Vertical Ground Source Heat Pump Research Articles

Economic analysis of vertical ground source heat pump systems in Melbourne

This study assesses some economic indicators for residential vertical Ground Source Heat Pump (GSHP) systems in Melbourne, Australia. Publicly available data on the performance and costs associated with such systems is rare. To redress this issue, detailed cost breakdowns are reported herein based on actual installation costs. The average upper bound capital cost is found to be around AUD 31,000, with lower costs possible depending on many factors, particularly when considering the early stage of development of the GSHP industry in Australia. Using the gathered cost data as well as other performance data such as recorded average coefficients of performance of 3.8 and 3.6 for heating and cooling respectively, several economic indicators are used to evaluate alternative heating/cooling systems. The analyses found that for a design life of 20 years, an Air Source Heat Pump (ASHP) system is marginally more financially attractive than a GSHP system; however, for a design life of 40 years, GSHP system provide considerably more savings than other alternatives including ASHP systems. The relatively low rate of return for GSHP systems over the first 20 years is due to current high capital costs as well as the mild weather conditions in Melbourne. Climate change was also factored into the economic analyses, with only minor effects observed. Finally, a scenario with government incentives was found to make GSHP systems much more financially attractive, a tax credit on capital cost of as low as 8% was found as such threshold for a design life of 20 years.

The effect of employing nanofluid on reducing the bore length of a vertical ground-source heat pump

In our era ground-source heat pumps are known as energy-efficient air conditioning systems. However, their high initial costs are a major obstacle to the widespread use of such systems. In this study, the effects of using Al2O3/water nanofluid as heat transfer fluid on reducing the bore length of a ground heat exchanger in a vertical ground-source heat pump are examined. For this purpose, the effective thermal conductivity and the effective viscosity of the nanofluid, which play prominent roles in the convective heat transfer, are optimized via using multi-objective Flower Pollination Algorithm. In this algorithm, the logic of the second version of non-dominated sorting is utilized to deal with the two objectives of this optimization. Then some of the best possible combinations of the thermal conductivity and the viscosity of the nanofluid, extracted from the obtained Pareto front, were used to compute the required bore length. The results were compared with the required bore length calculated using pure water as the heat transfer fluid in the ground heat exchanger. The comparison demonstrated that employing Al2O3/water nanofluid instead of water as heat transfer liquid reduced less than 1.3% of the bore length. Furthermore, investigating the reason of this low reduction in the bore length revealed that grout has the most potential to reduce the bore length among the heat transfer fluid, tubes, and grout.

Exergy, exergoenvironmental and exergoeconomic evaluation of a heat pump-integrated wall heating system

In this study, a vertical ground source heat pump wall heating system belonging to the Yıldız Renewable Energy House on the Davutpaşa Campus of Yıldız Technical University was experimentally and theoretically studied. The examination included energy, exergy, exergoenvironmental and exergoeconomic analyses from 1 January 2013 to 30 March 2013 (i.e., the “Winter Session”). Data were collected and uploaded to a MySQL database. “The moments when the heat pump is activated” was detected and “Monthly Average Values” were analysed. Theoretical analyses were conducted for the Winter Session and correlated with the experimental results. This study includes exergetically, exergoeconomically, and exergoenvironmental evaluate a building and its heating system from the generation stage to the envelope of the building. The findings are based on applying a low exergy, exergoenvironmental and exergoeconomic analysis to investigate the system performance. The energy and exergy efficiencies of the entire system were 67.36% and 27.40%, respectively, and the energy and exergy efficiencies of the wall heating system panels were 86.61% and 82.90%, respectively. The monthly average exergy-based environmental impact value was 0.212 mPts/s. The exergoeconomic factors changed from 74.97% to 75.77%.

Exergoenvironmental and exergoeconomic analyses of a vertical type ground source heat pump integrated wall cooling system

In this study, exergoenvironmental, and exergoeconomic analyses of wall cooling systems fed by a vertical type of ground source heat pump integrated wall cooling system for cooling were examined experimentally and theoretically in Yıldız Renewable Energy House at Davutpaşa Campus of Yıldız Technical University. The examination includes energy, exergy, exergoenvironmental and exergoeconomic analyses, between the dates of 1 July and 30 September 2013. The main aim of this objective is to minimize energy usage in Residential Sector as low as possible. Therefore, a particular system working with low temperature regime was chosen. According to the outcomes; energy and exergy efficiency of all the system have been found as 74.85% and 29.90%. Part-based environmental factor values are calculated. The compressor and underground heat exchanger have the highest values calculated as 0.040mPts/s, 0.026mPts/s respectively. The exergoenvironmental impact values of all system are detected as 42.60%. On the other hand; the exergoeconomic factor values of all system are calculated as 77.68%. The value of exergoeconomic factor changes depending on some particular components: accumulator tank, undersoil heat exchanger, evaporator and condenser calculated respectively as 69.43%, 62.59%, 62.53% and 29.15%. As a result; it is found that in order to determine economic and environmental impacts of irreversibilities occurring in the system and its components, economic and environmental analyses of thermal system as well as wall cooling systems, should be done based on exergy concept.

Performance prediction between horizontal and vertical source heat pump systems for greenhouse heating with the use of artificial neural networks

This paper presents the suitability of artificial neural networks (ANNs) to predict the performance and comparison between a horizontal and a vertical ground source heat pump system. Performance forecasting is the precondition for the optimal control and energy saving operation of heat pump systems. In this study, performance parameters such as air temperature entering condenser fan-coil unit, air temperature leaving condenser fan-coil unit, and ground temperatures (2 and 60 m) obtained experimental studies are input data; coefficient of performance of system (COPsys) is in output layer. The back propagation learning algorithm with three different variants such as Levenberg–Marguardt, Pola–Ribiere conjugate gradient, and scaled conjugate gradient, and also tangent sigmoid transfer function were used in the network so that the best approach can be found. The results showed that LM with three neurons in the hidden layer is the most suitable algorithm with maximum correlation coefficients R2 of 0.999, minimum root mean square RMS value and low coefficient variance COV. The reported results confirmed that the use of ANN for performance prediction of COPsys,H–V is acceptable in these studies.

Analysis of a wall cooling system using a heat pump

In this study, a vertical ground source heat pump wall cooling system that belongs to the Yıldız Renewable Energy House at the Davutpaşa Campus of Yıldız Technical University was studied both experimentally and theoretically. The principal objective was to perform a system analysis to determine the parameters that allow the energy usage of the cooling system to be as low as possible. For this reason, a system working in a low temperature regime was chosen. The examination includes energy and exergy analyses conducted during the period between 1 July and 30 September 2012, which is described as the “Summer Session”. By using the data that were collected on a per-second basis during these processes and conveyed to a MySQL database, “The moments when the heat pump is activated” were detected, and the “Monthly Average Values” were analyzed. Thus, a theoretical analysis was conducted for the Cooling Session and its correlations. These correlations were used in the energy and exergy analyses. According to the analysis results, the energy and exergy efficiencies of the entire system were found to be 74.85% and 29.90%, respectively, and the Wall Heating Cooling System panels calculated the heat with energy and exergy efficiencies of 90.29% and 80.4%, respectively.

Evaluation of different heat extraction strategies for shallow vertical ground-source heat pump systems

Shallow vertical ground-source heat pump systems (GSHPSs) have become a popular alternative to conventional heating systems. Typically more than one vertical ground heat exchanger (GHE) is required along with an increasing heat demand. The higher the number of GHEs, the more a system may benefit from optimal design and operation strategies that focus on costs and efficiencies. However, an optimisation of the heat and fluid flows in these systems, based on discretised models, can be computationally time-consuming and sometimes infeasible. To meet this challenge, one might apply simplified models and identify suitable constraints. In this work an analytical finite line source (FLS) model is compared by RockFlow, a finite element approach. The average absolute difference for a long-term investigation between these approaches is obtained at only approx. 0.2 °C, which was evaluated as sufficient. Subsequently, the FLS model is successfully applied to demonstrate the existence of borehole-specific heat flux distributions. For all case studies optimal solutions were found. These results confirmed the useful application of novel optimisation methods. The impact of the GHE specific heat flux distributions on the time-dependent and spatial temperature course in the vicinity of the GHE is impressively shown. The investigation of the soil and heat pump cycle revealed the system efficiency potential and costs. The efficiency improvement potential, caused by different optimal heat flux distributions, was approx. 2%. The best energy extraction improvement was nearly 20%, which equated to a monetary saving of 12%.

Experimental and computational investigation of multi U-tube boreholes

Abstract In ground source heat pump (GSHP) applications, borehole drilling cost constitutes an important part of the investment cost and it can be reduced by improving borehole performance. In vertical GSHP applications, usually double-U tube configurations are used to improve the heat transfer rate per unit length of a borehole, (unit HTR value). To determine the optimal number of U-tubes which maximizes the commercial and engineering benefits of multi U-tube applications, cost and performance analyses of multi U-tube boreholes are crucial. In this study, a triple U-tube is used in a borehole of 50 m depth. Time variation of unit HTR value of the borehole is experimentally measured when single, double and triple U-tubes are in operation separately. Furthermore a computational model is calibrated by fitting the computational results to the experimental ones, and effects of using four and five U-tubes in a borehole are computationally investigated. The relations between number of U tubes and time variation of unit HTR value of a borehole as well as investment cost are analyzed. Long term borehole performance predictions are made and compared for multi U-tube applications. Both experimental and computational results showed that performance improvements are remarkable for 2U-tube and 3U-tube configurations while it is nearly insignificant for 4U and 5U ones. If the investment cost per thermal power is considered, 2U-tube configuration is the optimal one if the prices of polyethylene pipes are relatively high, like in Turkey. When the cost of pipes decreases, then 3U-tube or even 4U–tube configuration can be the cheapest solution.

Intermittent experimental study of a vertical ground source heat pump system

In this paper, the intermittent experiment of a vertical ground source heat pump (GSHP) system is investigated and the corresponding geo-temperature variations are studied. The performance of the GSHP system under intermittent operation and the comparisons of different intermittent modes are presented in the paper. The parameters of soil backfill material, air temperature and inlet volume flow rate are also investigated. Experimental results suggest that, due to the recovery in ground thermal energy in intermittent time, the heat exchange rate and the operation performance coefficient (COP) of the heat pump increases, and the compressor power decreases in the successive working. But an insufficient soil recovery time leads to a rapid decline of the performance parameters and the soil temperature. The temperature transports faster under large soil thermal conductivity conditions and the soil temperature decreases more quickly and recovers more slowly with larger inlet flow rate and lower weather temperature for different soil thermal diffusivities. Through multiple nonlinear regression analysis, a curve formula can be fitted to predict the soil temperature variations under intermittent operation of the ground source heat pump in winter, Dalian. It can be found that the soil temperature increases at an exponential function with each factor.

Evaluating the performance of a large borehole ground source heat pump for greenhouses in northern Japan

Abstract The objective of this study was to use both field data and a numerical simulation to examine the long-term performance and environmental effects of a large GSHP (ground source heat pump) system that heats and cools industrial greenhouses in a cold region. A large vertical GSHP system was installed in the city of Akabira in the north of Hokkaido, Japan to provide heating and cooling for 12 greenhouses. The system has a maximum capacity of 640 and 648 kW for heating and cooling, respectively. The system was monitored and analyzed from Oct. 2010 through May 2011. The system had a COP (coefficient of performance) of 3.0 and SCOP (system coefficient of performance) of 2.7. The average heat extraction rate of the system was approximately 27.7 W/m. In addition, the ground temperature at a depth of 40 m decreased from approximately 7.8 °C to 0 °C after 8 months of operation. A numerical model of the system was developed in FEFLOW to predict its future behavior under conditions where the demand for heating surpasses the demand for cooling. The simulation results suggest that the system could maintain the heat exchange rate for several years without significantly compromising its performance. The risk of operating the system under unbalanced heating and cooling loads was addressed via case studies. Groundwater flow decreases the risk of operating the system when the heat extraction was much higher or lower than the heat injection.

Thermoeconomic optimization of vertical ground-source heat pump systems through nonlinear integer programming

Vertical ground-source heat pump systems (GSHPSs) use the ground’s undisturbed relative constant temperature as a source for space heating of residential and commercial buildings. The design of GSHPSs is focused in finding the optimal depth and amount of boreholes and also the connected power requirement like the amount and size of heat pumps. In this paper a mixed-integer nonlinear programming (MINLP) approach to solve the design problem of a vertical GSHPS is presented. The resulting mathematical model includes the calculation of the total annual costs (TAC) and the coefficient of performance to obtain estimates of both economic and ecological relevance to design an optimal equipment set-up. For desired constraints the numerically optimal values of the design parameters (borehole depth, mass flow rate, number of boreholes, type and number of the heat pumps) were calculated. Two numerical solution alternatives are investigated, namely Generalized Reduced Gradient (GRG2) and evolutionary algorithm. The GRG2 approach provides a more stable and faster optimal solution. Calculated results are presented through a validation example. The evaluation of the proposed objectives and studied sensitivity effects present the applicability of the model. This method was able to improve the TAC about more than 10%.

<b>Temperature distributions in pavement and bridge slabs heated by using vertical ground-source heat pump systems</b> - doi: 10.4025/actascitechnol.v35i4.15712

Temperature distribution which occurs in pavement and bridge slabs heated for de-icing and snow melting during cold periods is determined by using vertical ground-source heat pump (GSHP) systems with U-tube ground heat exchanger (GHE). The bridge and pavement models (slabs) for de-icing and snow melting were constructed. A three-dimensional finite element model (FEM) was developed to simulate temperature distribution of bridge slab (BS) and pavement slab (PS). The temperature distribution simulations of PS and BS were conducted numerically by computational fluid dynamics (CFD) program named ‘Fluent’. Congruence between the simulations and experimental data was determined.

Experimental performance analysis of a direct-expansion ground source heat pump in Xiangtan, China

The DX GSHP (direct-expansion ground source heat pump), which uses a buried copper piping network through which refrigerant is circulated, is one type of GSHP (ground source heat pump). This study investigates the performance characteristics of a vertical U-bend direct-expansion ground source (geothermal) heat pump system (DX GSHPS) for both heating and cooling. Compared with the conventional GCHP (ground coupled heat pump) system, the DX GSHP system is more efficient, with lower thermal resistance in the GHE (ground heat exchanger) and a lower (higher) condensing (evaporating) temperature in the cooling (heating) mode. In addition, the system performance of the whole DX GSHP system is also higher than that of the conventional GCHP system. A DX GSHP system in Xiangtan, China with a U-bend ground heat exchanger 42 m deep with a nominal outside diameter of 12.7 mm buried in a water well was tested and analysed. The results showed that the performance of this system is very high. The maximum (average) COPs of the system were found to be 6.08 (4.73) and 6.32 (5.03) in the heating and cooling modes, respectively.

Modeling and experiments on energy loss in horizontal connecting pipe of vertical ground source heat pump system

In a vertical ground source heat pump (GSHP) system, horizontal pipe is the connection between borehole heat exchanger (BHE) and building. In current estimation of system performance, the energy loss of fluid circulating through a horizontal connecting pipe is often ignored. However, such energy loss can seriously reduce the thermal efficiency of GSHP systems in cold regions. This paper investigates the impacts of pipe burial depth and pipe insulation on energy loss of horizontal connecting pipes of a GSHP system in Nuremberg, Germany. The fluid circulation in a horizontal connecting pipe is investigated via experimental measurement and numerical simulation. Both the on-site data and numerical results suggest that the fluid temperature is substantially influenced by pipe burial depth as well as insulation. The numerical modeling shows that the daily energy loss can vary in magnitudes, as determined by pipe burial depth. On the other hand, up to 50% energy loss can be avoided by adopting a 25 mm thick insulation. These findings suggest that the both pipe burial depth and pipe insulation are important factors to be seriously considered for energy saving in the design and implementation of GSHP systems.

Study on Engineering Construction with Three-Dimensional Heat Transfer Modeling for Double U-Tube Heat Exchangers in Ground-Source Heat Pump Systems

There are many ground source heat pumps in engineering construction application. However, Research on heat exchanger models of single-hole buried vertical ground source heat pump mostly focuses on single U-tube ground heat exchangers other than double U-tube ones in China currently. Compared with single U-tubes, double U-tubes have the heat transfer particularity of asymmetry. Therefore, the use of the traditional single tube models would have large error in the simulation of the actual double U-tube heat exchangers. This paper frames a three-dimensional heat transfer model for the vertical single-hole buried double u-tube heat exchanger in a ground source heat pump system. The model considers the performance of U-bube material and uses a dual coordinate system and makes the control elemental volumes superimposed.

주거용 직접순환식 수직밀폐형 지열원 열펌프의 연간 운전성능 평가

Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed -loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As results, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.

A performance comparison between a horizontal source and a vertical source heat pump systems for a greenhouse heating in the mild climate Elaziğ, Turkey

The investigation presented in this article is aimed at demonstrating the technical and design feasibility of using ground-source heat pump systems in the mild climate applications for greenhouse heating, where heating requirements are dominant. An experimental comparison between a horizontal ground-source heat pump system and a vertical ground-source heat pump system was shown by focusing on the heating performance. For this purpose, an experimental set-up was constructed. The heating system mainly consists of two different ground heat exchangers, a heat pump, measuring units and a heating space of a model-sized glass greenhouse with 30 m2 located in the greenhouse location.The heating coefficient of performances of the two ground-source heat pumps (COPHP,H–V) and the overall system (COPsys,H–V) were obtained to be in the range of 3.1–3.6 for HGSHP and 3.2–3.8 for VGSHP and 2.7–3.3 for HGSHP and 2.9–3.5 for VGSHP, respectively. Although significant savings are possible with these heating systems, a substantial investment in equipment and facilities may be required. The experimental results were obtained from November to April in heating seasons of 2007–2008. The results showed that the utilization of the ground-source heat pump is suitable for greenhouse heating in this district.

Performance evaluation under the actual operating condition of a vertical ground source heat pump system in a school building

This study is to evaluate the performance of a ground source heat pump (GSHP) system installed in the Pusan National University, Korea. The GSHP system consists of ground heat exchanger (GHE), measuring devices and heat pumps which have 2 compressors (inverter type and fixed type). The closed vertical type GHE is constructed with 24 boreholes of 175m in depth. The outdoor temperature, the indoor temperature and relative humidity, the inlet and outlet temperature of circulating water are obtained. Also, the electricity consumption of compressor and cooling (heating) load are measured in order to analyze the COP of heat pump. From the measuring data, the variation of ground temperature at 2.5m, 5.0m in depth are affected by outdoor air temperature. But it is proved that the ground temperature is almost constant below 10m in depth. In cooling period, the COP of the heat pump is 6.0–10.9 at partial load condition, while the overall system COP is 4.3–7.4. In heating period, the COP of the heat pump is 4.3–8.3 at partial load condition, while the overall system COP is 3.0–6.2.

A comparative investigation of various greenhouse heating options using exergy analysis method

This study deals with modeling and analyzing the performance of greenhouses from the power plant through the heating system to the greenhouse envelope using exergy analysis method, the so-called low exergy or LowEx approach, which has been and still being successfully used in sustainable buildings design, for the first time to the best of the author’s knowledge. For the heating applications, three options are studied with (i) a solar assisted vertical ground-source heat pump greenhouse heating system, (ii) a wood biomass boiler, and (iii) a natural gas boiler, which are driven by renewable and non-renewable energy sources. In this regard, two various greenhouses, the so-called small greenhouse and large greenhouse, considered have heat load rates of 4.15 kW and 7.5 MW with net floor areas of 11.5 m 2 and 7.5 ha, respectively. The overall exergy efficiency values for Cases 1–3 (solar assisted vertical ground-source heat pump, natural gas boiler and wood biomass boiler) of the small greenhouse system decrease from 3.33% to 0.83%, 11.5% to 2.90% and 3.15% to 0.79% at varying reference state temperatures of 0 to 15 °C while those for Cases 1 and 2 (wood biomass and natural gas boilers) of the large greenhouse system decrease from 2.74% to 0.11% and 4.75% to 0.18% at varying reference state temperatures of −10% to 15 °C. The energetic renewability ratio values for Cases 1 and 3 of the small greenhouse as well as Case 1 of the large greenhouse are obtained to be 0.28, 0.69 and 0.39, while the corresponding exergetic renewability ratio values are found to be 0.02, 0.64 and 0.29, respectively.

Techno-economic and spatial analysis of vertical ground source heat pump systems in Germany

The objective of the current study was to assess the technical and economic factors that influence the design and performance of vertical GSHP (ground source heat pump) systems and to evaluate the spatial correlation that these factors have with geographic components such as geology and climatic conditions. The data from more than 1100 individual GSHP systems were analysed. The average capital cost of one GSHP system is about 23,500 € ± 6800 €; the large standard deviation is primarily caused by local market dynamics. In comparison to other countries such as USA, Austria, Norway, UK and Sweden, the highest capital costs for vertical GSHP systems are in Germany and Switzerland, which is almost certainly partly due to economies of scale. Although geological, hydrogeological and thermal conditions in the studied state considerably vary spatially and the evaluated specific heat extraction rates are heterogeneously distributed, no correlation between the subsurface characteristics and the design of GSHP systems could be identified. This outcome suggests that as yet subsurface characteristics are not adequately considered during the planning and design of small-scale GSHP systems, which causes an under- or oversizing and therefore a long-term impact on the maintenance costs and payback time of such systems.