Vodacom Pty Ltd is a pan-African mobile telecommunications company, with the largest number of subscribers of cellular networks in South Africa. The business provides GSM services to more than 50 million customers in Southern Africa, Tanzania, Lesotho, Mozambique, and the Democratic Republic of the Congo.
maximize energy savings
To meet the increase in demand for its data center applications, Vodacom required a solution that would allow it to quickly roll out additional facilities without the time, high cost, and logistical barriers associated with new builds, or the constraints of retrofitting facilities in existing buildings.
Vodacom was also keen to maximize energy savings by integrating the most advanced air conditioning equipment technologies and exploiting free cooling opportunities, an added challenge in tropical and subtropical Africa.
Airedale’s Solution
- 2 or 3 x 40-95kW SmartCool™ dual-circuit air-cooled precision air conditioning (PAC) units
- 1 or 2 x 60-95kW condensers / dry coolers
- Three-stage indirect free cooling control achieved by adjusting fan speed, pump speed, and control valve, supplemented by DX cooling where necessary
- Optimized head pressure control: the condensing pressure set point modulates to maintain the most energy-efficient system operating point depending upon ambient temperature and room load
- Constant pressure control
- For comfort, and to prevent the ingress of unfiltered fresh air, a return air plenum airport above each air conditioning unit supplies one air change per hour (ACH) of filtered fresh air
Cooling Plant
Cooling specialist Airedale came up with an innovative, hybrid data center cooling plant. Each modular data center consists of either a single 64m² module equipped with 2 x 40, 65, 75, or 92kW free cooling SmartCool™ downflow PAC units, or two 128m² modules containing 3 x 95kW SmartCool™ units deployed in an N+1 configuration.
The smaller module houses a secure, fully dual redundant energy center accessed via its own entrance. Larger, separate fully dual redundant energy center modules with power output capacities of 1600 and 3200 Amps per phase can also be attached to the data/GSM network modules allowing up to 1000m² of white space to be constructed as required.
SmartCool™ Functions
SmartCool™ units are supplemented by an indirect air free cooling circuit to capitalize on free cooling The SmartCool™ units have dual DX air-cooled refrigeration circuits providing four stages of cooling, superior part-load efficiency, and N+1 redundancy.
To capitalize on free cooling opportunities, the SmartCool™ units are supplemented by an indirect air free cooling circuit connected to a roof-mounted hybrid condenser and dry cooling 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, thereby delivering the precise capacity match.
Process Of The Compressors
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.
To maximize the relatively limited free cooling opportunities that exist in the African climate, the units were designed with a supply air temperature of 25°C.
cutting-edge air conditioning
The solution was developed in conjunction with Airedale’s technical team in the UK and manufactured locally by Johannesburg-based, Airedale International South Africa, with installation and commissioning achieved within just 15 working days.
“Airedale delivered with speed and urgency, and the quality of their cutting-edge air conditioning plant designs will make a major contribution to Vodacom’s strategy. The energy efficiency of the modular data facilities fully complements Vodacom program to reduce the Group’s overall carbon footprint,” Fred R Weber, Pr Cert Eng, Pr Tech Eng, MSAI Mech Eng Senior Specialist – Vodacom Technical Facilities Division.
Benefits
- Modular system housing equipment and controls to meet varying cooling needs that can be rapidly deployed at any location and minimizes drain on capital expenditure
- Annualized EER of 5.63 achieved through 99% of the year in free cooling or partial free cooling
- Redundancy and reliability provided by run/standby pumps; free cooling system independent from DX cooling system with two independent DX circuits and microprocessor battery back-up
- Backward curved electronically commutated (EC) fans modulate to maintain constant floor void pressure and deliver up to 50% energy savings at part-load compared with AC equivalent units
- Energy-saving three-stage free cooling capacity control maximizes the benefits of EC fans and inverter-driven pumps; maintains free cooling by preventing sudden increases in water circuit temperatures on compressor start-up
Results
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.
By running the cooling at the lower return air temperature of 24°C, the units would deliver 22kW less cooling duty, increasing capital costs and floor space requirements.
