We wrote earlier in the week about issues in using PUE (power usage effectiveness) as a requirement in multi-tenant data center contracts, which a growing number of end users are including in requests for proposal for colocation.
ASHRAE (the American Society of Heating, Refrigerating, and Air Conditioning Engineers) apparently agrees. The group had been evaluating the best way to measure energy efficiency in data center environments, and an original draft standard required specific levels of PUE efficiency. But making PUE levels mandatory garnered significant pushback in the review process, resulting in PUE being dropped from consideration as metric of choice.
The most recent draft, available for review and comment here, has replaced PUE with Design MLC (mechanical load component). Design MLC is the sum of all cooling, fan, pump, and heat rejection design power divided by the data center ITE (information technology equipment) design power.
ASHRAE standards are not mandatory in and of themselves, but many local officials rely on the standards in building inspection and permitting. Reliance on ASHRAE at the local level is sensible given the extensive process that takes place to set the standards, as seen in the process that has led to PUE being dropped from the standard.