DATA CENTRES OVERCOOLING
unit’. The delta temperature (T) across the cooling unit is normally designed to around 10C, hence the air temperature supplied from the unit is 12C to 14C at full load. The cooling requirement is to control
the conditions of the air at the inlet to the IT equipment, which can vary greatly from the temperature observed at the CRAC unit return. This is often not well understood in the industry. The data centre IT staff are responsible for the ongoing availability of the IT services running on the IT equipment; and these staff are dependent on the electrical and mechanical infrastructure and facilities management (FM) team to provide continuous power and cooling. Overheating can cause failures of IT equipment, so IT staff often react to this risk by trying to run the data hall at very cold temperatures. The rationale for this is that, in the event of a cooling interruption such as a power cut, these low temperatures will help to increase the time buffer before unacceptably high temperatures are reached. This unnecessary overcooling of the
room has a high energy penalty. However, in many organisations the FM or estates department pays the energy bill, which means the cost does not impact on the IT department budget, so the incentive for them to operate the system with better energy efficiency is not there. Figure 3 shows that, while the cooling
units are working as designed, there is a wide range of air temperatures observed at the inlet to IT equipment. Ten per cent of the sample size is receiving air that is colder than required, representing an
www.cibsejournal.com
35 30 25 20 15 10 5 0
-5
30.0 28.0 26.0 24.0 22.0 20.0 18.0 16.0 14.0 12.0 10.0
0
Velocity pressure impact
Vel (m/s) Pv (Pa) Pt (Pa) Ps (Pa) % air Vol
T air supply (C)
1
2
3
4
5
6 Floor Grille No Figure 2: An example of air pressures and their impact in a cold aisle 5% over 27C ASHRAE maximum recommended
7
8
9
10
8% less than 18C ASHRAE minimum recommended 2% less than 15C ASHRAE minimum recommended 10 20 30 40 No. of server inlet temperatures sampled Figure 3: An example range of measured server inlet temperatures 50 60 70
April 2012 CIBSE Journal 41
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68