Data free-cooling in South Africa
20th March 2014
A robust, modular data centre cooling system is set to exploit free-cooling in the challenging climate of South Africa.
The system is the result of a partnership between Airedale International in Leeds, UK, and its wholly owned South African subsidiary, Johannesburg-based Airedale International South Africa.
It has been designed for pan-African mobile telecommunications company, Vodacom Pty Ltd to meet the increase in demand for its data centre applications. Vodacom required a solution that could be quickly rolled out within just 12-16 weeks from manufacture to installation and commissioning.
Cooling resilience and system uptime were critical factors which provided further complexity as the modular units need to deliver business continuity despite being sited under widely divergent environmental conditions ranging from the intense heat of sub-Saharan Africa, cooler coastal locations such as Cape Town, the hot and humid climate of Durban and the extremes of heat and cold of high altitude locations like Johannesburg. In addition, the threat of coastal corrosion, prevalent grass fires and dusty winds provided added design challenges, both structurally and in terms of cooling performance.
Each modular data centre consists of either a single 64m² module equipped with 2 x 40, 65, 75 or 92kW free-cooling SmartCool downflow precision air conditioning (PAC) units, or two 128m² modules containing 3 x 95kW SmartCool units.
The SmartCool units have dual mechanical (DX) air-cooled refrigeration circuits providing four stages of cooling, superior part-load efficiency and N+1 redundancy to deliver an annualised EER of 5.63 achieved through 99% of the year in free or partial free-cooling.
To capitalise on free-cooling opportunities, the SmartCool units are supplemented by an indirect free-cooling circuit connected to a roof-mounted hybrid condenser and dry cooler system.
Inverter driven run/standby pumps are positioned in a weatherproof housing with individual isolation valves and isolators on fans and pumps and a differential pressure sensor for each pump to deliver very precise capacity match. Under low temperature ambient conditions the pumps and fans run in isolation. As the ambient temperature increases, the three-way valve opens more fully, the pump speed increases, followed by the outdoor fan. If cooling demands cannot be met by free-cooling alone, the first stage of DX cooling starts. The compressors then stage sequentially to meet the demand.
Free-cooling
In order to achieve free-cooling in the heat of Southern Africa, air temperatures are elevated to 25°C and 38°C for supply and return respectively; raising the supply temperature by 1°C from a more standard return air temperature of 24°C, brings annual energy savings of 110% using an air cooled system alone and 138% from a free-cooling system. Running the units at the lower return air temperature of 24°C would deliver 22kW less cooling duty, increasing capital costs and floor space requirements.
Redundancy and reliability are provided by run/standby pumps; the free-cooling system is independent from the DX cooling system with two independent DX circuits and microprocessor battery back-up.
The container-based modules have been highly engineered to protect the external fabric, components and controls from extreme climatic conditions and corrosive coastal environments, delivering a life expectancy of up to 35 years.
A comprehensive BMS provides remote visibility of systems, SMS alerts and full trending and reporting.
