Performance evaluation of chiller system

Pao Yue-kong Library Electronic Theses Database

Performance evaluation of chiller system


Author: Lam, Kwok-chuen
Title: Performance evaluation of chiller system
Degree: M.Sc.
Year: 1997
Subject: Office buildings -- Air conditioning
Refrigeration and refrigerating machinery
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: viii, 60, [37] leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: Central chilled water plants are the largest energy consumers in modern commercial buildings, responsible for about 40% of the total energy use in such buildings. In this research study, guidelines have been established on selection of suitable combination of chillers as well as on development of optimal chiller on/off control strategies, taking into account the building load profiles and the part-load characteristics of chillers. The simulation softwares, HTB2 and BECON, were used for simulating heat transfer in buildings and predicting electricity consumption for air-conditioning. Predictions from the simulation softwares were verified by comparison with measurements in an existing plant, and were found reasonably accurate. Plant equipment models for chillers and variable speed pumps have been developed. The model equations were established by curve-fitting manufacturers' data. Comparison with chiller data from different manufacturers shows that a universal model can be used to cover similar type of chillers of different makes. Since the temperature of the cooling medium entering the condenser affects the power consumption of a chiller at a given load, a seawater temperature model was also established and incorporated into BECON to obtain more accurate simulation result for seawater cooled chillers. Potential saving of using the optimal chiller combination and sequencing control strategy in three hypothetical office buildings were evaluated. The results show that the use of water cooled centrifugal chillers will lead to the most energy efficient operation since this type of chillers have outstanding full load performance, i.e. a lower full load kW/TR. Moreover, the combination of 2 large plus 2 small capacity (half of the large capacity chiller) water cooled centrifugal chiller is found to be the optimal combination for office buildings. The use of optimized on/off sequencing control can save up to 2.2% in the year round total energy consumption for water cooled plants with reciprocating chillers, and up to 0.2% for an air cooled chiller plant with the same type of chillers. However, improper application of chiller part load performance data can lead to inaccurate performance evaluation and can cause inefficient operation.

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