Projects started off with five levels of hotel space , being changed to six levels and then adding an additional two floors on top of that . This also all happened after the tendering phase .
In terms of the HVAC system and accommodating this change , it was greatly advantageous that VMG chose a split phase VRF system as it allowed them to easily add more systems catering to the new levels . Had they opted for a central system such as a chilled water system , this may have compromised the initial design capacity . The VRF split phase option then also didn ’ t compromise the installation of floors below .
Another significant challenge of the building was power supply . There was a very limited power supply from the council to the building ( 600kVA ), and that brought into the design brief the requirement for an alternative source of power , and thus highly-efficient systems , which the VRF system meets .
To solve the power scenario , and which was another technological advancement that was added to the building , was the implementation of a gas generator . The Rosebank area has existing gas lines , with gas supply by Egoli Gas . The gas generator was implemented to feed off this supply and provide extra power to the building to supplement the low electrical supply provided by the city .
The building was determined to require at least a 1200kVA supply . To provide this power requirement , a system was designed as a hybrid renewable co-generation solution consisting of a solar photovoltaic ( PV ) rooftop installation of 90kVA and a 416kVA gas generator supplementing the 600kVA city connection . System redundancy was also included through a 700kVA diesel backup generator in place should the city connection be lost .
The co-generation solution enabled the entire hotel ’ s hot water requirements to be provided from the generator ’ s waste-heat . This is recovered through heat exchangers from the engine block and exhaust . The heat recovery system enabled significant electrical baseload reduction through utilising electrical elements thus producing a substantial cost saving .
All three of these power sources feed through a synchronised supply into the building . So the primary means of power supply to this building is now a mix of the gas generator and Solar PV , and the shortfall provided by council .
A further challenge on this project was plant space requirements . Traditionally with high-rise buildings , you would find very often a central system located on the roof or in the basement is specified with a chilled water system that would allow you to install long distribution lines , with limited space in the plant rooms themselves . A VRF system across every floor gave this project a lot of flexibility in terms of pipe runs , but importantly plant space .
Maintaining the existing façade dimensions of the building , a service level midway in the building between the fourth and fifth floors ( originally the roof space of the old building ) became the plant space level , where some of the plant is installed . This area it is also air-bricked to allow for natural ventilation to supply the required fresh air to various levels . This level also holds a number of condensing units and various water storage tanks and pumps . On top of the roof , more condensing units are installed as well as the fresh air and pressurisation systems . The hot water system for the hotel is also implemented on this services level . A 7 600 litre tank was installed which is heated from the second floor gas generator plantroom , and the buildings hot water ring main is circulated from here . This services level also houses the heat
Blackdot Energy Blackdot Energy
1 and 2 : The generator plant room showing the gas generator installed . Also indicated is the heat recovery system capturing waste heat to generate the building ’ s hot water needs and control system .
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www . hvacronline . co . za RACA Journal I February 2021 35