Western Cape Business News

Send  Share  RSS  Twitter  29 Sep 2008

ENGINEERING: Innovative Solutions at CTICC


Recent Western Cape Business News

SEW Eurodrive and Southern Air recently completed an innovative air conditioning system for the Cape Town Convention Centre’s new building.

SEW Eurodrive South Africa supplied more than sixty IP55 variable speed frequency drives to Southern Air Conditioning, who were the air conditioning contractors for this project. Ease of use, good technical support and backup, competitive pricing and IP55 as standard, were some of the reasons cited by Mark Botha from Southern Air Conditioning for using the SEW Movitrac LTE IP55 variable speed drives.

The building comprises of 15 storeys which includes basement parking and a ground floor comprising of a foyer and retail shops. Floors 3 to 7 are parking levels with the rest of the floors housing either single or multi-tenanted users.

The air conditioning in the office floors, used to overcome heat load generated in the building, is from a central water cooled chilled water system which is located in the basement, with variable air volume air handling units serving the separate zones on each of the office floors. One of the reasons for the necessity of separate zones is due to the size of the building and the relative position of the sun. For example in the morning the eastern side of the building is warmed by the rising sun while the west side is still in shadow, hence differing ambient temperatures in different zones. The use of variable volume air handling units allows for much better temperature control in the occupied space.

A central chilled water cooling plant is located in the basement. The chilled water is pumped through the building to the various air-handling units cooling coils which cool the air sufficiently to overcome the heat loads in the various zones.

All the office floors are air conditioned by variable air volume air handling units which are located in plant rooms within the floor space. The air handling units are connected by means of insulated chilled water piping to the chilled water generating plant. Conditioned air from the units is supplied through sheet metal ducting and distributed to the offices via variable volume diffusers. These variable volume air handling units are fully controlled by the building management system (BMS). The supply air volumes are varied to maintain constant static air pressure via duct mounted pressure sensors.

The supply fans have IP55 SEW Eurodrive variable speed frequency inverters mounted in the plant room and are controlled by a 0-10V DC control signal supplied from the BMS. The variable volume diffusers have stand alone controls complete with electric heaters. The control diffusers open and close to achieve the desired room temperature. As they open, the static pressure in the duct will drop and the fan will speed up to maintain the required static pressure. As the diffusers close, the static pressure will increase and the fan speed will decrease accordingly.

The staircase fans are speed controlled to pressurize the staircases to that of a higher pressure than in the rest of the building. This is to ensure that in the event of a fire, the smoke from the floors will not enter into the staircase. Pressure is maintained at a certain level from the BMS via a 0-10 volt signal. Should the pressure in the stairwell drop, a sensor will cause SEW Eurodrive variable speed drive to increase the speed of the fan to increase the pressure to the required level.

SEW Eurodrive variable speed frequency inverters were also used to vary the speed of the cooling tower fans in order to maintain a constant condenser water temperature. The condensed water temperature is monitored by the BMS and a 0-10 volt signal from the BMS enables the SEW Eurodrive variable speed frequency inverters to vary the speed of the fans in the cooling towers.

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