, if additional floor spaces are required, the payback period will increase. When the cost of additional space is greater than the cost of energy saving, it would never pay back. Therefore, to reduce the additional space requirement and to maintain original space requirement are essential in the application of economizer control. Analyses are conducted by considering different types of cost for the additional space for economizer control. Rent of space is taken when economizer control is added to the existing building whilst construction cost of space is taken when economizer control is considered before building construction. By assuming that the construction cost for additional space on economizer control needs to be taken into account, the payback period of selected zones vary from about 2-1/2 to 4-1/2 years. These results show that there will be economical benefits if the application of economizer control is considered during the preliminary design stage of the building. Further analysis is conducted on the addition of economizer control to demand ventilation control system. A shorter payback period ranging from 1-1/2 to 3 years is obtained. Finally, summaries of analyses and recommendations for designers on cost effective design are given.

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