Diagnostic studies on a chiller water distribution system

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Diagnostic studies on a chiller water distribution system


Author: Lee, Man-kwong
Title: Diagnostic studies on a chiller water distribution system
Degree: M.Sc.
Year: 2001
Subject: Air conditioning
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Building Services Engineering
Pages: x, 105 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1597786
URI: http://theses.lib.polyu.edu.hk/handle/200/2646
Abstract: Once a building starts to be occupied, any operational and maintenance problems with the HVAC systems will start to surface. These problems can be extensive and their causes can be traced back to the stages of design, installation, commissioning and acceptance. This dissertation focuses on diagnostic studies of the problems encountered in a chiller water distribution system. Through the snag lists, correspondences, fault reports, interviews with commissioning and maintenance personnel, records of building management system and review of literature, these faults and their causes were summarized and further analyzed. The information will be useful to the development of fault diagnostic program, like ASHRAE technical data bulletin (1996). One existing building that had been operated for over 2 years and selected for the study. One major fault studied was the poor water balancing in the water distribution system. Overflow in certain branches and underflow in other branches gave rise to many complaints on thermal discomfort, which reflect that the contractor had not balance the system well enough. The conventional proportional balancing method was rather time consuming to carry out manually. In this work, it was found that computer simulation was a good method for the prediction of the number of turns of balancing valves required and for troubleshooting any faults encountered. Not only it could lessen the burden of balancing work and save the commissioning time, it could also provide practical direction for energy saving and maintenance. Low return chilled water temperature arising from over-supply of chilled water was another common problem faced in water distribution circuit. Site investigation at the building was held and for solving the problem, modifications to the system design were recommended. Noises generated from control valve annoyed the occupants, which were found due to over-sized control valves. Both HVAC and control contractors selected the components of the chilled water system, and hence the supply pressure requirement deviated from the original design value. Wrong selections of control valves were found it caused by insufficient communication of design information. The problem of the building was verified by system simulation, which predicted the range of valve stroke under partial load conditions. Besides the replacement of control valves with higher authorities, differential pressure setback at partial load condition would be possible solutions to suit the characteristics of the existing building. Most of the operational problems with the HVAC system can be eliminated earlier at commissioning stage or even construction stage. ASHRAE (1996) points out that the commissioning should be a process from design to post-acceptance stage and professional commissioning teams with recognized qualification will be a key of success of the commissioning work. Therefore, existing practices of commissioning in Hong Kong or other countries and commissioning procedures of international standards have been reviewed. As the installation contractors generally are responsible for the commissioning work in Hong Kong, tightening construction period and saving resources drive them to complete the commissioning work with forfeit of the quality. Proper documentation and training to the operation and maintenance personnel are crucial procedures to keep the system operating in compliance with design intent.

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