Length Of Ground Heat Exchanger Research Articles

Assessment of installation suitability of a vertical closed loop ground source heat pump system in regional scale

Installation suitability of a vertical closed loop GSHP system in the Echigo Plain of Japan was assessed considering the regional scale groundwater flow and heat transport analysis. For evaluating and understand the variation of development potential of the system, the necessary length of ground heat exchanger (GHE) was analyzed at different points, where groundwater, geology and subsurface temperature distribution varies. The computation was done for the model case of the Japanese single-family dwelling with reference to standard for energy saving in Japan. The necessary length of GHE ranged from 67 m to 101 m within the plain and found comparatively longer at the central coastal area around the Niigata City. These results showing the variation of the necessary length of GHE in the plain scale is significant and essential for the proper design and site selection of the system in the Echigo Plain, and can also be beneficial for the development of GSHP system in Japan. Influence of the existing groundwater pumping system was also evaluated to determine if the pumping system can enhance heat exchange performance for space-heating. The effect of groundwater pumping was not so significant to improve heat exchange rates due to the natural existence of groundwater flow.

Comparative study of hybrid ground source heat pump in cooling and heating dominant climates

The ground source heat pump system (GSHP) has been an accepted technology to provide energy efficient and renewable air conditioning to the buildings. However, imbalanced heating and cooling load during the winter and summers especially in the regions with heating and cooling dominant climates may degrade the performance of the system over a long-term operation. Hybrid GSHP system which uses supplemental energy sources such as solar panel or cooling tower can balance the imposing load on the ground heat exchanger (GHE) and benefits the system by minimizing the GHE length in short-term and improves the overall performance in long-term. This research presents a study of application of hybrid GSHP system with an intention to compare its applicability in the regions with dominant heating and cooling loads. In this study, a student office and an actual heat pump system in Akita City, northern Japan was modeled in TRNSYS software and was validated using in-situ measured data. The hybrid system which coupled with a supplemental heating and cooling source devices was simulated to test its viability for the different heating and cooling loads in different regions within the country. The results revealed that hybrid system plays an effective role in both climates to balance the load on GHE, keeps constant the soil temperature, and consequently improves the long-term performance. Moreover, in short-term, it can reduce the GHE length and decrease drilling cost based on the meteoroidal condition of the region such as solar radiation. For instance, the GHE length was reduced to around half in cooling dominant region using cooling tower, while it was negligible in heating dominant region.

Thermo-economic analysis of geothermal heat pump system integrated with multi-modular water-phase change material tanks for underground space cooling applications

The geothermal heat pump system (GHPS) is cascaded with multi-modular water-phase change material (PCM) tanks to cool the underground shelter in the ordinary mode and emergency mode, respectively. Based on the load characteristic of an underground shelter in Beijing, China, the thermo-economic performance of the hybrid system in the two modes is investigated. By utilizing the Taguchi design method, the effect of pipe length, multi-modular water-PCM tank matrix (MMWPM), and cooling water flow ratio of the above-mentioned components on the energy and economic performance are explored and optimized. The result shows that considering 10 years’ operation, 75 % of the base ground heat exchanger (GHE) could guarantee the cooling water temperature within the limited range in the ordinary mode. In the emergency mode, although the buried pipe loop accounts for a small flow rate, e.g., with a value of 10 %, it effectively extends the effective discharging duration (EDD) of the hybrid cooling system by at least 97 %. The average initial cost per unit EDD in the emergency mode is selected as the most important evaluation index in this paper. The order of factors is flow ratio> GHE length> MMWPM. The superior GHE length, MMWPM, and their flow ratio are 2500 m, 3 × 4, and 3:7, respectively. Moreover, the interaction between factors has a descending order of GHE length × Flow ratio> GHE length × MMWPM > MMWPM × flow ratio. With the optimal design of the hybrid system, the initial cost per unit EDD decreased by 24.37 %. This study is expected to serve as a reference for the application of the hybrid system in the underground shelter, meeting the requirement of thermal camouflage and energy-saving requirement.

A methodology for lithology-based thermal conductivities at a regional scale for shallow geothermal energy – Application to the Brussels-Capital Region

A methodology for the determination of lithology-based thermal conductivities at a regional scale is proposed, assigning a saturated and unsaturated thermal conductivity to each stratigraphic unit encountered in the region. Such a methodology is paramount for GIS-supported mapping of shallow geothermal energy at a regional scale. The analysis is primarily based on the interpretation of thermal response tests (TRT), assuming that the thermal conductivity determined during TRT is a thickness-weighted average of the individual thermal conductivity of each stratigraphic unit constituting the ground along a ground heat exchanger (GHE). Enhanced thermal response tests, reference geological material-based thermal conductivities and laboratory optical scanning tests achieved on remolded specimen from drilling cuttings are used to validate the results. The relevance of the methodology is illustrated through its application to the Brussels-Capital Region (Belgium), and consistent saturated and unsaturated thermal conductivities are obtained for each stratigraphic unit. An uncertainty analysis on the thermal conductivity is proposed, and its impact on the design of GHE is discussed. In most cases, the relative error on the ground thermal conductivity is lower than 10 %, and its impact on GHE length remains limited.

10-year simulation of photovoltaic-thermal road assisted ground source heat pump system for accommodation building heating in expressway service area

The photovoltaic-thermal (PVT)-ground source heat pump (GSHP) system has been proved to have great potential in improving building energy efficiency, but ordinary PVT collector requires a large installation area and limits the popularization of PVT. In this paper, a novel solar energy collector, called photovoltaic-thermal road (PVTR), is proposed to replace the traditional PVT collector, and a novel energy system that is PVTR-GSHP system is proposed. In order to study the system performance, taking a typical expressway service accommodation building in Beijing as an example, a 10-year simulation is carried out to analyze the heating operation characteristics of the proposed system. Moreover, the effects of the PVTR area, the length and layout of ground heat exchanger (GHE) on the system performance are also discussed. Results show that, when the length of GHE is 5000 m, and the number of boreholes is 25 and the borehole depth is 100 m, the minimum area of PVTR satisfying the soil heat balance and meeting the system power consumption are 187.2 m2 and 216 m2, respectively. When the PVTR area is 216 m2, the minimum GHE length satisfying the soil heat balance is 4000 m. Finally, to realize system zero energy consumption and soil heat balance, the best combination of GHE length and PVTR area is 4000 m and 216 m2 under the cases of this paper. And in this case, the average COPHP and COPsys in ten years are 5.59 and 2.31 respectively.

A study on utilization of ground source energy for space heating using a nanofluid as a heat carrier

AbstractGround source heat pump (GSHP) systems are well established as an energy‐efficient space conditioning device. However, for better utilization of the ground source, improvement in GSHP performance is desirable, which limits the small temperature difference between the ground and the circulating fluid. In this study, efforts have been made to investigate the performance of a ground heat exchanger (GHX) with a nanofluid as a heat carrier. Mathematical modeling is performed for the closed‐loop vertical U‐tube GHX with six different (Al2O3, CuO, graphite, multiwalled carbon nanotube, graphene, and Cu) water‐based nanofluids. The effect of different operating parameters on GHX length, fluid temperature, and pressure drop with nanofluids is determined. On the basis of the analytical results, it is found that the graphite particle‐based nanofluid plays a prominent role to enhance the performance of the GHX as compared with other nanoparticles. The maximum enhancement in the increase in outlet fluid temperature and reduction in pipe length with graphite particle‐based nanofluid are 68.3% and 63.3%, respectively, for an increase in temperature difference from 7°C to 15°C between the atmosphere and the ground. Also, with the graphite particle‐based nanofluid and the increase in pipe diameter from 20 to 50 mm, the fluid outlet temperature increases up to 11.2%, and the requirement in GHX length reduces up to 55%.

A study on optimization of horizontal ground heat exchanger parameters for space heating application

Abstract In the present scenario, space heating/cooling has become essential for human comfort. Most of the demand is fulfilled by conventional devices, which consume high-grade energy and emit toxic gases. Due to this, now focus is turned on how to harness the renewable source of energy is becoming important. In recent times, GSHP systems are very popular for space conditioning applications. The ground heat exchanger (GHX) extracts and rejects the heat from the ground for heating & cooling, respectively. This work is proposed for optimizing the total length of GHX to achieve higher performance of GSHP system by Taguchi optimization technique. Five influencing operating parameters for GHX have been considered using the L27(53) orthogonal array. Lower the better concept is used for GHX length optimization. The results are investigated through optimum values of ANOVA and S/N ratio analysis. Simulation using L27 orthogonal array were carried out by considering 1.5 ton of total heating demand in wintertime. Based on trial runs, it is found that the minimum and maximum lengths were 12.17 m and 137.55 m, respectively. The optimum length of GHX is 11.05 m, which is 9.17% lower than the value predicted by the L27 orthogonal arrays.

Optimization of Earth Air Tube Heat Exchanger for Cooling Application Using Taguchi Technique

Earth air tube heat exchanger (EATHE) is one of the passive technologies which utilize the earth stored heat (renewable energy) for heating/cooling the buildings. EATHE releases heat to earth for cooling space in summer, making the earth a heat sink and extracts earth-stored energy for heating space in winter and makes the earth a heat source. This paper optimizes the Length of the ground heat exchanger and overall heat transfer coefficient of earth air heat exchanger using the Taguchi technique for cooling application. For this purpose, we select six factors such as installation depth of Pipe (A), Pipe's inner diameter (B), Thermal conductivity of pipe material (C), Inlet air temperature (D), Outlet air temperature (E), Inlet air velocity (F). All these factors are taken at three levels, and we select an L27 orthogonal array for experimental runs. The ground heat exchanger's Length and the overall heat transfer coefficient were then calculated for each experimental run. In the Taguchi method, we find the signal to noise ratio for an optimal combination of all six factors and ANOVA to find the order of influencing parameters and their percentage contributions for both the objective parameters. According to our results, the best combination for all the six factors for ground heat exchanger length and overall heat transfer coefficient were A1B1C3D1E3F1 and A2B3C2D3E1F3, respectively. The highest and lowest influencing factors for ground heat exchanger length were the pipe's inner diameter and the pipe's installation depth with their contribution factors of 69.12 and 0.32%, respectively. In contrast, the highest and lowest influencing factors for the overall heat transfer coefficient were the pipe's inner diameter and thermal conductivity of pipe material with their contribution factors of 75.97and 0%, respectively. Hence the order of influence of all the six factors for both the objective parameters was BEFDCA.

The application of thermoelectric and ejector in a CO2 direct-expansion ground source heat pump; energy and exergy analysis

The thermodynamic analysis of a horizontal CO2 direct-expansion ground source heat pump in transcritical cycle was performed to investigate the influence of using thermoelectric sub-cooler and the ejector on the performance parameters of the cycle. A comparative analysis was conducted between the Base cycle and the cycles with ejector and thermoelectric sub-cooler considering the pressure drops in the gas cooler and the ground heat exchanger. The effects of compressor inlet temperature, soil temperature, thermoelectric sub-cooler length, thermoelectric sub-cooler cooling water mass flow rate, and ground heat exchanger outlet temperature on different performance parameters of the cycles were studied. The results demonstrated that the application of ejector exhibits a more stable operation of the cycle and increasing its COP by 16.5% as compared to the Base cycle considering the same ground heat exchanger length. Also, the length of ground heat exchanger is considerably decreased by using the ejector considering the same COP for the Base and EJR cycles. Besides, thermoelectric sub-cooler decreases the irreversibilities of the cycle by generation more power, thereby COP is boosted by 16% as compared to the Base cycle. Furthermore, the major irreversibility in the cycle with thermoelectric and ejector is occurred in the compressor and followed by ejector, ground heat exchanger, gas cooler, thermoelectric sub-cooler, and the expansion valve, respectively.

Optimal Parameter Scenario of Borehole Thermal Resistance for Vertical Ground Heat Exchanger Using Taguchi Method

The borehole thermal resistance is a significant design indicator for the ground heat exchanger (GHE) and careful design procedure is required for this indicator to decrease the length of GHE and capital investments. In this study, a modified two-dimension numerical model with the resistance model is first applied to analyze the effects of parameters including the borehole radius, pipe-pipe distance, pipe radius, soil thermal conductivity and grout thermal conductivity on the borehole thermal resistance. To implement the analysis, an L27 (35) is established. Then, the Taguchi method is carried out to obtain the optimal scenarios of parameters combination. Results using the optimal parameters set reveal that the maximum borehole thermal resistance decreased value and rate can be up to 0.146 m.K/W and 81.56%. The analysis of variance technique is applied lastly to analyze the relative significance of different parameters. The results indicate that the borehole radius, grout thermal conductivity, and pipe radius are important driving parameters in determining the borehole thermal resistance, while the pipe-pipe distance and ground thermal conductivity almost play no role in it.

In pursuit of a replacement for conventional high-density polyethylene tubes in ground source heat pumps from their composites – A comparative study

Ground-source heat pumps, as the most environmentally friendly and energy-efficient air conditioning technology, suffer from a great required length of ground heat exchanger, partly arising from the low thermal conductivity of high-density polyethylene tubes commonly used in ground heat exchangers. In an attempt to find a replacement with an acceptable thermal conductivity for high-density polyethylene tubes, in this study, first, a comprehensive comparative study on fillers commonly used in thermally conductive polymer composites and resulting high-density polyethylene composites was conducted. Then, based on the advantages and disadvantages presented, an appropriate composite was selected and applied in the modeling of a case study to demonstrate the effect of thermal conductivity of the tube on the borehole length of the ground heat exchanger. The findings indicated that low-temperature in situ expandable graphite was a suitable filler to add to high-density polyethylene polymer, resulting in a composite with acceptable thermal and rheological properties. Investigating the effect of thermal conductivity of the tube on the borehole length revealed some intriguing findings. First, using a composite with a thermal conductivity of approximately 1.4 Wm−1 K−1, for instance, the affordable high-density polyethylene composite filled with 10 wt% of low-temperature in situ expandable graphite, the length of the ground heat exchanger reduced by a notable amount of 10 %, which is more than 68 % of the maximum potential for reducing borehole length could be achieved by improving thermal properties of the tube. Furthermore, using polymer composites with thermal conductivity in the range of 2 Wm−1 K−1 could obviate the need for using metal tubes, which are used even nowadays in certain cases. However, due to the lack of results of some specific test, such as Hydrostatic Design Basis, the mechanical properties of the newly introduced composite require further investigation.

Investigating the Effect of Soil Type and Moisture on the Performance of a Ground Source Heat Pump System Used for a Greenhouse in Iran

Abstract We investigate the effect of soil type and moisture on the operation of a ground source heat pump (GSHP) system in supplying the energy needs of a greenhouse in Karaj, Alborz province, Iran, in terms of the required length of ground heat exchanger, the working hours, the electricity consumption, as well as the coefficient of performance (COP) of heat pumps. In order to predict the capacity of heat pumps, we use the numerical heat transfer model of Noorollahi et al. (2016, “Numerical Modeling and Economic Analysis of a Ground Source Heat Pump for Supplying Energy for a Greenhouse in Alborz Province, Iran,” J. Cleaner Prod., 131, pp. 145–154) in which the governing equations of heat transfer in the ground heat exchanger are numerically solved through a novel finite difference method. Thermal properties of various soil types, namely sandy soil, sand, silty loam, and silty clay, with three different levels of moisture content referred to as dry, damp, and saturated, are considered as the main inputs for the computer code. The simulations indicate that when moisture is increased from dampness to saturation, the annual working hours of heat pumps decrease by 1.1%, 5.1%, 6.1%, and 4.6%, and their annual electricity consumption is reduced by 2.2%, 10.6%, 12.6%, and 9.7% for sandy soil, sand, silty loam, and silty clay, respectively. Moreover, the average COP of heat pumps increase by 0.9%, 4.0%, 5.2%, and 3.7% in heating mode and 2.4%, 13.0%, 16.5%, and 11.7% in cooling mode for the mentioned soils, respectively.

Feasibility Study of Ground Source Heat Pump System Considering Underground Thermal Properties

: A typical ground source heat pump (GSHP) system in South Korea has a ground heat exchanger (GHX) with a length of 100–150 m, which utilizes annually stable underground temperature to meet the loads of cooling, heating and hot water in buildings. However, most GSHP systems have been introduced in heating dominated areas because the system performance advantage is larger compared with air source heat pump system than that in cooling dominated areas. To effectively provide geothermal energy to the building in the limited urban area, it is necessary to install deep GHXs. Despite its large capacity, there are few studies on GSHP system with deep GHX over 300 m. In this study, to estimate the performance of the GSHP system with deep GHX and evaluate its feasibility, numerical simulation was conducted. To quantitatively analyze heat transfer between soil and GHX, the coupled model with GHX model and ground heat and groundwater transfer model was used. Furthermore, the heat exchange rate and the source temperature were calculated according to the operation modes, the length of GHX, and soil conditions such as geothermal gradient and thermal conductivity. As a result, the total heat exchange rate of GHX with a length of 300 m heat exchanger was 12.62 kW, 173% that of a length of 150 m. Finally, it was found that the GSHP system with deep GHX has realistic possibility in good condition of geothermal gradient.

지표수 열교환기의 용량과 적용 효과에 대한 설계 인자의 영향

Abstract : Commercial buildings are generally cooling-dominated and therefore reject more heat to a vertical ground heat exchanger(GHE) than they extract over the annual cycle. Shallow ponds can provide a cost- effective means to balance the thermal loads to the ground and to reduce the length of GHE. The objective of this work has been to develop a design tool for surface water heat exchanger(SWHE) submerged in shallow pond. This paper presents the analysis results of the impact of design parameters on the length of SWHE and its application effect on geothermal heat pump(GHP) system using vertical GHE. In order to analysis, We applied  -  method on designing the length of SWHE. Analysis results show that the required pipe length of SWHE was decreased with the increase of approach temperature difference and with the decrease of pipe wall thickness. In addition, when the SWHE was applied to the GHP system, the temperature of vertical GHE was more stable than that of standalone GHE system.

Optimization of ground heat exchanger parameters of ground source heat pump system for space heating applications

In this paper Taguchi and utility methods have been employed to optimize eight important parameters (i.e. radius of U tube, borehole radius, heating load, grout conductivity, entering water temperature, distance between U tubes, U tube thermal conductivity and mass flow rate) of GHX (ground heat exchanger) used for space heating applications. Length of GHX, COP (coefficient of performance) and thermal resistance of GHX are considered as the objective functions. In Taguchi method lower the better concept is applied to obtain optimum values for the length of the GHX and its thermal resistance and for COP higher the better concept is used. In utility concept higher the better method has been employed. Based on the results obtained using Taguchi optimization, the optimum parameters and levels for GHX length, COP and GHX thermal resistances are found to be, A2B1C1D1E3F3G1I3, A2B2C1D3E3F3G1I2 and A1B2C1D2E1F1G3I1 respectively. Results obtained using the above optimized set of parameters show 15.17% reduction in the length of GHX, 2.5% increase in COP and 17.1% reduction in thermal resistance of GHX. The implementation of utility concept to obtain a single set of optimum parameters and levels resulted in 3.2% increase in GHX length, about 1.2% decrease in COP and 13.23% decrease in thermal resistance.

New correlations for the prediction of the undisturbed ground temperature

The undisturbed ground temperature is an important parameter in the design of the ground heat exchanger connected to the ground source heat pump systems. Based on the heating mode for cold climates, the underestimation of this parameter leads to oversizing the ground heat exchanger length and therefore resulting in the additional cost of the system. Using measured data obtained from thermal response test (TRT) reports for seventeen sites covering a wide range of climates, two different correlations of the undisturbed ground temperature, global and simplified have been developed. The first one, obtained using the least square method, is a function of ambient air temperature, wind velocity, global solar radiation on a horizontal surface and sky temperature. It has been shown by using this correlation that the air ambient temperature is the dominant parameter on the undisturbed ground temperature. Following this conclusion, the simplified correlation which is only a function of the air ambient temperature was developed. Then using this latter correlation, isotherms of the undisturbed ground temperature for Canada were generated.

Optimization of solar assisted ground source heat pump system for space heating application by Taguchi method and utility concept

In the present research, a methodology is proposed to optimize the solar collector area and ground heat exchanger length for achieving higher COP of Solar Assisted Ground Source Heat Pump (SAGSHP) system using Taguchi method and utility concept. Four operating parameters for solar collector and four parameters for ground heat exchanger have been selected with mixed level variation using an L18 (21, 37) orthogonal array. The key parameters such as solar collector area, ground heat exchanger length and COP of the SAGSHP system are optimized to predict the best levels of operating parameters for maximum COP of SAGSHP system. Lower the better concept has been used for the solar collector area and ground heat exchanger length whereas higher the better concept has been employed for the COP of SAGSHP system and the results have been analyzed for the optimum conditions using signal-to-noise (SN) ratio and ANOVA method. Computations were carried out for 18 experimental trial runs by considering 2ton heating load in winter season. The optimum COP for SAGSHP was estimated to be 4.23 from the utility concept, which is 8.74% higher than the optimum COP predicted by Taguchi optimization. Optimization of solar collector area and ground heat exchanger length by the utility concept has shown only about 2.3% reduction in area and 1.6% reduction in length respectively compared to those values optimized by the Taguchi method.

Solar Assisted Heat Pump Systems with Ground Heat Exchanger – Simulation Studies

Different concepts of solar assisted heat pump systems with ground heat exchanger are simulated according to IEA SHC Task44/HPP Annex38 reference conditions. Two aspects of the concepts are investigated using TRNSYS simulations. First, the solar impact on system efficiency is assessed by the seasonal performance factor. Second, the solar impact on the possible shortening of the ground heat exchanger is evaluated by the minimum temperature at the ground heat exchanger inlet.The simulation results reveal diverging optimums for the concepts. The direct use of solar energy clearly achieves the best effect on the efficiency improvement. A simple domestic hot water system reaches a seasonal performance factor of 4.5 and solar combi-systems seasonal performance factors up to 6. In contrast, the use of solar energy on the cold side of the heat pump achieves the best effects on the shortening of the ground heat exchanger of up to 20%.Two highly sensitive influences are investigated with the developed transient system model. First, the minimum allowed heat source temperature is varied. Here 1K equals a variation of 0.25 in the seasonal performance or of around 10% ground heat exchanger length. Second, the ground heat exchanger model is simulated without and with a pre-pipe that improves the transient model behavior. The influence of this pre-pipe on the SPF is small for conventionally designed ground heat exchangers, but of around 2K for the minimum inlet temperature. Therefore, the dynamic model quality reveals potential to reduce the size of the ground heat exchanger corresponding to investment costs.

Feasibility of combined solar thermal and ground source heat pump systems in cold climate, Canada

This document presents a study for examining the viability of hybrid ground source heat pump (GSHP) systems that use solar thermal collectors as the supplemental component in heating dominated buildings. Loads for an actual house in the City of Milton near Toronto, Canada, were estimated. TRNSYS, a system simulation software tool, was used to model yearly performance of a conventional GSHP system as well as a proposed hybrid GSHP system. Actual yearly data collected from the site were examined against the simulation results. This study demonstrates that hybrid ground source heat pump system combined with solar thermal collectors is a feasible choice for space conditioning for heating dominated houses. It was shown that the solar thermal energy storage in the ground could reduce a large amount of ground heat exchanger (GHX) length. Combining three solar thermal collectors with a total area of 6.81m2 to a GSHP system will reduce GHX length by 15%. Sensitivity analysis was carried out for different cities of Canada and resulted that Vancouver, with mildest climate compared to other cities, was the best candidate for the proposed solar hybrid GSHP system with a GHX length reduction to solar collector area ratio of 7.64m/m2. Overall system economic viability was also evaluated using a 20-year life-cycle cost analysis. The analysis showed that there is small economic benefit in comparing to the conventional GSHP system. The net present value of the proposed hybrid system based on the 20-year life-cycle cost analysis was estimated to be in a range of 3.7%–7.6% (or $1500 to $3430 Canadian dollar) lower than the conventional GSHP system depending on the drilling cost.

Borehole Resistance and Heat Conduction Around Vertical Ground Heat Exchangers

Borehole thermal resistance in Ground Heat Exchanger (GHE) installations is affected by several parameters such as geometrical attributes of heat exchanger in the borehole, pipes' characteristics and grout’s thermal conductivity. A study is carried out to compare the values computed by Ground Loop Design (GLD) Software, GLD 2009, with three ana-lytical solutions for U-shaped tubes. The analysis is focused on dimensionless ratios of borehole geometrical parameters (borehole diameter to outside pipe diameter and shank spacing to borehole diameter) and pipes according to Standard Di-mension Ratio (SDR) and on eight common grouts. Finally, the effect of heat conduction in the borehole is examined by means of finite element analysis by Heat Transfer Module of COMSOL Multiphysics. A two-dimensional (2-D) steady-state simulation is done assuming working fluid temperatures for winter and summer conditions and typical Greek undis-turbed ground temperature in a field of four ground vertical U-tube heat exchangers surrounded by infinite ground. The temperature profile is presented and the total conductive heat flux from the pipe to the borehole wall per meter of length of ground heat exchanger is computed for pipes SDR11 (the outside diameter of the pipe is 11 times the thickness of its wall), SDR9 and SDR17 for summer working conditions and three different configurations. It is attempted to reach to comparative results for borehole thermal resistance value through different types of analysis, having considered the major factors that affect it and giving trends for the influence of each factor to the magnitude of its value.