Optimisation of outside air pre-cooling via underground conductive heat transfer

Shepherd, Nathan (2014) Optimisation of outside air pre-cooling via underground conductive heat transfer. [USQ Project]

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Abstract

The purpose of this research project was to provide building services mechanical engineers who are designing an underground pre-cooling system in NQ, in particular
Townsville, with tabled system selections dependent on the outside air design quantity required to meet the minimum requirements of Australian Standard AS1668.2

A challenge that engineers face is the requirement to deliver a product that is both energy efficient and will provide a cost benefit over the life of the structure. Soil temperatures below ground surface level can remain relatively constant for the entire duration of the year. At sufficient depth, the soil temperature is typically cooler than that of the ambient air temperature in summer. This means that this difference in temperature can be used as
a means of precooling during this time.

Site based measurements were undertaken, whereby soil temperatures at depths of 1 and 2 metres and dry bulb entering exiting air temperatures for the existing system were obtained. Through the use of these site based measurements and ANSYS Simulation Software a comparison model and simple straight run model was developed to portray
the effects that, pipe diameter, airflow velocity and system length has on the exiting air temperatures. This allowed numerical results from ANSYS to be compared against the existing operational system results obtained from site and against previous literature to conclude with the recommended findings and develop the tabled system selections.

Upon review of the results it could be seen that pipe diameter had the greatest effect on performance relative to pipe length and that the greatest change occurred within the first 10m with respect to length. It could also be seen that as velocity of air flow increased, the performance of the system decreased. During a review of the existing literature it was found that the typically installed pipe materials were found to have minimal effect on performance and that capital expenditure would be the determining factor on pipe material selection.

It was concluded that the ideal system selection is highly dependent on the design airflow quantity, however a number of smaller pipes performs greater than a single large pipe,
and that increasing velocity should be considered before increasing pipe diameter. It was also recommended that a control system be implemented to ensure that the efficiency of the system is not compromised throughout the cooler periods of the year whereby the system could act as a heater during these times.


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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Mechanical) project.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering
Supervisors: Mossad, Ruth
Date Deposited: 09 Sep 2015 05:14
Last Modified: 09 Mar 2016 02:37
Uncontrolled Keywords: earth to air heat exchange; underground pre-cooling; conductive heat transfer; Townsville; Queensland; airflow
Fields of Research : 09 Engineering > 0906 Electrical and Electronic Engineering > 090699 Electrical and Electronic Engineering not elsewhere classified
URI: http://eprints.usq.edu.au/id/eprint/27301

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