Energy Savings in Data Centres
Data centre growth in Ireland has been driven partly by our location within Europe and to a considerable degree by our climate. Design criteria for data centres in Ireland ranges from -10oC in Winter to 28.9oC in Summer. The ASHRAE guidance on managing the data centre environment between 5.5oC and 15oC ensures that direct cooled data centres can be cooled using fresh air and an adiabatic type humidifier with PUE’s approaching unity. In addition, modern servers are more resilient operating within wider temperature and humidity bands than the older ‘legacy’ systems. The major IT companies, such as Apple, Facebook, Amazon, Dell, Digital Realty and Google are establishing significant data centres here in Ireland.
Where does this leave all the older legacy data centres, telecom hubs, etc. ? While many of these were set up using older technology, there are many opportunities available to upgrade these systems and significantly reduce operating costs. Some low cost high return areas to review in seeking opportunities to reduce cost include:
A Determine the Real Load:
It is important to determine the real load within the data centre / hub. In a very recent enquiry for 6 x 100kW of cooling, it was suggested that the load be physically measured and it was found that 6 x 60kW would handle the load and provide redundancy. This provided not only capital savings to the client, but also considerable operating savings and freed up power.
B Match the airflow to the load and remove conflict:
In systems with oversize cooling capacities, many operators run all the systems all the time. For 12oC ∆T, 250m3/hr/kW is required, whereas, for 10oC ∆T, 300m3/hr/kW is required. In a recent improvement programme with Arup, fan absorbed power was reduced by an incredible 90%; this included upgrading the fans to EC type with tight load management. All systems should operate as one to avoid conflict with central sensor control and intersystem LAN’s.
C Manage the Underfloor Pressure:
Systems were typically designed around maintaining underfloor pressures of 75Pa / 0.3”. More modern systems operate at 20Pa and the floor tiles are designed around this. As pressure x volume is power, it is important not to over pressurise the floor. Note that up to 8W per kW of room load (10oC ∆T) can be eliminated by reducing the pressure from 75Pa to 20Pa.
D Raise the operating temperature within the Room:
Conservative IT managers continue to persevere with operating temperatures as low as 18oC. Raising this set-point increases the efficiency of any cooling system. For instance, with direct expansion systems, 1oC increase in evaporating temperature can increase the system efficiency by 3%; reducing the condensing temperature on the other hand by 1oC offers 2%.
E Manage Supply and Return Air Path – Aisle Containment:
With open rooms, where air movement is not controlled, a high level of mixing can occur causing the system ∆T to be compromised. Aisle containment can be used on the cold or hot aisles to manage this process and ensure that the maximum ∆T is attained for the room.
F Free Cooling:
If access can readily be gained to a source of outside air, and if the local Standard Operating Procedure (SOP) allows it, then direct air free cooling is an option with a short payback. If the SOP is conservative with regard to humidity, then the span over which the free cooling operates can be reduced. Fluid free cooling options with external drycoolers, where internal coils can be added to the airside plenums or the units themselves.
G Extend / Raise the operating envelope:
Many rooms are managed on very tight operating bands forcing dehumidification and humidification at the extents of the bands. Many direct expansion systems will tend to bottom out at 35/40% RH due to the normal operation of the direct expansion coil. In many cases, it is highly unlikely that dehumidification is required and depending on the integrity of the vapour barrier, a small amount of humidification may be required in very cold outdoor temperature conditions.
Finally, do not forget the lights ! – there may be several kW available here with switching them off or replacing them.
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