Earth-contact Heat Transfer Research Articles

Freezing soil effects on earth-contact heat transfer

The inclusion of soil freezing and snow cover within the context of a building energy simulation is explored. In particular, a method of including soil freezing within the simulation of heat flow from a building to the neighbouring foundation soils is considered. Non-linear thermal conductivity and heat capacity relations are explored that account for the effect of soil freezing. In addition, the work also considers latent heat generated by phase change that occurs as the soil water temperature reduces and ice forms. A simple approach to represent the insulating effect that snow cover may have on the net heat flow at the ground surface is also provided. The approach is illustrated by application to the simulation of a full-scale ground heat transfer experiment performed by others. The results provide a first indication of the potential significance of the inclusion of ground freezing within the context of modelling heat transfer from a full-scale monitored building. Overall transient temperature variations are shown to be dependent on ice content and latent heat effects. Non-linear, ice-content dependent, thermal conductivity and heat capacity are included in the work. Good correlation between measured and simulated temperature variations has been achieved. Practical application: The principle application relates to the assessment of heat transfer from buildings through to the underlying foundation soils. In addition, the work is of direct relevance to a wider range of applications, for example, ground source heat pumps, thermo-active piles and foundations. The model lends itself to application with respect to utilisation of ground energy within the context of pavement design, particularly, in relation to the alleviation of winter ice problems. It also applies within the context of assessment of urban heat island phenomenon and heat and moisture transfer beneath freezer foundations.

Numerical Simulation of Earth-Contact Heat Transfer

A two-dimensional simulation of earth-contact heat transfer by applying the finite element method is presented. Relevant thermal properties for each material type are determined and employed in the numerical model. Initial conditions and boundary conditions are carefully defined to improve the accuracy of this numerical investigation. The results demonstrate rational connection between the measured data set and simulated result. This research provides a useful contribution and reference to the earth-contact simulation.

A Review of Building Earth-Contact Heat Transfer

A review and categorization of the methods developed for the prediction of heat transfer in earth-coupled structures is presented. The thermal properties of soils are also briefly discussed. The four categories of tools reviewed are analytical and semi-analytical methods, numerical methods, manual methods and design guides. Numerical methods in three dimensions seem to be the most appropriate ones in building ground-coupled simulation due to their accuracy and ability to handle any complex configuration. Areas of future improvements are also discussed.

Development of the three-dimensional Numerical Generation of Response Factors (NGRF) method of conductive temperatures in passive cooling earth-contact components

This paper reports on the development and application of a method for the numerical prediction of temperatures within passive cooling components. In previous studies the basic idea was presented in an alternate form for the prediction of earth-contact heat transfer. The new method is demonstrated to be fast, accurate and flexible as a result of incorporating elements of the response factor method into a finite volume technique based numerical model. Initially, a ‘ pre-processing’ procedure is required to generate a certain number of hours for use as a time series by the response factor technique in the second stage of the method. It is here shown that even a reduced number of temperature response factors, e.g. 50 h, is sufficient to obtain accurate predictions of the component’s hourly temperature profile up to 1 year ahead. This study develops the equations addressing temperature profiles in structural components. The ‘state of the art’ of the presented method corresponds in the way that the conductive temperature response factors are calculated being numerically in the three-dimensional space. The method solves the three-dimensional earth-contact temperature profiles, which interact with indoors and outdoors temperature profiles. Once the numerical temperature response factors time series of an earth-contact component’s grid node have been generated then its future thermal performance due to any surrounding temperature variation can be predicted fast and accurately. The structural earth-contact passive cooling components’ response factors are generated by a three-dimensional numerical model, with no need of past experimental data and stored to be used at any time in future. The method is given the name NGRF (Numerical Generation of Response Factors). The way that the temperature response factors are determined in the three-dimensional space targets in the improvement of the prediction of earth-contact temperature profiles.

Multidimensional simulation of earth-contact heat transfer

A numerical investigation of earth-contact heat transfer adjacent to an experimental structure is presented. In particular, a comparison is made between a two- and a three-dimensional simulation. The results are compared directly with data measured from a purpose-built full-scale experiment. Indirect methods of estimating thermal conductivity and volumetric heat capacity are described and employed. The results show reasonable correlation between the simulated and measured thermal responses. The three-dimensional simulation appears to provide an improved representation of the field problem. Some of the challenges associated with simulating a full-scale field problem are considered. The determination of the representative boundary and initial conditions is shown to be important. Cet article présente l'analyse numérique d'un système de transfert thermique par contact avec la terre installé à proximité d'une structure expérimentale. On y compare, notamment, une simulation bidimensionnelle et une simulation tridimensionnelle. Les résultats sont comparés directement à des données mesurées dans le cas d'une expérience grandeur nature conçue spécifiquement dans ce but. L'auteur décrit les méthodes indirectes d'estimation de la conductivité thermique et de la capacité thermique volumétrique utilisées. Les résultats montrent une corrélation raisonnable entre les réponses simulées et les réponses thermiques mesurées. La simulation 3D semble être une représentation améliorée du problème de terrain. Certaines des difficultés associées à la simulation d'un problème de terrain à grande échelle sont prises en considération. La détermination de la limite de représentation et des conditions initiales est jugée importante. Mots-clés: bâtiments, contact avec la terre, efficacité énergétique, mesures sur le terrain, transfert de chaleur, simulation

Dynamic earth-contact building: A sustainable low-energy technology

Sustainable development includes low-energy buildings, which reduce energy consumption, green house gases emission, water usage, etc. The choice of subsurface wall at varying depths for construction of buildings has a direct impact on energy consumption and the environment. This paper includes in its scope all building structures in which a significant area is in direct contact with the earth, and excludes indirect earth contact. A two-dimensional simplified analytical Fourier boundary series was developed to study dynamic earth-contact heat transfer and humidity variation in building. It was used in conjunction with the whole-building energy simulation program developed in the TRNSYS environment. The predictions were compared with extensive experimental data measured from typical existing earth-contact buildings situated in the Indian Institute of Technology Delhi campus. Heat transfer through earth-contact building structures was predicted to decrease with increasing soil contact. The results obtained from the detailed model showed that earth-contact structures form excellent passive technology that can be exploited for energy conservation. This work is part of an effort to develop zero energy building models in India. The presented model can be easily incorporated into indirect earth-contact structures in order to describe the impact of cooling tubes, earth-air tunnels or heat pumps in indoor environment.

A comparative study of design guide calculations and measured heat loss through the ground

This study forms part of an in-depth investigation of the critical issue of earth-contact heat transfer to and from buildings. The overall research project involved in situ measurements, extensive simulation work and design guide calculations of heat loss through the ground from different real buildings. The results obtained from the application, where possible, of established calculation procedures are presented here in comparison with data obtained directly from full-scale experimental studies. It is shown that in some cases, when applicable, the methods used here agree relatively well with each other. However, different design methods can lead to very different estimations of earth-related heat losses.

Earth-contact heat transfer: improvement and application of a novel simulation technique

This paper reports on the improvement and application of a new method for the prediction of earth-contact heat transfer. In previous studies the new method was claimed to be fast, accurate and flexible as a result of incorporating elements of the response factor method into a finite volume technique based numerical model. Initially, a ‘pre-processing’ procedure is required to generate a certain number of hours for use as a time-series by the response factor technique in the second stage of the method. This paper shows that, it is possible to further improve the speed and accuracy of the ‘pre-processing’ procedure without losing the advantage of flexibility that the numerical models provide in the design of such cases. The improvement of the new method is presented which makes use of a ‘time-stepping control scheme’. A simple ‘extrapolation’ technique has been demonstrated previously. This method proved to be accurate and fast in solving the three-dimensional earth-contact heat transfer, which may involve a certain number of heating zones (rooms) interacting with several different temperature profiles. A multi-room configuration is utilised in this study and simulations are performed over one or more years according to the initial ground domain temperature conditions.

A novel tool for the prediction of earth-contact heat transfer: A multi-room simulation

This paper reports a new simulation method for the prediction of earth-contact heat transfer. The new method claims to be fast, accurate and flexible by means of incorporating elements of the response factor method into a numerical method based on the finite volume technique. More specifically, the development of the method is presented and implemented for a general multi-room structure. Work undertaken so far shows that the current combination of the finite volume and response factor techniques is at its most useful when the new tool is used in a parametric analysis process. Initially, a ‘pre-processing’ procedure is utilized to generate a certain number of simulated hours for use as a time series by the response factor technique in the second stage of the method. Assuming that the earth-contact parameters then remain constant, every subsequent simulation in which the non-earth-contact parameters are varied can incorporate the earth-contact heat transfer efficiently, by the use of the response factor technique, which takes a few seconds. Very good agreement has been achieved between a three-dimensional finite volume model and the present method, for a typical multi-room slab-on-ground floor, coupled with dramatically improved run times which is essential for the rapid parametric analysis of a structure.

Improving the efficiency of the numerical modelling of built environment earth-contact heat transfers

This paper reports on a method which has been developed to improve the efficiency of the numerical simulation of built environment earth-contact heat transfers. This method modifies a numerical method by incorporating elements of the response factor method. Additionally, this paper reports on the use of extrapolation techniques to further speed up one stage of the simulation. Essentially, the method requires that a numerical technique be initially used to generate a certain number of simulated hours for use as a time-series by the response factor element of the method. This first (‘pre-processing’) part of the procedure takes a certain time and this time can be significantly reduced by means of the extrapolation techniques described in the paper. However, assuming that the earth-contact domain remains unchanged from then on, this ‘pre-processing’ does not need to repeated, and every subsequent simulation that is performed to calculate the effect on the earth-contact heat transfer of changing another parameter (i.e. during a parametric analysis) takes only a few seconds. Reductions in run-time for these successive simulations are of the order of 1000 times faster than the full finite volume technique whilst still retaining the flexibility and accuracy of this method.

Development and inter-model comparative testing of a novel earth-contact heat-transfer simulation method

This paper describes the theory and inter-model comparative testing of a new earth-contact heat-transfer simulation method that is flexible, fast and accurate. The method combines the finite volume and response factor techniques and is intended to aid the design of buildings by contributing to the rapid parametric analysis of a structure. In other words, the method is at its most useful when being used to provide an accurate yearly simulation of the earth-contact heat transfer in situations when it is required to know the effect of repeatedly varying other aspects of the design. Work undertaken so far for a typical basement shows extremely good hourly heat transfer correlation between the time series method and a three-dimensional finite volume method, coupled with dramatically improved run times (of the order of a factor of 1000) when the method is used in its parametric analysis role.

Three-dimensional earth-contact heat flows: A comparison of simulated and measured data for a buried structure

If renewable energy sources are to be successfully utilised within the built environment then accurate simulation tools have an important role to play. This paper addresses a very specific part of the overall simulation process: that of earth-contact heat transfer which can be the cause of significant modelling errors. Using a three-dimensional numerical model, simulation results are compared with experimental data for a test room. It has been shown that for this case, neglecting climatic conditions (e.g. snow and rain) causes discrepancies between measured and calculated temperatures. A sensitivity study has also shown that thermophysical properties (like the soil thermal conductivity) have to be accurately known.