Underground Temperature Research Articles

Cooling pathways for deep Australian longwall coal mines of the future

Cooling of coal mines in the Bowen Basin, characterized by steep geothermal gradient, is presently achieved mostly through rental surface bulk air cooling in summer months. This paper argues that future mines will be required to focus their cooling resources more intensively to manage a challenging thermal environment where virgin coal temperatures over 50 °C at a depth of 500 m are expected. Currently, mine cooling systems are employed to maintain the wet bulb temperatures (WBT) to below 27 °C at which point the risks of heat stroke or other heat related issues are manageable. The capacities of these systems are in the range of 6–10 MW refrigeration power. The relationship between high working temperature environment and injury frequency rates is well established. Therefore, provision of appropriate cooling strategies and understanding their optimum performance and suitability are important to Australian coal mines of the future. This paper evaluates the underground temperature profiles of deep, gassy coal mines with propensity for spontaneous combustion and proposes the long term cooling pathways to effectively manage the thermal hazards. Thermodynamic modeling is performed on a longwall face and includes air leakage effects from goaf streams at various locations along the longwall face. The strategy summarizes the application of underground bulk air cooling, chilled water sprays on the shearer and the resulting temperature profiles. Considering the new mining projects planned for the Bowen Basin region, a review of implementable cooling strategies such as mid-gate mobile bulk air coolers (BACs), spot coolers, underground bulk air cooling and the use of chilled water to enhance the positional efficiency of cooling plants, are discussed in this paper. Finally, the comparison of ‘rental’ versus ‘ownership’ of cooling plants is analysed as part of long-term cooling strategies.

Experimental Study on the Heat Release Operational Characteristics of a Soil Coupled Ground Heat Exchanger with Assisted Cooling Tower

Hybrid ground source heat pump systems (HGSHPS) with assisted cooling towers is one of the most efficient cooling and heating technologies for buildings with cooling-dominated loads. For the system, the coupled heat release mode between the ground heat exchanger (GHE) and cooling tower is vital for underground soil temperature recovery characteristics and system operation performance. In order to obtain the heat release operation characteristics with different coupled modes of the GHE and cooling tower, a set of multi-functional heat release experimental systems of soil coupled GHE with assisted cooling tower was constructed. The experimental investigations on the system heat release operation characteristics operated in the separate GHE heat release mode, combination heat release mode and day and night alternate heat release mode were undertaken based on the experimental system. The results show that for the separate GHE heat release mode, the heat release rate of GHE rises rapidly during the first two hours of operation, then, gradually tends to be steady, and the soil excess temperatures at various depths gradually rise with time. For the combination heat release mode with continuous operation of cooling tower, in view of reducing soil heat accumulation and accelerating soil temperature recovery, it is more conducive to the heat release by opening the cooling tower on sunny days. For the combination heat release mode with intermittent operation of cooling tower, when the total time ratio of cooling tower running to stop is constant, the intermittent time is longer, the better the effect of soil temperature recovery. Additionally, the soil temperature recovery rate can be improved greatly by the release heat operation of cooling tower during night, and the longer the cooling tower runs, the closer the soil temperature is to the initial temperature.

Performance analysis of a wind tower in combination with an underground channel

In the present work, a new method was introduced in order to improve the performance of wind towers. In hot seasons, underground temperature is lower than that of the surface and it can be used as a free cooling source. Accordingly, in this work, the use of a wind tower in combination with an underground channel for passing the air was introduced and investigated. This research was done for two cases of dry and wet channels. In order to solve this problem numerically, governing equations were discretized using finite volume method, SIMPLE algorithm was used for pressure-velocity coupling and k−ε model was chosen as turbulent model. Considering the weather conditions of Yazd in Iran as a sample of the regions where using wind towers is common, this study concluded that using dry or/and wet channels, the entrance air temperature was reduced from 42°C to 34.4°C and 26.6°C, respectively. Using the wet channel, the relative humidity of air increased by 52%, from the initial value of 14% to 66%, and the water consumption of 0.006kg/s and air mass flow rate of 0.8466kg/s were achieved. Results showed that this method is efficient due to thermal comfort conditions.

Geothermal potential assessment of the Nevado del Ruiz volcano based on rock thermal conductivity measurements and numerical modeling of heat transfer

This work presents an estimation of the geothermal potential of the Nevado del Ruiz (NDR) volcano, bridging the knowledge gap to develop geothermal energy in Colombia and improve resource estimates in South America. Field work, laboratory measurements, geological interpretations, 2D numerical modeling, and uncertainty analysis were conducted to the northwest of the NDR to assess temperature at depth and define thermal energy content. About 60 rock samples were collected at outcrops to measure thermal conductivity with a needle probe. A 2D numerical model, built from an inferred geological cross-section, was developed with the software OpenGeoSys to simulate the underground temperature distribution and then estimate the geothermal potential of a 1 km2 area with sufficient temperature, assuming a recovery factor equal to 2.4% and a 30 years exploitation time. Coupled groundwater flow and heat transfer were simulated in steady-state considering two different thermal conductivity scenarios. Results show that the average estimated potential is 1.5 × 10−2 MWt m−1 of the reservoir thickness, considering temperatures greater than 150 °C located at a depth of approximately 2 km, in a selected area situated outside of the Los Nevados National Natural Park (NNP), to avoid any direct intervention on this protected area. According to a Monte Carlo analysis considering pessimist and optimist scenarios of thermal conductivity, the estimated geothermal power was 1.54 × 10−2 MW m−1 (σ = 2.91 × 10−3 MW m−1) and 1.88 × 10−2 MW/m (σ = 2.91 × 10−3 MW m−1) for the two modeling scenario considered.

Study on the thermal effect of the ground heat exchanger of GSHP in the eastern China area

The two-year operating performance and the variation in the underground thermal environment of a ground source heat pump (GSHP) system are presented in this work; the GSHP has been installed in an office building in Hangzhou. The system consists of two heat-pump units, each with a heating/cooling capacity of 470 kW/465 kW, and 201 boreholes. The flow rates and temperatures of water on the user- and buried-pipes side, the electrical power consumption of the heat-pump units and the water pumps, and the underground temperatures were monitored during this project. The result of the performance monitoring revealed that the average daily COP of the units and the system was approximately 5.0 and 3.0, respectively, during cooling seasons, and 4.5 and 2.7, respectively, during the heating seasons. It was found that the electricity consumption of the water pump accounted for 39.7% of the total electricity consumption, which is high enough to degrade the system performance. It was also found that the heat released by the GSHP system during the cooling season is more than the heat absorbed during the heating season at the hot-summer and cold-winter zone. The underground heat imbalance rate was approximately 24% in the first year, and was approximately 53% in the second year. The result of underground temperature monitoring showed that the underground temperature increased by 1.1 °C after two years of system operation. This reveals that the heat exchange between the GSHPs and the soil is unbalanced, which eventually caused “heat accumulation”. Moreover, the variation in the underground thermal environment was revealed by the changes in underground temperature according to time, depth, and season. Finally, in this work, a simple model is presented, which quantitatively verifies the underground heat imbalance through the underground temperature variation. Reasonable agreement of results verified the underground heat imbalance, and confirmed the reliability of the model. Overall, this study provides a significant amount of experimental data for the analysis of the underground thermal environment variation and the heat balance. The results of this study will contribute toward the development of more creative methods for the mitigation of the impact of “heat accumulation” on the environment at the hot-summer and cold-winter climate zone. In addition, the method used in this work can be applied to other climate zones for the study of the thermal effect of the GSHP ground heat exchanger.

都市化による地中温度の上昇に関する研究 : 第2報-異なる地表面下における地中温度の実測とモデル化

都市化による地中温度の上昇に関する研究 : 第2報-異なる地表面下における地中温度の実測とモデル化

A-40 地中温度推定手法の開発のための研究

A-40 地中温度推定手法の開発のための研究

APPROACHES TO THE GAS CONTROL IN UCG

Underground Coal Gasification represents an alternative for conventional coal mining. This technology is also less expensive than traditional mining. It is expected that coal will be an important energy source in the coming decades. In requirement to improve the gasification process we must ensure that the combustion reactions generated enough energy to heat the reactants. This can be achieved by controlling the flow of oxidizing agents and the underpressure control at the exit of the reactor UCG. This paper aims to propose the stabilization of air flow as a main gasification agent injected to the gasifier, underground temperature and concentration of O2 in syngas. Also there is proposed the mechanism that could cope with uncertainties in the process of UCG and its control on stabilization level. Paper presents utilization of discrete controller with adaptation in order to stabilization of UCG process variables. The controllers were verified on experimental ex-situ reactor (generator).

Measurement and modelling of the ground temperature profile in Zarqa, Jordan for geothermal heat pump applications

The use of Geothermal Heat Pumps (GHP) for cooling and heating applications is still to be assessed in Jordan. As a first step in the assessment of the technical and economic feasibility of GHP option, it is necessary to have an accurate understanding of the underground temperature distribution. Such distribution is key to the evaluation of the type, size, design, and depth of the ground heat exchanger of the proposed heat pump systems. For this purpose, this study was conducted to experimentally establish the year-round underground temperature distribution profile near the city of Zarqa in Jordan. The daily and seasonal ground temperature profiles are presented for various depths. It is demonstrated that despite the cyclic nature of the daily and seasonal variations of the ambient and ground surface temperatures, the underground temperature variations diminish with depth and stabilize throughout the year at around 21°C starting from a depth of 5m below the surface. A simplified semi-empirical model was also developed to predict the temperature profile as function of time, depth, the mean ground surface temperature, and soil properties with the help of the measured data.

Performance study on heat and moisture transfer in soil heat charging

ABSTRACTIn some cold areas, the system performance of the soil source heat pump system is reduced by the decreasing underground soil temperature, which is caused by the thermal imbalance between the heating demand in winter and the cooling demand in summer. Soil heat charging with solar energy in non-heating seasons is proposed for solving the problem. It has been found from previous studies that the effect of the moisture transfer on the heat transfer within porous media could not be neglected especially under higher temperature difference. Therefore, this paper provides an investigation on the heat and moisture transfer in soil during soil heat charging at high temperature. A numerical model is developed for the study. The simulation results are compared with the testing data from the authors' previous study for the model verification. Based on the verified model, the performance of the heat and moisture transfer in soil during soil heat charging in a longer time and a larger area is investigated in the paper. The results show that the testing data match very well with the simulation results within a relative error of ±9% and the mathematical model is reliable for the performance prediction of heat and moisture transfer in soil heat charging. The soil volumetric water content (VWC) distribution tends to be stable after soil heat charging for 13 days and the heat source has an effective influence on soil VWC distribution within 2.4 m. The effect of the heat source temperature and initial VWC on the soil temperature and VWC distribution and heat power is proved to be obvious. Loam has a better performance in soil heat charging than sand.

Near‐surface Geothermal Gradient Observation and Geothermal Analyses in the Xianshuihe Fault Zone, Eastern Tibetan Plateau

AbstractThe Xianshuihe fault (XSHF) zone, characterized by intense tectonic activity, is located at the southwest boundary of the Bayan Har block, where several major earthquakes have occurred, including the 2008 Wenchuan and the 2013 Lushan earthquakes. This study analysed underground temperature sequence data for four years at seven measuring points at different depths (maximum depth: 18.9 m) in the southeastern section of the XSHF zone. High‐frequency atmospheric noise was removed from the temperature sequences to obtain relatively stable temperature fields and heat fluxes near the measurement points. Our measurements show that the surrounding bedrock at (the seven stations distributed in the fault zone) had heat flux values range from −41.0 to 206 mW/m2, with a median value of 54.3 mW/m2. The results indicate a low heat flux in the northern section of Daofu‐Kangting and a relatively high heat flux in the southern section of Kangting, which is consistent with the temperature distributions of the hot springs near the fault. Furthermore, our results suggest that the heat transfer in this field results primarily from stable underground heat conduction. In addition, the underground hydrothermal activity is also an obvious factor controlling the geothermal gradient.

Time-lapse electrical resistivity imaging of the thermally affected zone of a Borehole Thermal Energy Storage system near Torino (Northern Italy)

A Borehole Thermal Energy Storage living lab was built up nearby Torino (Northern Italy). This living lab aims at testing the ability of the alluvial deposits of the north-western Po Plain to store the thermal energy collected by solar thermal panels and the efficiency of energy storage systems in this climatic context. Different monitoring approaches have been tested and analyzed since the start of the thermal injection in April 2014. Underground temperature monitoring is constantly undertaken by means of several temperature sensors located along the borehole heat exchangers and within the hydraulic circuit. Nevertheless, this can provide only pointwise information about underground temperature distribution. For this reason, a geophysical approach is proposed in order to image the thermally affected zone (TAZ) caused by the heat injection: surface electrical resistivity measurements were carried out with this purpose. In the present paper, results of time-lapse acquisitions during a heating day are reported with the aim of imaging the thermal plume evolution within the subsoil. Resistivity data, calibrated on local temperature measurements, have shown their potentiality in imaging the heated plume of the system and depicting its evolution throughout the day. Different types of data processing were adopted in order to face issues mainly related to a highly urbanized environment. The use of apparent resistivity proved to be in valid agreement with the results of different inversion approaches. The inversion processes did not significantly improve the qualitative and quantitative TAZ imaging in comparison to the pseudo-sections. This suggested the usefulness of apparent resistivity data alone for a rough monitoring of TAZ in this kind of applications.

Optimization of Ground Heat Exchangers in Area with Imbalanced Heating and Cooling Load

In order to improve the uniformity of underground temperature, three optimal layouts including 36 buried pipes are proposed with cooling/heating load ratio of 2.5:1.The results show that the less the number of tubes are located in the central area, the more uniform the temperature field will be. The surrounding temperature is slightly higher than that of traditional layout. The results proved that the proposed layouts can effectively reduce the peak value of temperature field, and the results also provide reference for ground source heat pump system designers.

直接膨張方式地中熱ヒートポンプの性能評価

The purpose of this study is to investigate the performance of a ground source heat pump using direct expansion method in case of hot water supply system. The underground temperature beneath about 10m maintains almost constant throughout a year. Ground Source Heat Pump (GSHP) utilizes this property. GSHP using direct expansion method has higher performance than GSHP using indirect heat exchanger method. GSHP using direct expansion method can also be reduced the number of parts and initial cost. GSHP using direct expansion method is difficult to evaluate the power of heating in the refrigerant side because the refrigerant becomes two phase flow and it reduces the measurement accuracy of flow rate. Therefore, we tried to evaluate the performance on GSHP using direct expansion method as hot water supply system. We get the amount of heat was evaluated by measuring the temperature difference and flow rate of supplying hot water. We used the closed loop vertical borehole which depth was 30m. Average of COP became 3.1.

The coupling effect of ventilation and groundwater flow on the thermal performance of tunnel lining GHEs

Tunnel lining ground heat exchangers (GHEs) in this paper have advantages such as not requiring extra space, a low construction cost, and more efficient in heat exchange, offering a solution to the utilization of geothermal energy in central urban areas. Ventilation and groundwater flow are two important factors that significantly affect the underground temperature field. Laboratory model tests were carried out to evaluate the coupling effect of ventilation and groundwater flow on the thermal performance of tunnel lining GHEs. The test results show that (i) ventilation enhances the heat exchange process between the GHEs and the surrounding rock; (ii) the depth to which the GHEs influence the surrounding rock temperature field in the downstream of the groundwater flow field is 2.6 times higher than that in the upstream, and the ventilation and groundwater flow aggravate uneven distribution of the temperature field of the surrounding rock, so the heat exchange pipes should be installed in the upstream of the groundwater flow field; (iii) the coupling heat transfer between air and lining should be taken into consideration when the heat exchange rate of the heat exchange pipe is calculated.

Study on Thermal Behavior of an Experimental Low-energy Building in the Hot Summer and Cold Winter Zone of China

This paper is based on a study of the expansion part of the architecture department building in Huazhong University of Science and Technology (hereinafter referred to as the experimental building). Thermal environment parameters, building energy consumption and other aspects of the experimental building are monitored. The results show that indoor air temperature can be improved to about 14°C in winter and 28°C in summer by the thermal regulation system, which was limited by the underground soil temperature in Wuhan. Because of the function of the under floor air distribution system, an uneven air temperature distribution is formed in the experimental building. The building energy consumption is 10.7kWh/(m2*a), much lower than the ordinary office buildings in Wuhan. In general, the experimental building can achieve a certain indoor thermal environment with low energy consumption, meeting the requirements of buildings with no-strict thermal comfort demands in the rural areas of hot summer and cold winter zone of China. A heat pump or auxiliary heating/cooling source should be added in the system to achieve a more comfortable indoor environment.

Winter Turf Growing Season Elongation Characteristics of a Thermosyphon Unit that Uses a Shallow Geothermal Source

AbstractLow temperature stress is an important factor for turf growth in the northern high‐latitude environment. A thermosyphon temperature controlling unit with a shallow geothermal source was proposed by analyzing present techniques to prolong the turf growing season in winter. Thermosyphon unit prototypes were developed and tested in a water park. The relations between ambient temperature, depth, material, structure, underground temperature, and root temperature were studied experimentally. The thermosyphon unit performance was analyzed. Results indicate that underground and root temperatures remain almost constant with an hourly ambient temperature. The root temperature remains steady due to the thermosyphon unit application. The underground temperature increases with the depth increase, and the increment is at most 1 °C. The root temperature of a copper thermosyphon unit is higher than that of a steel thermosyphon unit, and the temperature difference can reach 2 °C. The root temperature of a type I thermosyphon unit is higher than that of a type II, and the temperature increase is less than 1 °C. The root temperature variation due to the thermosyphon material is smaller with the increase in depth.

Enhancements to a Simple Pavement Frost Model

The ability to predict the timing of thaw is important to the design and the maintenance of roads. Such knowledge allows highway agencies to reduce the damage caused by enacting seasonal load restrictions during thawing. Because measurement by observation or testing requires time and resources, one desirable solution is a predictive model. Simple models, such as the Cornell Pavement Frost Model (CPFM), require only daily temperature weather inputs. Possible improvements to the CPFM were tried with a primary goal of improving thaw timing while keeping the model simple and applicable across New York State and beyond. The proposed modifications included changing the thaw reference temperature, providing better tracking of thermal properties throughout seasonal changes, and driving thaw from underneath with a constant underground temperature. During the investigation, further changes were tested involving ways to treat latent heat during thaw, including decoupling. Changes were tested against frost tube data from Ithaca, New York. The model was evaluated and adjusted at other sites in Maine and New Hampshire. The additional inputs required by the resulting modified model were depth and value of constant temperature, moisture content, and estimated shade. The modified model greatly improved the depth and timing of the model for most sites. The final model used the original formulation with minor modifications for freezing and a latent heat formulation for thawing. With more than one freezing–thawing front, the formulas were decoupled. Further investigation should be done to improve frost depth and timing, and in particular, to find out why rapid thawing from underneath does not occur at some sites.

直接膨張方式地中熱ヒートポンプシステムの性能評価

The purpose of this study is to investigate the performance of a ground source heat pump (hereafter, GSHP) using direct expansion method in case of hot water supply system. The underground temperature beneath about 10m maintains almost constant throughout a year. The GSHP utilizes this constant temperature. The GSHP using direct expansion method has higher performance than the GSHP using indirect heat exchange method. The GSHP using direct expansion method can also be reduced the number of parts and initial cost. However, the GSHP using direct expansion method is difficult to obtain an amount of heat removed in a refrigerant side because the refrigerant becomes two phase flow and it reduces the measurement accuracy of flow rate. Therefore, we tried to evaluate the performance of the GSHP using direct expansion method as hot water supplying system. The amount of heat removed was evaluated by measuring the temperature difference and flow rate of supplying hot water. We used the closed loop vertical borehole whose depth was 30m. In the case that the setting temperature of hot water was 45°C, the heating time was 7 hour 46 minutes and time averaged COP was 3.29.

Analysis of underground cable ampacity considering non-uniform soil temperature distributions

An analytical model for the assessment of cable ampacity due to non-uniform underground temperature distribution is presented. The uneven underground temperature is usually caused by a non-uniform surface heating (e.g., a street or parking crossing, etc.), which is extended for certain length along the cable installation and in depth. The underground temperature distribution is obtained by solving the heat equation with the respective boundary conditions. The cable ampacity reduction is calculated as a function of the surface temperature distribution and the cable depth of burial. The model is validated and several numerical results are obtained for different installation conditions.