Abstract
Data centers are energy-intensive facilities with substantial low-grade waste heat. High-temperature heat pumps can be critical in boosting the data center's waste heat for district heating, improving the system-level energy efficiency of data centers, and reducing CO2 emissions in district heating. This study built thermodynamic models to assess high-temperature heat pumps with six configurations using low global warming potential refrigerants to supply heat up to 120 °C. The heat pump configurations include single-stage or two-stage cycles with advanced components, such as internal heat exchanger, economizer, flash tank, or parallel compressor. The refrigerants include R1234ze(Z), R1233ed(E), R1224yd(Z), R600, and R600a, and R245fa is used as a reference. A case study was carried out to recover the waste heat from the Frontier high-performance computing data center and provide hot water for district heating at the US Department of Energy's Oak Ridge National Laboratory campus. The optimized performance of high-temperature heat pumps is characterized with various effectiveness of internal heat exchangers, and the operating parameters of economizer or flash tank, as well as their combination. The results show that the configurations of two-stage cycles with internal heat exchanger + flash tank and internal heat exchanger + economizer/parallel-compressor provide the highest coefficient of performance under scenarios of the maximum allowable value and a fixed value (0.3) of the internal heat exchangers’ effectiveness, respectively. R1234ze(Z) and R600a are the most promising refrigerants, considering trade-offs between the coefficient of performance and the volumetric heating capacity. The single-stage cycle with internal heat exchanger + economizer/parallel-compressor using R1234ze(Z) is recommended for utilizing Fronter's waste heat in district heating. A one mega-watt high-temperature heat pump will reduce 33,100–33,200 metric tons of CO2 emission annually, corresponding to 85.4 %–85.6 % of equivalent CO2 emissions from natural gas boilers. This study provides good guidelines for designing and deploying high-temperature heat pumps to support sustainable data centers and decarbonize district heating in the US.
| Original language | English |
|---|---|
| Article number | 114327 |
| Journal | Energy and Buildings |
| Volume | 315 |
| DOIs | |
| State | Published - Jul 15 2024 |
Funding
This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( https://energy.gov/downloads/doe-public-access-plan ). This work was sponsored by the Sustainable ORNL Potential Showcase Project \u201C5600/5700/5800 Complex Sustainability and Decarbonization using Waste Heat Recovery from Oak Ridge Leadership Computing Facility's High Performance Computing Data Center\u201D. We thank ORNL colleagues for their help and support with the work. The thanks also go to Mrs. Hames, Wendy, for her professional technical editing. This work was sponsored by the Sustainable ORNL Potential Showcase Project \u201C5600/5700/5800 Complex Sustainability and Decarbonization using Waste Heat Recovery from Oak Ridge Leadership Computing Facility's High Performance Computing Data Center\u201D. The authors would like to acknowledge the support from the Building Technology Office and the technology manager, Dr. Payam Delgoshaei. The authors thank ORNL colleagues for their help and support with the work. The thanks also go to Mrs. Hames, Wendy, for her professional technical editing.
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| Oak Ridge National Laboratory | |
| Building Technologies Office |
Keywords
- Data center
- District heating
- High-temperature heat pump
- Low-GWP refrigerant
- System configuration
- Waste heat recovery
