The research work presented applies a novel model to simulate and understand options for how an existing gas-supplied district heating network (EGS-DHN) for Holywell Park, Loughborough University (Loughborough, UK) could be transitioned to an ultra low-carbon district heating network (ULC-DHN). The ULC-DHN includes heat pumps (HPs) (powered by low carbon electricity from a range of sources) and evacuated-tube solar thermal collectors (ETSTCs), to both provide heat directly to buildings and to charge a potential seasonal thermal energy storage (STES) system. Three different configurations for the ULC-DHN are modelled, each corresponding to different electricity sources used to provide power to the HPs: zero-carbon grid electricity, on-site solar photovoltaic (PV) generated electricity and on-site wind generated electricity. For each Configuration the effect of a) the maximum amount of zero-carbon electricity used by the HPs to meet heat demands and/or to charge the STES, b) the area of ETSTC (AETSTC) and c) the volume of STES (VSTES) on the levelized cost of heat (LCOH) is predicted for the next 23 years. The predictions show that due to the high capacity factor of wind turbines in the UK, using on-site wind generated electricity to power HPs leads to the lowest LCOH value (3.33 p/kWh). Using on-site PV generated electricity to power HPs results in a similar minimum LCOH value to that obtained when using zero-carbon grid electricity. The predicted minimum cost break-even time, obtained when comparing the annual cumulative cost for the EGS-DHN and the ULC-DHN, is 5 years.

When discharging latent heat thermal energy storage (LHTES) systems, performance is influenced by the formation and adherence of a solid layer of phase change material (PCM) on heat eXchange (HX) surfaces. Super-liquid-repellent thin films (STFs) may be able to reduce solidifying PCM adhesion on HX surfaces during discharging, delay PCM solidification to lower temperatures, and by modifying nucleation sites potentially enable long-term seasonal thermal storage. Techniques employed previously to fabricate sintered polymeric STF coatings include chemical vapour deposition, dip-coating, spray-coating, spin-coating, layer-by-layer (LbL) assembly, sol-gel, anodizing, electrodeposition, electrospinning, so on. Dip-coating is considered attractive for fabricating thin films on simple and complex surface geometries due to process maturity, scalability, flexibility and cost-effectiveness. To identify suitable materials for preparing STFs on metal HX surfaces using the dip-coating process, more than 200 journal articles published in English during the period 2010 to 2022 were reviewed and the potential role of STFs in LHTES applications was assessed. The review identified key areas and applications stimulating STF material developments and formulations. The dip-coating of potential STF materials was classified under three major themes driving current research and development (R&D) activities, that is, high performance thin films, eco-friendly thin films and fundamental research formulations. This review provides a platform from which to develop coatings and HX systems to enable the cost-effective implementation of STFs for improved heat transfer in future mobile/stationery LHTES systems.

Medium and long-duration energy storage systems are expected to play a critical role in the transition towards electrical grids powered by renewable energy sources. ACAES is a promising solution, capable of handling power and energy ratings over hundreds of MW and MWh, respectively. One challenge with ACAES is achieving the required highly efficient operation in the compressor over the range of conditions encountered in the system as the pressure in the air store changes. In this paper, an application-oriented axial-flow compressor is designed, aiming towards efficient operation throughout the operation range, whilst also associating the performance prediction to a practical compressor geometry. A two-step design methodology based on inviscid, axisymmetric flow conditions has been implemented, leading to the flowtrack, blade-row geometries and the compressor performance map. The compressor model is integrated into an ACAES model, including two compression spools, two expansion stages with preheat, a constant volume high pressure storage operating between 5.5 and 7.7 MPa and two separate Thermal Energy Storage units. While the existing ACAES literature either ignores the transient off-design operation or uses generic numerical correlations (which are not associated to a particular geometry), the key novelty of this paper is the application of a detailed design method for turbomachinery to ACAES. The results indicate that the designed compressor requires 33 stages over the two spools, and is able to operate efficiently over the storage pressure range, showing that if the application-oriented design procedure is applied to the compressor, it does not stop ACAES reaching 70% round-trip efficiency, outputting 35MW for approximately 15 h. Importantly, the specific ACAES requirement of conserving heat at higher temperatures has been fulfilled by decreasing the number of intercoolers. Finally, it is recommended that a similar level of scrutiny is applied to the other components (i.e. expanders, heat exchangers and TES units), keeping in mind the unique set of operational requirements of ACAES. This work is an important step towards removing the common misconception that off-the-shelf components can be easily be used in typical ACAES designs.

A model was used to simulate and optimise a speculative district heating (DH) system for an existing urban area in Loughborough, UK. Heat was supplied using only renewable heat sources (RHS) with long and short duration thermal energy storage (TES) systems used to address mismatch between heat generation and demand. For an 18month simulation period, a) building heat loads, b) heat generated, c) heat flow to and from stores, and d), heat losses from the stores and network were calculated using hourly weather data, network and building characteristics. RHS included evacuated-tube solar thermal collectors (ETSTCs), and ground and air source heat pumps powered by electricity generated by solar-photovoltaic (PV) and Wind turbines (Wind). The effect of long-term TES system volume and charging temperature on the calculated DH system cost per dwelling, and the calculated DH system energy efficiency was assessed. The minimum cost of the DH system was obtained by modifying the capacity of installed Wind and PV, while ensuring that heat demands were met in every hour of the simulation. A minimum cost per dwelling of 12,278 pound was predicted with an energy efficiency of 84.84 % for a long term TES volume of 15,000 m3 and temperature of 60 degrees C.

An experimental study was undertaken to evaluate the thermal performance of a novel compact latent heat thermal energy storage (LH-TES) system. The heat exchanger immersed in the phase change material (PCM) CrodaTherm (TM) 53, enclosed in a cuboid shaped metal container was a Multi-Plate Heat Exchanger (MPHX). The heat exchanger in the thermal store was comprised of ten individual aluminium rectangular plates mounted vertically spaced at 30 mm intervals. The heat exchanger plates were connected in a parallel flow arrangement with two manifolds used to divide the flow equally between plates. During the charging process, a peak thermal input power of 4.2 kW was measured for an Heat Transfer Fluid (HTF) inlet temperature of 70 degrees C. To characterize the effect of HTF flow rate on the discharging process, experiments were performed with HTF an inlet temperature of 30 degrees C with volume flow rates of 2, 3, 4, 5 and 6 L/min. Temperatures within the store at different locations were measured and instantaneous heat output rates and cumulative heat output calculated. Based on the experimental results by adjusting the HTF inlet volume flow rate during the discharging process, the output thermal power and temperature can be controlled for domestic space and water heating applications.

When discharging latent heat thermal energy storage (LHTES) systems, performance is influenced by the formation and adherence of a solid layer of phase change material (PCM) on heat eXchange (HX) surfaces. Super‐liquid‐repellent thin films (STFs) may be able to reduce solidifying PCM adhesion on HX surfaces during discharging, delay PCM solidification to lower temperatures, and by modifying nucleation sites potentially enable long‐term seasonal thermal storage. Techniques employed previously to fabricate sintered polymeric STF coatings include chemical vapour deposition, dip‐coating, spray‐coating, spin‐coating, layer‐by‐layer (LbL) assembly, sol‐gel, anodizing, electrodeposition, electrospinning, so on. Dip‐coating is considered attractive for fabricating thin films on simple and complex surface geometries due to process maturity, scalability, flexibility and cost‐effectiveness. To identify suitable materials for preparing STFs on metal HX surfaces using the dip‐coating process, more than 200 journal articles published in English during the period 2010 to 2022 were reviewed and the potential role of STFs in LHTES applications was assessed. The review identified key areas and applications stimulating STF material developments and formulations. The dip‐coating of potential STF materials was classified under three major themes driving current research and development (R&D) activities, that is, high performance thin films, eco‐friendly thin films and fundamental research formulations. This review provides a platform from which to develop coatings and HX systems to enable the cost‐effective implementation of STFs for improved heat transfer in future mobile/stationery LHTES systems.

One problem with utilising solar renewable energy sources, for domestic space heating and domestic hot water in the UK is the mismatch between energy supply and energy demand due to the seasonal variation. One way to mitigate this phenomenon is to utilise seasonal thermochemical heat storage. 13X molecular sieves have received recent attention as a thermochemical energy storage material for domestic use due to the heat stored when dehydrated and released when rehydrated. Minimal attention has been paid to the dehydration conditions and the impact this has on the heat release from dehydrated 13X. The reported study experimentally characterised the charge and discharge enthalpy of 13X molecular sieves using a custom designed novel Differential-Scanning-Calorimeter apparatus and Thermogravimetric-Analyser for mass loss investigations. This study shows how employing different thermal analysis testing methodologies can produce different results. The impact that the grade of nitrogen employed has on the mass change of the 13X samples, and the length of time exposed to the nitrogen purge as the charged sample cools, can have a dramatic impact on the mass of the 13X sample. When using a nitrogen generator or technical grade nitrogen as the purge gas in the cooling phase after a 500 degrees C dehydration, (charging), the mass of the 13X sample increased by 13 % and 17 %, respectively, this could potentially impact the later adsorption potential leading to reduced hydration and energy output on discharge. The hydration enthalpy (energy output) of 13X for varying charge (60-150 degrees C) and discharge (25-60 degrees C) temperatures, with a discharging partial vapour pressure (pH(2)O) of 0.64 kPa are also presented. This work provides reference values for the expected energy output from 13X for a range of charge and discharge temperatures, for example, showing that the energy output varies from 660-500 J/g with different discharge temperatures if the sensible heat is not utilised.

A novel model was used to simulate how an existing district heating (DH) network for Holywell Park, Loughborough University (Loughborough, UK) could be transitioned to low/zero carbon heat. A simulation which includes heat pumps (HPs) and evacuated-tube solar thermal collectors (ETSTCs) to both provide heat for buildings and charge a potential seasonal thermal energy storage (STES) system was performed. Both a) real historic half-hourly CO2 emissions per kWh of electricity and b) real historic half-hourly heat demands for Holywell Park for the year 2021 were used in the simulations. The model assumes that HPs can only be used to charge STES systems at those times when the CO2 emissions associated with grid electricity are zero. A parametric analysis was used to investigate the effect of a) the inclusion of STES in the DH system and b) when including the STES 1) the volume of STES system and 2) maximum amount of zero-emissions electricity available to charge STES (E-CO2 = 0,E- STES) on the levelised cost of heat (LCOH) for a 23 year simulation period.

A model to simulate district heating networks (DHN) was applied to a hypothetical DHN in Loughborough, UK. The model includes different thermal energy storage (TES) systems: i) short-term water-based stores and phasechange material-based stores and ii) a seasonal thermal energy storage (STES) system. Heat pumps (HP) and evacuated-tube solar thermal collectors (ETSTC) are considered to both provide heat for dwellings and charge the TES systems. The model assumes that the HPs can only be used to charge TES at those times when the electricity is produced by zero-carbon sources. To assess this real CO2 emissions data per kWh of electricity produced in UK was used. The effect of both 1) the STES volume and 2) the half-hourly maximum amount of zero-emissions electricity available to charge TES on a) cost, b) efficiency and c) CO2 emissions was studied. The results showed that CO2 emissions and electricity cost can be reduced to 83.4 % and 12.3 %, respectively, using TES, when comparing with the scenario with no TES. Savings of 41.7 % can be achieved when comparing the cost of electricity used in the proposed DHN with TES with the current cost of the gas.

A model was established that allows the simulation and analysis of the performance of a district heating (DH) system supplied with heat generated from renewable sources (RHS) and a selection of different types of thermal energy storage (TES) systems. The model uses hourly weather data, building specifications and occupancies to calculate i) hourly domestic heat demands for both space and domestic hot water heating and ii) hourly heat produced by RHS. The heat flow to and from sources to loads and TES systems is calculated on an hourly basis. The model calculates hourly heat losses from dwellings, TES and pipes, and takes into consideration recent research related to latent and thermochemical heat storage systems. The model developed enables the analysis of the effects of different district heating system operating parameters (including installed capacity and penetration of different RHS, thermal energy storage capacity, number and distribution of TES) on system cost and system energy efficiency. The ultimate goal of developing the model was the determination of a system specification and operating conditions that i) minimises cost and ii) maximises the overall energy efficiency of the network while ensuring that domestic heat demands are met on an hourly basis for a specified time-period in an existing or planned town or urban area.

The experimental thermal characterization during charging and discharging of a prototype compact latent heat thermal energy storage system (LHTESS) with an embedded horizontally oriented finned multi-tube copper heat exchanger is presented. The thermal store was filled with a commercial-grade, CrodaTherm (TM) 60, phase change material (PCM) with a nominal melting temperature of 60 degrees C. The proposed heat exchanger (HX) configuration mitigates the effect of low PCM thermal conductivity and increases the rates of heat transfer to and from the store during the charging and discharging processes compared to multi-tube copper HX without fins. The experimental testing regime assessed the impact of heat transfer fluid (HTF) volume flow rate and inlet temperature on I) transient PCM temperature distribution, II) the total charging/discharging time and III) instantaneous/average power during the charging and discharging processes. The experimental results showed that the HTF volume flow rate and inlet temperature play a significant role in the thermal performance of the LHTESS during the charging/discharging process. During the charging process, the influence of increasing HTF inlet temperature is greater than that due to increasing HTF volume flow rate. Moreover, it is shown that during the first 30 minutes of the discharging process, the average power output was 4.3, 5.1 and 5.3 kW for HTF volume flow rate of 2.5 and 7.2 and 10.5 l/min, respectively.

This briefing reviews progress that was made at the 26th United Nations Climate Change Conference of the Parties (COP26) held in Glasgow, Scotland, UK over 1–12 November 2021. The context of the global climate change challenge is outlined, along with the aspirations of the major participating international groups. An overall balance sheet is provided that gives an assessment of the achievements and disappointments in the outcomes of COP26. This assessment sets a backdrop to what needs to be achieved when the Parties next meet at COP27 in Sharm El-Sheikh, Egypt in 2022 to address both immediate and longer-term climate change mitigation, adaptation and climate finance.

The UK will need to decarbonise low temperature industrial waste heat (up to asymptotic to 250 degrees C) to achieve net-zero greenhouse gas emission targets. Industrial waste heat production represents an opportunity for reduction in the use of primary fuels used in the production of commodities. Energy inefficient processes in addition to increased emissions raises the cost of plant operation, - an undesirable scenario for both industrial competitiveness and the environment. Less is known about the quantity and potential applications for recovered low temperature industrial waste heat in UK and the quantification and characterisation of the resource can provide the needed impetus for the development and adoption of green technologies to help achieve the 2050 Net-Zero target. In this work the potential magnitude of the low temperature industrial waste heat resource in the UK is analysed by using sector-level energy intensity values for different industries while drawing on corresponding estimates from previous studies in the USA and by closely mapping the UK Standard Industrial Classification (SIC 2007) against sectors in the USA (NAICS [North American Industry Classification System]). The assessment undertaken finds that the recoverable potential of low temperature waste heat up to asymptotic to 250 degrees C could be up to 83.7% of the total estimated waste heat potential in UK industry. Significant opportunities exist in this low temperature range for waste heat recovery actions at individual sites. Research and Development (R & D) into alternative improved methods for waste heat recovery, storage, and use (WHRSU) technologies could also produce significant positive environmental and industrial impact.

Recent theoretical studies have predicted that adiabatic compressed air energy storage (ACAES) can be an effective energy storage option in the future. However, major experimental projects and commercial ventures have so far failed to yield any viable prototypes. Here we explore the underlying reasons behind this failure. By developing an analytical idealized model of a typical ACAES design, we derive a design-dependent efficiency limit for a system with hypothetical, perfect components. This previously overlooked limit, equal to 93.6% under continuous cycling for a typical design, arises from irreversibility associated with the transient pressure in the system. Although the exact value is design dependent, the methodology we present for finding the limit is applicable for a wide range of designs. Turning to real systems, the limit alone does not fully explain the failure of practical ACAES research. However, reviewing the available evidence alongside our analytical model, we reason that underestimation of the system complexity, difficulty with the integration of off-the-shelf components, and a number of misleading performance claims are the primary reasons hindering ACAES development.

Mobilized-Thermal Energy Storage (M-TES) systems, are an attractive alternative solution to supply heat to distributed heat users by recovering and transporting the low-temperature industrial waste heat (IWH) by vehicular means, have the potential to reduce both the CO2 emissions and costs of energy consumption and lead to more efficient industrial activities as well as improve the quantity of low-carbon energy consumed for heat generation in the residential sector. This paper provides a state-of-the-art review of Phase Change Materials (PCM) applied in M-TES systems. The concept of the M-TES system is briefly described and summarized, including available IWH sources, heating and cooling facilities (for distributed end users), and the main features of two different types of M-TES containers. Recent research achievements in the field have been reviewed, focusing on developed prototypes, experimental and numerical studies, and economic and environmental evaluations. Finally, the barriers to the application of M-TES and possible solutions are discussed. The review highlighted that direct-contact M-TES storage systems can have up to 60% shorter charging and discharging periods when compared to indirect-contact M-TES storage systems with similar storage capacities. Using heat transfer enhancement techniques such as graphite additives, the charging and discharging period for indirect-contact M-TES container can be shortened by up to 74% and 67%, respectively, and that the charging time of direct-contact M-TES can be reduced by up to 29%. The use of M-TES to provide heat can significantly decrease the primary energy requirement, exergy losses and the CO2 emissions by up to 95%, 60% and 93%, respectively, compared to conventional heating facilities using fossil fuels. Recommendations for future research are presented, providing insights of where the current research in the M-TES field is heading and highlights the key challenges that remain to be resolved.

With the increasing awareness of building energy efficiency, indoor environment quality for human wellbeing and working efficiency, efforts have intensified in to inventing intelligent building components. This paper provides a first step in developing a novel multi-effect smart window system, which achieves enhanced energy efficiency and an improved indoor luminous environment by integrating a Transparent Insulation Material (TIM) structure incorporating a Thermotropic material. This system automatically regulates the admittance of solar heat and natural light into the building by responding to a changing environment while taking advantage of the increased thermal resistance and scattered daylight of window integrated TIM. A comprehensive workflow via EnergyPlus and RADIANCE was used to accurately predict the luminous and energy performance of applying the smart window system on a typical south-facing office under selected climates (London, Stockholm, Rome and Singapore). The effect of the optical properties and transition temperature of thermotropic material on building performance was explored in detail. Annual simulation results predict that, with a careful selection of the Thermotropic material properties, installing the TT PS-TIM window system is able to yield up to a 27.1% energy saving when compared with a conventional double glazed window, under the modelled Rome climate. TT PSTIM windows also provide dynamic daylight control, resulting in increased daylight availability with the percentage of working hours that fall into the UDI500-2000 lx range increasing to 62.3%. The results of this research provide guidance for the next step of the material design and development that seek to balance energy efficiency and solar and daylight control through the use of thermotropic materials.

To improve the energy efficiency of an industrial process thermochemical energy storage (TCES) can be used to store excess or typically wasted thermal energy for utilisation later. Magnesium carbonate (MgCO3) has a turning temperature of 396 °C, a theoretical potential to store 1387 J/g and is low cost (~GBP 400/1000 kg). Research studies that assess MgCO3 for use as a medium temperature TCES material are lacking, and, given its theoretical potential, research to address this is required. Decomposition (charging) tests and carbonation (discharging) tests at a range of different temperatures and pressures, with selected different gases used during the decomposition tests, were conducted to gain a better understanding of the real potential of MgCO3 for medium temperature TCES. The thermal decomposition (charging) of MgCO3 has been investigated using thermal analysis techniques including simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), TGA with attached residual gas analyser (RGA) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (up to 650 °C). TGA, DSC and RGA data have been used to quantify the thermal decomposition enthalpy from each MgCO3.xH2O thermal decomposition step and separate the enthalpy from CO2 decomposition and H2O decomposition. Thermal analysis experiments were conducted at different temperatures and pressures (up to 40 bar) in a CO2 atmosphere to investigate the carbonation (discharging) and reversibility of the decarbonation–carbonation reactions for MgCO3. Experimental results have shown that MgCO3.xH2O has a three-step thermal decomposition, with a total decomposition enthalpy of ~1050 J/g under a nitrogen atmosphere. After normalisation the decomposition enthalpy due to CO2 loss equates to 1030–1054 J/g. A CO2 atmosphere is shown to change the thermal decomposition (charging) of MgCO3.xH2O, requiring a higher final temperature of ~630 °C to complete the decarbonation. The charging input power of MgCO3.xH2O was shown to vary from 4 to 8136 W/kg with different isothermal temperatures. The carbonation (discharging) of MgO was found to be problematic at pressures up to 40 bar in a pure CO2 atmosphere. The experimental results presented show MgCO3 has some characteristics that make it a candidate for thermochemical energy storage (high energy storage potential) and other characteristics that are problematic for its use (slow discharge) under the experimental test conditions. This study provides a comprehensive foundation for future research assessing the feasibility of using MgCO3 as a medium temperature TCES material. Future research to determine conditions that improve the carbonation (discharging) process of MgO is required.

Vacuum flat plate (VFP) solar thermal collectors exhibit excellent optical and thermal characteristics due to a combination of wide surface area and high vacuum thermal insulation offering a high performance and architecturally versatile collector with a variety of applications for industrial process heat and building integration. A vacuum flat plate solar collector consists of a solar absorber in a flat vacuum enclosure comprising glass or glass and metal covers sealed around the periphery with an array of support pillars to maintain the separation of the enclosure under atmospheric pressure. The edge seal must be both mechanically strong and hermetic to ensure the durability of the internal vacuum over collector lifetime. This presents several challenges for the fabrication of flat vacuum enclosures. In this study a novel sealing technique is presented using a tin-based alloy, Cerasolzer 217, to create the vacuum seal between two glass panes and an edge separating spacer. The sealing process is undertaken at temperatures <= 250 C allowing the use of thermally tempered glass panes. The mechanical strength of the edge seal was investigated using a tensometer. It was demonstrated that the bond between glass and edge spacer was sufficiently strong to withstand induced stresses in the edge seal region. The edge seal was leak tested using a conventional Helium mass spectrometer leak detector and was shown to possess leak rates low enough to maintain an adequate vacuum pressure to supress conductive and convective heat transfer in the collector. A finite element method (FEM) is developed and validated against the experimental results and employed to predict the stresses in different regions of the enclosure. It was found that the mechanical strength limits of the seal and glass are higher than the stresses in the edge seal region and on the glass surface, respectively.