Brisbane Harbour

By Lynne Blundell

3 November 2010 – Brett Beeson, ESD and mechanical engineer with Cundall, presented a fascinating case study of seawater cooling used for the Environmental Protection Agency’s building on the edge of Manly Harbour just out of Brisbane.

(Read more about this issue in our coverage of the 2010 AIRAH conference)

Speaking at the  AIRAH conference in Melbourne on 16-17 September this year,  Beeson said that with little space for a cooling tower plant, the EPA was looking for alternative solutions.

“Right beside the building is the bay – a perfect heat sink,” he said.

The building was designed with shading on the northern and western facades. Condenser water is cooled by pumping the hot water out of the building and through submerged pipes in the harbour. Once cooled the water is brought back into the building. Such a system provides cooling without the water consumption used in traditional chillers.

The system incorporates a mixed mode airconditioning operation where the building’s airconditioning is turned off on mild days and windows opened. This reduces energy consumption while allowing the building’s occupants to connect with the outside via daylight and views.

This mixed mode operation is unusual in Brisbane and, according to Beeson, is highly regarded by the occupants when used. However, in practice it is only used for about two months of the year rather than the predicted four to six months.

Reasons for this include inertia of office staff to turn the system off, group dynamics (that is, if one person is uncomfortable the airconditioning stays on) and lack of awareness among staff of how the building operates.

When designing the system, Beeson found it difficult to get data on sea temperature, particularly variations in temperature.

“Sea surface temperatures are available from large scale maps but may not be accurate close to shore,” said Beeson.

“CSIRO data was eventually obtained for the harbour but this was incomplete and have been interpolated.

“To be honest, designing the system got a little hairy at times because there was nothing to check it against.”

Problems that had to be solved included how long to make the pipes, how much water to put through the pipes (too much and energy is wasted pumping it through), calculating water temperature accurately and hence return water temperature.

Despite these difficulties the system operates effectively with heat transfer results very close to calculated figures. Further designs will benefit from the work done on this project, says Beeson.

“For small systems, such as this one, the cost of installation is very high,” said Beeson.

“The method is best suited to buildings very close to the sea and hence is not widely applicable. Large buildings would be more suited to the system and this building provides a working example of the system’s possibilities.”

In addition mixed mode operation of air conditioning requires a high level of occupant education and co-operation.

“Mixed mode operation is challenging to get right but reducing air conditioning run time is an easy way to save energy,” said Beeson.

lblundell@thefifthestate.com.au