V&A Waterfront harnesses seawater cooling technology

18th September 2015

By: Dylan Stewart

Creamer Media Reporter

  

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Heating, refrigeration and air-conditioning solutions provider Carrier is installing a 6 MW cooling plant at the V&A Waterfront in Cape Town that uses the cold Atlantic seawater from the harbour to provide cooling for the property’s Silo District developments, says Carrier business development manager Jaco Smal.

The cooling system will supply cooling and heating, using seawater, to four new V&A Waterfront developments. Silo No 3 through to Silo No 6 are all on track for completion in 2017, at the substantial investment of R1.5-billion.

In addition, the same type of cooling system was used in the V&A Waterfront’s No 1 Silo and No 2 Silo developments, which were completed in June last year.

Smal notes that the V&A Waterfront’s No 1 Silo is one of Africa’s most advanced intelligent buildings, and was the first South African building to receive a six-star Green Star SA rating for ‘design and build’ by the Green Building Council of South Africa.


Smal says the company’s cooling solution is highly efficient, as it achieves a coefficient of performance between 10.37 and 16.04 under various conditions with their 23XRV variable-speed screw chiller.

By circulating seawater through heat exchangers, the cooling solution does not require cooling towers to reject heat into the atmosphere. Instead, it rejects unwanted heat into the ocean.

Smal highlights that the system, therefore, gains from the efficiencies associated with water cooling and avoids the pitfall of water use through evaporation in cooling towers.

He also cites water hardness as an additional challenge for water-cooled systems in certain areas in South Africa. Carrier will also provide heating solutions for the precinct.

Air-Cooled vs Water-Cooled
Some companies have moved away from using water-cooled equipment, particularly in water-scarce areas in South Africa, states Smal. This has been supported by the Green Building Council of South Africa, which awards points to buildings that do not use water for their cooling systems.

However, Smal notes that, in many instances, an air-cooled system – the main alternative to water-cooling – is significantly less energy efficient and, therefore, air-cooling is not favourable environmentally.

In terms of efficiency, when the dry-bulb ambient conditions are low, air-cooled devices can compete with water-cooled devices because heat transfer in cooling towers is less efficient when the wet bulb temperatures are high.

He explains that air-cooled equipment condenses its refrigerant in relation to the dry-bulb temperature, which, in a humid environment, is a lot closer to the wet-bulb temperature, which determines the temperature at which water-cooled equipment condenses its refrigerant.

While air-cooled equipment is much less complicated to install, it is significantly more elaborate as it uses fans and heat-rejection systems, making its initial capital layout more expensive, Smal adds.

In addition, the life expectancy of air-cooled equipment is up to 15 years shorter than water-cooled equipment, particularly in corrosive environments, he notes.

Smal states that, in the past ten years, significant strides have been made in terms of the efficiency of water- and air-cooled equipment: “A minimum of 30% better efficiency has been gained for cooling equipment under full load conditions.”

He explains that efficiency gains have been even higher under part-load conditions, particularly owing to variable-speed screw compressors, as they can optimise operations according to the load and lift under which the chiller is operating.

Further efficiency has been gained through enhanced control technologies for cooling systems, Smal concludes.

Edited by Samantha Herbst
Creamer Media Deputy Editor

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