Enterprise
n Load: When choosing a large UPS system, understand the need of electrical load and its dynamic response. This has to be matched to the capacity of UPS. UPS vendors specify VA (volts * amperes) and watts ratings to indicate the maximum amount of power that it can supply to the loads. The wattage ratings listed on an equipment like computer does not accurately represent the amount of power it consumes. One should either measure actual power drawn for buying a compatible UPS capacity or select a UPS with a VA rating that significantly exceeds (approx. double) the wattage rating on the equipment.

However with the advent of new technology, there has been significant improvement in power characteristics of most of servers in computer room. These servers are equipped with Power Factor Corrected Switch Mode Power Supply (PFC SMPS) which draw sine wave current with almost unity power factor.

n Hardware/Software: Look at the optional hardware and software or other features that the vendor provides before buying.

For example, if the UPS is supporting a group of servers, a communication software with ability to close applications running on each server and to ensure its safe shut down might be an essential feature.

n Standards’ Compliance: Look for standard compliance. To meet these standards defined by IEC, UPSs are typically subjected to various tests.

n Compare Basic Specs: There are five basic specifications. Compare this for different models.

• Maximum output load inrush current capacity (expressed in amps and time duration—more the better)
• Transient voltage surge suppression capability (expressed in joules—more the better)
• Output voltage tolerance and battery recharge time (faster is better). The output voltage tolerance is important than the response or recovery time, because the IT equipment have wide voltage range and till the time voltage is within the band of +/-5%, the recovery time does not matter
• Number of AC outlets/sockets (more is better).

n Battery Life: Compare battery backup times at specified watts output (how long the UPS will keep running following the mains power failure while supplying the rated watts output).

n Efficiency: When the UPS is operating from battery, the efficiency of the inverter determines the battery backup. When the UPS is operating from the mains, power is lost as heat inside the UPS.

n Cost: Besides the cost of the product, implementation cost, room cost, operational cost (electricity charges), and generator backup for prolonged power cuts, where batteries cannot be stretched, need to be taken into account. Also look at the cost of support and AMC.

n Vendor Selection: Ask about the vendor’s warranty terms and conditions and on-site service options. Battery replacement is quite expensive in comparison to the UPS purchase cost. Opting for on-site service options provided by the UPS vendor will free the IT staff.