Feasibility Analysis of Indirect Evaporative Cooling System Assisted by Liquid Desiccant for Data Centers in Hot-Humid Regions

Overview

In hot, humid regions, energy demand is largely driven by the air conditioning needed to maintain suitable operating temperatures. The study proposes a novel multi-stage IEC system with a liquid desiccant in the primary air channel: the first stage uses a liquid-desiccant IEC (LD-IEC) for dehumidification and the second stage uses the treated air as secondary air to enhance cooling. The model was validated against published data and run through a parametric study of inlet air state, solution concentration and mass flow ratio.

Findings: the first-stage LD-IEC lowers the wet-bulb temperature of the ambient air, enhancing the second-stage IEC. Higher ambient temperature, relative humidity and circulated air velocity reduce the temperature drop, while higher solution concentration and circulated air temperature increase it. Cooling performance improves as the mass flow ratio rises to 0.8 but falls at 0.9, so an optimum exists and must be chosen at design stage. Desiccant solution concentration is limited to 0.20-0.40 to avoid crystallisation, with solution temperature in the 20-50 °C range.

In the Hong Kong case study, the multi-stage LD-IEC improved the air temperature drop by 72.7% compared with a single IEC. With a 25 °C supply-air threshold, supplementary mechanical cooling hours fell from 5092 h to 31 h per year.

Limits: desiccant regeneration energy and economics are left for future work, so the benefit is shown for cooling performance only, not total energy or cost. The model was validated against published data, not site measurements of an installed system.

Key points

1. In the Hong Kong case study, the multi-stage LD-IEC improved the air temperature drop by 72.7% compared with a single IEC.
2. With a 25 °C supply-air threshold, supplementary mechanical cooling hours fell from 5092 h to 31 h per year.
3. Cooling performance improves as the mass flow ratio rises to 0.8 but falls at 0.9, so an optimum exists and must be chosen at design stage.
4. Higher ambient temperature, relative humidity and circulated air velocity reduce the temperature drop; higher solution concentration and circulated air temperature increase it.
5. Desiccant solution concentration is limited to 0.20-0.40 to avoid crystallisation, with solution temperature in the 20-50 °C range.

Using it in design

• Where plain IEC falls short in a hot-humid climate (high wet-bulb), consider a liquid-desiccant pre-stage; in the Hong Kong example supplementary mechanical cooling fell from 5092 to 31 h.
• Optimise the mass flow ratio at design stage (around 0.8, performance drops at 0.9) and keep solution concentration in the 0.20-0.40 range to avoid crystallisation.
• Calculate desiccant regeneration energy and economics separately; the study did not assess them.

Who should read it

Cooling designers and researchers applying or investigating indirect evaporative cooling in hot-humid regions.

Document contents

1. 1. Introduction
2. 2. Literature Review
3. 3. Methodology (3.1 System Configuration, 3.2 Model Establishment: IEC model, LD-IEC model; 3.3 Model Solution and Grid Independence Monitoring, 3.4 Model Validation)
4. 4. Results (effect of mass flow ratio, case study, 4.8 Discussions)
5. 5. Limitations and Future Works
6. 6. Conclusions

Related standards

• ASHRAE TC9.9 Thermal Guidelines

Read the document

Publication details

Authors

Wenchao Shi; Xiaochen Ma; Yunran Min; Hongxing Yang

Publisher

Sustainability (MDPI AG)

Year

2024

Volume

16

Issue

5

Pages

2011

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/su16052011

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation