Comparative study on the thermal performance and economic efficiency of vertical and horizontal ground heat exchangers

Abstract

The ground-coupled heat pump is a shallow geothermal exploitation method taking soil as the thermal energy source. The ground heat exchanger is an important component of this system, which includes vertical or horizontal configurations. However, to the best of our knowledge, few studies exist involving the comparison of thermal performances and installation costs of two heat exchanger types considering the influence of ground climate, which makes the selection of heat exchanger configuration challenging for a specific field application. Hence, a 3-dimensional numerical model considering the variations of atmospheric conditions and soil water content is constructed in this paper. Based on this model, the thermal performances and economical efficiencies of vertical and horizontal ground heat exchangers are compared. The results indicate that the thermal performance difference between the two heat exchangers is greater in winter than in summer. The thermal performance is hardly influenced by the injection mass flow rate, while it is considerably affected by the length of heat exchanger. The thermal power rises linearly with the increase in heat exchanger length, and the increment of the vertical ground heat exchanger is higher. In addition, when the heat exchanger length is shorter than 40 m, the installation cost and thereby the total cost of the horizontal ground heat exchanger is considerably higher. With regard to both the thermal performance and economic efficiency, a vertical ground heat exchanger is only recommended when installing a single shallow ground heat exchanger.

Document Type: Original article

Cited as: Cui, Q., Shi, Y., Zhang, Y., Wu, R., Jiao, Y. Comparative study on the thermal performance and economic efficiency of vertical and horizontal ground heat exchangers. Advances in Geo-Energy Research, 2023, 7(1): 7-19. https://doi.org/10.46690/ager.2023.01.02

References

Bear, J. Dynamics of Fluids in Porous Media. New York, USA, Elsevier Scientific Publishing, 1972.

Chalhoub, M., Bernier, M., Coquet, Y., et al. A simple heat and moisture transfer model to predict ground temperature for shallow ground heat exchangers. Renewable Energy, 2017, 103: 295-307.

Chen, X., Buchberger, S. G. Exploring the relationships between warm-season precipitation, potential evaporation, and “apparent” potential evaporation at site scale. Hydrology and Earth System Sciences, 2018, 22(8): 4535-4545.

Chen, S., Ding, B., Gong, L., et al. Comparison of multi-field coupling numerical simulation in hot dry rock thermal exploitation of enhanced geothermal systems. Advances in Geo-Energy Research, 2019, 3(4): 396-409.

Choi, W., Ooka, R., Nam, Y. Impact of long-term operation of ground-source heat pump on subsurface thermal state in urban areas. Sustainable Cities and Society, 2018, 38: 429-439.

Churchill, S. W. Friction-factor equation spans all fluid-flow regimes. Chemical Engineering Journal, 1977, 84: 91-92.

Cole, R. J. The longwave radiation incident upon inclined surfaces. Solar Energy, 1979, 22(5): 459-462.

Congedo, P. M., Colangelo, G., Starace, G. CFD simulations of horizontal ground heat exchangers: A comparison among different configurations. Applied Thermal Engineering, 2012, 33: 24-32.

Dada, M., Benchatti, A. Assessment of heat recovery and recovery efficiency of a seasonal thermal energy storage system in a moist porous medium. International Journal of Heat and Technology, 2016, 34(4): 701-708.

Dietrich, O., Fahle, M., Seyfarth, M. Behavior of water balance components at sites with shallow groundwater tables: Possibilities and limitations of their simulation using different ways to control weighable groundwater lysimeters. Agricultural Water Management, 2016, 163: 75-89.

Gosselin, J. S., Raymond, J., Gonthier, S., et al. Nanocomposite materials used for ground heat exchanger pipes. Paper Presented at IGSHPA Technical/Research Conference and Expo 2017, Denver, Colorado, 14-16 March, 2017.

Habibi, M., Hakkaki-Fard, A. Evaluation and improvement of the thermal performance of different types of horizontal ground heat exchangers based on techno-economic analysis. Energy Conversion and Management, 2018, 171: 1177-1192.

Hein, P., Kolditz, O., Görke, U. J., et al. A numerical study on the sustainability and efficiency of borehole heat exchanger coupled ground source heat pump systems. Applied Thermal Engineering, 2016, 100: 421-433.

Javadi, H., Ajarostaghi, S. S. M., Pourfallah, M., et al. Performance analysis of helical ground heat exchangers with different configurations. Applied Thermal Engineering, 2019, 154: 24-36.

Kayaci, N., Demir, H. Comparative performance analysis of building foundation ground heat exchanger. Geothermics, 2020, 83: 101710.

Kazemi, H., Ehyaei, M. A. Energy, exergy, and economic analysis of a geothermal power plant. Advances in Geo-Energy Research, 2018, 2(2): 190-209.

Kim, M. J., Lee, S. R., Yoon, S., et al. Evaluation of geometric factors influencing thermal performance of horizontal spiral-coil ground heat exchangers. Applied Thermal Engineering, 2018, 144: 788-796.

Kong, X. R., Deng, Y., Li, L., et al. Experimental and numerical study on the thermal performance of ground source heat pump with a set of designed buried pipes. Applied Thermal Engineering, 2017, 114: 110-117.

Lin, J., Nowamooz, H., Braymand, S., et al. Impact of soil moisture on the long-term energy performance of an earth-air heat exchanger system. Renewable Energy, 2020, 147: 2676-2687.

Lin, Z., Liu, K., Liu, J., et al. Numerical model for geothermal energy utilization from double pipe heat exchanger in abandoned oil wells. Advances in Geo-Energy Research, 2021, 5(2): 212-221.

Monteith, J. L. Evaporation and environment. Symposia of the Society for Experimental Biology, 1965, 19: 205-234.

Mualem, Y. A new model for predicting the hydraulic conductivity of unsaturated porous media. Water Resources Research, 1976, 12(3): 513-522.

Muther, T., Syed, F. I., Lancaster, A. T., et al. Geothermal 4.0: AI-enabled geothermal reservoir development-current status, potentials, limitations, and ways forward. Geothermics, 2022, 100: 102348.

Nikoosokhan, S., Nowamooz, H., Chazallon, C. Effect of dry density, soil texture and time-spatial variable water content on the soil thermal conductivity. Geomechanics and Geoengineering, 2016, 11(2): 149-158.

Pu, L., Xu, L., Qi, D., et al. Structure optimization for horizontal ground heat exchanger. Applied Thermal Engineering, 2018, 136: 131-140.

Qi, L. Application manual of charge standard for engineering investigation and design. Beijing, China Market Publishing House, 2018. (in Chinese)

Shi, Y., Cui, Q., Song, X., et al. Study on thermal performances of a horizontal ground heat exchanger geothermal system with different configurations and arrangements. Renewable Energy, 2022, 193: 448-463.

Shi, Y., Song, X., Li, G., et al. Numerical investigation on heat extraction performance of a downhole heat exchanger geothermal system. Applied Thermal Engineering, 2018, 134: 513-526.

Shi, Y., Song, X., Wang, G., et al. Numerical study on heat extraction performance of a multilateral-well enhanced geothermal system considering complex hydraulic and natural fractures. Renewable Energy, 2019a, 141: 950-963.

Shi, Y., Song, X., Wang, G., et al. Study on wellbore fluid flow and heat transfer of a multilateral-well CO2 enhanced geothermal system. Applied Energy, 2019b, 249: 14-27.

Song, X., Shi, Y., Li, G., et al. Numerical simulation of heat extraction performance in enhanced geothermal system with multilateral wells. Applied Energy, 2018, 218: 325-337.

Song, X., Shi, Y., Li, G., et al. Heat extraction performance simulation for various configurations of a downhole heat exchanger geothermal system. Energy, 2017, 141: 1489-1503.

Sun, D., Li, Q. Analysis on the performance-price ratio of the backfill of ground source heat pump in Tai’an area. Technology Innovation and Application, 2013, 36: 10. (in Chinese)

Tang, F., Nowamooz, H. Factors influencing the performance of shallow borehole heat exchanger. Energy Conversion and Management, 2019, 181: 571-583.

Tang, F., Nowamooz, H. Outlet temperatures of a slinky-type horizontal ground heat exchanger with the atmosphere-soil interaction. Renewable Energy, 2020, 146: 705-718.

Van Genuchten, M. T. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, 1980, 44(5): 892-898.

Yang, P., Xu, R., Wang, F., et al. Numerical simulation and experimental validation on the heat transfer characteristics of horizontal spiral coil ground heat exchanger. Journal of Engineering Thermophysics, 2021, 42(8): 2122-2131. (in Chinese)

Zhang, X., Hu, Q. Development of geothermal resources in China: A review. Journal of Earth Science, 2018, 29(2): 452-467.