Load-Adaptive Operational Control of an Indirect Evaporative Cooling System for Coordinated Energy and Water Use in a Modular Data Center in a Cold Region

Overview

The study builds an annual dynamic model in TRNSYS 18 to coordinate thermal safety with low electricity and water use of modular data centres in cold regions. The heat and mass transfer model of the indirect evaporative cooler was validated against experimental data, with a maximum relative error of 4.5% in outlet temperature. Supply airflow, fresh/return air ratio and spray efficiency were varied at full and partial load while room temperature, cooling electricity, water, PUE, WUE and CUE were tracked.

At full load (2.10 × 10^5 kg/h airflow, fresh/return air ratio 0.8, 95% spray efficiency), room temperature was held at 26.6-27.2 °C. Annual electricity was 7.308 × 10^6 kWh and water 9.93 × 10^7 kg, with PUE 1.3 and WUE 2.4 L/kWh (the abstract gives PUE 1.31, WUE 2.37 and CUE 1.46). That full-load setting exceeds a strict 27.0 °C annual upper bound by 0.2 °C, so the authors call it a near-limit candidate.

At full load, raising airflow from 1.2 × 10^5 to 2.1 × 10^5 kg/h raised annual electricity by 1.0% but water by 74.8%; at partial load (9.0 × 10^4 to 1.2 × 10^5 kg/h) the increases were 0.2% and 33.4%. Reducing the fresh/return air ratio from 0.90 to 0.80 cut annual electricity and water by 29.8% and 12.5%; lowering spray efficiency from 98% to 90% cut them by 25.3% and 8.9%. Going from load rate 0.7 to 1.0 raised annual electricity by 16.2% but water by 74.8% and WUE by 70.6%.

The finding is that airflow is the main lever for thermal safety but carries a large water penalty, while lower air ratios and spray efficiency save both energy and water. Staged control is proposed: airflow follows load rate, spray follows room temperature, and a low fresh/return air ratio is preferred. Limits: a single modular facility and a cold-region climate; results do not transfer directly to other climates.

Key points

1. The IEC heat- and mass-transfer model matched experiments with a maximum relative error of 4.5% in outlet temperature.
2. At full load (2.10 × 10^5 kg/h airflow, fresh/return air ratio 0.8, 95% spray efficiency), room temperature was held at 26.6-27.2 °C; annual electricity 7.308 × 10^6 kWh, water 9.93 × 10^7 kg, PUE 1.3 and WUE 2.4 L/kWh.
3. That full-load setting exceeds a strict 27.0 °C annual upper bound by 0.2 °C, so the authors call it a near-limit candidate.
4. At full load, raising airflow from 1.2 × 10^5 to 2.1 × 10^5 kg/h raised annual electricity by 1.0% but water by 74.8%; at partial load (9.0 × 10^4 to 1.2 × 10^5 kg/h), 0.2% and 33.4%.
5. Reducing the fresh/return air ratio from 0.90 to 0.80 cut annual electricity and water by 29.8% and 12.5%; lowering spray efficiency from 98% to 90% cut them by 25.3% and 8.9%.
6. Going from load rate 0.7 to 1.0 raised annual electricity by 16.2% but water by 74.8% and WUE by 70.6%.

Using it in design

• In IEC control, stage airflow to follow load rate and spray to follow room temperature, and prefer a low fresh/return air ratio.
• Weigh the water penalty of airflow increases (at full load electricity 1.0% against water 74.8%) against thermal-safety gain and report both with PUE and WUE.
• If a strict 27 °C upper bound is required, treat the full-load setting as a near-limit candidate (26.6-27.2 °C) and leave extra margin.

Who should read it

Engineers designing operation control and the energy-water balance of IEC-cooled modular data centres in cold regions.

Document contents

1. 1. Introduction
2. 2. Construction of Evaporative Cooling Systems in Modular Data Centers (2.1 Basic Principles of Evaporative Cooling Systems, 2.2 Construction of Heat and Mass Transfer Model for Evaporative Cooler, 2.3 Load Calculation Study and Simulation Methodology, 2.4 Model Validation)
3. 3. System Performance Evaluation Method
4. 4. Results and Discussion (4.1 The Optimal Design Condition Under Full Load Operation, 4.2 Optimization of Operating Parameters Under Normal Working Conditions: load rate, supply airflow rate, fresh/return air ratio, spray efficiency; 4.3 Determination of Optimal Regulation Method)
5. 5. Conclusions

Related standards

• ASHRAE TC9.9 Thermal Guidelines
• ISO/IEC 30134-9 (WUE)
• GB 50174

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Publication details

Authors

Chengjian Dong; Xiaosong Cheng; Lei Zhao; Dingfan Zhang; Luping Qu; Jie Shen; Junru Geng; Hongqiang Ma

Publisher

Buildings (MDPI AG)

Year

2026

Volume

16

Issue

21

Pages

4404

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/buildings16214404

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation