A contract can fix a PUE of 1.20 [TARGET] and still leave the number undefined, because the clause does not say where the numerator and the denominator are metered. Three candidate points are in play on this project: the utility main meter, the UPS output and the rack PDU output. Roughly 786 kW of electrical loss sits between the outer two [MODELED]. Against a 12,000 kW billable IT denominator [TARGET], that loss is 6.6 PUE points. The finding concerns the definition of the ratio, not the efficiency of any equipment inside it.
No Clause Names Which of Three Points Defines PUE
The same physical plant computes a different PUE at each of those three points. The heat-rejection basis therefore forbids any single PUE number that does not name its metering point. Every PUE conclusion has to travel with the conversion that applies if the point moves.
The load table is built on the most conservative of the three: the utility incomer. That is the only point that also corresponds to the 15,000 kW interconnection cap. If the contract later confirms the numerator at UPS output or at PDU output, the table truncates downward. The reverse cannot be reconstructed.
6.6 PUE Points Is the Same Order as the Route Spread
Divide 786 by 12,000 and the result is 6.6 percent of IT load, which converts one for one into PUE points because the same denominator appears in both expressions [MODELED]. The magnitude is what makes it a design problem rather than a bookkeeping one. A 6.6-point swing is the same order as the difference between the cooling routes still under comparison. A PUE figure quoted without its metering point cannot be used to choose between them.
The 786 kW itself is a stack, not a mysterious remainder: 126 kW of end-of-path loss, 461 kW of UPS conversion, 145 kW of critical-path transformer, 11 kW of mechanical-path transformer, and 43 kW of medium-voltage gear and cable [MODELED]. Moving the meter past any of those rows is a drafting choice, not an efficiency improvement.
Electrical Loss Barely Moved in the Independent Rebuild
An independent rebuild from the mechanical side supplies the check the original figure lacked. Reconstructing the loss schedule row by row across the transformer, UPS and distribution items gives 773 kW in the base column and 926 kW in the conservative column, or 6.4 to 7.7 percent of IT load [MODELED]. Bridged against the original 786 kW that is minus 13 kW and plus 140 kW. Electrical loss is the only line in the schedule that did not move materially as the mechanical design developed, which is what makes it usable as a fixed term while the rest of the schedule is still moving.
Inside that total, UPS double-conversion loss is the largest single non-IT item: 454 kW in the base column and 545 kW in the conservative column [MODELED]. It exceeds the rejection fans. It exceeds mechanical cooling in the base case. Half a point of UPS efficiency moves facility load by about 65 kW [MODELED], which is the same order as the entire non-critical house allowance. The efficiency curve across the part-load band is therefore a higher-priority input to a PUE negotiation than the detail of the cooling scheme. A single full-load efficiency point does not close it.
Two terms are still missing from the bridge. The share of the 773 to 926 kW that leaves through the mechanical cooling system rather than through direct ventilation has not been quantified. That share is the miscellaneous heat that still sits as an open item on the rejection total. If the distribution area is mechanically cooled, the share returns as a second-order increment on mechanical load at roughly one over the coefficient of performance. Facility load closes at 14,391 kW with 609 kW of headroom against the 15,000 kW supply cap [MODELED], so a term of that size does not disappear into the rounding.
Limits and open items
Modelled and not frozen: the 786 kW total, the 773 and 926 kW rebuilds, the 6.4 to 7.7 percent band, the 454 to 545 kW UPS line, the 65 kW efficiency sensitivity, and the facility load closure with its headroom. Each rests on equipment efficiency and loss rates that no supplier has confirmed. The arithmetic above them is reproducible; the inputs beneath them are not verified, and the item-by-item facility load schedule is itself still awaiting verification. [MODELED]
Open: which metering points the contract fixes for numerator and denominator, and specifically whether the 12,000 kW figure is the rack PDU output; the unquantified share of electrical loss rejected through the cooling system; and the weather condition under which any annual figure would be assessed, which on the current record has no site validity and so cannot produce an annual PUE at all. [HOLD]
No PUE value is stated in this note in any form, including ranges and hedged figures. Nothing here is approved, no efficiency is selected, no load schedule is released, and no Engineer of Record has reviewed these quantities.
Which meter the revenue meter sits on
The drafting point falls out of the arithmetic rather than the engineering. A clause that fixes 1.20 without fixing the meter has fixed nothing testable, because the party being measured can satisfy it by choosing the pair of points that excludes 786 kW. A workable clause does not need a tighter target. It needs a named numerator point, a named denominator point, and a stated conversion for the case where operational metering ends up elsewhere. The question worth putting to whoever drafts it is which of the three candidate points the revenue meter will physically sit on.
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Source: K&K Data Service Inc., “786 kW Between PUE Metering Points Moves PUE by 6.6 Points,” https://www.kkdatasvc.com/lab/heat-rejection-and-pue/786-kw-of-electrical-loss-is-6-6-pue-points/.
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