Fresh Air Cooling for a Server Room

1. Fresh Air Cooling for a Server Room Steve Gibbs and Alistair Gibbins

2. The Problem (1) • As IT infrastructure scale and complexity has grown, power consumption – and therefore heat production – has grown • There is a need to maintain a stable operating environment for equipment such as servers • The traditional response has been to install server room air conditioning, itself a large consumer of electrical power

3. The Problem (2) • This is compounded by a lack of understanding of the temperature requirements of modern equipment • 1960’s vintage mainframes needed to be kept at around 18oC (65oF) or less • That temperature is still being aimed for in many server rooms, at great cost • Modern kit is actually quite happy to work at a higher ambient air temperature as long as it is reasonably stable, typically 30oC - 40oC

4. The Problem (3) • All UK HEIs are tasked with reducing their carbon footprint. • The Climate Change Act (2008) sets a legally binding target for reducing UK CO2 emissions by 26 per cent by 2020 and 80 percent by 2050, compared to 1990 levels • Welsh Institutions have been given a target of 3% year-on-year reduction in energy usage over 10 years • At the risk of stating the obvious, we need to reduce our energy consumption for financial reasons too

5. Scale of the Problem (1) • The scale of the problem needs to be evaluated in each case: • What is the heat loading? • Can we reduce this? • How? • When we have done that, what is the residual peak energy input into the server room that we can not (currently) go below? • Re-evaluate on a regular basis

6. Scale of the Problem (2) • The total heat load in a server room is calculated by adding together: • Heat load from transmission through the fabric of the building • Area x R-Value x (Toutside – Tinside) = Watts • Internal walls • External walls (taking windows and orientation into account for sun loading) • Floor (is it a ground floor? Suspended? Concrete?) • Ceiling (is it a suspended ceiling? What is above it? A hot roof void?!) • Electrical energy consumed in the room = Watts • Servers + Switches + Lighting + Air Conditioning equipment, fans etc. • Heat load from occupancy (i.e. Techies working in there) = Watts • Any other sources of heat/energy, e.g. Heating pipes that go through the server room = Watts

7. Possible Solutions (1) • Virtualise or even eliminate some servers/services • Have an “N+1” number of virtual servers that can operate in a failover mode • Change hardware to more energy efficient modern models, e.g. “Blade” servers • Move away from the “Twin everything” mentality and halve your consumption that way • Lights off when not needed • Low voltage kit – removes the need for step-down transformers in every server etc.

8. Possible Solutions (2) • Use different or improved methods of cooling • e.g. Water cooling racks or even servers themselves removes the heat from precisely where it is generated • Segment the server room into hot and cold corridors – with effective plenums • Fresh air cooling • Run the equipment hotter • e.g. Run at 30oC (86oF) instead of 18oC (65oF) • Insulate the building fabric • reduces heat load entering the server room • Also reduces heat escape – which may mean that your peak load goes up. This is, after all, the UK, and most of the year losing heat through the fabric of the building works in our favour!

9. Fresh air cooling • The energy able to be extracted by air depends on: • Flow rate in metres3/min • Temperature change achieved in that air (∆T) • Will vary with different air density and humidity • Possible problems include: • Condensation (not really – warm moist air condenses on COLD surfaces) • Static electricity risk increases in low humidity conditions, e.g. winter • Temperature fluctuations can cause “Chip Creep” or component failure • Insect/small animal entry • Dirt and dust entry • Noise (in and out) • Lessened physical security

10. Server Room Layout

11. Outside Air Entry

12. Inside Air Entry

13. The Racks

14. Ceiling Air Extract Vents

15. Air Exit From Building Air exit mushrooms x 2 Note the afternoon sun loading on the walls and the roof (one window still glazed)

16. Server Room Air Flows

17. Temperatures Achieved 4/6/2010 30oC 13.9KVA 27oC 22oC 22oC/30%RH 24oC

18. Cost of Cooling: Before Fresh Air • Typical DAILY Electricity use by Air Conditioning • = 15 kW peak, assume 50% operation/24 hours • = 15 x 0.5 = 7.5 kW each hour (ignores lower load at night) • Cost per kW-h (Pence, Day units*) = 12.251 + VAT • Cost per kW-h (Pence, Night units*) = 8.079 + VAT • Day Rate Cost = 0.12251 x 7.5 x 17 x 1.175 = £18.35 • Night Rate Cost = 0.08079 x 7.5 x 7 x 1.175 = £4.98 • DAILY average Electricity cost for Air con = £23.33 • YEARLY average Electricity cost for Air con = £8,515.45 *Jan 2009 UWL Actual Costs

19. Cost of Cooling: After Fresh Air • Typical DAILY Electricity use by Air Conditioning • 15 kW peak, assume now 5% operation/24 hours • DAILY average Electricity cost for Air con = £2.33 • Typical DAILY Electricity use by Fresh Air Cooling Fans • 1.3 kW peak, assume 50% operation/24 hours = 0.65kW • Day Rate Cost = 0.12251 x 0.65 x 17 x 1.175 = £1.59 • Night Rate Cost = 0.08079 x 0.65 x 7 x 1.175 = £0.43 • DAILY average Electricity cost for Fans = £2.02 • DAILY average Electricity cost for BOTH = £4.35 • YEARLY average Electricity cost for BOTH = £1,587.75 • YEARLY saving = £ 6,927.70, a reduction of 81.35%!

20. Lessons Learned • Do the sums – or get someone to do them for you • Control the variables that you can control • Brick up windows • Insulate appropriately • Lights Out when unoccupied • Control airflow • Fit blanking plates in your empty rack slots • partitions can make very cheap simple plenums • Do not put sources of heat in the server room that do not need to be in the server room! E.g. Our wonderful UPS • New build is best • Design low energy usage in from the beginning • Capture low grade heat output and use for space heating, or warming water for hand washing etc., in sports halls, offices etc.

21. Other Ideas Download http://www.jisc.ac.uk/media/documents/publications/bpgreenictv1.pdf and http://www.jisc.ac.uk/media/documents/publications/overviewgreenictv1.pdf for lots of ideas