UPS systems are a big capital expenditure, so a degree of future-proofing is usually demanded. UPS systems are therefore often specified with a theoretical maximum or future load in mind - think 'follow the sun' - and are often operating at well below capacity. The problem with this is that older UPS systems become less efficient when working at partial capacity. With a traditional big datacentre UPS at really low loads, of less than perhaps 20%, more than a third of the power could be disappearing in the form of heat losses.
In this situation it can make economic sense to upgrade to a high-efficiency UPS or have one or more smaller UPS units operating to fulfil power requirements, switching themselves off as required so power is not wasted. This is the recommendation of the EU Code of Conduct for Data Centres, which adopts modular UPS units as the standard answer to this problem, and means that modular UPS will deliver better than 95% efficiency at loads as low as 20%.
Power and cooling
One of the big areas of inefficiency in datacentres is cooling, with batteries often seen as a particular headache. To ensure that power to IT equipment is never lost, the load is always fed via the UPS. This usually demands intensive cooling and environmental control of the UPS and battery system.
Although the battery bank generates relatively little heat, it is important to maintain it at a controlled temperature. The ideal temperature is between 20°C and 25°C, and this usually involves air-conditioning. The key to minimising air-conditioning costs is to select a high-efficiency UPS system so that heat losses are minimised.