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Challenges And Solutions For AVIVA DC3 AVIVA (aka Norwich Union) is set to open its third data centre (DC3) on a greenfield site in the UK this September. The shell contractor was Bowmer & Kirkland, responsible for base build phase 1 works and construction (completion April 2007). Fit out is being handled by EMCOR (completion August 2008) while WSP is lead designer and handling M&E. The architects were LSI while Arcadis AYH handled project management and QS; structures were the responsibility of Ramboli Whitbybird. Base requirements for AVIVA were 2,250 sq. m. net IT (white space) in a single volume, column-free space with capability to double in size; Tier-3 resilience/availability (concurrent maintainability of all systems); 1.5kW/sq, m. average with flexible low, medium and high density zones; flexibility for water-cooled HD racks (manufacturer to be pre-selected); energy efficient design plus free cooling; full technical installation at day one and no planned outages or shutdowns for 15 years. Now for the additional challenges – IBM Germany was appointed by AVIVA as the design authority. The internal environmental conditions had to be maintained during failure scenarios: site power outage/generator start-up/chiller restart and duty chiller failure/standby start-up. Chilled water to the HD racks had to be maintained stable at less than +/-1 degree C in these scenarios. CFD studies within the hall had to demonstrate airflows and the impact of local failures. Full load testing of the IT hall (3.4MW) including HD racks (1.7MW). Finally there had to be full load Integrated Systems Testing (IST) under every failure scenario – this is set to last 12 weeks (currently underway) and involves over 600 scenarios. There are 96 HD racks with 24kW per rack (0.75 density factor) with heat exchanger pumping units located at one end of the hall. A substation has been built on-site for future use. There is a 7.6MVA grid supply, with an estimate of 6.8MVA maximum demand for phase 1 (assuming the DC3 is fully loaded). That’s 21,895 tonnes carbon dioxide per year with free cooling or 24,029 tonnes without (grid supplied electricity is 0.422kg carbon dioxide/kWh). Only the building and offices had to comply with Part L of Building Regs, as the process load is exempt. No local planning requirement for (10-20%) on-site energy from renewable sources. The practical measure applied are: all AVIVA power is purchased on a green tariff from Scottish and Southern; there is free cooling and an elevated chilled water temperature of 10 degrees C; there are variable speed drives on all fans and pumps, and UPS module optimisation; there are zero ODP refrigerants; and heat recovery for on-site offices and workshops. Other renewables considered were: photovoltaics, wind turbines (both insignificant), ground source geothermal/water source (couldn’t work/not enough water); CCHP tri-generation (no carbon savings); and bio-fuels (a possibility but yet too happen). A potential lies in low grade heat available for adjacent developments – but “no-one wants it.” There are 23 CRAC units (aka RACUs – room air cooling units), and 24 heat exchanger pumping units (HEPUs) with four HD racks per HEPU. IBM threw in the googly question “what would happen if two chillers failed?” Space is too limited here to discuss the detailed work WSP did – suffice to say WSP utilised TRANSYS modelling software from the University of Strathclyde. The summary is that this was a 10,000 node model with motorised control valves, chiller start times and variable volume pumping all simulated. Run options were N, N+1 and N+2 chillers, with chiller load = 90% (N, i.e. 4 chillers), 70% (N+1, i.e. 5 chillers), 60% (N+2, i.e. 6 chillers) – the impact of 2x12 cu. m. and 2x6 cu. m. buffer storage was examined, with the chilled water travel time to “RACU 28” equal to 16 minutes. The output decisions? Two 12 cu. m. mixing buffer vessels were added to the design. The BMS action in case of chiller failure is to reset the chilled water supply setpoint to 6 degrees C and return to the normal setpoint when the system has recovered. The requirements were for 96 water-cooled cabinets of 24kW each, and AVIVA narrowed the choice down to Knurr, Rittal, AFCO, Schroff, CMU and HP. It was one week’s work to test each manufacturer, under a mock-up and load test scenario. Ultimately it was down to Knurr and Rittal with the latter winning. For CFD studies, WSP utilised 6 Sigma DC software for typical simulations of steady state at maximum load; HD rack failure (doors open); RACU failure/maintenance; and chiller failure/standby restart. For heat load testing, WSP went to Argos and utilised 8 x 96 3kW fan heaters. The DC3 electrical design was tested through simulating the electrical network using Paladin DesignBase software. AVIVA is to close its DC1 centre which is 18 years old. DC2 is much newer and will continue. The DC3 IT migration begins this August, the first servers going live in September – and there are no planned shutdowns or outages before 2023 …. Here, the client AVIVA got what it wanted. Well, so far.
Have you also seen our other consultant articles? Too Much
Greenwash?
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