Feasibility of Free Cooling Systems Utilising Phase Change Materials in the Brisbane Climate

Lim, Ryan (2013). Feasibility of Free Cooling Systems Utilising Phase Change Materials in the Brisbane Climate Honours Thesis, School of Engineering, The University of Queensland.

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Author Lim, Ryan
Thesis Title Feasibility of Free Cooling Systems Utilising Phase Change Materials in the Brisbane Climate
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2013
Thesis type Honours Thesis
Supervisor Michael Kearney
Total pages 168
Language eng
Subjects 0913 Mechanical Engineering
Formatted abstract
With air conditioners consuming slightly less than a quarter of all electricity generated in Australia on the hottest days of the year (CSIRO 2010), there is significant potential for using alternative technologies to reduce energy costs associated with space cooling; one proposed method is free cooling systems. Specifically, free cooling systems incorporating phase change materials (PCM) as thermal storage. This thesis seeks to investigate the feasibility of utilising such systems in Brisbane’s climate using a simulation study based around a hypothetical implementation. Reference to a particular climate is used as the effectiveness of these systems is strongly sensitive to climate conditions.

The investigation of this model system is performed by a composition of two models: one analysing the effect of the latent heat thermal storage on ambient air drawn into the system and one modelling the thermal response of the room to the air discharged from the system. The underlying mathematical models are selected predominantly on the basis of their computational complexity as expeditious simulations are required to efficiently execute design optimisation.

The performance of this PCM free cooling system is evaluated by combining the coupled mathematical models with climatic data for Brisbane’s 2012/2013 summer. The effective payback period of the system, calculated by comparison with the costs of a typical residential air conditioner, forms the primary metric for this study. By merging the effective payback period and amount of overheating experienced by the room into a single objective function, the design is optimised for both economic viability and cooling performance using the DIRECT algorithm.

The effective payback period of the optimised PCM free cooling system is found to be 9.3 years. This study also finds that the system meets the overheating criteria proposed by CIBSE (Spires 2011). Thus, it is concluded that PCM free cooling systems present an economically-viable cooling alternative to conventional air conditioning in Brisbane’s climate. However, with relatively comparable capital costs, advocation for its use depends on other factors. While PCM free cooling offers an autonomous solution with modest economic returns, it lacks the flexibility of conventional air conditioning both in terms of user control and adaptation to climate conditions. This study should be extended through consideration of humidity levels and a year-long simulation period to produce more definitive conclusions about system potential.
Keyword Brisbane Climate

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
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Created: Fri, 04 Dec 2015, 16:46:00 EST by Asma Asrar Qureshi on behalf of Scholarly Communication and Digitisation Service