Mt Haleakala, Hawaii USA
The multicolour active galactic nuclei monitoring (MAGNUM) observatory is an unmanned observatory designed and built in Australia, located on the island of Maui, and operated remotely from Japan by an astrophysicist. The Australian designers have developed and used software compensation to measure the exact location of satellites above the earth’s surface more accurately than NASA. Part of this compensation is to ensure when the observatory roof opens for the telescope to be operated, that internal temperatures exactly match external temperatures. Meteorological data is fed into the mechanical services control system from the US Air Force weather station on Mt Haleakala and a target temperature selected for each nights telescope use. Historical meteorological data were sourced by RCE and showed that ambient conditions on the mountain top varied from minus 5ºC to 30ºC. The problem that arose was how to cool the observatory building to minus 5ºC when conventional refrigeration equipment could only cool air to about 10ºC.
A special purpose chiller was specified and built, running on 50% glycol and 50% water and arranged to cool the mixture of glycol and water from minus 9ºC to as low as minus 15ºC. This in turn allowed air to be cooled from minus 6ºC to minus 10.8ºC using a massive 8 row cooling coil. In this way typical night time conditions of minus 5ºC to 10ºC could be achieved. To prevent the coil icing up, a 7.2kW electric defrost element was mounted integral with the cooling coil and arranged to melt ice when initiated by the frost sensor.