Mechanical Technology August 2015

⎪ Heating, cooling, ventilation and air conditioning ⎪

Durban mall’s highly efficient air con system

P hase 1 of the air conditioning upgrade at Durban’s Pavilion shopping centre involves the installation of three Carrier 19XRV centrifugal chillers, which boast a total cooling capacity of 10 050 kW. Carrier is part of UTC Building and Industrial Systems, a unit of United Technologies Corp. Shopping Centre investor Pareto, which owns the Pavilion, procured the new air conditioning system from an environmental sustainability perspective. “As a company committed to the basic principles of water conservation and energy and operational efficiency in all our centres, we were satisfied that the system fulfilled our requirements,” says Mark MacKaizer, The asset manager at the Pavilion shopping centre. “We were also happy with the price, and with the guarantee and maintenance support provided by the suppliers. Our mechanical engineers advised us that these chillers have been used at various sites, without any defects and with low operating costs. The system sounds tech- nically promising and we look forward to seeing how this new technology delivers at the Pavilion,” he adds. The advanced Carrier 19XRV cen- trifugal chillers provide exceptional value, with energy efficiency ratio (EER) levels as high as 6.8, by utilising proven technology designed specifically for chlorine-free refrigerants (R134a). The 19XRV units consist of a single stage aerodynamic impeller; tunnel diffusers based on aircraft engine technology; and a motor cooled by refrigerant gas injection. The compressors are controlled us- ing a unit-mounted variable frequency drive to maximise the chillers’ energy efficiency. This is used in conjunction with high-efficiency evaporator and condenser tubes, an expansion sub- cooler integrated into the condenser, The upmarket Pavilion shopping centre in Durban is currently in the process of upgrading its air conditioning system, by replacing its existing units with energy-efficient Carrier 19XRV centrifugal chillers.

Above: The upmarket Pavilion shopping centre in Durban. Right: Three Carrier 19XRV centrifugal chillers, which boast a total cooling capac- ity of 10 050 kW, have been installed in Durban’s Pavilion shopping centre.

and patented float valve technology for optimised sub-cooling and refrigerant level in the evaporator. The single-stage hermetic compressor increases product reliability by eliminat- ing the additional moving parts associ- ated with multiple-stage machines, such as additional guide vanes and complex economisers. The Carrier 19XRV chillers are also equipped with a compressor variable frequency system. By changing the compressor operating mode, this system considerably reduces power consumption based on the motor’s rotational speed. In addition, the variable frequency drive control box is cooled by refrigerant, minimising size and ensuring optimal component cooling for an extended operating life. This concept makes water- cooling unnecessary, and eliminates the associated maintenance cost and power consumption of the water pump. Capacity control is achieved by means of variable inlet guide vanes located at the impeller inlet. Load modulation ranges from 100% to 15% of the full compressor load, under nominal ARI conditions.

The guide vanes are pre- cisely positioned by a pro- portional integral derivative

(PID) control algorithm to ensure precise and quick control of the desired chilled- water temperature, without hunting or overshooting the set point. With the variable frequency drive, the compressor speed is regulated by the control of the voltage-frequency values applied to the motor. The voltage applied, generated by pulse width modulation, is proportional to the frequency. The feedback calculation of the water temperature parameter deviation results in an adjustment of the cooling capacity through a simultaneous and co-ordinated action on the guide vane opening and the compressor speed. The 19XRV centrifugal chillers were supplied to the mall upgrade proj- ect by AHI Carrier South Africa, and were sourced from Carrier’s factory in Charlotte, USA. Built on Willis Carrier’s invention of modern air conditioning in 1902, Carrier is a world leader in heating, air condition- ing and refrigeration solutions. q

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