When comparing uninterruptible power supplies, many of the leading UPS manufacturers offer systems for datacentre applications that are extremely comparable in terms of operating efficiency. What can make a difference is how they compare from a modular point of view and the ability to scale in environments responding to the rapid growth of server virtualisation.
Most on-line UPS systems operating in double-conversation (traditional) mode will achieve an operating efficiency of around 96-97%. These systems can often be put into an Eco Mode where there operating format mimics a line interactive or standby operation to increase operating efficiency to around 99%. This is an impressive energy saving feature and signals that UPS manufacturers are responding to datacentre market demands for more energy efficient product and also that the manufacturers have almost certainly reached the limit of how much improvement they can make in terms of operating efficiency.
Taken in context a move to 97% on-line UPS efficiency is only actually two or more percentage points improvement from that of legacy UPS systems operating around 94-95% efficiency. To really benefit from these improvements in UPS efficiency, the overall system must be very large and probably from several hundred kVA to more than 1MVA.
For small to medium sized datacentres therefore the energy savings are negligible. Secondly this size of datacentre may be better suited to selecting UPS systems based on their ability to scale and upgrade to meet a more rapidly growing demand for server processing power and storage.
This is what a modular uninterruptible power supply like the Eaton 93PM UPS offers. If we look at a 40kW load installation, a 50kW UPS module could be installed initially. The UPS module would be supplied in a UPS cabinet frame that could be expanded to 150kW total or house a 100kW N+1 or 50kW N+2 configuration at a later date. This system format offers more scalability than a traditional UPS system. They are also sized to sit ‘in-row’ to take up less datacentre floor space and scale vertically as well as horizontally.
Traditionally floor standing UPS systems can achieve the same level of scalability but they have to do this horizontally rather than vertically. The electrical installation can also be more complex as further interconnecting cables must be installed between the standalone UPS systems, under floor or through overhead containment. These cables include not just electrical supply cables but also the communications needed for parallel card synchronization.
Whilst modular UPS can be more expensive than traditional floor standing uninterruptible power supplies, their long term total cost of ownership (TCO) can be lower within rapidly expanding environments that must be right-sized for day one with the ability to scale rapidly.