Mechanical Technology

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Heating, cooling, ventilation and air conditioning

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Mechanical Technology — August 2015

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.

Durban mall’s highly efficient air con system

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.