The Energy-Saving Potential of Air-Side Economisers in Modular Data Centres: Analysis of Opportunities and Risks in Different Climates

Overview

The study examines the feasibility of using outside air for free cooling in modular data centres through an air-side economiser as an alternative to traditional mechanical cooling. The base case is a 90 kW modular data centre, with the model calibrated using OCP PUE values of 1.5 (Dubai) and 1.54 (Stockholm). Dynamic thermal modelling assessed the economiser's efficacy in four distinct climatic zones.

Annual cooling electricity fell by 86% in Stockholm and 76% in San Francisco with the airside economiser. In Dubai and Singapore the economiser case used slightly more electricity than no economiser (+2% and +4%) because of higher mechanical fan energy and extra cooling demand. In Dubai most ambient temperatures lie between 17 °C and 38 °C, so a 24 °C economiser threshold is ineffective much of the time, and daily swings of about 20 °C would cycle the dampers, which calls for adaptive control.

The reviewed literature suggested 15-30% savings for moderate climates with free cooling below 24 °C, well below this model's 76-86%. ASHRAE TC 9.9 guidance suggests that, with proper design and extended temperature and humidity operating zones for IT equipment, outside air could potentially fulfil 100% of cooling needs throughout the year in most climates except humid and tropical zones. The choice of economiser control strategy, such as differential dry-bulb versus enthalpy control, can influence savings.

Limits: a single 90 kW modular design and four cities; results rest on this model's calibration (two OCP PUE values). In hot, humid climates the economiser gives no benefit and can even raise energy slightly.

Key points

1. The base case is a 90 kW modular data centre; the model was calibrated using OCP PUE values of 1.5 (Dubai) and 1.54 (Stockholm).
2. Annual cooling electricity fell by 86% in Stockholm and 76% in San Francisco with the airside economiser.
3. In Dubai and Singapore the economiser case used slightly more electricity than no economiser (+2% and +4%) because of higher mechanical fan energy and extra cooling demand.
4. In Dubai most ambient temperatures lie between 17 °C and 38 °C, so a 24 °C threshold is ineffective much of the time; daily swings of about 20 °C would cycle the dampers, calling for adaptive control.
5. The reviewed literature suggested 15-30% savings for moderate climates with free cooling below 24 °C, well below this model's 76-86%.

Using it in design

• Treat an airside economiser as a strong option in moderate climates (Stockholm 86%, San Francisco 76%); in Dubai and Singapore energy can rise (+2% and +4%).
• In climates with large daily swings (about 20 °C in Dubai) define adaptive control that limits damper cycling, and verify the choice between dry-bulb and enthalpy control.
• Check the economiser threshold (24 °C) against the ambient temperature distribution; do not expect benefit in climates where the distribution mostly sits above the threshold.

Who should read it

Designers assessing airside economiser suitability for modular and containerised data centres in different climates.

Document contents

1. 1. Introduction (1.1 Background, 1.2 Data Centres: Past, Present, and Future)
2. 2. Methodology (2.1 Layout and Construction Materials, 2.2 Modelled, 2.3 Modelled Heat Loads and HVAC System, 2.4 Model Validation)
3. 3. Simulation Results and Analysis (3.2 Simulation Results for Each Location: Singapore, San Francisco, Stockholm, Dubai; 3.3 Analysis of Simulation Results Exploring Energy Saving Potentials for Each Location)
4. 4. Discussion
5. 5. Conclusions

Related standards

• ASHRAE TC9.9 Thermal Guidelines

Read the document

Publication details

Authors

Ali Badiei; Eric Jadowski; Saba Sadati; Arash Beizaee; Jing Li; Leila Khajenoori; Hamid Reza Nasriani; Guiqiang Li; Xin Xiao

Publisher

Sustainability (MDPI AG)

Year

2023

Volume

15

Issue

14

Pages

10777

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/su151410777

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation