Everyone knows which energy hogs to blame for those high energy bills in the data center, right? Computers, cooling them, lights and so on. We switch them on, they work, we can see lights blinking and we know energy is being used. But those smart data center energy efficiency guys have to look beyond the obvious. They have to capture all energy usage. Having berated the IT manager and the infrastructure operations teams for their energy usage he turns towards the "sparks," yes, the electrical engineer, responsible for the electrical distribution system and major components such as transformers and uninterruptible power supplies (UPS). And suddenly it's not so clear as to how much energy the electrical side of the house is using.
Do electrical distribution systems really consume energy? Well, yes they do! Typically the energy distribution system has built-in inefficiencies, and energy is burnt there. It gets worse. Energy is lost in the form of heat, which in turn requires more cooling from the air-handling units to cover its effect.
Power losses from transformers, switchgear, UPS, PDUs and ultimately IT equipment all create heat through distribution losses, and at the back end of that, the utility. While having redundancy built in through varying power distribution paths increases IT availability, albeit at varying loads, it actually decreases systems efficiency from the electrical systems perspective, which because they're distributed, are running at partial load. So the smart energy efficiency guy will look at those elements that have the biggest influence on system efficiency:
- UPS module efficiency
- Part load efficiencies
- System modularity
- System topology
- Cooling load based on electrical system losses
When designing data centers today, it's no longer the pure domain of IT requiring the highest level of redundancy or some kind of prediction as to future IT load requirement, the CFO requires that the data center needs to be cash-efficient, well, as cash efficient as it can be. IT and facilities, crossing the organizational void, have a common goal in terms of energy usage. Part of their bonuses may depend on it! But while everyone seems to focus on the mechanical aspects of cooling, there seems to be less focus on the electrical aspects of power distribution. And that's why there needs to be more effort to make the electrical engineer the coolest guy in the room.
Here's some tips
- Have the mechanical guy work with the electrical guy to capture the thinking on UPS. Size, type and efficiency.
- Model different loading percentages on the UPS. Logic suggests that full redundancy will be more power hungry, but there's a significant impact on these behavioral curves based on loading, so power hungry may also mean more power efficient too.
- Calculate IT load requirements to mimic actual operating load, not nameplate values
- Account for electrical equipment beyond UPS; transformers, generators, switchgear, power distribution units and distribution wiring. Based on the operating topology there will be a trade-off between efficiency and reliability. Where is that optimal point for you based on your IT load?
Estimate heat generation from system losses and build in to the overall cooling topology, again based on variable loads
Everyone seems to have learned the mantra of lowering PUE, but don't always recognize that losses from the electrical systems negatively impact the PUE value as extra cooling is required to address the heat generation from the loss.
Often too much emphasis to reduce the PUE is placed on mechanical inefficiencies, when in reality it's the electrical guy that's not cool.