Periodic Reporting for period 3 - SWS-HEATING (Development and Validation of an Innovative Solar Compact Selective-Water-Sorbent-Based Heating System)
Periodo di rendicontazione: 2021-06-01 al 2023-11-30
Τhe SWS project aims at further developing a novel storage technology of thermal energy in order to utilize solar energy in buildings in the most efficient way throughout the year.
The project concept is to develop an innovative Seasonal Thermal Energy Storage (STES) unit with a novel Selective-Water-Sorbent (SWS) heat storage material embedded in a compact STES unit. This will allow us to store and shift the harvested solar energy available abundantly during the summer to the less sunny and colder winter period thus covering a large fraction of thermal demand in buildings. Solar heat is used to provide hot water up to 60°C for space heating and domestic hot water, while the remainder will be used mainly to charge the seasonal storage unit during summer, allowing to store the heat for several months. During winter, the stored heat is discharged, and a backup gas heater will operate only when all stored heat has been fully discharged. By making use of even the lowest grade solar heat (within 5 – 30°C), the system allows to reach solar fraction currently not achievable at reasonable price and small space demands (e.g. with solar collectors and water-based Thermal Energy Storage). The detailed concept is presented in Figure 1, based on its two main operating modes (summer/winter).
The core objective of the SWS-HEATING project is to develop a new sorbent material of the SWS family with optimised sorption properties, matching the working conditions of a heat storage cycle with low temperature solar heat charging (70 – 95 °C) to allow efficient application also in northern European countries.
The project concept is to develop an innovative Seasonal Thermal Energy Storage (STES) unit with a novel Selective-Water-Sorbent (SWS) heat storage material embedded in a compact STES unit. This will allow us to store and shift the harvested solar energy available abundantly during the summer to the less sunny and colder winter period thus covering a large fraction of thermal demand in buildings. Solar heat is used to provide hot water up to 60°C for space heating and domestic hot water, while the remainder will be used mainly to charge the seasonal storage unit during summer, allowing to store the heat for several months. During winter, the stored heat is discharged, and a backup gas heater will operate only when all stored heat has been fully discharged. By making use of even the lowest grade solar heat (within 5 – 30°C), the system allows to reach solar fraction currently not achievable at reasonable price and small space demands (e.g. with solar collectors and water-based Thermal Energy Storage). The detailed concept is presented in Figure 1, based on its two main operating modes (summer/winter).
The core objective of the SWS-HEATING project is to develop a new sorbent material of the SWS family with optimised sorption properties, matching the working conditions of a heat storage cycle with low temperature solar heat charging (70 – 95 °C) to allow efficient application also in northern European countries.
A novel configuration for an STES system based on a novel SWS material was developed. The operational conditions of the system were defined by simulating the climatic conditions at central and northern Europe, whereas the system alongside its control software were designed to meet the specific needs of a typical single-family house in these regions. Devoted occupant-building interaction models were developed and integrated in the building models to fully define the demand profiles in the considered climatic zones while at the same time ensuring optimal thermal comfort for the end users. According to this analysis all the necessary components were designed and manufactured. The most crucial components were the Heat Exchangers (HEXs), the heating distribution system (i.e. a storage tank with minimal losses being able to store heat at different temperature levels) and naturally the SWS material.
The developed novel SWS material showed superior compactness showing high heat storage density (1.1-1.3 GJ/m3 - over 20 % greater than existing SWS materials). The SWS material was not degraded, nor did it lose adsorption capacity after 1,000 ageing test cycles under severe working conditions . A single-plate heat HEX was designed to be used as an adsorber/desorber as well as an evaporator/condenser. This technological feat will significantly reduce costs since only one type of HEX is needed. Critically, this HEX has more than double capacity of adsorbent volume compared to commercial HEXs. This means much more adsorbent to trap water molecules, enhancing storage density and performance. Simulations of the performance of tthis HEX were really promising. However, due to the COVID pandemic, commercial HEXs were used and the experimental confirmation of the benefits of the novel HEXs are one of the major future tasks for further developing this technology. As regards the designed compact vacuum combi-storage tank, it proved to be cost effective whilst achieving enhanced stratification and minimal heat losses.
All these components were individually tested before being installed at a demonstration prototype: a container was reformed into a prototype SWS-HEATING system next to a “living room” simulating the thermal needs of a single-family house.
The tests were successful and to study the system operation even under punishingly cold conditions. Most importantly, this technology can be considered as a proven technology but at low level towards commercialization. Moreover, according to system simulations, the advanced features of the control unit and the optimized design make it possible to achieve and overcome the performance threshold of 60% solar fraction. Finally, a technology roadmap was developed, showcasing the next steps towards further developing this promising technology. This roadmap alongside three videos showing the project concept and the developed technology can be found on the project website.
The developed novel SWS material showed superior compactness showing high heat storage density (1.1-1.3 GJ/m3 - over 20 % greater than existing SWS materials). The SWS material was not degraded, nor did it lose adsorption capacity after 1,000 ageing test cycles under severe working conditions . A single-plate heat HEX was designed to be used as an adsorber/desorber as well as an evaporator/condenser. This technological feat will significantly reduce costs since only one type of HEX is needed. Critically, this HEX has more than double capacity of adsorbent volume compared to commercial HEXs. This means much more adsorbent to trap water molecules, enhancing storage density and performance. Simulations of the performance of tthis HEX were really promising. However, due to the COVID pandemic, commercial HEXs were used and the experimental confirmation of the benefits of the novel HEXs are one of the major future tasks for further developing this technology. As regards the designed compact vacuum combi-storage tank, it proved to be cost effective whilst achieving enhanced stratification and minimal heat losses.
All these components were individually tested before being installed at a demonstration prototype: a container was reformed into a prototype SWS-HEATING system next to a “living room” simulating the thermal needs of a single-family house.
The tests were successful and to study the system operation even under punishingly cold conditions. Most importantly, this technology can be considered as a proven technology but at low level towards commercialization. Moreover, according to system simulations, the advanced features of the control unit and the optimized design make it possible to achieve and overcome the performance threshold of 60% solar fraction. Finally, a technology roadmap was developed, showcasing the next steps towards further developing this promising technology. This roadmap alongside three videos showing the project concept and the developed technology can be found on the project website.
A number of advances beyond the state of the art in the SWS-Heating related technologies were achieved :
At the components level:
• Development of a new sorbent material of the SWS-family which enhanced the heat storage density. The SWS material showed superior compactness - over 20 % greater than existing SWS material, while being chemically stable even under severe operating conditons.
• Development of optimized plate heat exchangers for both the adsorber and the condenser and evaporator of the SWS-STES configuration. The dedicated high-efficiency HEXs were designed to contribute to a reduced cost and volume by about 20%.
At the configuration level:
• Develop a compact multi-modular SWS-STES configuration with high durability. The innovative configuration of SWS-STES was proved to work as a proof of concept. Moreover, this type of storage technology with the developed configuration was proved to ensure negligible heat losses.
• Reach a solar fraction of 60% via an optimized SWS-Heating system. The advanced features of the control unit and the optimized design make possible to achieve and overcome the performance threshold of 60% solar fraction with reduced storage volume and collectors’ surface (the target of 20 m2 in north Europe for a new single-family house was reduced to a maximum of 11.5 m2)
Reducing life-cycle environmental impact:
• Sorption seasonal TES are promising technologies since they do not contain any hazardous materials (e.g. polluting refrigerants) and therefore could be a more sustainable alternative to conventional storage technologies
• From a LCC perspective, at a commercial scale the life cycle performance of the SWS-Heating is quite promising, achieving the desired targets of a total LCC 30% lower compared to the state of the art technologies.
At the social level:
• Nurturing the development of the industrial capacity to produce components and systems. The initial overall aim to validate this technology and reduce its technological risks, towards the commercialization of the new system has been achieved.
• The system compactness allows reducing installation effort (time and cost) compared to existing solar systems, since about the half solar collectors’ surface is required, while the SWS-STES compactness and simplified hydraulics contribute to the low installation time and effort. Economic performance over the life cycle of the system, has been calculated to less than 70% of the corresponding LCC of the state-of-the-art reference system.
• Identification of key opportunities and challenges for the uptake of SWS-Heating amongst end users. It should be emphasised that dedicated surveys to end-users in single family houses were conducted to estimate public acceptance and define policies for the implementation of the technology.
At the components level:
• Development of a new sorbent material of the SWS-family which enhanced the heat storage density. The SWS material showed superior compactness - over 20 % greater than existing SWS material, while being chemically stable even under severe operating conditons.
• Development of optimized plate heat exchangers for both the adsorber and the condenser and evaporator of the SWS-STES configuration. The dedicated high-efficiency HEXs were designed to contribute to a reduced cost and volume by about 20%.
At the configuration level:
• Develop a compact multi-modular SWS-STES configuration with high durability. The innovative configuration of SWS-STES was proved to work as a proof of concept. Moreover, this type of storage technology with the developed configuration was proved to ensure negligible heat losses.
• Reach a solar fraction of 60% via an optimized SWS-Heating system. The advanced features of the control unit and the optimized design make possible to achieve and overcome the performance threshold of 60% solar fraction with reduced storage volume and collectors’ surface (the target of 20 m2 in north Europe for a new single-family house was reduced to a maximum of 11.5 m2)
Reducing life-cycle environmental impact:
• Sorption seasonal TES are promising technologies since they do not contain any hazardous materials (e.g. polluting refrigerants) and therefore could be a more sustainable alternative to conventional storage technologies
• From a LCC perspective, at a commercial scale the life cycle performance of the SWS-Heating is quite promising, achieving the desired targets of a total LCC 30% lower compared to the state of the art technologies.
At the social level:
• Nurturing the development of the industrial capacity to produce components and systems. The initial overall aim to validate this technology and reduce its technological risks, towards the commercialization of the new system has been achieved.
• The system compactness allows reducing installation effort (time and cost) compared to existing solar systems, since about the half solar collectors’ surface is required, while the SWS-STES compactness and simplified hydraulics contribute to the low installation time and effort. Economic performance over the life cycle of the system, has been calculated to less than 70% of the corresponding LCC of the state-of-the-art reference system.
• Identification of key opportunities and challenges for the uptake of SWS-Heating amongst end users. It should be emphasised that dedicated surveys to end-users in single family houses were conducted to estimate public acceptance and define policies for the implementation of the technology.