Loop Ground Source Heat Pump Research Articles

Hellfire Exploration: the origins of ground source heat in early mining technology

The ground source heat pump (GSHP) was first used in 1862, for freezing ground in connection with sinking a shaft in Swansea, UK. It was subsequently developed in Germany in 1882-83 into the “Poetsch process” for freezing ground during construction of mine shafts. The Poetsch process was an indirect closed loop GSHP system, circulating a chilled brine from a heat pump around a network of coaxial borehole heat exchangers. These early systems typically employed ammonia as a refrigerant and a calcium or magnesium chloride solution as the brine. Such a system was used in 1904-1906 to sink the shafts of Dawdon Colliery, Co. Durham, UK through water-bearing Permian strata. Also, around 1904, the Newcastle-based turbine pioneer, Charles Parsons, suggested that such a GSHP system could transport heat to the surface during the construction of a 12 mile deep “Hellfire Exploration” shaft, that could potentially access geothermal power.

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.

Evaluation of measures to improve the performance of an open loop ground source heat pump system in the chalk aquifer: a case study

A case study documenting the development of a groundwater-fed district heat network in Colchester, UK, is presented. The performance of an open loop groundwater heating and cooling system (also known as a ground source heat pump (GSHP)) is a function of the performance of individual boreholes and interactions between the boreholes. When performance does not meet its design capacity or decreases with time, various measures can be undertaken to improve either the performance of individual wells or the performance of the system as a whole. Output from the first exploration borehole was less than expected, placing the business case for the development in jeopardy. Consequently, refinements to the remainder of the drilling programme were implemented including three to improve the performance of individual wells and two to improve performance of the system in its entirety. Results of these refinements are presented and may be used to inform the design of new open loop groundwater heat pump systems (GSHPs) and/or the rehabilitation of existing systems that have experienced diminished performance. Yields from three wells drilled using the reverse circulation method were more than double those drilled with the direct water flush method. A significant improvement in the performance of abstraction wells due to reinjection was observed. Specific capacity in abstraction wells increased by c. 40% due to reinjection, where the distance between abstraction and reinjection locations was 535–717 m. Allowing an excess pressure of up to 0.2 MPa in the reinjection boreholes meant that reinjection could be achieved with fewer wells. Outputs from abstraction wells were not increased by extending the depth of boreholes from 135 to 200 m or implementing additional acid treatments.

A simplified method to evaluate geothermal storage in an aquifer with consideration of heat transfer between aquifer and caprock/baserock

Storing and extracting heat during different seasons of the year is possible through the utilization of a ground aquifer with an open loop Ground Source Heat Pump (GSHP) system. Being able to predict the hydrothermal performance of geothermal storage is required for an efficient operation of the system for cooling and heating of buildings. Complex 2D and 3D hydrothermal numerical models can simulate the thermal performance of geothermal storage accurately but often lack the desired computational speed for conducting large number of simulations for performance optimization. Instead, a 1D radial model can be used to conduct fast evaluation. However, it is important that the model computes the amount of heat loss from an aquifer into the overburden and underlying layers accurately to evaluate the amount of geothermal storage in the aquifer at different times. In this study, a source term is introduced into a 1D model to simulate the heat transfer between the aquifer and caprock/baserock in the vertical direction. The following two heat loss models are introduced in the heat advection-conduction equation: (i) Newton’s heating/cooling law, which leads to a closed form solution, and (ii) a conduction-based semi-analytical model, which requires a 1D finite element solution. When compared to a full 2D axisymmetric simulation result, it was found that the Newton’s heating/cooling law model with a constant heat transfer coefficient works well in cases of fast heat flow rate in thick aquifers of around 100 meters. But large errors in estimating heat dissipation are observed in cases with low heat flow rate in thin aquifers, especially for simulations exceeding two to five years. On the other hand, the model with the conduction-based semi-analytical solution gives a better match for these conditions.

Groundwater heat pump feasibility in shallow urban aquifers: Experience from Cardiff, UK

Ground source heat pumps have the potential to decarbonise heating and cooling in many urban areas. The impact of using shallow groundwater from unconsolidated sedimentary aquifers for heating in urban areas is often modelled, but rarely validated from field measurements. This study presents findings from the ‘Cardiff Urban Geo-Observatory’ project. This study focuses on an experimental open loop ground source heat pump scheme retrofitted to a school building. Field monitoring for three years between 2015 and 2018 provided data on the environmental impact of the scheme on aquifer conditions. Average aquifer thermal degradation in the first three years was kept below 2 °C, with a maximum change of 4 °C measured during the heating season. The numerically modelled predictions of thermal degradation around the production and injection wells are compared with long-term field monitoring data, providing new insights into both aquifer, and user, behaviour. The Seasonal Performance Factor (SPFH4) of the pilot installation was 4.5 (W13/W50) in the monitoring period. An initial thermal resource estimation of the wider aquifer volume suggests that lowering the temperature of the aquifer by 8 °C could generate equivalent to 26% of the city's 2020 heating demand, but achievable heat extraction would in reality, be less. The study concludes that large parts of the aquifer can sustain shallow open loop ground source heat pump systems, as long as the local ground conditions support the required groundwater abstraction and re-injection rates. Future schemes can be de-risked and better managed by introduction of a registration of all GSHP schemes, with open sharing of investigation, design and performance monitoring data, and by managing thermal interference between systems using spatial planning tools.

Feasibility of closed loop ground source heat pump for residential heating and cooling applications in Serbia

Households sector in Serbia presents a great chance for energy savings and introduction of RES in the future. The public policies in Serbia are currently limited, but this kind of study can influence public measures that would undeniably generate long-term social and economic benefits to the country. The aim of the present work is to assess economic feasibility of closed loop heat pump systems for heating and cooling purposes in Serbia?s residential sector. The heat pump system was compared to the most commonly used heating fuels in households. Results indicate that the implementation of ground closed loop heat pump systems for heating and cooling purposes in Serbia?s residential sector as a substitute for electric heating is economically feasible. Inadequate prices of natural gas and electricity in public supply are the main problems associated with the project?s financial benefits. The best results were obtained in the scenario with combined debt ratio (40%) and grants (~30%) for the project realization, for which equity pay-back period is approximately three years, while benefit to cost ratio is 2.52. Investigated financial metrics (equity pay-back, internal rate of return assets and net present value) indicate the same positive results considering financial viability of the project.

Fouling and clogging surveillance in open loop GSHP systems

Fouling and clogging are some of the major water quality problems encountered in open loop ground source heat pump (GSHP) systems and aquifer thermal energy storage (ATES) systems. Here we present a surveillance strategy that can detect if and identify where in the system fouling and clogging might be developing without having to shut off the heat pump. In the presented system design, the test requires a minimum of four temperature sensors and two pressure sensors to describe the performance of the four major heat source system components, namely, the production well, the injection well, the submersible pump and the groundwater heat exchanger. The surveillance procedure involves conducting a step-test with incremental increases in the groundwater flow rate while measuring the pressure and temperature responses in the system components. The performance of the newly constructed installation functions as a baseline for future tests. By conducting the test systematically during operation an altered performance of the system can indicate clogging or fouling issues. Even though the cause of the problem must be identified through other means, the surveillance procedure presented here allows the operator to plan necessary maintenance and avoid critical damage to the heat source system.

Operational behavior characteristics and energy saving potential of vertical closed loop ground source heat pump system combined with storage tank in an office building

A ground source heat pump (GSHP) system utilizes a relatively stable underground temperature to achieve energy-saving for heating and cooling in buildings. Among various types of GSHP systems, Vertical Closed Loop Ground Source Heat Pump (VGSHP) has received increasing attention due to a variety of advantages such as the potential to be installed in a relatively small space and improved energy efficiency. In this research, in order to improve the system performance of a VGSHP, a VGSHP system coupled with heat storage tank was evaluated. For this purpose, the detailed analysis on the operational behavior of heat storage tank and the variations of heat pump energy performance due to the connection with heat storage tank was performed, and characteristics of heat pump part load ratios (PLRs) and the corresponding energy requirements, compared to chiller and boiler based conventional system, were analyzed in detail, using dynamic energy simulation after comprehensive validation process of heat pump performance curves. The results of this study showed that the VGSHP system coupled with heat storage tank showed an energy saving effect of about 20% for cooling and about 77% for heating compared to the conventional air conditioning system, and an energy saving effect of about 2% for cooling and about 15% for heating compared to the VGSHP system without heat storage tank, mainly due to the fact that the operational pattern of heat pump such as PLR and COP characteristics was changed by the operation of heat storage tank.

Ground-source heat pump systems: The effect of variable pipe separation in ground heat exchangers

Closed loop ground-source heat pump (GSHP) systems use ground heat exchangers (GHEs) to transfer heat to and from the ground and efficiently provide clean and renewable energy for heating and cooling purposes. Vertical GHEs contain pipes with circulating fluid (loops), which transfer thermal energy between the ground and the fluid. One very common assumption made in designing GSHP systems is that, when installed, these loops remain evenly separated along the length of the GHE, something that due to the nature of construction is rarely true. This can result in thermal interference not accounted for in the design, leading to a potential negative impact on the performance of the system. This paper investigates the effect of this interference, using detailed numerical simulations to compare different geometries, modelling fixed and variable pipe separations. A comprehensive parametric analysis is conducted to identify some of the most influential design parameters and the potential consequences on running and capital costs. Amongst the key findings of this study is the importance of the borehole filling material, as a highly thermally conductive material can minimise these negative effects from the thermal interference by up to 60%. Moreover, potential increases in drilling (capital) costs of up to 24% are shown, while the potential increases in running costs due to the reduced efficiency were found to be relatively minor.

Heat pump technology: An Alaska case study

Heat pumps are a proven technology around the world and are being increasingly used in Alaska. Technological advances have improved their performance at low temperatures, making them more suitable for arctic environments. This analysis identified data related to 17 heat pumps installed in Alaska, which included air source, ground source, and sea water source systems. The data show that the average installed cost/kW of the heat pumps studied was $5,579. The minimum cost was just over $700/kW for a small air source minisplit system and over $12 000 for a complex vertical loop ground source heat pump. Air source heat pumps in Alaska have operated successfully down to −15 °C. Technological advances are ongoing that should enable further heat pump operation in colder climates.

Cooling tests, numerical modeling and economic analysis of semi-open loop ground source heat pump system

Ground source heat pump (GSHP) systems are serving the heating and cooling demands of buildings worldwide. However, the widespread usage of these systems is limited because of their higher initial costs compared with conventional heating and cooling systems, especially in countries with high drilling costs like Japan. The semi-open loop GSHP system was introduced by authors and the results of heating tests and numerical modeling have been published. This system comprises two ungrouted vertical Ground heat exchangers (GHEs) in which groundwater is pumped from one well and injected to another using a water pump. The purpose of the water pumping and injection is to create an artificial groundwater flow around the GHEs to increase the heat advection between the GHEs and the surrounding environment.In this study, cooling tests on the semi-open loop GSHP system were performed and the thermal performance of the system was measured in each test. The developed numerical model was validated using the results of the cooling tests. Then, a sensitivity analysis was performed to evaluate the system performance under different operational and geological conditions during cooling operation. The results showed that in comparison with conventional GSHP operation, cooling coefficient of performance (COP) and system coefficient of performance (COPsys) can be enhanced by 13.1% and 6.6%, respectively, under fast groundwater flow conditions, as expected at the experimental site. In the absence of groundwater flow, the semi-open loop system is estimated to boost the cooling COP and COPsys by 101% and 62%, respectively, for cooling operations. Finally, an economic analysis was performed, considering the capital and running costs of the system and also the additional equipment costs associated with semi-open loop systems. The results of the economic analysis showed that water pumping and injection can reduce GSHP system costs by 22–36%.

Energy saving potentials from the application of heat pipes on geothermal heat pump system

A ground-loop heat exchanger is one of the key components to collect low grade ground heat for a ground source heat pump system. A typical ground source heat pump consists of a refrigerant loop operated by a compressor and a geothermal brine loop operated by a circulation pump. Although ground source heat pumps are known as one of the most efficient HVAC devices, their performance still need to be improved since the energy consumption by the peripherals like the circulation pump are considerable and estimated more than 10% of the total electricity input. In order to reduce the ground circulation energy, a variety of researches such as direct expansion geothermal heat pumps are studied, but no apparent performance improvement was found due to other negative effects like the increase of pressure drop in the ground loop. Geothermal heat pipe can be a good alternative to replace ground-loop heat exchanger for heating purpose. The energy saving potential using heat pipe as ground heat exchanger was investigated by comparing the energy consumption and COP of three types ground source heat pump. As a result, energy consumption for heating in Seoul by 10.3% than direct expansion ground source heat pump and 21.1% than secondary loop ground source heat pump. Therefore, ground source heat pump with geothermal heat pipe can be a suitable choice to save energy in a cold region.

The design and evaluation of an open loop ground source heat pump operating in an ochre-rich coal mine water environment

Mine water from the abandoned coal mines is considered a good source of low enthalpy energy resource as the temperature of the mine water remains stable throughout the year and is suitable to be used for heating and cooling applications when implemented in conjunction with Ground Source Heat Pump (GSHP). The GSHP is considered to be a low carbon technology and its application for space heating and cooling is being actively investigated and developed by companies and local councils around the world. The open loop GSHP installations, in comparison to closed loop systems, are suitable and economical for large scale heating and cooling demands. This is because there is no time delay for heat transfer when compared with closed loop systems and because they use large volumes of coal mine water at a relatively constant temperature. A few installations both large and small scale open loop mine water heating and cooling systems have been recently constructed throughout the world. However, coal mine water is associated with relatively poor water quality in some cases, often characterised by high salinity and pyrite oxidation. Despite the fact that mine water temperatures are favourably inclined for an efficient GSHP operations, concerns have been raised over the possibility of damage to the equipment due to poor water quality caused by clogging of the heat exchangers due to pyrite oxidation (ochre) in particular. Not much information is available on the impact of ochre has on the performance of an open loop GSHP when it is operated using the coal mine water rich in pyrite. This paper presents a novel design and implementation of an open loop system of GSHP operating in an ochre rich mine water environment. The results show that open loop systems, when combined with suitable heat pump and the associated design configurations of heat exchangers and maintenance procedures, could provide an efficient and reliable heating system at a lower cost.

Influence of GSHP system design parameters on the geothermal application capacity and electricity consumption at city-scale for Westminster, London

A city-scale renewable energy network for heating and cooling can significantly contribute to reduction of fossil fuel utilization and meeting the renewable energy targets. Ground source heat pump (GSHP) system is a technology that transfers heat stored over long periods to/from the ground to heat/cool the buildings. In particular, a vertical closed loop GSHP is a viable choice in densely populated urban areas. In this study, an ArcGIS-based simulation model has been developed to examine how many vertical closed loop GSHPs can be feasibly installed at city scale without overusing the geothermal energy underground. City of Westminster, in London, is used as a case study to identify and map areas where GSHPs can serve as a viable option for heating and/or cooling. A parametric study has been conducted to investigate the influence of how space heating and cooling demand is quantified on the potential utility of GSHP systems. The influence of COP variation during operation is also examined. The operational variation of COP influences the electricity consumption of the GSHP systems. Therefore, a comprehensive analysis including the capital cost, C/D ratio distribution, energy demand, and financial risk is highly recommended for district-level planning of GSHP systems.

Comparative thermal performances of a ground source heat pump and a variable capacity air source heat pump systems for sustainable houses

This paper presents a performance comparison of a variable capacity Air Source Heat Pump (ASHP) and a horizontal ground loop Ground Source Heat Pump (GSHP). Both these systems were installed side-by-side at the Archetype Sustainable Twin Houses at Kortright Center, Woodbridge, Ontario, Canada. The heat pumps were tested in both heating and cooling modes for extreme weather conditions of Ontario. For cooling mode, the coefficient of performance (COP) of ASHP ranged from 4.7 to 5.7 at an outdoor temperature of 33 °C and 16 °C respectively, while the COP of GSHP ranged from 4.9 (at an ELT of 8.5 °C and EST of 19.2 °C) to 5.6 (at an ELT of 12.4 °C and EST of 17.8 °C). For heating mode, the COP of ASHP ranged from 1.79 to 5.0 at an outdoor temperature of −19 °C and 9 °C respectively, while the COP of GSHP ranged from 3.05 (at an ELT of 44.4 °C and an EST of 2.7 °C) to 3.44 (at an ELT of 41.5 °C and an EST of 5.48 °C). Data extrapolation and TRNSYS simulation were also performed to predict annual performances of each system for major Canadian cities.

물 대 물 방식 수직 밀폐루프 지열원 히트펌프 시스템의 냉방성능에 대한 실험적 연구

A vertical closed loop ground source heat pump (GSHP) is used to produce heat from the low-grade energy source such as the outside air and ground source. It is known that a heat pump system type has better efficiency comparing to the electric heating system. This study only demonstrates that the vertical closed loop GSHP system is a feasible choice for space cooling of air conditioning. The coefficient of performance (COP) is the ratio of heat output to work supplied to the system in the form of electricity. For the vertical closed loop GSHP system in a cooling mode, the COP is the most commonly used way for judging the efficiency. For the purpose of this experiment, vertical closed loop GSHP system was installed in the laboratory and the experiment was executed. As a result, an average COP of vertical-closed loop GSHP system was 3.62 when the outside average temperature was .

Energetic and economic aspects of a heating and cooling district in a mild climate based on closed loop ground source heat pump

Over the next few years, thermal energy for heating residential buildings will be reduced, while cooling energy will be increasingly used. Therefore reversible heat pumps producing heating and cooling energy efficiently may become more popular in areas with mild climate. The Ground Source Heat Pump (GSHP) system is one of the most promising techniques which can be coupled with other solutions based on renewable energy.The present work considers a heating and cooling district based on a closed loop GSHP and its energetic and economic aspects, including the density of population in the district where the buildings are located. Economic analysis and payback times are investigated as a function of inhabitant density, adopted solutions, as well as different economical benefit scenarios.Primary energy consumption may be reduced in a range of 50–80%, compared to traditional systems. The district heating/cooling is more suitable in a medium density area and splitting a district into sub-district distribution systems may reduce the initial financial risk.Possible mechanisms for the diffusion of GSHP are here shown for district heating/cooling systems. Policy makers and stakeholders may use the results of this work for promoting possible incentives, which can be similar to the ones presented here.