Divide and Conquer: Understanding the Impact of Modular Data Room Design Approach on PUE (Jorge A. Gil)

Overview

Jorge A. Gil's article in the Fall 2024 issue of 7x24 Exchange Magazine (p. 31) models how splitting a 1 MW data room into PODs, each with dedicated power and cooling infrastructure, improves part-load PUE during IT load ramp-up. It is a freely readable expert article. The starting point is that design PUE is reached only at high load, while in the early years of operation the infrastructure runs inefficiently at low load.

In a non-modular room the PUE curve divides into three zones: an inefficiency range at 0-50% of IT load, an 'efficiency limbo' at 50-70% and an efficiency range above 70%, with the best (design) PUE at 100% load. Activating PODs on demand keeps the infrastructure better loaded. The price is 'jump' PUE steps and more equipment to maintain and monitor.

In the case study, a 1,000 kW data room with a design PUE of 1.615 is compared as one room, four 250 kW PODs and eight 125 kW PODs. At 10%, 20% and 25% IT load, the PUE difference between the non-modular and 4-POD designs is 3.59, 1.79 and 1.38. With evenly distributed load, modular ramp-up can save up to 48% energy during early growth.

Activating a new POD creates a temporary 'jump PUE', for example when POD D is activated at 75% load. The article's limit is that it rests on one case study and specific assumptions, so the results should not be transferred numerically to other facilities but read as an indication of direction and size. The related document is ISO/IEC 30134-2 (PUE).

Key points

1. Non-modular design PUE curve: inefficiency range 0-50% IT load, efficiency limbo 50-70%, efficiency range above 70%; best (design) PUE at 100% load.
2. Case study: 1,000 kW data room, design PUE 1.615, compared as one room vs four 250 kW PODs vs eight 125 kW PODs.
3. At 10%, 20% and 25% IT load the PUE difference between non-modular and 4-POD designs was 3.59, 1.79 and 1.38.
4. Modular ramp-up can save up to 48% energy during early growth with evenly distributed load.
5. Activating a new POD creates a temporary 'jump PUE' (for example when POD D is activated at 75% load).
6. Downsides: more infrastructure to maintain, more monitoring and operational readiness needed.
7. Related document: ISO/IEC 30134-2 (PUE).

Using it in design

• Compute and plot PUE versus IT load for phased designs, showing step changes when each POD or block is energized.
• Warn when a single-block design is expected to operate below 50% IT load for years.
• In that case, suggest modular phasing.
• Include the extra maintenance and monitoring burden of the modular option in the cost comparison.

Who should read it

Designers planning power and cooling phasing in data centres that grow in stages, and operations teams managing energy efficiency.

Related standards

• ISO/IEC 30134-2 (PUE)

Publication details

Authors

Jorge A. Gil

Publisher

7x24 Exchange Magazine

Year

2024

Document number

Fall 2024 issue, p. 31

Document language

English

Source type

Industry body

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation