When Dunedin International Airport Ltd decided to upgrade and extend its terminal facilities, MWH was commissioned to deliver designs for the mechanical and HVAC services. Addressing the complex demands of highly variable occupancy, the challenging environment (the outdoor temperature varies from -9°C to 35°C) and ambitious energy efficiency goals for the 10,000m² terminal, required an innovative solution.
The solution provided by MWH for this $25M project was an open loop groundwater heatpump system that utilises bore water as the heat source in winter and the heat sink in summer. The heatpumps move heat from the chilled water system to the heating water system. The bore water removes any imbalance on either system through heat exchangers. Thus all heating and cooling within different parts of the building is recovered and only the net imbalance requires the bore water. In addition, the public ground floor areas are served by displacement ventilation systems. By introducing the air at low level, the supply air can be warmer. Consequently the summer cooling load in these areas is provided directly by the bore water system without the need for the heatpump, except under extreme conditions. The system theoretically uses only 50% of the energy of a traditional air based heatpump system. However, after the first two and a half years of operation since commissioning in 2005, the energy use is a further 19% below these expectations.
There are also other benefits which aided other members of the design team. For example, the lack of roof plant meant there were no architectural issues, no major structural support systems needed and the lack of roof penetrations simplified the acoustic engineers work. To achieve this extremely low energy use, the entire system has been optimised for operation under all load conditions and careful consideration paid to commissioning. The control system continually adjusts the setpoints, flows and pressures in response to the building demands, occupancy and ambient conditions. All factory standard equipment has been used. The innovation is in the way the equipment is assembled to form a unique system. This greatly simplifies maintenance requirements. It is believed to be the first New Zealand use of groundwater heatpumps for both winter heating and summer cooling in a major building. This has been achieved within the capital cost of a traditional system.
Exceptionally low energy consumption for a main centre airport building.
Actual operating energy consumption is 19% below predictions.
The system is very tolerant to wide climatic conditions: the system has kept the Terminal warm on a -9°C day.
This project has won the commercial category in the 2007 EECA EnergyWise Awards, a 2008 ACENZ Gold Award of Excellence and a 2008 NZ Engineering Excellence Award.