Borehole Thermal Energy Storage: A Long Term Energy Storage Solution
M. Lanahan 1 , Dr. P. Tabares-Velasco 1
1. CSM Department of Mechanical Engineering
Colorado School of Mines, Golden, CO, USA
Introduction & objectives System Design
Trends for Large Scale Solar Assisted GSHP and BTES
References
Acknowledgments
1. Janet Nussbicker-Lux, “The BTES project in Crailsheim (Germany) - Monitoring Results,” presented at the 12th International Conference on Energy Storage, 2012.
2. Michael Lanahan, Dr. Paulo Tabares-Velasco “A Critical Review on the State of Large-Scale Seasonal Thermal Energy”, under review in Energies 02.23.2017.
3. A. Moradi, K. M. Smits, J. Massey, A. Cihan, and J. McCartney, “Impact of coupled heat transfer and water flow on soil borehole thermal energy storage (SBTES) systems:
Experimental and modeling investigation,” Geothermics, vol. 57, pp. 56–72, Sep. 2015.
4. Timothy P. McDowell and Jeff W. Thornton, “Simulation and Model Calibration of a Large-Scale Solar Seasonal Storage System,” presented at the Third National
Conference of IBPSA-USA, 2017.
5. Underground Energy LLC “BTES - Borehole Thermal Energy Storage” Accessed 11/19/2016
6. “90.1 Prototype Building Models- Medium Office | Building Energy Codes Program.” [Online]. Available: https://www.energycodes.gov/901-prototype-building-models-
medium-office. [Accessed: 24-Mar-2017].
7. “OpenStudio | OpenStudio.” [Online]. Available: https://www.openstudio.net/. [Accessed: 23-Jan-2017].
The authors would like to thank Colorado School of Mines for financial support during the research process.
Additionally the authors would like to thank Timothy
McDowell for critical review and advice during the research process.
Contact: Michael Lanahan
E-mail:mlanahan@mymail.mines.edu Phone: +1-541-908-3354
• U-tube pipes carry working fluid, with the pipe/soil interface facilitating heat exchange
• Cycle is reversed and cool liquid extracts heat from the warm soil when additional energy is required
• Ground Source Heat Pumps (GSHP) or direct heat exchange and packaged cooling coil and fan units can be used to extract energy
• GSHP technology provides greater efficiency than standard cycles
• Buildings consume approximately ¾ of the total electricity generated in U. S.
• Energy storage is critical for the smart grid, facilitating higher renewable energy penetration by mitigating the gap between generation and demand.
• Thermal energy typically sees however round trip efficiency then electrical energy.
Objective :
1. Provide an overview of Borehole Thermal Energy Technology (BTES) 2. Provide an implementation example that demonstrates cost and energy
usage reduction
• Thermal energy is stored in the soil
• Heat loss with small surface area to volume ratio
Borehole Thermal Energy Storage (BTES)
• Solar energy is collected using solar thermal panels.
• A working fluid then transfers the energy either to energy storage or end use depending on system & seasonal demand
• Diurnal storage may store energy during the day if it is available in system design
• Soil-based seasonal storage stores excess energy for seasonal periods when solar thermal energy is not readily available
End Uses
• Space Heating – using either fan coil systems or water heating coils
• Space Cooling – using the ground as a heat sink for the heat pump
• Domestic Hot Water – heating hot water for utility end use
Results
Case Study of GSHP Off-Season Purchased Heating
• Electric heating and cooling fan coil HVAC system transitioned to GSHP and BTES system with summer purchased district heating to supplement extracted heat energy
• ASHRAE standard 90.1 Medium Office Building [4980 m
2in Calgary, Alberta [6,7]
Conclusions and Discussion
• BTES with GSHP implementation saves significantly on cooling and heating energy cost
• BTES used in colder climates requires thermal energy input for thermal recitation, this is supported by the literature Further Work
• Integrate diurnal storage
• Integrate solar thermal energy
Conclusions from the Literature
(1) Diurnal and Seasonal storage used in conjunction yields higher system efficiency
(2) BTES requires thermal energy input for sustained efficiency in colder climates (3) BTES computational models with high accuracy and whole building analysis tools have no established link between the two
Energy Flow Diagram
