UPS Selection Criteria: What to Specify
Selecting a UPS is more than choosing a kVA rating. These are the items a complete specification covers, with links to how each is decided.
The specification checklist
| Criterion | What to settle |
|---|---|
| Capacity | Load, losses, growth, kW and kVA, output power factor. See UPS sizing example |
| Topology | Standby, line-interactive or double-conversion. See UPS topologies |
| Redundancy | N+1, 2N or block redundant, matching the tier target. See redundancy explained |
| Efficiency | At the expected loading, including any eco-mode and its trade-offs |
| Batteries | Chemistry, autonomy and footprint. See battery sizing and lithium-ion vs VRLA |
| Input characteristics | Harmonic distortion and input power factor. See harmonics |
| Bypass | Static and maintenance bypass arrangement |
| Generator compatibility | Behaviour on generator supply. See generator sizing |
| Scalability | Modular growth without shutting down the load |
| Monitoring | Protocols and integration with the facility monitoring system. See DCIM |
| Service | Support, spares and response times |
| Standards | The applicable UPS performance standard (IEC 62040 series) and test evidence |
How to use it
- Size the capacity and redundancy first, since they decide the module count.
- Write the specification so that vendors quote the same basis: load, power factor, efficiency points and autonomy.
- Compare total cost of ownership over the system's life, not only the price.
- Check factory test and witness requirements. See FAT, SAT and IST.
Run your numbers in the UPS sizing calculator.
Written by the Vision Matrix Institute editorial team. Worked examples use stated, illustrative assumptions; check them against your project data, the applicable standards and manufacturer datasheets before use.
Frequently Asked Questions
What are the key UPS selection criteria?
Capacity (kW and kVA) and output power factor, topology, efficiency at the expected load, redundancy arrangement, battery type and autonomy, input harmonics and power factor, bypass arrangement, scalability, monitoring and service support.
Should I size by kW or kVA?
Both. Size from the load in kW, check kVA, and confirm the UPS's rated kW at the load power factor from the datasheet.
Why does efficiency at part load matter?
UPS systems often run well below their rating in redundant configurations, so efficiency at the expected load, not at full load, decides running cost.
What about service?
Maintenance support, spare parts availability and response times matter over the life of the system and should be part of the selection.
Want to learn this properly?
This topic is covered in depth in our Electrical Design – Data Center Specialist program.
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