A comprehensive aero-hydro-structural analysis is conducted for a 5 MW offshore wind turbine system in this study. Soil–structure interaction under complex aero-hydro loading is analyzed to provide a suitable foundation design with high safety. With consideration of the wind turbine size and water depth, the monopile foundation design by the National Renewable Energy Laboratory (NREL) is selected in the current study. Both aerodynamic loading for the 5 MW wind turbine rotor defined by NREL and hydrodynamic loading on the foundation are simulated under different flow conditions using high-fidelity computational fluid dynamics methods. Structural dynamic analysis is then carried out to estimate the stress field in the foundation and soil. Results from the comprehensive analysis indicate that the Morison equation is conservative when looking at the stress field in the monopile foundation and underestimates the stress field in soil. A similar analysis strategy can be applied to other types of foundations such as jacket foundations and lead to more economical and reliable designs of foundations.

A solar heating system in greenhouse driven by Fresnel lens concentrator is built in this study. This system uses a soil thermal storage for greenhouse to supply heat in the absence of sunlight, ensuring the safety of the growth of crops. The structure and working principle of the device are introduced in this paper. The underground soil temperature was tested, compared with the indoor and outdoor temperature. The experimental testing result is given. A research shows that when the heating pipe buried 1.65 m underground, the time of heat transfer to the ground is about 5 days. The overall temperature rise of the soil is about 4 °C. In the condition of the coldest weather without additional energy supplement, the greenhouse's temperature is guaranteed above 8 °C, which can ensure the minimum temperature requirements of crop growth. According to the structural parameters of the existing system, the simulation of underground soil heat transfer and heat storage performance was carried out. Then, the temperature curves of different buried depths of the tube are given. The soil temperature steady time in different pipe-buried depths of heat storage temperature is theoretically calculated. It is proved that, to achieve the seasonal thermal storage in this system, the buried depth of the pipe should be over 2.5 m.

This paper presents a comparison of air conditioners using the conventional heating, ventilation, and air conditioning heat pumps and the one using solar heat stored underground, also known as shallow geothermal air conditioning. The proposed air conditioner with solar heat stored underground reunites practical data from an implementation of the heuristic perturb-and-observe (P&O) control and a heat management technique. The aim is to find out the best possible heat exchange between the room ambient and the underground soil heat to reduce its overall consumption without any heat pump. Comparative tests were conducted in two similar rooms, each one equipped with one of the two types of air conditioning. The room temperature with the conventional air conditioning was maintained as close as possible to the temperature of the test room with shallow geothermal conditioning to allow an acceptable data validation. The experiments made both in the winter of 2014 and in the summer of 2015 in Santa Maria, South Brazil, demonstrated that the conventional air conditioner consumed 19.08 kWh and the shallow geothermal conditioner (SGC) consumed only 4.65 kWh, therefore, representing a reduction of energy consumption of approximately 75%.

This paper describes a perturb-and-observe (P&O) control aiming to increase the heat exchange between solar heat stored underground and the ambient of a single conditioned room without any heat pump. This P&O control increases or decreases the water flow rate through an underground hosepipe heat exchanger. With this purpose, two power converters were used to activate, respectively, a low power water pump and a fan coil so as to keep the room within the limits of a reference temperature range (between 18 °C and 24 °C). Outside these limits, the P&O control searches for the best heat exchange between the ambient room and the underground soil and, when inside these limits, the water pump and fan coil are turned off. Two identical experimental rooms, referred in this study as “reference” and “test” rooms, had their temperatures measured every 1-min during winter and summer. For comparison purposes, the reference room was left at its natural conditions without any air conditioning. The experimental results show a remarkable improvement in the heat exchange and a considerable reduction in power demand when using the P&O control. As a result, it was obtained an energy saving of approximately 45% in one summer day and 22% in one winter day. It is important to point out that this paper refers, strictly, to the description of a P&O control for heat exchange systems involving solar heat stored underground in a single room.

In this paper, we review the main advances made by our research group on the heat transfer performance of complex flow architectures embedded in a conducting solid. The immediate applications of this work include the design of ground-coupled heat pumps, seasonal thermal energy storage systems, and district heating and cooling systems. Various configurations are considered: U-shaped ducts with varying spacing between the parallel portions of the U, serpentines with three elbows, and trees with T-shaped and Y-shaped bifurcations. In each case, the volume ratio of fluid to soil is fixed. We found the critical geometric features that allow the heat transfer density of the stream-solid configuration to be the highest. In the case of U-tubes and serpentines, the best spacing between parallel portions is discovered, whereas the vascular designs morph into bifurcations and angles of connection that provide progressively greater heat transfer rate per unit volume. We show that the flow of heat into or out of a solid volume must have an S-shaped history curve that is entirely deterministic. This constructal-design principle unites a wide variety of previously disconnected S-curve phenomena (ground heat storage and retrieval, population growth, cancer, chemical reactions, contaminants, languages, news, information, innovations, technologies, economic activity).

This paper presents a new three-dimensional analytical solution for transient ground-coupled heat transfer associated with slab-on-grade floor building foundations. The impact of above-grade walls on ground-coupled heat transfer is accounted for in the presented solution. The interzone temperature profile estimation (ITPE) technique is utilized to obtain the 3D solution suitable to determine soil temperature distributions and to estimate foundation heat loss/gain from slab-on-grade floors. The ITPE results are validated against results obtained from a closed-form solution in the case of steady-state conditions. It is found that that the above-grade walls can significantly affect the foundation heat losses especially for uninsulated slabs. Moreover, a simplified approach is proposed to obtain three-dimensional foundation heat losses from a two-dimensional solution.

A transient three-dimensional numerical solution is developed to analyze the thermal performance of thermo-active foundations used to heat and cool commercial buildings. Using laboratory testing data, the numerical solution is validated and used to carry out a sensitivity analysis to assess the most important design and operating parameters that affect the thermal performance of thermo-active foundations. It is found that the foundation depth, the shank space, the fluid flow rate, and the number of U-tube loops in each foundation pile are the main parameters that affect the thermal performance of a thermo-active foundation system. Based on the validated numerical solution, thermal response factors for a thermo-active foundation are developed, and implemented into a detailed building energy simulation program. These thermal response factors are then used to estimate the impact of installing thermo-active foundations on the total energy use of typical office buildings in representative US climates.

In order to create interior multiclimate zones suitable for plant cultivation in a solar chimney project proposed for the World Horticultural Exposition 2016 in China, the numerical investigation is performed to a solar chimney with 2 km radius and 1 km height. The simulation methodology is validated by experimental data. The impacts of inlet height and radius to interior thermal characteristics are evaluated. It is found that the temperature field is much similar when the inlet height decreases from 3.8 m to 0.5 m. With further decrease of the inlet height to 0.2 m, its impact to temperature field is significant. The temperature field is similar though the radius of solar chimney decreases from 2.0 km to 1.725 km. Further decrease to 1.13 km results in much lower temperature field as less radiate heat is obtained. The procedure of soil surface temperature calculation is also proposed to obtain the supplementary heat amount maintaining the required temperature for plant cultivation.

This paper presents an analytical solution associated with the steady-periodic heat transfer for a typical slab-on-grade floor building foundation in contact with a nonhomogeneous soil medium. In particular, the solution accounts for the impact of the above-grade wall thickness on the ground-coupled heat transfer. The interzone temperature estimation profile (ITPE) technique is utilized to obtain the analytical solution to determine soil temperature distributions and to estimate foundation heat loss/gain from slab-on-grade floors. In this paper, the impact of the nonhomogeneous soil properties on the transient foundation heat transfer is investigated for various slab configurations and soil thermal properties. The presented solution presents the first ITPE analytical solution for building foundation coupled with layered soil medium. The results indicate that nonhomogeneous soil properties have a significant effect on soil temperature distribution and on total slab heat loss. In particular, it is found that an error of up to 20% in estimating total slab heat transfer can be incurred if homogeneous soil medium is considered instead of a two-layered ground.

This paper presents a heat transfer model for thermo-active drilled-shaft foundations used for heating and cooling buildings. Specifically, this paper presents a numerical approach to evaluate the unsteady temperature distribution within the ground medium surrounding the foundation as well as indoor/outdoor heat fluxes. In particular, a 2D numerical solution was obtained using the finite difference technique with a purely implicit solution scheme. The results of the sensitivity analysis indicate that the efficiency of the thermo-active foundation can be significantly improved with a proper selection of design parameters including heat exchanger fluid flow velocity, foundation depth, and foundation materials.

This paper provides a numerical solution for simultaneous heat and moisture transfer within frozen soil beneath slab foundations of refrigerated warehouses. The developed solution is validated using data from experimental tests. A parametric analysis is then performed to determine the impact of slab insulation levels and to estimate the time required to reach steady-state ground-coupled heat transfer conditions. Finally, the solution is utilized to determine an effective soil thermal conductivity that could be used in a purely heat conduction model for ground-coupled heat transfer beneath freezers.

This paper discusses selected results from a numerical solution of two-dimensional heat and moisture transfer within frozen and unfrozen soils beneath freezer slab foundations. In particular, the numerical solution is used to determine soil temperature profiles as well as freezer foundation heat gains. Finally, an effective soil thermal conductivity is successfully utilized in a pure heat conduction model to predict ground-coupled heat gains for freezers.

In this paper, the effects of moisture on the heat transfer from two basic types of building foundations, a slab-on-grade and a basement, are examined. A two-dimensional finite element heat and moisture transfer program is used to show the effects of precipitation, soil type, foundation insulation, water table depth, and freezing on the heat transfer from the building foundation. Comparisons are made with a simple heat conduction model to illustrate the dependency of the soil thermal conductivity on moisture content.

Ground-heat transfer is tightly coupled with soil-moisture transfer. The coupling is threefold: heat is transferred by thermal conduction and by moisture transfer; the thermal properties of soil are strong functions of the moisture content; and moisture phase change includes latent heat effects and changes in thermal and hydraulic properties. A heat and moisture transfer model was developed to study the ground-coupled heat and moisture transfer from buildings. The model also includes detailed considerations of the atmospheric boundary conditions, including precipitation. Solutions for the soil temperature distribution are obtained using a finite element procedure. The model compared well with the seasonal variation of measured ground temperatures.

General semi-analytical solutions for the steady-state heat conduction problems for circular and three-dimensional rectangular slab-on-grade floors with uniform insulation are presented. The soil temperature field, and the total slab heat loss are presented and analyzed using the Interzone Temperature Profile Estimation (ITPE) technique. A parametric analysis is conducted to determine the effect of thermal insulation U-value, slab size, and water table depth on the total slab heat loss. In particular, it was found that the total slab heat loss is independent of its shape but is strongly affected by the slab size and thermal characteristics.

Analytical solutions for steady-periodic ground-coupled heat conduction problems for cylindrical and three-dimensional rectangular slab-on-grade floors beneath refrigerated structures with uniform and partial insulation are presented in this paper. The solutions provide the soil temperature field, and the total slab heat gain. A parametric analysis is conducted to determine the effect of thermal insulation U-value and insulation width on the mean, amplitude, and phase lag of total slab heat gain. In particular, it was found that the mean and the amplitude of the total slab heat gain are effectively independent of its shape but are strongly affected by the slab size and thermal characteristics. [S0199-6231(00)00502-5]

Using soil and groundwater for heat storage offers an opportunity to increase the potential for renewable energy sources. For example, solar heating in combination with high temperature storage, e.g., using ducts in the ground, has the potential of becoming an environment friendly and economically competitive form of heat supply. Technology is developed to reduce ground construction costs and to ensure that adequate attention is paid to the geotechnical potentials and limitations of such systems, in the temperature range between neutral ground temperature up to 90°C. Investigations of real plants and in the laboratory have given valuable knowledge on the thermal effects on clayey soils as well as on the surroundings of high temperature stores in soft clay. The operational function of heat stores, with respect to heat transfer capacity of ground heat exchangers and heat losses, can be predicted with good agreement. For the uppermost part of the temperature range, long term performance, cost verification and thermal endurance of materials involved including the storage medium, is recommended using a full-scale demonstration plant. [S0199-6231(00)00901-1]

A geothermal heat pump (GHP) system with three ground coils was installed in a residence in northern Idaho with a portion of the ground heat exchanger wrapped around the residential septic tank. The septic coil provided a significant portion of the heating for the residence over the heating season. There was no evidence of the septic tank freezing up or failing to properly function. Utilizing a septic tank as a heat source for GHP systems is feasible design option if the septic tank is used on a full-time basis. However, the tank should be surrounded on all sides by a large amount of soil and/or insulated from the ground surface to ensure that ground temperatures near the tank remain warm during the winter.

A large portion of the installation cost of a ground-coupled heat pump system is for the excavation necessary for ground coil placement. One possible method of reducing this cost is to place the ground coils beneath the slab floor of the building. This configuration of ground coil placement has not been specifically addressed in previous research. Freezing of the soil must be avoided in such a system. To simulate the temperature response of the surrounding soil to heat pump operation, a computer model was developed which incorporates line source theory in the form of a system of rings. The fluid temperature change along the length of the coil was used to determine the distribution of the ground load throughout the ring system. The model includes an adiabatic upper boundary, seasonal soil temperature variation, and thermal interference throughout the system. Using these results, the minimum soil temperature over a season was predicted. Based on these results, design recommendations for ground coil installation are provided based on available area, soil type, heat extraction rate, depth of coil beneath the slab floor, and depth of slab floor below grade. These include recommendations for pipe spacing, flow direction, and a method to determine whether this type of system is feasible for installation in a particular location.

The general solution of soil temperature distribution is developed for a slab-on-grade floor with a known heat flux distribution at the slab surface. The Interzone Temperature Profile Estimation (ITPE) technique is applied to determine the steady-state variation of temperature within the ground. A water table at constant temperature is assumed to exist at a given depth below the soil surface. As a first application of the general solution, the optimum thermal insulation distribution is obtained for a slabon-grade floor. A second application of the solution developed in this paper consists of a diagnostic method to determine the configuration and the R-value for the thermal insulation of the slabon-grade floor based on measured data for the heat flux at the slab surface. A parametric analysis is conducted to determine the effects of heat flux profiles and water table depths on the required insulation distribution at the slab surface.