By Eamonn Ryan
Cape Town’s growing data centre industry is raising an increasingly important engineering question: how can the enormous quantities of heat generated by digital infrastructure be rejected efficiently without placing additional pressure on scarce freshwater resources?
The V&A Waterfront has developed a seawater cooling and heating system that uses the Atlantic Ocean as part of its thermal infrastructure.
Kues1 | Magnific.com
One answer may already be operating at scale elsewhere in the city. The V&A Waterfront has developed a seawater cooling and heating system that uses the Atlantic Ocean as part of its thermal infrastructure. The system serves buildings in the Silo District and other areas of the precinct, demonstrating that seawater can form part of a sophisticated commercial cooling strategy. The Waterfront says its seawater cooling plant is expected to save around 25 million litres of water annually.
The technology does not mean that seawater is pumped directly through building air-conditioning equipment. Instead, the seawater acts as a heat-transfer medium, allowing heat to be rejected without relying on conventional evaporative cooling towers.
That distinction is important when considering whether seawater could have a role in data-centre cooling. The attraction is obvious. A large data centre needs a dependable heat sink, and the ocean represents an enormous thermal resource. In principle, a seawater-based system could reduce or eliminate the evaporative water consumption associated with cooling towers while potentially providing efficient heat rejection.
But seawater cooling is not a universal solution. The economics and engineering depend heavily on location. A coastal data centre with sufficient access to seawater has a very different proposition from an inland facility. Intake and discharge infrastructure, pumping energy, filtration, corrosion protection, marine fouling, heat exchangers, environmental permitting and redundancy all need to be considered.
The V&A Waterfront experience is valuable precisely because it demonstrates both the opportunity and the importance of designing the system around the specific application.
Two Oceans Air Conditioning identifies the V&A Waterfront EPP as a project incorporating a district-cooling plant using seawater for cooling, with IQ Consulting Engineers as the engineer. This will shortly be our featured project in a future issue.
The comparison with data centres should nevertheless be approached carefully. A commercial precinct and a high-density data centre have extremely different cooling profiles and reliability requirements. Data centres operate continuously and have extremely low tolerance for interruption, meaning that any seawater-based cooling system would need robust redundancy and carefully engineered interfaces with the IT cooling infrastructure.
The potential, however, is worth investigating. As Cape Town considers how much additional digital infrastructure its electricity and water systems can accommodate, cooling technology becomes part of the wider environmental equation.
The Equinix development illustrates the scale of the emerging challenge: around 170MW of proposed capacity. Its reported choice of dry, air-based cooling demonstrates one way of addressing water concerns.
The V&A Waterfront demonstrates another possibility: using the ocean as a heat sink. The question for future projects may therefore not be whether Cape Town should choose air, water or seawater cooling, but which combination of technologies makes the greatest engineering and environmental sense for each site.
Read next: Why Cape Town’s climate could give data centres a cooling advantage.
