Dynamic simulation of ground source heat pump systems with nonstationary convolutions

Advective processes related to groundwater motion and flow rates have a significant impact on the thermal performance of ground source heat pump systems. Including these elements during the design phase, however, remains a challenging task, as few computationally efficient modeling tools allow for their adequate and accurate representation. The present work addresses this issue by presenting the experimental validation of non-stationary convolutions for predicting the thermal response of a ground heat exchanger to both transient heat loads and advection. First, the method is outlined along with a simple demonstration case emulating the time-variation of groundwater velocity. Then, it is validated against experimental data retrieved from a 35-day multi-flow rate thermal response test conducted on a real standing column well. The results show a mean absolute error of 0.28 °C between the experimental and simulated results, which represents good accuracy considering the complexity of the thermo-hydro-processes at work. The high computing efficiency of the proposed technique is also demonstrated and suggests its potential for future implementation in common-use design tools

Hydrogeothermal characterization and modelling of a standing column well experimental installation

Standing column wells (SCW) are efficient ground heat exchangers that offer promising potential for integration in dense urban areas. Recent years have witnessed a growing interest in SCWs, resulting in the development of various simulation models incorporating heat transfer, groundwater flow and geochemical reactions within the well and the surrounding ground. However, these models commonly use a configuration that involves pumping at the bottom of the well and reinjection from its top, which can lead to installation and maintenance difficulties in deep wells. Furthermore, very few SCW models have been validated against reliable field data. This paper presents an original finite element model coupling advection-diffusion of heat and groundwater flow within a top pumped SCW and its surrounding ground as well as the experimental setup used for its validation. Within the scope of this study, experimental data obtained after an extensive field characterization campaign and a thermal response test performed with a large-scale geothermal laboratory were used directly as inputs in the numerical model. Experimental validation shows that without any calibration procedure, the model reproduces the experimental inlet and outlet groundwater temperatures with a mean absolute error of 0.14 °C. It is also shown that the placement of the pump at the top of the well offers a more practical design that has minor impact on the thermal performance of the system

Stationary and non-stationary deconvolution to recover long-term transfer functions

To design a ground heat exchanger, simulations are frequently used. One way to perform simulations is to use the well-known g-functions to obtain the ground temperature. These functions are usually obtained by analytical or numerical models, which limits the precision or takes long simulation time. Recent advances show that the short-term g-functions can also be retrieved by a deconvolution algorithm. However, the known deconvolution algorithm is only validated for a set of operating parameters and duration of less than 10 days. A first objective of this article is to demonstrate that longer g-functions can be retrieved with such an algorithm. Then, a second objective is to extend the application of the deconvolution to consider time varying operating parameters throughout a ground heat exchanger's operation. To achieve those objectives, the deconvolution will be first applied to various numerical year-long simulations of a ground source heat pump system with stationary conditions. Then, an extended multi-signal deconvolution will be applied to a non-stationary thermal response test of 30 days. Both tests show adequate temperature reconstruction with RMSE of less than 0.05 °C and 0.2 °C for the first and second scenarios respectively

Forecasting hydraulic head changes in injection wells using LSTM network

Monitoring of well's specific capacity is commonly used to plan maintenance of injection wells in open-loop GSHP and standing column well systems. However, this method does not consider the effect of temperature on hydraulic conductivity. A first step towards an alternative approach that does include the effect of temperature is proposed in this work. We present a long short-term memory network capable of predicting the water level in the injection well of an operating GSHP system. The methodology consists of building a training set using a numerical model. A total of 500 simulations were conducted to evaluate hydraulic head signals under various inlet temperatures and flow rates along with hydraulic and thermal parameters drawn from a uniform distribution. Predictive performance of the artificial neural network is tested on an operational data set. The resulting RMSE between the forecasted and operational data set is 14.8 cm

Control strategy evaluation framework for ground source heat pumps using standing column wells

Standing column wells (SCWs) are efficient ground heat exchangers (GHEs) that have a significant cost saving potential. Recent developments have shown that they can also adapt successfully to cold climates despite previous concerns about operating near the freezing point. Therefore, new research frontiers are now being explored as the integration of this type of GHE to a real case study building model has hardly been analyzed until now. An institutional building has been selected for a SCW demonstration project in Mirabel, Canada. This paper includes in one single model the building, the Heating Ventilation and Air Conditioning (HVAC) system and the SCWs. The objective is to develop a software framework to analyze the impact of building operation strategies on the entire system during winter. Peak loads revealed to be the most critical points to control as the groundwater can freeze if the heat extraction is too high. Night indoor air temperature setbacks can bring significantly high peak loads whenever the building is heated to be occupied during the day. This paper shows that, using a bleed ratio above 20 %, a night setback can be successfully operated ramping up the temperature in around 3 hours

Integrated immunovirological profiling validates plasma SARS-CoV-2 RNA as an early predictor of COVID-19 mortality.

peer reviewedDespite advances in COVID-19 management, identifying patients evolving toward death remains challenging. To identify early predictors of mortality within 60 days of symptom onset (DSO), we performed immunovirological assessments on plasma from 279 individuals. On samples collected at DSO11 in a discovery cohort, high severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA (vRNA), low receptor binding domain–specific immunoglobulin G and antibody-dependent cellular cytotoxicity, and elevated cytokines and tissue injury markers were strongly associated with mortality, including in patients on mechanical ventilation. A three-variable model of vRNA, with predefined adjustment by age and sex, robustly identified patients with fatal outcome (adjusted hazard ratio for log-transformed vRNA = 3.5). This model remained robust in independent validation and confirmation cohorts. Since plasma vRNA’s predictive accuracy was maintained at earlier time points, its quantitation can help us understand disease heterogeneity and identify patients who may benefit from new therapies

Convolution non stationnaire de fonctions de transfert pour la simulation efficace des systèmes géothermiques de puits à colonne permanente

Résumé Les puits à colonne permanente sont des systèmes géothermiques hautement efficaces dont le fonctionnement repose sur la recirculation de l’eau souterraine dans un puits profond et ouvert au roc. Le contact direct entre l’eau et la paroi du forage contribue à favoriser le transfert thermique, qui peut aussi être considérablement amélioré en déviant ou "saignant" une partie de l’eau pompée pour stimuler les influx advectifs et le renouvellement de l’eau à l’intérieur du puits. Ces pratiques sont associées à des réductions significatives de la longueur de l’échangeur de chaleur souterrain, des coûts d’installation et de l’espace au sol requis par rapport aux systèmes conventionnels en boucle fermée. En contribuant ainsi à accroître l’attrait économique et pratique des solutions géothermiques, les puits à colonne permanente offrent un potentiel intéressant de valorisation de cette option pour améliorer l’efficacité énergétique et réduire les émissions de gaz à effet de serre associées au chauffage et à la climatisation des bâtiments. Lors de la conception des systèmes géothermiques, l’un des principaux enjeux consiste à déterminer la longueur optimale de l’échangeur de chaleur souterrain qui puisse satisfaire les besoins thermiques du bâtiment tout en minimisant les coûts entraînés par les opérations de forage et l’aménagement des puits. À cet effet, il convient généralement de conduire une étude de conception détaillée, ce qui implique d’une part la caractérisation du site d’installation et d’autre part la modélisation de la réponse thermique du système au profil de charge envisagé. Dans le cas des puits à colonne permanente, cette dernière tâche est associée à une complexité particulière découlant entre autres du couplage important entre le transfert de chaleur et l’écoulement de l’eau souterraine. Si de nombreuses stratégies de modélisation numérique ont été proposées pour répondre à cette problématique, des limitations importantes subsistent néanmoins quant à leur fiabilité et à la lourdeur informatique associée à leur résolution. Le présent ouvrage s’attaque directement à ces enjeux en visant le développement et la validation d’outils de simulation des puits à colonne permanente qui soient flexibles, précis et suffisamment rapides pour permettre leur potentielle utilisation à des fins de conception et d’amélioration des stratégies de contrôles. Dans un premier temps, un modèle numérique d’éléments finis est donc développé et validé en utilisant les données issues de la caractérisation détaillée du site d’installation d’un puits à colonne permanente expérimental, une avancée importante en regard de la quantité et de la qualité des données mobilisées. Le modèle développé utilise comme valeurs d’entrée la charge thermique et les débits de pompage et de saignée imposés au puits, définit la présence d’un gradient géothermique et des variations saisonnières de température, et utilise une distribution hétérogène des propriétés physiques dans le milieu géologique. Il est démontré que ces derniers facteurs exercent une influence significative sur la performance des opérations de saignée en raison de leur impact sur la température des influx advectifs à la paroi des forages. Les résultats de l’exercice de validation suggèrent enfin que la stratégie de modélisation retenue permet de reproduire l’évolution du rabattement pendant un essai de pompage et la température du fluide pendant un essai de réponse thermique et 25 jours d’opération dynamique en chauffage avec des erreurs moyennes absolues respectives de 7.3 cm, 0.15 ℃ et 0.32 ℃. L’enjeu relié au temps de calcul élevé des simulations numériques est ensuite abordé en transférant aux puits à colonne permanente une méthode reposant sur le principe de superposition et le théorème de convolution. Celle-ci implique que la fonction de transfert représentant la réponse impulsionnelle du système – soit la température de l’eau souterraine à la sortie du puits en réponse à une impulsion thermique unitaire et constante – soit d’abord évaluée numériquement, puis convoluée afin d’obtenir une évaluation presque instantanée de la réponse thermique à un profil de charge dynamique. Pour tenir compte de la variation des débits de pompage et de saignée dans les puits à colonne permanente, une méthode originale est ensuite développée qui repose sur la convolution non stationnaire de fonctions de transfert. Flexible, la méthode proposée permet de considérer la présence de plusieurs puits, la distribution hétérogène des propriétés du milieu géologique, et s’applique aussi à des simulations faisant intervenir la variation des débits de circulation et des vitesses d’écoulement souterrain dans les systèmes en boucle fermée. La précision des estimations fournies est vérifiée numériquement et établie à quelques centièmes de degrés Celsius. Enfin, les gains d’efficacité sont mis en évidence par le temps requis pour compléter une simulation annuelle ayant un pas de temps d’une heure, qui est de seulement quelques minutes comparativement à plus de 11 jours pour un modèle numérique de référence. Afin de mettre en valeur l’efficacité des outils de simulation développés dans la thèse, un algorithme de simulation itératif est finalement implémenté, qui repose sur l’utilisation de fonctions de transfert numériques et la convolution non stationnaire pour représenter les composantes souterraines d’un système de puits à colonne permanente et la méthode utilisée dans le logiciel EnergyPlus pour évaluer l’efficacité des thermopompes en fonction de la charge thermique et des débits d’opération imposés. Cet algorithme est appliqué à l’évaluation de la performance de différentes stratégies de contrôle des débits de pompage et de saignée. À cet effet, 34 simulations annuelles sont conduites, dont les résultats suggèrent l’adoption de débits élevés en périodes d’opération soutenue pour modérer l’amplitude de l’évolution thermique de l’eau souterraine. Il s’agit d’une pratique qui permet de minimiser la sollicitation du système auxiliaire, ce qui se manifeste dans les scénarios étudiés par un important potentiel de réduction de la puissance électrique appelée et des coûts associés. En- fin, le contrôle complémentaire des débits, visant à maintenir une différence de température de 2 ℃ à l’échangeur de chaleur intermédiaire, est identifié comme une mesure efficace pour réduire la consommation énergétique du système tout en minimisant le volume d’eau extrait des puits par les opérations de saignée. En somme, l’ensemble des travaux conduits dans le cadre de la thèse mène à une meilleure compréhension des phénomènes qui favorisent une opération efficace des puits à colonne permanente, via le développement d’outils de simulation qui ont démontré être flexibles, fiables et efficaces. Des recherches futures, traitant notamment de l’intégration d’interférences thermiques indépendantes et de l’accélération de l’évaluation des fonctions de transfert, sont prévues afin d’élargir encore davantage le champ d’application et l’efficacité des techniques proposées. Il est attendu que ces avancées se traduisent par une amélioration des pratiques de conception et d’opération des puits à colonne permanente, menant par le fait même à des performances accrues et à une éventuelle adoption plus large de la géothermie comme mesure d’économie d’énergie et de gestion de la demande en puissance du secteur du bâtiment. ---------- Abstract Standing column wells are highly efficient ground heat exchangers that rely on the recirculation of groundwater in a deep and uncased borehole. The performance of these systems can be enhanced by discharging or "bleeding" part of the pumped water, an action that pro- motes advective heat transfer and renewal of the well’s water content. These elements are associated with higher heat exchange rates than the conventional closed-loop configuration, which allows to reduce the size and cost of the underground components. With an enhanced perspective regarding the practical and economic aspects of ground-source heat pumps installation, standing column wells may thus represent an important asset on the road towards a more sustainable and low-carbon built environment. To ensure an appropriate sizing of the ground heat exchanger that minimizes the costs while maintaining indoor thermal comfort at acceptable levels, it is common practice to perform a careful design analysis. This process usually involves proceeding to the detailed characterization of the experimental site and forecasting the system’s energy performance through the computation of the fluid’s temperature as a function of a thermal load signal. Advanced numerical modelling can serve this purpose as it allows the definition of complex geometries and coupling the thermal and hydraulic processes involved in the operation of standing column wells. However, the lack of comprehensive experimental validation studies and the heavy computational load associated with these methods still act as disincentives that prevent them from being routinely used. The present thesis intends to facilitate the conception of standing column wells and the development of innovative control strategies by working towards flexible, reliable and efficient simulation tools of these systems. Hence, a finite element numerical model is first developed and validated following the extensive characterization of an experimental standing column well, which constitutes an important step with regard to the quality and the comprehensive nature of the collected data. The model’s inputs are the thermal load imposed by the mechanical equipment and the pumping and bleeding flow rates. Advanced features, such as the geothermal gradient, the seasonal temperature fluctuations and the heterogeneous distribution of the ground’s physical properties, are also explicitly described. It is shown that these elements exert significant influence on the efficiency of the bleed operations, owing to their impact on the temperature of the advective influxes coming through the borehole wall. Simulations reproducing the drawdown at the well during a pumping test, and the operating temperatures during a thermal response test and 25 days of dynamic winter operation, show that the model allows evaluating these parameters with mean absolute errors of 7.3 cm, 0.15 ℃, and 0.32 ℃, respectively. The direct solution of differential equations involved in numerical modelling is associated with a heavy computational load that can be simplified by superposition and convolution schemes. For the first time, these techniques are applied to the simulation of standing column wells. A transfer function representing the normalized response of the numerical model to a constant heat load is first evaluated and convolved for a near-instant estimation of the system’s temperature evolution in response to a dynamic heat load pattern. To be able to represent the influence of dynamic pumping and bleeding flow rates, an original method is then developed that relies on non-stationary convolutions. Flexible, this method allows considering multi-borehole systems, a heterogeneous distribution of the ground’s physical properties, and also applies to the simulation of time-variant circulation flow rates and groundwater velocities in closed-loop systems. The accuracy of the proposed technique is evaluated following a numerical validation, and estimated to be around a few hundredths of a degree. On a last note, the few minutes required to achieve an annual simulation having hourly time steps stress the efficiency of the developed method, and compare very favourably to the 11 days required by the reference numerical model. At last, a powerful simulation algorithm is implemented to illustrate the potential application of the tools developed in this work to the performance assessment of various constant and dynamic flow rate control strategies. The iterative algorithm relies on numerical transfer functions and the non-stationary convolution technique to simulate the underground components of a standing column well system, and the EnergyPlus approach to represent the heat pump’s efficiency at full and part loads. The findings of 34 annual simulations suggest that using higher flow rates in peak conditions is a key element that minimizes auxiliary assistance, thus allowing the mitigation of peak power demand and the associated costs in the scenarios considered. It is also shown that complementary variable flow rate control aiming to maintain a 2 ℃ temperature difference across the plate heat exchanger provides significant energy savings while alleviating groundwater usage related to the bleeding operations. The body of work achieved throughout the thesis sheds light on various elements contributing to the efficiency of standing column wells, and lays down new modelling tools that are fit for the adequate and efficient simulation of their thermal behaviour. Future research activities, aiming towards the integration of independent thermal interferences and the acceleration of the transfer functions’ evaluation, should help further expand the scope of application of the proposed techniques as well as their efficiency. It is expected that these elements may foster improved design and operating practices, thus leading to enhanced performance and broader adoption of this energy-efficient and low-carbon technology

Violent reoffending in people released from prison: psychiatric epidemiology, risk assessment and psychological interventions

Violence was identified as a global public health concern by the World Health Assembly nearly three decades ago. Despite reported decreases in violent crime in many countries, reoffending rates worldwide remain high. Amongst people released from prison, there are some at high-risk of perpetrating interpersonal violence. Identifying these key individuals, who are most in need of effective interventions to prevent future criminality, is crucial to reducing societal violence, as their contribution to this major problem is considerable. In this thesis, I focus on violence risk assessment and prevention of future violence in people released from prison by employing methods from psychiatric epidemiology, public mental health and prediction modelling. I start by estimating the prevalence of a modifiable risk factor for violence (i.e. treatable mental disorders) amongst adolescents in juvenile detention and correctional facilities. I select this subgroup of the global prison population as most severe mental disorders emerge in late adolescence, and thus this period provides a critical window to improve prognosis and intervention. My second and third studies externally validate a novel, scalable and transparent violence prediction model—the Oxford Risk of Recidivism (OxRec) tool—in two new countries. I investigate the predictive ability of OxRec in both lower middle-income and high-income settings using data from Tajikistan and England to identify individuals who could be targeted for empirically supported interventions in prison and on release. Lastly, I evaluate the effectiveness of widely implemented psychological interventions for people in prison to reduce offending after release. I synthesise the evidence by solely including randomised controlled trials to identify the current most effective treatments, and inform future evidence-based research and policy in this area