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Buildings consume significant energy worldwide and account for a substantial proportion of greenhouse gas emissions. Therefore, building energy management has become critical with the increasing demand for sustainable buildings and energy-efficient systems. Simulation tools have become crucial in assessing the effectiveness of buildings and their energy systems, and they are widely used in building energy management. These simulation tools can be categorized into white-box and black-box models based on the level of detail and transparency of the model’s inputs and outputs. This review publication comprehensively analyzes the white-box, black-box, and web tool models for building energy simulation tools. We also examine the different simulation scales, ranging from single-family homes to districts and cities, and the various modelling approaches, such as steady-state, quasi-steady-state, and dynamic. This review aims to pinpoint the advantages and drawbacks of various simulation tools, offering guidance for upcoming research in the field of building energy management. We aim to help researchers, building designers, and engineers better understand the available simulation tools and make informed decisions when selecting and using them., QC 20240208

Ground source heat pump (GSHP) systems offer a low carbon heating and cooling solution for the decarbonization of buildings. As global temperatures rise, the cooling requirements of buildings will grow, even in regions where cooling systems have been historically uncommon due to their colder climate, such as Sweden. The combination of free cooling (FC) with GSHPs seems like a natural way to meet the increasing cooling needs, since the heat extracted from the building during the summer months can be injected into the ground to potentially regenerate the borehole field and enhance heat pump performance. However, a technology that is generally integrated with GSHP systems for borehole regeneration are photovoltaic/thermal collectors. This study investigates the performance of a ground source heat pump system with free cooling for a multi-family building in Stockholm, Sweden, and the interference on the free cooling capabilities of the system when photovoltaic/thermal collectors are present. The results demonstrate that the integration of PVT and FC not only maintains the cooling supply but also enhances heat pump performance, all the while reducing borehole length and land area requirements., QC 20240209

Integrating high-efficiency heat pumps to renewable electricity will significantly accelerate decarbonization progress. Despite the advancements in smart sensors and communication technologies that enhance data generation in heat pump units, much of this data remains underutilized for performance analysis. The primary issue is that the data often exhibits incompleteness, inconsistency, and inaccuracies. Consequently, data collection and storage impose an economic burden on manufacturers and end-users, and they have limited returns. This thesis aims to unlock the potential of various data resources, delivering knowledge-based services and addressing gaps in data availability and utilization. The dissertation introduces the Data-Information-Knowledge-Service (DIKS) framework as an adaptation of the traditional Data-Information-Knowledge-Wisdom (DIKW) hierarchy, emphasizing the practical application of turning inadequate data into knowledge-based services in heat pump technologies. The transformative process within the DIKS pyramid is illustrated, detailing how each layer converts inadequate raw heat pump data into actionable, knowledge-based services. It begins with the aggregation and integration of various data types, followed by advanced processing techniques to refine data quality and identify significant patterns. This foundation of knowledge is then applied to improve heat pump services, demonstrating the practical benefits of this structured approach. Five different scenarios are examined utilizing different types of data, including high-quantity, low-quality in-situ measurements, high-quality, low-quantity lab data, and technical specifications. The first scenario, utilizing in-situ field measurement data, develops an artificial neural network (ANN) model to create soft sensors that compensate for the absence of costly physical sensors in heat pump systems. These soft sensors use incomplete data to accurately estimate essential heat pump parameters, supporting, Integreringen av högeffektiva värmepumpar med förnybar elektricitet förväntas påskynda minskningen av koldioxidutsläppen avsevärt. Trots framsteg inom smarta sensorer och kommunikationstekniker som förbättrar dataproduktionen i värmepumpsenheter, förblir mycket av denna värdefulla data outnyttjad och används främst för enklare övervaknings- och felvarningsfunktioner snarare än för omfattande analys. Det största problemet är att datan ofta brister i fullständighet, konsekvens och noggrannhet. Detta innebär att datainsamling och lagring är en ekonomisk börda för tillverkare och slutanvändare som inte utnyttjas. Denna avhandling syftar till att fullt ut utnyttja hela potentialen hos olika dataresurser, så att kunskapsbaserade tjänster kan levereras och att hantera saknade data. Avhandlingen introducerar ramverket ``Data - Information-Knowledge-Service" (DIKS) som en anpassning av den traditionella hierarkin ``Data-Information-Knowledge-Wisdom" (DIKW), med betoning på den praktiska tillämpningen av att omvandla inadekvat data till kunskapsbaserade tjänster hos värmepumpssystem. Den transformerande processen inom DIKS-pyramiden illustreras och visar detaljerat hur varje lager kan omvandla otillräckliga rådata från värmepumpar till användningsbara, kunskapsbaserade tjänster. Ramverket börjar med sammanställning och integration av olika datatyper, följt av avancerade bearbetningstekniker för att förbättra datakvaliteten och identifiera signifikanta mönster. Denna kunskapsgrund tillämpas sedan för att förbättra värmepumptjänster, vilket visar de praktiska fördelarna med detta strukturerade tillvägagångssätt. Fem olika scenarier undersöks med olika typer av av dataanvändning, inklusive stora mängder av data med låg kvalitet från fältmätningar, högkvalitativa data av låg kvantitet från laboratoriedata och slutligen katalogdata. Det första scenariot, som använder data från fältet, utvecklar modeller med hjälp av artificiella neurala nätverk (ANN) för att skapa mjuka sensorer s

Modern heat pump systems often come equipped with sensors, enabling the collection of substantial operational data. However, many residential heat pumps installed in preceding decades lack pressure sensors, energy meters, or mass flow meters, primarily due to financial limitations. As a result of these incomplete measurements, the direct analysis of the heat pump system’s performance or the leveraging of the amassed data for inventive applications like prognosticating energy consumption, detecting and diagnosing faults, and implementing intelligent control becomes challenging.In existing literature, the focus of soft sensors in heat pump systems has been on estimating a single parameter. This approach, however, overlooks the reality that multiple parameters are often missing due to the lack of all-encompassing physical meters and sensors. Furthermore, current soft sensor models are typically developed using inputs such as compressor power consumption, pressures, evaporation, and condensation temperatures. These inputs, unfortunately, tend to be inaccessible within existing heat pump monitoring installations.In practice, it is a challenge to compensate for several critical measurements, encompassing mass flow rate, pressures, power consumption, and heating capacity, by using only commonly available sensors such as secondary loop temperatures and compressor frequency are available. Currently, there is a notable gap in research concerning this practical issue.To address the problems associated with inadequate measurements, this study presents the development and validation of soft sensors based on a data-driven approach, which can compensate for the parameters often unavailable with data collected from a limited number of commonly used sensors. Each component model employs a multivariate polynomial regression that calculates the evaporation temperature, condensation temperature, mass flow rate, and compressor power consumption, respectively. Subsequently, we present an, QC 20240906

This paper presents a new methodology to adjust map-based models to experimental data and reports the main results of a comprehensive experimental campaign of a Dual Source Heat Pump (DSHP) prototype. The prototype tested incorporates variable speed components (compressor, circulation pumps, and fan). The novelty of this prototype lies in its ability to select two possible heat sources: air or ground. Thus, it can operate as a geothermal or aerothermal heat pump, as well as a chiller, thanks to the additional capacity to reverse the cycle. Thanks to this hybrid approach, several advantages can be obtained compared to conventional equipment, such as higher efficiency, the requirement of smaller borehole heat exchangers, or the absence of defrost cycles. In a prior study, polynomial models were developed to accurately characterize the DSHP's performance (i.e., condenser and evaporator capacities and electrical energy consumption). These models were obtained considering the external variables to the unit as independent variables to facilitate their applicability using variables commonly measured in real installations. Due to the complexity of heat pump performance, which in current equipment can be influenced by up to 5 or 6 independent variables, the search for suitable polynomial models required the availability of a complete working map including more than 3000 working points. Thus, this previous work developed these models based only on simulation results. In this sense, this paper concludes the development of these models by focusing on two critical issues concerning empirical model development. The first aspect involves determining the minimum number and location of testing points needed to define the experimental sample for the model adjustment. The reported experimental data were obtained by analyzing the most suitable experimental design methodology to create the experimental matrices in each operating mode of the DSHP. The second aspect focuses on the final a, QC 20240719

The study investigated the characteristics of different natural refrigerants and their mixtures in a residential heat pump with low refrigerant charge. Three main evaluation criteria were utilized for comparing different mixtures: Coefficient of Performance (COP), Volumetric Heating Capacity (VHC), and a newly proposed indicator, the heating capacity at charge limit. Propane was used as a reference refrigerant. It was found that some mixtures significantly improved both COP and the heating capacity at charge limit while maintaining similar volumetric heating capacity and operating conditions. Alternative multi-criteria decision-making techniques were adopted to rank the best refrigerant mixtures. Mixtures rich in Dimethyl Ether (DME), such as DME-CO2 [0.96-0.04] and DME-Propylene [0.75-0.25] were found consistently among the best options. Those were followed by Propylene-rich mixtures such as Propylene-CO2, Propylene-Isobutane and Propylene-Butane. The levelized cost of heat (LCOH) could be improved by up to 12 %. To accelerate the transition to natural refrigerants, without compromises on efficiency and costs, further research and certification activities on non-fluorinated refrigerants based on Dimethyl Ether (R-E170), CO2 (R-744) and Propylene (R-1270) are recommended., QC 20240620

This study empirically investigates the optimal design features of photovoltaic-thermal (PVT) collectors for integration with ground source heat pump (GSHP) systems, considering technical and economic factors. Outdoor experiments are conducted in Stockholm, Sweden, comparing five unglazed and uninsulated PVT collector designs a) Reference Sheet & Tube b) Sheet & Tube with a narrow air gap between PV and absorber plate c) Box-channel polypropylene d) Finned tube and e) Box-channel aluminum with fins at operating temperatures below ambient. The findings indicate that the box-channel aluminum design with fins, characterized by a superior combination of high zero-loss efficiency and a high U-value, emerges as the ideal PVT design for integration with ground source heat pumps, taking into account both technical and economic considerations. Despite having a relative specific thermal cost 9% higher than the reference collector, this design demonstrates the capability to generate 2,096 kWh/(m2a) of thermal energy, marking an 83.3% increase compared to the reference, with a 136% higher energy-to-mass ratio., QC 20240617

Aqueous solutions of ethylene glycol are commonly used as secondary fluids in different indirect refrigeration systems and heat pumps as well as nanofluids. A very extensive literature review has been done, including more than 90 references published from 1905 to 2023. Despite the wide application and importance, especially in the energy sector, ethylene glycol solutions seem to be less investigated in low temperature ranges and more research is required to improve the quality and quantity of available data. The novelty of this paper is to investigate the most important thermophysical properties of ethylene glycol solutions in low temperatures. In this study a different approach was made and solutions having a specific freezing point temperature (between -5 and -50 ºC) rather than specific concentration were investigates in temperature ranges applicable for different cooling applications. The concentrations giving a certain freezing point temperature seemed to deviate in some cases with 1–2 wt-% between different sources. Nevertheless, the density results were in rather good agreement with all reference data. The viscosity results were lower by up to ±10% compared to reference values. Additionally, the obtained experimental results for thermal conductivity were higher by up to 12% compared to ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) data. The specific heat capacity results were higher by up to 14.6% and 5.4% than current reference data. There is a high probability that the current ASHRAE data for specific heat are actually indirectly calculated values from thermal conductivity data and not validated using differential scanning calorimetry techniques., QC 20231020

International Energy Agency predicts that the global number of installed heat pumps (HP) will increase from 180 million in 2020 to approximately 600 million by 2030, covering 20% of buildings heating needs. Electric power consumption is one of the main key performance indicators for the heat pump systems from techno-economic perspective. However a common issue prevalent in many existing heat pumps is the lack of electric power measurement. The modern installations might be equipped with electric power measurement sensors but this comes at a higher system cost for the manufacturers and end-users. The primary objective of this work is to propose a virtual measurement for estimating power consumption, thereby eliminating the need for field measurement of power for heat pumps. To achieve the objective, a data-driven approach is proposed. Firstly, the in-situ data is preprocessed through data merging, cleaning, and normalization. Then, input features are pre-selected using Spearman correlation coefficients, and further refined by addressing multicollinearity problem. Following this, Extreme Gradient Boosting (XGBoost) models and polynomial models are developed by considering different features as inputs. All models are finally validated against the in-situ data from multi-units of ground source heat pump (GSHP) and air source heat pump (ASHP) installations. The results showed that the electric power consumption of GSHP can be estimated with high accuracy (99% for R2, 10 W for MAE, and 1% for MAPE) through generic data-driven models using only four easy-to-measure input features. Taking three input features as inputs for ASHP generic model, the accuracy can be reached to 83% for R2, 125 W for MAE, and 9% for MAPE. The method presented in this paper can be applied to estimate power consumption of millions of heat pumps and consequently add a significant value as well as provide different types of services, such as cost-saving benefits for manufacturers and end-users, flexi, QC 20231115

Changes in the ground surface temperature, as it can occur in built-up areas or due to climate change, affect the temperatures of geothermal boreholes. Analytical models for the thermal simulation of boreholes and consid-ering this factor have been proposed. However, they all impose a uniform heat extraction boundary condition along the borehole walls. This boundary condition overestimates the temperature change in the underground caused by the borehole heat extraction and underestimates it in case of rejection. More accurate results are most often obtained by imposing a uniform temperature boundary condition.In this paper, we propose a new model to calculate the boreholes wall temperature taking into account both the heat extractions/rejections from all the boreholes in the area and the change in ground surface temperature. The model is tailored for areas with independent ground source heat pumps and imposes a uniform temperature boundary condition along the borehole walls, overcoming the limitation of the existing models.We apply the new model to a real Swedish neighbourhood and show that existing systems may already be significantly affected by the increased ground surface temperature due to urbanization. We also compare our new model with an existing similar model and show that while the two models provide similar results for smaller areas, their difference tends to be relevant for bigger areas - including the real Swedish neighbourhood analysed -thus making the application of our model important for neighbourhood-and city-scale studies., QC 20230307

The present study demonstrates and visualizes the two modes of constrained melting and close-contact melting in a rectangular cavity enhanced with fins. Three configurations of fin with different lengths and numbers are tested in different horizontal, inclined, and vertical orientations. N-eicosane is used as the phase change material, and the experiments are performed with water as the heat transfer fluid at the inlet conditions of 50 degrees C, 55 degrees C, and 60 degrees C. In general, the close-contact melting time is shorter by 42-50%, compared to the convection dominated constrained melting in the unenhanced cavity without fins. By using fins to enhance the process, the melting time is reduced by 49% and 35% in the constrained and the close-contact modes, respectively, compared to the unfinned cavity in each mode. The thermal performance is observed to be superior in the horizontal and the inclined orientations. In these orientations, the buoyancy-driven structures are not blocked by fins in the con-strained mode. In the close-contact mode, the solid specimens attain more consistent contact with the base of the cavity and with the extended heat transfer area at the inclined and horizontal conditions. In the vertical orientation, the asymmetrical melting by the fins results in a rotational movement of the solid PCM and close -contact perturbations. The variations in the number of fins are found to have minor effects on the overall close-contact-induced melting. On the other hand, increasing the length of the fins is a more promising measure, providing consistent and prolonged contact., QC 20230109

Ground Source Heat Pumps (GSHPs) have emerged as a promising technology for decarbonization of the heating sector. However, their increasing prevalence in densely populated areas may lead to considerable changes in the ground temperature, which can ultimately lead to reduced performance of the systems. Being able to forecast the ground temperature change in areas with a high density of GSHPs is therefore important for a correct management of the geothermal resource and the proper design of the systems. The main scope of this thesis is to propose a new heat transfer model that enable the calculation of the ground temperature development in areas with several GSHP systems connected to vertical borehole heat exchangers. This work resulted in two new models, here referred to as FLSIV and FLSIVTBC, which are built upon the Finite Line Source model, a classic building block for semi-analytical models dedicated to geothermal boreholes. The application of these models to realistic scenarios representative for Stockholm has revealed a potentially significant interference between neighboring geothermal boreholes in densely populated areas. Therefore, a secondary objective of this thesis is to explore possible strategies for limiting this interference. The last section of this thesis investigates the possibility of increasing the borehole length or reducing the thermal load to constrain the ground temperature change, and the possibility of limiting the number of GSHPs in an area to prevent a severe drop of system performance. The results showed that the first two strategies may require a significant change in the operation or design of the systems, while the third strategy may permit a high utilization of GSHPs without modifications of the systems. Keywords: Ground source heat pumps, Thermal interference, Neighboring geothermal borehole, Finite Line Source, Mitigation strategies., Bergvärmepumpar har utvecklats till en lovande teknik för avkarbonisering av uppvärmningssektorn. Men deras ökande spridning i tätbefolkade områden kan leda till stora förändringar i marktemperaturen, vilket i slutändan kan ledda till minskad prestanda hos systemen. Att kunna förutsäga förändringar i marktemperaturen i områden med hög densitet av bergvärmepumpar är därför viktigt för en korrekt hantering av geotermisk resurs och korrekt design av systemen. Huvudsyftet med denna avhandling är att föreslå nya modeller för värmeöverföring som möjliggör beräkning av marktemperaturutvecklingen i områden med flera bergvärmepump-system som är anslutna till vertikala borrhåls-värmeväxlare. Detta arbete resulterade i två nya modeller, som här benämns som FLSIV och FLSIVTBC, och som är byggda på Finite Line Source-modellen, en klassisk byggsten för halvanalytiska modeller som är dedikerade till geotermiska borrhål. Tillämpningen av dessa modeller på realistiska scenarier som är representativa för Stockholm har avslöjat en potentiellt betydande störning mellan närliggande geotermiska borrhål i tätbefolkade områden. Därför är ett sekundärt mål med denna avhandling att utforska möjliga strategier för att begränsa denna störning. Den sista delen av denna avhandling undersöker potentialen för att begränsa antalet bergvärmepumpar i ett område för att förhindra en allvarlig försämring av systemets prestanda. Resultaten visade att de första två strategierna kan kärva en betydande förändring i driften eller designen av systemen, medan den tredje strategin kan tillåta en hög användning av bergvärmepumpar utan modifieringar av systemen. Nyckelord: Bergvärmepumpar, Termisk interferens, Angärnsande geotermisk borrhål, Finite Line Source, Åtgärder för att minska påverkan

Many efforts are being made to mitigate the main disadvantage of most phase change materials - their low thermal conductivities - in order to deliver latent heat energy storage systems (LHESS) with adequate perfor-mance. However, the effect of applied methods is difficult to compare as they are mostly tested for different storage types and sizes and/or different boundary and initial conditions, which hinders rapid progress in the optimization of these approaches. In this work, a previously developed method for comparing the performance of LHESS is applied to experimental results of different storage systems under different conditions and subsequently analyzed and further refined. The main idea of the method is to normalize the power with the volume and a reference temperature difference and compare its mean value plotted over the normalized mean capacity flow of the heat transfer fluid (HTF). This enables the presentation of the results in a compact and easily comparative way. Attention has to be paid when it comes to the choice of the reference temperature difference, the reference volume and the method for calculating the mean value. Two variants of calculating the mean value (time-weighted and energy-weighted) and two variants of reference temperatures for determining the temperature difference to the inlet temperature of the HTF (initial temperature and melting temperature) are applied and discussed in detail. While the method significantly increases the comparability of results, none of the options listed above are without drawbacks. Approaches are shown to reduce or eliminate these drawbacks in the future. The recommendation for comparing different LHESS under different conditions is to use the method described here and clearly state the chosen reference temperature, reference volume and method for calculating the mean value., QC 20230911

Raman-based distributed temperature sensing (DTS) is a valuable tool for field testing and validating heat transfer models in borehole heat exchanger (BHE) and ground source heat pump (GSHP) applications. However, temperature uncertainty is rarely reported in the literature. In this paper, a new calibration method was proposed for single-ended DTS configurations, along with a method to remove fictitious temperature drifts due to ambient air variations. The methods were implemented for a distributed thermal response test (DTRT) case study in an 800 m deep coaxial BHE. The results show that the calibration method and temperature drift correction are robust and give adequate results, with a temperature uncertainty increasing non-linearly from about 0.4 K near the surface to about 1.7 K at 800 m. The temperature uncertainty is dominated by the uncertainty in the calibrated parameters for depths larger than 200 m. The paper also offers insights into thermal features observed during the DTRT, including a heat flux inversion along the borehole depth and the slow temperature homogenization under circulation., QC 20230721

The adoption of innovation in the building sector is currently too slow for the ambitious sustainability goals thatour societies have agreed upon. Living labs are open innovation ecosystems in real-life environments usingiterative feedback processes throughout a lifecycle approach of an innovation to create sustainable impact. In thecontext of the built environment, such co-creative innovation and demonstration platforms are needed tofacilitate the adoption of innovative technologies and concepts for more energy-efficient and sustainablebuildings. However, their feasibility is not extensively proven. This paper illustrates the implementation anddemonstrates the feasibility of the Living Labs Triangle Framework for buildings living labs. This conceptualframework has been used to conceive the KTH Live-In Lab, a living lab for buildings. The goal of the Live-In Labwas to create a co-creative open platform for research and education bridging the gap between industry andacademia, featuring smart building demonstrators. The Living Lab Triangle Framework has been deployed tomeet the goals of the Live-in Lab, and the resulting concept is described. This paper then analyses the meth-odological and operational results introducing performance metrics to measure the economic sustainability, thepromotion of multidisciplinary research and development projects, dissemination and impact. The results arecompleted with a SWOT analysis identifying its current strengths and weaknesses. The results collected in thiswork fill a missing gap in the scientific literature on the performance of living labs and provide empirical evi-dence on the sustainability and impact of living labs., QC 20230321

This study aims to quantify the techno-economic potential of using solar photovoltaics (PV) to support heat pumps (HP) towards the replacement of natural gas heating in a representative North American residence from a house owner's point of view. For this purpose, simulations are performed on: (1) a residential natural gas-based heating system and grid electricity, (2) a residential natural gas-based heating system with PV to serve the electric load, (3) a residential HP system with grid electricity, and (4) a residential HP+PV system. Detailed descriptions are provided along with a comprehensive sensitivity analysis for identifying specific boundary conditions that enable lower total life cycle cost. The results show that under typical inflation conditions, the lifecycle cost of natural gas and reversable, air-source heat pumps are nearly identical, however the electricity rate structure makes PV costlier. With higher rates of inflation or lower PV capital costs, PV becomes a hedge against rising prices and encourages the adoption of HPs by also locking in both electricity and heating cost growth. The real internal rate of return for such prosumer technologies is 20x greater than a long-term certificate of deposit, which demonstrates the additional value PV and HP technologies offer prosumers over comparably secure investment vehicles while making substantive reductions in carbon emissions. Using the large volume of results generated, impacts on energy policy are discussed, including rebates, net-metering, and utility business models., QC 20230404

Latent Thermal Energy Storage (LTES) is an interesting choice to storethermal energy in a sustainable energy system. The primary benefit of LTESis the relatively high latent heat of fusion of the materials, known as PhaseChange Materials (PCM), used in such a system as the storage medium.However, as the thermal conductivity of PCMs is often very low, there is aneed to enhance the rate of heat transfer within the charging/dischargingprocess and to improve the thermal performance of the LTES systems.This thesis addresses the enhancing effect of extending heat transfer area inrectangular LTES enclosures. A key contribution of this thesis is acomprehensive visualization of the phase change processes for an organicPCM, including solidification and melting, constrained as well asunconstrained, known as Close-Contact Melting (CCM), in a cavity with andwithout fins. Observations have been carried out for fins of different lengthsand numbers with a varying angle of inclination, and a comprehensive analysisin terms of phase change time and thermal power is conducted.The observations show fins are more influential in solidification than inmelting, reducing the solidification time by 80% and increasing the meanpower by 395%, at a cost of 10% loss in the extracted energy. In contrast, inmelting, fins have a modest effect in enhancing the process. The relativeenhancement effect of fin is higher in constrained melting than inunconstrained melting. In a case with maximum enhancement, a reduction by52% in the constrained melting time and a relative enhancement in the meanpower by 90% is achieved at a cost of 9% loss in the stored energy. As thevolume fraction of fin increases, the discrepancies in melting time betweenthe constrained and unconstrained melting diminishes.A numerical model for solidification and constrained melting is validatedbased on the experiments, and a more inclusive sensitivity analysis of finparameters is performed. The enhancing effect of different parameters, Latent termisk energilagring (LTES) är ett intressant val för att lagra termisk energi i ett hållbart energisystem. Den primära fördelen med LTES är den relativt höga smältvärmen av materialet, känt som fasändringsmaterial (PCM), som används som lagringsmedium i ett sådant system. I och med att värmekonduktiviteten hos PCM ofta är mycket låg finns det ett behov av att öka värmeöverföring-hastigheten för laddnings-/urladdningsprocessen samt att förbättra LTES-systemens termiska prestanda. Denna avhandling tar upp den förstärkande effekten av att utöka värmeöverföringsytor i rektangulära LTES-behållare. Ett nyckelbidrag i denna avhandling är en omfattande visualisering av fasförändringsprocesserna i ett organiskt PCM, inklusive frysning/stelning och smältning, både som begränsad (fastnat) smältning och obegränsad (rörande) smältning, även känt som Close-Contact Melting (CCM), i en behållare med och utan flänsar. Observationer har gjorts för flänsar av olika längd samt antal, med varierande lutningsvinkel och en omfattande analys av processerna vad gäller fasändringstid och medeleffekt genomförs. Observationerna visar att flänsar är mer effektiva vid stelning än vid smältning, vilket minskar stelningstiden med 80% och ökar medeleffekten med 395%, dock minskar den utvunna energin med 10%. Däremot har flänsar vid smältning en måttlig effekt vad gäller att förbättra processen. Den relativa förstärkningseffekten av flänsarna är högre vid begränsad smältning än vid obegränsad smältning. I ett fall med maximal förbättring uppnås en minskning på 50% av den begränsade smälttiden och en relativ förbättring av medeleffekten på 90%, samtidigt som den lagrade energin minskar med 9%. När volymfraktionen av flänsarna ökar, minskar skillnaderna i smälttid mellan den begränsade och obegränsade smältningen. En numerisk modell för stelning och begränsad smältning valideras baserat på experimenten, och en mer utförlig känslighetsanalys av flänsparametrar utförs. Den förstärkande effekte

This paper investigates ellipsoid-shaped macro-encapsulated phase change material (PCM) on a component scale. The selected PCM is a paraffin-based commercial material, namely ATP60; differential scanning calorimetry and transient plane source method are used to measure ATP60's thermo-physical properties. A 0.382 m(3) latent heat thermal energy storage (LHTES) component has been built and experimentally characterized. The temperature measurement results indicate that a thermocline was retained in the packed bed region during charging/discharging processes. The experimental characterization shows that increasing the temperature difference between the heat transfer fluid (HTF) inlet temperature and phase-change temperature by 20 K can shorten the completion time of discharge by 65%, and increasing HTF inlet flowrate from 0.15 m(3)/h (Re = 77) to 0.5 m(3)/h (Re = 256) can shorten the completion time of charge by 51%. Furthermore, a one-dimensional packed bed model using source-based enthalpy method was developed and validated by comparison to experimental results, showing discrepancies in the accumulated storage capacity within 6.6% between simulation and experiment when the Reynolds number of the HTF inlet flow ranges between 90 and 922. Compared with a conventional capsule shaped in 69-mm-diameter and 750-mm-long cylinders, the ellipsoidal capsule shows 60% less completion time of discharge but 23% lower storage capacity. Overall, this work demonstrates a combined experimental and numerical characterization approach for applying novel macro-encapsulated PCM geometries for heating-oriented LHTES., QC 20211021

This chapter provides an overview of the application of thermal energy storage in industrial scale systems, e.g. steel works, pulp mills, and also power generation and district heating and cooling utilities. The purpose is to illustrate the benefits of integrating thermal energy storage in such processes, from both a technical functional and economical perspectives. Examples of such benefits are resource efficiency, stability of operation, and lowered cost of fuel., QC 20220819Part of book: ISBN 9781119239352; 9781119239390

Compared to pure fluids, zeotropic mixtures have the potential to lower the irreversibilities in low temperature Rankine cycles by better temperature profile matching of the working fluid with the heat source/sink. However, having a gliding temperature does not guarantee performance boost over pure fluids, as many factors influence the exergy efficiency of the cycle. In this study, 25 pure fluids and 104 binary mixtures of natural working fluids are analyzed in subcritical ORCs with heat source temperature range of 125-300 degrees C and different condensing conditions and the results are investigated within two frameworks: (1) comparing the mixtures to their pure constituents, (2) comparing the mixtures to the best performing pure fluid. In one behavior type, the performance of the mixture falls between the performance of its pure constituents for all evaporator pressure range, and the mixture provides no benefit. However, some mixtures could provide performance boost in a specific evaporator range. Therefore, the maximum allowable evaporator pressure plays an important role in the performance comparison of zeotropic mixtures to their pure constituents. Mixtures which outperform their pure constituents in the first perspective, are further analyzed in the second perspective. Finally, a screening method is presented to map the binary mixtures with performance boost compared to their pure constituents and high absolute exergy efficiency. This method is based on the key thermophysical properties of the fluids including critical temperature and normal boiling point, as well as working conditions such as heat source and heat sink temperature and PPTD in the evaporator and the condenser., QC 20220715

The development of 100% renewable electricity (RE) systems play a pivotal role in ensuring climate stability. Many municipalities blessed with wealth, an educated and progressive citizenry, and large RE resources, have already reached 100% RE generation. Impoverished municipalities in unwelcoming environments both politically and climatically (e.g., northern latitudes with long, dark winter conditions) appear to be incapable of transitioning to renewables. This study challenges that widespread assumption by conducting a detailed technical and economic analysis for three representative municipalities in the Western Upper Peninsula of Michigan. Each municipality is simulated with their own hourly electricity demand and climate profiles using an electrical supply system based on local wind, solar, hydropower, and battery storage. Sensitivities are run on all economic and technical variables. Results show that transition to 100% RE is technically feasible and economically viable. In all baseline scenarios, the 100% RE systems produced a levelized cost of electricity up to 43% less than the centralized utility rates, which are predominantly fueled by gas and coal. Current policies, however, prevent such self-sufficient systems from being deployed, which are not only detrimental to the global environment, but also aggravate the economic depression of such regions. Potential energy savings advance the prohibitive energy justice principle., QC 20230908

Frost formation on evaporator surfaces is a well-known problem in air-source heat pump (ASHP) systems, which decreases the energy efficiency of the system and causes thermal comfort issues during defrosting. Coatings for evaporator heat exchanger surfaces are one potential way of decreasing the problems with frost and thus improve the performance of the HP. However, there is still no consensus on which type of coating that attributes more energy efficient HP performance: hydrophilic or hydrophobic coatings. This paper aims to investigate if superhydrophilic or superhydrophobic coatings, compared to an uncoated reference surface, help prolong the cycle lengths and time spent in frosting mode by performing cyclic frosting and defrosting experiments on aluminum surfaces. The study was performed on small aluminum substrates (40 x 50 x 10 mm, 1.57” x 0.20” x 0.39”). A total of five different surface coatings of the substrates were compared, including an elastomer surface and a Slippery Liquid-Infused Porous (SLIP) type surface. The substrates were subjected to cycles of frosting and active defrosting in a wind tunnel, placed in a climate chamber at The Royal Institute of Technology (KTH) in Stockholm, Sweden. The temperature and relative humidity of the air inside the climate chamber were kept at 2°C (35.6°F) and 84%, respectively, according to the Swedish standard for HP test conditions (SS-EN 14511-2:2018). Cycles of frosting and active defrosting of the substrates were achieved by means of a thermo electric cooler (TEC) and captured with images (front and top camera). The superhydrophilic surface displayed longer frosting periods than the superhydrophobic surface. Due to the active defrosting, all of the coatings displayed similar short defrosting periods, thus indicating that the length of the frosting period is the dominant time-component of the cycle length. The study found that superhydrophilic surfaces show potential for extending the length of frosting periods c, Part of ISBN 9781955516068QC 20230831

Extending the heat transfer area is a simple technique to improve the thermal performance of phase change materials with low thermal conductivity. However, as the governing mechanisms differ in solidification and melting, fins can affect the processes in different ways. This demands assessment of fin enhancement in a combined analysis on both solidification and melting, often neglected in literature. This paper presents visual-izations of solidification and melting of n-eicosane in a rectangular cavity and experimentally investigates the enhancing effect of vertical fins with varying number and length. Experiments were conducted at water inlet temperature ranges of 15-25 degrees C and 50-60 degrees C for the solidification and melting processes, respectively. The results show that the vertical fins can be more influential in solidification rather than in melting with similar losses in the storage capacity. In the solidification process, as natural convection is absent, the mean power is enhanced by a maximum of 395% with a 10% loss in the storage capacity, as compared to the benchmark. In the melting case, the mean power is increased by a maximum of 90% with a 9% loss in the storage capacity. Although increasing the surface area with vertical fins contributes to development of convective structures, it makes a modest enhancement. In overall, increasing the fin volume fraction, in exchange for the loss in the storage capacity, enhances the solidification significantly while it has relatively low enhancement effect in melting. At the end, the performed experiments could be helpful for validation of future simulation tools with complex features, particularly solidification models lacking in literature., QC 20211028

District cooling (DC) is gaining interest with global warming and rising demands on indoor comfort. As DC grid expansions are capital intensive, cost effective alternatives to meet these rising cooling demands are desired. Integrating cold storage (CS) into the grids is one attractive choice, allowing peak shaving, load shifting, and renewable electricity recovery via power-to cold. To analyze the impact of new CSs, the DC distribution grid dynamics must be investigated. This work evaluates the implementation of several new CSs into an existing DC system (called the base case-BC), to find the optimal solution. This is performed considering the case study DC system of Norrenergi AB, Sweden, catering to Solna and Sundbyberg via three production plants Solnaverket, Sundbybergsverket and Frosundaverket, and a 10 MW CS (in Solnaverket). The software tool Netsim is used for distribution grid dynamics analysis of the BC and three scenarios with additional cold storages, for the optimization of differential pressure (dP) of the grids to be within 100-800 kPa. These scenarios include: one additional 15 MW CS in Sundbybergsverket (Scenario 1), one additional 15 MW CS in Frosunda (Scenario 2) and two additional 3 MW CSs in Sundbybergsverket and Frosunda (Scenario 3). The CSs in Sundbybergsverket are centrally placed, whereas, those in Frosunda were positioned in a grid loop experiencing low differential pressure, identified in Netsim simulations of BC. The simulations were done for 24 h at 1-hour resolution, on a chosen historically highest demand day (02 August 2018). The results indicate that the optimal solution is implementing two additional CSs in Sundbybergsverket (centralized) and Frosunda (distributed), each with a capacity between 3-7.5 MW (6-15 MW total capacities). Further evaluations to determine the optimal sizing of these CSs is the next step in this study., QC 20211217

Artificial neural networks (ANNs) have been considered for assessing the potential of low GWP refrigerants in experimental setups. In this study, the capability of using R449A as a lower GWP replacement of R404A in different temperature levels of a supermarket refrigeration system is investigated through an ANN model trained using field measurements as input. The supermarket refrigeration was composed of two indirect expansion circuits operated at low and medium temperatures and external subcooling. The results predicted that R449A provides, on average, a higher 10% and 5% COP than R404A at low and medium temperatures, respectively. Moreover, the cooling capacity was almost similar with both refrigerants in both circuits. This study also revealed that the ANN model could be employed to accurately predict the energy performance of a commercial refrigeration system and provide a reasonable judgment about the capability of the alternative refrigerant to be retrofitted in the system. This is very important, especially when the measurement data comes from field measurements, in which values are obtained under variable operating conditions. Finally, the ANN results were used to compare the carbon footprint for both refrigerants. It was confirmed that this refrigerant replacement could reduce the emissions of supermarket refrigeration systems., QC 20220111

Smog pollution is a severe social and environmental concern for the space-heating regions in China due to fossil-intensive space heating. To reduce polluting emissions and improve social and environmental performance, local government agencies should choose adequate cleaner space-heating technologies based on diverse local conditions. This implies that all cleaner heating solutions should be considered, including low-emissions fossil fuel district heating and low-emissions fossil fuel decentralized heating as transitional technologies, as well as biomass and electricity-driven heat pumps as long-term solutions. However, stakeholders such as policy makers, equipment manufacturers, and house owners, often lack necessary information to assess the feasibility for installing adequate heating solutions at the local level. It is therefore necessary to establish a systematic method to evaluate each heating solution in various geolocations of China. This paper reviews the current heating situation in China and proposes a spatial system analysis method as a tool for heating-solution feasibility evaluation. By applying the spatial system analysis method, a qualitative investigation on the choice of heating solution in different regions of China is provided., QC 20211215

Thermal response tests are used to estimate the thermal properties of the ground and the borehole heat exchanger being tested. They are thus important for the design of borehole thermal energy storages and ground source heat pump systems. In this study, a theoretical framework is proposed in order to investigate if noise on the heat rate leads to a bias in the parameter estimation. Under the sole assumption of a linear time-invariant system and the use of the sum of squared errors as cost function, it is shown analytically that estimates are in fact biased when the heat rate is corrupted by noise. To understand how large this bias can be, a Monte-Carlo study is performed. It includes more than 126,000 simulations with different noises, thermal parameters and heat rate profiles. Negative biases as high as -0.44 W/(m K) (11%) and -11.10(-3) m K/W (4.1%) are observed for the thermal conductivity and borehole thermal resistance estimates, respectively. In addition, the parameter estimation is stochastic due to randomness of measurement noises. This cannot be ignored since only one thermal response test is performed, in general. Population of estimates with 95% confidence intervals as large as 1.0 W/(m K) (25%) and 24.10(-3) m K/W (9.4%) appear in this study. Although the bias and confidence intervals are not significant in all simulated cases, they cannot be generally disregarded and one should therefore be mindful of this potential issue when analyzing thermal response tests. An observed trend is that the confidence intervals and bias are higher for higher parameter values, with a particular dependency on thermal conductivity. To reduce the bias and spread of the estimates, having larger heat rate per meter appears to be a good strategy. Having a higher sampling frequency and/or longer tests might also help, but only in reducing the spread of the estimates, not the bias., QC 20211105

Latent heat thermal energy storage (LHTES) systems can be coupled with heat pump (HP) systems to realize heat load shifting on demand side. With phase change material (PCM), well designed LHTES components exhibit high storage energy density and thus have large potentials to be integrated in residence where a compact energy storage solution is needed. However, real installations of LHTES-HP integrated systems are still rare nowadays; feasibility of this technology in achieving technically sound and economically viable load shifting operations should be demonstrated and understood by stakeholders to promote its implementation. Therefore, this thesis presents an exemplary feasibility study for three selected off-the-shelf macro-encapsulated PCM products, encompassing in-depth experimental and numerical modelling investigations on three levels—material, component, and system. The feasibility is studied with a specific scenario where the macro-encapsulated LHTES systems are designed to integrate with HP-based heating systems in common Swedish residential buildings. On the material level, three commercial PCMs (C48, C58, and ATP60) are selected by the operating temperature levels in typical HP-based space heating systems. Differential Scanning Calorimetry and Temperature-History method are employed to measure PCM enthalpy-temperature profiles; Transient Plane Source method is used to measure the thermal conductivity of ATP60. C58 based on sodium acetate trihydrate is prioritized for in-depth feasibility analyses because of its highest volumetric heat storage capacity. On the component level, three full-scale macro-encapsulated LHTES components (Component 1: cylindrical encapsulation of C48; Component 2: cylindrical encapsulation of C58; Component 3: ellipsoidal encapsulation of ATP60) are developed for integration in single-family houses to achieve full peak load shifting. A test rig is built for characterizing the three components under possible operational conditions i, Latenta värmeenergilagringssystem (eng. LHTES) kan kopplas till värmepumpsystem (eng. HP) för att uppnå en förskjutning av värmebehovet. Med fasförändringsmaterial (eng. PCM) uppvisar väldesignade LHTES-komponenter hög lagringsenergitäthet och har således stora möjligheter att integreras i bostäder där en kompakt lagringslösning efterfrågas. Men installationer av LHTES-HP-integrerade system är fortfarande knappa nuförtiden eftersom att det är nödvändigt att demonstera möjligheten hos denna teknik att uppnå tekniskt och ekonomiskt sund förskjutning av värmelaster samt öka föreståelsen hos intressenter för att främja implementering av tekniken. Således presenterar denna avhandling en studie på implementeringen av tre utvalda och tillgängliga makroinkapslade PCM-produkter. Studien omfattar djupgående undersökningar med experimentella och numeriska modellering på tre nivåer – material-, komponent- och system-nivå. Implementeringen studeras utifrån ett specifikt scenario där de makroinkapslade LHTES-systemen är utformade för att integreras med HP-baserade värmesystem i typiska svenska bostadshus. På materialsidan väljs tre kommersiella PCM:er (C48, C58 och ATP60) utifrån arbetstemperatursnivån i typiska HP-baserade värmesystem. Metoderna Differential Scanning Calorimetry och Temperature History används för att mäta PCM:ens entalpi-temperaturprofiler; Metoden Transient Plane Source används för att mäta ATP60:s värmeledningsförmåga. C58, som är baserat på natriumacetat trihydrat, prioriteras för noggranna genomförbarhets analyser på grund av sin högsta värmelagringskapacitet. På komponentnivå utvecklas tre fullskaliga makroinkapslade LHTES-komponenter (Komponent 1: cylindrisk inkapsling av C48; Komponent 2: cylindrisk kapsling av C58; Komponent 3: ellipsoid inkapsling av ATP60) för integrering i enfamiljshus för att uppnå full Peak Load Shifting (förskjutning av värmelasten under toppeffekttimmarna). En testprototyp byggs för att testa dessa tre komponenter under olika dri

Rural electrification in developing countries has become one of the greatest challenges for achieving global access to electricity—one of the United Nation’s sustainable development goals. Governments, international entities and private companies are tasked with improving the quality of life for people and reducing environmentally harmful emissions. Bolivia’s political agenda has been working in coordination with international cooperation organizations, and it has achieved great improvements in access to electricity in recent years. Different strategies and technologies have been used in the various climate scenarios that span Bolivia’s territory. Although more Bolivians have access to electricity than 10 years ago, insufficient knowledge, training, and follow-up from local and national actors (such as power producers, power distributors, and electricity service providers) prevent these solutions from operating as expected. This study explores the integration of a Stirling engine into a small power production system for use in remote rural areas. The Stirling engine is a well-known technology that can use local fuels to generate power and heat. Here two different hybrid power systems in three case studies are compared: the first system is using photovoltaic (PV) panels, batteries, and diesel engines and the second is using PV panels, batteries, and Stirling engines. In a sustainability analysis the environmental effects, economy, and performances—efficiency and reliability—of the two systems are compared. In addition, the study discusses the maintenance of the Stirling engine in Bolivia rural conditions. The study began by gathering data from 17 households in different communities, which had just obtained access to electricity. These communities are characterized by different environmental and climate conditions, which allows us to better understand how the systems operate under Bolivia’s varying climate and to consider the state of its economy and technical capacit, Landsbygdselektrifiering i utvecklingsländer har blivit en av de största utmaningarna för global tillgång till el - ett av FN: s mål för hållbar utveckling. Regeringar, internationella enheter och privata företag står inför utmaningen att förbättra livskvaliteten för människor och minska miljöfarliga utsläpp. Bolivias politiska agenda har handlat om att arbeta samordnat med internationella samarbetsorganisationer och har uppnått stora förbättringar avseende tillgången till el de senaste åren. Olika strategier och tekniker har använts i de olika klimatscenarierna som spänner över Bolivias territorium. Även om fler bolivianer har tillgång till el än för tio år sedan, förhindrar otillräcklig kunskap, utbildning och uppföljning från lokala och nationella aktörer (som kraftproducenter, kraftdistributörer och elsleverantörer) att dessa lösningar fungerar som förväntat. Denna studie undersöker integrationen av en Stirling-motor i ett litet kraftproduktionssystem för användning i avlägsna landsbygdsområden. Stirling-motorn är en välkänd teknik som kan använda lokala bränslen för att generera energitjänster. Här jämförs två olika hybridsystem i tre fallstudier: det första systemet har solcellspaneler (PV), batterier och dieselmotorer [1] och det andra har solcellspaneler, batterier och Stirling-motorer. I en hållbarhetsanalys jämförs de två systemens miljöeffekter, kostnader och prestanda - effektivitet och tillförlitlighet. Dessutom diskuterar studien underhållet av Stirling-motorn i landsbygden i Bolivia. Studien började med insamling av data från 17 hushåll i olika samhällen, som just hade fått tillgång till el,. Dessa samhällen kännetecknas av olika miljö- och klimatförhållanden, vilket gör det möjligt för oss att bättre förstå hur systemen fungerar under Bolivias varierande klimat och att ta hänsyn till läget för dess ekonomi och tekniska kapacitet. Med hjälp av GIS-kartor (Geographical Information System) valdes tre bolivianska samhällen ut: Tirina, Tablani och El Carm

Supermarkets have become a vital feature of modern society. However, they have significant impact on the environment due to the large amount of refrigerants needed in the refrigeration system, and due to the large energy use in the supermarket, they are the commercial buildings with highest energy intensity. The largest energy-user in the supermarket is typically refrigeration systems; these systems consume and emit a large amount of high global warming potential (GWP) refrigerants. The impacts of the supermarket refrigeration systems on the environment has been under investigation, mainly in the recent decades. The solution to mitigate these two major impacts of high GWP refrigerant emissions, and high energy use is by building more energy efficient refrigeration systems that use environmentally friendly refrigerants. Refrigeration systems using CO2 as a refrigerant has been emerged and applied as a solution in the recent two decades. This PhD thesis explores methods to increase the energy efficiency of CO2 refrigeration systems in supermarkets. The objective is to present and evaluate technical solutions that make the system competitive with conventional systems in terms of energy, environment, and economics. This thesis focuses on design modifications and energy systems’ integration. This is based on computer simulations and field measurement analysis of a number of CO2 systems installed in Sweden. The conventional HFC solutions, as reference, and alternative cooling and heating systems are included in the comparative performance studies. As the starting point of this PhD thesis, the first study was to benchmark and compare the performance of emerging CO2 systems with conventional HFC systems, which was a completion of results from a previous project. To fulfil this objective, the field performance of five CO2 systems are compared with three HFC-based systems, all installed in Swedish supermarkets. The results show that the newer generation of CO2 systems are mo, Stormarknader har blivit ett viktigt inslag i det moderna samhället. De har emellertid betydande miljöpåverkan på grund av den stora mängden köldmedier som behövs i kylsystemet, och på grund av den stora energianvändningen i stormarknader; de är de kommersiella byggnader som har högst energiintensitet. Den största energianvändaren i stormarknader är vanligtvis kylsystemet; dessa system förbrukar och förlorar en stor mängd köldmedier med hög global uppvärmningspotential (GWP). Effekterna av kylsystemen i stormarknader på miljön har undersökts, främst under de senaste decennierna. Lösningen för att minska dessa två stora effekter, av utsläpp av köldmedium med hög GWP och hög energianvändning, är att bygga mer energieffektiva kylsystem som använder miljövänliga köldmedier. Kylsystem som använder CO2 som köldmedium har utvecklats och använts som en lösning under de senaste två decennierna. Denna doktorsavhandling undersöker metoder för att öka energieffektiviteten i CO2-kylsystem i stormarknader. Målet är att presentera och utvärdera tekniska lösningar som gör systemet konkurrenskraftigt med konventionella system när det gäller energi, miljö och ekonomi. Denna avhandling fokuserar på designändringar och integration i energisystemet utanför butiken. Detta baseras på datasimuleringar och fältmätningsanalyser av ett antal CO2-kylsystem installerade i Sverige. Konventionella HFC-lösningarna (som referens) och alternativa kyl- och värmesystem ingår i de jämförande prestandastudierna. Som utgångspunkt för denna doktorsavhandling var den första studien att jämföra prestandan hos nyutvecklade CO2-system med konventionella HFC-system, vilket var en komplettering av resultat från ett tidigare projekt. För att uppnå detta mål jämförs fältprestanda för fem CO2-system med tre HFC-baserade system, alla installerade i svenska stormarknader. Resultaten visar att den nyare generationen CO2-system är mer, eller lika, effektiva som avancerade HFC-systemlösningar. Viktiga systemparametrar

QC 20211117Not duplicate with diva 1605639 and diva 1605623 and diva 1605596 diva 1605627 and diva 1605635 and diva 1605600

The majority of Aquifer Thermal Energy Storage (ATES) systems studies have been conducted in aquifer systems located in large sand aquifers. Esker formation present a more challenging geometrical complexity compared to typical sand aquifers. This study aims to conduct comprehensive and long term performance evaluation of doublet type ATES system in esker geological formation in Stockholm, Sweden. The total heating and cooling used from the ATES are 673 MWh and 743 MWh respectively during the first 3 annual storage cycles of operation. The licensed total amount of water extraction and injection is 50 liters per second with undisturbed groundwater temperature of 9.5 degrees C. Over the first three storage cycles, the average injection and extraction temperatures for the warm side are 13.3 degrees C and 12.1 degrees C, and for the cold side 7.6 degrees C and 10.5 degrees C. The average temperature differences across the main heat exchanger from the ATES side are 4.5 K during winter and 2.8 K during summer which is 4-5 degrees lower than the optimum value. The average thermal recovery efficiency over the first 3 storage cycles were 47 % and 60 % for warm and cold storages respectively. The data analysis indicated annual energy and hydraulic imbalances which results into undesirable thermal breakthrough between the warm and cold side of the aquifer. This was mainly due to suboptimal operation of the building energy system which led to insufficient heat recovery from the warm side, and subsequently insufficient cold injection in the cold wells, despite the building heating demand and the available suitable temperatures in the ATES. The cause of the suboptimal operation is the oversizing of the heat pumps which were designed to be coupled to larger thermal loads as compared to the ones in the final system implementation. As a result, the heat pumps could not be operated during small-medium loads. Additionally, the paper discusses the limitations of currently used energy an, QC 20211026

QC 20211117

The phase-down of hydrofluorocarbons and substitution with low global warming potential values are consequences of the awareness about the environmental impacts of greenhouse gases. This theoretical study evaluated the energy and exergy performances and the environmental impact of three vapor compression system configurations operating with the hydrocarbons R290, R600a, and R1270 as alternatives to R134a. The refrigeration cycle configurations investigated in this study include a single-stage cycle, a cycle equipped with an internal heat exchanger, and a two-stage cycle with vapor injection. According to the results, the alternative hydrocarbon refrigerants could provide comparable system performance to R134a. The analysis results also revealed that using an internal heat exchanger or a flash tank vapor injection could improve the system's efficiency while decreasing the heating capacity. The most efficient configuration was the two-stage refrigeration cycle with vapor injection, as revealed by the exergy analysis. The environmental impact analysis indicated that the utilization of environmentally-friendly refrigerants and improving the refrigeration system's efficiency could mitigate equivalent CO2 emissions significantly. The utilization of hydrocarbons reduced the carbon footprint by 50%, while a 1% to 8% reduction could be achieved using the internal heat exchanger and flash tank vapor injection., QC 20210802

Well-integrated thermal energy storage units can enhance flexibility and profitability for a cogeneration system by enabling its decoupling of electricity and heat production. In the present study, novel latent heat thermal energy storage technologies are numerically investigated on their thermal and economic performance to evaluate their implementation at an existing combined cycle power plant. Three commercially available storage designs are analyzed: one shell-and-tube heat exchanger design based on planar spiral coils, and two types of advanced macro-encapsulated designs with capsules resembling ellipsoid and slab in shape, respectively. For the spiral coil design, three-dimensional flow velocity and temperature fields are simulated with finite volume method to predict the transient storage heat transfer process, including the effect of secondary flow induced by centrifugal forces. For the macro-encapsulated designs, effective heat transfer coefficients between heat transfer fluid (HTF) and phase change material (PCM) are inferred from scaled-down storage prototyping and testing. A onedimensional two-phase packed bed model was developed based on the apparent heat capacity-based enthalpy method to numerically study the heat transfer in macro-encapsulated PCM. With an operating temperature range of 46-72 degrees C and a HTF supplying flowrate range of 4.2-8.4 m3/h defined by the cogeneration strategy, thermal power and accumulated storage capacity are calculated and compared for the first three hours of charge and the first hour of discharge for the three designs. The effect from increasing the HTF flowrate to accelerate charging/ discharging processes is indicated by the simulation results. Performance comparison among the three designs shows that the slab capsule design exhibits the highest accumulated storage capacity (710 kWh) and state of charge (40%) after three hours of charge, though it has a lower theoretical total storage capacity (1760 kWh) than the spi, QC 20210915

This paper investigates the opportunity of utilizing the spare heating capacity of CO2 refrigeration systems in supermarkets to produce heat to be sold to district heating network operators. A comprehensive description and assessment of two control strategies that could be implemented to enable the heat export function are presented. To maximise the heating capacity during the coldest moments of the year, the integration of geothermal storage with the CO2 system was investigated as an additional scenario. The BIN method was used to perform annual energy calculations. Furthermore, a sensitivity analysis was carried out on the most critical parameters, namely the heating demand, price ratio and temperature levels of the district heating network. For the assumed prices and energy demands, the supermarket could make profits corresponding to up to 16% (10,000 (sic)/year) of the annual energy cost by selling part of the heat recovered to the district heating network operator. Furthermore, the heat exported could save up to 18% of the annual CO2 emissions of the supermarket compared to the baseline. Finally, the sensitivity analysis showed that the economics of this solution is the more profitable, the lower return temperature of the heating network where the installation is connected., QC 20210621

Ground Source Heat Pumps (GSHPs) connected to Borehole Heat Exchangers (BHEs) are a fast-growing technology for thermally efficient buildings. Therefore, areas with several independent GSHP installations close to each other are becoming more and more common. To guarantee an optimal operation of these systems, it is necessary to design them considering the influence of the neighbouring installations. However, a tailored model for this scope has not been found in the literature. In this paper, we aim at filling this gap by proposing and validating a methodology to calculate the thermal influence between neighbouring independent boreholes. It is based on the Finite Line Source (FLS) model and prescribes novel boundary conditions, tailored to hydraulically independent boreholes. The methodology allows to prescribe different thermal loads to different BHEs and imposes uniform temperature boundary condition on each borehole wall. We also show how to implement and apply the model. Our application shows a thermal influence of up to 1.5 K during the lifetime of a GSHP and of up to 0.8 K during the first year of operation in an area with a relatively low number of installations, underlying the importance of considering the thermal influence and the usefulness of our proposed model. Finally, a sensitivity study on the ground thermal conductivity shows the importance of a correct estimation of this property for accurate simulation results., QC 20210929

Given the need for decarbonization of the heating sector and the acute need of a propane replacement in the U.S. Upper Midwest, this study quantifies the techno-economic characteristics of sustainable heating electrification in isolated rural, residential buildings in cold climates without natural gas supply. Archetypal buildings are modeled under four levels of electrification. At each electrification level, a parametric solar photovoltaic (PV) sizing analysis is performed and the total life cycle cost, renewable fraction and greenhouse gas (GHG) emissions are calculated based on the primary energy supply for each building type. Cost optimal solutions are stress-tested with multi-dimensional sensitivity analyses. The results show that the total life cycle cost favors heating electrification in all cases and combining PV with heat pumps can reduce residential building GHG emissions by up to 50% immediately. This effect will grow over time, with over 90% reduction of building emissions if renewable energy targets are met. In using primary energy and emissions along with the multi-dimensional sensitivities, this study unique demonstrates the complex techno-economic interactions of PV and heat pumps. It is concluded that electrification is an economically viable decarbonization method for cold climates both now and in the future., QC 20211004

Part of proceedings: ISBN 9788794094016, QC 20230117

This study provides a global warming impact analysis of environmentally friendly refrigerants used as replacements for R134a and R245fa. R290, R1234yf, R1234ze(E), R513A and R450A are considered as refrigerants to replace R134a in medium temperature applications. For R245fa, there are five alternative refrigerants, R1224yd(Z), R600, R1336mzz(Z), R1233zd(E) and R1234ze(Z), which are selected for high-temperature applications. The analysis is done considering the emission factors in Brazil, Sweden, Canada and Poland. In Sweden and Brazil, the total equivalent warming impact per heating capacity of R134a is higher than its alternative refrigerants in medium temperature application, although R134a exhibits a higher coefficient of performance than its alternatives. In high-temperature applications, R1336mzz(Z) has the lowest total equivalent warming impact per heating capacity due to its higher coefficient of performance than other tested refrigerants. The highest total equivalent warming impact per heating capacity belongs to R245fa in all countries except in Poland, where R600 exhibits a higher value due to its lower coefficient of performance and the relatively higher emission factor in Poland compared to other selected countries. These results revealed that in addition to the global warming potential, the emission factor associated with the sources of electricity generation has a crucial impact on indirect emissions., QC 20210830

With the increasing amount of building renovations in Austria, the potential increases for replacing conventional national gas heating systems with heat pumps (HP) and thereby reduce CO2 emissions particularly when combined with solar photovoltaics (PV). The Austrian subsidization scheme for HP and PV systems are different for every state, creating confusion and inconstancy for potential adopters. This study provides a parametric technoeconomic analysis of PV + HP systems to identify the critical economic parameters on profitability and make policy recommendations. A case study in Vienna is modelled using demand from the Building Model Generator and black box efficiency models for the HP and PV simulated with hourly time steps. The results show that both air-source and ground source heat pumps are currently profitable with PV under current subsidy schemes. The benefit-to-cost ratio (BCR) is highly influenced by capital costs and subsidies, however natural gas prices have the greatest influence. Increasing natural gas prices by 0.01 euro/kWh, or 17%, is enough to replace all other complicated subsidies for both HP and PV. This is equivalent to a carbon emissions price of 33 euro/ton and could result in a reduction of CO2 emissions in multi-family houses by approximately 45%-60%., QC 20210818

The energy demand for tap water heating is significant in the developed world and significant to buildings energy performance. However, little attention is given to this untapped potential of heat recovery from wastewater. The purpose of this investigation is to investigate performance of different wastewater heat recovery systems to obtain more knowledge on how these systems perform in reality. Four systems were investigated showing that the annual heat recovery ratios between 17 and 43% and annual heat recovery per heat transfer areas between 1586 and 13 108 kWh/m(2). The paper also proposes a design equation with a validated accuracy of +/- 15% for sizing horizontal wastewater heat exchangers in wastewater heat recovery systems., QC 20210812

This paper aims to numerically investigate the thermal enhancement of a latent thermal energy storage component with mini-channels as air passages. The investigated channels in two sizes of internal air passages (channel-1 with d(h) = 1.6 mm and channel-2 with d(h) = 2.3 mm) are oriented vertically in a cuboid of 0.15 x 0.15 x 0.1 m(3) with RT22 as the PCM located in the shell. The phase change is simulated with a fixed inlet temperature of air, using ANSYS Fluent 19.5, with a varying number of channels and a ranging air flow rate entering the component. The results show that the phase change power of the LTES improves with by increasing the number of channels at the cost of a decrease in the storage capacity. Given a constant air flow rate, the increase in the heat transfer surface area of the increased number of channels dominates the heat transfer coefficient, thus increasing the mean heat transfer rate (UA). A comparison of the channels shows that the thermal performance depends largely on the area to volume ratio of the channels. The channel type two (channel-2) with a slightly higher area to volume ratio has a slightly higher charging/discharging power, as compared to channel type one (channel-1), at a similar PCM packing factor. Adding fins to channel-2, doubling the surface area, improves the mean UA values by 15-31% for the studied cases. The variation in the total air flow rate from 7 to 24 L/s is found to have a considerable influence, reducing the melting time by 41-53% and increasing the mean UA values within melting by 19-52% for a packing factor range of 77.4-86.8%. With the increase in the air flow rate, channel type two is found to have considerably lower pressure drops than channel type one, which can be attributed to its higher internal hydraulic diameter, making it superior in terms of achieving a relatively similar charging/discharging power in exchange for significantly lower fan power. Such designs can further be optimized in terms of pressure, QC 20210726

Integrating latent heat thermal energy storage (LHTES) units into building heating systems has been increasinglyinvestigated as a heat load management technology. A conventional LHTES integration method for heat pumpbased heating systems is to connect the heat pump’s condenser for charging the LHTES unit. This integratinglayout however usually leads to increased electricity input to the heating system. To underline this issue andprovide solutions, this paper presents three new LHTES integrating layouts where the LHTES unit is connectedwith the de-superheater of the main heat pump (Case 2), the condenser of a cascaded booster heat pump cycle(Case 3), or a combination of using both the de-superheater and the booster cycle (Case 4). In the context of amulti-family house in Stockholm, a quasi-steady state heating system model was developed to evaluate the newintegrating layouts, which were benchmarked against the baseline heating system without storage (Case 0) andthe conventional integrating layout using the main heat pump condenser (Case 1). Hourly electric power input tothe heating system was modelled for calculating the performance indicators including the heating performancefactor, the operational expense and justifiable capital expense, and the indirect CO2 emissions. Two load shiftingstrategies were simulated for an evaluation period of Week 1, 2019: 1) charge during off-peak hours (8 pm to 6am) and 2) charge during daytime hours (10 am to 7 pm). The simulation results of the off-peak charging strategyshow that, in Cases 2–4, the heating performance factor is 22%-26% higher than Case 1 and the operational expense can be reduced by 2%-5% as compared with Case 0. The savings in the operational expense can justifythe capital expense of 11 k-25 k Swedish Krona (SEK) for the LHTES systems in Cases 2–4 assuming a 15-yearoperation. Furthermore, the advantage of using the daytime charging strategy is principally the mitigation of CO2 emissions, which is up to 14% lower t, QC 20210521

This study aims to characterize experimentally the heat transfer in micro-milled multi-microchannels copper heat sinks operating with flow boiling, in the attempt to contribute to the development of novel and high heat flux thermal management systems for power electronics. The working fluid was R-134a and the investigation was conducted for a nominal outlet saturation temperature of 30 degrees C. The microchannels were 1 cm long and covered a square footprint area of 1 cm(2). Boiling curves starting at low vapor quality and average heat transfer coefficients were obtained for nominal channel mass fluxes from 250 kg/m(2)s to 1100 kg/m(2)s. The measurements were conducted by gradually increasing the power dissipation over a serpentine heater soldered at the bottom of the multi-microchannels, until a maximum heater temperature of 150 degrees C was reached. Infrared thermography was used for the heater temperature measurements, while high-speed imaging through a transparent top cover provided visual access over the entire length of the channels. The average heat transfer coefficient increased with the dissipated heat flux until a decrease dependent on hydrodynamic effects occurred, possibly due to incomplete wall wetting. Depending on the channel geometry, a peak value of 200 kW/m(2)K for the footprint heat transfer coefficient and a maximum dissipation of 620 W/cm(2) at the footprint with a limit temperature of 150 degrees C could be obtained, showing the suitability of the investigated geometries in high heat flux cooling of power electronics. The experimental dataset was used to assess the prediction capability of selected literature correlations. The prediction method by Bertsch et al. gave the best agreement with a mean absolute percent error of 24.5%, resulting to be a good design tool for flow boiling in high aspect ratio multi-microchannels as considered in this study., QC 20210401

What commonalities are there in sustainable or unsustainable heating practices in five high-income, high-emitting western European countries? What preferences do a nationally representative sample of the public in these countries hold towards low-carbon options? It is imperative that climate policy researchers and practitioners grapple with the difficulty of decarbonizing heat, which remains the largest single end-use service worldwide and which accounts about half of total final energy consumption. Based on a comparative assessment of five representative national surveys in Germany (N = 2009), Italy (N = 2039), Spain (N = 2038), Sweden (N = 2023), and the United Kingdom (N = 2000), this study explores the demographics and geography of household heat decarbonisation in Europe. By analyzing our country level data as well as our combined sample of 10,109 respondents, it investigates how people conceive of the purposes of low-carbon heat, their preferences for particular forms of heat supply, and their (at times odd) practices of heat consumption and temperature settings. Grounded in its original data, the study organizes its findings inductively across the five themes of literacy (heating knowledge, awareness and control), sustainability (heating practices, dynamics and conflicts), temperature (heating satisfaction and preferences), desirability of change (low-carbon heating priorities, business models and trust), and culture (country and national variation). The study also explores intersections between these dimensions, using multivariate analysis, as well as how preferences differ according to varying types of actors as well as geography and space., QC 20210329

Solar photovoltaic (PV) technology is now a profitable method to decarbonize the grid, but if catastrophic climate change is to be avoided, emissions from transportation and heating must also decarbonize. One approach to renewable heating is leveraging improvements in PV with heat pumps (HPs). To determine the potential for PV+HP systems in northern areas of North America, this study performs numerical simulations and economic analysis using the same loads and climate, but with local electricity and natural gas rates for Sault Ste. Marie, in both Canada and U.S. Ground-mounted, fixed-tilt, grid-tied PV systems are sized to match 100% of electric loads considering cases both with and without air source HPs for residences with natural gas-based heating. For the first time the results show North American residents can profitably install residential PV+HP systems, earning up to 1.9% return in the U.S. and 2.7% in Canada, to provide for all of their electric and heating needs. Returns on PV-only systems are higher, up to 4.3%; however, the PV capacities are less than half. These results suggest northern homeowners have a clear and simple method to reduce their greenhouse gas emissions by making an investment that offers a higher internal rate of return than savings accounts, CDs and GICs in both countries. Residential PV and solar-powered heat pumps can be considered 25-year investments in financial security and environmental sustainability., QC 20210331

Industry and other sectors are currently looking for solutions to decarbonize their processes, including heating, which is mainly based on fossil fuel boilers. Heat pumps can provide heating with higher performance based on their high coefficient of performance (COP). This work considers a multilevel heat pump (MTHP) for multi-source heating, based on a three-stage cascade in which excess heat in the condenser is used for external flows, that can be connected in series or parallel. Several available low GWP refrigerants have been considered, and a multi-parameter selection analysis has been carried out. For low, medium, and high-temperature stages, R1243zf, R-1224yd(Z), and R-1233zd(E) are the best refrigerants, respectively, selected. This system is able to operate between 0 and 160 degrees C, with three heating levels at 60, 110, 160 degrees C (31.75, 21.59, and 29.92 kW, respectively) at a COP of 2.181. The total cooling capacity of the system is 45.08 kW and the total heating capacity is 83.26 kW. The MTHP concept can provide a significant carbon footprint reduction compared to natural gas boilers used in European countries., QC 20221003Part of proceedings: ISBN 978-2-36215-048-7

This paper presents the comfort platform created within a research project carried out at KTH Live-In Lab in Stockholm, Sweden. The KTH Live-In Lab is a platform of buildings to test and promote innovation into the built environment. The Live-In Lab includes several buildings with state-of-the-art and expandable sensor infrastructure. The comfort platform has been created to manage user feedbacks in buildings. The comfort platform includes a user-friendly web application and a cost-efficient sensor device that allow to exchange feedbacks with the building users. The comfort platform is proposed as a possible solution to bridge the gap between modern smart buildings and existing buildings with limited sensor capability. This paper describes the comfort platform and the environment where it has been tested. The paper also summarizes the preliminary findings and the potential large-scale implementation., QC 20240925

Latent heat thermal energy storage has been receiving increasing interests in residential heating applications. In this paper, a numerical heat transfer model was built with finite element method for a cylindrically encapsulated latent heat storage prototype and used for investigating its thermal performance optimization measures. The model was validated against four sets of experimental results for both charge and discharge, as the difference in accumulated storage capacity between simulation and experiment is less than 4%. Transient storage inlet boundary conditions were set in simulation for discharge considering the thermal output from the coupled radiators. The results of the optimization analyses show that: 1) reducing the capsule diameter from 69 mm to 15 mm shortens the completion time of charge and discharge by up to 70%, however, at the expense of 23% decrease in total storage capacity; 2) using parabolic or linear time-increasing heat transfer fluid flowrate profiles than a time-constant one extends around twofold the useful discharge timespan; 3) increasing the storage vessel diameter from 0.6 m to 0.7 m and to 0.8 m prolongs the useful discharge timespan from 2 hrs to the recommended 3 hrs, though the further enlargement to 0.8 m results in a lower state of charge after 3 hrs due to increase in unexploited storage capacity. From the numerical optimization study, we proposed a storage design adjustment of using 15 mm-diameter phase change material capsules in a 0.7 m-diameter cylindrical storage vessel, coupled with a parabolic flow strategy, to improve the storage on-peak discharging performance., QC 20200818