Efficiency improvement of a ground coupled heat pump system from energy management

The installed capacity of an air conditioning system is usually higher than the average cooling or heating demand along the year. So, most of the time, the system is working under its actual capacity. In this contribution, we study the way to improve the efficiency of a ground coupled heat pump air conditioning system by adapting its produced thermal energy to the actual thermal demand. For this purpose, an air conditioning system composed by a ground coupled heat pump and a central fan coil linked to an office located in a cooling dominated area was simulated, and a new management strategy aiming to diminish electrical consumption was developed under the basic constraint that comfort requirements are kept. This strategy takes advantage of the possibility of managing the air flow in the fan, the water mass flows in the internal and external hydraulic systems, and the set point temperature in the heat pump to achieve this objective. The electrical consumption of the system is calculated for the new management strategy and compared with the results obtained for a conventional one, resulting in estimated energy savings around 30%This work has been supported by the Spanish Government under projects "Modelado y simulacion de sistemas energeticos complejos" (2005 Ramon y Cajal program), "Modelado, simulacion y validacion experimental de la transferencia de calor en el entorno de la edificacion" (ENE2008-0059/CON). A. Sala is grateful to the financial support of grants DPI2008-06731-c02-01 (Spanish Government), and Generalitat Valenciana Prometeo/2008/088.Pardo García, N.; Montero Reguera, ÁE.; Sala Piqueras, A.; Martos Torres, J.; Urchueguía Schölzel, JF. (2011). Efficiency improvement of a ground coupled heat pump system from energy management. Applied Thermal Engineering. 31(2):391-398. https://doi.org/10.1016/j.applthermaleng.2010.09.016S39139831

Geothermal based hybrid energy systems, toward eco-friendly energy approaches

Geothermal Energy is a very attractive source of naturally-occurring green renewable energy. Exploiting this natural resource is straightforward and causes almost no ill effects to the environment. But, while geothermal does not suffer the intermittence of other renewable sources, its extraction efficiency is fairly modest as compared to other sources. As a result, there has been significant interest recently in hybrid systems that integrate geothermal and other forms of energy to increase the output efficiency. This work will survey the different possible integrations involving geothermal energy. A review of the literature shows that the most common hybrid systems implementation involve the integration of geothermal with solar (45% of systems) followed by the integration of a cooling tower into the geothermal system (30% of systems). This work will also investigate the applications for geothermal hybrids and show that 44% of systems are designed for heating applications. Another 44% are used for cooling while only 12% are designed for electrical power generation. Complexity of control remains as the main obstacle facing hybrid multi-source energy systems including those involving geothermal energy

Modelling of shaded and unshaded shallow-ground heat pump system for a residential building block in a Mediterranean climate

Heat pumps may be coupled to shallow-ground geothermal fields and used for the purpose of space heating and cooling of buildings. However, quite often it is not possible to locate the geothermal field in cleared grounds, especially in cities where building density is high and land has a high premium. This leads to the possibility of burying the geothermal field under the basement of new building blocks, before construction of the building. In the present work, the shaded-unshaded arrangement is numerically studied by coupling the software DesignBuilder-EnergyPlus to assess the building's energy requirement with the software FEFLOW to solve the heat transfer equation in porous media. Assuming a standard residential building block, the coupling between the two software is performed by assigning the thermal energy requirement for air conditioning, as calculated by EnergyPlus, to a flat-panel typology of ground heat exchanger simplified in a 2D FEFLOW's domain. The results show that it is necessary to opt for a dual-source heat pump (air/geothermal) system to ensure that the ground is not frozen or over-heated at peak times and to improve the overall performance of the system.peer-reviewe

Modelling of waste heat recovery of a biomass combustion plant through ground source heat pumps- development of an efficient numerical framework

Development of a reliable and convenient dynamic modelling approach for ground source heat pumps remains as an important unresolved issue. As a remedy, in this work a novel, computationally-efficient modelling framework is developed and rigorously validated. This is based upon an implicit computational modelling approach of the ground together with an empirical modelling of heat and fluid flow inside U-tube ground heat exchangers and waste heat calculations. The coupled governing equations are solved simultaneously and the influences of parameters on the performance of the whole system are evaluated. The outcomes of the developed framework are, first, favorably compared against two different existing cases in the literature. Subsequently, the underground storage and recovery process of the waste heat through flue gases generated by a biomass combustion plant are modelled numerically. This reveals the history of temperature distributions in the ground under different configurations of the system. The results show that for a biomass combustion plant generating flue gases at 485.9 K as waste heat with the mass flow rate of 0.773 kg/s, the extracted heat from the ground is increase by 7.6%, 14.4% and 23.7% per unit length of the borehole corresponding to 40 °C, 50 °C and 60 °C storage temperatures. It is further shown that the proposed storage system can recover a significant fraction of the thermal energy otherwise wasted to the atmosphere. Hence, it practically offers a sizable reduction in greenhouse gas emissions

Study on the methods for predicting the performance of a hybrid solar-assisted ground-source heat pump system

It is critical to find suitable setting parameters for designing a hybrid solar-assisted ground-source heat pump system in the practical engineering application, but the heat pump performance is unpredictable after many years of operation. This paper used 2000 sets of performance data collected from solar-assisted GSHP systems that keep operating over 20 years to simulate long term used heat pump with a professional software called GeoStar. Adopted the classification and regression tree (CART) method, the design of solar energy collector areas can be predicted. The multi-linear regression is also utilized to predict average monthly per meter borehole heat exchange. Seasonal factor decomposition and exponential smoothing are used to analyze the average monthly temperature of the circulating fluid, circulating fluid inlet and outlet temperatures of the heat pump after 20 years when we perform the time series prediction. Experimental results demonstrate that CART, multi-linear regression, seasonal factor decomposition and exponential smoothing are promising for practical applications

Une approche systématique de récupération de chaleur pour la conception de systèmes intégrés de chauffage, de refroidissement et de ventilation pour les serres

Abstract : Heat recovery plays a pivotal role in enhancing energy efficiency and reducing operating costs in the energy sector. In the context of greenhouse energy management, heat recovery measures hold significant potential to improve overall efficiency and profitability while improving sustainability. By specifically targeting ventilation waste heat, it is aimed to identify efficient and innovative ways to harness this abundant but often overlooked energy source. The primary objective of this thesis is to present a systematic methodology that offers practical insights into the design of a heat recovery system for greenhouses using heat integration technique. Considering the dynamic nature of greenhouse processes, dynamic Pinch Analysis (PA) is applied for the very first time to design an integrated greenhouse heating, cooling, and ventilation system. So, in the first step, the greenhouse climate conditioning system is defined in terms of distinct streams representing different components and processes within the system. This stream-based representation allows for a comprehensive understanding of the system's thermal dynamics, facilitating heat recovery analysis. Then, the required data to fully define all streams as a function of time (i.e. thermal and ventilation requirements) are calculated using a greenhouse climate model developed in Matlab/Simulink. Dynamic PA is accomplished in two major steps: energy targeting and heat exchanger network design. By employing energy targeting techniques based on graphical PA (composite curves), the methodology identifies heat recovery opportunities and determines the integration possibilities within the greenhouse. In the next step, a heuristic approach is presented to allocate a suitable heat exchanger network to the streams, thereby achieving the set energy targets. In this approach, the HEN design problem is solved only for the most representative time periods (i.e. typical days) determined using clustering. This can considerably reduce the computational effort by limiting the integration scenarios to only a few typical days rather than a whole year. Then, a technoeconomic analysis is employed to select the best HEN configuration among these scenarios. This combined approach ensures efficient heat exchanger placement and maximizes energy and cost savings for the greenhouse climate conditioning system. The entire methodology is applied and implemented for a greenhouse case study located in Saskatoon, Canada. By exploring the application of dynamic PA in greenhouse heat recovery systems and identifying areas for methodological enhancement, this research contributes valuable insights and advancements in both PA's application and methodology.La récupération de chaleur joue un rôle crucial dans l'amélioration de l'efficacité énergétique et la réduction des coûts opérationnels dans le secteur de l'énergie. Dans le contexte de la gestion de l'énergie des serres, les mesures de récupération de chaleur offrent un potentiel significatif pour améliorer l'efficacité globale et la rentabilité tout en favorisant la durabilité. En ciblant spécifiquement la chaleur perdue par la ventilation, notre objectif est d'identifier des moyens efficaces et innovants pour exploiter cette source d'énergie abondante mais souvent négligée. Cette thèse a pour principal objectif de présenter une méthodologie systématique offrant des aperçus pratiques sur la conception d'un système de récupération de chaleur pour les serres en utilisant la technique d'intégration thermique. Compte tenu de la nature dynamique des processus des serres, l'Analyse Pinch dynamique (PA) est appliquée pour la toute première fois afin de concevoir un système de chauffage, de refroidissement et de ventilation intégré pour les serres. Ainsi, dans un premier temps, le système de conditionnement du climat des serres est défini en termes de flux distincts représentant les différents composants et processus au sein du système. Cette représentation basée sur les flux permet de comprendre de manière exhaustive la dynamique thermique du système, facilitant ainsi l'analyse de récupération de chaleur. Ensuite, les données requises pour définir entièrement tous les flux en fonction du temps (c'est-à-dire les besoins thermiques et de ventilation) sont calculées à l'aide d'un modèle climatique de serre développé dans Matlab/Simulink. L'Analyse Pinch dynamique est réalisée en deux étapes majeures: le ciblage énergétique et la conception du réseau d'échangeurs de chaleur. En utilisant des techniques de ciblage énergétique basées sur l'Analyse Pinch graphique (courbes composites), la méthodologie identifie les opportunités de récupération de chaleur et détermine les possibilités d'intégration au sein de la serre. Dans l'étape suivante, une approche heuristique est présentée pour attribuer un réseau d'échangeurs de chaleur adapté aux flux, permettant ainsi d'atteindre les objectifs énergétiques fixés. Dans cette approche, le problème de conception du réseau d'échangeurs de chaleur est résolu uniquement pour les périodes de temps les plus représentatives (c'est-à-dire les jours types) déterminées à l'aide du regroupement par clustering. Cela peut considérablement réduire l'effort de calcul en limitant les scénarios d'intégration à seulement quelques jours types plutôt qu'à une année entière. Ensuite, une analyse technico-économique est utilisée pour sélectionner la meilleure configuration de réseau d'échangeurs de chaleur parmi ces scénarios. Cette approche combinée garantit un placement efficace des échangeurs de chaleur et maximise les économies d'énergie et de coûts pour le système de conditionnement du climat des serres. L'ensemble de la méthodologie est appliqué et mis en oeuvre pour une étude de cas de serre située à Saskatoon, au Canada. En explorant l'application de l'Analyse Pinch dynamique dans les systèmes de récupération de chaleur des serres et en identifiant les domaines d'amélioration méthodologique, cette recherche apporte des connaissances précieuses et des avancées tant dans l'application de l'Analyse Pinch que dans la méthodologie générale

Optimization of the building-plant system for net/plus zero energy buildings using low enthalpy geothermal systems

This thesis work is aimed to evaluate the energy efficiency of HVAC plant solutions that exploit the low enthalpy geothermal energy of the ground. All this in order to provide a valid alternative for common building-system solutions (often not adequate to all climatic conditions) and thus to more easily made the complete self-sufficiency of the NZEB buildings and consequently the widespread diffusion of the Net/Plus ZEB in the near future. The thesis focuses mainly on the study of two components: 1- the Ground Source Heat Pump (GSHP), i.e., a heat pump which uses the ground as external source through buried probes. 2- the Earth-to-Air heat exchanger (EAHX), i.e., a system in which the outdoor air is pre-heated or pre-cooled trough buried pipes (in which there is a heat exchange between air and ground) to reduce the heating and cooling energy consumption in buildings. The present work first energetically analyses these two technologies separately, comparing them to more common alternative components. Lastly, the performance of these systems is compared with each other, in order to obtain an NZEB

Evaluación de la reducción de las emisiones de CO2; a partir del potencial de explotación de la energía geotérmica somera. Estudio de caso de la ciudad de València

[ES] Esta tesis describirá los procedimientos y los métodos que permitirán evaluar el potencial geotérmico somero de la ciudad de Valenicia entendida como los beneficios económicos y ambientales que se pueden lograr aumentando la explotación geotérmica somera en tres escenarios diferentes, con un nivel diferente de tecnología. penetración, según la situación del resto de países europeos. La bomba de calor geotérmica permitirá satisfacer la demanda de H&C y ACS de los edificios de una manera más eficiente en comparación con las tecnologías tradicionales La parte inicial introducirá la fuente de energía, desde su definición hasta el listado de las ventajas de su explotación. Luego se describirán las diferentes tecnologías utilizadas en este campo, introduciendo la posibilidad de solución híbrida y almacenamiento H&C estacional. El procedimiento evaluará la reducción de GEI obtenida gracias al aprovechamiento de la energía geotérmica somera pero también se evaluarán otros indicadores: - sobre terreno: se analizarán las propiedades del terreno necesarias para definir la perforabilidad - sobre el clima: se definirá la carga de construcción de H&C que debe satisfacerse - sobre economía: se evaluarán las factibilidades económicas del proyecto mediante el cálculo de algunos indicadores - sobre el medio ambiente: se definirá el ahorro de energía en comparación con la tecnología actual. Es dado por los diferentes COP. A partir de la energía ahorrada se evaluará la emisión equivalente de GEI ahorrada. Esos indicadores ayudarán a definir las áreas de la ciudad más adecuadas para aplicar la bomba de calor geotérmica. El procedimiento se explicará paso a paso y luego se implementará para los tres niveles de penetración. La conclusión resumirá el resultado de los resultados señalando cómo se pueden utilizar los indicadores para ayudar al Ayuntamiento de Valencia a tomar decisiones sobre la extracción geotérmica superficial en la ciudad.[EN] This thesis will describe the procedures and the methods that will allows to evaluate the shallow geothermal potential of the city of Valencia intended as the economic and environmental benefits that can be achieved increasing the shallow geothermal exploitation in three different scenarios, with a different level of technology penetration, according to the other European countries situation. Geothermal heat pump will allow to satisfy H&C and DHW buildings demand in a more efficient way compared to the traditional technologies The initial part will introduce the energy source, from its definition to the listing of the pros of its exploitation. Then will be described the different technologies used on this field, introducing the possibility of hybrid solution and seasonal H&C storage. The procedure will evaluate GHG reduction obtained thanks to the exploitation of shallow geothermal energy but as well will be evaluated other indicators: - about ground: will be analyzed the ground properties necessary to define the drillability - about clime: will be defined the H&C building load that has to be satisfied - about economics: will be evaluated the economical feasibility of the project by calculating some indicators - about environment: will be defined the energy saves compared to the actual technology. It is given by the different COP. From the energy saves will be evaluate the equivalent GHG emission saved. Those indicators will help to define the most suitable city areas in which to apply geothermal heat pump. The procedure will be explained step by step and then implemented for the three level of penetration. The conclusion will summarize the result of the results pointing on how the indicators can be utilized to help the City de Valencia to make decisions about the shallow geothermal extraction in the city.Pin, A. (2022). Evaluación de la reducción de las emisiones de CO2; a partir del potencial de explotación de la energía geotérmica somera. Estudio de caso de la ciudad de València. Universitat Politècnica de València. http://hdl.handle.net/10251/181878TFG

Doctor of Philosophy

dissertationThe primary focus of this work is an assessment of heat transfer to and from a reversible thermosiphon imbedded in porous media. The interest in this study is the improvement of underground thermal energy storage (UTES) system performance with an innovative ground coupling using an array of reversible (pump-assisted) thermosiphons for air conditioning or space cooling applications. The dominant mechanisms, including the potential for heat transfer enhancement due to natural convection, of seasonal storage of "cold" in water-saturated porous media is evaluated experimentally and numerically. Winter and summer modes of operation are studied. A set of 6 experiments are reported that describe the heat transfer in both fine and coarse sand in a 0.32 cubic meter circular tank, saturated with water, under freezing (due to heat extraction) and thawing (due to heat injection) conditions, driven by the heat transfer to or from the vertical thermosiphon in the center of the tank. It was found that moderate to strong natural convection was induced at Rayleigh numbers of 30 or higher. Also, near water freezing temperatures (0°C-10°C), due to higher viscosity of water at lower temperatures, almost no natural convection was observed. A commercial heat transfer code, ANSYS FLUENT, was used to simulate both the heating and cooling conditions, including liquid/solid phase change. The numerical simulations of heat extraction from different permeability and temperature water-saturated porous media showed that enhancement to heat transfer by convection becomes significant only under conditions where the Rayleigh number is in the range of 100 or above. Those conditions would be found only for heat storage applications with higher temperatures of water (thus, its lower viscosity) and large temperature gradients at the beginning of heat injection (or removal) into (from) soil. For "cold" storage applications, the contribution of natural convection to heat transfer in water-saturated soils would be negligible. Thus, the dominant heat transfer mechanism for air conditioning applications of UTES can be assumed to be conduction. An evaluation of the potential for heat transfer enhancement in air-saturated media is also reported. It was found that natural convection in soils with high permeability and air saturations near 1 becomes more important as temperatures drop significantly below freezing