4 research outputs found

    Phase-change materials, systems and applications for low- and medium-temperature thermal energy storage

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    Determining the ideal size of compact thermal energy storage containers has been an issue for many building designers due to the difficulty of determining the transient performance of the thermal storage systems. Research and development of compact thermal energy storage systems has been ongoing for more than 80 years with phase change materials (PCMs) used to replace conventional water based thermal stores. PCMs have the potential to store larger amounts of energy when compared to water-based thermal stores over a narrow temperature range, providing a greater thermal storage capacity for the same available volume. This research was undertaken to investigate theoretically and experimentally the thermal behaviour of various PCMs and the overall decarbonisation potential when integrated into current heating and cooling systems. The overall aim was to develop algorithms that could determine optimal and cost effective compact thermal storage geometries and their system integration into the various heating and cooling applications studied. Three operating temperatures were selected based on the application: office space cooling (10 to 24^\circC), residential domestic hot water and space heating (40 to 65^\circC) and district heating (55 to 80^\circC). The algorithms developed predict the energy performance and CO2CO_2 emissions reduction for each application with a latent heat thermal storage system compared to a reference (current system design) case in each application. Previous research has focused on the melting behaviour of the PCM within a specific geometry, modelling the heat transfer fluid (HTF) in a separate analysis. The algorithms developed focus on the modelling of these 2 elements simultaneously within the respective application. This provided a useful tool to evaluate the thermal performance of each storage technology compared to the reference case in each application studied. The levelized costs of energy (LCOE) in each application were compared. It was found that in all cases studied, the latent heat thermal energy storage system is an expensive solution, compared to the reference case in each application (72\% more expensive in the office space cooling study, 69\% more expensive in the domestic hot water and space heating study and 9\% more expensive in the district heating study); although the obtained emission reductions are considerable (36\% by shifting daily cooling loads, 57\% by shifting domestic hot water and space heating loads and 11\% by utilizing industrial waste heat via a compact portable thermal store). Further integration of renewable energy sources and the electrification of current heating and cooling applications with the possibility of shifting heating and cooling loads into periods with lower carbon emissions can significantly contribute to meet the UK s 80\% carbon emissions reduction targets by 2050

    Thermal energy storage for low and medium temperature applications using phase change materials – a review

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    A comprehensive review of phase change materials (PCMs) with phase transition temperatures between 0 and 250 °C is presented. From that review, organic compounds and salt hydrates seem more promising below 100 °C and eutectic mixtures from 100 to 250 °C. Practical indirect heat exchanger designs for latent heat storage systems were also assessed and feasible heat enhancement mechanisms reviewed. The focus on this temperature range is due to potential CO2 emissions reduction able to be achieved replacing conventional heating and cooling applications in the domestic, commercial and public administration sectors, which represented around a quarter of the UK’s final energy consumption in 2015

    Compact latent heat storage decarbonization potential for domestic hot water and space heating applications in the UK

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    A performance comparison is presented for a domestic space and hot water heating system with a conventional gas boiler and an air source heat pump (ASHP) with latent heat storage, both with solar thermal collectors for a typical UK climate, to demonstrate the potential of phase change material based energy storage in active heating applications. The latent heat thermal storage system consisted of 10 modules with RT54HC comprising a total storage capacity of 14.75kWh that provided 53% extra thermal storage capacity over the temperature range of 40 to 65°C compared to a water only store. The simulations predicted a potential yearly CO2 reduction of 56%, and a yearly energy reduction of 76% when operating the heat pumps using the economy 10 electricity tariff i.e a low tariff between 00.00-05.00 and 13.00-16.00 with current grid emission values compared to the conventional gas boiler system; successfully offsetting the electrical load to meet the required heat demand. Due to the high capital costs of the heat pump system with latent heat storage, its levelized cost of energy was 117.84£/MWh, compared to 69.66£/MWh for the gas boiler, on a 20-year life cycle

    Phase change materials to meet domestic space heating demand in the UK - A numerical study

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    This paper presents a performance evaluation of two domestic space heating systems that use air source heat pumps (ASHP) to replace conventional boilers with air source heat pumps (ASHP). The storage system consisted of encapsulated PCM spheres in a packed bed with twice the storage capacity over the temperature range of 40 and 65°C achievable with hot water. The simulations predicted a potential CO2 reduction of 23% for the detached dwelling and 20% for the semi-detached dwelling, operating the heat pumps in economy 10 electricity i.e a low tariff at times between 00.00-05.00 and 13.00-16.00; with current grid emission values by successfully offsetting the electrical load to meet the heat demand
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