Audit of Data centre at Citibank, Singapore

PowerQ undertook the audit of Citibank Data Centre by teaming up with Singapore Telco and Emerson. The review, measurement and monitoring was conducted by Tampines Singapore. The facility contains several data centres each having its dedicated CRAU’s which are supplied by central CHW system. The Citibank DC is supplied by 14 . CRAUs supplying cool air through ducted raised floor plenum. The return air is carried through false ceiling and returned from the top of CRAU. The current computer energy loads is 525 watts/m.sq.

Problem
It was found that some areas in the data centre were relatively hot and the operator was concerned about the situation. Other areas of the DC were reportedly having acceptable temperature. At the same time it was reported that the CHW flow rate at main header serving data centre had dropped. The room temperature set by the point design in the DC was 22.5 0C .

The objective of the audit was to find out if installed equipment was working as intended and to identify any areas in the air-conditioning distribution system that could enhance the system performance.

Approach
PowerQ conducted audit by performing the following tasks:

  1. Performed cooling capacity calculation based on 525 watts/m2 load.
  2. Physical inspection of CRAU units and airflow distribution in data centre.
  3. Physical test on CRAU to ascertain performance. The test results were summarised while the performance test of the CRAU was also undertaken
  4. 24 Hour room temperature monitoring was also carried out at various spots in DC.
  5. The actual cooling capacity with the demand (525 watts/sqm) was compared with the design load.

Observation
The audit revealed that several actions needed to be undertaken to improve and recover the DC temperature requirements. The following were the key observations:

  1. Measurements showed that the actual performance of the equipment was above the demand of 525W/sqm. Total sensible cooling capacity computed based on measurement was 681 w/m2 as against the design of 732 w/m2.
  2. There was a loss of capacity of CRAU 43 (about 16 Tr during the time when the problem was identified, this capacity was partially compensated by a temporary FCU). Post rectification this capacity’s now again available which will further enhance cooling capacity
  3. There was loss of capacity of CRAU 39 (This was confirmed by the fact that the supply air temperature was 210C and the pressure drop across coil was only 1 psi (compared to 3-4 psi for similar capacity CRAC units i.e. CRAU 38 and CRAU 40) indicating a very low or no flow. Once this CRAU 39 is rectified the additional cooling capacity would be available which will further enhance cooling capacity
  4. The temperature data logging at three locations in DC showed that at two locations the temperature was maintained. Only at location #03-31 (Area A close to non performing CRAU 43) the average temperature was 23.8 which was higher than the required (22.50 C).
  5. There was some exfiltration of air through the various doors in DC to air-conditioned corridor This explained why the total supply volume was higher than the return air volume at CRAU.

Recommendations
Following were the main recommended actions in the order of priority:

  1. Rectify CHW flow problem at CRAU . (Post audit -This problem was rectified and PowerQ re-tested the CHW flow of the unit to confirm the CHW flow requirements and unit is the performing satisfactorily.)
  2. Check for any underflow blockades for air flow to Improve air distribution in area served by CRAU by closing undesirable openings and providing an under floor partition and to prevent air loss to other areas.
  3. Check and tighten the loose belt (if any) of CRAU supplying lower airflow. (Consider this CRAU 34 and 35 are of same design and installed in same room CRAU 34 is having FLA of 5.5 A while CRAU 34 has FLA of 10.2 A indicating possible belt slippage at CRAU 340.
  4. Provide door seals at DC door to reduce exfiltration of air.
  5. Install the industry standard pressure test port for flow measurement.
  6. Consider to lower the set point for CRAU 43,44 and 45 (by 1-20C). It is noted that the Return air temperature sensor measure lower temperature than is actually in area .