Investigation on sensing topology for sequential control of chiller plants for efficient operation and control

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Investigation on sensing topology for sequential control of chiller plants for efficient operation and control

 

Author: Kwan, Chi-hung Alex
Title: Investigation on sensing topology for sequential control of chiller plants for efficient operation and control
Degree: M.Sc.
Year: 2001
Subject: Air conditioning
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Building Services Engineering
Pages: vi, 84 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1597776
URI: http://theses.lib.polyu.edu.hk/handle/200/2489
Abstract: This paper described the study on the sensing topology and potential further enhancement to the typical practice of sequencing control of central chiller plant equipped with building management system (BMS). Site survey on central chiller plants in Hong Kong has been conducted, and the result indicates that some operational and technical problems are commonly found. And it is found that central chiller plant using direct sequencing control based on calculated cooling load, which totally depends on three sensors, common return chiller water temperature, common supply chiller water temperature, and chiller water flow rate, are common in Hong Kong. A detailed case study on one of the site, with such configuration, is carried out and revealed that operational problems and sensor problems exists and leading inevitably to energy penalty, as the locus of control does not follow the optimal chiller efficiency curve. The uncertainty of the calculated total cooling load is estimated to be as large as 40 % for prolonged period, so the energy penalty is definitely significant. In addition, these type of sensor problems goes unnoticed by the operator, as the BMS does not offer any facility for early alert to them. It is proposed to involve all other sensors of a central chiller plant, on the top of the temperature sensors and flow meter, which is involved in calculation of cooling load, in alarming and control function. These sensors are typically for purely monitoring purpose only. In addition, it is raised that the importance of performance evaluation and energy auditing on central chiller plant, so the commonly available sensing topology is insufficient. A sensing topology serving this purpose is elaborated in this paper, and more than data logging purpose, it is proposed to employ these additional data for automatic error and abnormality detection. A error and abnormality detection logic is proposed, and trial run using real life on site data is conducted on a portion of the proposed logic. This type of automatic error and abnormality detection logic has great potential to be implemented, to improve the energy efficiency and operation of central chiller plant. After the recent advance in computing technology, this kind of software hosting the purposed algorithm, can be economically implemented. As the principle behind the purposed algorithm is simple and global, so this kind of software can be implement to large number of sites after development and fine tuning, and the development cost can be shared among numerous site. The additional investment from building owner, to have such sensing topology, and automatic error and abnormality detection problem is low, while the building owner can benefits from energy saving, operation cost saving, minimal down time and problem tracking hours, but without sacrificing the comfort of occupants.

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