SoSo CAD
Research paperPDF2024

Data Center Energy Evaluation Tool Development and Analysis of Power Usage Effectiveness with Different Economizer Types in Various Climate Zones

Buildings (MDPI AG) · Ji Hye Kim, Dae Uk Shin et al.

The authors build DCSim, an early-design PUE tool based on the EnergyPlus algorithms, validate it hour by hour against DesignBuilder, and compare a chilled-water baseline with direct and indirect airside economisers, with and without evaporative cooling, across 14 cities in ASHRAE climate zones.

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Overview

More than 95% of a data centre's total cooling load comes from heat generated by IT equipment, and economisers using outdoor air are among the most effective techniques for year-round cooling demand. The load composition is simple, but dynamic considerations such as weather, system conditions and economiser control make analysis complex. The authors developed the DCSim PUE interpretation tool to address the simplicity of data-centre loads and the complexity of system analysis. It was validated against DesignBuilder v7.0.2.4: hourly equipment power matched with CVRMSE of 0%-9.3% for the baseline and 1.4%-10.75% for the airside economiser, within ASHRAE criteria.

The simulation used a 25 °C cold-aisle setpoint, 23 °C CRAH supply air, a 12 °C CRAH temperature difference and 10/18 °C chilled water supply/return; economiser control locks out outdoor air when outdoor dew point is above 15 °C or dry-bulb exceeds the high limit. In zones 0A and 0B, indirect airside economiser (IASE) or IASE + evaporative cooling (EC) cut annual PUE by about 0.04-0.07 compared with direct (DASE) or DASE + EC. In dry zones (notably 1B, 3B, 4B), adding evaporative cooling cut PUE by about 0.02-0.05; in wet zones, IASE cut PUE by about 0.03-0.07 compared with DASE.

A two-level factorial sensitivity study ranked six cooling-medium temperature parameters: CRAH supply temperature and CRAH temperature difference were the most influential on annual PUE, with delta-T dominating for DASE systems and supply temperature for IASE systems. The most influential parameters were then varied in an uncertainty study.

Limits: DCSim is an early-design tool using a simplified form of EnergyPlus algorithms, and validation was against another simulation tool (DesignBuilder), not a measured facility. The work quantifies which economiser type fits dry and wet zones and how much CRAH setpoints widen the PUE band.

Key points

  1. More than 95% of a data centre's total cooling load comes from heat generated by IT equipment.
  2. Hourly equipment power from DCSim matched DesignBuilder v7.0.2.4 with CVRMSE of 0%-9.3% for the baseline and 1.4%-10.75% for the airside economiser, within ASHRAE criteria.
  3. In zones 0A and 0B, IASE or IASE + EC cut annual PUE by about 0.04-0.07 compared with DASE or DASE + EC.
  4. In dry zones (notably 1B, 3B, 4B), adding evaporative cooling cut PUE by about 0.02-0.05; in wet zones IASE cut PUE by about 0.03-0.07 compared with DASE.
  5. CRAH supply temperature and CRAH temperature difference were the most influential of six factors on annual PUE; delta-T dominates for DASE systems and supply temperature for IASE systems.
  6. The simulation used a 25 °C cold-aisle setpoint, 23 °C CRAH supply air, a 12 °C CRAH temperature difference and 10/18 °C chilled water supply/return.
  7. The economiser control locks out outdoor air when outdoor dew point is above 15 °C or dry-bulb exceeds the high limit.

Using it in design

  • Choose economiser type by climate zone: consider indirect economisers in 0A/0B and wet zones (PUE 0.03-0.07 lower) and adding evaporative cooling in dry zones (0.02-0.05).
  • Tune CRAH supply temperature and delta-T first in design optimisation as the most influential PUE parameters; delta-T dominates for DASE and supply temperature for IASE.
  • At early design, report PUE as a range with setpoint uncertainty rather than a single value.

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Who should read it

Cooling designers and energy modellers selecting economiser type and CRAH setpoints at early design.

Document contents

  1. 1. Introduction
  2. 2. Materials and Methods (2.1 DCSim, 2.2 System Description, 2.3 Economizer Operation Modes, 2.4 Energy Model)
  3. 3. Model Verification
  4. 4. Results and Discussion (4.1 Comparison of Economizer Performance by Climate Zone, 4.2 Sensitivity and Uncertainty Analysis of Cooling Medium Temperature on PUE)
  5. 5. Conclusions

Related standards

  • ASHRAE TC9.9 Thermal Guidelines
  • ASHRAE Guideline 14 (CVRMSE)
  • ASHRAE 90.4

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Publication details

Authors
Ji Hye Kim; Dae Uk Shin; Heegang Kim
Publisher
Buildings (MDPI AG)
Year
2024
Volume
14
Issue
1
Pages
299
Document language
English
Source type
Scientific
Access
Open licence — downloadable
Licence
CC BY 4.0 — share with attribution
Licence evidence
www.mdpi.com
Original licence note

p.1 states the article is open access under the Creative Commons Attribution (CC BY) licence.

Citation

Ji Hye Kim; Dae Uk Shin; Heegang Kim (2024). Data Center Energy Evaluation Tool Development and Analysis of Power Usage Effectiveness with Different Economizer Types in Various Climate Zones. Buildings (MDPI AG). 14(1), 299. https://doi.org/10.3390/buildings14010299

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