A capital project
Australia’s first 5 Green Star building, located at 8 Brindabella Circuit, Canberra airport, is a three-storey building comprising 4040sqm of lettable floor space. Among the ESD principles that helped it to achieve this top rating from the Green Building Council of Australia, are the use of active and passive heating and cooling systems and insulation.
“In terms of noise insulation the windows are double-glazed and we needed an extra layer of plasterboard within the ceiling space but only on the roof level to control noise,” James Andrews, associate at architectural firm Daryl Jackson Alistair Swayn, explains. “An Insulation Solutions’ Permastop 430 building blanket was also used. This is a large roll of fibreglass with the sarking laminated to the back. For wall insulation we used Bradford Glasswool Batts. The acoustic requirements were met using the overall wall and roofing system without the need for additional acoustic insulation treatments.”
For heating and cooling, an active chilled beam system was installed. Low temperature (11°C) conditioned air is supplied to the beams throughout the building, each.which can be controlled by its own individual temperature sensor but is zoned in groups of two. These units use a venturi action to draw room temperature return air from the room space through a secondary cooling coil (using 13.5°C) water to satisfy the required conditions. The main benefit of this system is that a significant proportion of the cooling occurs at the active chilled beams and therefore the main air handlers and ductwork sizes are greatly reduced. This in turn equates to smaller plant rooms and a considerable decrease in fan power consumption.
“The active chilled beam is like car radiator in that you’re pumping heating or chilled water through what is essentially a radiator,” Andrews explains, “You’re using a combination of air blown across that, which in turn drags air from the space back through it. The system uses less air that’s been pushed through the mechanical ventilation system than a standard VAV air-conditioning unit, so we’ve achieved efficiencies in the plant room because we’ve got smaller air handling units (AHUs). We’ve also got a centralised plant that’s running four buildings now and will be running five by the end of the year so we’re gaining energy efficiencies with our chillers and boilers.
“Instead of having a plant and chillers sized for one building, it’s sized for the five buildings. In a single building you’d usually have two chillers and boilers because you don’t want them running at 100 percent capacity and you usually have a smaller chiller that may be able to handle a third of the capacity of the building load and then you have a chiller that can handle the remaining two thirds of the capacity.With a central services plant you can afford to have less chillers and larger ones because the load, even if you’re in downtime, is such that you can still have a larger, more efficient chiller.”
The AHUs are able to run on full outside air at comparable running costs to a return air system. The combination of reducing air supply and heat transfer means the outside air provided is in excess of the minimum outside air requirements and results in better indoor air quality and Green Building Council credits. A Siemens Building Management System controls and monitors all the mechanical systems and provides operational and energy consumption readouts as determined.
Air quality control in various parts of the building can also be controlled manually to decrease energy consumption when they are unoccupied, such as large meeting and conference rooms which have additional chilled beam units or infusers to meet the increased outside air and cooling requirements. Each floor’s distribution ducts are provided with shut-off dampers to allow independent floor operation after hours. High equipment load areas are treated with 24-hour operation water-cooled supplementary air conditioning units. The waste heat rejected from these spaces is transferred by the heat exchanger in the central energy building to other areas and buildings requiring heating.
As the base building supply air system is full of outside air, it is used to supply the meeting rooms without the need for supplementary outside air ductwork. The AHUs and ductwork are sized with additional capacity and utilise variable speed drive motors to cater for this, and retail tenancies on the ground floor are treated with individual water-cooled packaged heat pump units with time-clock locally adjustable control systems and in the ceiling space with outside air ducted from a louvre in the façade.
Slab heating and cooling around the perimeter provides the building with more thermal mass, according to Andrews. “The perimeter is where you need it because the edges of the slabs are most active in the change of temperature during the day as the sun moves around,” he says. “In the morning, for example, especially in a Canberra winter, you’d have hydronic heating starting up a couple of hours before people enter the building so the heat is where you want it, which is at slab level where people get cold feet, and at the perimeter where the cold is trying to get into the warm air. In the summer you’ve got the reverse situation where you’re trying to cool down that edge so you can run cooler water through there.
“It’s generally more efficient because you’re not trying to heat up the air - you’re heating or cooling the building material.”n
2-Aug-2005