NGD specified 114 STULZ GE Hybrid Systems with Indirect Free Cooling, which work alongside 26 high performance air blast coolers and pump sets from Transtherm Cooling Industries.
The GE Hybrid utilises outdoor air for free cooling in cooler months and switches to energy saving mode as soon as the outside temperature permits. The indoor unit has two cooling components – a direct expansion (DX) cooling coil and a free cooling coil. In warmer months, when the external ambient temperature is above 20°C, the system operates as a water-cooled DX system and the refrigeration compressor rejects heat into the water via a plate heat exchange (PHX) condenser.
The water is pumped to the Transtherm air blast cooler where it is cooled, and the heat rejected to air. When in free cooling mode, dry cooler fans are allowed to run and cool the water to approximately 5°C above ambient temperature before it is pumped through the free cooling coil. Dependent on water temperature and/or heatload demands, the water can be used in ‘mixed mode’, where it is directed through both proportionally controlled valves, thus enabling proportional free cooling and water-cooled DX cooling to work together. Crucially, 25 per cent ethylene glycol is added to water purely as antifreeze in order to prevent the dry cooler from freezing when the outdoor ambient temperature is below zero.
The project required a reliable and creative supply chain solution, which could not only create the most efficient product packages, but also deliver products on a ‘just in time’ basis. Mark Vojkovic, sales manager at STULZ, states, ‘It’s vital on projects of this size that manufacturing partners can see the bigger picture and adjust their own production parameters to suit. Specified for installation into the floor of the new campus expansion, we altered the manufacturing process of our GE Hybrid units to enable us to deliver the technology in two halves. First to be delivered were the fan bases, which were installed on to their stands during the earlier stages of the build – just in time for the construction of the suspended floor. Later in the build programme, we delivered the upper coil sections of the air conditioning units and Transtherm delivered, installed and commissioned its equipment on the outside of the building.’