2018 Proceedings of the IGSHPA Research Track

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  • Publication
    2018 Research Conference Proceedings, International Ground Source Heat Pump Association
    (International Ground Source Heat Pump Association, 2018)
  • Publication
    Dynamic modeling of flow boiling within plate heat exchangers for heat pump and refrigeration applications
    (International Ground Source Heat Pump Association, 2018) Boese, Lennart; Opferkuch, Frank; Becker, Julian; Wensing, Michael
    Brazed Plate Heat Exchangers (BPHEs) are increasingly used as evaporators for refrigeration and heat pump applications. Detailed understanding of the underlying heat transfer phenomena is required for their effective design and use. The number of correlations which are suitable for modeling the dynamics of flow boiling within BPHEs is rather low compared to other evaporator types. In this paper some correlations that involve integral values of steam quality are evaluated for different sets of experimental data from literature. Modifications to the correlations are presented, which allow to predict the quasi-local heat transfer coefficient in each refrigerant cell. The cells equal finite volumes that are composed to a dynamic model of a BPHE acting as evaporator. Heat transfer coefficient and heat flow rate from simulation results are compared to those calculated from existing experimental data based on the same boundary conditions. The fine-tuned evaporator model is finally used to demonstrate effects of sudden load changes for the evaporator performance.
  • Publication
    Hydrogeothermal characterization and modelling of a standing column well experimental installation
    (International Ground Source Heat Pump Association, 2018) Beaudry, Gabrielle; Pasquier, Philippe; Marcotte, Denis
    Standing column wells (SCW) are efficient ground heat exchangers that offer promising potential for integration in dense urban areas. Recent years have witnessed a growing interest in SCWs, resulting in the development of various simulation models incorporating heat transfer, groundwater flow and geochemical reactions within the well and the surrounding ground. However, these models commonly use a configuration that involves pumping at the bottom of the well and reinjection from its top, which can lead to installation and maintenance difficulties in deep wells. Furthermore, very few SCW models have been validated against reliable field data. This paper presents an original finite element model coupling advection-diffusion of heat and groundwater flow within a top pumped SCW and its surrounding ground as well as the experimental setup used for its validation. Within the scope of this study, experimental data obtained after an extensive field characterization campaign and a thermal response test performed with a large-scale geothermal laboratory were used directly as inputs in the numerical model. Experimental validation shows that without any calibration procedure, the model reproduces the experimental inlet and outlet groundwater temperatures with a mean absolute error of 0.14 °C. It is also shown that the placement of the pump at the top of the well offers a more practical design that has minor impact on the thermal performance of the system.
  • Publication
    Performance analysis of a single underground thermal storage borehole using phase change material
    (International Ground Source Heat Pump Association, 2018) Bayomy, A. M.; Nguyen, Hiep V.; Wang, Jun; Dworkin, Seth B.
    Ground source heat pumps (GSHP) are used to provide both heating and cooling to a given system. These heat pumps transfer heat efficiently between the system and the ground. Despite this high efficiency, there has been a low adoption rate for GSHPs owing to limited usage in commercial structures and buildings primarily due to high installation costs, but also due to a lack of drilling space and unbalanced heating/cooling loads. Phase change materials (PCMs) can absorb, store and release large amounts of latent heat over a defined narrow temperature range while the material changes phase or state. The main goal of this paper is to be able to predict numerically the performance of a single borehole with the effect of implementing PCMs. In order to successfully proceed with the discussion, two main objectives for this paper are presented. The first objective is to establish a finite element model of a single borehole with accurate assumptions in order to achieve an accurate prediction over four years of operation for a GSHP. Then, the second objective of the paper is to investigate the effect of using PCM in the borehole of GSHP to help maintain a more stable ground temperature range. Two scenarios of different PCM volumes and melting temperatures are presented. It was found that the performance enhancement due to PCMs reaches up to 35% in monthly average COP. In addition, PCMs show great potential to smooth the ground thermal response.
  • Publication
    On the role of vertical ground heat flux for analytical simulation of borehole heat exchangers
    (International Ground Source Heat Pump Association, 2018) Bayer, Peter; Rivera, Jaime A.; Blum, Philipp
    Analytical modelling techniques are frequently used for prediction of the impacts of borehole heat exchangers (BHEs) on the thermal conditions in the subsurface. They are appealing because they are easy to use, compact and computationally efficient. However, analytical formulations also cut down the complexity of the conditions in the field by limited resolution of variations in space and time, and by often simplified specifications of boundary conditions. In this presentation, we focus on the definition of the land surface boundary condition in line source solutions. As BHEs are thin elongated forms that can be approximated by a linear shape function, main attention is on the radial heat transfer, but less on the axial effects. Given the long operation time, however, the sharp physical boundary at the top may exert a substantial influence on the temperature evolution in the shallow ground and thus influence the performance of the ground source heat pump. We examine different formulations with Dirichlet and Cauchy type boundaries included in the line source equation, with and without horizontal groundwater flow. Both homogeneous as well as inhomogeneous implementations are presented, which offer new flexibilities for simulation of nonuniform land surface impacts such as associated with varying land use types. The presented approach also facilitates to account for the accelerated ground heat flux due to global warming and due to urbanization such as observed in so-called subsurface urban heat islands in many cities.
  • Publication
    Carbon dioxide evaporation process in direct expansion geothermal boreholes
    (International Ground Source Heat Pump Association, 2018) Badache, Messaoud; Eslami, Parham; Bastani, Nejad Arash; Aidoun, Zine; Ouzzane, Mohamed
    Ground Heat Exchangers (GHE) play an important role in the performance of Ground Source Heat Pumps (GSHP). The impact is even more significant in direct expansion GSHP (DX-GSHP) systems as the refrigerant used in the heat pump also acts as the heat transfer fluid for the GHE. In this study, several experiments were carried out to investigate the performance of GHEs in a carbon dioxide (CO2) DX-GSHP. The evaporation of CO2 in the GHE was studied under various mass flow rates and number of active boreholes. For this purpose, a transcritical CO2 DX-GSHP test facility was built and fully equipped at CanmetENERGY-Varennes research laboratory. It was found that a partial two-phase flow regime along the GHE decreases the performance compared to the full two-phase flow and it has to be avoided for more efficient DX-GSHP systems.
  • Publication
    Comparison of two simplified approaches for ground temperature estimations in Australia
    (International Ground Source Heat Pump Association, 2018) Xing, Lu; Mao, Cuncun; Yu, Zhou; Mikhaylova, Olga; Hu, Pingfang
    Developing an accurate and practical method for ground temperature estimations are critical for the ground source heat pump system design and energy calculation procedures. In Australia, Baggs' method is a common procedure for ground temperatures predictions as a function of depth and time of year. Xing and Spitler developed a new procedure for ground temperature estimations for engineering applications at 4112 sites worldwide. This new procedure considers the variations of surface cover conditions (bare soil, vegetated, asphalt or concrete), effects of snow cover and soil freezing or melting. These important factors, which significantly affect the ground temperature results accuracy either are neglected or are simplified in Baggs' method. In this paper, we selected 6 sites in Australia which belongs to two climates: warm climates and arid or dry summer climates. Xing and Spitler's method and Baggs' method are used respectively to calculate the ground temperatures at depths of 10cm, 20cm, 50cm and 100cm. Calculation results of two methods are both compared to the 3-14 years of measurement results at the 6 sites and validation results are discussed and investigated. Results demonstrate the Xing and Spitler's method averaged root mean square error (RMSE) is 2.2°C of the 6 sites; Baggs' method averaged RMSE is 3.4°C of the 6 sites. This paper presents a new and improved procedure for ground temperature estimations in Australia. It enables a more accurate design of the ground heat exchangers so as to reduce the capital cost of the installed ground source heat pump systems.
  • Publication
    Double source heat pump: A case study
    (International Ground Source Heat Pump Association, 2018) Zarrella, Angelo; Zecchin, Roberto; Pasquier, Philippe; Guzzon, Diego; Ciantia, Michael; De Carli, Michele; Emmi, Giuseppe
    The design of a Ground Source Heat Pump (GSHP) system is critical because design choices affect the system's energy performance and operating conditions. If the thermal load profile on the ground side is unbalanced the ground temperature will change throughout the time and, consequently, also the energy efficiency of the heat pump. This phenomenon is known as "ground thermal drift". A possible solution to avoid this inconvenience is the adoption of a hybrid system.
  • Publication
    Parameters optimization of ground source heat pump system combined energy consumption and economic analysis using Taguchi method
    (International Ground Source Heat Pump Association, 2018) Xie, Yiwei; Hu, Pingfang; Lei, Fei; Zhu, Na; Xing, Lu
    In order to obtain a high performance and low cost of ground source heat pump (GSHP) system, a methodology based on Taguchi method and analysis of variance (ANOVA) is used to optimize design parameters of GSHP systems. Eight parameters of GSHP system are selected as control factors to investigate effect on the system. Energy efficiency ratio (EER), coefficient of performance (COP), net annual value (NAV) and the average temperature rise (TEM) in soil of GSHP system are chosen as response factors to evaluate the system performance. A GSHP system model software is established by TRNSYS to calculate the EER, COP, NAV and TEM for 36 times repeatedly according to the L36 (22, 63) mixed level Taguchi orthogonal array. The result showed that the design outlet temperature of heat pump unit is the most important parameter for EER and COP, of which the contribution of significance are 41.88% and 88.12% respectively. While the number of U-Tubes per borehole has the major contribution (84.64%) for NAV and borehole spacing contribute most (45.42%) to TEM. The optimum EER, COP, NAV and TEM for the system with the optimized parameters combination are found to be 3.9355, 3.0339, CNY 106445 yuan and 2.362 ℃ respectively, which have been validated by confirmatory experiment. The utility concept has been used in this paper to find the optimum parameters combination with comprehensive consideration of all response factors (EER, COP, NAV and TEM) and the optimum combination we can get is A2 B1 C3 D1 E1 F3 G1 H3 with the response factors of 3.873, 3.023, 107212 yuan and 2.774 ℃ for EER, COP, NAV and TEM respectively.
  • Publication
    Design and simulation tool for ground source heat pump systems considering groundwater advection
    (International Ground Source Heat Pump Association, 2018) Shoji, Yutaka; Katsura, Takao; Higashitani, Takashi; Nagano, Katsunori; Sakata, Yoshitaka
    Calculation of the underground temperature resulting from heat injection/extraction into/from ground heat exchangers (GHEXs) with hourly variation is one of the most noteworthy challenges to address when simulating and designing a ground source heat pump (GSHP) system. Especially in Japan, considering the groundwater flow is desirable because there is the possibility to reduce the installation cost for GSHP system. In order to overcome this challenge, the authors introduce a method to calculate the underground temperature, by considering heat injection/extraction into/from GHEXs with hourly variation. The method applies the superposition of the Moving Infinite Cylindrical Source (MICS) solution and the Moving Infinite Line Source (MILS) solution to calculate the temperature change due to heat injection/extraction into/from the certain GHEX and other neighboring GHEXs, respectively. In this paper, the outlines of the MICS and the method that calculate the MICS solution were firstly introduced. Next, the calculation method of underground temperature and the simulation model for the GSHP system were explained. Finally, the temperature variations of the heat carrier fluid were calculated by changing the conditions the geological layer and groundwater velocity.
  • Publication
    Foundation wall heat exchanger model and validation study
    (International Ground Source Heat Pump Association, 2018) Shafagh, Ida; Rees, Simon J.
    Making use of foundation substructural elements as ground heat exchangers is an attractive option for larger non-residential buildings. An alternative to Energy Piles is to use wall substructures - so called diaphragm or screen walls - with embedded pipes that are partly below ground and partly exposed to basement spaces. This paper will describe the development of a model of such a heat exchanger that uses a weighting factor approach known as Dynamic Thermal Networks (DTN). This approach allows for detailed representation of the wall section geometry and multiple boundary conditions. In this case thermal boundary conditions are applied at surfaces representing the adjacent ground and the semiexposed basement wall surface in addition to the pipe surface. The weighting factors for the model have been derived using a parametric numerical model that has been developed using the OpenFOAM library. Validation of the model has been carried out using data from an extended series of thermal response test (TRT) measurements at a full-scale diaphragm wall heat exchanger in Barcelona. In this paper, development of the model using the DTN approach will be briefly described along with the parametric numerical modelling approach used to derive the weighting factor data. Validation test procedures will be presented along with comparisons between the predicted and measured fluid temperatures and heat transfer rates. Given some uncertainty in the experimental thermal properties, the model was able to predict the dynamics of thermal response over a range of operating conditions with reasonable accuracy and using very modest computational resources.
  • Publication
    Experimental setup to measure the heat-exchange processes by controlling thermal and hydraulic conditions
    (International Ground Source Heat Pump Association, 2018) Scotton, Paolo; Teza, Giordano; Rossi, Daniele; Dalla Santa, Giorgia; Galgaro, Antonio
    The design of a Borehole Heat Exchanger (BHE) is based on the evaluation of the thermal exchange capacity of the whole system constituted by the probes and the surrounding ground. The energy performance of a BHE mainly depends on the thermal properties of the sediments, the possible groundwater flow and the changes in the thermal gradient in the probe's surroundings due to the continuous heat exchange with the subsoil. The interpretation of the in-field applications is often difficult because in many instances the information needed is unavailable due to difficulties of in-field measurements. An experimental device was built in order to assess, under controlled conditions, the evolution in time and space of the energetic processes that occur between a thermal probe and the surrounding ground. A copper probe was placed into a soil control volume of 1m3 and 24 high precision temperature sensors were distributed inside this volume at different distances from the probe. The configuration of the experimental settings was built to allow alterations in terms of sediments, groundwater flow conditions, thermal probe properties and operations, in order to simulate different physical conditions and to better understand the complex physical processes involved. Another goal of the experimental research was to produce reliable experimental data that can be used for the calibration and set up of numerical models. This paper describes the experimental apparatus and two experiments performed in order to assess its capability to satisfy the design requirements.
  • Publication
    Extending the Ashrae Tp8 method for vertical borefield design to uniform BHE temperature boundary conditions
    (International Ground Source Heat Pump Association, 2018) Rolando, Davide; Fossa, Marco; Priarone, Antonella
    The Ashrae method is a fast algorithm for calculating the overall length of closed-loop borehole heat exchangers, considering the ground thermal response and the building thermal load profile. The method includes a corrective variable called Temperature Penalty (Tp) to account for the thermal interaction between boreholes. Several authors proposed different approaches for calculating this parameter, but the majority is inaccurate or too complex. Recently, the same Authors suggested a very simple method, called Tp8. The coefficients included in the original formula were optimized against g-functions obtained by spatial superposition of a single source always working at the same heat rate. In this paper, the early Tp8 method is improved by the calculation of new constants based on g-functions calculated for uniform temperature borehole conditions. A large dataset of 300 borefield configurations have been considered for optimization and validation purposes. In this case, all the BHEs are at the same temperature and the overall heat transfer rate of the field is constant in time. Compared with EED software outputs, the results from present Tp8 method show a good accuracy (within 3% for the overall BHE field length) while maintaining a great simplicity in applying the method at engineering design level.
  • Publication
    Impacts of injection temperature on the relevant heat transport processes in groundwater heat pump (GWHP) systems
    (International Ground Source Heat Pump Association, 2018) Park, Byeong-Hak; Lee, Kang-Kun
    In many hydrogeological applications, the influence of temperature on fluid density and viscosity have often been neglected. However, high contrasts in temperature which occurs in the field applications such as groundwater heat pump (GWHP) systems, can make the effects of variable density and viscosity on flow and transport significant. A theoretical study suggests that free convection occurs in an infinitely extensive horizontal layer when the Rayleigh number exceeds about 40. Experimental investigations are still lacking on the conditions where the influence of temperature can be important.
  • Publication
    Virtual borehole for thermal response test unit calibration: Test facility and concept development
    (International Ground Source Heat Pump Association, 2018) Nejad, Parham Eslami; Badache, Messaoud; Corcoran, Alexia; Bernier, Michel
    Precise calculation of the borehole length requires good estimation of the ground thermal conductivity. In practice, the ground thermal conductivity is measured in-situ at a specific location using what is referred to as a thermal response test (TRT) unit. This paper presents a novel virtual borehole (VB) concept for calibrating TRT units. The VB replaces a real borehole with an above-ground compact heat exchanger and a chiller unit to mimic the thermal behavior of the ground with a user-set virtual ground thermal conductivity. In an attempt to develop the VB concept, three control scenarios are examined to emulate the ground thermal response for different thermal conductivity values. A test bench was built at the CanmetENERGY-Varennes research laboratory to validate the VB concept experimentally. A test is performed to calibrate a commercially available TRT unit for a thermal conductivity value of 3 W m-1 K-1. The TRT unit connected to the VB reported a value of 3.18 W m-1 K-1 representing a 6% error.
  • Publication
    Newton-Raphson method applied to the time-superposed ILS for parameter estimation in Thermal Response Tests
    (International Ground Source Heat Pump Association, 2018) Mazzotti, Willem; Firmansyah, Husni; Acuna, Jose; Stokuca, Milan; Palm, Bjorn
    Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of a Borehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that has commonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be non time-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power, although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.
  • Publication
    Preliminary research for eight possible groundwater energy utilisation sites in Southern Finland
    (International Ground Source Heat Pump Association, 2018) Arola, Teppo; Witick, Isa; Kouvo, Joonas; Kuusela, Jussi
    Groundwater energy utilisation has not been widely regognised as a significant renewable energy source for industry in Finland. This investigation provides example of cost-effective study to map groundwater energy utilisation possibilities. The purpose of this investigation is to increase knowledge and promote groundwater energy utilisation in Finland. The investigation was carried out for eight industrial sites located on Nastola, Southern Finland. The research include geological site investigation with groundwater temperature measurements and existing geological, hydrological, geotechnical and environmental literature review. Based on investigations and sites energy consumption data site specific groundwater energy capacity was estimated. Possible environmental barriers for groundwater energy utilisation and preliminary economical calculation was also assessed. Groundwater pumping and infiltration demand for all sites is approximately 43.3 l/s. No significant environmental issues was observed in this investigation. By utilising groundwater energy it is possible to save approximately 600 000 to 800 000 € in yearly energy costs. Hence groundwater energy utilisation can provide cost-effective renewable energy option to all sites. It is possible to plan common groundwater energy system for 2 to 3 companies and hence reduce investment costs. Further actions to continue site investigations is recommended to all sites.
  • Publication
    Are shallow boreholes a suitable option for inter-seasonal ground heat storage for the small housing sector?
    (International Ground Source Heat Pump Association, 2018) Naranjo-Mendoza, Carlos; Greenough, Richard M.; Wright, Andrew J.
    In recent years, various researchers have studied the performance of Solar Assisted Ground Source Heat Pump (SAGSHP) systems using borehole heat exchangers. However, the research conducted has been limited to conventional boreholes (30m to 150m depth), which are expensive and not suitable for the small housing sector. This paper reports an experimental analysis of a shallow SAGSHP system with inter-seasonal storage. The system, installed in Leicester UK, consists of seven photovoltaic-thermal (PVT) collectors connected in series with an array of 16 shallow boreholes (1.5 meters depth). Data regarding the energy fluxes involved in the soil-based thermal store have been monitored and analysed for one year. The results show that the shallow soil is able to serve as a storage medium to cover the heating demands of a near zero energy domestic building. However, it was noticed that in addition to the solar heat captured and stored in the soil, the system covers part of the heating demand from heat extracted from the soil surrounding the thermal store. During winter, the lowest temperature reached by the soil so far is 2 °C. Hence, no freezing problems have occurred in the soil. An analysis of the temperature variation of the ground storage under the system operation is also shown.
  • Publication
    Development of a thermal conductivity map of Stockholm
    (International Ground Source Heat Pump Association, 2018) Malmberg, Malin; Raymond, Jasmin; Perozzi, Lorenzo; Gloaguen, Erwan; Mellqvist, Claes; Schwarz, Gerhard; Acuna, Jose
    New methods have been suggested to spatially extend in situ thermal response test (TRT) assessments based on geostatistical analysis. These methods can be used to determine a stochastic distribution of the subsurface thermal conductivity beyond the test borehole on larger scales by interpolating the data with geostatistics, including sequential Gaussian simulations (SGS) used in the present study. This paper presents a simulated thermal conductivity map for Greater Stockholm in Sweden, based on the SGS method with input data from in situ measurements (TRT and DTRT). The geology of Stockholm is used as a background raster in the simulations, based on bedrock maps from the Geological Survey of Sweden (SGU). The resulting maps are compared with a point map of punctual ground thermal conductivity of Greater Stockholm earlier derived by SGU, compiled from laboratory data that were obtained by thermal conductivity scanning and modal analysis of surface rock specimens of the area.
  • Publication
    Design of a laboratory borehole storage model
    (International Ground Source Heat Pump Association, 2018) Mazzotti, Willem; Jiang, Yifeng; Monzo, Patricia; Lazzarotto, Alberto; Acuna, Jose; Palm, Bjorn
    This paper presents the design process of a 4x4 Laboratory Borehole Storage (LABS) model through analytical and numerical analyses. This LABS is intended to generate reference Thermal Response Functions (TRFs) as well as to be a validation tool for borehole heat transfer models. The objective of this design process is to determine suitable geometrical and physical parameters for the LABS. An analytical scaling analysis is first performed and important scaling constraints are derived. In particular, it is shown that the downscaling process leads to significantly higher values for Neumann and convective boundary conditions whereas the Fourier number is invariant. A numerical model is then used to verify the scaling laws, determine the size of the LABS, as well as to evaluate the influence of top surface convection and borehole radius on generated TRFs. An adequate shape for the LABS is found to be a quarter cylinder of radius and height 1.0 m, weighing around 1.2 tonnes. Natural convection on the top boundary proves to have a significant effect on the generated TRF with deviations of at least 15%. This convection effect is proposed as an explanation for the difference observed between experimental and analytical results in Cimmino and Bernier (2015). A numerical reproduction of their test leads to a relative difference of 1.1% at the last reported time. As small borehole radii are challenging to reproduce in a LABS, the effect of the borehole radius on TRFs is investigated. It is found that Eskilson's radius correction (1987) is not fully satisfactory and a new correction method must be undertaken.