Energy Consumption and Energy Saving Analysis of Air-Conditioning Systems of Data Centers in Typical Cities in China

Overview

The study examines the energy consumption status and saving potential of data-centre air-conditioning systems in seven cities with diverse climates (Xinjiang, Beijing, Jinan, Shanghai, Nanning, Guilin and Haikou), using PUE and cooling load factor (CLF) as indicators. The surveyed mechanically cooled data centres had CLF of 0.4-0.7 and PUE of 1.45-1.85, all above 1.3, with no clear relationship to city climate.

Two retrofit schemes are proposed: a water-side indirect evaporative chiller producing 15 °C water, and an air-side IEC air handler with dry, spray and mixed modes. In the water-side scheme, mode switching depends on outdoor wet-bulb: direct evaporative at Ts ≤ 13 °C; direct + indirect at 13 °C < Ts ≤ 15 °C; indirect + mechanical at Ts > 15 °C; the indirect evaporative chiller produces water 4-6 °C below ambient wet-bulb. For 15 °C chilled water, direct evaporative mode runs 6933 h in Urumqi, 5374 h in Beijing, 4020 h in Shanghai and only 262 h in Haikou, which needs indirect + mechanical cooling for 8112 h. The air-side IEC unit runs in dry mode 5773 h in Urumqi versus 415 h in Haikou, which spends 5997 h in mixed mode with compressor.

The water-system retrofit cut PUE from 1.62 to 1.13 (73.26% cooling energy saving) in Xinjiang and from 1.79 to 1.36 (41.23%) in Hainan; all retrofitted projects came in below 1.36. The air-system retrofit gave PUE below 1.39 everywhere, with the best case Xinjiang, 1.62 to 1.18 (69.26%).

Limits: saving estimates rest on simulation and operating-mode-hour calculation rather than measurement of installed systems, and the saving rate depends on climate and project specifics. The study provides a useful worked example of a climate potential-hours study for evaporative free cooling.

Key points

1. Surveyed mechanically cooled data centres had CLF of 0.4-0.7 and PUE of 1.45-1.85, all above 1.3, with no clear relationship to city climate.
2. Water-side scheme mode switching on outdoor wet-bulb: direct evaporative at Ts ≤ 13 °C; direct + indirect at 13-15 °C; indirect + mechanical above 15 °C; the indirect evaporative chiller produces water 4-6 °C below ambient wet-bulb.
3. For 15 °C chilled water, direct evaporative mode runs 6933 h in Urumqi, 5374 h in Beijing, 4020 h in Shanghai and only 262 h in Haikou, which needs indirect + mechanical cooling for 8112 h.
4. The air-side IEC unit runs in dry mode 5773 h in Urumqi versus 415 h in Haikou, which spends 5997 h in mixed mode with compressor.
5. Water-system retrofit cut PUE from 1.62 to 1.13 (73.26% cooling energy saving) in Xinjiang and from 1.79 to 1.36 (41.23%) in Hainan; all retrofitted projects came in below 1.36.
6. The air-system retrofit gave PUE below 1.39 everywhere; the best case was Xinjiang, 1.62 to 1.18 (69.26%).

Using it in design

• Show evaporative free-cooling feasibility with a potential-hours study that bins the city's hourly wet-bulb distribution against mode thresholds (13 and 15 °C); in a humid climate direct evaporative mode ran only 262 h a year.
• For retrofits of existing mechanically cooled halls, set the PUE target by climate (1.13-1.18 in arid climates, 1.36-1.39 in humid).
• Compare the water-side indirect evaporative chiller and the air-side IEC air handler on the same climate data.

Who should read it

Designers and energy specialists assessing evaporative free-cooling retrofits of existing data centres in China and similar climates.

Document contents

1. 1. Introduction
2. 2. Research Data (2.1 Evaluation indicators, 2.2 Analysis of Research Data)
3. 3. Introduction to Energy Saving Solutions
4. 4. Analyses of Urban Meteorological Characteristics and Operating Time (4.1 Analysis of Climate Characteristics: Urumqi, Beijing, Jinan, Shanghai, Nanning, Guilin, Haikou, summary; 4.2 Operating-mode hours: water systems with indirect evaporative cooling chillers, air systems)
5. 5. Analysis of Energy Saving Potential in Data Centers (5.2 Energy Savings from Air Systems Combined with Evaporative Cooling)
6. 6. Conclusions

Related standards

• GB 50174

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Publication details

Authors

Tiezhu Sun; Xiaojun Huang; Caihang Liang; Riming Liu; Yongcheng Yan

Publisher

Sustainability (MDPI AG)

Year

2023

Volume

15

Issue

10

Pages

7826

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/su15107826

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation