Data Center Chiller Plant: Simulation-based Comparative Control Design Case Study (2022 ASHRAE/IBPSA-USA Building Performance Analysis Conference and SimBuild)
ASHRAE / IBPSA-USA · Milica Grahovac, Paul Ehrlich et al.
A SimBuild 2022 paper uses the OpenBuildingControl toolchain to compare chiller-plant control sequences for a data centre; the ASHRAE Guideline 36-based sequence saves a quarter of annual cooling energy.
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Overview
The paper was presented at the ASHRAE/IBPSA-USA SimBuild meeting and written by Milica Grahovac, Paul Ehrlich, Jianjun Hu and Michael Wetter (DOI 10.26868/25746308.2022.C042, pp. 373-381). It uses the OpenBuildingControl toolchain, with the Control Description Language being standardised as ASHRAE 231P, to compare chiller-plant control sequences for a data centre.
The model is a closed-loop plant of one chiller, a water-side economizer and an evaporative cooling tower serving 27 C supply air in Sacramento, California. A base sequence and an alternative based on ASHRAE Guideline 36 are run. The Guideline 36-style sequence, including condenser-water reset, cuts cooling energy 25% annually and about 18% in a typical summer.
Annual PUE is about 1.3 for the base and 1.29 for the alternative; non-IT, non-cooling loads (UPS, distribution, lighting) are assumed equal to 20% of cooling energy. Condenser-water reset cut tower fan energy about 88% annually (67% in summer), with average tower fan speed at 29%, at the cost of higher chilled-water pump energy. In the sensitivity analysis, raising the supply set point by 2 K increased savings to 28% annually, while lowering it by 2 K reduced savings to 11%. The authors argue that simulating real control sequences should become part of controls delivery. Limit: a single climate and a single plant configuration.
Key points
- Plant: one chiller, water-side economizer and evaporative cooling tower serving a data centre at 27 C supply air in Sacramento, California.
- Alternative (Guideline 36-based) controls cut cooling energy 25% annually and about 18% in a typical summer.
- Annual PUE of about 1.3 (base) and 1.29 (alternative); non-IT, non-cooling loads assumed equal to 20% of cooling energy.
- Condenser-water reset cut tower fan energy about 88% annually (67% in summer), average fan speed 29%, at the cost of higher chilled-water pump energy.
- Sensitivity: raising the supply set point 2 K increased savings to 28% annually; lowering it 2 K reduced savings to 11%.
Using it in design
- Give cooling plant templates a control-sequence attribute (for example Guideline 36 condenser-water reset, economizer modes); it materially changes annual energy.
- Expose supply-air set point sensitivity in the energy model.
- Include the pump energy increase caused by condenser-water reset in the net energy calculation.
- Add simulation-based verification of control sequences before commissioning to the handover criteria.
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Who should read it
Mechanical engineers and energy modellers designing cooling plants and control sequences.
Related standards
- ASHRAE Guideline 36
- ASHRAE Standard 231P (CDL)
- ASHRAE Standard 90.4
Publication details
- Authors
- Milica Grahovac; Paul Ehrlich; Jianjun Hu; Michael Wetter
- Publisher
- ASHRAE / IBPSA-USA
- Year
- 2022
- Document number
- DOI 10.26868/25746308.2022.C042, pp. 373-381
- Event
- ASHRAE/IBPSA-USA SimBuild 2022
- Document language
- English
- Source type
- Standard
- Access
- Free to read
- Licence
- Copyright retained; citation only — the publisher’s terms apply to the original document
Citation
Milica Grahovac; Paul Ehrlich; Jianjun Hu; Michael Wetter (2022). Data Center Chiller Plant: Simulation-based Comparative Control Design Case Study (2022 ASHRAE/IBPSA-USA Building Performance Analysis Conference and SimBuild). ASHRAE / IBPSA-USA. DOI 10.26868/25746308.2022.C042, pp. 373-381. ASHRAE/IBPSA-USA SimBuild 2022. https://publications.ibpsa.org/conference/paper/?id=simbuild2022_C042
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