Ground Source Heat Pump Project Research Articles

Building energy consumption simulation and its application in underground-water source thermal energy management system

In order to analyze the rationality of the compound well structure and the degree of heat penetration of groundwater in a groundwater ground source heat pump project in a certain district of a city, the author proposed a method for building energy consumption simulation and groundwater flow numerical model. The variation trend of groundwater temperature under different heat transfer temperature difference is simulated and predicted. The experimental results show that the fitting points where the error between the simulated predicted temperature and the actual measured temperature does not exceed 0.5?C account for 51.7%, the fitting points where the error is 0.5~1?C account for 28.7%, the fitting points where the error is 1~2?C account for 18.1%, and the fitting points where the error is greater than 2?C account for 1.5%. The dynamic change trend of the simulated predicted temperature curve is basically consistent with that of the actual measured temperature curve. It is proved that the building energy consumption simulation and the numerical model of groundwater flow can effectively analyze the rationality of the compound well structure of the groundwater ground source heat pump project and the degree of groundwater heat penetration.

Enhancement technology of underground water flow field in coal mine to improve energy efficiency of heat pump system in geothermal energy development

In order to solve the problem that the cold/heat released from the underground pipe of coal mine into the soil layer is difficult to dissipate in a short time, the technology of enhancing the underground flow field of coal mine in geothermal energy development to improve the energy efficiency of the heat pump system is proposed. In this paper, based on the ground source heat pump project located in a coal mine, the energy efficiency enhancement technology of the artificial flow field ground source heat pump system is studied and tested. The test results show that when starting work at about 8:00, due to the increase of heating load, the accumulation of cooling capacity around the buried pipe increases gradually, and the return water temperature at the ground source side decreases gradually. At 14:05, the water was pumped for the operation of the artificial groundwater flow field. It can be seen that the temperature of the return water at the ground source side began to rise gradually, indicating that the accumulation of cold water around the buried pipe was relieved to a certain extent. In conclusion, the artificial groundwater flow field can alleviate the accumulation of cold water around the buried pipe heat exchanger to a certain extent, improve the return water temperature of the buried pipe heat exchanger, and improve the energy efficiency of the ground source heat pump system.

Analysis of Heat Balance of Energy Storage Ground Source Heat Pump Project in Beijing

Analysis of Heat Balance of Energy Storage Ground Source Heat Pump Project in Beijing

A method for fast economic optimization of large hybrid ground source heat pump systems

This paper presents a novel simulation-based method for fast economic optimization of large hybrid ground source heat pump systems. Rapid evaluation of the objective function is achieved by the joint use of previously developed efficient algorithms, including Delaunay triangulation, successive flux estimation and fast spectral convolution. The resulting objective function is concave and composed only of continuous parameters. The global optimal solution of a problem composed of several dozens of boreholes operating over a 30 year time span is found using the Ant Colony Optimization algorithm for continuous domains, and convergence is achieved in under 12 min of computation time. Results show that optimization is key for proposing a financially viable hybrid ground source heat pump project for large commercial buildings. We also show that proper project financing, such as government guaranteed loans, can significantly contribute towards achieving better economic performance. The proposed approach is fast, convergent, practical, and can help promoters present hybrid GSHP projects under a less risky type of business.

Improvements in the Water Retention Characteristics and Thermophysical Parameters of Backfill Material in Ground Source Heat Pumps by a Molecular Sieve

The thermophysical properties of backfill material (BM) in a heat exchange borehole significantly influence the heat exchange effect of ground source heat pumps (GSHPs). Several treatments such as compaction and adding bentonite, cement, and fine sands are often used to improve the thermophysical properties. In this study, a 3A molecular sieve (3A-MS), a type of porous material, was added to the BM to enhance its water maintaining capacity. Three types of backfill materials with different additive contents, named as BM-0, BM-1, and BM-2, were examined. The variation of the BM properties such as the soil–water characteristic curve (SWCC), thermal conductivity, specific heat capacity, and thermal diffusivity with the groundwater content were investigated through a series of experiments and simulations. A scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and the BET method for specific surface area pore size analysis were used to characterize the material. The results indicated that the specific heat capacity improved with the water content whereas the thermal conductivity and thermal diffusivity decreased with the water content. The variation of the buried pipe outlet temperature with the change of the thermal physical parameters of the BM were researched by a numerical simulation and theoretical calculations; the results showed that BM-2 could raise the heat transfer rate per meter by 45.9% in summer and 118.4% in winter compared with the backfill materials without groundwater (NW). The research results provide theoretical support for the improvement of BM for ground source heat pump projects where abundant groundwater is available.

Assessment of Energy Potential and Benefit under the Ground Source Heat Pump Air Conditioning System in Anqing Area of Eastern China

Now ground source heat pump is a more efficient way to develop and utilize shallow geothermal energy because it is clean and environmentally friendly and has a relatively low energy cost. In order to optimize the planning layout and geographical space development in the eastern new town of Anqing city, which can realize the transformation and upgrading of real space and urban sustainable development, the exploration for shallow geothermal energy will be carried out in this area, so as to find out the comprehensive thermophysical parameters of the shallow rock-soil body and the heat transfer capacity of the vertical heat exchanger, etc. This paper takes the CBD in the eastern new town of Anqing as an example to provide the basis for the feasibility construction of the ground source heat pump project in the study area and evaluate the economic and environmental benefits of the expected project. According to the simulation test data of 5 working conditions of 4 geothermal exploration holes in the study area, we can clearly know that the energy cost per square meter of the ground source heat pump is 11.8 yuan for a building of one hundred thousand square meters in which the heat removal power is expected to be 9481 kW in summer and 3070 kW in winter. And the annual emission of carbon dioxide, sulfur dioxide, nitrogen oxides, suspended dust, and other air pollutants to the atmosphere can be reduced by 1442.5 t, and the solid waste ash and slag can be reduced by 59.7 t. The annual environmental treatment cost will be saved by 166000 yuan.

Study on Storage Conditions and Suitability Zoning of Shallow Floor Energy in Nanchang City

In the context of China’s carbon summit strategy, as renewable clean energy, the development and utilization of shallow geothermal energy has broad prospects. Based on the analysis of the occurrence conditions of shallow geothermal energy in Nanchang City, the suitability zoning of the ground source heat pump project in Nanchang City is studied by using the analytic hierarchy process. The results show that Nanchang is very suitable for the construction of the ground source heat pump system. Among them, the suitable area of the groundwater ground source heat pump is 252.17 km2, the basically suitable area is 133.64 km2, and the unsuitable area is 124.29 km2. The suitable area of the buried pipe ground source heat pump is 180.49 km2, the basically suitable area is 320.82 km2, and the unsuitable area is 8.79 km2. The evaluation results can provide a basis for the development and utilization of shallow geothermal energy in Nanchang.

Experimental study on ground subsidence caused by pumping and recharging

The natural flow field of groundwater is slow at Binhai New Area in Tianjin, which leads to the decrease of heat exchange efficiency of ground source heat pump. To solve this problem, pumping wells around the buried pipe were arranged to accelerate the flow rate of groundwater. Pumping would improve heat exchange efficiency and make ground subsidence. Our aim is to find a method to improve heat exchange and reduce ground subsidence. Based on previous researches, the periodic alternately pumping and recharging method was designed. Through field test and physical model test, the water level in pumping well, recharging well, observation holes, and pore water pressure and subsidence at different points were monitored and analyzed. The results show that the periodic alternately pumping-recharging method makes smaller subsidence than that of conventional pumping methods. It is feasible to apply it to ground source heat pump project in Tianjin. At a reasonable flow rate, period, and pumping-recharging mode, subsidence is small or even negligible. In addition, the pore water pressure and subsidence in aquifer and aquitard have different characteristics. The clay layer is mainly plastic deformation. With the process of pumping and recharging, the plastic deformation becomes smaller and smaller. The sand layer presents both elastic and plastic deformation. With the process of pumping and recharging, the plastic deformation becomes smaller and smaller, and tends to have elastic deformation gradually. Additionally, when the flow rate is large enough, soil particles in aquitard below the aquifer move to the aquifer with the seepage force caused by drainage.

Analyzing the heave of an entire city: Modeling of swelling processes in clay-sulfate rocks

Ground source heat pump (GSHP) systems play a key role in the exploitation of shallow geothermal energy as a renewable energy source. In clay-sulfate rocks, however, rock swelling is a major threat to the success of GSHP projects that may require extensive and costly countermeasures to mitigate the effects. Swelling is in these cases triggered by water ingress into expansive anhydrite bearing rock layers, followed by the chemical transformation of the sulfate mineral anhydrite to gypsum upon contact with water. Thus, assessing, understanding and quantifying coupled hydraulic and geochemical changes in the swelling zone is essential for selecting effective countermeasures. The present study examines these processes for a study site in Staufen, Germany, where an improper borehole heat exchanger (BHE) installation has allowed ingress of water into the clay-sulfate bearing strata of the Gipskeuper, followed by swelling and substantial heave of the land surface. A reactive transport model was employed to isolate the key processes and to evaluate a range of mitigation scenarios. The model simulations allowed for the assessment of (i) water inflow into the swelling zone, (ii) water availability for the transformation of anhydrite into gypsum within the swelling zone, and (iii) the potential for future swelling for each of the considered scenarios. Our results indicate that even with incomplete BHE sealing, water flow into the swelling zone and thus the swelling process can be arrested through appropriate hydraulic countermeasures. In contrast, our worst case scenario simulation predicts a further 10 cm of heave at the ground surface by 2025. The results illustrate the importance of integrating geological, hydraulic and geochemical information when assessing and predicting the efficiency of site-specific mitigation measures.

Technical-economic evaluation of ground source heat pump for office buildings in China

The adoption of ground-source heat pump (GSHP) in building sector for space heating / cooling, has increased rapidly during the past several decades around the world, especially in China. Meanwhile, it also exposed a lot of problems such as poor economic and energy efficiency, and even failure to operate properly. The purpose of this paper is to post-assess the application of existing GSHP projects, and to analyze the feasibility of ground-coupled heat pumps (GCHP) applied to office buildings in different climatic zones in China. More than one hundred GSHP cases are investigated through literature surveys and field data collection. Based on the post-evaluation results, a model for assessing the adaptability of GCHP is established. The feasibility evaluation of GCHP applied to office buildings are carried out, and key indicators, such as available capacity, energy savings, and cost-efficiency, etc. are presented among different climatic zones in China.

Feasibility study and economical evaluations of geothermal heat pumps in Iran

Negative effects of fossil fuels and the fact that their reserves will be exhausted in the near future have made nations all around the world look for novel replacing technologies. In recent years, the Ground Source Heat Pump (GSHP) has been considered as one of those beneficial solutions in industrial countries. It is obvious that for a replacing technology to be economically favourable is as important as being technically feasible. Iran is a country of several climates and needs to expand its energy basket for development. In this paper, the impact of temperature and humidity variations on the economics of a GSHP system is studied. In order to find the best region to install GSHPs, 9 different areas are selected with respect to ambient temperature and humidity diversity. Then, feasibility studies are carried out using RETScreen software to estimate the profitability of the project. The result indicates that the impact of a humidity variation is negligible in comparison with the temperature variation. Also, to determine the importance of the Iranian government’s incentive on the feasibility of GSHP projects, the natural gas price trend is considered in two scenarios. Further, a predicting equation to calculate annual cost based on temperature and a relative cooling/heating load is conducted by a regression method. Finally, the reduction in CO2 emissions due to the possible utilization of a GSHP system is determined in each region.

Development of a Multi-Objective Sizing Method for Borehole Heat Exchangers during the Early Design Phase

Ground-source heat pump (GSHP) systems coupled with borehole heat exchangers (BHEs) are widely used as a renewable energy source. However, the high initial costs to install the BHEs still acts as an obstacle in the expansion of these renewable energy source systems. Specifically, in South Korea, a typical residential type corresponds to an apartment building with a high building-to-land ratio for land efficiency, and thus the space to install the BHEs is usually insufficient. Furthermore, the high initial cost issue of BHEs makes it difficult to ensure the feasibility of GSHP projects in this type of a situation. This study proposes a novel BHE sizing method to support the process of sizing energy sources in the design development phase of a construction project. Life cycle cost (LCC) analysis was combined with a tool to optimize BHE sizing by considering various economic aspects. Entering water temperatures (EWT) to heat pumps in conjunction with the LCC were used to define objective functions. Consequently, Pareto optimal solutions were obtained on the EWT–LCC plot. A group of Pareto optimal solutions forms a Pareto-curve, and each point on the curve indicates a possible sizing scenario or alternative. Finally, it is possible for decision makers to compare the solutions that include both technical and economic information. The Pareto optimal solutions are expected to support proper decision making in the early design phase.

Measurement and Analysis of the Groundwater Source Heat Pump System in Shenyang

IntroductionAs one of the pilot cities for renewable energy application, which is defined by Ministry of Housing and Urban-Rural Construction of the People's Republic of China, Shenyang has widely popularized and applied GSHP(Ground Source Heat Pump) technology in winter heating and summer cooling. MethodsThis paper uses the GSHP system of a residential district of Shenyang as an example to investigate, test and analyze the GSHP project. The test of the indoor temperature and humidity should be done after the buildings have achieved stable thermal. ConclusionsThe system had stable performance, which benefited the system to have long-term operation. Compared with traditional air conditioner, the operation cost of GSHP was lower and it saves about 21.39% annual operation cost, which leads to the result that GSHP is economic and energy saving. The paper focuses on the experimental verification, needs further simulation software to calculate the results. This project was financially supported by the National science and technology support plan sub-topic (2011BAJ05B01-04).

Thermal conductivity map of the Oslo region based on thermal diffusivity measurements of rock core samples

A thermal conductivity map can serve as a good basis for ground-source heat pump projects in the pre-design phase. However, due to large variations, a thermal response test is required for larger projects to get the accurate values needed for proper design of the ground-source heat pump system. This study describes the systematic methodology for producing such a thermal conductivity map of a larger geographic area around Oslo, Norway. The map is based on the results of 1,398 thermal diffusivity measurements of rock core samples. The thermal diffusivity is measured and used in the calculation of the thermal conductivity of the different geological units in the bedrock map of the Oslo region. Large variations in thermal conductivity data were registered within the data sets for the different rock polygons and geological units and the greatest variation is found in metamorphic and sedimentary rocks. Rock polygons and geological units with magmatic origin show the least variation within the data sets. The internal micro structures of the rocks can have a strong influence on the thermal conductivity. This is pronounced in some foliated metamorphic rocks where the thermal conductivity is highest parallel to the orientation of the foliation. The median value for the whole data set is 2.62 W/(m K), while the minimum and maximum value is 1.0 and 6.88 W/(m K), respectively. The minimum value is a breccia, and the maximum value was measured in a quartzite/metasandstone. The lower and upper quartiles for the sets of rock polygons and geological units are 2.1–3.9 W/(m K), respectively.

Study on the Influence of the Operation Parameters to the Ground Source Heat Pump Energy Efficiency Ratio

This paper is based on 30 ground source heat pump projects measured data which is comparative analyzed, using SPSS statistical software for modeling and find out several key independent variables that influence the system COP and the linear relationship between them. Verify this model in order to lay a foundation for unified evaluation criterion for the ground source heat pump energy efficiency ratio.

Simulation of Temperature Field of Soil Inside Drilling around a Vertically Buried Single-U-Tube Ground Heat Exchanger

In this paper, the mathematical physical model of the heat and moisture transfer, which is about a vertical single-U-tube heat exchanger of a ground source heat pump (GSHP), is used to simulate the soil temperature fields inside drilling around a vertical single-U-tube ground source heat exchanger. The soil temperature fields inside drilling in the GSHP project running for one year are computed numerically. It shows that soil structure, cooling and heating load, cooling and heating period, and convalescence period have been determined by practical engineering conditions, the distance in the plane between drillings have a huge influence on heat transfer effect, only when the distance is designed reasonably, can it be possible to make sure normal heat transfer efficiency.

Influence of Convalescence on Soil Temperature Field around a Vertically Buried Single-U-Tube Ground Heat Exchanger

The mathematical physical model of the heat and moisture transfer in the single-U-tube heat exchanger of a ground source heat pump (GSHP) is validated using observed data from the practical rock-soil thermal response test on a resident district in Taiyuan, the soil is layered according to the geological structure of an actual drill in the depth direction in this model. Inputting the dynamic design cooling and heating load of the district into the Realizable turbulent model in Fluent, the temperature fields of a single well in the GSHP project running for 1 year in 2 conditions in which convalescence is considered and not, are simulated numerically. It shows that it rather necessary to take the influence of convalescence into consideration while predicting the soil temperature field of a GSHP system running for a long term, or may not correspond to the reality and make a wrong theory guide to the practical engineering.