Why Is Everyone Picking on Electrical?

The old joke used to be because we can and often do.

Don’t get me wrong. This is not about the age-old argument about electrical vs. mechanical. It’s about looking at the entire building and its energy footprint in parcels, then summarizing them into a logical infrastructure. This is “tail piped” right into your PUE or DCiE expectation and results.

As we continue our journey and discussion on high-availability with uncompromised high-efficiency, I have noticed a tendency to focus on the utilization and conversion of power only. What hasn’t been addressed is the mechanical system, and the entire energy footprint for the building. While current thinking has been directed toward removing transformation steps (whether that be isolating or voltage transition) as well as the IT loads themselves. And what we have seen from mechanical has been more system selection than operation.

In previous blogs, we’ve made the comment that you pick up about 2% in electrical efficiency every time you remove a transformation step. There are a couple of caveats you have to honor here. First, this savings is only on the electrical input to the UPS. The pickup on the mechanical system is only made up when you render more efficient (and therefore reject less heat) in the IT platforms. While we have seen significant gains in the efficiency of IT loads, much is not made of where we can pick up mechanical efficiency on design-day conditions.

Let’s take a look where your power typically flows in the data center:

So, if you look at the electrical system losses in a traditional data center, they are broken up into 4 families:
· Substation transformer from the Utility distribution voltage to your service voltage.
· UPS input filter and isolation transformers.
· UPS output transformers and transformers on the bypass systems, if required.
· Raised floor utilization voltage (208/120V) transformers or PDUs.

At your best case for double-conversion static UPS with 208/120V IT service, you may chop the output transformer. With a 400/230V system, you would drop the PDU transformer, resulting in a ½ reduction in losses or about 4%. The 15% nominal loss starting point also includes the feeders and other systems, which can’t be eliminated. We feel that your best efficiency improvement electrically is a 5% pickup for the double –conversion box not running in an economy mode.

As a side note, a double-conversion UPS with input and output transformers versus a rotary or delta-conversion static UPS offers a 92-94% versus a 94-97% efficiency comparison for similar loads. This gain is the lack of input or output coil, depending on the technology. It’s the same argument as above. And you have to make sure you compare on-line (inverter on) to off-line (inverter-off) operation.

While not a concrete rule, the mechanical cooling plant and ventilation system consume 30-40% of the total power in the building, depending on the climate and mechanical plant configuration. My observation is that most mechanical systems aren’t very well-tuned when addressing the kW/ton or kW/CFM that result from the system. This is not a comment on the quality of the project’s air or water balance or the capabilities of the mechanics assigned to the site. It’s more a comment that this level of optimization takes a very skilled engineer and contractor to pull off. And it does not mean you have to change the design – it’s all about how you run the design.

Our point here is that we have seen operators modify chiller intake condenser water temperature, adjust drives and employ a host of Jedi-like mechanical skills resulting in an increase in output CFM and tonnage of the chiller plant by as much as 20%, without an increase an input kW. Like redundant electrical system, some of this was simply operating systems at their optimal load points (we discussed this a few blogs back electrically when examining UPS efficiency and redundancy). What this means is:

· The data center is a symbiotic building that demands a holistic approach.
· Your base building mechanical systems may compromise or enable your long-term energy strategy.
· Mechanical systems need to stay in optimal operating bands to achieve the highest-energy efficiency.

Same rules, different system.

Finally, site selection also has a lot to do with mechanical system efficiency. If you are presented with a site with proper wet bulb and outside air characteristics, this can reduce your overall cooling plant side, or allow you to run on outside air (with proper filtration) exclusively. In northern Europe of parts of the US, you can simply operate on outside air most of the year (with the caveat of proper filtration and humidity control).

And honestly, I really do like mechanical.