Google just updated their PUE measurement page with Q3 2009 numbers.

Quarterly energy-weighted average PUE:
1.22

Trailing twelve-month energy-weighted avg. PUE:
1.19

Individual facility minimum quarterly PUE:
1.15, Data Center B

Individual facility minimum TTM PUE*:
1.14, Data Center B

Individual facility maximum quarterly PUE:
1.33, Data Center H

Individual facility maximum TTM PUE*:
1.21, Data Center A

* Only facilities with at least twelve months of operation are eligible for Individual Facility TTM PUE reporting

What is nice is the Google guys have discussed their latest data center J even though it has only one data point. Data Centers G, H, and I are mentioned as well as not being tuned yet.

Notes:

We added one new facility, Data Center J, to our PUE report. Overall, our fleet QoQ results were as expected. The Q3 total quarterly energy-weighted average PUE of 1.22 was higher than the Q2 result of 1.20 due to expected seasonal effects. The trailing twelve-month energy-weighted average PUE remained constant at 1.19. YoY performance improved from facility tuning and continued application of best practices. The quarterly energy-weighted average PUE improved from 1.23 in Q3'08, and the TTM PUE improved from 1.21. New data centers G, H, I, and J reported elevated PUE results as we continue to tune operations to meet steady-state design targets.

The Google guys know they are going to get critiqued on how good their numbers are, so they described their measurement methods and error analysis.

Measurement Methodology

The PUE of a data center is not a static value. Varying server and storage utilization, the fraction of design IT power actually in use, environmental conditions, and other variables strongly influence PUE. Thus, we use multiple on-line power meters in our data centers to characterize power consumption and PUE over time. These meters permit detailed power and energy metering of the cooling infrastructure and IT equipment separately, allowing for a very accurate PUE determination. Our facilities contain dozens or even hundreds of power meters to ensure that all of the power-consuming elements are accounted for in our PUE calculation, in accordance with the metric definition⁶. Only the office space energy is excluded from our PUE calculations. Figure 3 shows a simplified power distribution schematic for our data centers.

Figure 3: Google Data Center Power Distribution Schematic

Equation for PUE for Our Data Centers

E_US1 Energy consumption for type 1 unit substations feeding the cooling plant, lighting, and some network equipment

E_US2 Energy consumption for type 2 unit substations feeding servers, network, storage, and CRACs

E_TX Medium and high voltage transformer losses

E_HV High voltage cable losses

E_LV Low voltage cable losses

E_CRAC CRAC energy consumption

E_UPS Energy loss at UPSes which feed servers, network, and storage equipment

E_Net1 Network room energy fed from type 1 unit substitution

Error Analysis

To ensure our PUE calculations are accurate, we performed an uncertainty analysis using the root sum of the squares (RSS) method. Our uncertainty analysis shows that the overall uncertainty in the PUE calculations is less than 2% (99.7% confidence interval). Our power meters are highly accurate (ANSI C12.20 0.2 compliant) so that measurement errors have a negligible impact on overall PUE uncertainty. The contribution to the overall uncertainty for each term described above is outlined in the table below.

Term
Overall Contribution to Uncertainty

E_US1
4%

E_US2
9%

E_TX
10%

E_CRAC
70%

E_UPS
<1%

E_HV
2%

E_LV
5%

E_Net1
<1%