1 Scope
2 References
3 Definitions
3.1 Terms defined elsewhere
3.2 Terms defined in this Recommendation
4 Abbreviations and acronyms
5 Comparative evaluation of energy efficiency of up to 400 VDC systems
5.1 Accuracy and additional measurements
5.2 AC input power factor
5.3 System energy efficiency
5.4 Energy efficiency of ICT equipment PSU
5.5 Comparative energy efficiency of the power feeding system
6 Methodology for evaluating the reliability/availability performance of
up to 400 VDC power feeding systems
6.1 Reliability model for system failure rate and availability
assessment
7 Methodologies for evaluating environmental impact of up to 400 VDC
systems
7.1 Input current total harmonic distortion of the system
7.2 EMC, noise of power feeding system and PSU equipment
7.3 Electrostatic discharge immunity of the DC system and DC PSU
Appendix I – Energy efficiency performance evaluation
I.1 General calculation principle
I.2 ATIS evaluation of rectifier efficiency
Appendix II – Measured efficiency values on AC UPS and up to 400 VDC power
systems
II.1 Test conditions
II.2 Test results
II.3 Analysis of the test results
Appendix III – Reliability/dependability evaluation method
III.1 Reliability performance
III.2 The quantitative approach
III.3 Dependability performance
Appendix IV – Reliability in EMerge Alliance and TGG
Appendix V – Availability calculation
Appendix VI – Examples of availability calculations
VI.1 Availability in Tier
VI.2 Availability for the power feeding systems described in [ITU-T
L.1201]
Appendix VII – Availability comparison between power feeding architectures
Bibliography
Introduction
The architecture of direct current (DC) power systems with an up to 400 VDC ICT
equipment interface [ITU-T L.1200] is recommended in [ITU-T L.1201]. This
Recommendation compliments [ITU-T L.1201] providing a framework for assessing
the performances of up to 400 VDC power feeding systems and savings incurred
when compared to other power feeding systems such as the −48 VDC
power system and the AC UPSs commonly used in ICT sites.
Energy efficiency results obtained by applying this Recommendation can be used
as input for the evaluation of the energy efficiency performance of DC power
systems for up to 400 VDC equipment in data centres and telecommunication
centres. A comparative assessment approach as described in [ITU-T L.1320]
allows an energy efficiency measurement of the up to 400 VDC power feeding system
at the level of the equipment to be compared with the energy efficiency
measurement of other power equipment.
A gain in energy savings of 5% to 20% has been assessed for the up to 400 VDC power
feeding system in many papers and presentations (see Bibliography).
This Recommendation also reports other benefits in terms of reliability,
maintainability, scalability and reduced electric power disturbance when
compared to AC UPS and distribution systems.
This Recommendation provides assessment tools for reliability and recommends
comparative assessment methods.
Gains are also foreseen in terms of battery use and in terms of the
environmental impact and waste reduction with a reduced electronic conversion
stage. As there is no loss in inverters with fewer current ripples, the battery
can last longer or its capacity can be slightly reduced. This Recommendation
recommends using the general life cycle environmental assessment method
described in [ITU-T L.1410] as the basic approach.