Projects
Continued from page 27
the AHU supply air fan speed varying under the variable air volume control sequence . Fresh air to fan coil units is supplied by constant volume tempering air handling units .
The Building ’ s smoke control system is incorporated into the overall air handling unit system . By utilising common systems and equipment , the system is economic yet functional . Each core has multiple air handling units connected to a single high-level return air point in the atrium . Each air handling unit system has a return air fan and economy cycle dampers .
Typically , one of the AHUs at each core has been adapted in such a way that it serves as a smoke exhaust system as well . The return air fan volume of the smoke facilitating AHUs return air fan matches the requirements for smoke exhaust – fire-rated in accordance with EN12101 .
The economy cycle dampers and ducts were also specified with the required fire rating . In the event of a fire , the control system will ramp up the return / smoke exhaust fan , close the bypass damper in the duct stream and open the relief damper downstream of the fan , exhausting smoke to atmosphere and preventing it from entering the AHU .
Exhaust air systems for ablutions are provided to the building in accordance with local regulations – SANS10400 Part-O . Ablutions are typically situated around the building cores . Exhaust air risers serve the ablutions on each floor of the core and is connected to a Toilet Exhaust Air fan located on the roof .
Plate heat exchanger and associated control valves .
Solving project challenges A particularly challenging part of the design and implementation was the coordination of the large supply air ducts within the available ceiling void space and the other trades . Due to the large area per floor plate and the available cores to locate riser shafts in , the airflow rate per riser shaft was quite high resulting in large duct take-offs to the floor .
A high-rise commercial building by comparison has smaller floor plate areas resulting in smaller duct branches to the floors . This issue was mitigated by leveraging the capabilities of 3D modelling and clash detection , but with limited tolerances , site intervention was required in certain instances to make it work .
Another challenging aspect was the requirement for rooftop plant to be located away from the building line in order to minimise visibility of the equipment from the ground level . This resulted in the plant space being extremely condensed . The use of 3D modelling also greatly assisted with the planning of the plantrooms together with strategically placed cross-over bridges to allow access to all the equipment .
www . hvacronline . co . za RACA Journal I November 2020 29