Assessment of Design Procedures for Vertical Borehole Heat Exchangers

The use of ground source energy systems is a well-established method to provide low cost heating to buildings, diversify the energy mix and help meeting increasingly stricter sustainability targets. However, considerable uncertainties remain over their efficient design, with several standards, guidelines and manuals being proposed over the last few years. This paper aims at providing insight into the implications to the design of a vertical borehole heat exchanger of the adoption of different design procedures. The hypothetical case of a typical dwelling located in London, UK, is analysed in order to highlight the impact on the final design of the chosen methodology. Moreover, a parametric study using an analytical design procedure was performed to point out the influence of various factors, such as borehole characteristics and thermal properties of the ground. It is shown that there are considerable discrepancies between design methods and that uncertainties in some input parameters, such as the thermal properties of the ground, which for relatively small systems are often selected from tables rather than measured in situ, may have a substantial influence on the length of borehole required

Numerical interpretation of the coupled hydromechanical behaviour of expansive clays in constant volume column tests

© The authors and ICE Publishing: All rights reserved, 2015.Experimental and numerical studies of the behaviour of expansive clays have been attracting increasing interest, due to their good sealing properties, which render them ideal to be used as engineered barriers (buffers) in both active (e.g. nuclear) and non-active waste disposal facilities. Both large scale and laboratory scaled experiments indicate that the sealing capabilities of the buffer are fundamentally governed by its volumetric behaviour when wetted. In this paper, a constant volume column infiltration test, performed under isothermal conditions on compacted MX80 bentonite, is modelled numerically using the Imperial College Finite Element Program (ICFEP). A modified version of the Barcelona Basic Model is used to simulate the behaviour of the buffer, which is inherently partly saturated. The numerical results agree well with the observed experimental data, especially with regard to the advancement of the wetting front. A detailed interpretation of the computed evolutions with time of stress state, suction and void ratio at different elevations along the samples axis is carried out, providing insight into the complex hydro-mechanical response of the buffer during the experiment. Indeed, even though the overall volume of the sample was kept constant, a region of localised dilation, which induced the contraction of other zones of the material, was observed to advance simultaneously with the wetting front along the height of the soil column

Dissipated energy in undrained cyclic triaxial tests

Energy-based methods are an emerging tool for the evaluation of liquefaction potential. These methods relate excess pore water pressure build-up to seismic energy dissipated per unit volume. Further development of these methods require their validation through laboratory testing. In this paper, a comprehensive study of energy dissipated during cyclic triaxial tests is undertaken. Results of undrained cyclic triaxial tests performed on air-pluviated samples of Hostun sand prepared with different initial densities and subjected to several confining pressures and loading amplitudes are presented. The energy dissipated per unit volume is estimated from the experimental results and correlated to the generated excess pore water pressure. The correlation between those quantities appear to be independent of the initial relative density of the sample, isotropic consolidation pressure and cyclic stress ratio used in the tests. Moreover, the relationship between observed doubleamplitude axial strain and the energy dissipated per unit volume is examined. It is found that this relationship is greatly dependent on the relative density of the sample

Planning travel as everyday design

This paper examines the implications of conceptualising planning as a type of design activity. This is explored through results from a two-month field study that investigated the planning and decision making behaviour of people engaged in preparing for multipoint, international air travel. Planning travel is a type of ill-structured complex problem that is characterised as being temporally sporadic, sometimes synchronous, often asynchronous, frequently collaborative, and spatially varied with participants at different times co-located and in separate places. Research participants were professional travel agents and non-professional but experienced travel planners. Ancillary material collected included photographs of the planning situation and drawings and notes made by participants. In contrast to the formalised prescriptive planning models common in cognitive science and operations research, the everyday planning activity featured in this study is situated and naturalistic. This research is undertaken with a view to designing systems to support the design and decision making activity of travel planners. Copyright the author(s) and CHISIG

On the assessment of energy dissipated through hysteresis in finite element analysis

The accurate reproduction of the hysteretic behaviour exhibited by soils under cyclic loading is a crucial aspect of dynamic finite element analyses and is typically described using the concept of damping ratio. In this paper, a general algorithm is presented for assessing the damping ratio simulated by any constitutive model based on the registered behaviour in three-dimensional stress-strain space. A cyclic nonlinear elastic model capable of accurately reproducing a wide range of features of soil behaviour, including the variation of damping ratio with deformation level, is chosen to illustrate the capabilities of the proposed algorithm. The constitutive model is described and subsequently employed in two sets of finite element analyses, one involving the dynamic response of a sand deposit subjected to different types of motion and another focussing on the simulation of a footing subjected to cyclic vertical loading. The application of the presented algorithm provides insight into the processes through which energy is dissipated through hysteresis

Investigating soil-water retention characteristics at high suctions using Relative Humidity control

A technique for controlling relative humidity (RH) is presented, which involves supplying a sealed chamber with a continuous flow of air at a computer-regulated RH. The desired value of RH is achieved by mixing dry and wet air at appropriate volumes and is measured for servo-control at three locations in the chamber with capacitive RH sensors and checked with a sensitive VAISALA sensor. The setup is capable of controlling RH steadily and continuously with a deviation of less than 0.2% RH. The technique was adopted to determine wetting soil-water retention curves (SWRC) of statically compacted London Clay, under both free-swelling and constant volume conditions. The RH within the chamber was increased in a step-wise fashion, with each step maintained until vapour equilibrium between the chamber atmosphere and the soil samples was established. Independent filter paper measurements further validate the method, while the obtained retention curves complement those available in the literature for lower ranges of suction

Investigating Women's Experiences of Asthma Care in Pregnancy: A Qualitative Study.

Background : Most asthmatic women have normal pregnancies and complications are infrequent when their asthma is well-controlled. Symptom control and medical treatment are concerning to pregnant asthma suffers, as is the impact that their illness and treatment might have on their unborn baby. The aim was to investigate in a qualitative study the thoughts and feelings of women's experiences of asthma in pregnancy. Twenty-two women with asthma who had a pregnancy within two years were asked to participate. Seven women were interviewed when data saturation was achieved. Interviews were transcribed and analysed using the 'Framework' Method, independently analysed by two researchers and consensus reached concerning the construction of themes. The key themes that emerged were Asthma and pregnancy; Pregnancy and post-natal experiences; and Health professionals. These findings are globally interesting because of the prevalence of maternal asthma and they illustrate participants' experiences concerning their asthma care and their views on its improvement. Pregnant asthmatic women have concerns about their care and treatment which might be alleviated by outreach, joint working between respiratory doctors and nurse specialists, midwives and General Practice nurses. Targeted educational activities could form a part of this care delivery

Functional traits and water transport strategies in lowland tropical rainforest trees

© 2015 Apgaua et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species' hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios