Performance and Applicability Analysis of Indirect Evaporative Cooling Units in Data Centers Across Various Humidity Regions

Overview

IEC, which uses natural cooling sources, is a promising technology for cutting data-centre cooling energy; the study asks how adaptable IEC units are in regions of different humidity. The modelled machine room uses 24 °C supply air and 36 °C return air; the heat-transfer core is 60% efficient in dry (FAIHT) mode and 70% in IEC mode. Mode switching is: dry heat exchange when outdoor T ≤ 16 °C; IEC (spray on) when T > 16 °C and wet-bulb ≤ 19 °C; hybrid with compressors when wet-bulb > 19 °C. Annual mode hours, COP, energy and mechanical-cooling demand were compared against packaged air-cooled DX units and a water-cooled chiller system.

Natural cooling (dry plus IEC modes) covered about 97.29% of the year in Urumqi, about 79% in Beijing and about 43% in Shanghai; average annual COP was 7.34, 6.33 and 5.42. In Urumqi the unit's total annual energy consumption was 279,498.77 kWh with 7253.52 kWh of mechanical cooling; in Beijing 339,930.91 kWh with 116,011.34 kWh of mechanical cooling.

Against packaged air-cooled DX units, IEC energy savings were 57.46% (Urumqi), 48.26% (Beijing) and 39.41% (Shanghai). Against a water-cooled chiller system, IEC saved 41.11%, 35.96% and 29.95% of power and 78.26%, 75.01% and 68.75% of water in the three cities. Average annual PUE with the IEC unit was below 1.3 in all three cities, compared with 1.42 for the packaged air-cooled DX system.

Limits: simulation results depend on a specific unit model and the 24/36 °C supply-return assumption; the benefit shrinks as humidity rises. IEC wins on energy everywhere and on water against the water-cooled chiller system, but the advantage narrows in humid regions.

Key points

1. The modelled machine room uses 24 °C supply air and 36 °C return air; the heat-transfer core is 60% efficient in dry (FAIHT) mode and 70% in IEC mode.
2. Mode switching: dry heat exchange when outdoor T ≤ 16 °C; IEC (spray on) when T > 16 °C and wet-bulb ≤ 19 °C; hybrid with compressors when wet-bulb > 19 °C.
3. Natural cooling (dry plus IEC modes) covered about 97.29% of the year in Urumqi, about 79% in Beijing and about 43% in Shanghai; average annual COP was 7.34, 6.33 and 5.42.
4. Against packaged air-cooled DX units, IEC energy savings were 57.46% (Urumqi), 48.26% (Beijing) and 39.41% (Shanghai).
5. Against a water-cooled chiller system, IEC saved 41.11%, 35.96% and 29.95% of power and 78.26%, 75.01% and 68.75% of water in the three cities.
6. Average annual PUE with the IEC unit was below 1.3 in all three cities, compared with 1.42 for the packaged air-cooled DX system.

Using it in design

• Assess an IEC unit by climate: natural cooling covered 97% of the year in a dry climate and 43% in a humid one; check the wet-bulb distribution (19 °C threshold) against project climate data.
• When comparing IEC with water-cooled chillers, report energy savings (30-41%) and water savings (69-78%) together; the benefit narrows in humid regions.
• Define the mode-switching thresholds (16 °C dry, 19 °C wet-bulb) as setpoints in the control logic and include annual mode hours in the design report.

Who should read it

Cooling designers assessing the suitability of indirect evaporative cooling units across humidity regions.

Document contents

1. 1. Introduction
2. 2. Material and Methods (2.2 Location Selection for DC Model, 2.3 Calculation and Analysis of Operating-Mode-Switching Set Values, 2.4 Unit Model Establishment, 2.5 Verification of Unit Model)
3. 3. Results and Discussion (3.1 Analysis of Operating-Mode Hours of IEC Units in Typical Cities: dry Urumqi, moderate-humidity Beijing, high-humidity Shanghai; 3.2 Performance Analysis of a Typical Urban IEC Unit: the same three cities)
4. 4. Comparative Analysis of Different Air-Conditioning Systems in DC (4.1 Comparative Analysis of Energy Consumption of Air-Conditioning Systems)
5. 5. Conclusions

Related standards

• ASHRAE TC9.9 Thermal Guidelines
• GB 50174

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Publication details

Authors

Qian Wei; Jun Lu; Xiaoping Xia; Bin Zhang; Xiang Ying; Leihong Li

Publisher

Buildings (MDPI AG)

Year

2024

Volume

14

Issue

11

Pages

3623

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/buildings14113623

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation