Low-energy resilient cooling through geothermal heat dissipation and latent heat storage

Conventional passive cooling techniques provide limited benefits in extremely hot climates in southern Asia, characterised by high daytime and night temperatures and frequent climate-related disruptions, such as power cuts. This study proposes and demonstrates a novel low-energy and resilient cooling solution for extremely hot regions in southern Asia. The novelty lies in the combination of geothermal heat dissipation and latent heat storage, specifically designed for the particular conditions of extremely hot climates in Southern Asia; considering the influence of climate-related disruptions such as power cuts, whose frequency is increasing in the region; and using discomfort hours as an indicator to measure the passive survivability of buildings in the absence of air-conditioning (following the adaptive comfort model). A numerical model was developed in TRNSYS for optimal sizing and configuration of the phase change material (PCM) integrated into a ceiling panel using a typical multi-family building archetype in three climatic regions of Pakistan. A parametric numerical analysis was performed concerning different PCM melting temperatures, amount of PCM, convective heat transfer capacity, and equivalent thermal conductivity. Moreover, daytime was considered the period with a higher probability of power cuts. The results showed how integrating PCM-based ceiling panels with geothermal heat dissipation can mitigate discomfort hours by 28 % in extremely hot climates, 55 % in very hot climates, and 91 % in hot climate areas with intermittent access to electricity. Latent heat storage maximised the benefits of geothermal heat dissipation by extending thermal comfort periods by 13 % and 18 % in extremely hot and very hot climates compared to the scenario without PCM. This low-energy resilient cooling solution, integrating PCM as a cool battery, can keep the home cool for longer when electricity is unavailable. This study demonstrates the importance of considering the specific climate-related disruptions from these extremely hot regions in building design, such as extreme heat events or power cuts, to enhance the heat resilience capacity of cities

Solar-driven absorption cooling system with latent heat storage for extremely hot climates

Novel renewable cooling systems are required worldwide to address the growing demand for cooling. This study proposes and demonstrates a novel integration of solar-driven absorption cooling with latent heat storage to maximise the use of renewable energy for cooling in extremely hot climates. A parametric analysis was performed in TRNSYS to identify the critical parameters for optimal sizing related to the solar field size, tank volume, tank insulation, auxiliary heating set point, and collector tilt angle. Moreover, the integration was compared with a conventional solar-driven absorption cooling system using sensible heat storage (a hot water tank) and an electric-driven vapour compression cooling system. The results show that a solar field size of 1.5 m2/kWc, a latent heat storage tank volume of 30 L/m2, adequate insulation below 0.8 W/m2.K, and appropriate set-point temperatures for the auxiliary boiler provide the optimal performance to maximise the solar fraction. Compared with conventional solar-driven absorption cooling, the study demonstrates how the phase change material (PCM) increased the solar fraction by 4.2 % (from 70.3 to 74.5 %) due to higher stable temperature and lower tank losses (reduced by 44 %). In addition, despite the higher initial investment cost of the proposed PCM-based solar-driven cooling system compared to the vapour compression cooling system, the findings highlight that the life cycle cost is much lower in extremely hot climates. After 25 years, the life cycle cost was lowered by 34 % compared to vapour compression and by 9 % compared to a conventional solar-driven cooling system. Compared to vapour compression refrigerant technology, the proposed system can save 31.6 % of primary energy and 1222 kgCO2eq annually. This research provides valuable insights into the optimal design and integration of renewable cooling for residential applications in extremely hot regions

Resilient cooling pathway for extremely hot climates in southern Asia

Global warming is increasing extreme heat conditions, with existing energy efficiency policies showing trade-offs between mitigation objectives and adaptation to climate change. This research aims to identify the best resilient cooling solutions that should be promoted in the built environment of extremely hot countries to increase their heat resilience capacity. The impact of climate change on climate zones, cooling thermal demand (kWh/m2), and indoor heat discomfort hours (DHh, hours) in buildings is evaluated in different extremely hot dry climates of southern Asia through a parametric analysis for 2020, 2050 and 2080 under the A2 (medium–high) emission scenario. Then, cooling alternatives with higher synergies and trade-offs between energy efficiency (energy consumption) and resiliency to extreme heat (passive survivability) are highlighted. TRNSYS simulation software and ASHRAE criteria were used to characterise climate zones and calculate buildings' cooling needs and discomfort hours. Pakistan, in southern Asia, was selected as a hot reference region characterised by various climatic regions. The simulated scenario shows how Pakistan's extremely hot dry climate surface may increase from 36.9 % to 78.1 % by 2080, increasing annual cooling needs ranging from 20.56 to 66.96 kWh/m2 and indoor discomfort hours ranging from 423 to 1267 h. The results demonstrate how the passive solutions with higher synergies between energy savings and indoor comfort hours are, in decreasing order, ventilative cooling, reflective and ventilated roofs, shading in windows, and roof insulation. They can provide energy savings ranging from 13.1 to 7.1 kWh/m2 while reducing indoor discomfort by 320 to 131 h for extremely hot climates. Moreover, the sufficiency action related to higher thermostat settings, from 24 to 25 °C to 25–26.5 °C, was the most effective strategy to decrease energy demand. Additionally, there are trade-offs between energy-saving and heat resilience with highly insulated alternatives when ventilation is not adequately addressed. Despite increasing energy savings by 14.4 kWh/m2, discomfort hours are increased by 256 hours when air conditioning is unavailable, increasing building overheating by 5.1 %

Energy flexible building through smart demand-side management and latent heat storage

One of the greatest challenges for long-term emissions reduction is the decarbonisation of heating and cooling due to the large scale, seasonal variation and distributed nature. Energy flexible buildings with electric heating, smart demand-side management and efficient thermal energy storage are one of the most promising strategies to deploy low-carbon technologies which can benefit the electricity system by reducing the need of reinforcing existing networks and their ability to use electricity in times of low demand and high supply. Combined with spot price contracts, in which the electricity tariff changes every half-hour depending on supply and demand, they can effectively reduce on-peak demand periods, achieve economic profits for end-users and retailers, and reduce the environmental impact of the electricity grid by operating in periods with lower CO2 emissions rate. To achieve these benefits, it is crucial to develop accurate models for energy flexible buildings as well as control strategies to optimise the complex system operation. This paper proposes a novel flexible energy building concept, based on smart control, high density latent heat storage and smart grids, able to predict the best operational strategy according to the environmental conditions, economic rates and expected occupancy patterns. The smart integration model, carried out in TRNSYS for a Scottish case study, solves a multi-criteria assessment based on future energy demand prediction (learning machine model supported by end-user’s predefined occupancy by Internet of Things, present and forecast weather data, and building load monitoring), electricity tariff evolution and building performance. The results show that end-user’s electricity bill savings of 20% are obtained and retailer’s associated electricity cost is reduced by 25%. In addition, despite an increase in final energy consumption of up to 8%, the environmental impact remains constant due to operation at times with lower CO2 emissions rate in electricity generation. The developed tools enable the design of smart energy systems for energy flexible buildings which can have a large positive impact on the building sector decarbonisation

Sodium acetate-based thermochemical energy storage with low charging temperature and enhanced power density

The electrification of heat necessitates the development of innovative domestic heat batteries to effectively balance energy demand with renewable power supply. Thermochemical heat storage systems show great promise in supporting the electrification of heating, thanks to their high thermal energy storage density and minimal thermal losses. Among these systems, salt hydrate-based thermochemical systems are particularly appealing. However, they do suffer from slow hydration kinetics in the presence of steam, which limits the achievable power density. Additionally, their relatively high dehydration temperature hinders their application in supporting heating systems. Furthermore, there are still challenges regarding the appropriate thermodynamic, physical, kinetic, chemical, and economic requirements for implementing these systems in heating applications. This study analyzes a proposal for thermochemical energy storage based on the direct hydration of sodium acetate with liquid water. The proposed scheme satisfies numerous requirements for heating applications. By directly adding liquid water to the salt, an unprecedented power density of 5.96 W/g is achieved, nearly two orders of magnitude higher than previously reported for other salt-based systems that utilize steam. Albeit the reactivity drops as a consequence of deliquescence and particle aggregation, it has been shown that this deactivation can be effectively mitigated by incorporating 10 % silica, achieving lower but stable energy and power density values. Furthermore, unlike other salts studied previously, sodium acetate can be fully dehydrated at temperatures within the ideal range for electrified heating systems such as heat pumps (40 °C – 60 °C). The performance of the proposed scheme in terms of dehydration, hydration, and multicyclic behavior is determined through experimental analysis

Change in cooling degree days with global mean temperature rise increasing from 1.5 °C to 2.0 °C

Limiting global mean temperature rise to 1.5 °C is increasingly out of reach. Here we show the impact on global cooling demand in moving from 1.5 °C to 2.0 °C of global warming. African countries have the highest increase in cooling requirements. Switzerland, the United Kingdom and Norway (traditionally unprepared for heat) will sufer the largest relative cooling demand surges. Immediate and unprecedented adaptation interventions are required worldwide to be prepared for a hotter world

Mobility patterns of scholar communities in Southwestern European countries

The present study aimed to provide an in-depth assessment of the commuting patterns of scholar communities of southwestern European countries and to identify measures to improve their sustainable performance regarding mobility. The adopted methodology characterized the mobility pattern of students as a sustainability indicator and the availability of related infrastructures and local public transport networks. Data were gathered by qualitative (behavioral questionnaires) and quantitative (technical audits) approaches, based on measurable indicators (key performance indicators and scores (ranging between 0–5)). Overall, French schools showed the best sustainable performance regarding mobility (2.0) and Gibraltar had the lowest (1.2). The existence of bike parking and electric car charging points were the main weaknesses founds (with their related mean scores being 0.6 and 0.2, respectively). The score associated with annual CO2 emissions due to students’ mobility had the best performance, where all countries managed to obtain an average of 3.1. The global score, which assessed the sustainable performance of scholar communities regarding mobility, had a mean value of 1.5 for all studied countries, which highlights the potential for improvement of the studied schools, mainly targeting the public transport network optimization and the enhancement of scholar infrastructures concerning bicycle parking and electric cars.This research was funded by the Interreg SUDOE funding program of the European Regional Development Fund, through ClimACT Project (SOE1/P3/P0429). J. Lage acknowledges the support of the FCT—Fundação para a Ciência e Tecnologia, I.P. (Portugal) for the contract CEEC-IND/02366/2020 and N. Canha also acknowledges the support of FCT, through the contract 2021.00088.CEECIND. The FCT support is also gratefully acknowledged by C2TN/IST authors (UIDB/04349/2020 + UIDP/04349/2020) and by CESAM author (UIDB/50017/2020+UIDP/50017/2020). The authors also acknowledge the support of H2020 Project ECF4CLIM (Grant agreement ID: 101036505).info:eu-repo/semantics/publishedVersio

A national data-based energy modelling to identify optimal heat storage capacity to support heating electrification

Heating decarbonisation through electrification is a difficult challenge due to the considerable increase in peak power demand. This research proposes a novel modelling approach that utilises easily accessible national-level data to identify the required heat storage volume in buildings to decrease peak power demand and maximises carbon reductions associated with electrified heating technologies through smart demand-side response. The approach assesses the optimal shifting of heat pump operation to meet thermal heating demand according to different heat storage capacities in buildings, which are defined in relation to the time (in hours) in which the heating demand can be provided directly from the heat battery, without heat pump operation. Ten scenarios (S) are analysed: two baselines (S1–S2) and eight load shifting strategies (S3–S10) based on hourly and daily demand-side responses. Moreover, they are compared with a reference scenario (S0), with heating currently based on fossil fuels. The approach was demonstrated in two different regions, Spain and the United Kingdom. The optimal heat storage capacity was found on the order of 12 and 24 h of heating demand in both countries, reducing additional power capacity by 30–37% and 40–46%, respectively. However, the environmental benefits of heat storage alternatives were similar to the baseline scenario due to higher energy consumption and marginal power generation based on fossil fuels. It was also found that load shifting capability below 4 h presents limited benefits, reducing additional power capacity by 10% at the national scale. The results highlight the importance of integrated heat storage technologies with the electrification of heat in highly gas-dependent regions. They can mitigate the need for an additional fossil-based dispatchable generation to meet high peak demand. The modelling approach provides a high-level strategy with regional specificity that, due to common datasets, can be easily replicated globally. For reproducibility, the code base and datasets are found on GitHub

Overcoming the incumbency and barriers to sustainable cooling

This article examines cooling in the built environment, an area of rapidly rising energy demand and greenhouse gas emissions. Specifically, the status quo of cooling is assessed and proposals are made for how to advance towards sustainable cooling through five levers of change: social interactions, technology innovations, business models, governance and infrastructure design. Achieving sustainable cooling requires navigating the opportunities and barriers presented by the incumbent technology that currently dominates the way in which cooling is provided—the vapour-compression refrigerant technology (or air-conditioners). Air-conditioners remain the go-to solution for growing cooling demand, with other alternatives often overlooked. This incumbent technology has contributed to five barriers hindering the transition to sustainable cooling: (1) building policies based exclusively on energy efficiency; (2) a focus on temperature rather than other thermal comfort variables; (3) building-centric design of cooling systems instead of occupant-centric design; (4) businesses guided by product-only sales; and (5) lack of innovation beyond the standard operational phase of the incumbent technology. Opportunities and priority actions are identified for policymakers, cooling professionals, technicians and citizens to promote a transition towards sustainable cooling. Policy relevance The priority actions that can overcome key barriers to a sustainable cooling pathway are as follows. (1) Moving building policies beyond energy efficiency to address climate mitigation and adaptation for improving the heat resilience of the built environment. Building indicators are needed to measure the passive survivability to heat. (2) Conventional cooling control and related regulations based exclusively on air temperature require expansion in scope to consider a wider range of thermal comfort variables, thus stimulating technological innovation. (3) Shifting building-centric cooling control to an occupant-centric design, downsizing centralised cooling requirements and enabling adaptive environments integrating personalised environmental control systems. (4) Business models moving from product-oriented to service-based businesses. (5) Environmental cooling considerations that address the humidity influence, the role of energy storage to support renewables through energy flexibility in cooling, and the impact of F-gases. Regulation and citizen empowerment through better environmental labelling can play an important role

Integration of solar latent heat storage towards optimal small-scale combined heat and power generation by Organic Rankine Cycle

Thermal energy and distributed electricity demand are continuously increased in areas poorly served by a centralized power grid. In many cases, the deployment of the electricity grid is not economically feasible. Small-scale Organic Rankine Cycle (ORC) appears as a promising technology that can be operated by solar energy, providing combined heat and power (CHP) generation. Additionally, thermal energy storage can ensure stable and continuous operation in case of scarce thermal energy availability. This paper evaluates the potential application of latent heat storage to enhance solar ORC performance at operating temperatures between 80 °C and 140 °C, aiming at improving the efficiency and capacity of ORC for low-cost non-concentrating solar-thermal collectors. Three thermal energy storage scenarios are considered. Scenario 1 and 2 consist of reference cases based on a solar ORC system integrated with a conventional hot water tank and a pressurised water tank. Scenario 3 implements a storage unit based on a phase change material. The simulation was carried out through models developed in TRNSYS for solar energy balance and ASPEN for ORC system performance. The results show that solar latent heat storage tank can provide 54% of useful collector gains with a higher and narrower temperature range in the evaporator, increasing the annual thermal energy capacity by 19%, reducing annual heat losses by 66% and decreasing the investment cost by 50% in comparison with a pressurised water tank. It also allows increasing the efficiency of ORC cycle by approximately 18% (from 8.9% to 10.5%) with a higher net generated power than a conventional water tank integration, scaled up from 498 W to 1628 W. These results highlight the potential benefits that latent heat integration provides to improve the low-cost solar ORC performance for powering electricity and thermal energy supply