Analysis of influence of pipe group arrangement and heat exchanger type on operation performance of the ground source heat pump
Introduction
The ground source heat pump system (GSHPS), because of its higher environmental protection value and reliable operation, can arguably be considered one of the most sustainable and efficient technologies in the heating and air conditioning industry (Jin et al., 2020; Nguyen, 2021). It can save 40% energy consumption in comparison with conventional air-conditioning systems (Xu et al., 2021). Ground heat exchangers (GHEs) are the crucial parts of the GSHPS (Noorollahi et al., 2018). The arrangement of pipe group and the type of GHEs are important engineering design factors that affect the operation performance of the GSHPS, and many researchers have carried out research on them.
In the installation process of GHEs, reasonable arrangement of pipe group will not only improve the performance of the GSHPS, but also save the floor space, so many researchers have focused their attention on this (Beck et al., 2013; Hecht-Méndez et al., 2013; Zhang et al., 2015). Choi et al. (Choi et al., 2013) examined the effects of direction and rate of groundwater seepage on the performance of GHEs with different arrangements by using a two-dimensional coupled heat conduction-advection model. The results showed that the performance of GHEs with L and single line type arrangements (non-square rectangular arrangement) was noticeably influenced by the direction and rate of groundwater seepage. Gultekin et al. (Gultekin et al., 2019) established the models of GHEs with 1 × 64, 2 × 32, 4 × 16 and 8 × 8 (width × length) arrangements respectively, and compared the thermal performance of GHEs under different aspect ratios (width divided by length) of geometric arrangement. They found that the smaller the aspect ratio is, the weaker the heat interference between GHEs is, and the larger the unit heat transfer rate of GHEs is. Li et al. (Li et al., 2017) introduced a GSHPS model considering groundwater seepage, and studied the influence of the arrangement of pipe group on the performance of the GSHPS. The results indicated that increasing the number of GHEs in the downstream region of seepage could improve the performance of the system. Kurevija et al. (Kurevija et al., 2012) established the pipe group model of 7 × 6 and 21 × 2 arrangements, and carried out numerical simulation. It was found that under the heating peak load condition, the average working fluid temperature with 21 × 2 arrangement is 2.70 °C higher than that with 7 × 6 arrangement.
The change of type of GHEs will change the heat exchange area between GHEs and the soil, and then affect the thermal performance of GHEs (Javadi et al., 2019; Zarrella et al., 2017). Zhao et al. (Zhao et al., 2016) established a transient 3D heat transfer model for the interactions between the ground and the circulating fluid, and conducted a comparative analysis of the heat transfer processes for three types of the ground heat exchanger (single-U, W and spiral types). Numerical results showed that the spiral type heat exchanger had better thermal performance than the single-U and W type heat exchangers in terms of long-term and short-term thermal loads. Luo et al. (Luo et al., 2016) investigated the thermal efficiency of the ground heat exchanger with different types by conducting thermal performance tests. They found that spiral and double-W type heat exchangers had similar thermal performance, and the double-U type heat exchanger had the worst heating and cooling performance, accounting for 67 ∼ 69% of the thermal efficiency of spiral and double-W type heat exchangers. Li et al. (Li et al., 2020) assessed the influence of the type of GHEs on the heat transfer effect of GHEs through experiments. The results showed that the heat transfer fluxes per meter of casing and double-U type heat exchangers were 20.3% and 21.8% higher than that of single-U type heat exchangers in order. Sivasakthivel et al. (Sivasakthivel et al., 2017) compared the effectiveness of single-U and double-U type heat exchangers through experimental study. The results showed that the average effectiveness of the single-U type heat exchanger in heating and cooling mode was less by 26% and 30% respectively compared to the double-U type heat exchanger for the same operation condition. Mehrizi et al. (Mehrizi et al., 2016) used FLUENT software to simulate the outlet temperature of the ground heat exchanger with different types under cooling mode. They found that the outlet temperature of the W-shaped-all round type heat exchanger (six single-U type heat exchangers in series) was roughly 1.526 °C and 0.888 °C lower than that of single-U and W type heat exchangers respectively.
In a word, the arrangement of pipe group and the type of GHEs will have different degrees of influence on the performance of the GSHPS. However, most of the previous researchers only consider the groundwater seepage when they study the influence of pipe group arrangement on the system performance (Choi et al., 2013; Li et al., 2017), and do not take into account the heat and moisture transfer and freezing of soil, which will make the heat transfer environment of soil very different between simulation and reality (Gao et al., 2020; Wu et al., 2020). Furthermore, most researchers do not consider any one of the factors in heat and moisture transfer, groundwater seepage and soil freezing during the process of studying the influence of heat exchanger type on the GSHPS (Zhao et al., 2016; Luo et al., 2016; Li et al., 2020; Sivasakthivel et al., 2017; Mehrizi et al., 2016), and most of the heat exchanger models they established are the single hole (Zhao et al., 2016; Luo et al., 2016; Sivasakthivel et al., 2017; Mehrizi et al., 2016), which will make the heat transfer process of GHEs studied by them very different from that in actual engineering. To make the soil environment of heat exchange with GHEs closer to the actual working condition, a three-dimensional dynamic simulation platform of the GSHPS considering heat and moisture transfer, groundwater seepage and freezing simultaneously has been established in the previous work, which has a total of 9 boreholes (H. Zhang et al., 2021). Based on the established simulation platform, this paper studies the impact of above two engineering design factors on the operation performance of the GSHPS, hoping to provide some suggestions for the future engineering design of GHEs.
Section snippets
Establishment and verification of the model
Fig. 1 shows the three-dimensional geometric model of buried pipe group built by COMSOL Multiphysics software. The model is composed of unsaturated and saturated soil regions. It is assumed that the volume of unsaturated and saturated regions is the same. This assumption can make the soil heat transfer characteristics of unsaturated and saturated regions not affected by the depth of unsaturated and saturated regions. Heat and moisture transfer and freezing are considered in unsaturated soil
Results and discussion
During the operation process of the GSHPS, the arrangement of pipe group will affect the close-packed degree of buried pipes, and then affect the thermal performance of GHEs and the floor area of the GSHPS. The type of GHEs will affect the heat transfer area between circulating medium in pipes and soil, and then affect the heat transfer effect of GHEs. This paper selects an office building in Harbin as the research object to study the influence of these two engineering design factors on the
Conclusions
Based on the built three-dimensional dynamic simulation platform of the GSHPS, this paper studies the influence of pipe group arrangement and heat exchanger type on the operation performance of the system when heat and moisture transfer, groundwater seepage and freezing exist at the same time. The conclusions are as follows:
- (1)
The influence of moisture transfer on the heat transfer effect of GHEs with different arrangements is smaller. At the distance of 0.0 m from the center of #5 borehole, the
CRediT authorship contribution statement
Hongzhi Zhang: Conceptualization, Methodology, Software, Data curation, Writing – original draft, Validation, Writing – review & editing. Zongwei Han: Conceptualization, Methodology, Writing – review & editing, Supervision. Mingzhen Ji: Supervision, Validation, Writing – review & editing. Gui Li: Validation, Writing – review & editing. Xinlu Cheng: Writing – review & editing. Ziwei Yang: Writing – review & editing. Lingyan Yang: Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors gratefully acknowledge the support from the Natural Science Foundation of China (grant No.51778115) and the Fundamental Research Funds for the Central Universities (grant No. N182502043).
References (25)
- et al.
Thermal performance analysis of multiple borehole heat exchangers in multilayer geotechnical media
Energy
(2020) Determination of the ground source heat pump system capacity that ensures the longevity of a specified ground heat exchanger field
Renew. Energy
(2021)- et al.
Hybrid ground source heat pump system for overcoming soil thermal imbalance: a review
Sustainable Energy Technol. Assessments
(2021) - et al.
The effects of ground heat exchanger parameters changes on geothermal heat pump performance – A review
Appl. Therm. Eng.
(2018) - et al.
Geometric arrangement and operation mode adjustment in low-enthalpy geothermal borehole fields for heating
Energy
(2013) - et al.
Optimization of energy extraction for vertical closed-loop geothermal systems considering groundwater flow
Energy Conversion Manage.
(2013) - et al.
Investigation on influential factors of engineering design of geothermal heat exchangers
Appl. Therm. Eng.
(2015) - et al.
Numerical evaluation of the effects of groundwater flow on borehole heat exchanger arrays
Renew. Energy
(2013) - et al.
Effects of arrangement geometry and number of boreholes on thermal interaction coefficient of multi-borehole heat exchangers
Appl. Energy
(2019) - et al.
Effects of load optimization and geometric arrangement on the thermal performance of borehole heat exchanger fields
Sustainable Cities Soc.
(2017)
Effect of borehole array geometry and thermal interferences on geothermal heat pump system
Energy Conversion Manage.
Performance analysis of helical ground heat exchangers with different configurations
Appl. Therm. Eng.
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2022, GeothermicsCitation Excerpt :Thus, heat transfer rate between GHE and the surrounding soil environment play an important role in the overall efficiency of the GSHP system. Several studies have been performed on influencing factors on the effectiveness of the GHEs, such as surface area of the pipe in contact with the soil (Kayaci and Demir, 2018), thermal shunt effect (pipe-to-pipe distance) (Sandler et al., 2017), backfill grout material (Zhao et al., 2021; Agrawal et al., 2021) medium types and flow rate (Diglio et al., 2018, ; Yusof et al., 2018), soil thermal properties (Li et al., 2018; Tang and Nowamooz, 2019), shape and arrangement of the buried pipe (Jahanbin, 2020; Zhang et al., 2021). Hassanzadeh et al. (Hassanzadeh et al., 2018) comparatively assessed the heat transfer performance of a GHE with and without longitudinal galvanized bridges.
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2022, GeothermicsCitation Excerpt :The coefficient of performance (COP) for the GSHP is closely related to the performance of the GHE that has something to do with the heat transfer and flow characteristics of oneself (Javadi et al., 2019a). There are many reviews of GHE such as a thorough introduction and analysis of heat transfer with various analytical models (Ahmad and Prakash, 2021; Ahmadfard and Bernier, 2019; Lamarche and Pasquier, 2019; Rashidi et al., 2021; Zhang et al., 2021). For a single U-shaped GHE, Li and Lai (2015) compared six analytical models (an infinite cylinder-source model, two infinite line-source models, two finite line-source models, and a composite-medium line-source model) for the unit-step temperature response based on G-function.