ups sizing

Power Factor (PF) is the ratio of working power to apparent power, or the formula PF = kW / kVA. A high PF benefits both the customer and utility, while a low PF indicates poor utilization of electrical power.

kW (kilowatts) or Working Power – the “true” or “real” power used in all to perform the work of heating, lighting, motion, server function, etc.

The equipment used in a data center will list its kW rating on the UL listing plate. You should average or keep in context the cumulative power factor of your data center loads to properly size the UPS system.

UPS system internal power loss as well as the additional power required for battery charging. UPS efficiency varies between product models and varies dramatically depending on the loading of the UPS. UPS are rarely run at the operating points where their advertised efficiency is provided. A realistic and sufficiently accurate value for UPS efficiency in a typical installation is 88%. Battery charging is a significant but intermittent power consumer. Under normal operation with a charged battery the battery charging load is negligible. However, when a battery has been partially or completely discharged the battery charging power can be on the order of 20% of the rated UPS load. Although this load only rarely occurs, the generator and service entrance must be sized for this load.

These additional power requirements contribute to the oversized input breakers required for UPS systems upon installation. Load, plus, inefficiency, overload capability, and also the charging of the battery contribute to overall input breaker sizing.

The UPS must be able to handle full load while also charge the battery system post an electrical outage.