Underground thermal heating
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Underground Thermal Heating: Insights and Innovations
Temporary Heating for Underground Stations
Heat Consumption in Construction Phases
During the construction of underground facilities, temporary heating is essential due to the absence of permanent heating networks. Research has quantified the specific thermal performance required for heating underground stations constructed using the open-cut method. The study determined that the estimated rate of heat energy consumption for temporary heating is 3.87 Gcal per 1,000 cubic meters per month, depending on factors such as outdoor temperatures, construction completion stages, and station depth1. This information is crucial for contractors to forecast financial costs accurately.
Ground Source Heat Pump Systems
No-Dig Method for Cost Reduction
An improved underground heat exchanger using a no-dig method has shown significant cost reductions in space heating and cooling systems. Experiments conducted at Hokkaido University demonstrated that this system could achieve a 78% energy reduction compared to conventional vertical earth heat exchangers. Additionally, the primary energy reduction rate, including system installation and operation, was 29% compared to typical air source heat pumps2.
Deep Ground Heat Exchangers
In South Korea, ground source heat pump (GSHP) systems with deep ground heat exchangers (GHX) over 300 meters have been studied for their feasibility and performance. These systems utilize stable underground temperatures to meet heating and cooling demands. Numerical simulations revealed that a 300-meter GHX could achieve a total heat exchange rate of 12.62 kW, which is 173% higher than a 150-meter GHX, indicating the potential for effective geothermal energy utilization in urban areas5.
Solar-Assisted and Seasonal Thermal Storage
Solar-Assisted Ground Source Heat Pumps
Solar-assisted ground source heat pumps (SAGSHP) have been integrated into conventional GSHP systems to reduce the size of ground heat exchangers and provide seasonal heat storage. An experimental study showed that after 19 months of operation, the system effectively met the space heating requirements of a building during winter. The solar energy injected into the ground helped recover soil thermal imbalance and store heat, highlighting the need for improved control strategies to optimize performance8.
Underground Seasonal Thermal Energy Storage (USTES)
USTES systems facilitate the efficient use of renewable energy by storing heat during summer or transition seasons for use in winter. These systems address the mismatching characteristics of renewable energy heating in terms of time, space, and strength. Despite their significant economic, social, and environmental benefits, challenges such as large heat loss and low solar fraction remain. Further research is needed to optimize design parameters, understand heat loss mechanisms, and develop effective control strategies10.
Geothermal Energy and Air-Pipe Systems
Geothermal Cooling and Heating
Geothermal energy, accessible for low-grade thermal energy supply, is utilized through ground heat exchangers (GHE). These systems consist of underground pipes that condition air by exchanging heat with the surrounding soil. This method provides indoor thermal comfort without additional cooling or heating loads, making it suitable for regions with both hot summers and cold winters4.
Underground Air-Pipe Systems
The heating and cooling potential of underground air-pipe systems has been evaluated for various climatic conditions. For instance, in hot-dry climates like Jodhpur, a 50-meter pipe at a 6-meter depth can achieve a cooling potential of 4472 kWh. In cold-dry climates like Leh, the heating potential under specific earth surface conditions can reach 9097 kWh, demonstrating the system's effectiveness in diverse environments6.
Conclusion
Underground thermal heating technologies, including temporary heating for construction, ground source heat pumps, solar-assisted systems, and seasonal thermal storage, offer promising solutions for efficient and sustainable energy use. Continued research and optimization are essential to overcome existing challenges and enhance the performance and viability of these systems.
Sources and full results
Most relevant research papers on this topic
Heat consumption for temporary heating of underground stations under construction
The estimated heat energy consumption for temporary heating of open-cut metro stations is 3.87 Gcal/(1,000 m3 month), depending on outdoor temperatures, construction completion, and station volume.
Improved underground heat exchanger by using no-dig method for space heating and cooling
The improved underground heat exchanger using a no-dig method can achieve 78% energy reduction compared to conventional vertical earth heat exchangers and 29% primary energy reduction compared to a typical air source heat pump.
Solar district heating with underground thermal energy storage: Pathways to commercial viability in North America
UTES systems need to achieve market viability in North America by offering attractive investment costs compared to natural gas-based systems for residential space heating.
Geothermal cooling/heating using ground heat exchanger for various experimental and analytical studies: Comprehensive review
Ground heat exchangers can provide indoor thermal comfort in regions with both hot summers and cold winters, reducing additional cooling or heating loads without additional construction.
Literature Review
Highly CitedFeasibility Study of Ground Source Heat Pump System Considering Underground Thermal Properties
Deep ground heat exchangers (GHX) can effectively provide geothermal energy to buildings in limited urban areas, with a total heat exchange rate of 12.62 kW, making them a realistic option with good geothermal gradient conditions.
Heating and cooling potential of an underground air‐pipe system
An underground air-pipe system can provide both heating and cooling potential, depending on the earth surface treatment and climate, with potential savings of up to 45% in Jodhpur and Leh climates.
Experimental study of a domestic solar-assisted ground source heat pump with seasonal underground thermal energy storage through shallow boreholes
The Solar Assisted Ground Source Heat Pump (SAGSHP) system effectively meets domestic heating needs with seasonal heat storage in shallow boreholes, but requires improved control strategy to avoid excessive inlet fluid temperatures.
Highly Cited